Redox-Controllable Amphiphilic [2]Rotaxanes

FULL PAPER

Hsian-Rong Tseng,^[a]Scott A. Vignon,^[a]Paul C. Celestre,^[a]Julie Perkins,^[a]

Jan O. Jeppesen,^[b]Alberto Di Fabio,^[c]Roberto Ballardini,^[d]M. Teresa Gandolfi,*^[c]

Margherita Venturi,*^[c]Vincenzo Balzani,^[c]and J. Fraser Stoddart*^[a]

Abstract: With the fabrication of mo-

lecular electronic devices (MEDs) and

the construction of nanoelectrome-

chanical systems (NEMSs) as incen-

tives, two constitutionally isomeric,

redox-controllable [2]rotaxanes have

been synthesized and characterized in

solution. Therein, they both behave as

near-perfect molecular switches, that is,

to all intents and purposes, these two

rotaxanes can be switched precisely by

applying appropriate redox stimuli be-

tween two distinct chemomechanical

states. Their dumbbell-shaped compo-

nents are composed of polyether

chains interrupted along their lengths

by i) two p-electron rich recognition

sites–a tetrathiafulvalene (TTF) unit

mechanically interlocked around the

dumbbell-shaped components. Both

the TTF unit and the DNP moiety are

potential stations for CBPQT⁴⁺, since

they can establish charge-transfer and

hydrogen bonding interactions with the

bipyridinium units of the cyclophane,

thereby introducing bistability into the

[2]rotaxanes. In both constitutional iso-

mers, ¹H NMR and absorption spec-

troscopies, together with electrochemi-

cal investigations, reveal that the

CBPQT⁴⁺ring is predominantly locat-

ed on the TTF unit, leading to the exis-

tence of a single translational isomer

(co-conformation) in both cases. In ad-

dition, a model [2]rotaxane, incorporat-

ing hydrophobic tetraarylmethane stop-

pers at both ends of its dumbbell-

shaped component, has also been syn-

thesized as a point of reference. Molec-

ular synthetic approaches were used to

construct convergently the dumbbell-

shaped compounds by assembling pro-

gressively smaller building blocks in

the shape of the rigid spacer, the TTF

unit and the DNP moiety, and the hy-

drophobic and hydrophilic stoppers.

The two amphiphilic bistable [2]rotax-

anes are constitutional isomers in the

sense that, in one constitution, the TTF

unit is adjacent to the hydrophobic

stopper, whereas in the other, it is next

to the hydrophilic stopper. All three bi-

stable [2]rotaxanes have been isolated

as green solids. Electrospray and fast

atom bombardment mass spectra sup-

port the gross structural assignments

given to all three of these mechanically

interlocked compounds. Their photo-

physical and electrochemical properties

have been investigated in acetonitrile.

The results obtained from these investi-

gations confirm that, in all three [2]ro-

taxanes, i) the CBPQT⁴⁺cyclophane

encircles the TTF unit, ii) the

CBPQT⁴⁺cyclophane shuttles between

the TTF and DNP stations upon elec-

trochemical or chemical oxidation/re-

duction of the TTF unit, and iii) folded

conformations are present in which the

CBPQT⁴⁺cyclophane, while encircling

the TTF unit, interacts through its p-

accepting bipyridinium exteriors with

other p-donating components of the

dumbbells, especially those located

within the stoppers.

and

a 1,5-dioxynaphthalene (DNP)

moiety–with ii) a rigid terphenylene

spacer placed between the two recogni-

tion sites, and then terminated by iii) a

hydrophobic tetraarylmethane stopper

at one end and a hydrophilic dendritic

stopper at the other end of the dumb-

bells, thus conferring amphiphilicity

upon these molecules. A template-di-

Keywords: molecular

shuttle

¥

rected protocol produces

a means

nanoscale

processes

template-directed

tetrathiafulvalene

switches

¥

redox

to introduce the tetracationic cyclo-

phane, cyclobis(paraquat-p-phenylene)

(CBPQT⁴⁺), which contains two p-

electron accepting bipyridinium units,

¥

self-assembly

synthesis

¥

Fax : (+45)66-15-87-80

E-mail: joj@chem.sdu.dk

[a] Dr. H.-R. Tseng, S. A. Vignon, P. C. Celestre, Dr. J. Perkins,

Prof. Dr. J. F. Stoddart

[c] A. Di Fabio, Prof. M. T. Gandolfi, Prof. M. Venturi, Prof. V. Balzani

Dipartimento di Chimica ™G. Ciamician∫

Universit‡ di Bologna

Department of Chemistry and Biochemistry

University of California, Los Angeles

405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)

Fax : (+1)310-206-1843

Via Selmi 2, 40126 Bologna (Italy)

Fax : (+39)051-209-9456

E-mail: stoddart@chem.ucla.edu

E-mail: vbalzani@ciam.unibo.it

[b] Dr. J. O. Jeppesen

Department of Chemistry

[d] Dr. R. Ballardini

Odense University (University of Southern Denmark)

Campusvej 55, 5230, Odense M (Denmark)

Ist. ISOF-CNR, Via Gobetti 101

40129 Bologna (Italy)

155

Chem. Eur. J. 2004, 10, 155 172

DOI: 10.1002/chem.200305204

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

FULL PAPER

Introduction

[2]rotaxanes when it comes to fabricating MEDs and engi-

neering NEMSs.

Supramolecular chemistry^[1]and self-assembly^[2]have

emerged as a powerful vehicle and key concept, respectively,

for the development of synthetic chemistry^[3]to a point

where making rotaxanes using template-directed protocols^[4]

is now routine. A [2]rotaxane is a molecule composed of a

ring and a dumbbell-shaped component.^[5]The ring compo-

nent encircles the linear, rod-like portion of the dumbbell-

shaped component and is trapped mechanically by two

bulky stoppers. If two identical recognition sites for the ring

component are located within the dumbbell-shaped compo-

nent, then the outcome is a degenerate equilibrium state in

which the ring shuttles back and forth along the linear por-

tion of the dumbbell. Such a [2]rotaxane constitutes a mo-

lecular shuttle.^[6]When the two different recognition sites

which are incorporated into the dumbbell component differ

in their constitutions, then the [2]rotaxane can exist in two

different equilibrating translational isomers^[7]or co-confor-

mations;^[8]their populations reflect the relative free ener-

gies, as determined primarily by the strengths of the two dif-

ferent sets of noncovalent bonding interactions present in

the mechanically interlocked molecules. Moreover, these

molecules can be activated by switching the recognition sites

on and off between the components chemically,^[9]electro-

chemically,^[10]electrically,^[11]and optically,^[12]such that their

components perform relative motions–that is, overall, the

[2]rotaxane behaves as a controllable molecular shuttle^[6]

wherein the movement of the ring component can be in-

duced by an appropriate stimulus to shuttle in a linear fash-

ion between the two recognition sites. Since the ring and

dumbbell-shaped components of these highly ordered inter-

locked molecules can be induced to perform these relative

internal motions, rotaxanes are now prime candidates for

the construction of artificial molecular machines,^[13,14]which,

in the appropriate solid-state settings, become the blueprints

for the fabrication^[11,15]of molecular electronic devices

(MEDs) and the engineering of nanoelectromechanical sys-

tems (NEMSs).

In an attempt to produce [2]rotaxanes which will function

as linear motor-molecules with 100% precision, we have

elected to employ a simple disubstituted TTF unit in compe-

tition with the DNP moiety. Since we already knew that

TTF forms a strong green 1:1 complex (K_a=10000m^À1in

MeCN)^[6b,20]with CBPQT⁴⁺, whereas 1,5-dihydroxynaphtha-

lene forms a much weaker red 1:1 complex (K_a=770m^À1in

MeCN)^[21]with CBPQT⁴⁺, the idea seemed to be a poten-

tially productive one. Moreover, a closely related non-de-

generate [2]catenane, based on identical TTF and DNP rec-

ognition sites has been demonstrated to behave as a nearly

perfect switch, both in solution^[22a,b]and in a solid-state de-

vice.^[22c]

In a recent preliminary communication,^[23]we have describ-

ed i) the synthesis of the model [2]rotaxane 1¥4PF₆in

which the ring component is CBPQT⁴⁺and the dumbbell-

shaped component contains both TTF and DNP recognition

sites, separated by a rigid terphenylene spacer and terminat-

ed by two hydrophobic tetraarylmethane stoppers, and

ii) the characterization by UV/Vis and ¹H NMR spectroscop-

ies of the ™clean∫ redox switching action in solution of this

bistable rotaxane, wherein a relative mechanical movement

of several nanometers on the part of the CBPQT⁴⁺ring

occurs along the axis of the dumbbell, assuming the gross

structure of its rod section to be linear, as portrayed in

Figure 1.

In order to investigate the properties and characteristics

of solid-state devices, based on this nearly perfect electro-

mechanical switch, we have identified, as synthetic targets,

two amphiphilic bistable [2]rotaxanes, 3¥4PF₆and 5¥4PF₆in

which the ring component (CBPQT⁴⁺) and the rod sec-

tion–containing TTF and DNP recognition sites separated

by a terphenylene spacer–of the dumbbell-shaped compo-

nent are retained but in which one of the two hydrophobic

stoppers is replaced in turn by a hydrophilic dendritic one.

It is clear from a perusal of Figure 1 that these two rotax-

anes are constitutional isomers in the sense that, in 3⁴⁺, the

TTF unit encircled by the CBPQT⁴⁺ring, is adjacent to the

hydrophobic stopper, whereas, in 5⁴⁺, it is next to the hydro-

philic stopper. Although we would expect these two bistable

rotaxanes, because of their amphiphilic character, to be

largely elongated within Langmuir monolayers at the air-

water interface, and in Langmuir Blodgett (LB) films in

device settings (Figure 1b and c), the fact that all three of

these rotaxanes, namely 1⁴⁺, 3⁴⁺, and 5⁴⁺, are relatively long

and flexible means that quite a number of alongside intra-

molecular interactions involving the CBPQT⁴⁺ring and the

DNP moiety, as well as p-electron rich aromatic units pres-

ent in the hydrophilic-dendritic and hydrophobic stoppers of

3⁴⁺and 5⁴⁺, could lead to some rather contorted and exotic

conformations^[10c,19,24]being populated in solution. It is im-

portant that the solution-state properties of these bistable

amphiphilic [2]rotaxanes are understood at the same time as

their performances in devices are being evaluated.

Not so long ago, we described^[16]the template-directed

syntheses^[4]of amphiphilic, bistable rotaxanes composed of

dumbbell-shaped components with two recognition sites–

namely a monopyrrolo-tetrathiafulvalene (MP-TTF) unit

and a 1,5-dioxynaphthalene (DNP) moiety–and a common

ring component, that is, cyclobis(paraquat-p-phenylene)^[17]

(CBPQT⁴⁺). In the ideal switch, [p p] stacking and other

interactions^[18]involving the CBPQT⁴⁺ring and the stronger

(MP-TTF) of the two p-electron-donating recognition sites

would result in these [2]rotaxanes existing as a single trans-

lational isomer with the CBPQT⁴⁺ring encircling only the

MP-TTF unit. In practice, however, electrochemical studies,

supported by spectroscopic results, have shown^[16,19]that, in

these particular rotaxanes, both translational isomers are

present in approximately 1:1 ratios in Me₂CO solutions at

room temperature. It follows that, if this equilibrium is the

starting point, then oxidation of the MP-TTF units will only

activate half of the molecules, that is, only 50% of them are

available to undergo switching. This inherent lack of precise

mechanical control compromises the performance of these

In this paper, we describe the template-directed synthesis

of the three bistable [2]rotaxanes shown in Figure 1–

namely i) the model rotaxane 1¥4PF₆and ii) the two consti-

156

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

the amphiphilic [2]rotaxanes

3¥4PF₆and 5¥4PF₆revealed a

considerable range of possible

synthetic pathways. Common to

all of these possible routes is

the key clipping reaction to

form the CBPQT⁴⁺ring around

the

dumbbell-shaped

com-

pounds,

a

template-directed

procedure which always consti-

tutes the last step of the synthe-

ses, which are presented in

Schemes 1 5. In order to obtain

the dumbbell compounds 2, 4,

and 6 as conveniently as possi-

ble, a modular synthetic ap-

proach was adopted for the

progressive assembly of the five

different

i) the hydrophobic tetraaryl-

methane 12

stopper^[11c,27]

fragments–namely

(Scheme 1), ii) the hydro-

philic dendritic stopper^[11c,26]

(Schemes 4 and 5), iii) the TTF

building block 10, (Scheme 1),

iv) the DNP building block^[25]

24 (Scheme 4), and v) the ter-

phenylene spacer which was in-

troduced by first incorporating

the biphenyl 16 into an inter-

mediate compound, followed

by coupling (Schemes 2and 4)

with the Grignard reagent 19.

Since all the synthetic pathways

share these common intermedi-

ates, the syntheses of [2]rotax-

anes 1¥4PF₆, 3¥4PF₆, and 5¥4PF₆

Figure 1. a) Structural formulas of the bistable [2]rotaxane 1¥4PF₆and amphiphilic bistable [2]rotaxanes

3¥4PF₆and 5¥4PF₆. b) and c) Idealized graphical representations of the two constitutional isomers 3⁴⁺and 5⁴⁺

,

respectively, in device settings between polysilicon and Ti/Al electrodes. The LB technique is used in the first

place to self-organize these two amphiphilic bistable [2]rotaxanes.

tutional isomers 3¥4PF₆and 5¥4PF₆, prior to iii) presenting

and discussing the results of mass spectrometry and

¹H NMR spectroscopic, photophysical, and electrochemical

investigations carried out on all

can be achieved efficiently with reasonably little effort.

Moreover, the reactions, which were chosen (Schemes 1 5)

for connecting each fragment, are nucleophilic substitutions

three [2]rotaxanes, as well as on

the corresponding dumbbell

compounds 2, 4, and

6

(Schemes 3 5) and their model

compounds (Figure 2)–namely,

10, 35, CBPQT⁴⁺(36⁴⁺), 37,^[25]

38,^[19]and 39^[26]The discussion

is concluded by iv) presenting

the results of redox-switching

experiments carried out on all

three bistable [2]rotaxanes.

Results and Discussion

Design and synthetic strategy:

Retrosynthetic analyses of the

model [2]rotaxane 1¥4PF₆and Figure 2. Structural formulas of the cyclophane 36¥4PF₆, and of the compounds used as models.

157

Chem. Eur. J. 2004, 10, 155 172 www.chemeurj.org ¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

one equivalent of TsCl afforded

the monotosylate 11 in 45%

yield after flash column chro-

matography. The high yielding

(95%) alkylation of the phenol-

ic tetraarylmethane stopper^[11c,

27]

12 with the monotosylate 11

was achieved in MeCN with

LiBr and [18]crown-6 as cata-

lysts in the presence of K₂CO₃

as base. Tosylation of the result-

ing alcohol 13 gave the tosylate

14 in 88% yield. The prepara-

tion of the DNP-containing

half-dumbbell-shaped

com-

pound 21 is outlined in

Scheme 2. Using conventional

alkylation conditions (K₂CO₃/

Scheme 1. Synthesis of the TTF containing half-dumbbell compound 14.

LiBr/[18]crown-6/MeCN),

4-

bromo-(1,1’-biphenyl)-4-ol (16)

was treated with the bromide^[16,

15 to give compound 17 in 77% yield. The synthesis of

19]

between the bromides or monotosylates and the appropriate

alcohols in the presence of basic reagents and these reac-

tions are usually high yielding and reproducible. Using this

modular strategy, the model [2]rotaxane 1¥4PF₆, and the two

amphiphilic [2]rotaxanes 3¥4PF₆and 5¥4PF₆, were obtained

(Schemes 1 5) with relative ease.

the terphenylene compound 20 was accomplished by means

of a Pd⁰-catalyzed cross-coupling reaction in THF with the

freshly prepared Grignard reagent 19 from the THP-ether

18 of p-bromophenol. HCl-Catalyzed deprotection of com-

pound 20 gave the phenol 21 in 71% yield overall. The

[2]rotaxane 1¥4PF₆was obtained (Scheme 3) by a template-

directed synthesis, using the dumbbell compound 2 as a tem-

plate, to form a CBPQT⁴⁺ring from its dicationic precur-

sor^[30]22¥2PF₆and a,a’-dibromoxylene (23). The [2]rotaxane

1¥4PF₆was isolated in 39% yield as an analytically pure

green solid after chromatography on silica gel using a 1%

NH₄PF₆solution in Me₂CO as the eluent.

The sequence of steps employed in the synthesis of the ro-

taxane 3¥4PF₆and its precursor dumbbell compound 4 is

summarized in Scheme 4. The monobromination of the

diol^[25]24 with CBr₄and PPh₃afforded in 35% yield the

bromide 25 which was subsequently treated with TBDMSCl

to obtain the silyl ether 26 in quantitative yield. Alkylation

of 26 with 4-bromo-(1,1’-biphenyl)-4-ol (16) gave compound

Synthesis: The route for the synthesis of the model [2]rotax-

ane 1¥4PF₆is described in Schemes 1 3. The dumbbell-

shaped compound 2 was obtained (Scheme 3) in 47% yield

by alkylating the phenol 21 (produced in Scheme 2), with

the tosylate 14 (produced in Scheme 1) using LiBr and

[18]crown-6 as catalysts in the presence of K₂CO₃as base.

The preparation of the TTF-containing half-dumbbell com-

pound 14 (Scheme 1) begins with alkylation of the diol^[28]

7

by the iodide^[29]8 in THF using eight equivalents of NaH.

Without purification, the resulting compound 9 was convert-

ed into the diol 10 by HCl-catalyzed deprotection in a

MeOH/CH₂Cl₂solvent mixture with an overall yield of 60%

for the two steps. Subsequent tosylation of the diol 10 with

Scheme 2. Synthesis of the DNP containing half-dumbbell compound 21.

158

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

Scheme 3. Synthesis of the bistable [2]rotaxane 1¥4PF₆.

27 in 62% yield. The synthesis of the terphenylene deriva-

tive 28 was accomplished by the cross-coupling reaction be-

tween 27 and the freshly prepared Grignard reagent 19 in

the presence of [Pd(PPh₃)₄]. TFA-Catalyzed deprotection of

28 gave the phenol 29 in 71% yield overall. The TTF-DNP-

containing half-dumbbell 30 was obtained in 82% yield by

carrying out an alkylation between phenol 29 and tosylate

14 with K₂CO₃as base in MeCN. In the presence of

NaH, the half-dumbbell compound 30 was treated with the

dendritic chloride^[11c,26]31 with NaI and [15]crown-5 as cata-

lysts to afford the dumbbell compound 4 in 51% yield. The

template-directed synthesis of the [2]rotaxane 3¥4PF₆pro-

ceeded in 60% yield when the reaction of the dumbbell

compound 4, the dicationic salt 22¥2PF₆and dibromide 23,

using exactly the same reaction and isolation conditions of

those employed in the preparation of 1¥4PF₆, was carried

out.

bell compound 6, using the protocol already described for

making 3¥4PF₆.

The model compound 35 was synthesized (Scheme 6) by

alkylation of the diol^[31]33 with the chloride 34 in DMF in

the presence of K₂CO₃and LiBr.

Mass spectrometric investigation: Mass spectral data for the

[2]rotaxanes 1¥4PF₆, 3¥4PF₆, and 5¥4PF₆are summarized in

Table 1. The model [2]rotaxane 1¥4PF₆was characterized by

electrospray (ES) mass spectrometry. The ES mass spectrum

of 1¥4PF₆revealed five peaks which correspond to the

doubly positively-charged ions [MÀ2PF₆]²⁺and [MÀ3PF₆]²⁺

,

the triply positively-charged ion [MÀ3PF₆]³⁺

, and the

quadruply positively-charged ion [MÀ4PF₆]⁴⁺. The amphi-

philic [2]rotaxanes 3¥4PF₆and 5¥4PF₆were characterized by

fast atom bombardment (FAB) mass spectrometry. In both

cases, six major peaks, corresponding to the singly positive-

ly-charged ions [MÀ2PF₆]⁺, [MÀ2PF₆]⁺, and [MÀ3PF₆]⁺

The template-directed synthesis of the rotaxane 5¥4PF₆

from its dumbbell-shaped precursor 6 is summarized in

Scheme 5. The half-dumbbell 32 was obtained in 64% yield

and doubly positively charged ions [MÀ2PF₆]²⁺

,

[MÀ3PF₆]²⁺, and [MÀ4PF₆]²⁺, were observed in their FAB

from

a

substitution reaction (K₂CO₃/LiBr/[18]crown-6/

mass spectra.

MeCN) carried out between monotosylate 11 and phenol

21. The dendritic chloride^[11c,26]31 and the half-dumbbell 32

were treated in the presence of NaH, NaI and [15]crown-5

to afford the dumbbell compound 6 in 66% yield. Once

again, the template-directed synthesis of the [2]rotaxane

5¥4PF₆was achieved, this time in 57% yield from the dumb-

¹H NMR Spectroscopic investigation: Only one translational

isomer–the one in which the CBPQT⁴⁺ring encircles the

1

TTF unit–is indicated by H NMR spectroscopy to be pres-

ent in the intensely green CD₃CN solutions of each of the

three [2]rotaxanes 1¥4PF₆, 3¥4PF₆, and 5¥4PF₆recorded at

159

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

Scheme 4. Synthesis of the amphiphilic, bistable [2]rotaxane 3¥4PF₆.

room temperature. The ¹H NMR spectra (Figure 3) of all

three of these compounds in CD₃CN at 500 MHz exhibit a

highly characteristic signature -that is, in each case, two

pairs of signals of unequal intensities resonating at d 5.98,

6.06, 6.17, and 6.23 for 1¥4PF₆(Figure 3a), at d 5.96, 6.06,

6.16, and 6.22 for 3¥4PF₆(Figure 3b), and at d 5.92, 5.98,

6.10, and 6.20 for 5¥4PF₆(Figure 3c)–for the constitutional-

ly heterotopic methine protons on the CBPQT⁴⁺-encircled

TTF units with equilibrating (slow on the ¹H NMR time-

scale but fast on the isolation one) pairs of cis and trans iso-

mers as a result of torsion about the formal double bond in

the midst of the disubstituted TTF units. So far, we have not

been able to assign the two pairs of singlets of unequal in-

tensities to the cis and trans isomers, but we believe they are

the only two species that are significantly populated in solu-

and minor isomers in relation to the cis-trans configurations

associated with the CBPQT⁴⁺-encircled TTF units in 1⁴⁺

,

3⁴⁺, and 5⁴⁺. Incontroversial evidence for the presence in

these three rotaxanes of folded conformations, wherein p-

donating residues in the dumbbell components associate

themselves with the p-accepting bipyridinium exteriors of

the CBPQT⁴⁺rings, will be presented subsequently in the

subsections (see below) of this Results and Discussion sec-

tion on photophysical and electrochemical investigations.

We just wish to make the point here that there is some cir-

cumstantial evidence, from a comparison (Table 2and

1

Figure 3) of the H NMR spectra of the three rotaxanes, not

only for the existence of such folded conformations, but also

for their different proportions, and possibly structures as

well. Parts a), b), and c) of Figure 3 show, respectively, the

¹H NMR spectra of the rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺recorded

in CD₃CN at room temperature. Disregarding the peaks in

the spectrum (Figure 3b) for 3⁴⁺that result from the por-

tions in the hydrophilic stopper, it is evident from close in-

spections of the relevant spectra (Figure 3a and b) that ro-

taxane 1⁴⁺and 3⁴⁺display a very similar array of signals. By

contrast, the spectrum (Figure 3c) for the rotaxane 5⁴⁺is

À

tions of 1⁴⁺, 3⁴⁺, and 5⁴⁺as their 4PF₆salts. Variable tem-

1

perature H NMR experiments were performed on all three

compounds in both CD₃CN and CD₃COCD₃over 1708

ranges between 190 and 360 K. No temperature dependent

behavior was observed that might be indicative of more

than one translational isomer existing in solutions of these

[2]rotaxanes. They do, however, exist as a mixture of major

160

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

Scheme 5. Synthesis of the amphiphilic, bistable [2]rotaxane 5¥4PF₆.

observations anticipate the more detailed analysis (see

below), based on electrochemical data, wherein 1⁴⁺and 3⁴⁺

are found to behave quite similarly, while 5⁴⁺is the odd one

1

out. It should be noted that the H NMR spectroscopic data

is concentration independent, an observation which rules

out intermolecular aggregation as a significant contribution

to the overall picture.^[32]

Photophysical investigations: The photophysical properties

were studied in air-equilibrated MeCN solutions at room

temperature. Each dumbbell component in the three [2]ro-

taxanes contains five distinct chromophoric units–namely, a

TTF unit, a DNP moiety, a terphenylene spacer, and two

stoppers, the same in 1⁴⁺and different in 3⁴⁺and 5⁴⁺. In ad-

dition, all three of the [2]rotaxanes contain, of course, the

CBPQT⁴⁺ring which consists of two equivalent and non-in-

teracting^[33]bipyridinium chromophoric units.

Scheme 6. Synthesis of the terphenyl compound 35.

significantly different from those (Figure 3a and b) of the

other two. This point is further emphasized by the chemical

shift data presented in Table 2for selected proton probes in

the three rotaxanes. The d values shown in italics for

5¥4PF₆, differ significantly from those for 1¥4PF₆and 3¥4PF₆,

which are themselves very similar, one with the other. These

Table 1. MS data for the [2]rotaxanes 1¥4PF₆, 3¥4PF₆and 5¥4PF₆.

[2]Rotaxane

M^[a]

[MÀPF₆]⁺

[MÀ2PF₆]⁺

[MÀ3PF₆]⁺

[MÀ2PF₆]²⁺

[MÀ3PF₆]²⁺

[MÀ4PF₆]²⁺

[MÀ3PF₆]³⁺

[MÀ4PF₆]⁴⁺

[b]

1¥4PF₆

(3020)

(3324)

1366

1517

1293

1445

1446

862

610

[c]

3¥4PF₆

3179

3178

3034

3035

2888

2889

1372

[c]

5¥4PF₆

[a] The peaks corresponding to the molecular ion were not observed. The molecular weights are shown in parentheses. [b] ESI-MS data. [c] FAB-MS

data.

161

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

1

Table 2. Selected chemical shifts (d values) from the H NMR spectra^[a]of the [2]rotaxanes 1¥4PF₆, 3¥4PF₆and

5¥4PF₆

model compounds 10, 35, 37,^[25]

38,^[19]and 39^[26](Figure 2),

ii) the dumbbell compounds 2,

4, and 6, and iii) the model

[2]rotaxane 1⁴⁺and the consti-

tutionally isomeric [2]rotaxanes

[b]

[2]Rotaxane

H_a

TTF Protons^[b]

-(CH₂O)₃C₆H₂CH₂O-^[b]

-CH₂-N^+[b]

[c]

1¥4PF₆

3¥4PF₆

5¥4PF₆

8.97, 8.87, 8.79

8.95, 8.86, 8.77

8.88, 8.76, 8.62

6.23, 6.17, 6.06, 5.98

6.22, 6.16, 6.06, 5.96

6.20, 6.10, 5.98, 5.92

5.76 5.47

5.71 5.43

5.66 5.32

[c]

4.90, 4.80

4.80, 4.74

[c]

1

3⁴⁺and 5⁴⁺

.

[a] The H NMR spectra were recorded at 500 MHz in CD₃CN at ambient temperature with concentrations of

approximately 1 mm. [b] The protons mentioned are depicted on the structural formulas in Figure 1. [c] The

¹H NMR spectra corresponding to 1¥4PF₆, 3¥4PF₆, and 5¥4PF₆are shown in a), b), and c), respectively, in

Figure 9.

Cyclophane CBPQT⁴⁺(36⁴⁺

)

and model compounds 10, 35,

37, 38, and 39: The absorption

spectra of 36⁴⁺and the model

compounds, serving as referen-

ces for the appropriate chromo-

phore units of the dumbbell

components 2, 4, and 6 are

shown in Figure 4. None of

these compounds shows absorp-

tion bands in the visible region

with the exception of com-

pound 10 which has a very

weak absorption band with a

maximum at around 450 nm.

Compounds 35, 37, and 38 dis-

play, as expected,^[34]strong fluo-

rescence bands in the region of

300 400 nm (Figure 4, inset)

whereas compound 10, the cy-

clophane 36⁴⁺and compound

39 do not show any emission.

The lack of emission by 39,

which contains potentially fluo-

rescent aryloxy subunits, has

been noted previously.^[19]The

lowest energy emission band

(l_max=360 nm) is that exhibited

Figure 3. ¹H NMR Spectra of the rotaxanes a) 1¥4PF₆, b) 3¥4PF₆and c) 5¥4PF₆recorded in CD₃CN at 500 MHz

at room temperature.

by the dialkoxyterphenylene spacer 35: it is characterized by

a very high quantum yield (0.95) and a short lifetime (1.4 ns).

Dumbbells 2, 4, and 6: The absorption spectra of the dumb-

bell compounds 2, 4, and 6 are very similar to the sum of

the spectra of the model compounds 10, 35, 37, 38, and 39

for their component units. None of the dumbbells, however,

exhibit any emission, which shows that the potentially fluo-

rescent excited states of components 35, 37, and 38 are

quenched very efficiently.^[35]This observation indicates that,

in the ground state, there is no significant intramolecular in-

teraction among the various chromophoric groups present in

the dumbbell compounds. This result is not unexpected

since, in the dumbbells, the lowest excited state is that of

the non-emitting TTF unit 10^[22b]as shown by the absorption

spectra displayed in Figure 4. In fact, i) the fluorescent excit-

ed states of the DNP moiety and the aryloxy units of the tet-

raarylmethane stopper reference compounds 37 and 38, re-

spectively, can be quenched efficiently by Fˆrster-type

energy transfer^[36]since their emission bands overlap the ab-

sorption bands of the TTF and spacer model compounds 10

and 35, respectively, and ii) the fluorescent excited state of

the terphenylene reference compound 35, in its turn, can be

Figure 4. Absorption spectra of the free cyclophane 36⁴⁺and of the

model compounds of the chromophoric units incorporated in dumbbell-

shaped compounds 2, 4, and 6. The emission spectra of the fluorescent

compounds 35, 37, and 38 are shown in the inset (air equilibrated MeCN

solution, room temperature).

The photophysical investigations were carried out on

three major groups of compounds, i) the reference com-

pounds, namely the cyclophane^[17]CBPQT⁴⁺(36⁴⁺) and the

162

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

quenched efficiently since its fluorescence band overlaps the

absorption band of the TTF compound 10. Moreover, a re-

ductive electron transfer of the excited states of the DNP

moiety, the terphenylene spacer, and the hydrophobic stop-

per by the ground state of the TTF unit can also be expect-

ed in view of its low oxidation potential (+0.35 V vs SCE)

and the high energies of the excited states.

(see below). The non-negligible absorbance in the 350

550 nm region shows, however, that the CBPQT⁴⁺cyclo-

phane, while encircling the TTF unit, is also involved in CT

interactions with other electron-donor residues. This obser-

vation is consistent with folded conformations; their pres-

1

ence is also indicated by the results of H NMR spectroscop-

ic and electrochemical experiments. In view of the small dif-

ferences in the absorbance values and the wide variety of

possible CT interactions that can arise in folded conforma-

tions, we believe that further speculation concerning which

moiety (or moieties) of the dumbbells is (are) engaged in

alongside interactions with the CBPQT⁴⁺cyclophane would

be premature. The existence of folded conformations could

also affect the interaction between the CBPQT⁴⁺cyclo-

phane and the encircled TTF units, a situation which could

account for the differences in the values of the molar ab-

sorption coefficients for the three rotaxanes at 840 nm.

[2]Rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺: A comparison between the

absorption spectra of the rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺with

the sum of the spectra of the CBPQT⁴⁺cyclophane and of

the respective dumbbells, 2, 4, and 6 shows that there are

small differences in the UV spectral region and a generally

higher absorbance in the rotaxane spectra above 350 nm,

characterized by a broad and relatively weak band with

l_max=840 nm (see, for example, Figure 5). Such an absorp-

Electrochemical investigations: Electrochemical experi-

ments–namely, cyclic voltammetry (CV) and differential

pulse voltammetry (DPV)–were carried out in argon-

purged MeCN solutions at room temperature. All potential

values are referred to SCE. Since the redox-active bistable

rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺contain several electrochemically

active units, they display a rather complex electrochemical

behavior. In order to render a potentially daunting task a

practical one, we have focused our investigations on the oxi-

dation processes associated with the p-electron-rich units,

that is, the TTF unit and the DNP moiety, in the dumbbell

components, and on the reduction processes involving the p-

electron deficient bipyridinium units of the cyclophane com-

ponent. For comparison purposes, the electrochemical prop-

erties of the free dumbbell compounds 2, 4, and 6, the free

cyclophane 36⁴⁺and the model compounds 10, 35, 37, 38,

and 39 for the electro-active units contained in the dumb-

bells have also been investigated. Some of the results from

the electrochemical investigations are summarized in

Table 3.

Figure 5. Comparison of the absorption spectrum of [2]rotaxane 3⁴⁺

(solid line) and the sum (dashed line) of the spectra of its dumbbell (4)

and ring (36⁴⁺) components. The inset shows the CT region of the ab-

sorption spectra of the [2]rotaxanes 1⁴⁺, 3⁴⁺and 5⁴⁺(MeCN solution,

room temperature).

tion band is typical of charge transfer (CT) interactions aris-

ing when a TTF unit is encircled by the CBPQT⁴⁺cyclopha-

ne.^[22b]It is also known that the CT interaction, arising when

the CBPQT⁴⁺cyclophane encircles a DNP moiety (which is

more difficult to oxidize than a TTF unit), results^[22a]in an

absorption band at 520 nm. CT Bands at higher energies are

expected to arise from the interactions between the cyclo-

phane CBPQT⁴⁺and other, weaker electron-donor units

present within the dumbbells. It should be noted (inset in

Table 3. Electrochemical data^[a]for the TTF and DNP model compounds

10 and 37, the dumbbell compounds 2, 4, and 6, the ring component

CBPQT⁴⁺and the [2]rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺

.

Compounds

TTF^[b]

E_ox[V]

DNP^[b]

4,4’-bipyridinium^[b]

E_red[V]

E_ox[V]^[c]

10

+0.35 +0.71

37

+1.17

+1.18

dumbbell 2

dumbbell 4

dumbbell 6

CBPQT⁴⁺

+0.35 +0.72

+0.35 +0.73

Figure 5) that the spectra of the three rotaxanes 1⁴⁺, 3⁴⁺

,

À0.29^[d]À0.71^[d]

and 5⁴⁺in the CT region are similar but not identical. The

presence of absorption bands with maxima at 840 nm and

the absence of bands around 520 nm demonstrate that, in all

cases, by far the most predominant, if indeed not the only,

translational isomer populated is the one in which the

CBPQT⁴⁺cyclophane encircles the TTF unit as portrayed

by the structural formulas shown in Figure 1. This conclu-

sion is entirely consistent with the results obtained from

¹H NMR spectroscopy (see above) and electrochemistry

[2]rotaxane 1⁴⁺

[2]rotaxane 3⁴⁺

[2]rotaxane 5⁴⁺

+0.74^[d,e]

+0.73^[d,e]

>+1.30

À0.30 À0.37 À0.82^[d]

À0.31 À0.36 À0.81^[d]

À0.31 À0.40 À0.83^[d]

[a] Argon-purged MeCN, room temperature, tetraethylammonium hexa-

fluorophosphate (TEAPF₆) as supporting electrolyte, glassy carbon as

working electrode; potential values in V vs. SCE; reversible and mono-

electronic process, unless otherwise indicated. [b] Unit involved in the

observed process. [c] Irreversible process; potential value estimated by

the DPV peak. [d] Bielectronic process. [e] Process affected by kinetic

complications; potential value estimated by the DPV peak.

163

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

1) Oxidation processes: For the rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺

the first oxidation process (Table 3 and Figure 6) is bielec-

tronic and occurs at +0.74 V. This result shows that the two

reversible and monoelectronic oxidation processes associat-

FULL PAPER

Model compounds 10, 35, 37, 38, and 39: These five com-

pounds undergo only oxidation processes in the potential

window examined (À2.0/+2.0 V). Compound 10, a model

for a free TTF unit, exhibits (Table 3) two one-electron re-

versible oxidation processes at +0.35, +0.71 V, characteris-

tic of TTF.^[38]Compound 37 shows (Table 3) an irreversible

oxidation process at +1.17 V, that can be easily assigned to

the DNP moiety.^[22b,37]The other model compounds for the

terphenylene spacer 35, the tetraarylmethane hydrophobic

stopper 38 and the dendritic hydrophilic stoppers 39 can

only be oxidized at higher potentials: three oxidation pro-

cesses at +1.29, +1.43 and +1.52V, two at +1.55 and

+1.76 V, and four at +1.27, +1.32, +1.59 and +1.73 V

were obtained, respectively, for compounds 35, 38, and 39.

,

4+

Dumbbell compounds 2, 4, and 6 andthe CBPQT

cyclo-

phane 36⁴⁺: The free dumbbell compounds 2, 4, and 6 ex-

hibit several oxidation processes. The two reversible and

mono-electronic processes observed at +0.35 and +0.72V

can be assigned clearly to the TTF unit by comparison with

the model compound 10, and the irreversible process that

follows at +1.17 V can be assigned to the DNP moiety by

comparison with the behavior of the reference compound 37

(Table 3). At more positive potentials, several overlapping

processes, related to the oxidation of the spacer and stop-

pers, can be observed. In conclusion, the electrochemical

properties of the dumbbell components are those expected

from the redox behavior of their model compounds, without

evidence of inter-component interactions. The electron-ac-

cepting cyclophane CPBQT⁴⁺shows (Table 3) the well-

known^{[21a,22b,33,39]}reversible and bielectronic reduction pro-

cesses at À0.29 and À0.71 V which can be assigned to the

first and, respectively, second reduction of the two equiva-

lent non-interacting bipyridinium units.

Figure 6. Anodic DPV patterns of the model compound 10, the dumbbell

compound 6 and the [2]rotaxane 5⁴⁺. The current intensities have been

corrected to take into account differences in concentrations and diffusion

coefficients (Argon purged MeCN solution, room temperature, scan rate

4 mVs^À1, pulse height 10 mV).

ed with the TTF unit, which are well separated in the model

compound 10, as well as in the dumbbells 2, 4, and 6, take

place at the same potential. The lack of an oxidation process

taking place around +0.35 V, at least within the limits of

the experimental error, and the large shift (ca. 400 mV)

toward more positive potential values of the first oxidation

process, shows that, in each rotaxane, there is only one

translational isomer that is populated–namely, that in

which the CBPQT⁴⁺cyclophane encircles the TTF unit. The

electron-accepting tetracationic cyclophane increases the

first oxidation potential of the encircled TTF unit for two

reasons–i) it engages the TTF unit in donor acceptor inter-

actions and ii) it makes more difficult the formation of a

monocationic TTF⁺C species inside the cyclophane. The

second oxidation process of the TTF unit in the rotaxanes

takes place (Table 3 and Figure 6) at the same potential

value as that of the corresponding dumbbell. This result and

the observation that the cyclic voltammetric pattern corre-

sponding to the TTF unit is affected by kinetic complica-

tions demonstrate that, after the first oxidation process in-

volving the TTF unit, the CBPQT⁴⁺cyclophane moves

away from this unit. It should also be noted (Table 3 and

Figure 6) that, in all three rotaxanes, the oxidation of the

DNP moiety is shifted toward more positive potential

values, compared to those observed in the dumbbells. Al-

though, in all cases, the exact potential associated with the

DNP oxidation process is difficult to establish, because of

the presence of processes involving other units of the dumb-

bell above +1.30 V, the observed shift shows that, after

TTF oxidation, the CBPQT⁴⁺cyclophane moves onto the

DNP moiety, thereby destabilizing the formation of its radi-

cal cation.^[40]In conclusion, the results obtained from elec-

[2]Rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺: Prior to an analysis of the

results obtained for these three redox-active, bistable [2]ro-

taxanes, it is worth contemplating the anticipated effects

upon the redox processes of the cyclophane and dumbbell

components brought about by their being interlocked. The

oxidation of a TTF unit or a DNP moiety is strongly condi-

tioned by the presence of an encircling CBPQT⁴⁺because

of i) the presence of donor acceptor interactions and ii) the

strong electrostatic repulsion arising between the generated

radical cation and the tetracationic cyclophane. The oxida-

tion of the encircled TTF unit or DNP moiety should hardly

be affected, however, by conformational folding because of

the shielding effect provided by the surrounding tetracation-

ic cyclophane toward external interactions. By contrast, it is

known that the reduction of the 36⁴⁺cyclophane is weakly

influenced by threading an uncharged electron donor be-

cause electrostatic effects are not involved. However, the re-

duction processes should be affected by folding since the

highly charged cyclophane is strongly exposed to external

interactions.^[21,33]It follows that the oxidation processes

should give information on the nature of the translational

isomerism and, when appropriate, on the occurrence of shut-

tling movements, whereas the reduction processes should

reveal the occurrence of conformational folding.

164

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

trochemical oxidation show that, in all three rotaxanes, the

CBPQT⁴⁺cyclophane is originally located around the TTF

unit and shuttles between the TTF and DNP ™stations∫

upon ox-red stimulation. These results are fully confirmed

by the chemical oxidation/reduction experiments described

in the final subsection of this paper. It is interesting to note

that the nature and relative positions of the stoppers do not

seem to play any role regarding the location of the tetracat-

ionic cyclophane and the occurrence of the shuttling pro-

cess, whereas, in similar rotaxanes^[19]the nature of the stop-

pers influences the relative populations of the two transla-

tional isomers.

2) Reduction processes: The CBPQT⁴⁺cyclophane in MeCN

solutions shows^{[21a,22b,33,39]}two reversible, bielectronic pro-

cesses at À0.29 and À0.71 V, assigned to the first and, respec-

tively, second reductions of the two equivalent and non-in-

teracting bipyridinium units. The electrochemical properties

of CBPQT⁴⁺(36⁴⁺) are known to change when this cyclo-

phane is threaded by a p-electron donor. The first bielec-

tronic reduction process is expected to and, in fact, does

i) move slightly toward more negative potential values in

pseudorotaxanes^[41]and rotaxanes,^[35b]and ii) split into two

distinct processes in catenanes^[21a,22b,33]in which the two bi-

pyridinium units are topologically non-equivalent. Splitting,

however, has also been observed in the case of some pseu-

dorotaxanes^[22b]and rotaxanes.^[19,42]

Figure 7. Cathodic DPV patterns of the cyclophane 36⁴⁺and of the [2]ro-

taxanes 1⁴⁺, 3⁴⁺and 5⁴⁺. The current intensity has been corrected to

take into account differences in concentrations and diffusion coefficients

(Argon purged MeCN solution, room temperature, scan rate 4 mVs^À1

pulse height 10 mV).

,

teractions. Interestingly, the successive reduction of the two

bipyridinium units of the cyclophane takes place at the same

potential which is shifted toward more negative values com-

pared with (Table 3) the free tetracationic cyclophane.^[43]

This result shows that, after the first reduction process, the

two bipyridinium units still interact with p-electron-donating

units, but then become equivalent, suggesting that unfolding

takes place after one-electron reduction of the two bipyridi-

nium units.

That electrochemical stimulation can cause not only shut-

tling, but also conformational folding and unfolding process-

es in long and flexible rotaxanes is a novel, yet clearly not

unexpected result, since such folding and unfolding process-

es in proteins are known^[44]to be redox controlled.

For the rotaxanes 1⁴⁺, 3⁴⁺, and 5⁴⁺the first bielectronic

reduction process of the tetracationic cyclophane splits

(Table 3 and Figure 7) into two distinct processes, indicating

that the equivalence of the two bipyridinium units is lost.

This result can be accounted for by assuming that the cyclo-

phane, while encircling the TTF unit, is also involved in

other non-symmetric alongside interactions. Such behavior

requires the presence of folded conformations, an explana-

tion previously advanced for other long and flexible pseu-

dorotaxanes^[22b]and rotaxanes.^[19]Interestingly, whereas the

presence of folded conformations is required to explain the

splitting of the first bielectronic reduction for each one of

the three rotaxanes, a detailed examination of the electro-

chemical data shows that each compound displays some pe-

culiar features. Since the three rotaxanes differ only in the

nature and relative positions of the stoppers, it seems likely

that these appendages are directly involved in determining

the observed differences.

The behavior (Table 3 and Figure 7) of the rotaxane 3⁴⁺is

very similar, but not identical to that of 1⁴⁺. Replacement of

the tetraarylmethane stopper, which is distant from the tet-

racationic cyclophane encircling the TTF unit with an aryl-

oxy dendritic stopper apparently has a very weak perturbing

effect.

In the case of the rotaxane 5⁴⁺, the first process takes

place (Table 3 and Figure 7) at a potential similar to that of

1⁴⁺and 3⁴⁺, while the second process is displaced toward

more negative potentials. Furthermore, the first and second

processes observed in the case of 5⁴⁺involve an electron

each, suggesting that, in this rotaxane, 50% of the bipyridi-

nium units are engaged in folding interactions. The different

behavior of the constitutionally isomeric rotaxanes 3⁴⁺and

5⁴⁺confirms the presence of folded conformations and

demonstrates that the dendritic stopper plays a more impor-

tant role when it is closer to the tetracationic cyclophane.

The successive reduction of the two bipyridinium units

occurs at the same potential also in rotaxane 5⁴⁺indicat-

ing that, once again, after the first reduction, unfolding

occurs.

In the case of the rotaxane 1⁴⁺, which contains two identi-

cal tetraarylmethane stoppers, deconvolution of the DPV

peaks shows (Figure 7) that the first reduction process

occurs at À0.30 V, that is, at a potential slightly more nega-

tive than that (À0.29 V) of the free CBPQT⁴⁺, but slightly

less negative than that expected^[22b,41]for a bipyridinium unit

engaged in CT interactions with a threaded TTF unit. The

second process occurs at a considerably more negative po-

tential (À0.37 V), suggesting that there are bipyridinium

units that are also involved in alongside interactions in

folded conformations. Deconvolution of the DPV peaks

shows also that the first and second processes account for

1.3 and 0.7 exchanged electrons, respectively, indicating that

35% of the bipyridinium units are involved in the folded in-

165

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

Chemical oxidation/reduction and shuttle control: It is

known^[22]that TTF can be oxidized stoichiometrically to the

mono and dicationic forms, TTF⁺C and TTF²⁺, by Fe^IIIper-

chlorate. Such an oxidation process can be followed by

changes in the absorption spectra^[45](TTF⁺C: l=434 nm, e=

15000m^À1cm^À1and l=577 nm, e=4000m^À1cm^À1; TTF²⁺

:

l=348 nm, e=9000m^À1cm^À1). We have verified that the

TTF units contained within compound 10 and the dumbbell

components 2, 4, and 6, as well as the rotaxanes 1⁴⁺, 3⁴⁺

,

and 5⁴⁺, can be oxidized stoichiometrically by Fe^IIIperchlo-

rate. In the rotaxanes, the absorption band with l_max

=

840 nm, assigned to the CT interactions between the TTF

unit and the tetracationic cyclophane, disappears (Figure 8)

upon addition of a stoichiometric amount of Fe^IIIperchlo-

Figure 9. a) ¹H NMR Spectrum recorded at 500 MHz for the [2]rotaxane

5⁴⁺in CD₃CN at 243 K. The solid box highlights the peaks for the H-c/t

(cis/trans) in the neutral TTF unit encircled by the CBPQT⁴⁺cyclophane.

The dashed box highlights the region that contains the resonances for the

ring protons of the DNP system that is ™free∫ in 5⁴⁺. b) ¹H NMR Spec-

trum recorded at 500 MHz of the bis-oxidized 5⁶⁺in CD₃CN at 243 K.

The solid box highlights the peaks for the ™free∫ dicationic TTF²⁺resi-

dues and the dashed boxes indicate the peaks for H-2/6 and H-3/7 (at

lower field) and for H-4/8 (at higher field) in the DNP ring system encir-

cled by the CBPQT⁴⁺cyclophane.

Figure 8. Absorption spectra of the [2]rotaxane 3⁴⁺and of its mono- and

di-oxidized forms 3⁵⁺and 3⁶⁺obtained by Fe(ClO₄)₃oxidation of the

TTF station in MeCN. Addition of silver powder to the oxidized solu-

tions restores the original spectrum.

rate. An isobestic point is maintained at l=645 nm through-

out the titration. Addition of a second equivalent of Fe^II

leads to the two-electron oxidized species with an isobestic

point at 415 nm. These processes are reversible. Addition of

silver powder regenerates the starting species. When the

spectra of mono-oxidized dumbbells are subtracted from the

spectra of the corresponding mono-oxidized rotaxanes, weak

absorption bands with maxima at about 520 nm are ob-

tained, confirming that the tetracationic cyclophane shuttles

between the TTF and DNP ™stations∫ upon ox/red stimula-

tion.

(Figure 9b) after this oxidation, the signals for the hetero-

topic protons on the TTF unit were observed to move from

d 6.15, 6.19, 6.30, and 6.35–reflecting the fact that the TTF

unit in 5⁴⁺is in its slowly interconverting cis and trans iso-

meric states and encircled by the CBPQT⁴⁺ring–to d 9.12

and 9.22, characteristic of the free TTF²⁺dication in the oxi-

dized version of the rotaxane. Further evidence for the

translation of the CBPQT⁴⁺ring from the oxidized TTF

unit to the DNP moiety can be found in the dramatic

changes of the chemical shifts of the DNP protons. In the

starting rotaxane 5⁴⁺, the resonances appear at d 6.86 and

6.88 (H-4/8), d 7.28 and 7.32 (H-3/7) and d 7.72and 7.74 (H-

2/6) as expected. Upon oxidation of the rotaxane, the signals

for the DNP moiety experience large upfield shifts to d 2.28

and 2.29 (H-4/8), d 5.92and 5.94 (H-3/7), and d 6.21 and

6.23 (H-2/6) on account of the shielding effect of the encir-

cling CBPQT⁴⁺ring. Reduction with zinc dust restores the

original spectrum. The chemically controlled shuttling,

within the rotaxane 5⁴⁺, of the CBPQT⁴⁺ring between the

dumbbell×s TTF and DNP ™stations∫, on oxidation of the

TTF unit and its subsequent reduction, is summarized in

Figure 10.

Previously, some of us had described^[23]how the chemical-

ly controlled shuttling of the rotaxane 1⁴⁺could be moni-

1

tored by H NMR spectroscopy. In order to confirm the fact

that the addition of the hydrophilic stopper has no major

effect on the redox-based chemical switching, an identical

procedure was performed on the rotaxane 5⁴⁺. After record-

1

ing the H NMR spectrum (Figure 9a) in CD₃CN at 243 K,

2.2 equivalents of the oxidant, tris(p-bromophenyl)ammini-

um hexafluoroantimonate were added.^[46]The low tempera-

ture was employed to ensure the stability of the oxidized ro-

taxane. When the ¹H NMR spectrum was recorded again

166

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

Experimental Section

General methods: Chemicals were purchased from Aldrich and used as

received. The compounds 4,4’(5’)-bis(hydroxymethyl)-D^2,2’-bi-1,3-di-

thiole^[28](7), 2-[2-(2-iodoethoxy)-ethoxy]tetrahydropyran^[29](8), 4-[bis(4-

tert-butylphenyl)-(4-ethylphenyl)methyl]phenol^[27](12), compound^[16]15,

a,a’-[1,4-phenylenebis(methylene)]bis(4,4’-bipyridium) bis(hexa-fluoro-

phosphate)^[30](22¥2PF₆), 2-(2-{5-[2-(2-hydroxy-ethoxy)ethoxy]naphthalen-

1-yloxy}ethoxy)ethanol^[25](24), the dendritic hydrophilic stopper^[11c,26]31

and [1,1’:4’,1’’]terphenyl-4,4’’-diol^[31](33) were all prepared according to

literature procedures. Solvents were dried following methods described

in the literature.^[48]All reactions were carried out under an anhydrous

argon atmosphere. Thin-layer chromatography (TLC) was performed on

aluminum sheets coated with silica gel 60F (Merck 5554). The plates

were inspected by UV light and, if required, developed in I₂vapor.

Column chromatography was carried out by using silica gel 60 (Merck

9385, 230 400 mesh). Melting points were determined on an Electrother-

mal 9100 melting point apparatus and are uncorrected. All ¹H and

¹³C NMR spectra were recorded on either i) a Bruker ARX400

(400 MHz and 100 MHz, respectively), ii) a Bruker ARX500 (500 MHz

and 125 MHz, respectively) or iii) a Bruker Avance500 (500 MHz and

125 MHz, respectively), using residual solvent as the internal standard.

Samples were prepared using CDCl₃, CD₃COCD₃or CD₃CN purchased

from Cambridge Isotope Labs. All chemical shifts are quoted using the d

scale, and all coupling constants (J) are expressed in Hertz (Hz). Fast

atom bombardment (FAB) mass spectra were obtained using a ZAB-SE

mass spectrometer, equipped with a krypton primary atom beam utilizing

a m-nitrobenzyl alcohol matrix. Cesium iodide or poly(ethylene glycol)

were employed as reference compounds. Electrospray mass spectra

(ESMS) were measured on a VG ProSpec triple focusing mass spectrom-

eter with MeCN as the mobile phase. Microanalyses were performed by

Quantitative Technologies, Inc.

Figure 10. Idealized graphical representation of redox switching in the

amphiphilic, bistable [2]rotaxane 5⁴⁺

.

Conclusion

A systematic photophysical, electrochemical and spectro-

scopic investigation of the three [2]rotaxanes introduced in

Figure 1 has indicated that, although the nature and relative

positions of the hydrophobic and hydrophilic stoppers do

not appear to have any noticeable effect on the shuttling

properties of the rotaxanes, they do play a perceptible role

in the formation of folded conformations wherein presum-

ably stopper components interact in a stabilizing manner with

the exterior surface of the ring component. Whereas ox/red

stimulation of the tetrathiafulvalene ™station∫ causes shut-

tling of the tetracationic cyclophane between the dumbbell×s

two ™stations∫, ox/red stimulation of the cyclophane initiates

the unfolding/folding processes. These results are important

in the context of designing, synthesizing and fabricating

nanoscale systems and devices. Since the mechanically

active molecules come into contact with substrates and elec-

trodes in nanoscale systems and solid-state devices, it is un-

likely that all their fine solution-state, structural features

will be carried over into the condensed matter phase^[47]

(Figure 11). Nonetheless, forewarned of complexity means

prepared for the unexpected.

Compound 10: A solution of the iodide 8 (9.09 g, 30.3 mmol) in THF

(200 mL) was added dropwise under an Ar atmosphere to a solution

(900 mL) of the diol 7 (2.00 g, 7.89 mmol) and NaH (1.39 g, 60.6 mmol)

in THF (900 mL) and the reaction mixture was heated under reflux for

1 h. The mixture was then stirred under reflux for 48 h before being

cooled down to room temperature. After the addition of MeOH (20 mL),

the mixture was filtered though silica gel and the solution was evaporated

in vacuo to obtain the crude compound 9 as a brown oil which was dis-

solved in MeOH/CH₂Cl₂(1:1, 200 mL). A conc. HCl aqueous solution

(0.5 mL) was added and the reaction mixture was stirred at room temper-

ature for 2h. 1 n NaOH aqueous solution (200 mL) was added to the re-

action mixture and it was extracted by CH₂Cl₂(3î100 mL) and dried

(MgSO₄). After removal of the solvent, the residue was purified by

column chromatography (silica gel: CH₂Cl₂/MeOH 100:3) to give the

diol 10 (2.08 g, 60%) as an orange oil. ¹H NMR (CD₃CN, 400 MHz): d=

2.48 (br, 2H), 3.30 3.60 (m, 16H), 4.26 (s, 4H), 6.38 (s, 2H); ¹³C NMR

(CD₃CN, 100 MHz): d=62.0, 68.6, 70.2, 70.9, 73.4, 117.8, 117.9, 118.3,

135.5, 135.6; MS (FAB): m/z (%): 440

(100) [M]⁺.

Monotosylate 11: A solution of TsCl

(634 mg, 3.3 mmol) in CH₂Cl₂(10 mL)

was added dropwise to a solution of

the diol 10 (1.63 g, 3.7 mmol), Et₃N

(2.57 mL, 18.5 mmol) and DMAP

(15 mg) in CH₂Cl₂(90 mL) at 08C.

The mixture was then stirred for 16 h

at room temperature. After addition

of Al₂O₃(10 g, neutral, Brockmann I),

the mixture was evaporated and sub-

jected to column chromatography

(silica gel: CH₂Cl₂/EtOH 100:3). The

second yellow band was collected to

give the monotosylate 11 (989 mg, 45

%) as a yellow oil. ¹H NMR (CD₃CN,

500 MHz): d=2.42 (s, 2H), 2.74 (t, 1

H, J=3.7 Hz), 3.45 3.47 (m, 6H),

Figure 11. Idealized graphical representations drawing attention to the possible differences between amphiphil-

ic, bistable [2]rotaxane molecules a) equilibrating between folded and unfolded conformations in the solution

state, and b) self-organized in a condensed matter phase.

3.53 3.60 (m, 8H), 4.09 (t, 2H, J=

4.3 Hz), 4.21 (s, 2H), 4.25 (s, 2H), 6.34

(s, 1H), 6.37 (s, 1H), 7.41 (d, 2H, J=

167

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

8 Hz), 7.76 (d, 2H, J=8 Hz); ¹³C NMR (CD₃CN, 125 MHz): d=20.6,

60.7, 68.1, 68.9, 69.1, 69.8, 69.8, 69.9, 72.2, 116.7, 116.8, 127.7, 129.9, 132.7,

134.4, 134.5, 134.6, 145.3; MS (FAB): m/z (%): 748 (6) [M]⁺, 594 (51),

307 (100).

down to room temperature, the solvent was evaporated, yielding com-

pound 20 as an yellow oil, which was then dissolved in CH₂Cl₂(25 mL).

A concentrated aqueous HCl solution (0.5 mL) was added to the mixture

and it was stirred at room temperature for another 16 h. H₂O (20 mL)

was added and the mixture was extracted with CH₂Cl₂(3î30 mL) and

dried (MgSO₄). After removal of the solvent, the residue was subjected

to column chromatography (silica gel: EtOAc/hexanes 1:2) to yield 21

Compound 13: A solution of the monotosylate 11 (990 mg, 1.67 mmol),

the tetraarylmethane stopper 12 (2.38 g, 5.00 mmol), K₂CO₃(1.38 g,

10 mmol), LiBr (10 mg), and [18]crown-6 (10 mg) in dry MeCN (50 mL)

was heated under reflux for 16 h. After cooling down to room tempera-

ture, the reaction mixture was filtered and the residue was washed with

MeCN (50 mL). The combined organic phase was concentrated in vacuo

and the crude product was purified by column chromatography (silica

gel: CH₂Cl₂/EtOH 100:3) to give compound 13 (1.59 g, 95%) as a yellow

solid. M.p. 40 428C; ¹H NMR (CDCl₃, 500 MHz): d=1.16 (t, J=7.5 Hz,

3H), 1.25 (s, 18H), 2.57 (q, J=7.5 Hz, 2H), 2.70 (brs, 1H), 3.40 3.47 (m,

2H), 3.52 3.61 (m, 10H), 3.71 3.74 (m, 2H), 4.03 4.05 (m, 2H), 4.20

4.25 (m, 4H), 6.30, 6.33 (2îs, 2H), 6.75 6.78 (m, 2H), 7.06 7.13 (m, 10

H), 7.23 7.27 (m, 4H); ¹³C NMR (CD₃CN, 125 MHz): d=14.8, 25.1, 27.6,

30.4, 33.8, 60.9, 63.0, 67.3, 67.4, 69.1, 69.2, 69.8, 70.0, 70.1, 70.2, 72.2,

113.3, 116.6, 116.7, 116.7, 124.3, 126.9, 130.2, 130.5, 131.6, 134.5, 134.6,

139.5, 141.5, 144.4, 144.7, 148.3, 156.6; MS (FAB): m/z (%): 898 (42),

[M]⁺, 383 (100); elemental analysis calcd (%) for C₅₁H₆₂O₆S₄(898): C,

68.11; H, 6.95; found: C 67.99, H 5.65.

(1.58 g, 71%) as

a

white solid. M.p. 121 1238C; ¹H NMR (CDCl₃,

500 MHz): d=1.31 (t, J=7.6 Hz, 3H), 1.36 (s, 18H), 2.68 (q, J=7.6 Hz, 2

H), 4.05 (t, J=4.8 Hz, 2H), 4.08 4.13 (m, 4H), 4.15 (t, J=4.8 Hz, 2H),

4.19 4.22 (m, 2H), 4.27 (t, J=4.6 Hz, 2H), 4.36 (t, J=4.8 Hz, 2H), 4.39

(t, J=4.8 Hz, 2H), 6.86 (d, J=8.9 Hz, 2H), 6.89 (d, J=8.0 Hz, 1H), 6.90

(d, J=8.0 Hz, 1H), 6.94 (d, J=8.6 Hz, 2H), 7.05 (d, J=8.6 Hz, 2H),

7.10 7.18 (m, 10H), 7.29 (d, J=8.6 Hz, 4H), 7.38 (t, J=8.0 Hz, 1H), 7.39

(t, J=8.0 Hz, 1H), 7.52(d, J=8.6 Hz, 2H), 7.59 (d, J=8.6 Hz, 2H), 7.59

7.64 (m, 4H), 7.94 (d, J=8.0 Hz, 1H), 7.95 (d, J=8.0 Hz, 1H); ¹³C NMR

(CDCl₃, 125 MHz): d=15.3, 28.2, 30.9, 31.3, 34.2, 63.1, 67.3, 67.6, 67.9,

67.9, 69.9, 70.0, 70.0, 105.7, 113.1, 114.6, 114.7, 115.0, 115.7, 124.0, 125.1,

126.6, 126.7, 126.9, 126.9, 127.9, 128.1, 130.6, 131.0, 132.2, 133.1, 133.4,

138.9, 139.0, 139.8, 141.3, 144.1, 144.6, 148.2, 154.2, 154.3, 155.3, 156.5,

158.2; MS(FAB): m/z (%): 1038 (20) [M]⁺, 1025 (15); elemental analysis

calcd (%) for C₇₁H₇₄O₇(1038): C 82.05, H 7.18; found: C 82.09, H 7.16.

Compound 2: A solution of compound 21 (727 mg, 0.70 mmol), 14

(733 mg, 0.70 mmol), K₂CO₃(484 mg, 3.5 mol), LiBr (5 mg) and

[18]crown-6 (5 mg) in anhydrous MeCN (20 mL) was heated under reflux

for 16 h. After cooling down to room temperature, the reaction mixture

was filtered and the residue was washed with MeCN (30 mL). The com-

bined organic phase was concentrated in vacuo and the crude product

was purified by column chromatography (silica gel: EtOAc/hexanes 1:2)

to give the dumbbell-shaped compound 2 (664 mg, 47%) as a light

Compound 14: A solution of compound 13 (853 mg, 0.95 mmol), TsCl

(362mg, 1.9 mmol), DMAP (10 mg) and Et ₃N (1.1 mL, 7.6 mmol) in an-

hydrous CH₂Cl₂(50 mL) was stirred for 16 h at room temperature. After

addition of Al₂O₃(5 g, neutral, Brockmann I), the mixture was concen-

trated and the residue was subjected to column chromatography (silica

gel: CH₂Cl₂/EtOH 100:3). The first yellow band was collected and afford-

ed compound 14 (880 mg, 88%) as

a yellow solid. M.p. 45 478C;

¹H NMR (CD₃CN, 500 MHz): d=1.17 (t, J=7.6 Hz, 3H), 1.27 (s, 18H),

2.40 (s, 3H), 2.57 (q, J=7.6 Hz, 2H), 3.45 3.48 (m, 4H), 3.55 3.62 (m, 6

H), 3.73 (t, J=4.7 Hz, 2H), 4.03 4.05 (m, 2H), 4.09 4.12 (m, 2H), 4.17

4.19 (m, 2H), 4.22 (m, 2H), 6.26, 6.29 (2îs, 2H), 6.75 6.78 (m, 2H),

7.05 7.13 (m, 10H), 7.26 (m, 4H), 7.38 (d, J=8.3 Hz, 2H), 7.76 (d, J=

8.3 Hz, 2H); ¹³C NMR (CDCl₃, 125 MHz): d=14.6, 20.6, 27.6, 30.5, 33.8,

63.1, 67.4, 67.5, 68.2, 69.1, 69.3, 69.3, 69.3, 69.7, 70.0, 70.2, 110.0, 110.0,

110.1, 113.4, 113.4, 116.3, 116.4, 116.5, 124.2, 126.7, 127.6, 129.9, 130.2,

130.5, 131.7, 133.1, 134.5, 134.6, 134.6, 134.7, 139.6, 141.6, 144.4, 144.7,

145.1, 148.4, 156.7; MS (FAB): m/z (%): 1052(50) [ M]⁺, 383 (100);

HRMS (MALDI-TOF): calcd for C₅₈H₆₈O₈S₅Na: 1075.3415; found:

1075.3414.

1

yellow solid. M.p. 106 1088C; H NMR (CD₃COCD₃, 500 MHz): d=1.22

(t, J=7.6 Hz, 6H), 1.31 (s, 36H), 2.63 (q, J=7.6 Hz, 4H,), 3.62 3.64 (m,

2H), 3.64 3.68 (m, 4H), 3.70 3.73 (m, 2H), 3.79 3.82 (m, 2H), 3.85 3.87

(m, 2H), 3.96 (t, J=4.8 Hz, 2H), 4.01 (t, J=4.8 Hz, 2H), 4.04 (t, J=

4.7 Hz, 2H), 4.07 (t, J=4.7 Hz, 2H), 4.10 4.13 (m, 2H), 4.18 (t, J=

4.8 Hz, 2H), 4.20 4.23 (m, 2H), 4.25 (t, J=4.7 Hz, 2H), 4.30 4.38 (m, 8

H), 6.44, 6.46, 6.47 (3îs, 2H), 6.81 6.86 (m, 4H), 6.94 6.99 (m, 2H),

7.02 7.07 (m, 4H), 7.09 7.20 (m, 18H), 7.30 7.35 (m, 10H), 7.56 7.68 (m,

8H), 7.87 (d, J=8.3 Hz, 2H), 7.89 (d, J=8.3 Hz, 2H); MS (FAB): m/z

(%): 1920 (100) [M]⁺; elemental analysis calcd (%) for C₁₂₂H₁₃₄O₁₂S₄

(1920): C 76.29, H 7.03; found: C 76.13, H 7.06.

[2]Rotaxane 1¥4PF₆: A solution of compound 2 (588 mg, 0.31 mmol), the

dicationic salt^[30]22¥2PF₆(648 mg, 0.92mmol) and a,a’-dibromo-p-xylene

(23) (242 mg, 0.92 mmol) in anhydrous DMF (30 mL) was stirred for 10 d

at room temperature. The reaction mixture was subjected directly to

column chromatography (silica gel) and unreacted 2 was eluted with

Me₂CO, whereupon the eluent was changed to Me₂CO/NH₄PF₆(1.0 g

NH₄PF₆in 100 mL Me₂CO) and the green band containing 1¥4PF₆was

collected. Most of the solvent was removed under vacuum. After adding

H₂O (50 mL) to the residue, the precipitate was collected by filtration,

washed with Et₂O (30 mL), and dried in vacuo to afford 1¥4PF₆(357 mg,

39%) as a green powder. M.p. 2288C (decomposed without melting);

¹H NMR (CD₃CN, 500 MHz): d=1.20 (two triplets, 6H, J=7.5 Hz),

1.26 1.30 (m, 36H), 2.61 (q, J=7.5 Hz, 4H), 3.82 4.42 (m, 36H), 5.53

5.70 (m, 8H), 6.03, 6.11, 6.22, 6.28 (4îs, 2H), 6.55 (d, J=8.6 Hz, 1H),

6.59 (d, J=8.6 Hz, 1H), 6.65 (d, J=8.6 Hz, 1H), 6.72(d, J=8.6 Hz, 1H),

6.79 (d, J=8.7 Hz, 2H), 6.94 (d, J=8.7 Hz, 2H), 7.02 7.19 (m, 24H),

7.18 7.45 (m, 10H), 7.50 7.70 (m, 16H), 7.72 7.92 (m, 8H), 8.84 9.01 (m,

Compound 17: A mixture of compound 15 (1.72g, 2.0 mmol), K ₂CO₃

(0.42g, 3.0 mmol) and 4-bromo-(1,1 ’-biphenyl)-4-ol (16) (0.74 g,

3.0 mmol) was suspended in MeCN (20 mL) and heated under reflux for

16 h. After the reaction mixture had been allowed to cool down to room

temperature, it was filtered and the residue was washed with MeCN

(50 mL). The combined organic phases were concentrated in vacuo and

the crude product was purified by column chromatography (silica gel:

CH₂Cl₂/MeOH 99:1) to afford compound 17 (1.58 g, 77%) as a white

solid. M.p. 133 1358C; ¹H NMR (CDCl₃, 500 MHz): d=1.23 (t, J=

7.6 Hz, 3H), 1.30 (s, 18H), 2.62 (q, J=7.6 Hz, 2H), 3.99 (t, J=4.8 Hz, 2

H), 4.03 (t, J=4.8 Hz, 2H), 4.05 4.10 (m, 4H), 4.15 (t, J=4.8 Hz, 2H),

4.21 (t, J=4.8 Hz, 2H), 4.30 4.34 (m, 4H), 6.80 (d, J=8.0 Hz, 2H), 6.83

(d, J=8.7 Hz, 2H), 6.99 (d, J=8.8 Hz, 2H), 7.04 7.11 (m, 10H), 7.22 (d,

J=8.6 Hz, 4H), 7.31 (t, J=8.7 Hz, 2H), 7.39 (d, J=8.6 Hz, 2H), 7.45 (d,

J=8.6 Hz, 2H), 7.52 (d, J=8.6 Hz, 2H), 7.87 (d, J=8.7 Hz, 2H);

¹³C NMR (CDCl₃, 125 MHz): d=15.3, 28.2, 31.4, 34.3, 53.4, 63.1, 67.4,

67.7, 68.0, 68.0, 70.0, 70.0, 70.1, 105.7, 113.2, 114.6, 114.7, 115.1, 120.8,

124.1, 125.1, 126.6, 126.8, 126.8, 127.9, 128.3, 130.7, 131.0, 131.8, 132.2;

139.7, 141.4, 144.2, 144.6, 148.3, 154.3, 154.3, 156.5, 158.6; MS(FAB): m/z

(%): 1026 (37) [M+2]⁺, 1025 (100) [M+H]⁺, 1024 (39) [M]⁺.

8H); MS (ESI): m/z (%): 1366 (23) [MÀ2PF₆]²⁺, 862(40) [ MÀ3PF₆]³⁺

,

610 (23) [MÀ4PF₆]⁴⁺

;

elemental analysis calcd (%) for

C₁₅₈H₁₆₆F₂₄N₄O₁₂P₄S₄(3024): C 62.81, H 5.54, N 1.85; found: C 62.55, H

5.57, N 1.81; UV/Vis (MeCN): l_max=846 nm, e=3700 Lmol^À1cm^À1

.

Preparation of 1.0m Grignard reagent 19: A solution of the 2-(4-bromo-

phenoxy)-tetrahydropyran (18) (2.57 g, 10 mmol) and Mg powder

(36.5 mg, 15 mmol) in THF (10 mL) was stirred at room temperature for

2h. A clear 1.0 m Grignard reagent 19 in THF was obtained after precipi-

tation of the insoluble inorganic residue.

Compound 25: PPh₃(2.16 g, 8.24 mmol) was added in portions during

15 min to a stirred solution of compound 24^[25](2.52 g, 7.49 mmol) and

CBr₄(2.74 g, 8.26 mmol) in dry THF (25 mL) at room temperature. The

reaction mixture was stirred for 2h and then Et ₂O (50 mL) was added.

The mixture was filtered and concentrated in vacuo to give a brown oil

which was then subjected to column chromatography (silica gel: CH₂Cl₂/

MeOH 24:1) to afford compound 25 (1.04 g, 35%) as a white solid. M.p.

79 818C; ¹H NMR (CDCl₃, 200 MHz): d=2.20 (s, 1H), 3.52 (t, J=

6.2 Hz, 2H), 3.69 3.80 (m, 4H), 3.92 4.03 (m, 6H), 4.27 4.31 (m, 4H),

Compound 21: A solution of the 1.0m Grignard reagent 19 (3 mL,

3 mmol) was added to

a solution of 16 (800 mg, 0.8 mmol) and

[Pd(PPh₃)₄] (80 mg, catalytic amount) in anhydrous THF (10 mL), and

the reaction mixture was heated under reflux for 16 h. After cooling

168

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

6.84 (d, J=8.0, 2H), 7.37 (t, J=8.0 Hz, 2H), 7.88 (d, J=8.0 Hz, 2H);

¹³C NMR (CDCl₃, 50 MHz): d=30.5, 61.9, 61.9, 68.0, 69.8, 69.8, 71.5,

72.7, 105.9, 105.9, 114.7, 114.8, 125.2, 125.3, 126.8, 126.8, 154.3, 154.3; MS

(FAB): m/z (%): 401 (58) [M+H+2]⁺, 400 (100) [M+2]⁺, 399 (61)

[M+H]⁺, 398 (96) [M]⁺; elemental analysis calcd (%) for C₁₈H₂₃O₅Br

(399): C 54.15, H 5.81; found: C 53.91, H 5.71.

the solid was washed with Me₂CO (30 mL). The combined organic solu-

tion was concentrated and the residue was purified by column chroma-

tography (silica gel: CH₂Cl₂/EtOH 100:3) to give the half-dumbbell-

shaped compound 30 (664 mg, 82%) as a yellow powder. M.p. 115 117

8C; ¹H NMR (CDCl₃, 400 MHz): d=1.22 (t, J=7.5 Hz, 3H), 1.29 (s, 18

H), 2.10 (t, J=5.8 Hz, 1H), 2.61 (q, J=7.5 Hz, 2H), 3.59 3.63 (m, 4H),

3.70 3.79 (m, 8H), 3.80 3.85 (m, 2H), 3.88 3.93 (m, 2H), 4.00 4.08 (m, 4

H), 4.08 4.14 (m, 4H), 4.17 4.25 (m, 4H), 4.27 4.37 (m, 8H), 6.20, 6.21

(2îs, 2H), 6.76 (d, J=8.7 Hz, 2H), 6.86 (d, J=8.7 Hz, 2H), 6.97 7.11

(m, 14H), 7.23 (d, J=8.5 Hz, 4H), 7.31 7.42(m, 2H), 7.50 7.63 (m, 8H),

7.85 (d, J=9.0 Hz, 2H); ¹³C NMR (CDCl₃, 100 MHz): d=15.1, 28.2, 29.6,

31.2, 34.2, 61.4, 63.1, 67.5, 67.6, 67.6, 67.9, 67.9, 68.1, 68.2, 68.3, 69.2, 69.3,

69.5, 70.0, 70.2, 70.5, 72.6, 105.6, 113.1, 114.6, 114.7, 116.0, 116.6, 116.6,

124.0, 125.0, 126.4, 126.8, 126.8, 127.8, 130.2, 130.5, 133.4, 134.2, 134.3,

134.4, 134.4, 139.0, 139.7, 141.7, 143.2, 144.9, 147.3, 154.2, 156.4, 158.1;

Compound 26: A solution of compound 25 (4.07 g, 10.2mmol) tert-butyl-

chlorodimethyl silane (1.95 g, 13 mmol) and imidazole (0.88 g, 13 mmol)

in anhydrous DMF (20 mL) was stirred at room temperature for 16 h.

The reaction mixture was then poured into H₂O (20 mL) and extracted

with Et₂O (3î200 mL). The combined organic layers were washed with

H₂O and brine, and dried (MgSO₄). The solvent was evaporated in vacuo

to give a crude product as a yellow oil, which was purified by column

chromatography (silica gel: CH₂Cl₂/hexanes 1:9) to yield compound 26

(5.19 g, 99%) as a colorless oil. ¹H NMR (CDCl₃, 500 MHz): d=0.09 (s,

6H), 0.92(s, 9H), 3.51 (t, J=6.2Hz, 2H), 3.71 (t, J=5.2Hz, 2H), 3.82(t,

J=5.2Hz, 2H), 3.95 (t, J=6.2Hz, 2H), 3.97 4.02(m, 4H), 4.26 4.30 (m,

4H), 6.84 (d, J=8.0, 1H), 6.84 (d, J=8.0, 1H), 7.35 (t, J=8.0 Hz, 1H),

7.35 (t, J=8.0 Hz, 1H), 7.87 (d, J=8.0 Hz, 1H), 7.90 (d, J=8.0 Hz, 1H);

¹³C NMR (CDCl₃, 125 MHz): d=À5.3, 18.3, 25.9, 30.3, 62.8, 67.8, 67.9,

69.6, 69.8, 71.4, 72.9, 105.6, 105.6, 114.4, 114.8, 124.9, 125.0, 126.6, 126.7,

154.0, 154.3; MS (FAB): m/z (%): 514 (70) [M+2]⁺, 513 (100) [M+H]⁺,

512(61) [ M]⁺; HRMS (FAB): calcd for C₂₄H₃₇BrO₅Si: 512.1594; found:

512.1597.

MS(FAB): m/z (%): 1460 (100) [M]⁺

; HRMS (FAB): calcd for

C₈₇H₉₆O₁₂S₄: 1460.5785; found: 1460.5785.

Dumbbell-shaped compound 4: A solution of compound 30 (100 mg,

0.07 mmol), the dendritic chloride 31 (109 mg, 0.14 mmol), NaH (48 mg,

2.0 mol), NaI (10 mg, cat. amount) and [15]crown-5 (10 mg, cat. amount)

in anhydrous THF (10 mL) was heated under reflux for 16 h. After cool-

ing down to room temperature, MeOH (1 mL) was added to the reaction

mixture. The solvent was evaporated and the residue was purified by

column chromatography (silica gel: EtOAc/CH₂Cl₂1:2) to give the

dumbbell-shaped compound 4 (80 mg, 51%) as a yellow powder. M.p.

Compound 27: A solution of compound 26 (1.60 g, 3.11 mmol), K₂CO₃

(0.85 g, 6.22 mmol), 4-bromo-(1,1’-biphenyl)-4-ol (16) (1.16 g, 4.66 mmol),

and [18]crown-6 (20 mg, cat. amount) in dry MeCN (20 mL) was heated

under reflux for 16 h. After cooling down to room temperature, the reac-

tion mixture was filtered and the solid was washed with CH₂Cl₂

(100 mL). The combined organic solution was concentrated and the resi-

due was purified by column chromatography (silica gel: CH₂Cl₂) to

afford compound 27 (1.31 g, 62%) as an off-white powder. M.p. 89 91

8C; ¹H NMR (CD₃Cl₃, 500 MHz): d=0.07(s, 6H), 0.90 (s, 9H), 3.71 (t,

J=5.3 Hz, 2H), 3.82 (t, J=5.3 Hz, 2H), 4.00 (t, J=5.0 Hz, 2H), 4.03 (t,

J=4.8 Hz, 2H), 4.09 (t, J=4.8 Hz, 2H), 4.22 (t, J=4.8 Hz, 2H), 4.27 (t,

J=5.0 Hz, 2H), 4.34 (t, J=4.8 Hz, 2H), 6.83 (d, J=6.8 Hz, 1H), 6.85 (d,

J=6.8 Hz, 1H), 6.98 (d, J=8.8 Hz, 2H), 7.32 (dd, J=6.8, 9.1 Hz, 1H),

7.34 (dd, J=6.8, 9.1 Hz, 1H), 7.40 (d, J=8.5 Hz, 2H), 7.46 (d, J=8.8 Hz,

2H), 7.52 (d, J=8.5 Hz, 2H), 7.86 (d, J=9.1 Hz, 1H), 6.83 (d, J=9.1 Hz,

1H); ¹³C NMR (CDCl₃, 125 MHz): d=À5.2, 18.4, 25.9, 62.9, 67.7, 68.0,

68.0, 69.9, 70.0, 73.0, 105.6, 105.7, 114.5, 114.8, 115.1, 120.8, 125.0, 125.1,

126.8, 126.8, 127.9, 128.3, 131.8, 132.7, 139.7, 154.3, 154.4, 158.6; MS

1

65 688C; H NMR (CD₃COCD₃, 500 MHz): d = 1.20 (t, J=7.5 Hz, 3H),

1.30 (s, 18H), 2.57 (q, J=7.5 Hz, 2H), 3.28 (s, 6H), 3.29 (s, 3H), 3.47

3.51 (m, 6H), 3.59 3.70 (m, 16H), 3.75 3.80 (m, 10H), 3.81 3.83 (m, 2

H), 3.97 (t, J=4.7 Hz, 4H), 4.03 (t, J=4.7 Hz, 2H), 4.08 4.14 (m, 8H),

4.18 4.21 (m, 2H), 4.23 (t, J=4.7 Hz, 2H), 4.28 4.32 (m, 8H), 4.47 (s, 2

H), 4.90 (s, 2H), 4.98 (s, 4H), 6.32, 6.44, 6.59 (3îs, 2H), 6.73 (s, 2H),

6.78 6.85 (m, 4H), 6.91 6.96 (m, 6H), 7.00 7.04 (m, 4H), 7.04 7.14 (m,

10H), 7.25 7.35 (m, 12H), 7.55 7.65 (m, 8H), 7.85 (d, J=8.2Hz, 1H),

7.87 (d, J=8.2Hz, 1H); ¹³C NMR (CD₃COCD₃, 125 MHz): d=14.6, 27.7,

29.1, 30.6, 33.8, 57.8, 63.1, 67.5, 67.5, 67.5, 67.6, 67.6, 67.7, 68.1, 69.3, 69.4,

69.5, 69.5, 69.6, 69.6, 70.3, 70.4, 70.4, 70.7, 71.7, 72.5, 74.2, 105.9, 105.9,

107.2, 107.2, 113.3, 114.0, 114.3, 114.4, 115.0, 116.1, 116.2, 123.9, 124.9,

126.5, 126.6, 126.6, 126.9, 127.5, 127.6, 129.1, 129.7, 129.7, 130.5, 130.7,

131.8, 132.9, 134.1, 134.3, 134.7, 134.9, 137.8, 138.8, 139.4, 141.3, 144.3,

144.6, 148.2, 152.8, 154.4, 157.0, 158.7, 158.8; MS(FAB): m/z (%): 2224

(70) [M]⁺, 1460 (100); elemental analysis calcd (%) for C₁₃₀H₁₅₀O₂₄S₄: C

70.18, H 6.79; found: C 69.88, H 6.87.

(FAB): m/z (%): 683 (80) [M+H]⁺, 682(100) [ M]⁺, 681 (84) [MÀH]⁺

;

[2]Rotaxane 3¥4PF₆:

A solution of dumbbell-shaped compound 4

HRMS (MALDI-TOF): calcd for C₃₆H₄₅BrO₆SiNa: 703.2067; found:

703.2061.

(200 mg, 0.10 mmol), the dicationic salt 22¥2PF₆(212 mg, 0.30 mmol) and

a,a’-dibromo-p-xylene (23) (79 mg, 0.30 mmol) in anhydrous DMF

(10 mL) was stirred for 10 d at room temperature (after approximately

2d, the color changed to dark green and a white precipitate formed).

The green suspension was subjected to column chromatography (silica

gel) and the unreacted compound 4 was eluted with Me₂CO. Thereafter,

the eluent was changed to Me₂CO/NH₄PF₆(1.0 g NH₄PF₆in 100 mL

Me₂CO) and a green band containing the rotaxane 3¥4PF₆was collected.

Most of the solvent was removed under vacuum. After adding H₂O

(50 mL) to the residue, the precipitate was collected by filtration, washed

with Et₂O (30 mL), and dried in vacuo to afford the rotaxane 3¥4PF₆

(210 mg, 60%) as a green powder. M.p. 1158C (decomposed without

melting); ¹H NMR (CD₃CN, 500 MHz): d=1.18 (2ît, J=7.5 Hz, 3H),

1.26 1.30 (m, 18H), 2.57 (q, J=7.5 Hz, 2H), 3.26 (s, 9H), 3.45 3.48 (m, 6

H), 3.57 3.61 (m, 6H), 3.71 3.80 (m, 8H), 3.85 4.28 (m, 40H), 4.42 (s, 2

H), 4.78 (s, 2H), 4.89 (s, 4H), 5.43 5.70 (m, 8H), 6.03, 6.11, 6.22, 6.28

(4îs, 2H), 6.50 (d, J=6.8 Hz, 1H), 6.55 (d, J=6.8 Hz, 1H), 6.60 6.70

(m, 4H), 6.71 6.94 (m, 6H), 6.96 7.12(m, 14H), 7.14 7.37 (m, 16H),

7.427.62(m, 14H), 7.64 7.82(m, 8H), 8.84 9.01 (m, 8H); MS (FAB):

m/z: 3179 [MÀPF₆]⁺, 3034 [MÀ2PF₆]⁺, 2888 [MÀ3PF₆]⁺, 1517

[MÀ2PF₆]²⁺, 1445 [MÀ3PF₆]²⁺, 1372[ MÀ4PF₆]²⁺; elemental analysis

calcd (%) for C₁₆₆H₁₈₂F₂₄N₄O₂₄P₄S₄(3324): C 59.96, H 5.52, N 1.68;

found: C 59.69, H 5.43, N 1.65; UV/Vis (MeCN): l_max=846 nm, e=

Compound 29: A solution of the Grignard reagent 19 (5 mL, 5 mmol)

was added to

a solution of compound 27 (1.93 g, 2.83 mmol) and

Pd(PPh₃)₄(0.16 g, cat. amount) in anhydrous THF (10 mL), and the mix-

ture was heated under reflux for 16 h. After cooling down to room tem-

perature, the solvent was evaporated yielding a yellow powder, which

was dissolved in CH₂Cl₂(25 mL). Trifluoroacetic acid (0.5 g, cat. amount)

was added to this mixture and it was stirred at room temperature for an-

other 16 h, whereupon the mixture was poured into H₂O (50 mL), ex-

tracted with CHCl₃and dried (MgSO₄). The combined organic layers

were concentrated and the residue was subjected to column chromatogra-

phy (silica gel: EtOAc/hexanes 1:2) to yield compound 29 (1.58 g, 71%)

as a white powder. M.p. 166 1688C; ¹H NMR (CD₃COCD₃, 500 MHz):

d=3.57 (brs, 1H), 3.64 3.66 (m, 4H), 3.94 (t, J=4.7 Hz, 2H), 3.98 (t, J=

4.7 Hz, 2H), 4.05 (t, J=4.7 Hz, 2H), 4.23 (t, J=4.7 Hz, 2H), 4.27 (t, J=

4.7 Hz, 2H), 4.33 (t, J=4.7 Hz, 2H), 6.91 (d, J=4.7 Hz, 2H), 6.91 (d, J=

8.6 Hz, 2H), 6.94 (d, J=8.7 Hz, 1H), 6.97 (d, J=7.6 Hz, 1H), 7.03 (d, J=

8.6 Hz, 2H), 7.33 (dd, J=4.7, 9.0 Hz, 1H), 7.34 (dd, J=4.7, 9.0 Hz, 1H),

7.53 (d, J=8.6 Hz, 2H), 7.59 (d, J=8.7 Hz, 2H), 7.81 (d, J=9.0 Hz, 1H),

7.83 (d, J=9.0 Hz, 1H), 8.42(s, 1H); MS (FAB): m/z (%): 580 (100)

[M]⁺; elemental analysis calcd (%) for C₃₆H₃₆O₇(580): C 74.46, H 6.25;

found: C 74.11, H 6.29.

2900 Lmol^À1cm^À1

.

Half-dumbbell-shaped compound 30:

A solution of compound 14

(842mg, 0.80 mmol), compound 29 (465 mg, 0.8 mmol), K₂CO₃(484 mg,

4.0 mol), LiBr (10 mg, cat. amount) and [18]crown-6 (10 mg, cat. amount)

in anhydrous MeCN (10 mL) was heated under reflux for 16 h. After

cooling down to room temperature, the reaction mixture was filtered and

Half-dumbbell-shaped compound 32:

A solution of compound 21

(519 mg, 0.50 mmol), compound 11 (297 mg, 0.50 mmol), K₂CO₃(267 mg,

2.0 mol), LiBr (10 mg, cat. amount) and [18]crown-6 (10 mg, cat. amount)

in anhydrous MeCN (10 mL) was heated under reflux for 16 h. After

169

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

cooling, the reaction mixture was filtered and the solid was washed with

Me₂CO. The combined organic solution was concentrated, and the resi-

due was purified by column chromatography (silica gel: CH₂Cl₂/EtOH

100:3) to give the half-dumbbell-shaped compound 32 (467 mg, 64%) as

[MÀ3PF₆]⁺, 1517 [MÀ2PF₆]²⁺, 1446 [MÀ3PF₆]²⁺, 1372[ MÀ4PF₆]²⁺; ele-

mental analysis calcd (%) for C₁₆₆H₁₈₂F₂₄N₄O₂₄P₄S₄: C 59.96, H 5.52, N

1.68; found: C 59.74, H 5.55, N 1.65; UV/Vis (MeCN): l_max=850 nm, e=

4200 Lmol^À1cm^À1

.

1

a yellow powder. M.p. 106 1088C; H NMR (CDCl₃, 400 MHz): d = 1.23

Photophysical experiments: All the measurements were performed at

room temperature in air-equilibrated MeCN solutions (2î10^À51î10^À4

(t, J=7.6 Hz, 3H), 1.30 (s, 18H), 2.15 (brs, 1H), 2.62 (q, J=7.5 Hz, 2H),

3.58 3.63 (m, 4H), 3.64 3.68 (m, 4H), 3.72 3.77 (m, 4H), 3.89 (t, J=

4.4 Hz, 2H), 3.98 (t, J=4.8 Hz, 2H), 4.04 (t, J=4.8 Hz, 2H), 4.06 (t, J=

4.9 Hz, 2H), 4.09 (t, J=4.8 Hz, 2H), 4.15 (t, J=4.8 Hz, 2H), 4.20 (t, J=

4.8 Hz, 2H), 4.23 (t, J=4.8 Hz, 2H), 4.28 (s, 2H), 4.30 (s, 2H), 4.31 4.34

(m, 4H), 6.19, 6.20 (2îs, 2H), 6.76 (d, J=8.9 Hz, 2H), 6.84 (d, J=

8.7 Hz, 2H), 7.01 (d, J=8.8 Hz, 2H), 7.02 (d, J=8.9 Hz, 2H), 7.03 7.10

(m, 10H), 7.22 (d, J=8.5 Hz, 4H), 7.31 (t, J=8.7 Hz, 1H), 7.32(t, J=

8.7 Hz, 1H), 7.54 (d, J=8.8 Hz, 2H), 7.56 (d, J=8.8 Hz, 2H), 7.60 (s, 4

H), 7.86 (d, J=8.70 Hz, 1H), 7.87 (d, J=8.7 Hz, 1H); ¹³C NMR (CDCl₃,

125 MHz): d=15.2, 28.1, 29.6, 31.3, 34.2, 61.7, 63.0, 67.2, 67.4, 67.6, 67.9,

67.9, 68.1, 68.2, 68.2, 69.1, 69.2, 69.2, 69.3, 69.8, 69.9, 69.9, 70.0, 70.2, 70.7,

72.3, 105.6, 113.1, 114.5, 114.6, 114.9, 114.9, 116.2, 116.3, 116.5, 124.0,

125.0, 126.5, 126.7, 126.9, 127.8, 130.6, 130.9, 132.1, 133.4, 134.2, 134.3,

134.4, 134.4, 139.0, 139.7, 141.3, 144.0, 144.5, 148.2, 154.2, 154.2, 156.4,

158.2; MS (FAB): m/z (%): 1460 (100) [M]⁺; HRMS (MALDI-TOF):

calcd for C₈₇H₉₆O₁₂S₄Na: 1483.5682; found: 1483.5684.

m). UV/Vis absorption spectra were recorded with

a Perkin-Elmer

Lambda 40 spectrophotometer. Uncorrected fluorescence spectra were

obtained with a Perkin-Elmer LS-50 spectrofluorimeter equipped with a

Hamamatsu R928 phototube. The estimated experimental errors are:

2nm on band maxima, Æ5% on the molar absorption coefficients and

fluorescence intensity. The emission quantum yield of the p-dimethoxy-

terphenyl spacer was obtained using 1,5-dimethoxynaphthalene as a ref-

erence (f_em=0.38 in aerated MeCN solution).^[49]An Edinburgh

199 single-photon counting apparatus was used for lifetime measure-

ments. The experimental error on the lifetime values is estimated to be

Æ10%.

Electrochemical experiments: Cyclic voltammetric (CV) and differential

pulse voltammetric (DPV) experiments were carried out in argon-purged

MeCN solution at room temperature with an Autolab 30 multipurpose

instrument interfaced to a personal computer. The working electrode was

a glassy carbon electrode (0.08 cm², Amel); its surface was routinely pol-

ished with 0.05 mm alumina/water slurry on a felt surface, immediately

prior to use. In all cases, the counter electrode was a Pt spiral, separated

from the bulk solution with a fine glass frit, and an Ag wire was used as

a quasi-reference electrode. 1,1-Dimethylferrocene^[50](+0.30 V vs SCE)

was present as an internal standard for all rotaxanes. For the dumbbells,

because of peak overlapping problems, it was more convenient to use

decamethylferrocene^[51]as internal standard (À0.11 V vs SCE). The con-

centrations of the compounds were in the range 1î10^À45î10^À4m; the

experiments were carried out in the presence of 0.05m tetraethylammoni-

um hexafluorophosphate as supporting electrolyte. Cyclic voltammo-

grams were obtained with sweep rates in the range 0.05 1.0 Vs^À1; the

DPV experiments were performed with a scan rate of 20 or 4 mVs^À1

(pulse height 75 and 10 mV, respectively) and a duration of 40 ms. The

reversibility of the observed processes was established by using the crite-

ria of i) separation of 60 mV between cathodic and anodic peaks, ii) the

close to unity ratio of the intensities of the cathodic and anodic currents,

and iii) the constancy of the peak potenial on changing sweep rate in the

cyclic voltammograms. The same halfwave potential values were ob-

tained from the DPV peaks and from an average of the cathodic and

anodic CV peaks, as expected for reversible processes. For irreversible

processes the potential values were estimated from the DPV peaks. The

number of exchanged electrons in the redox processes of the investigated

dumbbells and rotaxanes was measured by comparing the current intensi-

ty of the CV waves and the area of the DPV peaks with those found for

the two reversible and bielectronic reduction processes of the cyclopha-

ne^[21a,33,39]36⁴⁺after correction for differences in concentration and diffu-

sion coefficients.^[52]The fitting and deconvolution of the DPV peaks were

obtained by employing the equations proposed by Parry and Oster-

young.^[53]The experimental error on the potential values was estimated

to be Æ10 mV and Æ20 mV for reversible and irreversible processes, re-

spectively.

Dumbbell-shaped compound 6: A solution of compound 32 (350 mg,

0.24 mmol), the dendritic chloride 31 (278 mg, 0.35 mmol), NaH (18 mg,

0.75 mol), NaI (10 mg, cat. amount) and [15]crown-5 (10 mg, cat.

amount) in anhydrous THF (20 mL) was heated under reflux for 16 h.

After the reaction had been cooled down to room temperature, the sol-

vent was evaporated and the residue was purified by column chromatog-

raphy (silica gel: EtOH/CH₂Cl₂2:100) to give the dumbbell-shaped com-

pound 6 (352mg, 66%) as a yellow powder. M.p. 78 80 8C; ¹H NMR

(CD₃COCD₃, 500 MHz): d=1.18 (t, J=7.5 Hz, 3H), 1.27 (s, 18H), 2.57

(q, J=7.5 Hz, 2H), 3.27 (s, 9H), 3.47 (t, J=4.8 Hz, 6H), 3.55 3.68 (m, 16

H), 3.74 3.81 (m, 8H), 3.92(t, J=4.8 Hz, 2H), 3.95 (t, J=4.8 Hz, 2H),

3.99 (t, J=4.8 Hz, 2H), 4.01 (t, J=4.8 Hz, 2H), 4.08 (t, J=4.8 Hz, 2H),

4.08 4.16 (m, 8H), 4.20 (t, J=4.8 Hz, 2H), 4.26 (s, 2H), 4.28 4.32 (m, 8

H), 4.43 (s, 2H), 4.90 (s, 2H), 5.01 (s, 4H), 6.39, 6.40, 6.41, 6.43 (4îs, 2

H), 6.73 (s, 2H), 6.78 6.81 (m, 4H), 6.91 6.94 (m, 6H), 6.98 7.02 (m, 4

H), 7.04 7.14 (m, 10H), 7.23 7.31 (m, 8H), 7.36 (d, J=8.3 Hz, 4H), 7.53

7.64 (m, 8H), 7.82(d, J=8.3 Hz, 1H), 7.84 (d, J=8.3 Hz, 1H); ¹³C NMR

(CD₃COCD₃, 125 MHz): d=14.6, 27.7, 29.1, 30.6, 33.8, 57.8, 63.1, 67.5,

67.5, 67.5, 67.6, 67.6, 67.7, 68.1, 69.3, 69.4, 69.5, 69.5, 69.6, 69.6, 70.3, 70.4,

70.4, 70.7, 71.7, 72.5, 74.2, 105.9, 105.9, 107.2, 107.2, 113.3, 114.0, 114.3,

114.4, 115.0, 116.1, 116.2, 123.9, 124.9, 126.5, 126.6, 126.6, 126.9, 127.5,

127.6, 129.1, 129.7, 129.7, 130.5, 130.7, 131.8, 132.9, 134.1, 134.3, 134.7,

134.9, 137.8, 138.8, 139.4, 141.3, 144.3, 144.6, 148.2, 152.8, 154.4, 157.0,

158.7, 158.8; MS(FAB): m/z (%): 2224 (100) [M]⁺, 1460 (50); elemental

analysis calcd (%) for C₁₃₀H₁₅₀O₂₄S₄(2224): C 70.18, H 6.79; found C

69.96, H 6.81.

[2]Rotaxane 5¥4PF₆:

A solution of dumbbell-shaped compound 6

(320 mg, 0.14 mmol), the dicationic salt 22¥2PF₆(304 mg, 0.43 mmol) and

a,a’-dibromo-p-xylene (23) (114 mg, 0.43 mmol) in anhydrous DMF

(20 mL) was stirred for 10 d at room temperature (after approximately

2d the color changed to dark green and a white precipitate formed). The

green suspension was subjected to column chromatography (silica gel)

and unreacted compound 6 was eluted with Me₂CO, whereupon the

eluent was changed to Me₂CO/NH₄PF₆(1.0 g NH₄PF₆in 100 mL Me₂CO)

and a green band containing the rotaxane 5¥4PF₆was collected. Most of

the solvent was removed under vacuum. After adding H₂O (50 mL) to

the residue, the precipitate was collected by filtration, washed with Et₂O

(30 mL), and dried in vacuo to afford the rotaxane 5¥4PF₆(265 mg, 57%)

as a green powder. M.p. 185 1878C; ¹H NMR (CD₃CN, 500 MHz): d =

1.20 (t, J=7.6 Hz, 3H), 1.29 (s, 18H), 2.61 (q, J=7.5 Hz, 2H), 3.30 (s, 6

H), 3.31 (s, 3H), 3.50 3.52(m, 6H), 3.63 3.65 (m, 6H), 3.79 3.83 (m, 10

H), 3.84 3.93 (m, 8H), 3.97 3.99 (m, 6H), 4.02 4.19 (m, 16H), 4.26 4.32

(m, 10H), 4.79 (s, 2H), 4.81 (s, 2H), 4.83 (s, 2H), 5.38 5.64 (m, 8H),

5.97, 6.03, 6.16, 6.24 (4îs, 2H), 6.47 (d, J=8.4 Hz, 2H), 6.76 6.87 (m, 6

H), 6.92 6.96 (m, 6H), 7.03 (d, J=8.8 Hz, 1H), 7.04 (d, J=8.8 Hz, 1H),

7.10 7.17 (m, 10H), 7.24 (d, J=8.4 Hz, 4H), 7.29 7.37 (m, 8H), 7.48 (d,

J=8.8 Hz, 1H), 7.49 (d, J=8.8 Hz, 1H), 7.53 7.67 (m, 18H), 7.69 7.74

(m, 4H), 7.81 (d, J=8.8 Hz, 1H), 7.83 (d, J=8.8 Hz, 1H), 8.65 8.95 (m,

8H); MS (FAB): m/z: 3178 [MÀPF₆]⁺, 3035 [MÀ2PF₆]⁺, 2888

Chemical redox experiments: Titration with a standardized Fe(ClO₄)₃so-

lution was performed in MeCN solution at room temperature. The con

centration of [2]rotaxane solution was 2.0î10^À5m. In the NMR spectro-

scopic experiments, 2.2 equivalents of the oxidant, tris(p-bromophe-

nyl)amminium hexafluroantimonate,^[23]were added to a 1 mm solution of

5¥4PF₆in CD₃CN at 243 K.

Acknowledgement

This research was supported at the University of California at Los An-

geles by the Defense Advanced Research Projects Agency (DARPA).

Some of the compound characterizations were supported by the National

Science Foundation under equipment grant no CHE-9974928. In Italy,

this research was supported by the European Community (HPRN-CT-

2000-00029 project), the University of Bologna (Funds for Selected Re-

search Topics) and MIUR (Supramolecular Devices Project). In Den-

170

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Redox-Controllable Amphiphilic [2]Rotaxanes

155 172

mark, this research was supported by Carlsbergfondet and the Familien

Hede Nielsen Fond.

Org. Chem. 2000, 591 602; d) J.-P. Collin, J.-M. Kern, L. Raehm, J.-

P. Sauvage in Molecular Switches (Ed.: B. L. Feringa), Wiley-VCH,

Weinheim, 2000, p. 249 280; e) B. X. Colasson, C. Dietrich-Bu-

checker, M. C. Jimenez-Molero, J.-P. Sauvage, J. Phys. Org. Chem.

2002, 15, 476 483.

[1] a) J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995;

b) Comprehensive Supramolecular Chemistry (Eds.: J.-M. Lehn, J. L.

Atwood, J. E. D. Davies, D. D. MacNicol, F. Vˆgtle), Pergamon,

Oxford, 1996; c) H.-J. Schneider, A. Yatsimirsky, Principles and

Methods in Supramolecular Chemistry, Wiley-VCH, Weinheim,

2000; d) J. W. Steed, J. L. Atwood, Supramolecular Chemistry,

Wiley-VCH, Weinheim, 2000; e) J.-M. Lehn, Science 2002, 295,

2400 2403; f) O. Ikkala, G. ten Brinke, Science 2002, 295, 2407

2409; g) M. D. Hollingsworth, Science 2002, 295, 2410 2413; h) T.

Kato, Science 2002, 295, 2414 2418; i) G. M. Whitesides, B. Grzy-

bowski, Science 2002, 295, 2418 2421.

[2] a) J. S. Lindsey, New J. Chem. 1991, 15, 153 180; b) G. M. White-

sides, J. P. Mathias, C. T. Seto, Science 1991, 254, 1312 1319; c) D.

Philp, J. F. Stoddart, Synlett 1991, 445 458; d) M. Fujita, Acc. Chem.

Res. 1999, 32, 53 61; e) J. Rebek, Jr., Acc. Chem. Res. 1999, 32,

278 286; f) D. T. Bong, T. D. Clark, J. R. Granja, M. R. Ghadiri,

Angew. Chem. 2001, 113, 1016 1041; Angew. Chem. Int. Ed. 2001,

40, 988 1011; g) L. J. Prins, D. N. Reinhoudt, P. Timmerman,

Angew. Chem. 2001, 113, 2446 2492; Angew. Chem. Int. Ed. 2001,

40, 2382 2426; h) S. R. Seidel, P. J. Stang, Acc. Chem. Res. 2002, 35,

972 983.

[11] a) C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K. Beverly, J.

Sampaio, F. M. Raymo, J. F. Stoddart, J. R. Heath, Science 2000, 289,

1172 1175; b) A. R. Pease, J. O. Jeppesen, J. F. Stoddart, Y. Luo,

C. P. Collier, J. R. Heath, Acc. Chem. Res. 2001, 34, 433 444;

c) C. P. Collier, J. O. Jeppesen, Y. Luo, J. Perkins, E. W. Wong, J. R.

Heath, J. F. Stoddart, J. Am. Chem. Soc. 2001, 123, 12632 12641;

d) Y. Luo, C. P. Collier, J. O. Jeppesen, K. A. Nielsen, E. DeIonno,

G. Ho, J. Perkins, H.-R. Tseng, T. Yamamoto, J. F. Stoddart, J. R.

Heath, ChemPhysChem 2002, 3, 519 525; e) Y. Chen, D. A. A. Ohl-

berg, X. Li, D. R. Stewart, R. S. Williams, J. O. Jeppesen, K. A. Niel-

sen, J. F. Stoddart, D. L. Olynick, E. Anderson, Appl. Phys. Lett.

2003, 1610 1612; f) Y. Chen, G.-Y. Jung, D. A. A. Ohlberg, X. Li,

D. R. Stewart, J. O. Jeppesen, K. A. Nielsen, J. F. Stoddart, R. S. Wil-

liams, Nanotechnology 2003, 14, 462 468; g) J. R. Heath, M. A.

Ratner, Physics Today 2003, May, 43 49.

[12] a) P. R. Ashton, R. Ballardini, V. Balzani, A. Credi, R. Dress, E.

Ishow, O. Kocian, J. A. Preece, N. Spencer, J. F. Stoddart, M. Ven-

turi, S. Wenger, Chem. Eur. J. 2000, 6, 3558 3574; b) A. M. Brouw-

er, C. Frochot, F. G. Gatti, D. A. Leigh, L. Mottier, F. Paolucci, S.

Roffia, G. W. H. Wurpel, Science 2001, 291, 2124 2128; e) F. G.

Gatti, S. LeÛn, J. K. Y. Wong, G. Bottari, A. Altieri, M. A. F. Mo-

rales, S. J. Teat, C. Frochot, D. A. Leigh, A. M. Brouwer, F. Zerbetto,

Proc. Natl. Acad. Sci. USA 2003, 100, 10 14.

[3] a) D. N. Reinhoudt, M. Crego-Calama, Science 2002, 295, 2403

2407.

[4] a) S. Anderson, H. L. Anderson, J. K. M. Sanders, Acc. Chem. Res.

1993, 26, 469 475; b) J. P. Schneider, J. W. Kelly, Chem. Rev. 1995,

95, 2169 2187; c) F. M. Raymo, J. F. Stoddart, Pure Appl. Chem.

1996, 68, 313 322; d) TemplatedOrganic Synthesis (Eds.: F. Dieder-

ich, P. J. Stang), Wiley-VCH, Weinheim, 1999; e) J. F. Stoddart, H.-

R. Tseng, Proc. Natl. Acad. Sci. USA 2002, 99, 4797 4800.

[5] a) G. Schill, Catenanes, Rotaxanes, andKnots, Academic Press, New

York, 1971; b) Molecular Catenanes, Rotaxanes andKnots (Eds.: J.-

P. Sauvage, C. O. Dietrich-Buchecker), Wiley-VCH, Weinheim,

1999.

[6] a) P.-L. Anelli, N. Spencer, J. F. Stoddart, J. Am. Chem. Soc. 1991,

113, 5131 5133; b) P.-L. Anelli, M. Asakawa, P. R. Ashton, R. A.

Bissell, G. Clavier, R. GÛrski, A. E. Kaifer, S. J. Langford, G. Mat-

tersteig, S. Menzer, D. Philp, A. M. Z. Slawin, N. Spencer, J. F. Stod-

dart, M. S. Tolley, D. J. Williams, Chem. Eur. J. 1997, 3, 1113 1135;

c) D. A. Leigh, A. Troisi, F. Zerbetto, Angew. Chem. 2000, 112,

358 361; Angew. Chem. Int. Ed. 2000, 39, 350 353; d) J. Cao,

M. C. T. Fyfe, J. F. Stoddart, G. R. L. Cousins, P. T. Glink, J. Org.

Chem. 2000, 65, 1937 1946; e) A. M. Elizarov, T. Chang, S.-H. Chiu,

J. F. Stoddart, Org. Lett. 2002, 4, 3565 3568.

[13] a) J. F. Stoddart, Chem. Aust. 1992, 59, 576 577 and J. F. Stoddart,

Chem. Aust. 1992, 59, 581; b) M. GÛmez-LÛpez, J. A. Preece, J. F.

Stoddart, Nanotechnology 1996, 7, 183 192; c) V. Balzani, M.

GÛmez-LÛpez, J. F. Stoddart, Acc. Chem. Res. 1998, 31, 405 414;

d) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew. Chem.

2000, 112, 3484 3530; Angew. Chem. Int. Ed. 2000, 39, 3348 3391;

e) A. Harada, Acc. Chem. Res. 2001, 34, 456 464; f) C. A. Schalley,

K. Beizai, F. Vˆgtle, Acc. Chem. Res. 2001, 34, 465 476; g) J.-P.

Collin, C. Dietrich-Buchecker, P. GaviÊa, M. C. Jimenez-Molero, J.-

P. Sauvage, Acc. Chem. Res. 2001, 34, 477 487; h) R. Ballardini, V.

Balzani, A. Credi, M. T. Gandolfi, M. Venturi, Struct. Bonding 2001,

99, 163 188; i) L. Raehm, J.-P. Sauvage, Struct. Bonding 2001, 99,

55 78; j) C. A. Stainer, S. J. Alderman, T. D. W. Claridge, H. L. An-

derson, Angew. Chem. 2002, 114, 1847 1850; Angew. Chem. Int. Ed.

2002, 41, 1769 1772; k) V. Balzani, A. Credi, M. Venturi, Chem.

Eur. J. 2002, 8, 5524 5532; l) H.-R. Tseng, J. F. Stoddart in Modern

Arene Chemistry (Ed.: D. Astruc), Wiley-VCH, Weinheim, 2002,

p 574 599; m) V. Balzani, A. Credi, M. Venturi, Molecular Devices

andMachines–A Journey into the Nano World , Wiley-VCH, Wein-

heim, 2003.

[7] a) G. Schill, K. Rissler, H. Fritz, W. Vetter, Angew. Chem. 1981, 93,

197 201; Angew. Chem. Int. Ed. Engl. 1981, 20, 187 189.

[8] a) M. C. T. Fyfe, P. T. Glink, S. Menzer, J. F. Stoddart, A. J. P. White,

D. J. Williams, Angew. Chem. 1997, 109, 2158 2160; Angew. Chem.

Int. Ed. Engl. 1997, 36, 2068 2070; b) M. C. T. Fyfe, J. F. Stoddart,

Acc. Chem. Res. 1997, 30, 393 401.

[9] a) P. R. Ashton, R. A. Bissell, N. Spencer, J. F. Stoddart, M. S.

Tolley, Synlett 1992, 923 926; b) E. CÛrdova, R. A. Bissell, N.

Spencer, P. R. Ashton, A. E. Kaifer, J. F. Stoddart, J. Org. Chem.

1993, 58, 6550 6552; c) W. Devonport, M. A. Blower, M. R. Bryce,

L. M. Goldenberg, J. Org. Chem. 1997, 62, 885 887; d) P. R.

Ashton, R. Ballardini, V. Balzani, M. GÛmez-LÛpez, S. E. Lawrence,

M.-V. MartÌnez-DÌaz, M. Montalti, A. Piersanti, L. Prodi, J. F. Stod-

dart, D. J. Williams, J. Am. Chem. Soc. 1997, 119, 10641 10651;

e) P. R. Ashton, R. Ballardini, V. Balzani, I. Baxter, A. Credi,

M. C. T. Fyfe, M. T. Gandolfi, M. GÛmez-LÛpez, M.-V. MartÌnez-

DÌaz, A. Piersanti, N. Spencer, J. F. Stoddart, M. Venturi, A. J. P.

White, D. J. Williams, J. Am. Chem. Soc. 1998, 120, 11932 11942;

f) A. M. Elizarov, H.-S. Chiu, J. F. Stoddart, J. Org. Chem. 2002, 67,

9175 9181.

[14] a) T. R. Kelly, H. De Silva, R. A. Silva, Nature 1999, 401, 150 152;

b) N. Koumura, R. W. Zijlstra, R. A. van Delden, H. Harada, B. L.

Feringa, Nature 1999, 401, 152 155; c) Y. Yokoyama, Chem. Rev.

2000, 100, 1717 1740; d) G. Berkovic, V. Krongauz, V. Weiss, Chem.

Rev. 2000, 100, 1741 1754; e) B. L. Feringa, R. A. van Delden, N.

Koumura, E. M. Geertsema, Chem. Rev. 2000, 100, 1789 1816;

f) T. R. Kelly, Acc. Chem. Res. 2001, 34, 514 522; g) S. Shinkai, M.

Ikeda, A. Sugasaki, M. Takeuchi, Acc. Chem. Res. 2001, 34, 494

503.

[15] a) C. P. Collier, E. W. Wong, M. Belohradsky, F. M. Raymo, T. Shi-

mizu, J. F. Stoddart, P. J. Kuekes, R. S. Williams, J. R. Heath, Science

1999, 285, 391 394; b) E. W. Wong, C. P. Collier, M. Belohradsky,

F. M. Raymo, J. F. Stoddart, J. R. Heath, J. Am. Chem. Soc. 2000,

122, 5831 5840; c) R. F. Service, Science 2001, 291, 426 427;

d) R. F. Service, Science 2001, 294, 2442 2443; e) M. Jacoby, Chem.

Eng. News 2002, Sept. 30, 38 43.

[16] J. O. Jeppesen, J. Perkins, J. Becher, J. F. Stoddart, Angew. Chem.

2001, 113, 1256 1261; Angew. Chem. Int. Ed. 2001, 40, 1216 1121.

[17] M. Asakawa, W. Dehaen, G. L’abbÿ, S. Menzer, J. Nouwen, F. M.

Raymo, J. F. Stoddart, D. J. Williams, J. Org. Chem. 1996, 61, 9591

9595.

[18] For reviews on CT and hydrogen bonding interactions, which are

also a source of stabilization at these recognition sites, see: a) D.

Philp, J. F. Stoddart, Angew. Chem. 1996, 108, 1242 1286; Angew.

[10] a) R. A. Bissell, E. CÛrdova, A. E. Kaifer, J. F. Stoddart, Nature

1994, 369, 133 137; b) L. Raehm, J.-M. Kern, J.-P. Sauvage, Chem.

Eur. J. 1999, 5, 3310 3317; c) R. Ballardini, V. Balzani, W. Dehaen,

A. E. Dell×Erba, F. M. Raymo, J. F. Stoddart, M. Venturi, Eur. J.

171

Chem. Eur. J. 2004, 10, 155 172

www.chemeurj.org

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

M. T. Gandolfi, M. Venturi, J. F. Stoddart et al.

FULL PAPER

Chem. Int. Ed. Engl. 1996, 35, 1154 1196; b) S. J. Rowan, S. J. Can-

trill, G. R. L. Cousins, J. K. M. Sanders, J. F. Stoddart, Angew. Chem.

2002, 114, 938 993. Angew. Chem. Int. Ed. 2002, 41, 898 952. For

accounts and reviews on [p¥¥¥p] stacking interactions, see: c) C. A.

Hunter, J. K. M. Sanders, J. Am. Chem. Soc. 1990, 112, 5525 5534;

d) M. H. Schwartz, J. Inclusion Phenom. 1990, 9, 1 35; e) J. H. Wil-

liams, Acc. Chem. Res. 1993, 26, 539 598; f) C. A. Hunter, Angew.

Chem. 1993, 105, 1653 1655; Angew. Chem. Int. Ed. Engl. 1993, 32,

1584 1586; g) C. A. Hunter, J. Mol. Biol. 1993, 230, 1025 1054;

h) T. Dahl, Acta. Chem. Scand. 1994, 48, 95 116; i) F. Cozzi, J. S.

Siegel, Pure Appl. Chem. 1995, 67, 683 689; j) C. G. Claessens, J. F.

Stoddart, J. Phys. Org. Chem. 1997, 10, 254 272; k) G. Chessari,

C. A. Hunter, C. M. R. Low, M. J. Packer, J. G. Vinter, C. Zonta,

Chem. Eur. J. 2002, 8, 2860 2867.

[34] I. B. Berlman, Handbook of Fluorescence Spectra of Aromatic Mole-

cules, Academic Press, London, 1971.

[35] a) P. R. Ashton, R. Ballardini, V. Balzani, M. Belohradsky, M. T.

Gandolfi, D. Philp, L. Prodi, F. M. Raymo, M. V. Reddington, N.

Spencer, J. F. Stoddart, M. Venturi, D. J. Williams, J. Am. Chem.

Soc. 1996, 118, 4931 4951; b) R. Ballardini, V. Balzani, W. Dehaen,

A. E. Dell’Erba, F. M. Raymo, J. F. Stoddart, M. Venturi, Eur. J.

Org. Chem. 2000, 591 602.

[36] A. Gilbert, J. Baggott, Essentials of Molecular Photochemistry,

Blackwell Scientific Publications, Oxford, 1991.

[37] a) K. B. Simonsen, J. Becher, Synlett 1997, 1211 1220; b) M. R.

Bryce, J. Mater. Chem. 2000, 10, 590 598; c) J. O. Jeppesen, J.

Becher, Eur. J. Org. Chem. 2003, 3245 3266.

[38] A. Zweig, A. H. Maurer, B. G. Roberts, J. Org. Chem. 1967, 32,

1322 1329.

[19] J. O. Jeppesen, K. A. Nielsen, J. Perkins, S. A. Vignon, A. Di Fabio,

R. Ballardini, M. T. Gandolfi, M. Venturi, V. Balzani, J. Becher, J. F.

Stoddart, Chem. Eur. J. 2003, 9, 2982 3007.

[39] E. A. Smith, R. R. Lilienthal, R. J. Fonseca, D. K. Smith, Anal.

Chem. 1994, 66, 3013 3020.

[40] The DNP moiety encircled by CBPQT⁴⁺is oxidized at +1.55 V; see

ref. [22a].

[20] P. R. Ashton, V. Balzani, J. Becher, A. Credi, M. C. T. Fyfe, G. Mat-

tersteig, S. Menzer, M. B. Nielsen, F. M. Raymo, J. F. Stoddart, M.

Venturi, D. J. Williams, J. Am. Chem. Soc. 1999, 121, 3951 3957.

[21] a) P. R. Ashton, R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi,

D. J.-F. Marquis, L. Pÿrez-Garciµ, L. Prodi, J. F. Stoddart, M. Ven-

turi, A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 1995, 117,

11171 11197; b) R. Castro, K. R. Nixon, J. D. Evenseck, A. E.

Kaifer, J. Org. Chem. 1996, 61, 7298 7303.

[22] a) M. Asakawa, P. R. Ashton, V. Balzani, A. Credi, C. Hamers, G.

Mattersteig, M. Montalti, A. N. Shipway, N. Spencer, J. F. Stoddart,

M. S. Tolley, M. Venturi, A. J. P. White, D. J. Williams, Angew.

Chem. 1998, 110, 357 361; Angew. Chem. Int. Ed. 1998, 37, 333

337; b) V. Balzani, A. Credi, G. Mattersteig, O. A. Matthews, F. M.

Raymo, J. F. Stoddart, M. Venturi, A. J. P. White, D. J. Williams, J.

Org. Chem. 2000, 65, 1924 1936; c) M. Asakawa, M. Higuchi, G.

Mattersteig, T. Nakamura, A. R. Pease, F. M. Raymo, T. Shimizu,

J. F. Stoddart, Adv. Mater. 2000, 12, 1099 1102.

[23] H.-R Tseng, S. A. Vignon, J. F. Stoddart, Angew. Chem. 2003, 115,

1529 1533; Angew. Chem. Int. Ed. 2003, 42, 1491 1495.

[24] P.-L. Anelli, P. R. Ashton, N. Spencer, A. M. Z. Slawin, J. F. Stod-

dart, D. J. Williams, Angew. Chem. 1991, 103, 1052 1055; Angew.

Chem. Int. Ed. Engl. 1991, 30, 1036 1039.

[25] P. R. Ashton, R. Ballardini, V. Balzani, S. E. Boyd, A. Credi, M. T.

Gandolfi, M. GÛmez-LÛpez, S. Iqbal, D. Philp, J. A. Preece, L.

Prodi, H. G. Ricketts, J. F. Stoddart, M. S. Tolley, M. Venturi, A. J. P.

White, D. J. Williams, Chem. Eur. J. 1997, 3, 152 170.

[26] J. O. Jeppesen, J. Perkins, J. Becher, J. F. Stoddart, Org. Lett. 2000, 2,

3547 3550.

[41] M. Asakawa, P. R. Ashton, V. Balzani, A. Credi, G. Mattersteig,

O. A. Matthews, M. Montalti, N. Spencer, J. F. Stoddart, M. Venturi,

Chem. Eur. J. 1997, 3, 1992 1996.

[42] a) E. CÛrdova, R. A. Bissell, N. Spencer, P. R. Ashton, J. F. Stoddart,

A. E. Kaifer, J. Org. Chem. 1993, 58, 6550 6552; b) E. CÛrdova,

R. A. Bissell, A. E. Kaifer, J. Org. Chem. 1995, 60, 1033 1038.

[43] The peak asymmetry (Figure 7) associated with the second reduc-

tion process for the [2]rotaxanes 1⁴⁺and 3⁴⁺disappears when the

differential pulse voltammograms are performed under standard

À1

conditions (v=2 0 mVs , pulse height=75 mV). This observation

suggests that a very small amount of another electroactive species

might be present in the MeCN solution at room temperature. This

species could be a trace of impurity or a minor quantity of the other

translational isomer where the CBPQT⁴⁺ring is located on the

DNP moiety.

[44] a) T. Pascher, J. P. Chesick, J. R. Winkler, H. B. Gray, Science 1996,

271, 1558 1560; b) E. Chen, P. Wittung-Stafshede, D. S. Kliger, J.

Am. Chem. Soc. 1999, 121, 3811 3817; c) J. C. Lee, H. B. Gray, J. R.

Winkler, Proc. Natl. Acad. Sci. USA 2001, 98, 7760 7764; d) G. P.

Dado, S. H. Gellman, J. Am. Chem. Soc. 1993, 115, 12609 12610.

[45] a) S. H¸nig, G. Kie˚lich, H. Quast, D. Scheutzow, Liebigs Ann.

Chem. 1973, 310 323; b) G. Schukat, E. Fangh‰nel, J. Prakt. Chem.

1985, 327, 767 774; c) A. Credi, M. Montalti, V. Balzani, S. J. Lang-

ford, F. M. Raymo, J. F. Stoddart, New J. Chem. 1998, 22, 1061

1065.

[46] This oxidant was chosen for three reasons–1) it has a high enough

oxidative potential (0.7 V vs ferrocene) to oxidize the TTF unit

completely to TTF²⁺, 2) the reduced form will give only two signals

in the ¹H NMR spectrum and will not interfere with the interpreta-

tion of the data, and 3) the solubilities of both the oxidant and its re-

duced form are as good in the same solvents as the rotaxanes of in-

terest. For details, see: a) N. G. Connelly, W. E. Geiger, Chem. Rev.

1996, 96, 877 910; b) E. Steckhan, Top. Curr. Chem. 1987, 142, 1

69.

[47] T. J. Huang, H.-R. Tseng, L. Sha, W. Lu, B. Brough, B. Yu, P. C. Cel-

estre, P. J. Chang, J. F. Stoddart, C.-M. Ho, submitted.

[48] D. D. Perrin, W. L. F. Armarego, Purification of Laboratory Chemi-

cals, Pergamon Press, New York, 1998.

[27] P. R. Ashton, R. Ballardini, V. Balzani, M. Belohradsky, M. T. Gan-

dolfi, D. Philp, L. Prodi, F. M. Raymo, M. V. Reddington, N.

Spencer, J, F. Stoddart, M. Venturi, D. J. Williams, J. Am. Chem.

Soc. 1996, 118, 4931 4951.

[28] R. Andreu, J. GarÌn, J. Orduna, M. SavÌron, J. Cousseau, A. Gor-

gues, V. Morisson, T. Nozdryn, J. Becher, R. P. Clausen, M. R.

Bryce, P. J. Skabara, W. Dehaen, Tetrahedron Lett. 1994, 35, 9243

9246.

[29] J. G. Hansen, K. S. Bang, N. Thorup, J. Becher, Eur. J. Org. Chem.

2000, 11, 2135 2144.

[30] P. R. Ashton, G. R. Brown, N. S. Isaacs, D. Giuffrida, F. H. Kohnke,

J. P. Mathias, A. M. Z. Slawin, D. R. Smith, J. F. Stoddart, D. J. Wil-

liams, J. Am. Chem. Soc. 1992, 114, 6330 6353.

[49] R. Ballardini, V. Balzani, M. T. Gandolfi, R. E. Gillard, J. F. Stod-

dart, E. Tabellini, Chem. Eur. J. 1998, 4, 449 459.

[50] S. F. Nelsen, L.-J. Chen, M. T. Ramm, G. T. Voy, D. R. Powell, M. A.

Aceola, T. R. Seehafer, J. J. Sabelko, J. R. Pladziewicz, J. Org. Chem.

1996, 61, 1405 1412.

[51] I. Noviandri, K. N. Brown, D. S. Fleming, P. T. Gulyas, P. A. Lay,

A. F. Masters, L. Phillips, J. Phys. Chem. B 1999, 103, 6713 6722.

[52] J. B. Flanagan, S. Margel, A. J. Bard, F. C. Anson, J. Am. Chem. Soc.

1978, 100, 4248 4253.

[31] Y.-K. Han, A. Reiser, Macromolecules 1998, 31, 8789 8793.

[32] In the case of the [2]rotaxane 5¥4PF₆, it has been demonstrated that

no intermolecular aggregation occurs in the concentration range

from 4.8î10^À6m up to 4.8î10^À4m in MeCN. Starting from a solution

of 5¥4PF₆with the higher concentration and diluting it stepwise

down to the lower concentration, no deviation from linear Lam-

bert Beer behavior was observed at five different wavelengths,

namely 337, 361, 470, 700, and 845 nm.

[33] P.-L. Anelli, P. R. Ashton, R. Ballardini, V. Balzani, M. Delgado,

M. T. Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp, M. Pietrasz-

kiewicz, L. Prodi, M. V. Reddington, A. M. Z. Slawin, N. Spencer,

J. F. Stoddart, C. Vicent, D. J. Williams, J. Am. Chem. Soc. 1992, 114,

193 218.

[53] E. P. Parry, R. A. Osteryoung, Anal. Chem. 1965, 37, 1634 1637.

Received: June 4, 2003

Revised: August 21, 2003 [F5204]

172

¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

Chem. Eur. J. 2004, 10, 155 172

Article Doi

Redox-Controllable Amphiphilic [2]Rotaxanes

DOI: 10.1002/chem.200305204

Source and publish data:

Authors:

Article abstract of DOI:10.1002/chem.200305204

Full text of DOI:10.1002/chem.200305204

Products guided by the article

R&D Labs maybe for 666729-04-0

Relevant to this article

Hot Product