Altering intercomponent interactions in a photochromic multi-state [2]rotaxane

Article abstract of DOI:10.1039/c1ob05307h

Rotaxanes have attracted much attention because of their challenging constructions and potential applications. In this paper, a multi-state [2]rotaxane, in which a dithienylethene-functionalized dibenzo-24-crown-8 macrocycle was interlocked onto a thread

Full text of DOI:10.1039/c1ob05307h

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PAPER
Altering intercomponent interactions in a photochromic multi-state
[2]rotaxane†
Hui Zhang, Xin-Xin Kou, Qiong Zhang, Da-Hui Qu* and He Tian*
Received 25th February 2011, Accepted 15th March 2011
DOI: 10.1039/c1ob05307h
Rotaxanes have attracted much attention because of their challenging constructions and potential
applications. In this paper, a multi-state [2]rotaxane, in which a dithienylethene-functionalized
dibenzo-24-crown-8 macrocycle was interlocked onto a thread component bearing a
4-morpholin-naphthalimide fluorescent stopper and two distinct recognition sites, namely,
dibenzylammonium and N-methyltriazolium recognition sites, was prepared and studied. By
introducing a dithienylethene photochrome into the macrocycle component, multi-mode alteration of
the intercomponent interactions, such as energy transfer, electron transfer, and charge transfer
interaction between the photochrome and the fluorescent naphthalimide stopper could be altered in
this multi-state rotaxane system in response to the combination of chemical and photochemical stimuli.
Introduction
During the past few decades, research on mechanically interlocked
molecules, better known as rotaxanes and catenanes, has grown
to an unprecedented level of activity, because of their interesting
physical and chemical properties, applications in molecular elec-
tronics and smart materials with adjustable surface properties and
as components of molecular machinery.1–2 A bistable [2]rotaxane,
in which the competitive binding ability of a macrocycle with two
distinct, well-separated recognition sites on the thread component,
can be changed in response to an external stimuli, and can function
as molecular switches or molecular logic gates if functional units
are introduced into a rotaxane molecule.2 Up until now various
functional units were introduced into mechanically interlocked
structures to achieve specific functions2 and to realize intercompo-
nentinteractions such as electron transfer,3 energytransfer,4 charge
transfer5 interactions etc. To develop more advanced molecular
Fig. 1 The chemical structures of a photochromic rotaxane 1-H-o,
machines and to increase functional complexity, it is necessary
to combine and alter the common intramolecular interactions on
a unimolecular platform.6 In this paper, we have demonstrated
that the combination of multi-mode intercomponent interactions
can be altered in a photochromic multi-stable [2]rotaxane, with
its structure shown in Fig. 1. By introducing a dithienylethene
(DTE) photochromic7 functional group in this system, multi-
mode alteration of intercomponent interactions such as energy
transfer, electron transfer, charge transfer interaction etc., can be
a dumbbell-shaped thread component 2-H, dithienylethene-containing
crown ether 3-o and its photo-induced reversible interconversions between
the ring-opened form (3-o) and the ring-closed form (3-c).
realized within a controllable configuration and spatial distance
(Scheme 1), along with UV/Vis absorption and fluorescence
spectral changes in response to the combination of chemical and
photochemical stimuli. This kind of multi-state molecular shuttle
holds the potential to construct multi-level molecular machines
and complicated logic gates.6,8
Key Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science & Technology, Shanghai, 200237, P. R.
China. E-mail: dahui_qu@ecust.edu.cn, tianhe@ecust.edu.cn; Fax: +86-21
64252288
Results and discussion
Molecular design and syntheses
† Electronic supplementary information (ESI) available: Full experimental
procedures and characterization data; UV/Vis absorption and fluores-
cence spectra. See DOI: 10.1039/c1ob05307h
The chemical structures of the multi-state [2]rotaxane 1-H-o,
along with its dumbbell-shaped thread component 2-H and
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Scheme 1 Schematic representations and interconversions between the
four states of rotaxane 1-H-o, and the fluorescence spectral changes
for rotaxane 1-H-o in response to different combinations of chemical
and photochemical stimuli. The fluorescence spectral changes a, b, c, d
correspond to routes a, b, c, d, respectively.
Fig. 2 Preparation of compound 2-H and [2]rotaxane 1-H-o.
for DB24C8, was terminated at one end by a dimethyl 5-
hydroxyisophthalate stopper, and at the other end by an azide
functional group. Compound 12 was obtained in high yield in two
steps, starting from the known compounds 9 and 10, as shown in
Scheme S1.
dithienylcyclopentene-containing crown-ether 3-o are shown in
Fig. 1. Rotaxane 1-H-o has several key features: a pho-
tochromic dithienylethene (DTE) unit was incorporated into a
dibenzo-24-crown-8 ring (DB24C8) that was interlocked onto a
dumbbell-shaped thread component 2-H, bearing a 4-morpholin-
naphthalimide (MA) fluorescent stopper situated at one end. Two
distinguishable binding sites for DB24C8, namely dibenzylam-
monium (DBA)9 and N-methyltriazolium (MTA)10 recognition
sites, were separated by a long-distance alkyl chain. 4-Morpholin-
naphthalimide unit was chosen as a fluorescent stopper situated
at one end of the thread because of its high photostability, high
fluorescent quantum yield, and desirable spectroscopic properties.
A mono-chloride substituted perhydrodithienylcyclopentene unit,
covalently attached to a 24-crown-8 macrocycle ring, was chosen as
the photochromic unit. The interaction between secondary dialky-
The synthesis of the key macrocycle ring, dithienylcyclopentene-
containing crown ether 3-o, was illustrated in Scheme S2.†
Bischlorodithienylcyclopentene 13 was treated with one equivalent
n-butyl lithium to yield dithienylcyclopentene monoboronic acid
dimethyl ester, followed by a Suzuki coupling with 4-bromo-
dibenzo-24-crown-8 14 to afford 3-o in a moderate yield. As shown
in Scheme 1, alkyne 8 and crown ether 3-o was mixed in dry CH2Cl2
at room temperature, after which azide 12 and Cu(CH3CN)4PF6
catalyst were added to the solution, and the mixture was stirred
for two days to form the rotaxanes 1-H-o in 20% isolated yield.
The thread component 2-H was prepared in 50% isolated yield
under the same conditions as for the preparation of rotaxane 1-
H-o in the absence of macrocycle ring 3-o. Rotaxane 1-H-o and
+
lammonium ions (R2NH2 ) and dibenzo-24-crown-8 (DB24C8)
ring has been chosen as the binding motifs in our design. An
1,2,3-triazolium receptor, namely the N-methyltriazolium moiety,
was selected as a less favorable recognition site for DB24C8
upon the deprotonation of a more favorable R2NH2+ binding site.
The well-known Cu(I)-catalyzed azide-alkyne cycloaddition, also
called “click chemistry” was chosen as the stoppering strategy
of rotaxane preparation due to its high efficiency and functional
group tolerance.
1
thread compound 2-H were well characterized using H NMR,
13C NMR and HR-ESI mass spectrometry. The HR-ESI mass
spectrum revealed that the most intense peak occurred at m/z
887.3704 as a doubly charged peak for rotaxane 1-H-o, with an
isotope distribution corresponding to the consecutive loss of two
-
PF6 counterions, i.e. [M - 2PF6]2+.
The syntheses of the [2]rotaxanes 1-H-o, the thread component
2-H, dithienylcyclopentene-containing crown-ether 3-o and the
key intermediates involved in the preparation of the rotaxane
system are outlined in Fig. 2, Scheme S1 and S2 (supporting
information†) and described in detail in the experimental section.
As shown in Scheme S1, the alkyne 8, incorporating a DBA unit
as a primary recognition site for DB24C8 in the middle of the
chain, terminated at one end by a 4-morpholin-naphthalimide
fluorescent stopper, and at the other by a terminal alkyne
group, was obtained in high yield in three steps, starting from
the known compounds 4, 5, and 7. The azide 12, containing
a N-methyltriazolium moiety as a secondary recognition site
1H NMR measurements
1
The H NMR of 1-H-o in CD3COCD3 confirmed the location
of the macrocycle to be predominantly over the DBA binding
site. As shown in Fig. 3a and 3b, the peak for the methylene
protons H8 neighbouring to the naphthalimide fluorescent stopper
become split, and the peak for the methylene protons H11, H12
on the DBA recognition station are shifted downfield with a Dd
of 0.16 compared with the one of dumbbell 2-H. Moreover, the
protons (H21, H22, H23) on the unencircled N-methyltriazolium
unit have the same chemical shifts as the ones on dumbbell 2-
H, proving the fact that the DB24C8 ring exhibit a predominant
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Table 1 Excitation wavelength (lex), monitoring wavelength (lem), fluorescence lifetime (t), and relative emission intensity (Ir) of 2-H and 1-H-o obtained
from the time-resolved fluorescence measurement in dichloromethane solution
a
lex (nm)
lem (nm)
t (ns)
Ir
2-H
398
395
398
396
398
398
513
510
512
510
511
510
8.96
8.27
0.87
0.85
0.63
0.90
0.30
0.59
2-H + DBU
1-H-o
8.15 (78.21%), 4.38 (21.79%)
8.44
8.72 (90.70%), 3.47 (9.30%)
8.34
1-H-o + DBU (1-o)
1-H-o at PSS (1-H-c)
1-H-o + DBU at PSS (1-c)
a The relative emission intensity (Ir) was calculated using a reference compound, namely N-ethyl-4-morpholin-naphthalimide, whose emission intensity
in a dichloromethane solution at a concentration of 1.0 ¥ 10-5 M was defined as 1.
The photophysical properties of 1-H-o, 2-H and 3-o
The physical properties of dithienylethene-containing crown ether
3-o and the dumbbell 2-H were investigated. Irradiation of a
dichloromethane solution containing 3-o with 254 nm resulted
in an immediate decrease in the intensity of the absorption band
at around 300 nm corresponding to the disappearance of the
ring-opened isomer 3-o along with a concomitant increase in an
absorption band at 450–600 nm (Figure S3†), corresponding to the
appearance of the ring-closed isomer 3-c (Fig. 1). A clear isosbestic
point was observed around 335 nm, indicating a unimolecular
process. The generated red 3-c solution returns to colorless 3-o
upon irradiation with visible light (> 450 nm). Compound 2-H
showed an absorption band with lmax at 398 nm and a strong
emission band with lem at 511 nm (Figure S4†). The decay profile
of dumbbell 2-H was a single exponential with a lifetime of 8.96 ns
(Table 1), typical of MA fluorophore. Upon addition of 5 eq.
DBU, which can deprotonate the ammonium center to a secondary
amine group, a small spectral change was observed. Moreover, as
shown in Table 1, the fluorescence lifetime of compound 2-H upon
addition of 5 eq. DBU almost hardly changes. It is reasonable
because deprotonation of the ammonium center does not affect
the fluorescent moiety and the efficiency of the PElT process from
the free amine to the fluorescent moiety is extremely low in this
case.11,12 This also helps to study the photophysical properties of
the [2]rotaxane 1-H-o.
Next we focused on the physical properties of the [2]rotaxane
1-H-o in response to chemical and photochemical stimuli. As
shown in Scheme 1, starting from 1-H-o, addition of excess
DBU can drive the functionalized macrocycle shuttling to the
N-methyltriazolium recognition station, generating 1-o (route a),
followed by irradiation at 254 nm to reach the photostationary
state (PSS) to give 1-c (route d), in which the DTE unit is in its ring-
closed form; starting from 1-H-o, irradiation at 254 nm results in
the formation of 1-H-c (route b), which was treated by addition of
excess DBU to yield 1-c (route d). Each route was characterized by
time-resolved fluorescence spectroscopy and UV/Vis absorption
spectroscopy, as discussed below.
The emission intensity of the rotaxane 1-H-o is around 72%
of that of the dumbbell 2-H, and the time-resolved fluores-
cence of 1-H-o showed a bi-exponential decay with lifetimes
of 8.15 ns (78.21%) and 4.38 ns (21.79%) compared with the
mono-exponential decay of dumbbell 2-H, which is attributed to
photoinduced electron transfer process (PElT) from the opened-
form DTE photochrome to the excited state of 4-morpholin-
naphthalimide fluorophore. The HOMO and LUMO values of the
Fig. 3 1H NMR spectra (400 MHz, CD3COCD3, 298 K) of (a) thread
2-H, (b) [2]rotaxane 1-H-o, (c) deprotonation with addition of 1.2 eq. of
DBU to sample b, (d) reprotonation with addition of 1.4 eq. of TFA to
sample c. The assignments corresponding to the structures were shown in
Fig. 1.
+
selectivity for the encirclement of the DBA (R2NH2 ) recognition
site.
Addition of 1.2 eq. 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
resulted in the migration of the DB24C8 ring to the N-
methyltriazolium recognition site (Fig. 3c), generating 1-o (shown
in Scheme 1). The methylene protons H11 and H12 in the DBA
station are shifted upfield with a Dd of -1.05 ppm. The peaks
for the N-methyltriazolium protons are shifted due to association
with the DB24C8 ring, for H21 with a Dd of 0.34 ppm and H22,
H23 with Dd of -0.33, -0.17 ppm, respectively. Moreover, the
peak for the methylene protons H8 becomes singlet relative to
the original multiplet because of the migration of the DB24C8
ring from the DBA recognition station to the N-methyltriazolium
station. Reprotonation of the -NH- center with the addition of
1.4 eq. of CF3CO2H resulted in the return of the DB24C8 ring to
the DBA recognition station as evidenced by the regeneration
of the original 1H NMR spectrum (Fig. 3d). Thus, by 1H
NMR spectroscopic measurements, chemically driven reversible
shuttling motion of the [2]rotaxane 1-H-o has been demons-
trated.
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fluorophore, N-ethyl-4-morpholin-naphthalimide, was calculated
as -5.66 eV and -2.12 eV, respectively. The HOMO and LUMO
values of ring-opened 3-o, was calculated as -5.05 eV and -0.77 eV,
respectively. The HOMO values of the two functional units further
showed it is possible that an electron from the HOMO of the
opened-form photochrome was transferred to the vacancy in the
HOMO of the excited 4-morpholin-naphthalimide fluorophore,
and this PElT process partially quenched the fluorescence of the
4-morpholin-naphthalimide moiety. After addition of 5 eq. DBU
to convert 1-H-o to 1-o (route a in Scheme 1), the emission
intensity increased 43% (Scheme 1a) and became the same value
as that of dumbbell 2-H. Moreover, time-resolved fluorescence of
1-o exhibited a mono-exponential decay with lifetime of 8.44 ns,
further proving the distance-dependent PElT is eliminated because
of the large distance between the two functional units. Irradiating
1-o at 254 nm to reach the PSS containing 1-c (route d in Scheme
1), the emission intensity decreased 35% (d in Scheme 1), due to
less efficient photoinduced energy transfer process (PEnT) between
naphthalimide and ring-closed DTE moieties in 1-c.
Upon irradiation of rotaxane 1-H-o at 254 nm (route b in
Scheme 1), generating 1-H-c, the emission intensity decreased
54% at the PSS (b in Scheme 1), indicating a conversion of an
efficient PElT process to an efficient PEnT process, which occurred
between the excited naphthalimide fluorophore and closed-form
DTE unit.12,13 To this PSS solution, 5 eq. DBU was added to
generate 1-c, in which the closed-form dithienylethene-containing
macrocycle was encircled on the N-methyltriazolium station (route
c in Scheme 1). The emission intensity increased 97% compared
to that of the PSS mixture (c in Scheme 1), and the time-resolved
fluorescence became a mono-exponential decay with a lifetime
of 8.34 ns from the original bi-exponential decay, both of which
indicate an conversion of an efficient PEnT process to a less efficient
PEnT process between the functional units. It should be mentioned
that the two strategies to generate 1-c, namely routes a + d and
routes b + c (Scheme 1), gave the same UV/Vis absorption and
fluorescence spectra, indicating the same mixture ratio at the
photostationary states of both strategies.
-5
Fig. 4 UV/Vis spectra of [2]rotaxane 1-H-o in CH2Cl2 (1 ¥ 10 M) at
room temperature, a) upon irradiation at 254 nm for 210 s to reach the
PSS. Insert: enlargement of the spectra in the band of 550–700 nm; b) upon
irradiation at 254 nm for 210 s to reach the PSS in the presence of 5 eq.
DBU.
UV/Vis absorption spectroscopy was also employed to inves-
tigate the photochromic properties of 1-H-o and 1-o, in which
the dithienylethene-containing crown ether 3-o was located at two
different recognition stations, namely, the DBA site and the MTA
site, respectively. As shown in Fig. 4, new absorption bands at 450–
600 nm arose upon irradiation of the 1-H-o and 1-o solutions at
254 nm, indicative of the appearance of ring-closed DTE units in
1-H-c and 1-c, respectively. However, as shown in Fig. 4a (insert),
an additional peak at around 580–700 nm was observed during the
photoisomerization process of 1-H-o, compared with that of 1-o,
which might be attributed to the intercomponent charge transfer
interaction between the electron-deficient naphthalimide unit and
the electron-rich closed-form dithienylethene unit. Addition of 5
eq. DBU can drive the closed-form DTE photochrome shuttling
to the N-methyltriazolium station and eliminated the intercompo-
nent charge transfer interaction, evident from disapearance of the
absorption band at 580–700 nm (Figure S5†). Irradiation of either
macrocycle 3-o (Figure S3†), rotaxane 1-o (Fig. 4b), or a mixture
of 3-o and 2-H (Figure S6†) could not result in the formation of
the absorption band at 580-700 nm, further proving there is an
intercomponent charge transfer between the two functional units
in rotaxane 1-H-c. The photochemical conversions of both 1-H-
o and 1-o are reversible, which are similar to the photochemical
process of 3-o.
Experimental
General
1H NMR and 13C NMR spectra were measured on a Bru¨ker
AV-400 spectrometer. The electronic spray ionization (ESI) mass
spectra were tested on a LCT Premier XE mass spectrometer. The
UV-Vis absorption spectra and fluorescence spectra were obtained
on a Varian Cary 100 spectrometer and a Varian Cary Eclipse
(1 cm quartz cell used), respectively. The fluorescence lifetime
measurements were performed by using the time correlated single
photon counting (TCSPC) technique following excitation by a
nanosecond flash lamp (Edinburgh instruments FL920). The
photoirradiation was carried out by a CHF-XM 500-W high-
pressure mercury lamp in a sealed Ar-saturated 1 cm quartz cell.
The distance between the lamp and the sample cell was 20 cm.
Photostationary states were ensured by monitoring composition
changes in time by taking UV spectra at distinct intervals until
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no changes were observed. The fluorescence intensity of all com-
pounds that contain 4-morpholin-naphthalimide was normalized.
Synthesis of compound 3-o
To the solution of 1,2-bis(5-chloro-2-methylthien-3-yl) cyclopen-
tene 13 (0.50 g, 1.52 mmol) in anhydrous THF (10 ml), n-BuLi
(0.5 ml of 2.5 M solution in hexane, 1.6 mmol) was added using a
syringe in two portions under nitrogen at -78 ◦C and then stirred
for 1 h. After tri-n-butyl borate (98%, 0.5 ml, 1.6 mmol) was added,
the reddish solution was stirred for 8 h at room temperature. A
mixture of 4-bromo-dibenzo-24-crown-8 14 (0.8 g, 1.52 mmol) and
Pd(PPh3)4 (0.10 g) was stirred in THF (10 ml) for 15 min at room
temperature. Then aqueous Na2CO3 (10 ml, 2 M) was added. The
reactive mixture was stirred at 50 ◦C, and the reddish solution of
BTE-containing boronic acid dibutyl ester was added dropwise
using a syringe. Subsequently, the mixture was refluxed for 24 h
and cooled to room temperature. The reactive mixture was poured
into H2O and extracted with CH2Cl2 and dried with anhydrous
Na2SO4. The residue was purified using column chromatography
(SiO2, CH2Cl2–MeOH = 50/1) to give compound 3-o (0.3 g, 28%).
1H NMR (CDCl3, 500 MHz, 298 K): d 7.20–7.10 (m, 2H), 7.10–
7.02 (m, 5H), 6.89 (s, 1H), 6.63 (s, 1H), 4.35–4.27 (m, 8H), 3.83–
3.76 (m, 8H), 3.67–3.60 (d, J = 4.9 Hz, 8H), 2.82 (t, J = 7.2 Hz,
2H), 2.74 (t, J = 7.3 Hz, 2H), 2.10–2.03 (m, 2H), 2.02 (s, 3H), 1.77
(s, 3H). 13C NMR (CDCl3, 100 MHz, 298 K): 148.28, 148.05,
138.40, 136.45, 135.36, 135.25, 134.56, 133.97, 133.33, 126.92,
124.83, 124.12, 123.63, 120.62, 117.16, 116.78, 116.70, 113.82,
77.34, 77.02, 76.71, 38.24, 22.93. HRMS (ESI) (m/z): [M + Na]+
calcd for C39H45ClNaO8S2, 763.2142; found, 763.2140.
Material
Chemicals were used as received from Acros, Aldrich, Fluka,
or Merck. All solvents were reagent grade, which were dried
and distilled prior to use according to standard procedures. The
1
molecular structures were confirmed using H NMR, 13C NMR
and high-resolution ESI mass spectroscopy. The syntheses of
compounds 4, 7, 9, 10, 13 and 14 are described in the supporting
information.†
Synthesis of compound 8
A
mixture of compound 6 (0.2 g, 0.43 mmol), 4-(2-
propynyloxy)benzylamine 7 (0.35 g, 2.15 mmol), K2CO3 (0.12 g,
0.86 mmol) in acetonitrile (15 ml) was stirred under reflux for 12 h.
After the reaction mixture had been cooled to room temperature,
the solvent was removed under reduced pressure. The residue was
purified using column chromatography (SiO2, CH2Cl2–MeOH =
30/1) to give a yellow solid. The yellow solid (0.19 g, 0.35 mmol)
was dissolved in MeOH (20 ml), and HCl (6 M, 2 ml) was added.
After stirring for a few minutes, the solvent was removed under
reduced pressure. The residue was dissolved in MeOH (20 ml),
followed by the addition of saturated NH4PF6 solution. After
the mixture was stirred for 2 h, the mixture was extracted with
CH2Cl2 (3 ¥ 20 ml). The combined organic layer was evaporated,
and the residue was purified using column chromatography (SiO2,
CH2Cl2–MeOH = 30/1) to give 8 (0.12 g, 50%) as a yellow powder.
1H NMR (CD3COCD3, 400 MHz, 298 K): d 8.59 (d, J = 8.4 Hz,
1H), 8.54 (d, J = 7.2 Hz, 1H), 8.48 (d, J = 8.0 Hz, 1H), 7.81 (dd,
J = 8.4 Hz, 7.3 Hz, 1H), 7.49 (br d, J = 7.2 Hz, 6H), 7.39 (d, J = 8.4
Hz, 1H), 7.03 (m, 2H), 5.32 (s, 2H), 4.80 (d, J = 2.4 Hz, 2H), 4.46
(d, J = 4.0 Hz, 4H), 3.97 (t, J = 4.4 Hz, 4H), 3.29 (t, J = 4.4 Hz,
4H), 3.10 (t, J = 2.4 Hz, 1H). 13C NMR (CD3COCD3, 100 MHz,
298 K): d 164.8, 164.2, 159.3, 157.1, 140.3, 133.3, 132.4, 131.8,
131.7, 130.9, 130.6, 129.4, 127.0, 126.9, 125.6, 124.0, 117.4, 116.1,
116.0, 79.5, 77.2, 67.4, 56.3, 54.3, 52.2, 43.5. HRMS (ESI) (m/z):
[M - PF6]+ calcd for C34H32N3O4, 546.2393; found, 546.2388.
Preparation of dumbbell 2-H
A mixture of 8 (20 mg, 0.03 mmol), 12 (37.9 mg, 0.06 mmol), and
Cu(CH3CN)4PF6 (11.2 mg, 0.03 mmol) was stirred in dry CH2Cl2
(1 mL) at room temperature for two days. After removal of the
solvent, the residue was purified using column chromatography
(SiO2, CH2Cl2–MeOH = 15/1) to give compound 2-H (33.7 mg,
50%) as a yellow solid. 1H NMR (CD3COCD3, 500 MHz, 298 K):
d 9.10 (s, 1H), 8.63 (d, J = 8.5 Hz, 1H), 8.57 (d, J = 7.5 Hz, 1H),
8.51 (d, J = 8.0 Hz, 1H), 8.27 (s, 1H), 8.07 (s, 1H), 7.90 (s, 2H),
7.84 (t, J = 7.5 Hz, 1H), 7.51 (d, J = 5.5 Hz, 6H), 7.42 (d, J = 8.0
Hz, 1H), 7.10 (d, J = 8.5 Hz, 2H), 5.81 (s, 2H), 5.34 (s, 2H), 5.18
(s, 2H), 4.84 (t, J = 7.0 Hz, 2H), 4.60 (s, 3H), 4.56 (m, 4H), 4.41
(t, J = 7.3 Hz, 2H), 3.98 (t, J = 4.5 Hz, 4H), 3.94 (s, 6H), 3.31
(t, J = 4.5 Hz, 4H), 2.11 (m, 2H), 1.90 (m, 2H), 1.37 (m, 12H).
13C NMR (CD3COCD3, 100 MHz, 298 K): d 166.0, 164.8, 164.3,
160.4, 158.6, 157.1, 143.8, 140.6, 140.5, 133.3, 133.3, 132.7, 132.6,
131.8, 131.7, 131.1, 131.0, 130.9, 130.7, 129.8, 129.4, 128.7, 127.0,
126.9, 124.6, 124.5, 124.2, 124.0, 122.6, 120.7, 117.4, 116.6, 116.3,
116.1, 116.0, 67.4, 62.4, 59.8, 54.9, 54.3, 52.9, 52.2, 52.1, 50.6, 43.5,
39.3, 31.0, 27.0, 26.6. HRMS (ESI) (m/z): [M - 2PF6]2+ calcd for
C58H67N9O9, 516.7531; found, 516.7522.
Synthesis of compound 12
A solution of 11 (1 g, 2.12 mmol) in CH3I (15 ml) was stirred
at 40 ◦C for 12 h. The reaction mixture was cooled to room
temperature, and CH3I was evaporated off in vacuo. The residue
was dissolved in MeOH (15 ml), followed by the addition of a
saturated NH4PF6 solution. After the mixture was stirred for 2 h,
the mixture was extracted with CH2Cl2 (3 ¥ 20 ml). The combined
organic layer was evaporated, and the residue was purified using
column chromatography (SiO2, CH2Cl2–MeOH = 100/1) to give
12 (1.07 g, 80%) as a white powder. 1H NMR (CDCl3, 400 MHz,
298 K): d 8.52 (s, 1H), 8.28 (s, 1H), 7.77 (s, 2H), 5.39 (s, 2H),
4.54 (t, J = 7.4 Hz, 2H), 4.34 (s, 3H), 3.91 (s, 6H), 3.25 (t, J = 6.8
Hz, 2H), 2.01 (m, 2H), 1.58 (m, 2H), 1.28 (br, 12H). 13C NMR
(CDCl3, 100 MHz, 298 K): d 165.5, 156.8, 139.1, 132.3, 129.9,
124.7, 119.7, 58.1, 54.4, 52.6, 51.4, 38.6, 29.2, 29.1, 29.1, 29.0,
28.8, 28.7, 26.6, 26.0. HRMS (ESI) (m/z): [M - PF6]+ calcd for
C24H35N6O5, 487.2669; found, 487.2671.
Preparation of [2]rotaxane 1-H-o
A mixture of 8 (20 mg, 0.03 mmol) and crown ether 3-o (44.5 mg,
0.06 mmol) was stirred in dry CH2Cl2 (1 mL) at room temperature
for 2 h. After 12 (37.9 mg, 0.06 mmol) and Cu(CH3CN)4PF6
(11.2 mg, 0.03 mmol) were added to the solution, the mixture was
stirred for two days. After removal of the solvent, the residue was
purified using column chromatography (SiO2, CH2Cl2–MeOH =
15/1) to give compound 1-H-o (12.4 mg, 20%) as a yellow solid.
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1H NMR (CD3COCD3, 400 MHz, 298 K): d 9.10 (s, 1H), 8.63
(d, J = 8.4 Hz, 1H), 8.56 (d, J = 7.2 Hz, 1H), 8.51 (d, J = 8.0
Hz, 1H), 8.27 (s, 1H), 7.99 (s, 1H), 7.90 (s, 2H), 7.83 (t, J = 7.8
Hz, 1H), 7.41 (dd, J = 8.4 Hz, 4.0 Hz, 3H), 7.34 (d, J = 8.0 Hz,
2H), 7.26 (d, J = 8.0 Hz, 2H), 7.05 (s, 2H), 6.95–6.70 (m, 9H),
5.81 (s, 2H), 5.20 (m, 2H), 5.04 (s, 2H), 4.84 (t, J = 7.2 Hz, 2H),
4.72 (br, 4H), 4.60 (s, 3H), 4.41 (t, J = 7.2 Hz, 2H), 4.26 (m, 2H),
4.19–4.10 (m, 6H), 3.97 (t, J = 4.4 Hz, 4H), 3.94 (s, 6H), 3.90 (m,
2H), 3.88–3.80 (m, 6H), 3.70–3.57 (m, 8H), 3.30 (t, J = 4.4 Hz,
4H), 2.11 (m, 2H), 1.99 (s, 3H), 1.91 (s, 3H), 1.89 (m, 2H), 1.30 (m,
12H). 13C NMR (CD3COCD3, 100 MHz, 298 K): d 166.1, 164.8,
164.3, 160.1, 158.7, 157.1, 148.9, 148.6, 148.6, 148.1, 144.0, 140.8,
140.5, 140.0, 137.4, 136.7, 136.7, 134.7, 134.4, 134.3, 133.4, 131.9,
131.9, 131.8, 130.9, 130.8, 130.4, 129.3, 128.8, 128.3, 127.1, 127.0,
125.5, 125.2, 124.7, 124.6, 124.6, 124.2, 122.2, 122.1, 120.8, 119.0,
117.6, 116.1, 115.7, 113.8, 113.5, 110.6, 71.7, 71.7, 71.3, 71.2, 69.2,
68.9, 67.5, 62.5, 59.9, 55.1, 54.4, 53.1, 53.0, 50.7, 43.6, 39.4, 39.0,
38.8, 31.2, 27.2, 26.7, 23.7, 14.5, 14.4. HRMS (ESI) (m/z): [M -
2PF6]2+ calcd for C97H112ClN9O17S2, 887.3670; found, 887.3704.
(20090074120017), Shanghai Chenguang project (09CG26), the
Fundamental Research Funds for the Central Universities
(WJ1014001) and the Scientific Committee of Shanghai for
funds. We thank Mr. L.-L. Zhu and Mr. J.-Y. Jin for helpful
discussions.
Notes and references
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Conclusions
Combining the switching processes performed by rotaxane 1-H-
o in response to different combinations of chemical and photo-
chemical stimuli, it can be summarized that the photochromic
DTE unit played a very important role as a controlling unit in this
multi-level molecular machine, in which multi-mode alteration
of intercomponent interactions can be realized. When the DTE
unit is in its open form, the PElT process between the open-
form DTE unit and the naphthalimide fluorescent unit can be
tuned by a chemically driven large-amplitude positional change
of the subunit. On the other hand, when the DTE unit is in
its closed-form, the PEnT process and charge transfer interac-
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fluorescent unit can be chemically regulated. In conclusion, we
have demonstrated reversible multi-mode alteration of intercom-
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advantage of UV/Vis absorption spectroscopy and time-resolved
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Acknowledgements
We thank the NSFC/China (20902024 and 20972053), National
Basic Research 973 Program (2011CB808400), the Foundation for
the Author of National Excellent Doctoral Dissertation of China
(200957), Shanghai Pujiang Talent Program (10PJ1402700),
Fok Ying Tong Education Foundation (121069), SRFDP
4056 | Org. Biomol. Chem., 2011, 9, 4051–4056
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The Royal Society of Chemistry 2011
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