Multi-input/multi-output molecular response system based on the dynamic redox behavior of 3,3,4,4-tetraaryldihydro[5]helicene derivatives: Reversible formation/destruction of chiral fluorophore and modulation of chiroptical properties by solvent polarity

Article abstract of DOI:10.1002/chem.200900968

3,3,4,4-Tetaaryldihydro[5]helicenes (1) and l, l'-binaphthyl-2, 2'-diylbis(diarylcarbenium)s (2²⁺) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formati

Full text of DOI:10.1002/chem.200900968

DOI: 10.1002/chem.200900968
Multi-Input/Multi-Output Molecular Response System Based on the
Dynamic Redox Behavior of 3,3,4,4-Tetraaryldihydro[5]helicene Derivatives:
Reversible Formation/Destruction of Chiral Fluorophore and Modulation of
Chiroptical Properties by Solvent Polarity
Takanori Suzuki,*[a] Yusuke Ishigaki,[a] Tomohiro Iwai,[a] Hidetoshi Kawai,[a, b]
Kenshu Fujiwara,[a] Hiroshi Ikeda,[c, d] Yusuke Kano,[c] and Kazuhiko Mizuno[c, d]
Dedicated to Professor Takashi Tsuji on the occasion of his 70th birthday
Abstract: 3,3,4,4-Tetaaryldihydro[5]he-
licenes (1) and 1,1’-binaphthyl-2,2’-diyl-
bis(diarylcarbenium)s (22+) can be re-
versibly interconverted upon electron
transfer, which is accompanied by a
vivid color change (electrochromism)
as well as by the formation/cleavage of
fluorescent properties of the pair. Due
to the configurational stability of the
additional output. The CD spectra of
dications 22+ exhibit solvent dependen-
cy (chiro-solvatochromism), which is
accompanied by solvatochromic behav-
ior based on the p–p interaction of the
two cationic chromophores as well as
coordinative interaction of the Lewis
basic solvent to the Lewis acidic triar-
ylcarbenium moieties. Thus, the present
system is endowed with multi-input
functionality for modifying multiple
output signals.
helicity in 1 and axial chirality in 22+
,
the redox reaction of optically pure
material proceeds stereospecifically,
which induces
a chiroptical change
such as circular dichroism (CD) as an
À
a C C bond (“dynamic redox behav-
ior”). Because only the neutral donor 1
exhibits strong fluorescence, electro-
chemical input can further modify the
Keywords: chirality · fluorescence ·
molecular response systems · redox
chemistry · solvatochromism
[a] Prof. T. Suzuki, Y. Ishigaki, T. Iwai, Dr. H. Kawai, Prof. K. Fujiwara
Department of Chemistry, Faculty of Science
Hokkaido University
Introduction
Kita 10, Nishi 8, Kita-ku, Sapporo, 060-0810 (Japan)
Fax : (+81)11-706-2714
E-mail: tak@sci.hokudai.ac.jp
While multi-input/multi-output response systems[1] are rare,
they have attracted considerable attention from the view-
point of potential applications in molecular sensing and
switches.[2] Since multi-input systems are prototypes of mo-
lecular-level logic operators,[3] the addition of a multi-output
response would endow such systems with the ability to act
as parallel operating logic elements (“molecular CPU” [4]).
In this study, we examined novel electrochromic systems
that incorporate a chiral fluorophore, which were designed
according to the following concept to realize a three-way-
output response system.
[b] Dr. H. Kawai
PRESTO, Science and Technology Agency (Japan)
[c] Prof. H. Ikeda, Y. Kano, Prof. K. Mizuno
Department of Applied Chemistry
Graduate School of Engineering
Osaka Prefecture University
Sakai, Osaka, 599-8531 (Japan)
[d] Prof. H. Ikeda, Prof. K. Mizuno
The Research Institute for Molecular Electronic Device (RIMED)
Osaka Prefecture University
Sakai, Osaka, 599-8531 (Japan)
Dihydro[5]helicene (dihydrodibenzoACTHNUTRGNEUNG[c,g]phenanthrene) is
a rigid p framework that exhibits strong fluorescence.[5]
When this skeleton can be formed/destroyed by the applica-
tion of an external stimulus, this system can serve as a fluo-
rescence ON/OFF switch.[6] By adopting a “dynamic-redox”
Supporting information (experimental details of new-compound prep-
aration; cyclic voltammograms of 1a and 2aACHTNURTGNEUNG[(BF4)2]; solvatochrom-
ism of (R)-2a2+ and (R)-2b2+; scattering plots of UV/Vis data: lmax
(2c2+) versus several solvent parameters; electrochromic behavior of
1a, 1c, 3b, and 3c; reaction scheme under photoinduced electron-
transfer conditions) for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.200900968. CCDC 722229 and 722230
contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre by logging on to www.ccdc.cam.ac.uk/data_
request/cif.
protocol[7] based on reversible C C bond formation/cleav-
À
age upon electron transfer, the title electron donors 1 with
this fluorophore could be produced from 1,1’-binaphthyl-
2,2’-diyl(diarylcarbenium)s (22+), which shows strong ab-
sorption in the visible region that is characteristic of triaryl-
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FULL PAPER
methylium dye.[8] Due to the configurational stabilities in
both the neutral (helicity) and dicationic (axial chirality)
states, interconversion of the redox pairs would proceed ste-
if we use a range of solvents with the different coordinating
properties. On the other hand, the solvent-dependent associ-
ation of triarylmethyliums is a well-known process.[14] When
p–p interaction between two chromophores in 22+ is modi-
fied by the solvent polarity, this may also change the UV/
Vis and CD spectral properties. To attain high solubility in
less-polar solvents such as benzene or cyclohexane, dications
2b2+ and 2c2+ with long alkoxyl chains were also included
in this study.
reospecifically ((P)-1/(S)-22+
; ; Scheme 1).
(M)-1/(R)-22+
In this report, we first describe the preparation and X-ray
structures of chiral pairs of 1/22+. Configurationally unstable
biphenyl derivatives 3/42+ were also included as reference
compounds. The redox behavior as well as the detailed
mechanism of the electrochemical interconversion are then
described, as determined by laser flash photolysis of 3 to ob-
serve the transient absorption of cation radical intermediate
4+ . Next, the electrochemical response is studied in detail
C
by using three kinds of spectroscopy. Finally, the solvato-
chromic behavior as well as the solvent dependency of the
CD spectrum are also demonstrated.
Results and Discussion
Preparation and X-ray structure: (R)-/(S)-1,1’-Binaphthols
with configurationally stable axial chirality were selected as
the starting material for 3,3,4,4-tetrakis(4-methoxyphenyl)-
3,4-dihydro[5]helicenes ((M)-/(P)-1a). Thus, both enantio-
mers of binaphthol were converted, respectively, to optically
Scheme 1. Dynamic redox pairs with a chiral fluorophore (a: n=1; b: n=
8; c: n=16).
pure methyl esters (R)-/(S)-5 by means of bisACHTUNGTRENNUNG(triflate)
through Pd-catalyzed CO insertion[15] under atmospheric
pressure.[16] Diol (R)-6a in 73% yield was obtained from
(R)-5 by the four-time addition of 4-methoxyphenyllithium.
Upon treatment with trimethylsilyl perchlorate (TMSClO4)
in (CF3)2CHOH (Ichikawaꢁs method),[17] the chiral diol was
converted into dication (R)-2a2+, which was directly re-
duced with Zn powder to give optically pure (M)-1a ([a]2D4 =
À2318 (c=0.47 in CHCl3)) as colorless crystals in 98% yield
over two steps (Scheme 3a). When ester (R)-5 was reacted
with 4-octyloxyphenyllithium or 4-hexadecyloxyphenyllithi-
um,[18] (M)-1b,c with four long alkyl chains were obtained in
respective yields of 79 and 68%. They also exhibit a huge
optical rotatory power ([a]2D3 =À1538 (c=0.35 in CHCl3) for
1b; [a]2D6 =À1098 (c=0.76 in CHCl3) for 1c), which is char-
acteristic of helicene derivatives.[19] When the antipode of
the ester (S)-5 was used as a starting material, helical
donors with P helicity (P)-1a–c were prepared in a similar
manner by means of diols (S)-6a–c in 79–85% yields over
three steps.
Thus, chiroptical changes such as circular dichroism (CD)
would also be available as an output.[9] The asymmetric ele-
ments of helicity and axial chirality in a biaryl-related skele-
ton are suitable for obtaining huge CD signals[10] through an
exciton-coupling mechanism.[11] In this way, the optically
active pair should be able to exhibit three kinds of spectral
changes in response to an electrochemical input (Scheme 2).
Scheme 2. Three-way-output molecular response system.
The methoxyphenyl group is selected as an aryl group in
anticipation of strong coloration and sufficient stability for
the cationic moiety in 2a2+, as exemplified by bis(4-methoxy-
Racemic donors rac-1a–c were obtained in 97–100%
yield over two steps from the corresponding racemic diols
rac-6a–c, which were more conveniently obtained from
phenyl)phenylcarbenium (labs =514 nm (loge=4.87); pKR+
=
commercially
available
rac-2,2-dibromo-1,1’-binaphthyl
À1.24[12]). At the same time, the cationic center would
through subsequent treatment with nBuLi followed by 4,4’-
dialkoxybenzophenones[20] (Scheme 3b). As shown in the
preliminary communication,[21] a similar protocol was first
used to prepare 9,9,10,10-tetrakis(4-methoxyphenyl)dihydro-
behave as a Lewis acid, so that coordinative interaction with
[13]
a Lewis base might affect the spectral properties of 22+
.
Thus, the dications should exhibit solvatochromic behavior
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T. Suzuki et al.
(R)- and (S)-22+ were generated from (M)- and (P)-1, re-
spectively. All of the dications ((R)-/(S)-/rac-2a–2c-
AHCTUNGRTEGN[NNU (SbCl6)2]) were quantitatively converted to the correspond-
ing dihydrohelicenes ((M)-/(R)-/rac-1a–c) upon treatment
with Zn powder in THF.
The detailed structural features of tetraaryldihydro[5]heli-
cene were revealed by X-ray analysis of (M)-1a (Figure 1a).
The dihedral angle of the two naphthalene units is 49.4(1)8,
which is much smaller than that in the precursor dication
À
(vide infra) due to the formation of a new Csp3 Csp3 bond
upon reduction. This bond length is 1.646(5) ꢂ, which is
Scheme 3. a) Preparation of optically pure (M)-/(P)-1a–c by means of
(R)-/(S)-diol 6a–c, and b) preparation of racemic diols rac-6a–c.
phenanthrene 3a and related compounds, which readily un-
dergo a ring-flip with an inversion of helicity. In this study,
tetrakis(4-octyloxyphenyl)- and tetrakis(4-hexadecyloxyphe-
nyl)dihydrophenanthrenes 3b,c were also prepared in 99
and 93% yield as reference compounds from diols 7b,c with
four long alkyl chains, which in turn were obtained by the
reactions of 2,2’-dilithiobiphenyl and 4,4’-dialkoxybenzophe-
nones. The high-yield formation of 1a–c and 3b,c from the
corresponding diols 6a–c and 7b,c clearly shows that reduc-
tive generation of the dihydro[5]helicene/dihydrophenan-
threne skeleton from the intermediary dicationic species
(22+/42+) proceeds very smoothly.
At the same time, it is clear that the dications were pro-
duced very efficiently from the diols upon treatment with
TMSClO4. The binaphthylic dications 2a2+–2c2+ were not
À
isolated as ClO4 salts from the acidic mixture at that
point,[22] but rather were more conveniently isolated as
À
SbCl6 salts in high yield by oxidation of the dihydro[5]heli-
C
cene donors 1a–c with two equivalents of [(4-BrC6H4)3N ]-
À
[SbCl6] (Scheme 4). Oxidative cleavage of the C C bond
proceeds while preserving the chiral sense, and thus only
Figure 1. ORTEP drawings of a) (M)-1a and b) (R)-2a2+ in the (R)-2a-
ACHTUNGRTEN[NUNG (SbCl6)2] salt as determined by low-temperature X-ray analyses.
Scheme 4. Interconversion of 1a–c and 2a2+–2c2+
.
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Multi-Input/Multi-Output Molecular Response System
FULL PAPER
much greater than the standard value of 1.54 ꢂ, but is typi-
cal for sterically congested hexaphenylethane derivatives.[23]
Two methoxyphenyl groups at the pseudo-equatorial posi-
tions are located in proximity and face each other over the
Both peaks correspond to the two-electron transfer pro-
cess, and there are no other peaks in the voltammograms.
The negligible steady-state concentration of the intermedi-
+
+
+
ary cation radicals 1+ /2 (and 3 /4 ) can be accounted for
C
C
C
C
long C C bond (the shortest C C contact: 3.14(1) ꢂ). The
other two at the pseudo-axial positions face outward.
Figure 1b shows the ORTEP drawing of (R)-2a2+ in the
by assuming the reaction mechanism shown in Scheme 5.[21b]
À
À
À
SbCl6 salt obtained by low-temperature X-ray analysis. The
absolute configuration of the dication was confirmed by the
anomalous dispersion of X-ray (Flack parameter: x=
0.000(17)). The dihedral angle of the two naphthalene units
is 68.5(1)8 with a separation of 3.54(1) ꢂ between the two
À
carbenium centers. A much closer C C contact (3.29(1) ꢂ)
was observed between the two methoxyphenyl groups facing
each other (dihedral angle: 10.8(2)8), which reflects the ef-
fective p–p overlap of two diarylcarbenium units. The
broadness of the first band in the electronic absorption
(labs =534 nm in CH2Cl2) in 2a2+ may be related to Davy-
dov splitting through p–p interaction, although this band
may represent several transitions.
Scheme 5. Mechanism of interconversion.
In the oxidation process of the donors, the as-prepared
+
C
C
Redox behavior and mechanism of interconversion: The
redox potentials of newly prepared electron donors 1a–c
were measured by cyclic voltammetry in CH2Cl2 (238C, scan
rate 100 mVsÀ1) and the oxidation potentials (Eox) are sum-
marized in Table 1 along with those of reference compounds
cation radicals 1+ (and 3 ) would undergo rapid long-bond
fission[24] to give more stable species 2+ (and 4 ), in which
+
C
C
the unpaired electron and positive charge can be delocalized
over each of the triarylmethane units. The lifetimes of 2+
C
(and 4+ ) would also be very short during the oxidation pro-
cess because their oxidation potentials (ca. +0.2 V) must be
far less positive than those of the neutral donors 1 (and 3).
In the reduction process, electron capture at the two cationic
sites in 22+ (and 42+) would proceed in a stepwise manner
with marginal separation between the two reduction poten-
tials (Er1ed, Er2ed) due to electronic interaction of the two chro-
C
Table 1. Redox potentials[a] of dihydro[5]helicene-donors 1a–c and bi-
naphthylic dications 2a2+–2c2+ measured in CH2Cl2 along with those of
related compounds.
n
Eox [V]
Ered [V]
1a
1b
1c
3a
3b
3c
1
+1.29
+1.32
+1.32
+1.48
+1.50
+1.53
–
–
–
–
8
16
1
8
16
1
mophores through the face-to-face overlap.[6h,21a,25] Due to
the facile disproportionation of 2+ into 2 /2 (and 4+ into
2+
C
2C
C
2+
2C
2C
4 /4 ) as well as the rapid bond formation of 2 to 1 (and
to 3), the steady-state concentration of the intermediary
species would also be negligible upon reduction.
2C
4
2a2+
2b2+
2c2+
4a2+
4b2+
4c2+
+0.23
+0.21
+0.21
+0.21
+0.18
+0.17
8
16
–
–
The above idea regarding the mechanism shown in
Scheme 5 was supported by the following experimental re-
sults. For the reduction process, voltammetric analyses were
carried out at low temperature (À788C) with a fast scan
rate (5 VsÀ1) in CH2Cl2, which supported the sequential
[a] E versus SCE, scan rate 100 mVsÀ1, 0.1m Bu4NBF4 as a supporting
electrolyte, Pt electrode, 298 K.
two-step one-electron reduction (Er1ed =+0.09 V; E2red
=
À0.05 V for 2a2+) by retarding the disproportionation pro-
cess (Figure S1c in the Supporting Information). In those
voltammograms, the oxidation waves remained unchanged,
suggesting that a much faster method is necessary to eluci-
date the mechanism of the oxidation process. Therefore, for
this purpose, photoinduced electron-transfer (PET) reac-
tions of 3a,b were conducted with nanosecond-absorption
3a–c. The electrochemical oxidation of 1 occurs at approxi-
mately +1.3 V versus SCE, which is slightly less positive
than Eox of 3 (ca. +1.5 V), probably due to the electron-do-
nating properties of the binaphthyl core. The oxidation pro-
cess is irreversible since the corresponding reduction peak
was observed in the far cathodic region (ca. +0.2 V), which
was assigned to the reduction process of the bond-dissociat-
ed dication, as confirmed by the independent measurements
of 22+ (and 42+) under similar conditions (Figures S1a and b
in the Supporting Information). Such separation of redox
peaks in the voltammogram is a characteristic feature of dy-
namic redox systems,[7] and provides electrochemical bista-
bility for the redox pairs of 1/22+ (and 3/42+).
spectroscopy on laser flash photolysis.
system that used an N-methylquinolinium tetrafluoroborate
([NMQ][BF4], sensitizer, 1.0 mm)–toluene (cosensitizer,
A cosensitizing
AHCTUNGTRENNUNG
1.0m) couple in aerated MeCN at ambient temperature was
used, since this system allows us to directly detect the inter-
mediary cation radicals in a one-electron oxidation process
(Scheme S1 in the Supporting Information).[26]
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9437

T. Suzuki et al.
At a delay time of 100 ns after the laser excitation of
[NMQ]
[BF4] with the methoxy derivative 3a (10À5 m) using a
ACHTUNGTRENNUNG
100 ns pulse from the yttrium aluminum garnet (YAG) laser
(335 nm), transient absorption spectra were observed, as
shown in Figure 2. A characteristic band with labs at 523 nm
Figure 2. Transient absorptions of cation radical species generated by
photoinduced electron-transfer reactions of 3a and 3b by laser flash pho-
tolytic conditions. Inset shows the time-course of the absorption intensity.
is assigned to the transient 4a+ , formed by rapid bond
C
cleavage of 3a+ , since this band corresponds to the intense
C
chromophore of bis(4-methoxyphenyl)phenylcarbenium.
Absorption of the bis(4-methoxyphenyl)phenylmethyl part
must be much less than that of the cationic chromophore,[21b]
which would explain its absence in the spectrum. A similar
transient spectrum with labs at 527 nm assigned to 4b+ was
C
observed with the octyloxy derivative 3b but appeared
much slower than 4a+ (Figure 2, inset), which suggested the
C
+
slower ring-opening of 3b+ than of 3a . This difference in
C
C
reactivity between 3a+ and 3b+ may be accounted for by
C
C
the solvatophobic/fastener effects,[27] which give two octy-
loxy groups on the vicinal phenyl groups of 3b+ with an at-
C
tracting force.
Three-way-output response: Figure 3 shows the continuous
changes in the three kinds of spectra of (M)-1b upon con-
stant-current oxidation in CH2Cl2. The colorless solution
gradually turned deep red with a steady increase in absorp-
tions at 429 and 541 nm in the UV/Vis spectrum (Figure 3a),
which are assigned to dication 2b2+. Complete regeneration
of 1b with decoloration was attained by reverse electrolysis
of the as-prepared dicationic solution. Similar electrochro-
mic behavior was also observed with the use of other donors
1a,c/3b,c (Figure S3 in the Supporting Information). Since
Figure 3. Changes (every 20 min) in a) UV/Vis, b) fluorescence, and
c) CD spectra upon constant current (24 mA) electrolysis of (M)-1b in
CH2Cl2 containing 0.05m Bu4NBF4 as a supporting electrolyte.
only the neutral donors 1a–c, but not dications 2a2+–2c2+
,
have the fluorophore of dihydro[5]helicene (lem =407, 408,
and 409 nm and y=0.18, 0.16, and 0.18 for 1a, 1b, and 1c,
respectively, in CH2Cl2), electrochemical oxidation to the
corresponding binaphthylic dication induced a steady de-
crease in the fluorescence intensity (Figure 3b).
Both the optically pure donors and dications ((M)-1/(R)-
22+ and (P)-1/(S)-22+) exhibit strong CD signals thanks to
the exciton coupling, but in different wavelength regions.
Thus, electrochemical input induced drastic changes in the
CD spectrum, as shown in Figure 3c. The emerging couplet
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Multi-Input/Multi-Output Molecular Response System
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with a large amplitude (A>100) in the longer-wavelength
region upon electrolysis is notable. This represents a suc-
cessful demonstration of a three-way-output molecular re-
sponse system based on the reversible formation/destruction
of a configurationally stable chiral fluorophore of dihy-
dro[5]helicene upon electron transfer.[28]
other solvents with intermediate polarity between MeCN
and cyclohexane, the first band of 2c2+ appeared at the po-
sitions expected from their dielectric constants (Table 2, Fig-
ures S2a and c in the Supporting Information).
Table 2. UV/Vis spectral data[a] of 2a–2c
Dielectric constant 2a2+
ACHTUNGTRENNUNG
Solvatochromic and chiral-solvatochromic behavior: Triaryl-
methylium dyes often form intermolecularly associated dyad
or higher oligomeric species, depending on the nature of the
solvent, such as its polarity, which causes changes in their
spectral properties. As shown by the X-ray structure of the
(R)-2a2+ salt, the binaphthylic dications adopt a conforma-
tion in which two dye chromophores can electronically inter-
act with each other through p–p overlap. Thus, the dications
22+ would be associated with different degrees of intramo-
lecular association of dye chromophores in various solvents
to exhibit solvatochromic behavior. This is indeed the case,
and the electronic spectra of dications 22+ exhibit a batho-
chromic shift of the first band when the solvent is changed
from MeCN to CH2Cl2, benzene, and cyclohexane (Fig-
ure 4a), with a color change from red to purple. The strong
absorption band of hexadecylated dication 2c2+ at 532 nm
in MeCN is shifted to 543 nm in cyclohexane, and is accom-
panied by new shoulder absorptions at 500 and 592 nm. In
MeCN
CH2Cl2
CHCl3
37.5
9.1
4.9
524
534
–
N
G
532
542
543
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
benzene
2.28
2.05
–
–
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
cyclohexane
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[a] Data of absorption maxima (labs and e) and shoulders for the first
band.
Such behavior can be accounted for by considering the
lower stabilization of the cationic chromophores in 22+ by
solvation in the nonpolar solvents, where p–p interaction
through the effective overlap of two chromophores is impor-
tant (Scheme 6). On the other hand, the coordinative inter-
Scheme 6. Plausible mechanism of solvatochromism.
action with a Lewis basic solvent would be a dominant
factor in a polar solvent, and this would reduce the contribu-
tion of the p–p interaction. Accordingly, the degree of p–p
overlap would be greater in nonpolar solvents than in polar
solvents, which would induce greater Davydov splitting and
more low-energy absorption in the former. The coordinative
interaction at the cationic center raises the energy level of
the LUMO, which might also cause the blueshift of the ab-
sorption in Lewis basic solvents.
The CD spectra of optically pure 22+ are also changed by
solvent polarity (Table 3, Figure 4b; Figures S2b and d in the
Table 3. CD spectral data[a] of 2a–2c
ACHTUNGTRENNUNG
Dielectric constant
MeCN
37.5
N
N
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
CH2Cl2
9.1
N
N
ACHTUNGTRENNUNG
A
G
ACHTUNGTRENNUNG
CHCl3
4.9
–
–
–
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
benzene
cyclohexane
2.28
2.05
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
–
595
549
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Figure 4. a) UV/Vis and b) CD spectra of the (R)-2cACTHNUGTRNEUNG[(SbCl6)2] salt mea-
sured in various solvents.
[a] Data of extrema (lext and De) of Cotton effects for the first band.
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T. Suzuki et al.
Supporting Information).[29] Along with the above explana-
tion for the absorption-band shift, a more distinct and larger
couplet is observed for (M)-2c2+ in cyclohexane (lext (De)=
595 (+242), 549 nm (À112 molÀ1 dm3 cmÀ1)), whereas Cotton
effects in MeCN are much weaker. Thus, chiroptical proper-
ties are also modified by solvent polarity (chiro-solvatochro-
mism),[1b,c,30,31] and this provides the multi-input (electric po-
tential and solvent polarity) and multi-output (UV/Vis, fluo-
rescence, CD) functionalities in the present molecular sys-
tems.
[6] a) A. P. de Silva, H. Q. N. Gunaratne, C. P. McCoy, Nature 1993, 364,
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Conclusion
The present results demonstrate that the reversible forma-
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Since we adopted a “dynamic redox” protocol, the steady-
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Acknowledgements
The authors express sincere thanks to Prof. Takashi Ooi at the Depart-
ment of Applied Chemistry, Graduate School of Engineering, Nagoya
University for his valuable and helpful suggestions. The financial support
from the Global COE Program by MEXT “Catalysis as the Basis for In-
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9440
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Multi-Input/Multi-Output Molecular Response System
FULL PAPER
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Received: April 11, 2009
Published online: July 20, 2009
Chem. Eur. J. 2009, 15, 9434 – 9441
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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9441