Tuning the CD spectrum and optical rotation value of a new binaphthalene molecule with two spiropyran units: Mimicking the function of a molecular "AND" logic gate and a new chiral molecular switch

Article abstract of DOI:10.1021/jo050489k

With the view to developing new chiral molecular switches and logic gates, a new binaphthalene molecule with two spiropyran units (1) was synthesized and characterized. Absorption and ¹H NMR spectral studies of 1 after reaction with acid/base indicate acidichromism can occur to compound 1. The synergistic actions of acid and UV light irradiation result in a remarkable change for the CD spectrum of the relatively dilute solution of 1, mimicking the behavior of a chiral "AND" gate, since the "ouput" is the CD signal. Furthermore, the optical rotation value of the relatively concentrated solution of 1 can be reversibly tuned after sequential reactions with acid and base, and thus a chiral molecular switch with nondestructive "output" signal is realized. The present results not only add a new example of chiral molecular switch with nondestructive readout but also provide a chiral "AND" gate based on the axial chiral binaphthalene to which switchable units are linked.

Full text of DOI:10.1021/jo050489k

Tuning the CD Spectrum and Optical Rotation Value of a New
Binaphthalene Molecule with Two Spiropyran Units: Mimicking
the Function of a Molecular “AND” Logic Gate and a New Chiral
Molecular Switch
Yucheng Zhou,†,‡ Deqing Zhang,*,† Yazhou Zhang,†,‡ Yalin Tang,† and Daoben Zhu*,†
Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100080, China, and Graduate School of Chinese Academy of Sciences, Beijing 100080, China
dqzhang@iccas.ac.cn
Received March 10, 2005
With the view to developing new chiral molecular switches and logic gates, a new binaphthalene
molecule with two spiropyran units (1) was synthesized and characterized. Absorption and 1H NMR
spectral studies of 1 after reaction with acid/base indicate acidichromism can occur to compound
1. The synergistic actions of acid and UV light irradiation result in a remarkable change for the
CD spectrum of the relatively dilute solution of 1, mimicking the behavior of a chiral “AND” gate,
since the “ouput” is the CD signal. Furthermore, the optical rotation value of the relatively
concentrated solution of 1 can be reversibly tuned after sequential reactions with acid and base,
and thus a chiral molecular switch with nondestructive “output” signal is realized. The present
results not only add a new example of chiral molecular switch with nondestructive readout but
also provide a chiral “AND” gate based on the axial chiral binaphthalene to which switchable units
are linked.
Introduction
established on the basis of these organic molecules.
Molecular switches and logic gates are key components
of the future molecular level devices, and accordingly they
have received significant attention in recent years. Usu-
ally, molecular switches are associated with one “input
signal”, while molecular logic gates entail two or more
“input signals”. When the “output signals” of molecular
switches are related to the properties of molecular
Reversibly tuning the conformations and the electronic
states of organic molecules by external stimulations
(input signals) is fundamentally interesting in terms of
mechanism and potential applications. When the changes
with regard to the conformations and the electronic states
are associated with detectable signals (output signals),
molecular switches1 and even logic gates2-15 can be
(2) The first single molecular AND logic gate was reported by: de
Silva, A. P.; Gunaratne, H. Q. N.; McCoy, C. P. Nature 1993, 364, 42.
For recent reviews, see: (a) de Silva, A. P.; McClenaghan, N. D. Chem.
Eur. J. 2004, 10, 574. (b) de Silva, A. P.; Fox, D. B.; Moody, T. S.;
Weir, S. M. Pure Appl. Chem. 2001, 73, 503. (c) Raymo, F. M. Adv.
Mater. 2002, 14, 401. (d) Steinitz, D.; Remacle, F.; Levine, R. D.
ChemPhysChem 2002, 3, 43. (e) Balzani, V.; Venturi, M.; Credi, A.
ChemPhysChem 2003, 4, 49. (f) Balzani, V.; Credi, A.; Venturi, M.
Chem. Eur. J. 2002, 8, 5534.
† Center for Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences.
‡ Graduate School of Chinese Academy of Sciences.
(1) For comprehensive reviews, see: (a) Molecular Switches; Feringa,
B. L., Ed.; Wiley-VCH: Weinheim, 2001. (b) Photochromism: Memories
and Switches. Irie, M., Guest Ed.; Chem. Rev. 2000, 100, 1683-1890.
(c) Optical Sensors and Switches; Ramamurthy, V., Schanze, K. S.,
Eds.; Marcel Dekker: New York, 2001.
10.1021/jo050489k CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/01/2005
6164
J. Org. Chem. 2005, 70, 6164-6170

Chiral Molecular “AND” Logic Gate and Switch
SCHEME 1. Illustration of Structure and Transformation of Compound 1 upon Addition of Acid and Base
chirality, they are regarded as chiral molecular switches.16
Two types of chiral molecular switches have been de-
scribed: one related to the modulation of intrinsic chiral-
ity of the system represented by sterically overcrowded
chiral alkenes reported first by Feringa et al.,16a,17 and
the other based on the magnitude change of chirality, as
reported just recently.16d,e,18 Herein we report a new chiral
molecular switch of the latter type based on the binaph-
thalene skeleton (R-) with two spiropyran (SP) units (1,
Scheme 1). The “output signal” of our chiral molecular
switch is the optical rotation value of the solution, and
thus it can be addressed in a nondestructive way.16a,19
Moreover, the circular dichroism (CD) spectrum of 1 can
be tuned by the combined actions of acid and UV light
irradiation, which mimics the function of an “AND” logic
gate.
The design rationale is explained as follows: (1) Axially
chiral binaphthalenes show strong CD signals and large
optical rotation values, which are dependent on the
dihedral angle of the two naphthalene moieties,20 with
the latter strongly influenced by the nature of the
substituents on the naphthalene rings. Therefore, chiral
binaphthalenes are good candidates for the construction
of chiral molecular switches and even molecular logic
gates. (2) Spiropyran (SP) can be transformed to the
corresponding merocyanine species (MC) and protonated
MC species (MCH) upon external stimulations.21-27 As
SP, MC, and MCH show different electronic structures
and can impose different steric hindrances, it is possible
to modulate the CD spectrum and optical rotation value
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J. Org. Chem, Vol. 70, No. 16, 2005 6165

Zhou et al.
SCHEME 2. Synthetic Scheme for Compound 1
of binaphthalene by external signals when two spiro-
pyran units are separately linked to the two naphthalene
rings of binaphthalene. It should be mentioned that a
few examples of chiral molecular switches based on
binaphthalene and photochromic16e,18 or redox active
units16d have been described. In this paper, we describe
the synthesis and characterization of compound 1 (Scheme
1). Upon reaction with acid or the combined actions of
acid and UV light irradiation, the SP units in 1 are
transformed to the corresponding MCH units, leading
to the variations of CD spectrum and optical rotation
value. The CD spectrum and optical rotation value of the
solution can be restored after further reaction with
equivalent amounts of base.
is very likely due to the absence of the electron-
withdrawing groups in the binaphthalene unit.31 How-
ever, upon the addition of acid (CF3COOH) the colorless
solution of 1 turns yellow and a new absorption band
appears around 427 nm (Figure 2). According to previous
studies, this new absorption band can be ascribed to the
protonated merocyanine (MCH) form of spiropyran units
of 1,26,27,32 indicating that SP units of 1 can be trans-
formed into the corresponding MCH units upon reaction
with acid. Namely, compound 1 can undergo acid-
ichromism33 and can be transformed to 1a, which can be
Results and Discussion
Synthesis. Compound 1 was synthesized starting from
the commercially available (R)-2,2′-dihydroxy-1,1′-bi-
naphthalene (2, Scheme 2), from which (R)-2,2′-dihy-
droxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (3) was ob-
tained by following the reported procedures.28 Reaction
of compound 3 with 1,3,3-trimethyl-2-methyleneindoline
afforded compound 1 in a total yield of 43% after
separation. Because of the two spiro-chiral carbon atoms
in 1,29 there exist four possible steric isomers for 1, as
demonstrated by the four singlet signals of the protons
of N-CH3 in the region of 2.41-2.54 ppm of the 1H NMR
spectrum (Figure 1). By integrating the intensity of each
singlet signal, the ratio of the four steric isomers was
determined to be about 1:1:1:1, implicating that the axial
chiral binaphthalene unit has no direct chiral effect on
the formation of the two spiro-carbon atoms in 1.
1
FIGURE 1. Partial H NMR spectrum of 1 (1.0 × 10-2 M in
CDCl3) in the region of 2.41-2.54 ppm (the part for the protons
of N-CH3).
UV-Vis and CD Spectral Studies. UV light irradia-
tion of the solution of 1 (1.0 × 10-5 M in ethanol) does
not lead to any changes of its absorption spectrum.30 This
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FIGURE 2. UV-vis and CD (inset) spectra of 1 (1.0 × 10-5
M
in ethanol) before (black) and after addition of 10 equiv (red),
and 40 equiv (green) of CF3COOH.
(29) Eggers, L.; Buss, V. Angew. Chem., Int. Ed. Engl. 1997, 36, 881.
6166 J. Org. Chem., Vol. 70, No. 16, 2005

Chiral Molecular “AND” Logic Gate and Switch
further converted to 1b upon exposure to acid. As shown
in Figure 2, the absorption intensity around 427 nm
increases gradually by increasing the amounts of CF3-
COOH added to the solution, indicating that the amounts
of 1 converted to 1a/1b are dependent on the amounts of
acid added to the solution.34 This is not unexpected since
the transformation of SP units into MCH units should
follow a bimolecular mechanism and the reaction process
should be dependent on the concentration of acid in the
solution. In addition, it is also reasonably assumed that
compound 1 is first converted to 1a, which reacts further
with acid to generate 1b as shown in Scheme 1.
As the MCH and SP species represent different
electronic and steric structures, it can be expected that
the dihedral angle of two naphthalene rings of 1 with
two SP units should be different from that of 1a with
one SP and one MCH units and that of 1b with two
MCH units. Besides, the conjugation in 1a and 1b
becomes more extended compared with that in 1. There-
fore, the CD spectrum of 1 should be different from that
of 1a and 1b,20 namely, the CD spectrum of 1 may be
tuned upon reaction with acid. However, the difference
between 1 and 1a in terms of CD spectrum may be small
since only one SP unit is transformed into MCH unit
from 1 to 1a. These expectations are in agreement with
the experimental observation as illustrated by the inset
of Figure 2, where the CD spectra of 1 in the presence of
different amounts of CF3COOH are displayed. The CD
spectrum (black curve in the inset of Figure 2) of the pure
solution of 1 (1.0 × 10-5 M in ethanol) shows a strong
bisignated band at about 235 and 260 nm.35 Upon
reaction with CF3COOH, the intensities of the CD signals
at about 235 and 260 nm decrease gradually accompanied
by slight absorption maximum change and the emergence
of a new bisignated band at about 362 and 438 nm. As
shown in the inset of Figure 2, the intensities of the new
absorptions at 362 and 438 nm (albeit weak) increase by
increasing the amounts of CF3COOH. Nevertheless,
variation of the CD spectrum of 1 (1.0 × 10-5 M in
ethanol) upon reaction with acid is rather small. For
instance, the CD signal intensity at 260 nm is only
reduced by 14% even after addition of 40 equiv of CF3-
COOH.
FIGURE 3. CD and UV-vis (inset) spectra of 1 (1.0 × 10-5
M in ethanol) before (black) and after addition of 40 equiv of
CF3COOH (red), after addition of 40 equiv of CF3COOH
followed by UV light irradiation for 5 min (green), and after
combined actions of CF3COOH and UV light, followed by
addition of 40 equiv of NaOH (blue); the black and blue curves
are almost overlapped.
FIGURE 4. Truth table (left) and logic circuit (right) corre-
sponding to the truth table. I1, I2, and O1 are UV light (365
nm, 120 W, 5 min), acid (40 equiv of CF3COOH), and CD value
at 235 or 260 nm, respectively. The output singal (O1) is off
when the CD value at 235 nm is smaller than -20 mdeg and
it is on when the CD value is larger than -20 mdeg, or O1 is
off when the CD value at 260 nm is larger than 30 mdeg and
it is on when the CD value is smaller than 30 mdeg.
change of 1, and addition of CF3COOH to the solution of
1 only led to small change of its CD spectrum. The results
in Figure 3 indicate that large CD spectrum change can
occur to the solution of 1 only after the synergistic actions
of CF3COOH and UV light irradiation. These spectral
changes can be understood as follows. Because of the lack
of electron-withdrawing groups on the two naphthalene
rings of 1, the open form of SP units cannot be stabilized.
As a result, variation of the absorption spectrum was not
observed for 1 upon UV light irradiation. Upon reaction
with acid, the SP units can be converted to the corre-
sponding MCH units, leading to the transformation of 1
into 1a, which was confirmed by 1H NMR spectral studies
as discussed below. In 1a, the nitrogen atom of the
indoline ring (MCH unit) possesses positive charge, i.e.,
implying that the MCH unit of 1a can function as an
electron-withdrawing group to stabilize the open form of
SP unit. Accordingly, UV light irradiation would facili-
tate the transformation of 1a into 1b in the presence of
acid. Such behavior of 1 mimics the function of an “AND”
logic gate (Figure 4) when CF3COOH (I1), UV light (365
nm) (I2), and the CD signal intensity at 235 or 260 nm
(O1) are regarded as the two input signals and output
signal, respectively. As the “output signal” is CD signal
Interestingly, further UV light irradiation of the solu-
tion of 1 (1.0 × 10-5 M in ethanol) that had been treated
with CF3COOH resulted in large CD spectrum change
as illustrated in Figure 3. Significant change was also
observed for the absorption spectrum of 1 under identical
conditions (see the inset of Figure 3). The UV light
irradiation alone could not induce any CD spectrum
(30) UV light irradiation was performed using 365 nm light from a
120-W high pressure Hg lamp for 2 h.
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(34) The reaction of compound 1 with CF3COOH was carried out in
the dark.
(35) The CD signals should be due to the axial chirality of binaph-
thalene unit rather than the spiro-carbon chirality since four steric
isomers of 1 are equally present in the solution based on the 1H NMR
data.
J. Org. Chem, Vol. 70, No. 16, 2005 6167

Zhou et al.
intensity, this “AND” gate may be regarded as a chiral
“AND” gate. To the best of our knowledge, such a chiral
“AND” gate was not described previously.
amounts of the SP units of 1 that were transformed to
MCH units was larger for the more concentrated solution
of 1 when the same amounts of CF3COOH were used.
For instance, the integration intensity ratio between the
signal around 4.3 ppm and that in the region of 2.4-2.6
ppm increased from 1:12.3 to 1:5.0 after addition of 1.0
equiv of CF3COOH when the concentration of the solution
of 1 was changed from 1 × 10-4 M to 1 × 10-2 M (see
Figure 5, b and e).37 This result is not unexpected since
the transformation of SP units to MCH units follows a
bimolecular reaction mechanism, and thus the reaction
process must be affected by the concentrations of both
compound 1 and CF3COOH.
Both the absorption spectrum and CD spectrum of 1
can be restored if equal amounts of base (NaOH) were
added to the solution of 1 that had been treated with CF3-
COOH alone or treated by both CF3COOH and UV light
irradiation (see Figure 3). This is due to the fact that the
transformation of spiropyran units from MCH species to
the corresponding SP ones of 1, namely, the intercon-
version between 1 and 1a (1a and 1b) (Scheme 1), can
reversibly proceed upon reaction with acid (and UV light
irradiation) and base. Therefore, the “AND” gate based
on compound 1 can be easily reset by reaction with equal
amounts of base and thus can be reversibly performed.
The interconversion between SP and MCH units is
accompanied by the disappearance and reformation of
spiro-chiral carbon centers in 1. However, they cannot
account for the variation of CD spectra of 1 discussed
above, because (1) the four steric isomers are equally
1H NMR spectra of 1 were also measured after com-
bined actions of CF3COOH and UV light (Figure 5g,h).
Compared with the cases where only CF3COOH was
added, the integration intensity ratio between the signal
around 4.3 ppm and that in the region of 2.4-2.6 ppm
increased after further UV light irradiation: from 1:12.3
to 1:4.4 for the addition of 1.0 equiv of CF3COOH and
from 1:6.2 to 1:1.1 for the addition of 2.0 equiv of CF3-
COOH. These results show that the combined actions of
CF3COOH and UV light facilitate the conversion of SP
units to MCH units, which is consistent with the CD and
absorption spectral studies as discussed above.
The concentrated solution of 1 showed such a strong
absorption around 260 nm that it was difficult to measure
a reliable CD spectrum for 1 under this condition, but
the optical rotation value of the concentrated solution of
1 in the presence of CF3COOH could be measured. As
illustrated in Figure 6 (left), the optical rotation value of
the solution of 1 (c ) 0.66, 1.0 × 10-2 M in ethanol, 20
°C) increased by increasing the amounts of CF3COOH
added to the solution and reached maximum when about
10 equiv of CF3COOH was added. As for the CD spec-
trum, the optical rotation value can return to the initial
magnitude (for the pure solution of 1) after equal
amounts of NaOH were added to the CF3COOH-treated
solution of 1. More interestingly, the optical rotation
value of solution of 1 can be reversibly tuned after
sequential reaction with acid and base as shown in
Figure 6 (right). Therefore, a new chiral molecular switch
with the optical rotation value as the “output signal” is
realized. On the basis of the fact that the light wave-
length used in the optical rotation measurement is longer
than the absorption region of 1, our chiral molecular
switch is attractive because of its nondestructive read-
out.16a,19
1
present in the solution according to the H NMR spec-
trum as shown in Figure 1, and (2) the axial chiral
binaphthalene unit has no direct chiral effect on the
formation of the spiro-carbon atoms in 1 synthesized from
(R)-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarbaldehyde and
1,3,3-trimethyl-2-methyleneindoline. Thus, it cannot be
expected that the axial chiral binaphthalene unit has
chiral induction effect on the formation of the spiro-
carbon atoms during the transformation between SP and
MCH units.
1H NMR Spectral and Optical Rotation Studies.
The transformation of 1 to 1a (1a to 1b) was also
confirmed by 1H NMR spectra of 1 (in CDCl3, 1.0 × 10-4
M and 1.0 × 10-2 M) in the presence of acid (CF3COOH)
(Figure 5). Upon addition of CF3COOH, a new singlet
signal around 4.3 ppm appeared, which can be ascribed
to the protons of N+-CH3 of 1a/1b (Scheme 1), by
reference to the 1H NMR spectra of MCH species of
similar spiropyran molecules.32 As shown in Figure 5, the
integration intensity for the signal around 4.3 ppm
increased, while that in the region of 2.4-2.6 ppm (N-
CH3) decreased by increasing the amounts of CF3COOH
added to the CDCl3 solution of 1 (Figure 5b-d). These
results implied that the amounts of 1 transformed to 1a/
1b increased by adding more CF3COOH to the solution
of 1. When 1.0 or 2.0 equiv of CF3COOH was added
(Figure 5b-c), four singlet signals were observed in the
region of 2.4-2.6 ppm (N-CH3), indicating the presence
of 1 in the solution besides 1a/1b since there should exist
only two signals for 1a and no signal for 1b in this region.
If we assumed that the amounts of 1b can be neglected
in the solution of 1 containing 1.0 equiv of CF3COOH,
the molar ratio of 1 and 1a was estimated to be about
85/15 based on the integration intensity ratio between
the signal around 4.3 ppm and that in the region of 2.4-
2.6 ppm. When 10.0 equiv of CF3COOH was used, the
signals around 2.4-2.6 ppm due to the protons of N-CH3
almost disappeared (Figure 5d), indicating that the SP
units of 1 were nearly transformed to MCH units under
this condition.36
(36) When 10.0 equiv of CF3COOH was added to the solution of 1
(ethanol, 1.0 × 10-5 M), only minor change was observed in the CD
spectrum of the solution. However, there is no disagreement between
the CD and 1H NMR (CDCl3, 1.0 × 10-4 M) spectral studies of 1 in the
presence of CF3COOH because the transformation of SP units to MCH
units follows a bimolecular reaction mechanism, and thus the reaction
process must be affected by the concentrations of both compound 1
and CF3COOH. The transformation process may also be affected by
solvent effects.
(37) The signals for the protons of N-CH3 in the region of 2.4-2.6
ppm became singlet (four singlet signals before addition of acid) after
reaction with CF3COOH for the (relatively concentrated) CDCl3
solution of 1 (1.0 × 10-2 M). This is likely due to the aggregation of 1
(1a and 1b) or, alternatively, intermolecular proton transfer from the
MCH unit of 1 to the SP unit of surrounding molecules of 1, leading
to formation of a new MCH unit and a MC unit, which may be in the
quinonoid form in CDCl3. As expected, the protons of N-CH3 of the
quinonoid form show a singlet signal in 1H NMR spectrum. This may
also contribute to the collapse of the signals in the 2.4-2.6 ppm region
into a single signal.
1
The H NMR spectra of 1 in the presence of different
amounts of CF3COOH were also measured in the rela-
tively concentrated solution of 1 (in CDCl3, 1.0 × 10-2
M, Figure 5e,f). Interestingly, it was found that the
6168 J. Org. Chem., Vol. 70, No. 16, 2005

Chiral Molecular “AND” Logic Gate and Switch
FIGURE 5. 1H NMR spectra of N-CH3 and N+-CH3 region of 1, 1a, and 1b (CDCl3, a-d,g,h 1.0 × 10-4 M and e, f 1.0 × 10-2 M)
before (a) and after addition of 1.0 equiv (b,e), 2.0 equiv (c,f), and 10 equiv (d) of CF3COOH; after addition of 1.0 equiv (g) and 2.0
equiv (h) of CF3COOH followed by UV light irradiation for 5 min.
J. Org. Chem, Vol. 70, No. 16, 2005 6169

Zhou et al.
FIGURE 6. (left) The optical rotation values [R]20D [c 0.66 (1.0 × 10-2 M), ethanol] of 1 before and after addition of 0.5, 1.0, 1.5,
2.0, and 10.0 equiv of CF3COOH, and after addition of 10.0 equiv of CF3COOH followed by injection of 10.0 equiv of NaOH.
(right) Illustration of the switchable behavior with optical rotation values as “output signal” after sequential addition of 2 equiv
of CF3COOH and NaOH.
point shows a relatively long melting range (155-160 °C), and
Conclusion
1H NMR and 13C NMR display more signals. [R]20 327.6 (c
D
0.66, ethanol). 1H NMR (CDCl3, 600 MHz): δ 7.72 (d, J ) 8.4
Hz, 2H/4), 7.67 (d, J ) 8.4 Hz, 2H/4), 7.63 (d, J ) 7.8 Hz, 2H/
4), 7.59 (d, J ) 7.8 Hz, 2H/4), 7.55 (s, 2H/4), 7.51 (s, 2H/4),
7.48 (s, 2H/4), 7.45 (s, 2H/4), 7.07-7.22 (m, 20H/4), 6.94-7.04
(m, 16H/4), 6.81-6.87 (m, 4H/4), 6.78 (d, J ) 6.6 Hz, 2H/4),
6.72 (d, J ) 7.2 Hz, 2H/4), 6.66 (d, J ) 6.6 Hz, 2H/4), 6.65 (s,
2H/4), 6.54-6.59 (m, 6H/4), 6.50 (t, J ) 7.5 Hz, 2H/4), 6.33 (d,
J ) 7.8 Hz, 2H/4), 6.23 (d, J ) 7.2 Hz, 2H/4), 6.05 (d, J ) 7.8
Hz, 2H/4), 6.00 (d, J ) 7.8 Hz, 2H/4), 5.78 (d, J ) 10.2 Hz,
2H/4), 5.73 (d, J ) 10.2 Hz, 2H/4), 5.69 (d, J ) 9.6 Hz, 2H/4),
5.67 (d, J ) 10.2 Hz, 2H/4), 2.52 (s, 6H/4), 2.51 (s, 6H/4) 2.47
(s, 6H/4), 2.43 (s, 6H/4), 1.08 (s, 6H/4), 1.07 (s, 6H/4), 1.06 (s,
6H/4), 0.97 (s, 6H/4), 0.88 (s, 6H/4), 0.83 (s, 6H/4), 0.66 (s, 6H/
4), 0.62 (s, 6H/4). 13C NMR (CDCl3, 150.9 MHz): δ 149.4, 149.3,
148.8, 147.4, 147.1, 136.6, 136.5, 136.3, 134.5, 134.4, 134.2,
129.2, 129.0, 128.7, 128.7, 128.6, 128.3, 128.2, 128.1, 127.6,
127.1, 127.0, 126.9, 125.9, 125.8, 125.6, 125.5, 125.4, 123.4,
123.2, 123.1, 122.0, 121.4, 121.3, 121.0, 120.3, 120.1,119.8,
118.2, 118.0, 115.8, 106.2, 106.0, 105.9, 50.9, 49.8, 49.6, 49.4,
31.0, 29.1, 28.9, 28.6, 28.5, 25.3, 24.9, 24.6, 24.5, 22.0, 21.7,
21.4, 21.0. MS (MALDI-TOF): m/z 652.5 (M+). FT-IR (KBr):
1608 cm-1 (CdC). Anal. Calcd for C46H40N2O2: C, 84.63; H,
6.18; N, 4.29. Found: C, 84.69; H, 6.56; N, 4.16.
A new binaphthalene with two spiropyran units (1)
was synthesized and characterized. Absorption and H
1
NMR spectral studies of the solution of 1 indicate the
reversible transformation between the SP units and the
corresponding MCH units in 1 after sequential reaction
with acid/base. The reversible transformation of the SP
units to the corresponding MCH units in 1 leads to the
reversible modulation of the CD spectra, but the variation
of the CD spectrum is rather small. However, the
synergistic actions of acid and UV light irradiation result
in a large CD spectrum change for the relatively dilute
solution of 1, which mimics the behavior of an “AND”
gate that may be regarded as a chiral “AND” gate since
the “ouput” signal is the CD signal intensity. Further-
more, the optical rotation value of the relatively concen-
trated solution of 1 can be reversibly tuned after sequen-
tial reaction with acid and base, and thus a chiral
molecular switch with nondestructive “output” signal is
realized. The present results not only add a new example
of chiral molecular switch but also provide a chiral “AND”
gate based on the axial chiral binaphthalene to which
switchable units are linked. Further investigations will
be directed toward fully light-driven chiral switches that
are analogues of compound 1 with electron-withdrawing
functional groups on the binaphthalene rings.
Experimental Details for the Chiral Switch and “AND”
Logic Gate. (1) To a solution of 1 (1.0 × 10-2 M in ethanol)
was added 2.0 equiv of CF3COOH, and then the optical
rotation value of the solution was measured. After that, 2.0
equiv of NaOH was added to the above solution, and again
the rotation value was measured. The experiments were
repeated by following the sequences. The reactions with CF3-
COOH and NaOH were carried out in the dark. (2) A solution
of 1 (1.0 × 10-5 M in ethanol) in quartz cell was first treated
with 40 equiv of CF3COOH, followed by UV light irradiation
(120-W high pressure Hg lamp) for 5.0 mim.; after that, the
CD spectrum of the solution was recorded.
Experimental Section
General Experimental Methods. All chemicals are com-
mercially available. Ethanol was distilled over Mg and tet-
rahydrofuran (THF) over Na with benzophenone as indicator.
Synthesis of Compound 1. Compound 1 was prepared
from (R)-2,2′-dihydroxy-1,1′-binaphthyl-3,3′-dicarbaldehyde,
which was synthesized according to the literatures in a total
yield of 69%,28 and 1,3,3-trimethyl-2-methyleneindoline.
(R)-2,2′-Dihydroxy-1,1′-binaphthyl-3,3′-dicarbaldehyde (3) (0.50
g, 1.5 mmol) and 0.5 mL (0.51 g, 3.0 mmol) of 1,3,3-trimethyl-
2-methyleneindoline were dissolved in 120 mL of anhydrous
ethanol under nitrogen atmosphere. The mixture was stirred
magnetically and heated to reflux. After 3 h, solvents were
removed under reduced pressure to give a red oil. The residue
was subjected to column chromatography (silica gel) with
dichloromethane/petroleum ether (60-90 °C) (1:2, v/v) as
eluent to give 1 (0.61 g, 62%) as a white solid.
Acknowledgment. The present research was finan-
cially supported by NSFC, Chinese Academy of Sciences,
and State Key Basic Research Program. D.-Q. Zhang
thanks National Science Fund for Distinguished Young
Scholars. The authors want to thank Prof. Yongjun
Chen and Qinghua Fan of the Institute for helpful
discussion. The authors also thank the anonymous
reviewers for the critical comments that enabled us to
improve the manuscript significantly.
As mentioned above, the obtained sample of 1 contained four
equally present steric isomers. For this reason, its melting
JO050489K
6170 J. Org. Chem., Vol. 70, No. 16, 2005