Synthesis and spectral investigations of a new dyad with spiropyran and fluorescein units: Toward information processing at the single molecular level

Article abstract of DOI:10.1021/jo034243w

A new dyad 1 with two spiropyran units as the photochromic acceptors and one fluorescein unit as the fluorescent donor was synthesized and characterized. External inputs (ultraviolet light, visible light, and proton) induce the reversible changes of the structure and, concomitantly, the absorption spectrum of dyad 1 due to the presence of two spiropyran units. Only the absorption spectrum of the ME form of the spiropyran units in dyad 1 has large spectral overlap with the fluorescence spectrum of the fluorescein unit. Thus, the fluorescence intensity of dyad 1 is modulated by reversible conversion among the three states of the photochromic spiropyran units and the fluorescence resonance energy transfer (FRET) between the ME form and the fluorescein unit. Based on the fact that dyad 1 could read out three external input signals (ultraviolet light, visible light and proton) and write a compatible specific output signal (fluorescence intensity), dyad 1 described here can be considered to perform an integrated circuit function with one OR and one AND interconnected logic gates. The present results demonstrate an efficient strategy for elaborating and transmitting information at the single molecular level.

Full text of DOI:10.1021/jo034243w

Syn th esis a n d Sp ectr a l In vestiga tion s of a New Dya d w ith
Sp ir op yr a n a n d F lu or escein Un its: Tow a r d In for m a tion
P r ocessin g a t th e Sin gle Molecu la r Level
Xuefeng Guo,†,‡ Deqing Zhang,*,† Yucheng Zhou,†,‡ and Daoben Zhu*,†
Organic Solids Laboratory, Center for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China, and Graduate School,
Chinese Academy of Sciences, Beijing 100080, China
dqzhang@iccas.ac.cn
Received February 24, 2003
A new dyad 1 with two spiropyran units as the photochromic acceptors and one fluorescein unit as
the fluorescent donor was synthesized and characterized. External inputs (ultraviolet light, visible
light, and proton) induce the reversible changes of the structure and, concomitantly, the absorption
spectrum of dyad 1 due to the presence of two spiropyran units. Only the absorption spectrum of
the ME form of the spiropyran units in dyad 1 has large spectral overlap with the fluorescence
spectrum of the fluorescein unit. Thus, the fluorescence intensity of dyad 1 is modulated by reversible
conversion among the three states of the photochromic spiropyran units and the fluorescence
resonance energy transfer (FRET) between the ME form and the fluorescein unit. Based on the
fact that dyad 1 could “read out” three external input signals (ultraviolet light, visible ligh,t and
proton) and “write” a compatible specific output signal (fluorescence intensity), dyad 1 described
here can be considered to perform an integrated circuit function with one OR and one AND
interconnected logic gates. The present results demonstrate an efficient strategy for elaborating
and transmitting information at the single molecular level.
In tr od u ction
Like photoinduced electron transfer, energy transfer
is another mechanism for quenching the excited states
of fluorophores. If the fluorescence intensity of the
fluorophore can be regulated by the controlled energy
transfer process in response to external signals, the
corresponding molecular switch or logic gate can be
designed.5 One of the energy transfer mechanisms is
fluorescence resonance energy transfer (FRET), for which
the basic requirement is the certain degree of spectral
overlap between the emission spectrum of the fluorophore
and the absorption spectrum of the “quencher”. The three
states of spiropyran SP, ME, and MEH6a show different
The expectation of potential application in molecular
devices, such as molecular wires, sensors, switches, logic
gates, and signal nanoprocessors,1 has been inspiring
active investigations into designing and synthesizing
functional molecules. Photochromic compounds are prom-
ising candidates due to their reversible structural inter-
conversion in response to external optical, chemical, and
thermal stimulation.2 Among them, the system taking
advantage of the interconversion between spiropyran
(SP)3 and merocyanine (ME) has been extensively inves-
tigated.4
† Organic Solids Laboratory.
(3) The IUPAC nomenclature of spiropyran is 1′,3′-dihydro-1′,3′,3′-
trimethyl-spiro[2H-1-benzopyran-2, 2′-(2H)-indole].
‡ Graduate School.
(1) (a) Carter, F. L.; Siatkowsky, R. E.; Woltjien, H. In Molecular
Electroic Devices; Elsvier: Amsterdam, The Netherlands, 1988. (b)
Ratner, M. A.; J ortner, J . In Molecular Eletronics; J ortner, J ., Ranter,
M., Eds.; Blackwell: Oxford, UK, 1997; pp 5-72. (c) Drexler, E.
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and further references therein. (g) de Silva, A. P.; McClenaghan, N.
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H.; Bouas-Laurent, H., Eds. In Photochromism, Molecules and Systems;
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Moore, T. A.; Gust, D. J . Am. Chem. Soc. 2001, 123, 7124. (b) Norsten,
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14, 918. (e) Otsuki, J .; Yasuda, A.; Takido, T. Chem. Commun. 2003,
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Am. Chem. Soc. 2002, 124, 7668.
(6) (a) Raymo, F. M.; Giorgani, S. J . Am. Chem. Soc. 2001, 123, 4651.
(b) Raymo, F. M.; Giorgani, S. J . Am. Chem. Soc. 2002, 124, 2004. (c)
Raymo, F. M.; Giorgani, S. Org. Lett. 2001, 3, 1833. (d) Raymo, F. M.;
Giorgani, S. Org. Lett. 2001, 3, 3475.
10.1021/jo034243w CCC: $25.00 © 2003 American Chemical Society
Published on Web 06/12/2003
J . Org. Chem. 2003, 68, 5681-5687
5681

Guo et al.
nm, at which SP, ME, and MEH have very weak
absorption. Thus, excitation of fluorescein at 430 nm will
perturb none of the three states of spiropyran (SP, ME,
and MEH). With these thoughts in mind, we started the
studies of the photoswitching behavior of SP units in the
presence of the fluorescein unit. Here we report the
synthesis and spectral studies of a well-defined dyad 1
with both spiropyran and fluorescein units (SP-Flu-SP,
see Scheme 1). By considering the ease of synthesis, two
SP units are covalently attached to the fluorescein unit
in dyad 1. The results demonstrate that the fluorescence
intensity of the fluorescein unit can be controlled by
alternating ultraviolet light, visible light, and proton
stimulations, which implies that this SP-Flu-SP dyad can
lend itself to be an efficient molecular design for process-
ing and communicating information at the single molec-
ular level. For comparable studies, the intermolecular
communicating behavior of the mixture solution of a
fluorescein derivative (compound 9, see Scheme 1) and
a SP molecule (compound 10, see Scheme 1) (in a molar
ratio of 2:1) were also investigated.
F IGURE 1. Absorption spectra of reference compound 10 (see
Scheme 1) (1.0 × 10-4 M, 25 °C) (a) before and (b) after
irradiation with ultraviolet light at 365 nm for 5 min and (c)
after irradiation with ultraviolet light followed by the addition
of 1 equiv of CF3COOH in THF and (d) absorption spectra of
the reference compound 9 (see Scheme 1) (5.0 × 10-5 M, THF,
25 °C). The inset curve is the emission spectrum of 9 in THF
(5.0 × 10-5 M, 25 °C) excited at 430 nm. For the UV irradiation
experiments, a 140-W high-pressure mercury lamp (λ ) 365
nm) was held above the cuvettes containing solutions by about
3 cm.
Resu lts a n d Discu ssion
Syn th esis. The preparation of dyad 1 was depicted in
Scheme 1. Condensation of 4-methoxyphenylhydrazine
hydrochloride 2 with methyl isopropyl ketone afforded
Fisher’s base 3, which was demethylated with boron
tribromide to yield Fisher’s base 4.8 Fisher’s base 4 was
then methylated with methyl iodide to give the inter-
mediate salt 5. The condensation of 5 with 5-nitro-
salicylaldehyde led to spiropyran 6 in good yield.8 Fluo-
rescein derivative 8 was prepared from fluorescein di-
sodium 7 according to the reference.9 Finally, reaction
of 8 with spiropyran 6 in DMF at room temperature in
the presence of anhydrous K2CO3 gave the target com-
pound 1 in 42.7% yield after separation with column
chromatography.
The reference compounds 9 and 10 were prepared in
ways similar to those for compounds 8 and 6, respec-
tively.
Absor p tion Sp ectr a . As for the spiropyran reported
by Raymo et al.,6 the reference compound 10 also shows
the reversible interconversion among the corresponding
SP, ME, and MEH states upon irradiation of ultraviolet
and visible light and addition of acid. Similar phenomena
were observed for the mixed solution of reference com-
pounds 9 and 10 (in a molar ratio of 1:2).
Figure 2 shows the absorption spectrum of dyad 1 and
those of the solution after treatment with ultraviolet light
and acid in THF. The absorption peaks at 430, 450, and
485 nm are essentially identical with those observed for
reference compound 9 (Figure 1). As shown in Figure 2,
the absorption spectra of dyad 1 before irradiation by
ultraviolet light are essentially a simple addition of the
spectra of the fluoroscein and nitrospiropyran chro-
mophores (for their absorption spectra, see Figure 1), and
thus there is no significant electronic interactions be-
tween fluorescein and nitrospiropyran units of dyad 1 in
the ground state. After the THF solution of dyad 1 was
absorption spectra, and thus it is possible to regulate the
fluorescence intensity of a suitable fluorophore by ir-
radiation of the solution containing both spiropyran and
the fluorescent molecule. Indeed, Raymo and his col-
leagues6 studied the “signal communication” between
pyrene (naphthalene, anthracene, and tetracene) and
spiropyran, and proposed the corresponding integrated
logic gates and communication network. By attaching
spiropyran covalently to porphyrin, Moore et al.5a studied
the quenching process of the porphyrin excited states
upon irradiation by ultraviolet light.
Fluorescein is the most widely used fluorophore for
labeling and sensing biomolecules7 due to its high extinc-
tion coefficient, high fluorescence quantum yield, and the
fact that its excitation wavelength lies in the visible-
wavelength range. As shown in the inset curve of Figure
1, fluorescein shows the emission in the range of 500-
650 nm, and hence the overlap between its fluorescence
spectrum and the absorption spectrum of ME is signifi-
cantly large (see Figure 1), as compared to that between
porphyrin and pyrene.5a,6 By contrast, there is almost no
overlap between the fluorescence spectrum of fluorescein
and the absorption spectra of SP and MEH (see Figure
1). Consequently, for the fluorescein-spiropyran system
the corresponding fluorescence “on/ off” ratio as well as
the “output” ratio (signal-to-noise ratio) can be enhanced.
Besides, fluorescein shows strong absorption around 430
(7) Examples of Fluorescein-based probes for labeling and sensing
biomolecules: (a) Hirano, T.; Kikuchi, K.; Urano, Y.; Nagano, T. J .
Am. Chem. Soc. 2002, 124, 6555. (b) Tanaka, K.; Miura, T.; Umezawa,
N.; Urano, Y.; Kikuchi, K.; Higuchi, T.; Nagano, T. J . Am. Chem. Soc.
2001, 123, 2530. (c) Hirano, T.; Kikuchi, K.; Urano, Y.; Higuchi, T.;
Nagano, T. J . Am. Chem. Soc. 2000, 122, 12399. (d) Umezawa, N.;
Tanaka, K.; Urano, Y.; Kikuchi, K.; Higuchi, T.; Nagano, T. Angew.
Chem., Int. Ed. 1999, 38, 2899. (e) Chen, C. A.; Yeh, R. H.; Lawrence,
D. S. J . Am. Chem. Soc. 2002, 124, 3840. (f) Miyawaki, A.; Liopis, J .;
Heim, R.; McCaffery, J . M.; Adams, J . A.; Ikura, M.; Tsien, R. Nature
1997, 388, 882. (g) Tolbert, T.; Wong, C. H. Angew. Chem., Int. Ed.
2002, 41, 2171.
(8) Shragina, L.; Buchholtz, F.; Yitzchaik, S.; Krongauz, V. Liq.
Cryst. 1990, 7, 643.
(9) J ing, B. W.; Zhang, D. Q.; Zhu, D. B. Tetrahedron Lett. 2000,
41, 8559.
5682 J . Org. Chem., Vol. 68, No. 14, 2003

Synthesis and Spectral Investigations of a New Dyad
SCHEME 1. Syn th etic Sch em e for Dya d 1 (SP -F lu -SP ) a n d Ch em ica l Str u ctu r es of Refer en ce Com p ou n d s
9 a n d 10
irradiated with ultraviolet light at 365 nm, the main
absorption bands of the fluorescein unit were still un-
changed, but the characteristic absorption band of the
ME form with a maximum at 580 nm emerged. This
indicates the formation of the corresponding ME form by
reference to the absorption spectrum of compound 10
upon irradiation under the same conditions. Upon addi-
tion of 2 equiv of CF3COOH, the absorption band at 580
nm disappeared due to the complete transformation of
ME to MEH. The initial absorption was recovered after
irradiation of the above solution, which had been treated
with UV light and acid, with visible light (λ > 460 nm)
(not shown).
F lu or escen ce Sp ectr a . Figure 3 shows the fluores-
cence spectra of the solution of dyad 1 in THF under
several different conditions with excitation wavelength
at 430 nm. Before irradiation with ultraviolet light, it
showed a broad emission band in the range of 500-650
nm with the maximum around 550 nm (curve a, Figure
3). Upon irradiation with ultraviolet light for 5 min, the
intensity of the fluorescence band around 550 nm de-
creased to 45% of that of the initial solution (curve b,
Figure 3). This fluorescence intensity reduction is sig-
nificantly large compared to that of the porphyrin-
spiropyran dyad.5a Besides, a new emission band with
maxima at ∼650 nm appeared. Ultraviolet light irradia-
tion induced the formation of the ME moiety in dyad 1,
which quenched the excited state of the fluorescein unit
through fluorescence resonance energy transfer. Energy
transfer from the excited fluorescein state to ME pro-
duced the excited ME state, which should be responsible
for the appearance of this new emission band. A control
experiment with reference compound 10 confirms this
conclusion: no significant fluorescence emission was
observed upon excitation of the SP form of reference
compound 10. After irradiation of the THF solution of
10 with ultraviolet light at 365 nm for 5 min, the
corresponding ME form was produced. This solution
J . Org. Chem, Vol. 68, No. 14, 2003 5683

Guo et al.
of acid did not affect the fluorescence intensity of refer-
ence compound 9 as shown in Figure 4B.
The above fluorescence modulation observed for dyad
1 can be explained with the switching cycles starting and
ending with SP-Flu-SP as showed in Scheme 2. There
should exist seven states of dyad 1 due to the partial
conversion between SP and ME on exposure to ultraviolet
light.10 Since changes of the fluorescence intensity are
the sole result of irradiation with ultraviolet light, we
simplify them to the three extreme states (see Scheme
2) to interpret the mechanism clearly. Upon irradiation
with ultraviolet light, the SP moieties in dyad 1 are
converted to ME units [formation of ME-Flu-ME (SP)],
which quench the excited state of the fluorescein unit,
and as a result, the fluorescence intensity of the fluores-
cein unit is reduced to about 45% of the initial value.
Upon addition of 2 equiv of CF3COOH, the ME units are
transformed to the MEH unit [formation of MEH-Flu-
MEH (SP)], whose absorption spectrum has almost no
overlap with the fluorescent spectrum of the fluorescein
unit. Thus, effective energy transfer cannot take place,
and consequently the fluorescence intensity of the fluo-
rescein unit returns to its initial value. On the other
hand, upon irradiation of the solution of ME-Flu-ME (SP)
with visible light, the fluorescence intensity also returns
to its initial value as a result of the complete conversion
from ME-Flu-ME (SP) to SP-Flu-SP. Thus, alternating
ultraviolet light, visible light, and proton inputs can
regulate the fluorescence intensity of the fluorescein unit.
For comparative studies, similar experiments were
performed for the mixtures of reference compounds 9 and
10 (in a molar ratio of 1:2) (Figure 5). Before ultraviolet
light irradiation, the solution showed a broad and
featureless emission band with the maximum around 550
nm. After irradiation of the solution at 365 nm for 5 min,
the fluorescence intensity was reduced by about 13%,
which should be due to the quenching of the excited state
of the fluorescein unit by the corresponding ME form
generated from the SP form of 10 upon ultraviolet light
irradiation. Similar to what is described above for dyad
1, the fluorescence intensity of the solution returned to
its initial value upon addition of 2 equiv of CF3COOH or
upon irradiation with visible light. As compared to dyad
1, the fluorescence intensity reduction for the mixed
solution of 9 and 10 is less significant. This may be
interpreted as follows: According to the Fo¨rster theory,11
the energy transfer efficiency is strongly dependent on
the donor-acceptor distance. The donor and acceptor
units in dyad 1 are much closer to each other than those
in the case of the mixed solution of 9 and 10 (inter-
molecular). Thus, the intermolecular energy transfer is
not as effective as that for the intramolecular case. In
addition, the emission band ascribed to the ME form was
not obvious for the mixed solution. This also may be due
to the ineffective energy transfer from the excited state
of fluorescein to the ME form of 10. As a result, only a
rather limited amount of the ME form of 10 was excited.
The excited state of the ME form may be easily deacti-
vated by the surrounding solvents, so that the emission
around 650 nm due to the excited state of the ME form
was too weak to be observed.
F IGURE 2. Absorption spectra of dyad 1 (5.0 × 10-5 M, THF,
25°C) (a) before and (b) after irradiation with ultraviolet light
for 5 min and (c) after irradiation with ultraviolet light
followed by addition of 2 equiv of CF3COOH in THF. For the
UV irradiation experiment, a 140-W high-pressure mercury
lamp (λ ) 365 nm) was held above the cuvette containing the
solution by about 3 cm.
F IGURE 3. Emission spectra of dyad 1 (5.0 × 10-5 M, THF,
25 °C) excited at 430 nm (a) before and (b) after irradiation
with ultraviolet light for 5 min and (c) after irradiation with
ultraviolet light followed by addition of 2 equiv of CF3COOH.
The inset curve is the emission spectrum of the ME form of
compound 10 (1.0 × 10-4 M in THF, 25 °C, after irradiation
with ultraviolet light for 5 min) excited at 563 nm. For the
UV irradiation experiments, a 140-W high-pressure mercury
lamp (λ ) 365 nm) was held above the cuvettes containing
solutions by about 3 cm.
displayed a fluorescence band with the maximum at 650
nm after excited at 563 nm (Figure 3, inset curve). After
addition of 2 equiv of CF3COOH to the solution of dyad
1 after UV light irradiation, the fluorescence intensity
of the solution was restored to its initial value (curve c,
Figure 3). Irradiation with visible light for 5 min on the
solution of dyad 1 just after treatment with ultraviolet
light irradiation showed a similar effect as the case where
treatment with ultraviolet light irradiation was followed
by addition of acid.
This fluorescence intensity alteration can be repeated
consecutively. As an example, Figure 4A illustrates this
effect of the fluorescence intensity of the fluorescein unit
at 550 nm for several switching cycles. Control experi-
ments indicated that both light irradiation and addition
For the above studies, the quantitative estimates were
not performed for the following reasons: (1) since ir-
radiation was not carried out during the recording of the
5684 J . Org. Chem., Vol. 68, No. 14, 2003

Synthesis and Spectral Investigations of a New Dyad
F IGURE 4. (A) Reversible modulation of the fluorescence intensity of the fluorescein unit at 550 nm for dyad 1 (5.0 × 10-5 M,
THF, 25 °C) excited at 430 nm. (B) The relative fluorescence intensity of the reference compound 9 at 550 nm under the action
of three external inputs; the excitation wavelength is 430 nm. The three inputs I1, I2, and I3 are UV light, visible light, and
proton, respectively.
SCHEME 2 Th e Rever sible Sw itch in g Cycle for Dya d 1 u n d er th e Action of Th r ee Exter n a l In p u ts: UV
Ligh t, Visible Ligh t, a n d P r oton
fluorescent spectra, thermal reversion to the closed SP
form may occur before and during the collection of the
fluorescent spectra; (2) since both the SP and ME forms
of the spiropyran units and the fluorescein unit absorb
at 365 nm, irradiation at this wavelength causes only
photostationary equilibrium of the two forms (SP and
ME) of spiropyran units, rather than driving the system
totally to one form; and (3) the overlap of the fluorescence
bands of the ME form and fluorescein unit partially
offsets the fluorescence quenching of the fluorescein
moiety in the same wavelength region as mentioned
above.
An a lysis of th e In for m a tion Tr a n sm ission P a t-
ter n . The dependence of the fluorescent spectra of dyad
1 on the external stimulationssultraviolet light, visible
light, and protonsmimics the function of an integrated
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Guo et al.
F IGURE 5. Fluorescence spectra of the mixture of 9 and 10
excited at 430 nm (5.0 × 10-5 M for 9, 1.0 × 10-4 M for 10,
THF, 25 °C) (a) before and (b) after irradiation with ultraviolet
light for 5 min and (c) after irradiation with ultraviolet light
followed by addition of 2 equiv of CF3COOH. For the UV
irradiation experiment, a 140-W high-pressure mercury lamp
(λ ) 365 nm) was held above the cuvette containing the
solution by about 3 cm.
F IGURE 6. Truth table (up) for all the possible strings of
three binary inputs data and the corresponding output digit,
and the combinational logic circuit (below) corresponding to
the truth table. I1, I2, I3, and O1 are ultraviolet light, visible
light, proton, and the fluorescence of fluorescein unit at 550
nm. The output signal (O1) is off when the relative emission
intensity at 550 nm is about 45% (relative to the initial value),
and it is on when the relative intensity is 100%.
logic gate.1g-j,12 This behavior can be analyzed with the
aid of binary logic.13 The three input signals are I1
(ultraviolet light), I2 (visible light), and I3 (proton). The
output signal is O1, the emission band at 550 nm of the
fluorescein unit. Each signal can be either off or on and
can be represented by a binary digit. Consequently, dyad
1 reads a string of three binary inputs and writes a
specific output. For example, when the three input
stimulations I1, I2, and I3 are on, off, and off, respec-
tively, the input string is 100. Under these conditions,
dyad 1 exists as the ME-Flu-ME (SP) form in solution,
which has strong absorption bands in the visible range
with a maximum at 580 nm. As a result, the excited state
of the fluorescein unit is quenched and the fluorescence
intensity is reduced. Hence, the output signal is off. And
the output digit is 0. If both I1 and I3 are on, and I2 is
off, the input string is 101. Under these conditions, dyad
1 is in the MEH-Flu-MEH (SP) state, which shows no
absorption bands at wavelengths longer than 500 nm.
Accordingly, the fluorescence intensity of the fluorescein
unit returns to its initial value. Thus the output signal
is on, and the digit is 1. All the possible strings of three
binary inputs data and the corresponding output digit
are included in the truth table as showed in Figure 6.
The two entries in the truth table where both I1 and I2
are 1 imply that the sample is simultaneously irradiated
by UV and visible light.
The combinational logic circuit equivalent to the truth
table is also shown in Figure 6. It can be seen from the
truth table (Figure 6) that I2 has no influence on O1,
and thus the combinational logic circuit includes only the
two inputs: I1 and I3. Then inputs I1 and I3 were
transmitted into the output O1 through one OR operation
and one AND logic operation in this circuit.
Besides the intensity reduction of the fluorescein
fluorescence upon UV light irradiation of the solution of
dyad 1, a new broad emission band around 650 nm
appears due to the absorption-energy transfer-emission
(AETE)14 process from the excited fluorescein unit to the
ME forms. This emission band can be regarded as
another output signal (O2). Compared with that of the
fluorescein unit of dyad 1 in the SP-Flu-SP state (Scheme
2), this emission band is relatively weak.
Con clu sion
Since the absorption spectrum of the ME form of
spiropyran matches very well with the fluorescence
spectrum of fluorescein, a new dyad 1 with two SP units
and one fluorescein unit was designed for studies of the
information transmission at the single molecular level.
The fluorescence of this new dyad can be modulated by
three inputs: ultraviolet light, visible light, and proton
based on the resonance energy transfer mechanism.
Thus, new dyad 1 can “read out” three external input
signals and “write” a compatible specific output signal.
This behavior corresponds to an integrated circuit with
one OR and one AND logic gates. It should be noted that
the communicating components are covalently linked,
and as a result the energy transfer is more effective than
(10) The two SP units are not symmetrically attached to the
fluorescein unit in dyad 1. Thus, under the action of UV light
irradiation and acid, there exist seven possible states for dyad 1: SP-
Flu-SP, ME-Flu-SP, MEH-Flu-SP, SP-Flu-ME, SP-Flu-MEH, ME-Flu-
ME, and MEH-Flu-MEH.
(11) (a) Fo¨rster, T. Naturewissenschaften 1946, 6, 166. (b) Fo¨rster,
T. Discuss. Faraday Soc. 1959, 27, 7. (c) Lakowicz, J . R. Principles of
Fluorescence Spectroscopy, 2nd ed.; Plenum: New York, 1999.
(12) Examples of similar chemical systems with logic operations:
(a) De Silva, A. P.; Dixon, I. M.; Gunaratne, H. Q. N.; Gunnlaugsson,
T.; Maxwell, P. R. S.; Rice, T. E. J . Am. Chem. Soc. 1999, 121, 1393.
(b) Brown, G. J .; De Silva, A. P.; Pagliari, S. Chem. Commun. 2002,
2461 and further references therein. (c) Gunnlaugsson, T.; MacDo´nail,
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5686 J . Org. Chem., Vol. 68, No. 14, 2003

Synthesis and Spectral Investigations of a New Dyad
40 mL) and saturated aqueous NaCl (20 mL), dried (MgSO4),
and concentrated in vacuo. After column chromatography on
silica gel with ethyl acetate/petroleum (60-90 °C) (3:2, v/v)
as eluant, dyad 1 was obtained as yellow powder (0.22 g) in
42% yield. Mp 159-160 °C. FTIR (KBr): 1721, 1642, 1481
1338 cm-1. 1H NMR (CDCl3): δ 1.19 (s, 6H), 1.28 (s, 6H), 1.82
(m, 2H), 2.33 (m, 2H), 2.70 (s, 3H), 2.71 (s, 3H), 3.71 (t, 2H, J
) 5.6 Hz), 4.17 (m, 6H), 5.85 (d, 2H, J ) 10.2 Hz), 6.47 (d, 2H,
J ) 10.2 Hz), 6.56 (d, 1H, J ) 9.8 Hz), 6.63 (s, 1H), 6.76 (m,
7H), 6.90 (m, 4H), 6.99 (s, 1H), 7.32 (d, 1H, J ) 7.7 Hz), 7.75
(m, 2H), 8.02 (m, 4H), 8.29 (d, 1H, J ) 7.7 Hz). 13C NMR
(CDCl3): δ 20.3, 26.2, 28.9, 29.6, 30.1, 52.8, 63.0, 64.9, 65.1,
65.9, 101.4, 106.3, 107.2, 107.5, 107.6, 110.5, 112.4, 112.7,
114.1, 115.3, 115.8, 118.1, 119.1, 121.8, 121.9, 123.1, 126.2,
128.6, 129.3, 130.1, 130.4, 130.6, 130.9, 131.8, 133.1, 134.7,
138.1, 138.2, 141.3, 142.4, 142.6, 153.5, 153.6, 154.6, 159.2,
160.2, 163.8, 165.8, 185.9. MALDI-TOF-MS: m/z 1089.2. Anal.
Calcd for C64H56N4O13: C, 70.58; H, 5.18; N, 5.14. Found: C,
70.44; H, 5.08; N, 4.99.
that of the intermolecular case. These results will be
useful for further molecular design of new dyads that will
mimic the function of the complex logic gates. Searching
for a new fluorophore whose emission spectrum has a
large overlap with the absorption spectra of both ME and
MEH forms (but, still the spectrum overlap of the
fluorophore with the ME form is different from that with
the MEH form) should have priority in our future work.
Exp er im en ta l Section
1′,3′-Dih yd r o-5′-h yd r oxyl-1′,3′,3′-tr im eth yl-6-n itr osp ir o-
[2H-1-ben zop yr a n -2,2′-(2H)-in d ole] (Com p ou n d 6). 6 was
prepared from 4-methoxyphenylhydrazine hydrochloride ac-
cording to ref 8. Mp > 280 °C; MS (EI) m/z 338 (M+). Anal.
Calcd for C19H18N2O4: C, 67.45; H, 5.36; N, 8.28. Found: C,
67.19; H, 5.48; N, 7.98.
9-(o-(3′-Br om op r op yl)ca r b oxyp h e n yl)-6-(3′-b r om o-
p r op oxy)-3-xa n th a n on e (Com p ou n d 8). To a solution of
uranine (2.00 g, 5.32 mmol) in DMF (60 mL) was added 1,3-
dibromopropane (5 mL) and anhydrous K2CO3 (7.35 g, 53.2
mmol). Then, the mixture was stirred at room temperature
overnight before 200 mL of H2O was added. The aqueous
solution was extracted with dichloromethane (3 × 100 mL),
and the combined extracts were washed with H2O (2 × 50 mL)
and saturated aqueous NaCl (20 mL), dried (MgSO4), and
concentrated in vacuo. After column chromatography on silica
gel with ethyl acetate/petroleum (60-90 °C) (1:4, v/v) as eluant,
8 was obtained as red crystals (2.60 g) in 85% yield. Mp 107-
1′,3′-Dih yd r o-5′-m eth oxy-1′,3′,3′-tr im eth yl-6-n itr osp ir o-
[2H-1-ben zop yr a n -2,2′-(2H)-in d ole] (Com p ou n d 10).15 10
was prepared similarly as for compound 6 in 27% yield. Mp
149-150 °C. FTIR (KBr): 2957, 1482, 1336 cm-1 1H NMR
.
(CDCl3): δ 1.21 (s, 3H), 1.29 (s, 3H), 2.71 (s, 3H), 3.82 (s, 3H),
5.88 (d, 1H, J ) 10.3 Hz), 6.48 (d, 1H, J ) 10.3 Hz), 6.76 (m,
3H), 6.94 (d, 1H, J ) 9.8 Hz), 8.04 (m, 2H). 13C NMR (CDCl3):
δ 19.9, 25.8, 29.2, 52.4, 55.9, 106.8, 107.2, 109.6, 111.5, 115.5,
119.1, 121.6, 122.7, 125.9, 128.2, 137.8, 140.9, 141.9, 154.2,
159.9. EI MS: m/z 352 (M+). Anal. Calcd for C20H20N2O4: C,
68.17; H, 5.72; N, 7.95. Found: C, 68.20; H, 5.55; N, 7.80.
108 °C. FTIR (KBr): 1721, 1642 cm-1 1H NMR (CDCl3): δ
.
1.89 (m, 2H), 2.40 (m, 2H), 3.11 (t, 2H, J ) 6.5 Hz), 3.61 (t,
2H, J ) 6.2 Hz), 4.14 (t, 2H, J ) 5.6 Hz), 4.25 (t, 2H, J ) 5.7
Hz), 6.51 (s, 1H), 6.58 (d, 1H, J ) 9.2 Hz), 6.77 (d, 1H, J ) 9.2
Hz), 6.90 (m, 2H), 7.00 (s, 1H), 7.32 (d, 1H, J ) 7.6 Hz), 7.74
(m, 2H), 8.25 (d, 1H, J ) 7.6 Hz). 13C NMR (CDCl3): δ 28.7,
29.3, 31.1, 31.6, 63.2, 66.1, 100.9, 105.6, 113.9, 114.8, 117.5,
128.9, 129.5, 129.7, 130.1, 130.2, 130.3, 131.2, 132.7, 133.9,
150.9, 154.3, 158.7, 163.4, 165.0, 184.9. EI MS: m/z 574 (M+).
Anal. Calcd for C26H22O5Br2: C, 54.38; H, 3.86. Found: C,
54.23; H, 3.87.
Dya d 1. To a solution of 8 (0.28 g, 0.49 mmol) in DMF (20
mL) was added 6 (0.33 g, 0.98 mmol) and anhydrous K2CO3
(1.35 g, 9.80 mmol). Then the mixture was stirred at room
temperature for 2 days before 150 mL of H2O was added. The
aqueous solution was extracted with dichloromethane (3 × 70
mL), and the combined extracts were washed with H2O (2 ×
Ack n ow led gm en t. The present research was finan-
cially supported by NSFC (90101025), the Chinese
Academy of Sciences, and the State Key Basic Research
Program (G2000077505). D.-Q.Z. thanks the National
Science Fund for Distinguished Young Scholars.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal methods; conditions for light irradiation experiments;
characterization data for reference compound 9. This material
is available free of charge via the Internet at http://pubs.acs.org.
J O034243W
(15) Hinnen, A.; Audic, C.; Gautron, R. Bull. Soc. Chim. Fr. 1968,
2066.
J . Org. Chem, Vol. 68, No. 14, 2003 5687