Photomodulation of the electrode potential of a photochromic spiropyran-modified Au electrode in the presence of Zn2+: A new molecular switch based on the electronic transduction of the optical signals

Article abstract of DOI:10.1039/b606141a

The electrode potential of a photochromic spiropyran-modified Au electrode could be reversibly modulated by UV/visible light irradiation in the presence of Zn²⁺, and a new molecular switch and an AND logic gate based on this electronic transduction of the optical signals were established. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b606141a

View Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Photomodulation of the electrode potential of a photochromic
spiropyran-modified Au electrode in the presence of Zn2+: a new
molecular switch based on the electronic transduction of the optical
signals{
Guoyong Wen,ab Jie Yan,b Yucheng Zhou,ab Deqing Zhang,*a Lanqun Mao*a and Daoben Zhu*a
Received (in Cambridge, UK) 2nd May 2006, Accepted 25th May 2006
First published as an Advance Article on the web 14th June 2006
DOI: 10.1039/b606141a
as photo-responsive ligands.7 Molecules with spiropyran and
The electrode potential of a photochromic spiropyran-modified
–SH/–S–S– units are able to self-assemble on the Au surface8 to
Au electrode could be reversibly modulated by UV/visible light
irradiation in the presence of Zn2+, and a new molecular switch
generate a self-assembled monolayer-modified Au electrode, which
can be regarded as a membrane electrode as shown in Scheme 1.
and an ‘‘AND’’ logic gate based on this electronic transduction
When this electrode is immersed into an electrolyte solution, a
membrane potential is generated.9 Upon UV light irradiation, the
of the optical signals were established.
spiropyran unit will be transformed into the corresponding MC
form, which can coordinate with metal ions present in the solution.
As a result, the concentration of ions in the membrane will be
altered, leading to variation of the membrane potential of the
modified electrode after UV light irradiation.9 On the other hand,
further visible light irradiation will cause the conversion of the MC
form into the SP form. Concomitantly, the coordinated metal ions
will be released, leading to the restoration of the membrane
potential. Therefore, the electrode potential recorded with this
spiropyran-modified Au electrode can be reversibly modulated by
UV/visible light irradiation of the electrode.
It is well known that signal transduction is one of the important
steps for processing information. More and more results indicate
that signal transduction is involved in some biological functions.1
In fact, a molecular switch can be regarded as the device
performing the signal transduction at the molecular level.
Willner et al. described several unique examples of electronic
transduction of optical signals by taking advantage of photo-
chromic compounds.2 For instance, they immobilized photo-
chromic compounds on surfaces through self-assembly approach
to construct ‘‘photo-command surfaces’’; the electron-transfer
processes taking place on the surfaces were tuned by light
irradiation, and as a result the optical signals were successfully
converted into electronic ones.2b,c Signal transduction with other
types of combinations of input and output signals was also
reported.3
Compound 1 (Scheme 1) with two spiropyran units and one
–S–S– group was synthesized and characterized.10 As expected,
compound 1 shows typical photochromism: a new absorption
spectrum around 556 nm emerged upon UV light irradiation
(365 nm), which gradually disappeared after further visible light
irradiation (Fig. 1). This is clearly due to the reversible
In this communication, we report a new example of the
electronic transduction of optical signals based on an Au electrode
modified with molecules containing photochromic spiropyran
units. The design rationale is schematically demonstrated in
Scheme 1. It is well known that the closed form of spiropyran
(SP) can be transformed into the corresponding open form
(merocyanine form, MC) by UV light irradiation, and the MC
form can be converted back to the original SP form by visible light
irradiation.4 By making use of the reversible transformation
between SP and MC forms, molecular switches and logic gates
were described.5 The unique feature of the photochromic
spiropyran is that the MC form is able to coordinate with metal
ions,6 and that the SP form does not show such a property.
Therefore, molecules with the spiropyran unit can function
aBeijing National Laboratory for Molecular Sciences, Organic Solids
Laboratory, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100080, China. E-mail: dqzhang@iccas.ac.cn;
Fax: +86 1062569564
bGraduate School of the Chinese Academy of Sciences, Beijing, 100080,
China
{ Electronic supplementary information (ESI) available: Synthesis and
characterization details, UV-vis spectra of 1, electrode potential data for 1
as well as the preparation of the modified Au electrode. See DOI: 10.1039/
b606141a
Scheme 1 The chemical structure of compound 1 and illustration of the
reversible structural transformations of SP units into MC units as well as
coordination with metal ions on the surfaces of an Au electrode.
3016 | Chem. Commun., 2006, 3016–3018
This journal is ß The Royal Society of Chemistry 2006

View Online
Fig. 1 The absorption spectra of 1 (1.0 6 1024 M ) in THF–H2O (9 : 1,
v/v) before (a) and after (b) irradiation with ultraviolet light (365 nm) for
3.0 min, together with (c) that upon addition of 50 equiv. of ZnCl2
immediately after irradiation with ultraviolet light (365 nm) and (d) further
irradiation with visible light in the presence of ZnCl2.
Fig. 2 The reversible variation of the electrode potential (vs. Ag/AgCl )
recorded with the spiropyran-modified Au electrode in the presence of
ZnCl2 (1.0 6 1022 M in H2O) under alternating UV/visible light
irradiation.
alternating UV and visible light irradiation in the presence of
Zn2+, but there was no potential variation in the presence of alkali
metal ions, such as K+. This is in agreement with the absorption
spectral changes observed for the solution of 1 in the presence of
different metal ions (see Fig. 1 and Fig. S1{). Thus, it can be
assumed that the electrode potential variation recorded with the
spiropyran-modified Au electrode under light irradiation is due to
the transformation of the SP form into the corresponding MC
form and its sequential coordination with metal ions as
schematically demonstrated in Scheme 1.
transformation of closed forms of the SP units and the
corresponding MC forms. When Zn2+ was present in the solution
of 1, the corresponding absorption band of MC form became
weak and a new absorption appeared at around 486 nm after
exposure to UV light (see Fig. 1), because of the coordination of
Zn2+ with the MC form as reported previously.6 The association
constant of 1 in the MC state with Zn2+ was determined to be K =
633 (see Fig. S2 of ESI{). Similarly, further visible light irradiation
led to the original absorption spectrum of 1 as displayed in Fig. 1,
implying the simultaneous occurrence of the release of Zn2+ from
the MC–Zn2+ complex and the transformation of the MC form
into the SP form. Such absorption spectral variation of 1 in the
presence of Zn2+ can be repeated under light irradiation. But,
addition of alkali metal ions such as K+ could not induce any
absorption spectral change for the solution of 1 under the same
conditions (see Fig. S1 of ESI{).
The spiropyran-modified Au electrode was prepared by soaking
the electrode in a solution of 1 (1.0 6 1024 M in ethanol) for
6 days at room temperature.{ The surface coverage of the SAM of
compound 1 on the Au electrode surface was estimated to be
1.57 6 10210 mol cm22 after self-assembly for 6 days at room
temperature.11 After that, the modified electrode was air-dried and
put into an aqueous solution of ZnCl2 (1.0 6 1022 M). The
electrode potential vs. Ag/AgCl was measured. As anticipated, the
electrode potential increased after UV light (365 nm) irradiation of
the spiropyran-modified electrode, and the maximum enhance-
ment (ca. 35 mV) in the potential was achieved after continuous
UV light irradiation of the modified electrode for 200 s. Further
visible light irradiation led to reduction of the potential, and the
initial potential was restored after visible light irradiation for 300 s
as shown in Fig. 2. Such electrode potential variation recorded
with the spiropyran-modified Au electrode can be reversibly
performed at least for five cycles. The preliminary results also
indicated that the potential enhancement was dependent on the
concentration of Zn2+.
Consequently, the electronic transduction of optical signals was
realized with compound 1, and a new molecular switch was
established with UV/visible light and the electronic potential as the
input and output signals, respectively. Since the electrode potential
variation recorded with the modified Au electrode needs both UV
light irradiation and the presence of Zn2+, this signal transduction
mimics the performance of an ‘‘AND’’ logic gate,12 with UV light
and Zn2+ as the input signals and the electronic potential as the
output signal; visible light can be used to reset the electrode
potential to its initial value.
In summary, by making use of the features of photochromic
spiropyran, compound 1 with two spiropyran units linked by one
–S–S– group was designed and synthesized for studies of the
electronic transduction of optical signals. Assembly of compound
1 on the surface of an Au electrode led to a photochromic
However, the electrode potential of the spiropyran-modified Au
electrode was unchanged after either UV or visible light irradiation
when the electrode was immersed in a solution containing alkali
metal ions, such as K+ (Fig. 3) or in pure water (see Fig. S3 of
ESI{). To summarize, the electrode potential of the spiropyran-
modified Au electrode can be reversibly modulated after
Fig. 3 The electrode potential (vs. Ag/AgCl ) of the spiropyran-modified
Au electrode in an aqueous solution of KCl (1.0 6 1022 M in H2O ) under
UV/visible light irradiation.
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 3016–3018 | 3017

View Online
Acc. Chem. Res., 2001, 34, 433; K. Matsuda and M. Irie, J. Am. Chem.
Soc., 2000, 122, 7195.
4 G. Berkovic, V. Krongauz and V. Weiss, Chem. Rev., 2000, 100, 1741;
V. I. Minkin, Chem. Rev., 2004, 104, 2751.
spiropyran-modified Au electrode. The results show that the
electrode potential of the modified Au electrode can be reversibly
modulated by UV/visible light irradiation in the presence of
Zn2+.13 The variation of the electrode potential was assumed to be
due to the membrane potential change of the modified electrode,
as a result of the reversible transformation of the SP and MC
forms of spiropyran units and the coordination of metal ions by
the MC form upon alternating UV and visible light irradiation.
Accordingly, the electronic transduction of optical signals was
successfully achieved with compound 1, and a new molecular
switch based on this signal transduction was established.
Moreover, such electronic transduction of optical signals also
mimics the performance of an ‘‘AND’’ logic gate.
5 F. M. Raymo, Adv. Mater., 2002, 14, 401; S. Giordani and
F. M. Raymo, Tetrahedron, 2004, 60, 10973; M. Tomasulo,
S. Giordani and F. Raymo, Adv. Funct. Mater., 2005, 15, 787;
K. Nakatani and P. Yu, Adv. Mater., 2001, 13, 1411; X. Guo, D. Zhang,
G. Zhang and D. Zhu, J. Phys. Chem. B, 2004, 108, 11942; X. Guo,
D. Zhang, G. Yu, M. Wan, J. Li, Y. Liu and D. Zhu, Adv. Mater.,
2004, 16, 636; X. Guo, D. Zhang, H. Tao and D. Zhu, Org. Lett., 2004,
6, 2491; W. Yuan, L. Sun, H. Tang, Y. Wen, G. Jiang, W. Huang,
L. Jiang, Y. Song, H. Tian and D. Zhu, Adv. Mater., 2005, 17, 156;
X. Guo, L. Huang, S. O’Brien, P. Kim and C. Nuckolls, J. Am. Chem.
Soc., 2005, 127, 15045.
6 J. T. C. Wojtyk, P. M. Kazmaier and E. Buncel, Chem. Commun., 1998,
1703; J. T. C. Wojtyk, P. M. Kazmaier and E. Buncel, Chem. Mater.,
2001, 13, 2547; J. T. C. Wojtyk, A. Wasey, P. M. Kazmaier, S. Hoz and
E. Buncel, J. Phys. Chem. A, 2000, 104, 9046; T. Suzuki, T. Kato and
H. Shinozaki, Chem. Commun., 2004, 2036; X. Guo, D. Zhang, T. Wang
and D. Zhu, Chem. Commun., 2003, 914.
The present research was financially supported by NSFC,
Chinese Academy of Sciences and State Key Basic Research
Program. D.-Q. Zhang thanks the National Science Fund for
Distinguished Young Scholars.
7 G. E. Collins, L.-S. Choi, K. J. Ewing, V. Michelet, C. M. Bowen and
J. D. Winkler, Chem. Commun., 1999, 321.
8 S. Kado, K. Yamada, T. Murakami and K. Kimura, J. Am. Chem.
Soc., 2005, 127, 3026; B. I. Ipe, S. Mahima and K. G. Thomas, J. Am.
Chem. Soc., 2003, 125, 7174.
9 H. Matsumoto, R. Yamamoto and A. Tanioka, J. Phys. Chem. B, 2005,
109, 14130.
Notes and references
{ Electrode preparation and modification was carried out as follows: Au
electrodes (0.18 cm in diameter) were polished with alumina powder (0.3
and 0.05 mm) and sonicated in acetone and doubly distilled water (each for
5 min). The electrodes were then electrochemically cleaned by consecutively
cycling the potential between 20.2 and +1.8 V (vs. Ag/AgCl) at 0.2 V s21 in
0.5 M H2SO4 solution until a cyclic voltammogram characteristic for a
clean Au electrode was obtained. The self-assembled monolayer (SAM) of
compound 1 on the Au electrode surface was prepared by immersing the
cleaned Au electrode into an ethanol solution containing compound 1
(1.0 6 1024 M) for 6 days. The SAM-modified Au electrode was then
rinsed with ethanol and doubly distilled water and dried in air before
electrochemical measurements.
10 The synthesis details are provided in ESI.{ The characterization data for
compound 1: FT-IR (KBr, cm21): n = 2976, 2926, 2854, 1620, 1402,
1338, 1274; 1H NMR (400 MHz, CDCl3, TMS, ppm): d = 1.18 (s, 6H),
1.25–1.38 (m, 38H), 1.66–1.69 (m, 4H), 1.76–1.79 (m, 4H), 2.67–2.71 (m,
10H), 3.90–3.94 (t, 4H, J = 6.54 Hz), 5.84–5.86 (d, 2H, J = 10.28 Hz),
6.44–6.46 (d, 2H, J = 8.64 Hz), 6.71–6.73 (m, 4H), 6.76–6.78 (d, 2H, J =
8.64 Hz), 6.90–6.92 (d, 2H, J = 10.28 Hz), 8.00–8.03 (m, 4H); 13C NMR
(100 MHz, CDCl3): d = 19.9, 25.8, 26.1, 28.5, 29.0, 29.2, 29.3, 29.4, 29.5,
29.6, 39.6, 52.4, 68.8, 106.9, 107.2, 110.3, 112.1, 115.5, 118.7, 121.7,
122.7, 125.9, 128.2, 137.7, 140.9, 141.8, 153.7, 159.9. HRMS: Anal.
calcd. for C62H82N4O8S2 [MH+]: 1075.5646; found 1075.5623.
11 The surface coverage was measured by following the method described
previously: J. C. Hoogvliet, M. Dijksma, B. Kamp and W. P. V.
Bennekom, Anal. Chem., 2000, 72, 2016; A. Dalmia, C. C. Liu and
R. F. Savinell, J. Electroanal. Chem., 1997, 430, 205.
1 A. C. Guyton and J. E. Hall, Human Physiology and Mechanisms of
Disease, W. B. Saunders Company, Philadelphia, 1997.
2 (a) I. Willner, Acc. Chem. Res., 1997, 30, 347; (b) A. N. Shipway and
I. Willner, Acc. Chem. Res., 2001, 34, 421; (c) I. Willner, A. Doron and
E. Katz, J. Phys. Org. Chem., 1998, 11, 546.
3 See, for example: Y. Liu, A. H. Flood, P. A. Bonvallet, S. A. Vignon,
B. H. Northrop, H.-R. Tseng, J. O. Jeppesen, T. J. Huang, B. Brough,
M. Baller, S. Magonov, S. D. Solares, W. A. Goddard, C.-M. Ho and
J. F. Stoddart, J. Am. Chem. Soc., 2005, 127, 9745; A. R. Pease,
J. O. Jeppesen, J. F. Stoddart, Y. Luo, C. P. Collier and J. R. Heath,
12 A. P. de Silva and N. D. McClenaghan, Chem.–Eur. J., 2004, 10, 574;
D. Steinitz, F. Remacle and R. D. Levine, ChemPhysChem, 2002, 3, 43;
V. Balzani, M. Venturi and A. Credi, ChemPhysChem, 2003, 4, 49.
13 Besides Zn2+, the electrode potential variation was also observed for the
spiropyran-modified electrode when it was immersed into the solution of
CuSO4. Studies with other metal ions will be carried out.
3018 | Chem. Commun., 2006, 3016–3018
This journal is ß The Royal Society of Chemistry 2006