Intramolecular electron transfer within the substituted tetrathiafulvalene-quinone dyads: Facilitated by metal ion and photomodulation in the presence of spiropyran

Article abstract of DOI:10.1021/ja0702824

Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)-quinone dyads 1 and 2 in the presence of metal ions. On the basis of the electrochemical studies of reference compound 5 and the comparative studies with dyad 3, it was proposed that the synergic coordination of the radical anion of quinone and the oligoethylene glycol chain with metal ions may be responsible for stabilizing the charge-separation state and thus facilitating the electron-transfer process. Most interestingly, the intramolecular electron-transfer processes within these two dyads can be modulated by UV-vis light irradiation in the presence of spiropyran, by taking advantage of its unique properties.

Full text of DOI:10.1021/ja0702824

Published on Web 05/08/2007
Intramolecular Electron Transfer within the Substituted
Tetrathiafulvalene-Quinone Dyads: Facilitated by Metal Ion
and Photomodulation in the Presence of Spiropyran
Hui Wu,†,‡ Deqing Zhang,*,† Lei Su,† Kei Ohkubo,§ Chunxi Zhang,† Shiwei Yin,†
Lanqun Mao,† Zhigang Shuai,† Shunichi Fukuzumi,§ and Daoben Zhu*,†
Contribution from the Beijing National Laboratory for Molecular Sciences, Organic Solids
Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, China,
Graduate School of Chinese Academy of Sciences, Beijing 100080, China, and Department of
Material and Life Science, DiVision of AdVanced Science and Biotechnology, Graduate School of
Engineering, Osaka UniVersity, SORST, Japan Science and Technology Agency (JST),
Suita, Osaka 565-0871, Japan
Received January 14, 2007; E-mail: dqzhang@iccas.ac.cn
Abstract: Intramolecular electron transfer is observed for two new substituted tetrathiafulvalene (TTF)-
quinone dyads 1 and 2 in the presence of metal ions. On the basis of the electrochemical studies of reference
compound 5 and the comparative studies with dyad 3, it was proposed that the synergic coordination of
the radical anion of quinone and the oligoethylene glycol chain with metal ions may be responsible for
stabilizing the charge-separation state and thus facilitating the electron-transfer process. Most interestingly,
the intramolecular electron-transfer processes within these two dyads can be modulated by UV-vis light
irradiation in the presence of spiropyran, by taking advantage of its unique properties.
diimide,8 naphthalene diimide,9 and porphyrin/phthalocyanine,10
etc. We have recently described redox molecular fluorescence
switches and chemical sensors based on TTF-anthracene
dyads.11
In comparison to the intramolecular photoinduced electron
transfer, the intramolecular electron transfer has seldom been
observed for D-A molecules containing TTF units. Perepichka
et al. and later Tsiperman et al. have very recently described
1. Introduction
Tetrathiafulvalene (TTF) and its derivatives as strong electron
donors have been extensively investigated as the components
of organic conductors and superconductors for the past 3
decades.1 In recent years, electron donor (D)-acceptor (A)
molecules with TTF as the electron-donating unit have received
significant attention.2-11 This is mainly because (1) these D-A
molecules show potential photovoltaic applications by taking
advantage of efficient photoinduced electron-transfer (PET)
processes between TTF and electron-accepting units (e.g., C60);
(2) these D-A molecules can be employed as models to study
charge-transfer (CT) interactions. The electron-accepting units
which have been covalently linked to TTF units include
quinone,4 C60,5 TCNQ (tetracyano-p-quinodimethane),6,7 perylene
(4) (a) Frenzel, S.; Mu¨llen, K. Synth. Met. 1996, 80, 175-182. (b) Segura, J.
L.; Mart´ın, N.; Seoane, C.; Hanack, M. Tetrahedron Lett. 1996, 37, 2503-
2506. (c) Scheib, S.; Cava, M. P.; Baldwin, J. W.; Metzger, R. M. J. Org.
Chem. 1998, 63, 1198-1204. (d) Moriarty, R. M.; Tao, A.; Gilardi, R.;
Song, Z.; Tuladhar, S. M. Chem. Commun. 1998, 157-158. (e) Gonza´lez,
M.; Illescas, B.; Mart´ın, N.; Segura, J. L.; Seoane, C.; Hanack, M.
Tetrahedron 1998, 54, 2853-2866. (f) Tsiperman, E.; Regev, T.; Becker,
J. Y.; Bernstein, J.; Ellern, A.; Khodorkovsky, V.; Shames, A.; Shapiro,
L. Chem. Commun. 1999, 1125-1126. (g) Gautier, N.; Dumur, F.; Lloveras,
V.; Vidal-Gancedo, J.; Veciana, J.; Rovira, C.; Hudhomme, P. Angew.
Chem., Int. Ed. 2003, 42, 2765-2768. (h) Dumur, F.; Gautier, N.; Gallego-
Planas, N.; Sahin, Y.; Levillain, E.; Mercier, N.; Hudhomme, P.; Masino,
M.; Girlando, A.; Lloveras, V.; Vidal-Gancedo, J.; Veciana, J.; Rovira, C.
J. Org. Chem. 2004, 69, 2164-2177.
(5) (a) Prato, M.; Maggini, M.; Giacometti, C.; Scorrano, G.; Sandona, G.;
Farnia, G. Tetrahedron 1996, 52, 5221-5234. (b) Mart´ın, N.; Sa´nchez,
L.; Seoane, C.; Andreu, R.; Gar´ın, J.; Orduna, J. Tetrahedron Lett. 1996,
37, 5979-5982. (c) Llacay, J.; Veciana, J.; Vidal-Gancedo, J.; Bourdelande,
J. L.; Gonza´lez-Moreno, R.; Rovira, C. J. Org. Chem. 1998, 63, 5201-
5210. (d) Mart´ın, N.; Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem. ReV. 1998,
98, 2527-2547. (e) Simonsen, K. B.; Konovalov, V. V.; Konovalova, T.
A.; Kawai, T.; Cava, M. P.; Kispert, L. D.; Metzger, R. M.; Becher, J. J.
Chem. Soc., Perkin Trans. 2 1999, 657-665. (f) Guldi, D. M.; Gonza´lez,
S.; Mart´ın, N. J. Org. Chem. 2000, 65, 1978-1983. (g) Mart´ın, N.; Sa´nchez,
L.; Herranz, M. A.; Guldi, D. M. J. Phys. Chem. A 2000, 104, 4648-
4657. (h) Kreher, D.; Cariou, M.; Liu, S.-G.; Levillain, E.; Veciana, J.;
Rovira, C.; Gorgues, A.; Hudhomme, P. J. Mater. Chem. 2002, 12, 2137-
2159. (i) Diaz, M. C.; Herranz, M. A.; Illescas, B. M.; Mart´ın, N.; Godbert,
N.; Bryce, M. R.; Luo, C.; Swartz, A.; Anderson, G.; Guldi, D. M. J. Org.
Chem. 2003, 68, 7711-7721. (j) Gorgues, A.; Hudhomme, P.; Salle´, M.
Chem. ReV. 2004, 104, 5151-5184. (k) Baffreau, J.; Dumur, F.; Hud-
homme, P. Org. Lett. 2006, 8, 1307-1310.
† Institute of Chemistry, Chinese Academy of Sciences.
‡ Graduate School of Chinese Academy of Sciences.
§ Osaka University.
(1) (a) Williams, J. M.; Ferraro, J. R.; Thorn, R. J.; Carlson, K. D.; Geiser, U.;
Wang, H. H.; Kini, A. M.; Whangbo, M.-H. Organic Superconductors
(Including Fullerenes); Prentice Hall: Englewood Cliffs, NJ, 1992. (b)
Coronado, E.; Day, P. Chem. ReV. 2004, 104, 5419-5448. (c) Shibaeva,
R. P.; Yagubskii, E. B. Chem. ReV. 2004, 104, 5347-5378. (d) Yamada,
J.-i.; Akutsu, H.; Nishikawa, H.; Kikuchi, K. Chem. ReV. 2004, 104, 5057-
5084.
(2) (a) Bryce, M. R. AdV. Mater. 1999, 11, 11-23. (b) Bryce, M. R. J. Mater.
Chem. 2000, 10, 589-598. (c) Segura, J. L.; Mart´ın, N. Angew. Chem.,
Int. Ed. 2001, 40, 1372-1409. (d) Bendikov, M.; Wudl, F.; Perepichka,
D. F. Chem. ReV. 2004, 104, 4891-4945.
(3) (a) Pease, A. R.; Jeppesen, J. O.; Stoddart, J. F.; Luo, Y.; Collier, C. P.;
Heath, J. R. Acc. Chem. Res. 2001, 34, 433-444. (b) Jeppesen, J. O.;
Perkins, J.; Becher, J.; Stoddart, J. F. Angew. Chem., Int. Ed. 2001, 40,
1216-1221. (c) Tseng, H.; Vignon, S.; Stoddart, J. F. Angew. Chem., Int.
Ed. 2003, 42, 1491-1495. (d) Liu, Y.; Flood, A. H.; Stoddart, J. F. J. Am.
Chem. Soc. 2004, 126, 9150-9151. (e) Steuerman, D. W.; Tseng, H.; Peters,
A. J.; Flood, A. H.; Jeppesen, J. O.; Nielsen, K. A.; Stoddart, J. F.; Heath,
J. R. Angew. Chem., Int. Ed. 2004, 43, 6486-6491.
9
10.1021/ja0702824 CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 6839-6846
6839

A R T I C L E S
Wu et al.
Scheme 1. Synthetic Scheme for the Preparation of Dyads 1-3a
a Reagents and conditions: (a) CsOH‚H2O, hexaethyleneglycol-monotoluenesulfonate, THF, ambient temperature; (b) NaH, tetrachloro-1,4-benzoquinone,
THF, ambient temperature; (c) succinic anhydride, K2CO3, DMF, ambient temperature; (d) DCC, DMAP, CH2Cl2, ambient temperature.
the charge/electron transfer within the TTF-TCNQ dyads.7
Only in one substituted TTF-quinone dyad with a short rigid
spacer a weak CT band was observed.4f Herein we report two
new substituted TTF-quinone dyads 1 and 2, each of which
has a long oligoethylene glycol chain as the spacer (Scheme
1). The initial motivation of this research is to study the
intramolecular donor-acceptor interaction effected by the
coordination of the oligoethylene glycol chain with metal ions.12
It is interesting to note that intramolecular electron transfer is
indeed observed for dyads 1 and 2 in the presence of metal ion
(Pb2+, Zn2+, and Sc3+). In order to understand the metal ion-
promoted electron-transfer mechanism, comparative studies with
reference compounds 3-5 were performed. The results indicate
that (1) the reduction potential of reference compound 5 is
positively shifted to a large extent in the presence of metal ion
(Pb2+, Sc3+, Zn2+), and thus the electron transfer between TTF
and quinone units of dyads 1 and 2 would become thermody-
namically feasible; (2) the synergic coordination of the oligo-
ethylene glycol chain and the radical anion of quinone with
metal ion would stabilize the charge-separation state and thus
further facilitate the electron-transfer process.
On the basis of the fact that the intramolecular electron
transfer within dyads 1 and 2 is facilitated by metal ion
coordination, it is anticipated that the competitive binding of
metal ions by additional ligands would affect the electron-
transfer processes. It is known that the open form (merocyanine,
MC) of spiropyran (SP) can coordinate with metal ions (MC‚
M
n+), while SP does not show this property. By taking
advantage of this unique property of SP, we successfully
demonstrate that the intramolecular electron-transfer processes
within these two dyads can be modulated by alternating UV-
vis light irradiation in the presence of SP.
(6) (a) Aviram, A.; Ratner, M. Chem. Phys. Lett. 1974, 29, 277-283. (b)
Perepichka, D. F.; Bryce, M. R.; Batsanov, A. S.; Howard, J. A. K.; Cuello,
A. O.; Gray, M.; Rotello, V. M. J. Org. Chem. 2001, 66, 4517-4524 and
references therein.
2. Results and Discussion
(7) (a) Perepichka, D. F.; Bryce, M. R.; Pearson, C.; Petty, M. C.; McInnes,
E. J. L.; Zhao, J. P. Angew. Chem., Int. Ed. 2003, 42, 4636-4639. (b)
Tsiperman, E.; Becker, J. Y.; Khodorkovsky, V.; Shames, A.; Shapiro, L.
Angew. Chem., Int. Ed. 2005, 44, 4015-4018.
2.1. Synthesis. The synthetic approaches to dyads 1 and 2
as well as dyad 3 are shown in Scheme 1. Compound 6 was
prepared based on the procedure reported by us previously.13
Reaction of compound 6 with hexaethyleneglycol monotolu-
enesulfonate14 led to compound 4. Further reaction of compound
4 with tetrachloro-1,4-benzoquinone in the presence of NaH
(8) (a) Guo, X.; Zhang, D.; Zhang, H.; Fan, Q.; Xu, W.; Ai, X.; Fan, L.; Zhu,
D. Tetrahedron 2003, 59, 4843-4850. (b) Leroy-Lhez, S.; Baffreau, J.;
Perrin, L.; Levillain, E.; Allain, M.; Blesa, M.-J.; Hudhomme, P. J. Org.
Chem. 2005, 70, 6313-6320.
(9) Guo, X.; Gan, Z.; Luo, H.; Araki, Y.; Zhang, D.; Zhu, D.; Ito, O. J. Phys.
Chem. A 2003, 107, 9747-9753.
(10) (a) Blower, M. A.; Bryce, M. R.; Devonport, W. AdV. Mater. 1996, 8,
63-65. (b) Wang, C.; Bryce, M. R.; Batsanov, A. S.; Stanley, C. F.; Beeby,
A.; Howard, J. A. K. J. Chem. Soc., Perkin Trans. 2 1997, 1671-1678.
(c) Becher, J.; Brimert, T.; Jeppesen, J. O.; Pedersen, J. Z.; Zubarev, R.;
Bjørnholm, T.; Reitzel, N.; Jensen, T. R.; Kjaer, K.; Levillain, E. Angew.
Chem., Int. Ed. 2001, 40, 2497-2500. (d) Farren, C.; Christensen, C. A.;
FitzGerald, S.; Bryce, M. R.; Beeby, A. J. Org. Chem. 2002, 67, 9130-
9139. (e) Li, H.; Jeppesen, J. O.; Levillain, E.; Becher, J. Chem. Commun.
2003, 846-847. (f) Loosli, C.; Jia, C.; Liu, S.-X.; Haas, M.; Dias, M.;
Levillain, E.; Neels, A.; Labat, G.; Hauser, A.; Decurtins, S. J. Org. Chem.
2005, 70, 4988-4992.
(12) (a) Baran, P. S.; Monaco, R. R.; Khan, A. U.; Schuster, D. I.; Wilson, S.
R. J. Am. Chem. Soc. 1997, 119, 8363-8364. (b) Brondstet Nielsen, M.;
Lomholt, C.; Becher, J. Chem. Soc. ReV. 2000, 29, 153-164. (c) Le Derf,
F.; Mazari, M.; Mercier, N.; Levillain, E.; Trippe´, G.; Riou, A.; Richomme,
P.; Becher, J.; Gar´ın, J.; Orduna, J.; Gallego-Planas, N.; Gorgues, A.; Salle´,
M. Chem. Eur. J. 2001, 7, 447-455. (d) Le Derf, F.; Levillain, E.; Trippe´,
G.; Gorgues, A.; Salle´, M.; Sebastian, R. M.; Caminade, A. M.; Majoral,
J. P. Angew. Chem., Int. Ed. 2001, 40, 224-227. (e) Trippe´, G.; Levillain,
E.; Le Derf, F.; Gorgues, A.; Salle´, M.; Jeppesen, J. O.; Nielsen, K.; Becher,
J. Org. Lett. 2002, 4, 2461-2464. (f) Lyskawa, J.; Le Derf, F.; Levillain,
E.; Mazari, M.; Salle´, M.; Dubois, L.; Viel, P.; Bureau, C.; Palacin, S. J.
Am. Chem. Soc. 2004, 126, 12194-12195. (g) Delogu, G.; Fabbri, D.;
Dettori, M. A.; Salle´, M.; Le Derf, F.; Blesa, M.-J.; Allain, M. J. Org.
Chem. 2006, 71, 9096-9103.
(11) (a) Zhang, G.; Zhang, D.; Guo, X.; Zhu, D. Org. Lett. 2004, 6, 1209-
1212. (b) Li, X.; Zhang, G.; Ma, H.; Zhang, D.; Li, J.; Zhu, D. J. Am.
Chem. Soc. 2004, 126, 11543-11548. (c) Zhang, G.; Li, X.; Ma, H.; Zhang,
D.; Li, J.; Zhu, D. Chem. Commun. 2004, 2072-2073. (d) Feng, M.; Guo,
X. F.; Lin, X.; He, X. B.; Ji, W.; Du, S. X.; Zhang, D. Q.; Zhu, D. B.;
Gao, H. J. J. Am. Chem. Soc. 2005, 127, 15338-15339. (e) Lu, H.; Xu,
W.; Zhang, D.; Chen, C.; Zhu, D. Org. Lett. 2005, 7, 4629-4632. (f) Zhang,
G.; Zhang, D.; Zhao, X.; Ai, X.; Zhang, J.; Zhu, D. Chem. Eur. J. 2006,
12, 1067-1073. (g) Zhang, G.; Zhang, D.; Zhou, Y.; Zhu, D. J. Org. Chem.
2006, 71, 3970-3972.
(13) (a) Jia, C.; Zhang, D.; Guo, X.; Wan, S.; Xu, W.; Zhu, D. Synthesis 2002,
15, 2177-2182. (b) Zou, L.; Shao, X.; Zhang, D.; Wang, Q.; Zhu, D. Org.
Biomol. Chem. 2003, 1, 2157-2159.
(14) McCairn, M. C.; Tonge, S. R.; Sutherland, A. J. J. Org. Chem. 2002, 67,
4847-4855.
9
6840 J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007

Tetrathiafulvalene−Quinone Dyads
A R T I C L E S
Figure 2. ESR spectrum of dyad 1 (1.0 × 10-4 M) in CH2Cl2/CH3CN
(1:1, v/v) in the presence of 1.0 equiv of Pb2+ [Pb(ClO4)2] recorded at room
temperature; the solution was degassed before measurement.
the splitting of one H atom of the TTF unit (g ) 2.0086, aH )
1.16 G). This assumption was supported by the fact that direct
oxidation of reference compound 4 by PhI(OAc)2 and CF3-
SO3H17a led to similar doublet ESR signals with g ) 2.0086
and aH ) 1.18 G (see Figure S2 of the Supporting Information).
The radical anion was not seen here probably because of the
facile disproportionation of the radical anion of quinone (Q•-)
into the corresponding Q2- and neutral Q in the presence of
metal ion at room temperature.16,17b The possibility of direct
oxidation of the TTF unit by Pb2+ can be ruled out because a
control experiment with reference compound 4 showed that
oxidation of 4 by Pb2+ did not take place under the same
conditions. These results indicated that in the presence of Pb2+
intramolecular electron transfer occurred between the TTF and
quinone units within dyad 1,18 in which the end-end distance
between donor and acceptor units was estimated to be 36 Å
(see Figure S14 of the Supporting Information).
Figure 1. Absorption spectra (with an ꢀ scale) of dyad 1 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Pb2+ [Pb(ClO4)2]; inset shows the variation of ꢀ at
845 nm upon addition of 0-1.4 equiv of Pb2+
.
afforded dyad 1 in 44% yield after purification (Scheme 1).
Compound 4 was allowed to react with succinic anhydride to
yield compound 7, which was then coupled with compound 5
in the presence of DCC/DMAP to yield dyad 2 in 30% yield.
Dyad 3 was obtained by the reaction of compound 813 and
tetrachloro-1,4-benzoquinone.
2.2. Absorption and ESR Spectral Studies. Figure 1 shows
the absorption spectrum of dyad 1 and those in the presence of
different amounts of Pb2+. The absorption spectrum of dyad 1
without addition of Pb2+ is almost the superposition of those
of the reference compounds 4 and 5. This result clearly indicates
that there is no detectable interaction between the TTF and
Among the metal ions tested, Sc3+ and Zn2+ can also facilitate
the intramolecular electron transfer between the TTF and
quinone units of dyad 1. As shown in Figures 3 and 4, absorption
bands at 450 and 845 nm due to the TTF radical cation of dyad
quinone units of dyad 1 in the absence of Pb2+
.
After addition of Pb2+ to the solution of dyad 1, new
absorption bands around 450 and 845 nm emerged, and their
absorption intensities increased by increasing the amount of Pb2+
(Figure 1). According to previous studies,15 the absorption bands
around 450 and 845 nm can be assigned to the radical cation
of the TTF unit of dyad 1. This assumption can also be
supported by the spectroelectrochemical studies as discussed
below. The same absorption bands at 450 and 845 nm were
detected if the solution of dyad 1 was subjected to electrochemi-
cal oxidation at 0.80 V (vs Ag/AgCl), higher than the first
oxidation potential of the TTF unit of dyad 1. The inset of Figure
1 shows the variation of the absorbance (with an ꢀ scale) at
1 were detected in the presence of Sc3+ and Zn2+ 19
Also,
.
doublet ESR signals were observed (see the insets of Figures 3
and 4).20 These results demonstrated that electron transfer also
occurred for dyad 1 in the presence of Sc3+/Zn2+. When the
absorption and ESR spectra of dyad 1 (the same concentration)
in the presence of equal amounts of Sc3+/Pb2+/Zn2+ are
compared, the absorption intensity at 845 nm and ESR signal
intensity varied in the following order: 1 + Sc3+ > 1 + Pb2+
> 1 + Zn2+ 21 This leads us to conclude that Sc3+ can promote
.
the electron transfer within dyad 1 more efficiently.
(17) (a) Giffard, M.; Mabon, G.; Leclair, E.; Mercier, N.; Allain, M.; Gorgues,
A.; Molinie, P.; Neilands, O.; Krief, P.; Khodorkovsky, V. J. Am. Chem.
Soc. 2001, 123, 3852-3853. (b) Fukuzumi, S.; Nishizawa, N.; Tanaka, T.
J. Chem. Soc., Perkin Trans. 2 1985, 371-378. (c) Fukuzumi, S.; Hironaka,
K.; Nishizawa, N.; Tanaka, T. Bull. Chem. Soc. Jpn. 1983, 56, 2220-
2227.
845 nm vs the molar fraction of Pb2+ 16
.
As shown in Figure 2, the solution of dyad 1 in the presence
of 1.0 equiv of Pb2+ exhibited strong doublet ESR signals. The
doublet ESR signals were likely due to the radical cation of the
TTF unit of dyad 1, and the doublet signals were ascribed to
(18) The use of molecular and/or ion recognition to promote ICT (rather than
intramolecular electron transfer) was reported previously: (a) Witulski, B.;
Weber, M.; Bergstrasser, U.; Desvergne, J.-P.; Bassani, D. M.; Bouas-
Laurent, H. Org. Lett. 2001, 3, 1467-1470. (b) McClenaghan, N. D.; Grote,
Z.; Darriet, K.; Zimine, M.; Williams, R. M.; De Cola, L.; Bassani, D. M.
Org. Lett. 2005, 7, 807-810.
(15) (a) Spanggaard, H.; Prehn, J.; Nielsen, M. B.; Levillain, E.; Allain, M.;
Becher, J. J. Am. Chem. Soc. 2000, 122, 9486-9494. (b) Zhou, Y.; Zhang,
D.; Zhu, L.; Shuai, Z.; Zhu, D. J. Org. Chem. 2006, 71, 2123-2130.
(19) On the basis of the absorbance variation at 845 nm vs the amount of Sc3+
,
(16) On the basis of the absorbance variation at 845 nm vs the amount of Pb2+
,
the reaction stoichiometry between dyad 1 (abbreviated as TTF-Q) and
Sc3+ was estimated to be 2:1 (see ref 16). In the case of Zn2+, the absorbance
at 845 nm was rather weak and moreover it was found that the absorbance
also varied with the reaction time. Thus, it was difficult to estimate the
corresponding stoichiometry.
the reaction stoichiometry between dyad 1 (abbreviated as TTF-Q) and
Pb2+ was estimated to be 2:1. This can be explained as follows: (1) as to
be discussed below, addition of Pb2+ would lead to the intramolecular
electron transfer, and Pb2+ is coordinated to the radical anion of the quinone
unit and the oligoethylene glycol chain (see Scheme 2), namely, TTF-Q
+ Pb2+ f TTF•+-Q•--Pb2+; (2) as reported earlier (see ref 17b), the
disproportionation of Q•- into Q2- and Q in the presence of metal ion may
take place. Thus, 2×TTF•+-Q•--Pb2+ f TTF•+-Q2--Pb2+ + TTF•+-Q
+ Pb2+; (3) the overall reaction can be represented as 2×TTF-Q + Pb2+
f TTF•+-Q2--Pb2+ + TTF•+-Q.
(20) In the case of Sc3+, an additional ESR signal was detected in the diluted
solution, which may be ascribed to the radical anion-Sc3+ complex (see
Figure S1 of the Supporting Information). This may be understandable since
the disproportionation equilibrium among Q•-, Q2-, and Q in the presence
of metal ions is dependent on the Lewis acidity of the metal ion (see ref
24e).
9
J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007 6841

A R T I C L E S
Wu et al.
Figure 5. Absorption spectra (with an ꢀ scale) of dyad 2 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Pb2+ [Pb(ClO4)2]; inset shows the ESR spectrum of
dyad 2 (1.0 × 10-4 M) in CH2Cl2/CH3CN (1:1, v/v) in the presence of
Pb2+ (1.0 × 10-4 M) recorded at room temperature.
Figure 3. Absorption spectra (with an ꢀ scale) of dyad 1 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Sc3+ [Sc(SO3CF3)3]; inset shows the ESR spectrum
of dyad 1 (1.0 × 10-4 M) in CH2Cl2/CH3CN (1:1, v/v) in the presence of
Sc3+ (1.0 × 10-4 M) recorded at room temperature.
Figure 6. Absorption spectra (with an ꢀ scale) of dyad 2 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Sc3+ [Sc(SO3CF3)3]; inset shows the ESR spectrum
of dyad 2 (1.0 × 10-4 M) in CH2Cl2/CH3CN (1:1, v/v) in the presence of
Sc3+ (1.0 × 10-4 M) recorded at room temperature.
Figure 4. Absorption spectra (with an ꢀ scale) of dyad 1 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Zn2+ [Zn(ClO4)2]; inset shows the ESR spectrum of
dyad 1 (1.0 × 10-4 M) in CH2Cl2/CH3CN (1:1, v/v) in the presence of
Zn2+ (1.0 × 10-4 M) recorded at room temperature.
of the Supporting Information).22 These results clearly showed
that intramolecular electron transfer can also occur within dyad
Efficient intramolecular electron transfer was even observed
for dyad 2 (Scheme 1) with an even longer spacer (containing
oligoethylene glycol chain) as indicated by the absorption spectra
of dyad 2 in the presence of metal ions. As shown in Figure 5,
where the absorption spectra of dyad 2 in the presence of Pb2+
is displayed, absorption bands at 450 and 845 nm are observed,
indicating the formation of the radical cation of the TTF unit.22
Their intensities were weaker than those of dyad 1 (see Figure
1) but still 6 times higher than those of dyad 3 (see Figure 7).
Strong ESR signals with two peaks were also detected for dyad
2 in the presence of Pb2+ as shown in the inset of Figure 5.
Similar absorption and ESR spectra were also detected for dyad
2 in the presence of Sc3+ and Zn2+ (see Figure 6 and Figure S4
2 with a much longer spacer in the presence of metal ion (Sc3+
,
Pb2+, Zn2+).
The absorption spectra of dyad 3 in which the TTF and
quinone units are linked by an alkyl chain were recorded in the
presence of metal ions under the same conditions as those for
dyad 1. Figure 7 shows the absorption spectra of dyad 3 in the
presence of different amounts of Pb2+. Although the absorption
bands at 450 and 845 nm were observed, their intensities were
rather weaker than those of dyad 1 in the presence of Pb2+
.
Only rather weak ESR signals were detected for the solution
of dyad 3 containing 1.0 equiv of Pb2+. Such comparative results
implied that the oligoethylene glycol chain in dyad 1 (besides
the radical anion of quinone) may also coordinate with metal
ions (e.g., Pb2+) as to be discussed below.
2.3. Electrochemical Studies. In order to understand the
electron-transfer mechanism within dyads 1 and 2, electro-
chemical studies were carried out. The redox potentials of dyads
1 and 2 were determined: E1/2(ox1) ) 0.55 V, E1/2(ox2) ) 0.87
(21) For dyad 1 in the presence of 1 equiv of Sc3+, the absorbance at 845 nm
was 0.18 (ꢀ ) 3600) and the ESR signal intensity (integration area) was
49 840; for dyad 1 in the presence of 1 equiv of Pb2+, they were 0.14 (ꢀ
) 2800) and 19 780; for dyad 1 in the presence of 1 equiv of Zn2+, they
were 0.03 (ꢀ ) 600) and 9210.
(22) On the basis of the absorbance variation at 845 nm vs the amount of Pb2+
or Sc3+ (see Figures 5 and 6), the reaction stoichiometry between dyad 2
(abbreviated as TTF-Q) and Pb2+ or Sc3+ was estimated to be ca. 2:1
(see ref 16).
9
6842 J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007

Tetrathiafulvalene−Quinone Dyads
A R T I C L E S
Figure 7. Absorption spectra (with an ꢀ scale) of dyad 3 recorded in a
mixture of CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Pb2+ [Pb(ClO4)2].
Figure 9. Cyclic voltammograms of dyad 1 (1.0 × 10-3 M) (a, black)
before and (b, red) after addition of 2.0 equiv of Pb(ClO4)2 in CH2Cl2/
CH3CN (1:1, v/v) at a scan rate of 100 mV s-1
.
metal ion. Moreover, the new irreversible cathodic waves upon
addition of metal ions (Pb2+, Sc3+, Zn2+) were found to be
dependent on the sweep rates (see Figures S8-S10 of the
Supporting Information). This was due to the fact that the
disproportionation of the radical anion of quinone (Q•-) into
the corresponding Q2- and neutral Q in the presence of metal
ion was fast on the time-scale of cyclic voltammetric measure-
ment.17b On the basis of the method reported by Fukuzumi and
co-workers,17b,c the reduction potential (Ered°) of 5 was estimated
to be 0.33, 0.45, and 0.28 V in the presence of Pb2+ (4.0 equiv),
Sc3+ (4.0 equiv), and Zn2+ (4.0 equiv), respectively (Figures
S11-S13 of the Supporting Information). These results clearly
showed that the reduction potential of the reference compound
5 was significantly shifted to the positive region after addition
of metal ions (Pb2+, Sc3+, Zn2+). Under the same conditions,
the variation of the oxidation potentials of reference compound
4 was negligible.
Figure 8. Cyclic voltammograms of compound 5 (2.0 × 10-3 M) before
(a, black) and after addition of 4.0 equiv of Pb(ClO4)2 (b, red), Sc(SO3-
CF3)3 (c, blue), and Zn(ClO4)2 (d, green) in CH2Cl2/CH3CN (1:1, v/v) at a
scan rate of 100 mV s-1
.
The cyclic voltammograms of dyads 1 and 2 were also
measured in the presence of metal ion (Pb2+, Sc3+, Zn2+) (see
Figures S6 and S7 of the Supporting Information). As an
example, Figure 9 shows the cyclic voltammogram of dyad 1
in the presence of Pb2+ together with that of dyad 1 in the
absence of Pb2+. Clearly, the original reduction wave (corre-
sponding to Q/Q•- redox couple) of the quinone unit was absent
after addition of Pb2+, and two redox waves in the range of
0.5-1.0 V were detected. For the first redox wave, the cathodic
peak current was found to be much larger than the corresponding
anodic peak current. As discussed for compound 5, the redox
wave due to the quinone unit of dyad 1 would be shifted to
positive range and became irreversible. Therefore, it is probable
that the redox wave due to the quinone unit became overlapped
with those of the TTF unit upon addition of metal ions. The
second oxidation and reduction peaks should be related to the
redox reaction between the radical cation (TTF•+) and dication
(TTF2+) of the TTF unit.
V, and E1/2(red) ) -0.05 V for dyad 1; E1/2(ox1) ) 0.54 V,
E1/2(ox2) ) 0.86 V, and E1/2(red) ) -0.04 V for dyad 2.23 For
comparison, redox potentials of reference compounds 4 and 5
were also measured: E1/2(ox1) ) 0.54 V, E1/2(ox2) ) 0.86 V
for 4; E1/2(red1) ) -0.05 V (corresponding to Q/Q•- redox
couple); E1/2(red2) ) -0.76 V (corresponding to Q•-/Q2- redox
couple) for 5. These results can lead to the following conclu-
sions: (1) the electron donor-acceptor interaction within dyads
1 and 2 can be neglected in their ground states. This agrees
well with the absorption spectral studies as discussed above;
(2) the electron transfer between the TTF and quinone units of
dyads 1 and 2 is not thermodynamically feasible.
Figure 8 shows the cyclic voltammograms of compound 5
in the presence of metal ions (Pb2+, Sc3+, Zn2+) at a scan rate
of 100 mV s-1. The original redox wave around -0.05 V
(corresponding to the Q/Q•- redox couple) disappeared, and an
irreversible redox wave was detected in the presence of each
On the basis of the reduction potentials of 5 in the presence
of metal ion (Pb2+, Sc3+, Zn2+) and the oxidation potential of
4, it can be concluded that the electron transfer between the
TTF and quinone units of dyads 1 and 2 would become
(23) Additional irreversible redox waves in the range of -0.78 to -0.92 V and
-0.84 to -0.91 V were detected for dyads 1 and 2, respectively (see Figure
S5 of the Supporting Information). All redox potentials were represented
by reference to Ag/AgCl.
9
J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007 6843

A R T I C L E S
Wu et al.
Scheme 2. Proposed Mechanism for the Metal Ion-Promoted Intramolecular Electron Transfer and the Photomodulation in the Presence of
Spiropyran
thermodynamically more feasible in the presence of these metal
ions. But, the electron-transfer processes within dyads 1 and 2
are still endothermic by just considering the redox potentials
oxidophile, preferring the much softer sulfur ligands. This may
also explain the fact that Pb2+ can facilitate the electron-transfer
processes within dyads 1 and 2 more efficiently than Zn2+. In
fact, a similar mechanism was proposed for the metal ion-
promoted intramolecular π-π interactions.27
of the TTF and quinone units in the presence of metal ion (Pb2+
,
Sc3+, Zn2+). As to be discussed below, other forces come into
play by stabilizing the charge-separated transitional state,
therefore making the electron-transfer process exothermic.
According to the previous results reported by Fukuzumi and
co-workers,24,25 the variation of the reduction potentials of 5 in
the presence of Pb2+/Sc3+/Zn2+ is due to the coordination of
the radical anion of quinone (Q•-) with metal ions. Therefore,
we propose that the intramolecular electron transfer within dyad
1 in the presence of metal ions is promoted by the coordination
of the radical anion of the quinone (Q•-) unit with metal ions.26
At least, this proposition is supported by the following finding:
addition of thiourea to the solution of dyad 1 containing Pb2+
leads to the disappearance of the absorption bands at 450 and
845 nm. This is likely due to the stronger binding of thiourea
with Pb2+ than the radical anion of quinone.
2.4. Photomodulation of the Electron Transfer. On the
basis of the synergic coordination model (Scheme 2), it was
anticipated that it was possible to modulate the thermal electron-
transfer processes within dyads 1 and 2 through competitive
binding of metal ions by other ligands. The competitive binding
of metal ions by additional ligands would shift the dispropor-
tionation equilibrium among Q•-, Q2-, and Q (quinone unit) in
the presence of metal ion (see refs 16 and 17b), and thus the
back electron transfer from Q•- to TTF•+ (radical cation of the
TTF unit) would occur accordingly. As described earlier, the
open form (MC) of SP can coordinate with metal ions (MC‚
M
n+), while SP does not show this property; moreover, metal
ion can be released from MC‚Mn+ after visible light irradiation,
and concomitantly MC is transformed into SP.28,29 Therefore,
it would be interesting to study the intramolecular electron-
transfer processes within dyads 1 and 2 in the presence of metal
ions and SP under UV and visible light irradiation.
Moreover, the comparative studies of dyad 3 with dyads 1
and 2 as discussed above indicate that the oligoethylene glycol
chain in dyad 1, besides the radical anion of quinone (Q•-),
may also coordinate with metal ions (e.g., Pb2+). The synergic
coordination of the oligoethylene glycol chain and the radical
anion of quinone with metal ion could further stabilize the
corresponding charge-separation state by enhancing the in-
tramolecular electronic attraction between the radical cation of
TTF and the radical anion of quinone (Q•-)26 as illustrated in
Scheme 2, thus further facilitating the electron-transfer processes
within dyads 1 and 2. It is known that Sc3+ shows a preference
for oxygen coordination. Apart from the oxygen atoms of the
oligoethylene glycol chain, the sulfur atoms of the TTF unit
(see Scheme 2) may be also involved in the coordination with
metal ions, in particular for Pb2+, which is a very poor
Because the reversible transformation among SP, MC, and
MC‚Mn+ can be easily carried out in THF, the mixture of CH2-
Cl2 and THF (v/v, 1:1) was employed for absorption spectral
measurements. As an example, Figure 10 shows the variation
of the absorption spectra of dyad 1 containing Pb2+ (1.0 equiv)
in the presence of SP (6.0 equiv) under UV and visible light
irradiation. After UV light irradiation for 100 s, the absorption
intensity at 845 nm was reduced to 27% of that of the initial
value. But, the absorption band at 845 nm as well as that at
450 nm still existed even after UV light irradiation for 300 s.
(27) (a) Ajayaghosh, A.; Arunkumar, E.; Daub, J. Angew. Chem., Int. Ed. 2002,
41, 1766-1769. (b) Arunkumar, E.; Chithra, P.; Ajayaghosh, A. J. Am.
Chem. Soc. 2004, 126, 6590-6598. (c) Arunkumar, E.; Ajayaghosh, A.;
Daub, J. J. Am. Chem. Soc. 2005, 127, 3156-3164.
(28) (a) Wojtyk, J. T. C.; Kazmaier, P. M.; Buncel, E. Chem. Commun. 1998,
1703-1704. (b) Winkler, J. D.; Bowen, C. M.; Michelet, V. J. Am. Chem.
Soc. 1998, 120, 3237-3242. (c) Wojtyk, J. T. C.; Wasey, A.; Kazmaier,
P. M.; Hoz, S.; Buncel, E. J. Phys. Chem. A 2000, 104, 9046-9055. (d)
Wojtyk, J. T. C.; Kazmaier, P. M.; Buncel, E. Chem. Mater. 2001, 13,
2547-2551. (e) Suzuki, T.; Kawata, Y.; Kahata, S.; Kato, T. Chem.
Commun. 2003, 2004-2005. (f) Suzuki, T.; Kato, T.; Shinozaki, H. Chem.
Commun. 2004, 2036-2037. (g) Wang, G.; Bohaty, A. K.; Zharov, I.;
White, H. S. J. Am. Chem. Soc. 2006, 128, 13553-13558.
(29) (a) Guo, X.; Zhang, D.; Wang, T.; Zhu, D. Chem. Commun. 2003, 914-
915. (b) Guo, X.; Zhang, D.; Tao, H.; Zhu, D. Org. Lett. 2004, 6, 2491-
2494. (c) Guo, X.; Zhang, D.; Zhu, D. J. Phys. Chem. B 2004, 108, 212-
217. (d) Guo, X.; Zhang, D.; Zhu, D. AdV. Mater. 2004, 16, 125-130. (e)
Wen, G.; Yan, J.; Zhou, Y.; Zhang, D.; Mao, L.; Zhu, D. Chem. Commun.
2006, 3016-3018.
(24) (a) Fukuzumi, S.; Yoshida, Y.; Okamoto, K.; Imahori, H.; Araki, Y.; Ito,
O. J. Am. Chem. Soc. 2002, 124, 6794-6795. (b) Fukuzumi, S.; Okamoto,
K.; Imahori, H. Angew. Chem., Int. Ed. 2002, 41, 620-622. (c) Fukuzumi,
S.; Okamoto, K.; Yoshida, Y.; Imahori, H.; Araki, Y.; Ito, O. J. Am. Chem.
Soc. 2003, 125, 1007-1013. (d) Okamoto, K.; Imahori, H.; Fukuzumi, S.
J. Am. Chem. Soc. 2003, 125, 7014-7021. (e) Fukuzumi, S.; Ohkubo, K.;
Okamoto, T. J. Am. Chem. Soc. 2002, 124, 14147-14155.
(25) (a) Fukuzumi, S.; Mori, H.; Imahori, H.; Suenobu, T.; Araki, Y.; Ito, O.;
Kadish, K. M. J. Am. Chem. Soc. 2001, 123, 12458-12465. (b) Yuasa, J.;
Suenobu, T.; Fukuzumi, S. J. Am. Chem. Soc. 2003, 125, 12090-12091.
(c) Fukuzumi, S. Org. Biomol. Chem. 2003, 1, 609-620. (d) Yuasa, J.;
Suenobu, T.; Fukuzumi, S. Chem. Phys. Chem. 2006, 7, 942-954.
(26) The disproportionation reaction of Q•- into the corresponding Q2- and
neutral Q unit may occur easily in the presence of metal ions at room
temperature (see refs 16 and 17b). This is in agreement with the fact that
no ESR signals due to the Q•- were detected for the solutions of dyads 1
and 2 after addition of metal ions at room temperature.
9
6844 J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007

Tetrathiafulvalene−Quinone Dyads
A R T I C L E S
5 and the comparative studies with dyad 3, it was proposed
that the synergic coordination of the radical anion of quinone26
and the oligoethylene glycol chain with metal ions should be
responsible for stabilizing the charge-separation state and thus
facilitating the electron-transfer process. But, the proposed
structure of the coordination complex needs to be investigated
further. Most interestingly, it was demonstrated that it was
possible to modulate the intramolecular electron-transfer process
within dyad 1 by employing the unique features of SP.
4. Experimental Section
Chemicals. The following chemical reagents were purchased from
the indicated suppliers and used without purification: CsOH‚H2O
(Acros), tetra-n-butylammonium hexafluorophosphate (Acros), 2-bro-
moethanol (Acros), hexaethylene glycol (Fluka), tetrachloro-1,4-
benzoquinone (Acros), succinic anhydride (Acros), 4-(dimethylamino)-
pyridin (Merck), N,N′-dicyclohexyl-carbodiimide (Acros), lead perchlorate
(Acros), and scandium triflate (Aldrich). CH2Cl2 and CH3CN were
distilled from CaH2, and THF was distilled from sodium/benzophenone
prior to use. All other chemicals were local products of analytical grade.
Deionized and distilled water was used throughout.
Figure 10. Absorption spectra (with an ꢀ scale) of the mixture of dyad 1
(5.0 × 10-5 M) and SP (3.0 × 10-4 M) (a, black) before and (b, red) after
addition of Pb(ClO4)2 (5.0 × 10-5 M), (c, green) after UV light (365 nm)
irradiation for 100 s, and (d, blue) after further visible light irradiation for
100 s; inset shows the variation of ꢀ at 845 nm.
Characterization Techniques. 1H NMR spectra and 13C NMR were
recorded on a Bruker 400 MHz instrument. Mass spectra (MS) were
recorded with AEI-MS50 and BEFLEX III spectrometer. ESR spectra
were obtained by a Bruker-E500 spectrometer. Absorption spectra were
measured with JASCO V-570 UV-vis spectrophotometer in a 1 cm
quartz cell. Cyclic voltammetric measurements were performed on a
CHI 660B system in a standard three-electrode cell, with Pt as the
working and counter electrodes and Ag/AgCl electrode (saturated KCl)
as the reference electrode which was connected to the electrochemical
cell through a Luggin capillary. The scan rate was 100 mV/s, and n-Bu4-
NPF6 (0.1 M) was used as supporting electrolyte. The light irradiation
experiments were carried out by putting the solutions ca. 10 cm below
the light sources; a 100 W UV lamp (365 nm) and 150 W tungsten
lamp were used as UV and visible light sources, respectively.
Compound 4. To a solution of 6 (0.68 g, 1.8 mmol) in anhydrous
degassed THF was added a solution of CsOH‚H2O (0.36 g, 2.1 mmol)
in anhydrous degassed MeOH over a period of 10 min. The mixture
was stirred for an additional 30 min. A solution of hexaethyleneglycol-
monotoluenesulfonate (1.57 g, 3.6 mmol) in anhydrous degassed THF
was added. The solution was stirred overnight. After separation by
column chromatography (silica gel) using ethylacetate as eluant,
This is likely due to the fact that the binding constant of MC
with Pb2+ is not so large that Pb2+ in the solution could not be
fully coordinated by MC. Interestingly, visible light irradiation
of the above solution that had been treated by UV light
irradiation led to the restoration of the absorption intensity at
845 nm (also that at 450 nm). This is obviously due to the
release of Pb2+ from MC‚Pb2+ after visible light irradiation. In
fact, up to four cycles of such increase-decrease for the
absorption intensity at 845 nm, by applying UV light and visible
light alternatively, can be realized (see the inset of Figure 10)
for the solution of dyad 1 containing Pb2+ in the presence of
SP.
Moreover, the ESR signal intensity of the solution of dyad 1
containing Pb2+ and SP can be tuned by alternating UV and
visible light irradiation; the ESR signal intensity became rather
weak after UV light irradiation, and it can be almost recovered
after further visible light irradiation (see Figure S3 of the
Supporting Information). On the basis of these absorption and
ESR spectral studies, it may be concluded that the intramolecular
electron-transfer process within dyad 1 facilitated by Pb2+ can
be reversibly modulated by UV-vis light irradiation in the
presence of SP.
1
compound 4 (0.88 g) was obtained as a yellow oil in 83% yield. H
NMR (400 MHz, CDCl3): δ 6.44 (1H, s), 3.72 (2H, m), 3.66-3.60
(20H, m), 3.29 (4H, s), 2.93 (2H, t, J ) 6.4 Hz), 2.67 (1H, br). 13C
NMR (100 MHz, CDCl3): δ 126.5, 122.9, 117.9, 113.9, 113.8, 106.6,
72.5, 70.6, 70.52, 70.49, 70.44, 70.3, 69.6, 61.7, 35.2, 30.2. HR-MS
(EI): calcd for C20H30O6S7, 590.0087; found, 590.0084.
Similarly, the Pb2+-promoted electron transfer between the
TTF and quinone units of dyad 2 can also be modulated by
UV and visible light irradiation in the presence of SP. The
complex MC‚Sc3+ was found to be rather stable, and thus Sc3+
could be only partially released from MC‚Sc3+ after visible light
irradiation. Therefore, the Sc3+-promoted electron transfer with
dyads 1 and 2 cannot be reversibly tuned by UV-vis light
irradiation in the presence of SP.30
Compound 5. To a solution of hexaethylene glycol (0.29 g, 1.0
mmol) in dry THF was added petroleum ether rinsed NaH (52%, 46
mg, 1.0 mmol) in N2 atmosphere at 0 °C. The mixture was stirred for
20 min. Tetrachloro-1,4-benzoquinone (0.49 g, 2.0 mmol) was added,
after which the mixture was allowed to attain room temperature. After
being stirred for 1 h the reaction mixture was filtered. The filtrate was
concentrated in vacuo. The residue was purified by column chroma-
tography on silica gel using ethylacetate as eluant; 5 was obtained as
1
3. Conclusion
a yellow oil (0.14 g) in 26% yield. H NMR (400 MHz, CDCl3): δ
4.66 (2H, t, J ) 5.4 Hz), 3.74 (2H, t, J ) 5.5 Hz), 3.69-3.53 (20H,
m), 2.88 (1H, br). 13C NMR (100 MHz, CDCl3): δ 172.4, 171.6, 155.1,
139.9, 138.4, 125.2, 73.2, 72.3, 70.5, 70.4, 70.3, 70.2, 70.0, 61.3. MS
(MALDI-TOF): m/z 512.9 [M + Na]+. HR-MS: calcd for C18H25-
Cl3O9 + H+, 491.0642; found, 491.0648.
In summary, we reported for the first time the intramolecular
electron transfer within a substituted TTF-quinone dyad 1 (and
dyad 2) in the presence of metal ions (Sc3+, Pb2+, Zn2+). On
the basis of the electrochemical studies of reference compound
Compound 7. A solution of 4 (0.59 g, 1.0 mmol), succinic anhydride
(0.2 g, 2.0 mmol), K2CO3 (0.69 g, 5.0 mmol) in dry DMF (25 mL)
was stirred for 24 h at ambient temperature. A volume of 20 mL of
(30) Because the intensities of absorption bands at 845 and 450 nm were weak
for dyads 1 and 2 in the presence of Zn2+ in CH2Cl2/THF (v/v, 1:1), the
corresponding photomodulation experiments were not performed.
9
J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007 6845

A R T I C L E S
Wu et al.
HCl (1 N) was added carefully under vigorous stirring at 0 °C. The
mixture was extracted with CH2Cl2 (3 × 50 mL). The combined organic
phases were washed with water (5 × 50 mL), dried (MgSO4), and
concentrated under reduced pressure to give 7 (0.66 g) as a red oil in
2.92 (2H, t, J ) 7.5 Hz), 2.65 (4H, s). 13C NMR (100 MHz, CDCl3):
172.6, 172.2, 171.8, 155.3, 151.7, 140.2, 138.7, 126.5, 125.5, 122.9,
117.9, 113.9, 113.8, 106.6, 73.4, 70.74, 70.71, 70.6, 70.5, 70.3, 69.6,
69.0, 63.8, 35.2, 30.2, 28.9. HR-MS (MALDI-TOF) calcd for C42H57-
Cl3O17S7 + 2H+, 1164.0857, 1166.0835, 1168.0814; found, 1164.0828,
1166.0805, 1168.0781.
Dyad 3. This was prepared in a similar manner as for dyad 1 from
compound 8 as a gray solid in 48% yield. 1H NMR (400 MHz,
CDCl3): δ 6.41 (1H, s), 4.66 (2H, t, J ) 8.4 Hz), 3.29 (s, 4H), 3.08
(2H, t, J ) 8.4 Hz). 13C NMR (100 MHz, DMSO-d6): δ 173.3, 170.2,
155.0, 139.9, 138.9, 126.0, 123.9, 120.9, 113.8, 113.7, 106.4, 72.3,
35.5, 29.9. HR-MS (EI): calcd for C16H9Cl3O3S7, 577.7662, 579.7633;
found, 577.7651, 579.7639.
1
96% yield. H NMR (400 MHz, CDCl3): δ 9.65-8.10 (1H, br), 6.44
(1H, s), 4.26 (2H, t, J ) 5.9 Hz), 3.66-3.59 (20H, m), 3.28 (4H, s),
2.92 (2H, t, J ) 6.3 Hz), 2.64 (4H, s). 13C NMR (100 MHz, CDCl3):
δ 175.8, 171.9, 126.3, 122.8, 117.7, 113.7, 113.6, 106.4, 70.39, 70.38,
70.30, 70.26, 69.4, 68.8, 63.7, 35.0, 30.0, 28.9, 28.8. MS (MALDI-
TOF): m/z 690.1 [M + H]+.
Dyad 1. To a solution of 4 (0.59 g, 1.0 mmol) in dry THF was
added petroleum ether rinsed NaH (52%, 0.23 g, 5.0 mmol) in N2
atmosphere at room temperature. The mixture was stirred for 20 min,
whereupon tetrachloro-1,4-benzoquinone (0.49 g, 2.0 mmol) was added.
After being stirred overnight the reaction mixture was filtered. The
filtrate was concentrated in vacuo. After column chromatography (CH2-
Cl2/EtOAc, 4:1) on silica gel, 1 was obtained as a yellow oil (0.35 g)
in 44% yield. FT-IR (KBr, cm-1): 1682 (CdO). 1H NMR (400 MHz,
CDCl3): δ 6.44 (1H, s), 4.69 (2H, t, J ) 4.4 Hz), 3.78 (2H, t, J ) 4.4
Hz), 3.66-3.30 (18H, m), 3.29 (4H, s), 2.94 (2H, t, J ) 6.0 Hz). 13C
NMR (100 MHz, CDCl3): δ 172.6, 171.8, 155.3, 140.1, 138.7, 126.5,
125.5, 122.9, 117.9, 113.8, 106.6, 73.5, 70.7, 70.6, 70.5, 70.4, 70.3,
69.6, 35.3, 30.1. HR-MS (EI): calcd for C26H29Cl3O8S7, 797.8973,
799.8944; found, 797.8960, 799.8953.
Dyad 2. A solution of 5 (0.49 g, 1.0 mmol), 7 (0.69 g, 1.0 mmol),
and DMAP (12 mg, 0.1 mmol) in 30 mL of dry CH2Cl2 was stirred at
0 °C for 10 min. A solution of DCC (0.25 g, 1.2 mmol) in 10 mL of
dry CH2Cl2 was added dropwise under N2 atmosphere. After addition
the temperature was allowed to reach room temperature, and the mixture
was stirred overnight. The white urea precipitate was removed by
filtration. Evaporation of the solvent afforded a crude material that was
purified by column chromatography (ethyl acetate/methanol, 50:1); 2
was obtained as a yellow oil (0.35 g, 0.3 mmol) in 30% yield. 1H NMR
(400 MHz, CDCl3): δ 6.43 (1H, s), 4.69 (2H, t, J ) 5.4 Hz), 4.23
(4H, m), 3.67 (2H, t, J ) 5.3 Hz), 3.70-3.56 (38H, m), 3.28 (4H, s),
Acknowledgment. The present research was financially
supported by the NSFC, the Chinese Academy of Sciences, and
the State Key Basic Research Program (2006CB806201).
D.-Q.Z. thanks the National Science Fund for Distinguished
Young Scholars. The authors also thank the anonymous review-
ers for the critical comments which enabled us to improve the
manuscript greatly.
Supporting Information Available: ESR spectrum of the
diluted solution of dyad 1 in the presence of Sc3+, ESR spectrum
of compound 4 (TTF•+) after oxidation, ESR spectra of dyad 1
in the presence of Pb2+ and spiropyran after UV-vis light
irradiation, absorption and ESR spectra of dyads 2 in the
presence of Zn2+, cyclic voltammograms of dyads 1 and 2 and
compounds 4 and 5 and those in the presence of metal ions,
energy-minimized conformation of dyad 1 by theoretical
calculation, absorption spectra of dyads 1-3 with an ꢀ scale
and with an energy scale in wavenumbers. This material is
available free of charge via the Internet at http://pubs.acs.org.
JA0702824
9
6846 J. AM. CHEM. SOC. VOL. 129, NO. 21, 2007