Modulation of absorption and fluorescence of photochromic diarylethene by intramolecular hydrogen bond

Article abstract of DOI:10.1002/poc.1885

Photochromic diarylethenes bearing an intramolecular hydrogen bond in bridge moiety have been prepared. It is found that intramolecular hydrogen bonding has a great effect on both absorption and fluorescence of diarylethenes. The color change of diarylethenes in a wide range (purple, blue and green) can be achieved by simple modification of the electronic properties of substituents in bridge moiety, and fluorescent diarylethenes are also obtained when diarylethenes bear an intramolecular hydrogen bond in bridge moiety.

Full text of DOI:10.1002/poc.1885

Research Article
Received: 17 February 2011,
Revised: 4 May 2011,
Accepted: 8 May 2011
Published online in Wiley Online Library: 18 July 2011
(wileyonlinelibrary.com) DOI 10.1002/poc.1885
Modulation of absorption and fluorescence of
photochromic diarylethene by intramolecular
hydrogen bond
Huan‐Huan Liua and Yi Chena*
Photochromic diarylethenes bearing an intramolecular hydrogen bond in bridge moiety have been prepared. It is
found that intramolecular hydrogen bonding has a great effect on both absorption and fluorescence of diary-
lethenes. The color change of diarylethenes in a wide range (purple, blue and green) can be achieved by simple mod-
ification of the electronic properties of substituents in bridge moiety, and fluorescent diarylethenes are also
obtained when diarylethenes bear an intramolecular hydrogen bond in bridge moiety. Copyright © 2011 John Wiley
& Sons, Ltd.
Keywords: color change; diarylethene; fluorescence; intramolecular hydrogen bond; photochromism
by either the extension of π‐conjugation linked to thio-
INTRODUCTION
phene rings[29,30] or the modification of the electron properties
The importance of the hydrogen bond in chemistry and biology
is highlighted in numerous books published, and it plays a prom-
inent role in both biology and chemistry.[1–3] The hydrogen bond
enables an extraordinary range of physiological processes such
as the inhibition of enzymes,[4–6] functionalization of peptides
and activation of proteins,[7–9] and chemical processes such as
catalytic reactions,[10–12] assembly, and supermolecular and tem-
plate chemistry.[13–15]
Switches at the molecular level have attracted considerable
attention during recent years because they afford promising
devices such as machines, sensors and memories. Molecule
switches are, usually, based on a system in which properties
and molecular conformation of the bistable chemical species
are capable of interconversion under the action of various exter-
nal sources. Among various external sources, phototriggered
switches are the most promising for applications because they
are simple to handle and easy to control.
Photochromic diarylethenes have attracted considerable
attention from both fundamental and practical points of
view.[16,17] Although photochromic diarylethenes are being ex-
tensively explored for application as optical switch devices based
on the change of magnetic properties,[18,19] electrochemical
behavior[20,21] and chemical reactivity,[22,23] the major applica-
tions of photochromic diarylethenes are based on the following
two aspects: one is to take advantage of their inherent ability
to produce switches between two isomers with distinct color
change;[24,25] another is to create a fluorescent diarylethene that
shows an on/off fluorescent switch between two isomers by UV–
Vis phototrigger.[26–28]
In general, diarylethenes show very large spectral shifts upon
photocyclization of open isomers (absorption bands at UV re-
gion, colorless) to closed isomers (absorption bands at visible
light region, colored) because of π‐electron delocalization
throughout the two condensed thiophene rings and further ex-
tension of the substituents (Scheme 1). Usually, the modulation
of the absorption bands (color) of closed isomers is achieved
of substituents.[31–33]
It is known that the 1,2‐bis(thien‐3‐yl) fragment has little or
weak emission. A strong fluorescent diarylethene is usually con-
structed by covalently attaching a fluorescent group to a diary-
lethene molecule,[34,35] and in most instances, the open
isomers have strong emission, while the closed isomers have lit-
tle or very weak emission because of the efficient energy transfer
between the excited fluorescent chromophores group and the
closed diarylethene fragment.[36,37] Although many elegant dia-
rylethene systems have been developed by covalently attaching
a fluorescent group to a diarylethene fragment, development of
a fluorescent diarylethene system that has a common structure
that can be modified easily using similar synthesis methods
would be useful.
Recently, photochromic diarylethenes with a different bridge
moiety have been successfully developed for the photomodula-
tion manipulation of various properties of molecular and poly-
mer materials[38–40] and exhibit interesting photochromic
behavior.[26,41,42] Herein, we describe a novel photochromic dia-
rylethene system (1a–3a) containing an intramolecular hydro-
gen bond bridge moiety (Scheme 2). With such a system, both
color change in a wide range and fluorescence emission can
be obtained by simply changing the substituent group of the
bridge moiety. This may be beneficial for providing a simple
and efficient strategy for the design of photochromic diary-
lethenes with fluorescence emission and large color change in
the visible light region.
* Correspondence to: Yi Chen, Key Laboratory of Photochemical Conversion
and Optoelectronic Materials, Technical Institute of Physics and Chemistry,
The Chinese Academy of Sciences, Beijing 100190, China.
E‐mail: yichencas@yahoo.com.cn
a H.‐H. Liu, Y. Chen
Key Laboratory of Photochemical Conversion and Optoelectronic Materials,
Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences,
Beijing 100190, China
J. Phys. Org. Chem. 2012, 25 142–146
Copyright © 2011 John Wiley & Sons, Ltd.

A CLASS OF PHOTOCHROMIC DIARYLETHENES BEARING INTRAMOLECULAR
with CHCl3 (3 ×00A020 ml). The combined organic phase was
washed with water and dried over MgSO4. After evaporation of
the solvent, the crude product was purified by flash column
chromatography (elute: petroleum ether / ethyl acetate = 20:1)
to afford target compounds
UV
Vis
S
S
R
R
R
R
S
S
a
b
1a: 70 %. 1H‐NMR (DMSO‐d6) δ: 13.06 (s, 1H), 12.66 (s, 1H),
8.04 (d, J = 7.7 Hz, 1H), 7.37 (t, J1 = 7.2 Hz, J2 = 7.1 Hz, 1H), 7.27
(s, 1H), 7.06–7.02 (m, 2H), 6.92 (s, 1H), 2.31 (s, 3H), 2.13 (s, 3H).
13 C‐NMR (101 MHz, DMSO) δ: 157.22, 146.54, 137.30, 134.68,
131.76, 130.85, 129.01, 127.72, 127.46, 125.46, 125.19, 124.62,
122.58, 119.58, 117.47, 113.41, 14.54, 14.13. HRMS (m/z): calcd.
for C19H14Cl2N2OS2 : 419.9925, Found: 420.0016.
open isomer (colorless)
closed isomer (colored)
Scheme 1. Illustration of photochromism of diarylethene with UV–Vis
light irradiation
EXPERIMENTAL
2a: 75 %. 1H‐NMR (DMSO‐d6) δ: 12.73 (s, 1H), 12.66 (s, 1H),
9.75 (s, 1H), 7.69 (d, J = 8.1 Hz, 1H), 7.12 (s, 1H), 6.78 (s, 1H), 6.35
(d, J = 9.2 Hz, 1H), 6.32 (s, 1H), 2.48 (s, 3H), 2.01 (s, 3H). 13 C‐NMR
(101 MHz, DMSO) δ: 160.09, 158.94, 147.25, 136.94, 134.37,
132.12, 131.15, 129.38, 129.02, 127.74, 126.57, 125.05, 124.48,
121.59, 107.76, 105.47, 103.55, 14.54, 14.14. HRMS (GC ‐ TOF)
(m/z): calcd. for C19H14Cl2N2O2S2 : 435.9874, Found: 435.9847.
3a: 68 %. 1H‐NMR (DMSO‐d6) δ: 12.66 (s, 1H), 12.57 (s, 1H),
7.78 (d, J = 8.8 Hz, 1H), 7.23 (s, 1H), 6.90 (s, 1H), 6.37 (d, J = 8.9 Hz,
1H), 6.23 (s, 1H), 3.48 (t, 4H), 2.28 (s, 3H), 2.21 (s, 3H), 1.21 (q, 6H).
13 C‐NMR (101 MHz, DMSO) δ: 159.61, 150.54, 148.52, 137.34,
134.85, 132.05, 131.77, 129.73, 128.59, 128.47, 127.15, 125.65,
125.09, 121.77, 104.60, 102.22, 99.29, 44.93, 15.23, 14.84, 13.86.
HRMS (GC ‐ TOF) (m/z): calcd. for C23H23Cl2N3OS2 : 491.0660,
Found: 491.0279.
General methods
1H‐NMR spectrum was recorded at 400 MHz with tetramethylsilane
as an internal reference and DMSO‐d6 as solvent. HRMS spectra
were recorded with matrix‐assisted laser desorption/ionization
mass spectrometry. Absorption spectra and fluorescence spectra
were measured with an absorption spectrophotometer (Hitachi
U‐3010) Hitachi High-Technologies Corporation, Japan and a fluo-
rescence spectrophotometer (F‐2500) Hitachi High‐Technologies
Corporation, Japan., respectively. All chemicals for synthesis were
purchased from commercial suppliers, and solvents were purified
according to standard procedures. Reaction was monitored by thin
layer chromatography silica gel plates (60 F‐254). Column chroma-
tography was performed on silica gel (Merck, 70–230 mesh) Merck
Chemicals Co. Ltd., Shanghai, China. A 360‐nm lamp (36 W) and a
Xenon light (500 W), with different wavelength filters, were used as
light sources for photocoloration and photobleaching, respectively.
1
4a: 62 %. H‐NMR (DMSO‐d6) δ: 12.17 (s, 1H), 8.14 (d, J = 7.7 Hz,
1H), 7.50 (t, J1 = 8.7 Hz, J2 = 8.6 Hz, 1H), 7.46 (d, J = 8.1 Hz, 1H),
7.15 (t, J1 = 7.2 Hz, J2 = 7.1 Hz, 1H), 7.01 (s, 2H), 4.02 (s, 3H),
2.23 (s, 6H). 13 C‐NMR (101 MHz, DMSO) δ: 156.47, 143.84,
134.17, 130.43, 129.19, 128.52, 128.33, 128.22, 124.32, 122.66,
119.15, 112.21, 56.09, 14.37. HRMS (GC ‐ TOF) (m/z): calcd.
for C20H16Cl2N2OS2 : 434.0081, Found: 434.0014.
Synthesis of diarylethenes 1a–6a
Target compounds 1a–6a were prepared according to the
synthetic route presented in Scheme 3. Diketone was obtained
starting from commercially available 2‐methylthiophene, which
was chlorinated at the 5‐position with N‐chlorosuccinimide in
AcOH,[43] followed by acylation with oxalyl chloride in dichloro-
methane. Treatment of diketone with salicylaldehyde in the
presence of NH4Ac afforded target compounds. The details of
the procedure are as follows: to a solution of diketone
(100 mg, 0.31 mmol) in acetic acid (10 ml) was added substi-
tuted benzaldehyde derivatives (0.37 mmol) and NH4Ac
(143 mg, 1.86 mmol), and the mixture was heated at reflux until
the starting material disappeared (thin layer chromatography
detection). The mixture solution was then slowly poured into a
NaHCO3 solution (10%, 50 ml), and the product was extracted
5a: 72 %. 1H‐NMR (DMSO‐d6) δ: 12.42 (s, 1H), 9.69 (s, 1H),
7.81 (d, J = 8.6 Hz, 2H), 7.32 (s, 1H), 7.11 (s, 1H), 6.83 (d,
J = 8.7 Hz, 2H), 2.16 (s, 3H), 2.0 (s, 3H). 13 C‐NMR (101 MHz, DMSO)
δ: 157.89, 146.19, 135.38, 133.68, 133.26, 132.13, 128.41, 127.99,
127.63, 126.74, 124.17, 123.35, 121.99, 121.46, 115.49, 13.93,
13.58. HRMS (GC ‐ TOF) (m/z): calcd. for C19H14Cl2N2OS2
:
419.9925, Found: 420.9842.
1
6a: 60 %. H‐NMR (DMSO‐d6) δ: 12.44 (s, 1H), 7.93 (d, J = 8.8 Hz,
2H), 6.86 (d, J = 8.7 Hz, 2H), 7.18 (s, 1H), 6.88 (s, 1H), 3.06
(s, 6H), 2.27 (s, 3H), 2.10 (s, 3H). 13 C‐NMR (101 MHz, DMSO)
δ: 150.32, 146.58, 133.37, 131.86, 130.11, 128.05, 126.18, 123.65,
118.04, 111.89, 40.33, 13.72. HRMS (GC ‐ TOF) (m/z): calcd. for
C21H19Cl2N2S2 : 447.0397, Found: 447.0477.
R
R
RESULTS AND DISCUSSION
O
H
Intramolecular
hydrogen bond
OH
The ring‐opening and ring‐closing photoisomerization of diary-
lethenes is illustrated in Scheme 1. Upon irradiation with UV light
(254 nm), the ring‐open isomers underwent photocyclization to
ring‐closed isomers. The absorption spectra also changed during
photocyclization. Figure 1 represents the absorption changes of
1a with UV light irradiation. The absorption of 1a, appearing at
HN
N
HN
N
Cl
Cl
Cl
S
S
Cl
S
S
1a R = H
2a R = OH
3a R = NEt2
λ
max = 314 nm, decreased and two main absorptions at 542 nm
and 345 nm, corresponding to 1b, appeared and increased until
the photostationary state was reached. The clear isosbestic point
showed that the photo‐conversion occurred between 1a and 1b,
Scheme 2. Structure of photochromic diarylethenes 1a–3a
J. Phys. Org. Chem. 2012, 25 142–146
Copyright © 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

H.‐H. LIU AND Y. CHIN
R2
R2
R1
R1
O
O
CHO
(COCl)2
N
NH
Cl
S
Cl
NH4Ac
Cl
S
S
Cl
Cl
S
S
1a R1 = OH,
2a R1 = OH,
3a R1 = OH,
R2 = H
R2 = OH
R2 = NEt2
4a R1 = OCH3, R2 = H
5a R1 = H,
6a R1 = H,
R2 = OH
R2 = NMe2
Scheme 3. Synthesis of diarylethenes 1a–6a
and the photocyclization process was accompanied by a color
change of the solution from colorless to purple. Upon irradiation
with visible light, the purple solution was bleached back to color-
less solution. Similar results were obtained when the solution of
diarylethenes 2a and 3a was irradiated with UV light, and their
absorption data are summarized in Table 1.
The fluorescence of 1a in acetonitrile showed that the emis-
sion of 1a was at λem = 445 nm with 315 nm excitation wave-
length, and a moderate fluorescence quantum yield of ϕf = 0.25
(in CH3CN) was obtained by using quinine sulfate (ϕf = 0.58, in
H2SO4) as a reference. The fluorescence of 1a was decreased
when it photo‐converted to 1b, and the fluorescence of 1a
was completely quenched when the solution of 1a was irradi-
ated with 254 nm light to the photo‐stationary state (Fig. 2). No
fluorescence was detected when the solution of 1b was excited
with 545 nm excitation wavelength. The fluorescence quench of
1b is due to the efficient energy transfer between the excited
fluorescent chromophore unit and the ring‐closed diarylethene
unit. A similar result was obtained when the solution of 2a was
excited with λex = 316 nm wavelength excitation.
Table 1. Absorption and fluorescence data of diarylethenes
1a–3a and 3a‐H in CH3CN solvent
Compound
λmax
λmax
λem
ϕf
Color
(nm)
(nm)
(nm)
(Open
isomer)
(Closed (Open (Open (Closed
isomer) isomer) isomer) isomer)
1a/1b
2a/2b
3a/3b
3a‐H+
314
316
338
348
542
560
648
—
445
428
448
408
0.25
0.10
0.002 green
0.10
purple
blue
—
suggestion was confirmed by protonation of 3a in a solution
with the addition of acid (CF3COOH). The twist intramolecular
charge transfer of 3a in the excited state was dismissed when
the strong electron‐donating group (NEt2) was changed to a
strong electron‐acceptor group (HN+Et2) with the addition of
acid, and protonated 3a‐H+ showed fluorescence emission
(Fig. 3). Further investigation found that protonated 3a‐H+
showed no photocyclization reaction with UV light irradiation.
The photocyclization of diarylethene was probably inhibited by
the strong electron‐acceptor group in the bridge moiety unit.
It is noteworthy that no fluorescence was detected when the
solution of 3a was excited with λex = 350 nm wavelength excita-
tion. This is probably because the twist intramolecular charge
transfer of 3a was formed in excited state, which resulted from
a strong electro‐donating group (NEt2) in the bridge unit. The
5000
4000
3000
2000
1000
0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
400
450
500
550
wavelength (nm)
wavelength (nm)
Figure 2. Fluorescence changes of 1a (25 μM, CH3CN, λex = 315 nm)
upon irradiation with 254‐nm light (irradiation time periods: 0, 15, 30, 45 s)
Figure 1. Absorption changes of 1a (25 μM, CH3CN) upon irradiation
with 254‐nm light (irradiation time periods: 0, 15, 30, 45 s)
wileyonlinelibrary.com/journal/poc
Copyright © 2011 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2012, 25 142–146

A CLASS OF PHOTOCHROMIC DIARYLETHENES BEARING INTRAMOLECULAR
3000
fluorescence of diarylethenes. The color change of diarylethenes
in a wide range can be achieved by simple modification of the
electronic properties of substituents in the bridge moiety. Com-
pared with diarylethenes without intramolecular hydrogen
bonding, diarylethenes bearing intramolecular hydrogen bond-
ing in the ethene bridge show strong fluorescence emission. This
may provide a simple and efficient strategy for designing photo-
chromic diarylethenes with fluorescence emission and distin-
guished color change in the visible light region.
2500
2000
1500
1000
500
3a-H+
3a
0
Acknowledgements
350
400
450
500
550
This work was supported by the National Natural Science
Foundation of China (No. 60337020, 21073214) and the Beijing
Natural Science Foundation (No. 4082033).
wavelength (nm)
Figure 3. Fluorescence emission of 3a and 3a‐H+ (λex = 350 nm, in
CH3CN)
REFERENCES
[1] Hydrogen Bond Research (Eds: P. Schuster, W. Mikenda), Springer‐
Verlag: Berlin, Heidelberg, 1999.
[2] Templated Organic Synthesis (Eds: F. Diederich, P. J. Stang), Wiley‐
VCH: Weinheim, 2000.
The fluorescence data of 1a–3a together with 3a‐H+ are summa-
rized in Table 1.
Control experiments were performed by using diarylethenes
4a–6a as analogues (Scheme 3) to compare absorption and
fluorescence of diarylethenes with and without intramolecular
hydrogen bond. It was found that diarylethenes 4a–6a exhibited
photochromic properties with UV–Vis light irradiation, and their
absorption and fluorescence data are listed in Table 2. Comparing
the absorption of 4b with that of 1b, we found that a blue‐shift
of 26 nm was obtained when the OH group was replaced by the
OCH3 group, which suggested that the intramolecular hydrogen
bond promoted the red‐shift of the colored isomer probably
because of strong intramolecular charge transfer resulting
from co‐planarity. This suggestion was confirmed by the com-
parison of absorptions of 5b and 6b with that of 2b and 3b,
both a blue‐shift of 28 nm (5b) and 40 nm (6b), respectively,
were obtained when the OH group was replaced by the H group.
Further investigation found that intramolecular hydrogen bond-
ing is beneficial to the fluorescence emission of diarylethenes. As
presented in Table 2, the fluorescence of diarylethenes was sig-
nificantly decreased when the OH group was replaced by the
OCH3 group or by the H group.
[3] The Weak Hydrogen Bond; Structural Chemistry and Biology (Eds:
G. R. Desiraju, T. Steiner), Oxford University Press: Oxford, 1999.
[4] E. S. Radisky, C.‐J. K. Lu, G. Kwan, D. E. Koshland, Jr. Biochemistry
2005, 44, 6823–6830.
[5] T. Yoshida, M. Murai, M. Abe, N. Ichimaru, T. Harada, T. Nishioka, H.
Miyoshi, Biochemistry 2007, 46, 10365–10372.
[6] B. Zhao, M. R. Waterman, E. M. Isin, M. Sundaramoorthy, L. M.
Podust, Biochemistry 2006, 45, 7493–7500.
[7] K. Kar, S. Ibrar, V. Nanda, T. M. Getz, S. P. Kunapuli, B. Brodsky,
Biochemistry 2009, 48, 7959–7968.
[8] H.‐K. Lee, M. D. Smith, J. Grussendorf, L. Xu, R. J. Gillies, H. Steve
White, G. Bulaj, ACS Chem. Biol. 2009, 4, 659–671.
[9] P. A. Sigala, J. M. M. Caaveiro, D. Ringe, G. A. Petsko, D. Herschlag,
Biochemistry 2009, 48, 6932–6939.
[10] V. B. Gondi, M. Gravel, V. H. Rawal, Org. Lett. 2005, 7, 5657–5660.
[11] T. W. Hudnall, M. Melaimi, F. P. Gabbai, Org. Lett. 2006, 8,
2747–2749.
[12] D. Menche, J. Hassfeld, J. Li, G. Menche, A. Ritter, S. Rudolph, Org.
Lett. 2006, 8, 741–744.
[13] W.‐J. Chu, Y. Yang, C.‐F. Chen, Org. Lett. 2010, 12, 3156–3159.
[14] R.‐S. Shih, C.‐H. Lu, S.‐W. Kuo, F.‐C. Chang, J. Phys. Chem. C 2010, 114,
12855–12862.
[15] X. Zhang, T. Chen, H.‐J. Yan, D. Wang, Q.‐H. Fan, L.‐J. Wan, K. Ghosh,
H.‐B. Yang, P. J. Stang, Nano 2010, 4, 5685–5692.
[16] M. Irie, Chem. Rev. 2000, 100, 1685–1716.
[17] S. Kawata, Y. Kswata, Chem. Rev. 2000, 100, 1777–1788.
[18] K. Mastuda, M. Irie, J. Am. Chem. Soc. 2000, 122, 7195–7201.
[19] N. Tanifuji, M. Irie, K. Matsuda, J. Am. Chem. Soc. 2005, 127,
13344–13353.
[20] T. Kawai, Y. Nakashima, Adv. Mater. 2005, 17, 309–314.
[21] A. C. Whalley, M. L. Steigerwald, X. Guo, C. Nuchkollus, J. Am. Chem.
Soc. 2007, 129, 12590–12591.
CONCLUSIONS
We have developed a kind of photochromic diarylethene with an
intramolecular hydrogen bond in an ethene bridge. It was dem-
onstrated that intramolecular hydrogen bonding in the ethene
bridge has a great influence on both the absorption and
[22] J. J. D. de Jong, L. N. Lucas, R. M. Kellogg, J. H. Van Esch, B. L. Feringa,
Science 2004, 304, 278–281.
[23] D. Sud, T. J. Wigglesworth, N. R. Branda, Angew. Chem. Int. Ed. 2007,
46, 8017–8019.
[24] A. J. Myles, N. R. Branda, Mocromolecules 2003, 36, 298–303.
[25] H. Tian, S. Wang, Chem. Commun. 2007, 46, 781–792.
[26] H. Nakagawa, S. Kawai, T. Nakashima, T. Kawai, Org. Lett. 2009, 11,
1475–1478.
[27] W. Tan, Q. Zhang, J. Zhang, H. Tian, Org. Lett. 2009, 11, 161–164.
[28] Y. Zou, T. Yi, S. Xiao, F. Li, X. Gao, J. Wu, M. Yu, C. Huang, J. Am. Chem.
Soc. 2008, 130, 15750–15751.
[29] A. T. Bens, D. Frewert, K. Kodatis, C. Kryschi, H.‐D. Martin, H. P.
Trommosdorf, Eur. J. Org. Chem. 1998, 2333–2338.
[30] G. M. Tsivgoulis, J.‐M. Lehn, Angew. Chem. Int. Ed Engl. 1995, 34,
1119–1122.
Table 2. Absorption and fluorescence data of diarylethenes
4a/4b–6a/6b in CH3CN solvent
Compound
λmax
λmax
λem
ϕf
Color
(nm)
(nm)
(nm)
(Open
isomer)
(Closed (Open (Open (Closed
isomer) isomer) isomer) isomer)
4a/4b
5a/5b
6a/6b
310
294
320
516
532
608
384
408
393
0.009 red
0.006 purple
0.001 blue
[31] M. Irie, M. Mohri, J. Org. Chem. 1988, 53, 803–808.
[32] Y. Nakayama, K. Hayashi, M. Irie, J. Org. Chem. 1990, 55, 2592–2596.
[33] S. Pu, G. Liu, L. Shen, J. Xu, Org. Lett. 2007, 9, 2139–2142.
J. Phys. Org. Chem. 2012, 25 142–146
Copyright © 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

H.‐H. LIU AND Y. CHIN
[34] H. Cho, E. Kim, Macromolecules 2002, 35, 8684–8687.
[35] T. Fukaminato, T. Sasaki, T. Kawai, N. Tamai, M. Irie, J. Am. Chem. Soc.
2004, 126, 14843–14849.
[39] T. Nakagawa, Y. Hasegawa, T. Kawai, J. Phys. Chem. A 2008, 112,
5096–5103.
[40] V. W.‐W. Yam, C.‐C. Ko, N. Zhu, J. Am. Chem. Soc. 2004, 126,
[36] T. Fukaminato, T. Doi, M. Tanaka, M. Irie, J. Phys. Chem. C 2009, 113,
12734–12735.
11623–11627.
[41] P. H.‐M. Lee, C.‐C. Ko, N. Zhu, V. W.‐W. Yam, J. Am. Chem. Soc. 2007,
129, 6058–6059.
[42] J. Shie, S. Yang, C.‐T. Chen, J.‐M. Fang, Org. Lett. 2002, 4, 1099–1102.
[37] T. Kawai, T. Sasaki, M. Irie, Chem. Commun. 2001, 48, 711–712.
[38] X. Meng, W. Zhu, Y. Feng, W. Tan, H. Tian, J. Phys. Chem. B 2008, 112,
15636–15645.
[43] Y. Chen, D. X. Zeng, M. Fan, Org. Lett. 2003, 5, 1435–1437.
wileyonlinelibrary.com/journal/poc
Copyright © 2011 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2012, 25 142–146