Synthesis, photochromism, and effects of metal ions on fluorescence of dithienylethenes containing imidazo[2,1-a] isoquinoline

Article abstract of DOI:10.1080/00397911.2011.644845

Dithienylethene derivatives containing imidazo[2,1-a]isoquinolines were directly synthesized by treatment of the diketone with 2-ethynylbenzaldehyde in one pot. Their photochromism indicated that they can easily isomerize between the ring-open and ring-closed isomers upon irradiation with ultraviolet or visible light in CH₂Cl₂. At the same time, they display high selectivity toward Fe³⁺ by the fluorescence titration, such that the addition of Fe3+ can obviously suppress their fluorescence intensity. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications1 to view the free supplemental file. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911.2011.644845

This article was downloaded by: [University of Hong Kong Libraries]
On: 11 March 2013, At: 14:49
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis, Photochromism, and
Effects of Metal Ions on Fluorescence
of Dithienylethenes Containing
Imidazo[2,1-a]isoquinoline
Sisi Li a , Ziyong Li a , Shuyuan Huang a , Jun Yin a & Sheng Hua Liu a
a Key Laboratory of Pesticide and Chemical Biology, Ministry of
Education, College of Chemistry, Central China Normal University,
Wuhan, P. R. China
Accepted author version posted online: 14 Mar 2012.Version of
record first published: 06 Mar 2013.
To cite this article: Sisi Li , Ziyong Li , Shuyuan Huang , Jun Yin & Sheng Hua Liu (2013): Synthesis,
Photochromism, and Effects of Metal Ions on Fluorescence of Dithienylethenes Containing
Imidazo[2,1-a]isoquinoline, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 43:11, 1530-1537
To link to this article: http://dx.doi.org/10.1080/00397911.2011.644845
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 43: 1530–1537, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.644845
SYNTHESIS, PHOTOCHROMISM, AND EFFECTS OF
METAL IONS ON FLUORESCENCE OF
DITHIENYLETHENES CONTAINING IMIDAZO[2,1-a]
ISOQUINOLINE
Sisi Li, Ziyong Li, Shuyuan Huang, Jun Yin, and
Sheng Hua Liu
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education,
College of Chemistry, Central China Normal University, Wuhan, P. R. China
GRAPHICAL ABSTRACT
Abstract Dithienylethene derivatives containing imidazo[2,1-a]isoquinolines were directly
synthesized by treatment of the diketone with 2-ethynylbenzaldehyde in one pot. Their photo-
chromism indicated that they can easily isomerize between the ring-open and ring-closed iso-
mers upon irradiation with ultraviolet or visible light in CH2Cl2. At the same time, they
display high selectivity toward Fe3þ by the fluorescence titration, such that the addition of
Fe3þ can obviously suppress their fluorescence intensity.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Dithienylethene; effects of metal ions; imidazo[2,1-a]isoquinoline; photochro-
mism
INTRODUCTION
Photo switches are some of the most attractive subjects in recent years because
of their applications in molecular devices.[1,2] Photochromism is the reversible trans-
formation between two isomers with different absorption spectra caused by alternat-
ing irradiation with ultraviolet (UV) and visible light. For example, azobenzene,
spiropyran, and dithienylethene are common systems in organic photochromism.[3]
Received July 13, 2011.
Address correspondence to Jun Yin or Sheng Hua Liu, Key Laboratory of Pesticide and Chemical
Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079,
P. R. China. E-mail: yinj@mail.ccnu.edu.cn or chshliu@mail.ccnu.edu.cn
1530

DITHIENYLETHENE IMIDAZO[2,1-a]ISOQUINOLINE
1531
Among the various systems of photochromic compounds, dithienylethene derivatives
with heterocyclic aryl rings, especially those bearing two thiophene or benzothio-
phene rings, are considered the most promising candidates for photoelectric applica-
tions because of the excellent thermal stability, remarkable fatigue resistance, and
high sensitivity.[4] Moreover, they have been widely applied in optical memories.[5]
Imidazole is an important building block that was widely used in fields of
medicine,[6] ionic liquids,[7] sensors,[8] and electronic and optical materials.[9] When
imidazole was introduced into dithienylethene, it is expected to obtain dithieny-
lethenes with excellent photochromism. Xiao et al.[10] and Yam et al.[11] have
reported imidazole-substituted dithienylethenes. Recently we reported a series of
imidazole-substituted dithienylethenes and found that the introduction of imidazole
can affect their fluorescence.[12] Moreover, imidazole as a conjugated bridge has sub-
stituted cyclopentene in dithienylethene.[13] As we have mentioned, imidazole can be
used as the building block of chemsensors. However, there are few reports describing
the recognition of imidazole-based dithienylethenes.[14] Herein, we report dithieny-
lethenes containing the imidazo[2,1-a]isoquinoline unit. In particular, we found that
such a heterocycle can be formed in one pot by condensation of diketone with
2-ethynylbenzaldehyde. The photochromism showed that they can easily isomerize
between the ring-open and ring-closed isomers. Furthermore, they display very high
selectivity toward Fe3þ, such that the addition of Fe3þ obviously suppresses their
fluorescence intensity.
RESULTS AND DISCUSSION
Scheme 1 shows the synthesis of dithienylethenes 1–3. 2-Methylthiophene was
used as the starting material, and after chlorination and Friedel–Crafts reaction, dike-
tone was obtained. Diketone was treated with aldehyde in the presence of ammonium
acetate and acetic acid to give dithienylethenes 1–3. According to previous literature,
we found imidazole-substituted phenylacetylene was cyclized in the catalysis of pal-
ladium to get imidazo[2,1-a]isoquinoline cycle in usual.[15] For example, Larock
had reported 2,3-disubstituted indoles by the reaction of iodoanilines with internal
Scheme 1. Synthesis and photoisomerization of dithienylethenes 1–3.

1532
S. LI ET AL.
Table 1. Absorption maxima and quantum yields of dithienylethenes 1o–3o in CH2Cl2 at 2.0 ꢁ 10ꢂ5 mol=L
ko,maxAbs=nma
kc,maxAbs=nmb
(e ꢁ 10ꢂ3=L molꢂ1 cmꢂ1
)
(e ꢁ 10ꢂ4=L molꢂ1 cmꢂ1
)
uo-c
uc-o
ufd
c
c
Compound
1o
2o
3o
264 (2.20)
276 (0.95)
284 (4.00)
622 (3.12)
612 (4.03)
582 (4.30)
0.540
0.192
0.243
0.067
0.020
0.028
0.012
0.018
0.013
aAbsorption maxima of ring-open isomers.
bAbsorption maxima of ring-closed isomer.
cQuantum yields of ring-open (uc-o) and ring-closed isomers (uo-c).
dFluorescence quantum yields of 1–3 before UV irradiation.
acetylenes. Pd-catalyzed conversion of alkyne has also been used in the synthesis of
pyrroles, tryptophans, benzofurans, benzopyrans, furopyridines, benzimidazo[2,1-a]
isoquinolines.[16] Imidazo[5,1-a]isoquinoline via a sequential alkyl–aryl and aryl–
heteroaryl bond formation on the imidazole ring has been reported by Jafarpour
and Ashtiani.[17] In addition, gold(I) can catalyze such cyclization.[18] Fujii et al.
reported a novel copper-catalyzed synthesis of 3-(aminomethyl)isoquinoline polycyc-
lic compounds.[19] However, it is surprising that the dithienylethene imidazo[2,1-a]
isoquinolines were synthesized by diketone and aldehyde in one step, in which we
did not use the expensive catalysis of palladium to get imidazo[2,1-a]isoquinoline
cycle as usual. At the same time, we did not observe the existence of intermediate
4. Therefore, it is expected that such a one-pot method will be widely applied in the
synthesis of functional imidazo[2,1-a]isoquinolines in the future.
The UV=vis absorption spectra of 1o–3o were measured at room temperature in
CH2Cl2. As shown in Table 1, the absorption maxima ꢀwere observed at 270–280 nm
because of similar conjugation, as a result of a p ! p transition.[20] Subsequently,
photochromism of 1o–3o were measured at room temperature in CH2Cl2. For
example, Fig. 1 shows the changes in the absorption spectra of 3o in CH2Cl2, induced
by irradiation with UV and visible light (k > 450 nm). The absorption maximum 3o
Figure 1. (left) Absorption spectral change of 3o; (right) emission intensity changes of compound 3.
(Figure is provided in color online.)

DITHIENYLETHENE IMIDAZO[2,1-a]ISOQUINOLINE
1533
Figure 2. Fluorescence responses of 1o (left) and 3o (right) undergo different metal ions (10 eq.) in
acetonitrile (2.0 ꢁ 10ꢂ5 mol=L) solution. (Inset) The fluorescence response changes by the addition of
Fe3þ from 0 to 10 equiv.
was observed at 284 nm. After irradiation with 365-nm UV light, the colorless CH2Cl2
solution reverted to purple immediately. At the same time, a new absorption band
was observed at 582 nm because of the formation of ring-closed isomer 3c and the
delocalization of p-electrons over both thiophene rings.[21] Subsequently, upon
irradiation with visible light, the decrease of an absorption band was observed at
582 nm along with the increase of the absorption band at 284 nm. Similar results were
observed when the solutions of 1 and 2 in CH2Cl2 were irradiation with UV light or
visible light. These results indicated that dithienylethenes 1–3 can easily isomerize
between the ring-open and ring-closed isomers upon irradiation with UVlight or vis-
ible light in solution. Furthermore, such heterocycle unit can substitute cyclopentene
and imidazole bridge as conjugated bridge in dithienylethene.[10–12] Therefore, decor-
ation on the bridge as a strategy will be used to synthesize dithienylethenes with novel
structures and excellent properties in the future. The relative quantum yields of
cyclization reaction (uo-c) and cycloreversion reaction (uc-o) were determined in
CH2Cl2 by comparing reaction yield with 1,2-bis(2-methyl-5-phenyl-3-thienyl)
perfluorocyclopentene.[16] The data are summarized in Table 1, in which we found
that the cyclization reaction (uo-c) and cycloreversion reaction (uc-o) of 1 were much
greater than 2 and 3, respectively. The results indicated that the introduction of
substituted groups such as phenyl and propyl groups in imidazo[2,1-a]isoquinoline
heterocycle can decrease the cyclization reaction (uo-c) and cycloreversion reaction
(uc-o) in such a system.
Subsequently, we investigated the fluorescence spectral changes in CH2Cl2 upon
irradiation with UV light at room temperature. As shown in Fig. 1, when dithieny-
lethene 3o was excited at 284-nm light, the fluorescence maxima of the ring-open
isomer was observed at 380 nm. However, the fluorescence intensity decreased signifi-
cantly after irradiation with 365-nm light because of the formation of the ring-
closed isomer. Similar results were also observed for 1o and 2o upon irradiation with
UV light. The fluorescence quantum yields were measured as shown in Table 1. Sub-
sequently, we investigated the changes of fluorescence properties of 1–3 in acetonitrile
at room temperature when different metal cations (Kþ, Ca2þ, Cu2þ, Zn2þ, Co2þ
,

1534
S. LI ET AL.
Ni2þ, Cd2þ, Fe3þ, and Hg2þ) were added. As shown in Fig. 2, the fluorescence
intensity of 1 decreased significantly in the presence of the Fe3þ ion, whereas the other
metal cations did not exhibit such a quenching effect under the same conditions,
which indicated that the compound 1 displayed the ‘‘turn-off’’ fluorescence and high
selectively toward Fe3þ. Moreover, the fluorescence quenching of the compounds
upon the addition of Fe3þ may be attributed to a complex formed between 1 and
Fe3þ, and there was a ligand-to-metal charge transfer (LMCT),[22] in which the
electronic charge is transferred from the ligand to the coordinating metal. The Job
plot for the binding between 1 and Fe3þ showed a 1:1 stoichiometry, and the binding
constant (Kb ¼ 4.4 ꢁ 104 Mꢂ1) was estimated from the change in the spectral
intensities (Fig. 2).
Subsequently, to understand the effect of Fe3þ ion on the fluorescence proper-
ties of 1o more clearly, we performed the titration experiment as shown in Fig. 2
(Inset). According to the titration experiment, we found that with the increase of
Fe3þ ion equivalent, the fluorescence intensity decreased significantly. However, the
quenching intensity slowly tended to be saturated when the amount of Fe3þ ion is
more than 7 equivalents. Similar results were obtained when the Fe3þ ion was added
to the solution of 2 and 3 in acetonitrile. Formation of 1:1 complexes formed among
2, 3 and Fe3þ were determined from the emission spectra changes, and their binding
constants were Kb ¼ 5.3 ꢁ 104 and Kb ¼ 3.8 ꢁ 104 Mꢂ1. According to the experiments,
we found that dithienylethenes 1–3 displayed high selectivity to Fe3þ, such that the
addition of Fe3þ can obviously suppress their fluorescence intensity.
In conclusion, a class of dithienylethenes containing imidazo[2,1-a]isoquino-
lines was directly synthesized in one pot by condensation and cyclization, when
the thiophene-substituted diketone and 2-ethynylbenzaldehyde were used as starting
materials. Their photochromism were investigated in CH2Cl2 solution. The results
indicated that they can easily isomerize between the ring-open and ring-closed iso-
mers upon irradiation with UV light or visible light. Furthermore, we investigated
their recognition properties toward metal cations, which indicated that they display
high selectivity to Fe3þ, such that the addition of Fe3þ can obviously suppress their
fluorescence intensity. In our studies, the decoration of the bridge will be probably
used as a strategy to synthesize the multifunctional photochromic dithienylethenes.
EXPERIMENTAL
All manipulations were carried out under an argon atmosphere using standard
Schlenk techniques, unless otherwise stated. Tetrahydrofuran (THF) was distilled
under nitrogen from sodium-benzophenone. 1,2-Bis(5-chloro-2-methylthiophen-3-
yl)ethane-1,2-dione 6 was prepared by literature methods.[15] Different acetylene-
substituted benzaldehydes 9 were prepared by modified procedures of reported
methods.[16] All other starting materials were obtained commercially as analytical-
grade and used without further purification. The relative quantum yields were deter-
mined by comparing reaction yield with the known yield of the compound 1,2-bis(2-
methyl-5-phenyl-3-thienyl)perfluorocyclopentene.[16] Elemental analyses (C, H, N)
1
were performed by the Microanalytical Services, College of Chemistry, CCNU. H
and 13C NMR spectra were collected on American Varian Mercury Plus 400 spec-
1
trometer (400 MHz). H and 13C NMR chemical shifts are relative to TMS. UV-vis

DITHIENYLETHENE IMIDAZO[2,1-a]ISOQUINOLINE
1535
spectra were obtained on U-3310 UV spectrophotometer. Fluorescence spectra were
taken on a Fluoromax-P luminescence spectrometer (Horiba Jobin Yvon Inc.).
General Synthetic Method
Compound 9 (1.0 mmol) and ammonium acetate (0.62 g, 8.0 mmol) were added
to a solution of compound 6 (0.32 g, 1.0 mmol) in acetic acid (15 mL), and the mix-
ture was refluxed until the staring material disappeared [thin-layer chromatographic
(TLC) detection]. The mixture solution was cooled to room temperature and then
slowly poured into NaHCO3 solution (10%, 100 mL), and the product was extracted
with CH2Cl2 (3 ꢁ 50 mL). The combined organic phase was washed with water and
dried with Na2SO4. After evaporation of the solvent, the crude product was purified
by flash column chromatography (petroleum ether=dichloromethane ¼ 1:1) to afford
target compounds 1o–3o in 19–51% yields.
Compound 1o
1
Yield 49%. H NMR (400 MHz, CDCl3): d ¼ 2.00 (s, 3H, CH3), 2.31 (s, 3H,
CH3), 6.82 (s, 1H, thiophene-H), 6.84 (s, 1H, thiophene-H), 6.99 (d, J ¼ 7.6 Hz, 1H,
ethylene-H), 7.51–7.67 (m, 4H, Ar-H), 8.69 (d, J ¼ 7.6 Hz, 1H, Ar-H). 13C NMR
(100 MHz, CDCl3): d ¼ 13.7 (s, CH3), 14.2 (s, CH3), 113.0, 117.2, 120.8, 123.2,
123.5, 124.9, 125.2, 126.7, 126.8, 127.2, 127.3, 128.1, 128.2, 129.3, 130.5, 135.5,
137.7, 138.6, 142.5 (s, Ar, thiophene). MS (m=z): 428.05 [M]þ. Anal. calcd for
C21H14Cl2N2S2: C, 58.74; H, 3.29; N, 6.52. Found: C, 58.62; H, 3.21; N, 6.64.
Compound 2o
1
Yield 51%. H NMR (400 MHz, CDCl3): d ¼ 1.88 (s, 3H, CH3), 2.36 (s, 3H,
CH3), 5.99 (s, 1H, thiophene-H), 6.57 (s, 1H, thiophene-H), 6.97 (s, 1H, ethylene-H),
7.01–7.04 (m, 2H, Ar-H), 7.25–7.37 (m, 3H, Ar-H), 7.60–7.72 (m, 3H, Ar-H), 8.77 (d,
J ¼ 7.6 Hz, Ar-H). 13C NMR (100 MHz, CDCl3): d ¼ 13.8 (s, CH3), 14.4 (s, CH3),
115.6, 118.2, 123.0, 123.5, 125.1, 125.4, 126.5, 127.0, 127.4, 127.8, 128.0, 128.6,
128.9, 129.4, 130.6, 133.7, 136.0, 136.7, 136.9, 139.0, 144.1 (s, Ar, thiophene). MS
(m=z): 504.11 [M]þ. Anal. calcd. for C27H18Cl2N2S2: C, 63.90; H, 3.97; N, 5.52.
Found: C, 63.99; H, 3.91; N, 5.38.
Compound 3o
1
Yield 19%. H NMR (400 MHz, CDCl3): d ¼ 0.75 (t, J1 ¼ 7.2 Hz, J2 ¼ 7.2 Hz
3H, CH3), 1.41–1.49 (m, 2H, CH2), 2.16 (s, 3H, CH3), 2.46 (s, 3H, CH3), 2.50–
2.68 (m, 2H, CH2), 6.64 (s, 1H, thiophene-H), 6.83 (s, 1H, ethylene-H), 6.87 (s,
1H, thiophene-H), 7.53–7.65 (m, 3H, Ar-H), 8.70 (d, J ¼ 7.2 Hz, 1H, Ar-H). 13C
NMR (100 MHz, CDCl3): d ¼ 13.6 (s, CH3), 13.8 (s, CH3), 14.6 (s, CH3), 21.9 (s,
CH2), 34.4 (s, CH2), 112.4, 117.4, 122.6, 123.5, 124.9, 125.8, 126.2, 127.0, 127.3,
127.7, 128.4, 129.2, 129.6, 130.2, 135.3, 136.4, 137.7, 139.2, 144.5 (s, Ar, thiophene).
MS (m=z): 473.89 [M]þ. Anal. calcd. for C24H22Cl2N2S2: C, 60.88; H, 4.68; N, 5.92.
Found: C, 60.68; H, 4.79; N, 5.71.

1536
S. LI ET AL.
Additional details can be found online in the Supporting Information.
ACKNOWLEDGMENTS
The authors acknowledge financial support from the National Natural Science
Foundation of China (Nos. 2072039, 20931006, and 21072070) and the Program for
Changjiang Scholars and Innovative Research Team in University (No. IRT0953).
REFERENCES
1. Balzani, V.; Credi, A.; Venturi, M. Molecular Devices and Machines—A Journey into the
Nano World; Wiley-VCH: Weinheim, 2003.
2. Tian, H.; Qu, D. H.; Wang, Q. C.; Ren, J. Org. Lett. 2004, 6, 2085–2088.
3. (a) Guo, X. F.; Zhang, D. Q.; Zhu, D. B. Adv. Mater. 2004, 16, 125–130; (b) Guo, X. F.;
Zhang, D. Q.; Yu, G. et al. Adv. Mater. 2004, 16, 636–640; (c) Guo, X. F.; Zhang, D. Q.;
Wang, T. G. Chem. Commun. 2003, 914–915; (d) Tian, H.; Yang, S. J. Chem. Soc. Rev.
2004, 33, 85–97; (e) Irie, M. Chem. Rev. 2000, 100, 1685–1716; (f) Matsuda, K.; Irie,
M. J. Photochem. Photobiol. C 2004, 5, 169–182.
4. (a) Irie, M.; Fukaminato, T.; Sasaki, T.; Tamai, N.; Kawai, T. Nature 2002, 420, 759–760;
(b) Matsuda, K.; Irie, M. Chem. Eur. J. 2001, 7, 3466–3473; (c) Morimoto, M.; Kobatake,
S.; Irie, M. J. Am. Chem. Soc. 2003, 125, 11080–11087; (d) Morimitsu, K.; Shibata, K.;
Kobatake, S.; Irie, M. J. Org. Chem. 2002, 67, 4574–4578.
5. (a) Pu, S. Z.; Zhang, F. S.; Xu, J. K.; Shen, L.; Xiao, Q.; Chen, B. Mater. Lett. 2006, 60,
485–489; (b) Pu, S. Z.; Tang, H. H.; Chen, B.; Xu, J. K.; Huang, W. H. Mater. Lett. 2006,
60, 3553–3557; (c) Pu, S. Z.; Yang, T. S.; Yao, B. L.; Wang, Y. L.; Lei, M.; Xu, J. K.
Mater. Lett. 2007, 61, 855–859; (d) Dulic, D.; Kudernac, T.; Puzys, A.; Feringa, B. L.;
Vanwees, B. J. Adv. Mater 2007, 19, 2898–2902; (e) Barachevsky, V. A.; Strokach, Y.
P.; Puankov, A.; Krayushkin, M. M. J. Phys. Org. Chem. 2007, 20, 1007–1020; (f) Iwata,
S.; Ishihara, Y.; Qian, C. P.; Tanaka, K. J. Org. Chem 1992, 57, 3726–3727.
6. Bellina, F.; Cauteruccio, S.; Montib, S.; Rossi, R. Med. Chem. Lett. 2006, 16, 5757–5762.
7. Peter, W.; Wilhelm, K. Angew. Chem. Int. Ed. 2000, 39, 3772–3789.
8. (a) Zhao, Q.; Liu, S. J.; Shi, M.; Li, F. Y.; Jing, H.; Yi, T.; Huang, C. H. Organometallics
2007, 26, 5922–5930; (c) Zapata, F.; Caballero, A.; Tarraga, A.; Molina, P. J. Org. Chem.
2010, 75, 162–169.
9. (a) Bellina, F.; Cauteruccio, S.; Rossi, R. S. Tetrahedron 2007, 63, 4571–4624; (b) Park, S.;
Kwon, O. H.; Kim, S.; Choi, M. G.; Cha, M.; Park, S. Y.; Jang, D. J. J. Am. Chem. Soc.
2005, 127, 10070–10074; (c) Sun, Y. F.; Cui, Y. P.; Dyes Pigm. 2009, 81, 27–34.
10. Xiao, S.; Yi, T.; Zhou, Y.; Zhao, Q.; Li, F.; Huang, C. Tetrahedron 2006, 62,
10072–10078.
11. (a) Lee, P. H.-M.; Ko, C.-C.; Zhu, N.; Yam, V. W-W. J. Am. Chem. Soc. 2007, 129,
6058–6059; (b) Yam, V. W-W.; Lee, J. K.-W.; Ko, C.-C.; Zhu, N. J. Am. Chem. Soc.
2009, 131, 912–913.
12. (a) Li, Z.; Lin, Y.; Xia, J.; Zhang, H.; Fan, F.; Zeng, Q.; Feng, D.; Yin, J.; Liu, S. H. Dyes
Pigm. 2011, 90, 245–252; (b) Yuan, J.; Li, Z.; Hu, M.; Li, S.; Huang, S.; Yin, J.; Liu, S. H.
Photochem. Photobiol. Sci. 2011, 10, 587–591.
13. Liu, H.; Chen, Y. J. Phys. Chem. A 2009, 113, 5550–5553.
14. Hu, H.; Zhu, M.; Zhang, Z.; Wei, K.; Guo, Q. J. Photochem. Photobiol. A 2007, 189,
307–313.
15. LaVoie, J.; Sun, Q. Heterocycles 1996, 43, 737–743.

DITHIENYLETHENE IMIDAZO[2,1-a]ISOQUINOLINE
1537
16. (a) Liao, H. Y.; Cheng, C. H. J. Org. Chem. 1995, 60, 3711–3716; (b) Larock, R. C.; Yum,
E. K. J. Am. Chem. Soc. 1991, 113, 6689–6690; (c) Wensbo, D.; Eriksson, J. T.; Annby, U.;
Gronowitz, S.; Cohen, L. A. Tetrahedron Lett. 1993, 34, 2823–2826; (d) Larock, R. C.;
Yum, E. K.; Doty, M. J.; Sham, K. C. J. Org. Chem. 1995, 60, 3270–3271; (e) Houpis, I.
N.; Choi, W. B.; Reider, P. J.; Molina, A.; Churchill, H.; Lynch, J.; Vplante, R. P. Tetra-
hedron Lett. 1994, 35, 9355–9358.
17. Jafarpour, F.; Ashtiani, P. T. J. Org. Chem. 2009, 74, 1364–1366.
18. Patil, N. T.; Mutyala, A. K.; Lakshmi, P. G. V. V.; Raju, P. V. K.; Sridhar, B. Eur. J. Org.
Chem. 2010, 10, 1999–2007.
19. Fujii, N.; Ohno, H.; Usuke, Y. J. Org. Chem. 2009, 74, 6299–6302.
20. Li, Z. X.; Liao, L. Y.; Sun, W.; Xu, C. H.; Zhang, C.; Fang, C. J. J. Phys. Chem. C. 2008,
112, 5190–5196.
21. Li, X.; Tian, H. Tetrahedron Lett. 2005, 46, 5409–5412.
22. Liu, X.; Chen, C. Eur. J. Org. Chem. 2009, 30, 5261–5265.