Environment-responsive multicolor fluorescent dyes based on nitrophenyl or nitrophenylethynyl oligothiophene derivatives: Correlation between fluorescence and π-conjugation length

Article abstract of DOI:10.1016/j.tetlet.2013.03.054

We report the unique environment-responsive fluorescence of nitrophenyl or nitrophenylethynyl oligothiophene derivatives with different numbers of thiophene rings. With an increase in the number of thiophene rings, the maximum fluorescence quantum yield (

Full text of DOI:10.1016/j.tetlet.2013.03.054

Tetrahedron Letters xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Environment-responsive multicolor fluorescent dyes based on nitrophenyl
or nitrophenylethynyl oligothiophene derivatives: correlation between
fluorescence and p-conjugation length
Sojiro Hachiya a, Kengo Asai a, Gen-ichi Konishi a,b,
⇑
a Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
b PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the unique environment-responsive fluorescence of nitrophenyl or nitrophenylethynyl oli-
gothiophene derivatives with different numbers of thiophene rings. With an increase in the number of
thiophene rings, the maximum fluorescence quantum yield (UF) was obtained even in low-polarity sol-
vents. For 5,500-bis(4-nitrophenyl)-2,20-bithiophene (BNP2T), a nitro-group-containing fluorescent dye
without a strong donor moiety, the maximum UF of 0.43 was observed in CHCl3, which is a large value,
and multicolor fluorescence with a moderate quantum yield was observed in various solvents. Thus, we
can design functional nitrophenyl-based fluorescent dyes that would find applications as bioimaging
probes, polarity sensors, etc.
Received 2 February 2013
Revised 28 February 2013
Accepted 4 March 2013
Available online xxxx
Keywords:
Solvatochromic fluorescence
Nitro group
Ó 2013 Elsevier Ltd. All rights reserved.
Oligothiophene
Environment-responsive fluorescent dyes have received con-
siderable attention as they find potential applications as fluores-
cence sensors and in vivo imaging probes.1 Fluorescence
solvatochromism is an environment-sensitive phenomenon. Be-
cause of their large transition moment, dyes showing strong fluo-
rescent solvatochromism have both donor and acceptor moieties
fluorescence depended strongly on the solvent polarity, because
of the strong electron-withdrawing nature of the nitro group.
Introduction of a nitro group via a linker moiety such as a phenyl
group is an effective means of inducing fluorescence in nitro-
group-containing compounds. Interestingly, the optimal solvent
in which fluorescence was induced from nitro-group-containing
compounds changed depending on the chromophore. Thus, it is
possible to develop novel environment-responsive dyes based
on the specific fluorescence of the nitro group.
in the same
p
-conjugated system.2,3 While many dyes bearing
various substituents have been reported, there are very few re-
ports on dyes with a nitro group as the acceptor moiety.4 This
is because the nitro group is a very strong electron-withdrawing
(deactivating) group, which can cause a dramatic change in the
Oligothiophene is a suitable core structure that can be used to
develop the abovementioned class of dyes because they show
strong fluorescence with various substituents and exhibit weak do-
photophysical properties when introduced into a p-extended sys-
tem, such as marked fluorescence suppression or redshift of the
absorption spectra.5 Extensive studies have been carried out to
understand the unique effect of the nitro substituent on the
nor capacity.4c,11 Additionally, the
p-conjugation length of oligoth-
iophene can be easily tuned by modifying the number of thiophene
rings, which means that it is possible to change the chromophore
systematically.
photophysical properties of
p-extended compounds, including
electron absorption,6 excited-state dynamics,7 and phosphores-
cence.8 In these compounds, the main mode of relaxation from
an excited state to the ground state is internal conversion (IC),
which immediately follows intersystem crossing (ISC); hence,
other modes of relaxation such as fluorescence are not usually
observed.9 However, in our previous study, we observed strong
and specific solvent-dependent fluorescence when a nitro group
In this study, we synthesized oligothiophenes with different
numbers of thiophene rings and introduced a nitrophenyl moiety
at both ends of the molecules directly (BNPnT) or through an
ethynyl linker moiety (BNPEnT). Then, we investigated the influ-
ence of
p-conjugation length on the fluorescence properties. We
succeed in the development of an environment-responsive multi-
color fluorescence dye with a moderate quantum yield in various
solvents, BNP2T, which showed strong fluorescence in weak polar
solvents.
was introduced into the phenyl moiety of a
p-conjugated system
with a weak donor-strong acceptor system.10 In this case, the
BNPnT was synthesized from the corresponding dibromothio-
phene and p-nitrophenyl boronic acid by Pd-catalyzed Suzuki–
Miyaura cross coupling.12,13 For additional
p-extension, we
⇑
Corresponding author. Tel.: +81 3 5734 2321; fax: +81 3 5734 2888.
E-mail address: konishi.g.aa@m.titech.ac.jp (G. Konishi).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.03.054
Please cite this article in press as: Hachiya, S.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.03.054

2
S. Hachiya et al. / Tetrahedron Letters xxx (2013) xxx–xxx
inserted an ethynyl moiety between the oligothiophene and nitro-
phenyl moieties to obtain BNPEnT by Pd- and Cu-catalyzed Sono-
gashira cross coupling of the corresponding dibromothiophene and
1-ethynyl-4-nitrobenzene.14,15 The number of thiophene rings was
varied (n = 1–3), and the photophysical properties of the resulting
compounds were evaluated (Scheme 1).
Figure 1 shows the UV–vis absorption and fluorescence spectra of
BNPnT and BNPEnT in CH2Cl2, and Table 1 summarizes the photo-
physical data in various solvents. Unfortunately, the photophysical
measurements were not too accurate the photophysical measure-
ments were limited because of the poor solubility of these com-
pounds in polar solvents such as acetonitrile and methanol and in
non-polar solvents such as hexane. Extension of
p-conjugation is
Scheme 1. Synthesis of BNPnT and BNPEnT.
clearly indicated by the redshift of the spectra with an increase in
the number of thiophene rings. While the UV–vis spectra showed
a slight shift upon the introduction of an ethynyl moiety, the fluores-
cence spectra showed a much larger shift. This result indicated that
the excited state of BNPEnT is more polarized as compared to that of
BNPnT, thus facilitating the introduction of an ethynyl moiety,
which resulted in a large Stokes shift. In the case of BNPE1T, the
maximum Stokes shift was about 9620 cmꢀ1 in DMSO.
While the UV–vis absorption of BNPnT and BNPEnT showed only
slight differences in various solvents, the fluorescence spectra varied
greatly depending on the solvent. The spectra of all compounds were
redshifted with increasing solvent polarity, indicating internal
charge transfer (ICT) from the thiophene moiety to the nitrophenyl
moiety, because the nitro group is a strong acceptor and thiophene
is a weak donor. This ICT character was confirmed by Lippert-Mat-
aga equation and ET(30) increasing number of thiophene rings (see
supporting information). The fluorescence quantum yield (UF) also
depended on the solvent polarity. In the case of BNPnT, solvent-
polarity-dependent maximum UF of BNPnT decreased with an in-
crease in the number of thiophene rings. The maximum UF of
BNP1T, BNP2T, and BNP3T was 0.396 in DMSO, 0.434 in CHCl3,
and 0.387 in PhCH3, respectively. This solvent dependence was also
Figure 1. UV–vis absorption and fluorescence spectra of BNPnT and BNPEnT in
CH2Cl2. BNPE3T did not show fluorescence. Excitation wavelength for fluorescence
measurements was the absorption maxima.
Table 1
Photophysical properties of BNPnT and BNPEnT in various solvents
(cmꢀ1
)
UF
sc,d (ns)
kf (108 sꢀ1
)
knr (10 sꢀ1
)
a
a,b
8
Compound
Solvent
kabs (nm)
kem (nm)
D
m
BNP1T
THF
387
386
388
393
396
420
423
424
425
431
436
442
443
444
446
383
390
389
386
388
413
411
412
420
436
436
485
498
501
528
549
497, 523
543
598
605
635
667
528, 559
587
667
684.
493
538
553
578
5220
5830
5810
6510
7040
3690
5220
6860
7000
7450
7940
3690
5540
7530
7940
5830
7050
7620
8610
9620
3640
6350
8500
8350
3630
6520
0.01
0.03
0.06
0.26
0.40
0.22
0.29
0.43
0.40
0.11
0.09
0.39
0.25
0.08
0.04
0.01
0.12
0.16
0.03
0.02
0.34
0.19
0.04
0.01
0.44
0.05
––
––
––
CHCl3
CH2Cl2
DMF
DMSO
PhCH3
THF
CHCl3
CH2Cl2
DMF
DMSO
PhCH3
THF
CHCl3
CH2Cl2
THF
CHCl3
CH2Cl2
DMF
DMSO
PhCH3
THF
CHCl3
CH2Cl2
PhCH3
THF
0.26
0.24
0.98
1.44
0.51
0.85
1.57
1.64
0.61
0.52
0.86
0.86
0.41
0.34
0.28
0.69
0.78
0.29
0.21
0.33
0.62
0.18
0.22
0.33
0.80
1.2
2.4
2.7
2.8
4.2
3.4
2.8
2.5
1.8
1.7
4.5
2.9
1.8
1.1
0.4
1.7
2.1
1.0
0.9
10.2
3.1
2.4
0.4
13.4
0.6
37.3
39.3
7.5
4.2
15.3
8.4
3.6
3.6
14.6
17.6
7.1
BNP2T
BNP3T
8.8
22.6
28.3
35.3
12.8
10.7
33.5
46.8
20.2
13.0
50.3
45.1
16.9
11.9
BNPE1T
619
486, 514
556
634
647
BNPE2T
BNPE3T
518, 547
609
Data corresponding to no-fluorescence cases have been omitted.
a
The solutions were prepared with 0.1 absorption at kabsꢁ kex = kabs
.
b
Measured as absolute quantum yield.
c
Detection fluorescence wavelength is kem
.
d
Excitation wavelength is 355 nm.
Please cite this article in press as: Hachiya, S.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.03.054

S. Hachiya et al. / Tetrahedron Letters xxx (2013) xxx–xxx
3
Supplementary data
Supplementary data (experimental details, 1H NMR and 13C
NMR spectra, UV–visible absorption and fluorescence spectra)
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.tetlet.2013.03.054.
References and notes
1. (a) Marini, A.; Munoz-Losa, A.; Biancardi, A.; Mennucci, B. J. Phys. Chem. B 2010,
114, 17128–17135; (b) Callan, J. F.; de Silva, A. P.; Magri, D. C. Tetrahedron 2005,
61, 8551–8588; (c) Huang, G. J.; Ho, J. H.; Prabhakar, C.; Liu, Y. H.; Peng, S. M.;
Yang, J. S. Org. Lett. 2012, 14, 5034–5037; (d) Hu, R.; Gómez-Durán, C. F. A.; Lam,
J. W. Y.; Belmonte-Vázquez, J. L.; Deng, C.; Chen, S.; Ye, R.; Peña-Cabrera, E.;
Zhong, Y.; Wong, K. S.; Tang, B. Z. Chem. Commun. 2012, 10099–10101; (e)
Kudo, K.; Momotake, A.; Tanaka, J. K.; Miwa, Y.; Arai, T. Photochem. Photobiol.
Sci. 2012, 11, 674–678; (f) Uchiyama, S.; Kimura, K.; Gota, C.; Okabe, K.;
Kawamoto, K.; Inada, N.; Yoshihara, T.; Tobita, S. Chem. Eur. J. 2012, 18, 9552–
9563; (g) Matsumoto, K.; Takahashi, N.; Suzuki, A.; Morii, T.; Saito, Y.; Saito, I.
Bioorg. Med. Chem. Lett. 2011, 21, 1275–1278; (h) Dong, J.; Solntsev, K. M.;
Tolbert, L. M. J. Am. Chem. Soc. 2006, 128, 12038–12039; (i) Okamoto, A.;
Tainaka, K.; Fujiwara, Y. J. Org. Chem. 2006, 71, 3592–3598; (j) Seo, J.; Kim, S.;
Park, S. Y. J. Am. Chem. Soc. 2004, 126, 11154–11155; (k) Cohen, B. E.;
McAnaney, T. B.; Park, E. S.; Jan, Y. N.; Boxer, S. G.; Jan, L. Y. Science 2002, 296,
1700–1703; (l) Strehmel, B.; Sarker, A. M.; Malpert, J. H.; Strehmel, V.; Seifert,
H.; Neckers, D. C. J. Am. Chem. Soc. 1999, 121, 1226–1236; (m) Niko, Y.; Konishi,
G. Tetrahedron Lett. 2011, 52, 4843–4847; (n) Niko, Y.; Konishi, G. J. Org. Chem.
2012, 77, 3986–3996.
2. (a) Steeger, M.; Lambert, C. Chem. Eur. J. 2012, 18, 11937–11948; (b) Riedl, J.;
Pohl, R.; Ernsting, N. P.; Orsag, P.; Fojta, M.; Hocek, M. Chem. Sci. 2012, 3, 2797–
2806; (c) Nourmohammadian, F.; Gholami, M. D. Helv. Chim. Acta 2012, 95,
1548–1555; (d) Dong, Y. M.; Bolduc, A.; McGregor, N.; Skene, W. G. Org. Lett.
2011, 13, 1844–1847; (e) Collado, D.; Casado, J.; Gonzalez, S. R.; Navarrete, J. T.
L.; Suau, R.; Perez-Inestrosa, E.; Pappenfus, T. M.; Raposo, M. M. M. Chem. Eur. J.
2011, 17, 498–507; (f) Abelt, C. J.; Sun, T.; Everett, R. K. Photochem. Photobiol.
Sci. 2011, 10, 618–622; (g) Nandy, R.; Sankararaman, S. Beilstein J. Org. Chem.
2010, 6, 992–1001; (h) Panthi, K.; Adhikari, R. M.; Kinstle, T. H. J. Phys. Chem. A
2010, 114, 4542–4549; (i) Kucherak, O. A.; Didier, P.; Mely, Y.; Klymchenko, A.
S. J. Phys. Chem. Lett. 2010, 1, 616–620; (j) Signore, G.; Nifosi, R.; Albertazzi, L.;
Storti, B.; Bizzarri, R. J. Am. Chem. Soc. 2010, 132, 1276–1288; (k) Loving, G.;
Imperiali, B. J. Am. Chem. Soc. 2008, 130, 13630–13638; (l) Palayangoda, S. S.;
Cai, X. C.; Adhikari, R. M.; Neckers, D. C. Org. Lett. 2008, 10, 281–284; (m) Yuan,
M. S.; Liu, Z. Q.; Fang, Q. J. Org. Chem. 2007, 72, 7915–7922; (n) Tainaka, K.;
Tanaka, K.; Ikeda, S.; Nishiza, K.; Unzai, T.; Fujiwara, Y.; Saito, I.; Okamoto, A. J.
Am. Chem. Soc. 2007, 129, 4776–4784; (o) Jenekhe, S. A.; Lu, L. D.; Alam, M. M.
Macromolecules 2001, 34, 7315–7324.
3. (a) Ooyama, Y.; Kushimoto, K.; Oda, Y.; Tokita, D.; Yamaguchi, N.; Inoue, S.;
Nagano, T.; Harima, Y.; Ohshita, J. Tetrahedron 2012, 68, 8577–8580; (b) Umeda,
R.; Nishida, H.; Otono, M.; Nishiyama, Y. Tetrahedron Lett. 2011, 52, 5494–5496;
(c) Saito, Y.; Suzuki, A.; Ishioroshi, S.; Saito, I. Tetrahedron Lett. 2011, 52, 4726–
4729; (d) Lee, D. Y.; Singh, N.; Jang, D. O. Tetrahedron Lett. 2011, 52, 1368–1371;
(e) Saito, R.; Matsumura, Y.; Suzuki, S.; Okazaki, N. Tetrahedron 2010, 66, 8273–
8279; (f) Yamaguchi, I.; Seo, K.; Kawashima, Y. Tetrahedron 2010, 66, 6725–
6732; (g) Hirano, T.; Sekiguchi, T.; Hashizume, D.; Ikeda, H.; Maki, S.; Niwa, H.
Tetrahedron 2010, 66, 3842–3848; (h) Saito, Y.; Suzuki, A.; Imai, K.; Nemoto, N.;
Saito, I. Tetrahedron Lett. 2010, 51, 2606–2609; (i) Fujimoto, K.; Shimizu, H.;
Furusyo, M.; Akiyama, S.; Ishida, M.; Furukawa, U.; Yokoo, T.; Inouye, M.
Teterahedron 2009, 65, 9357–9361; (j) Batista, R. M. F.; Costa, S. P. G.; Belsley,
M.; Lodeiro, C.; Raposo, M. M. M. Teterahedron 2008, 64, 9230–9238; (k)
Takamuki, Y.; Maki, S.; Niwa, H.; Ikeda, H.; Hirano, T. Tetrahedron 2005, 61,
10073–10080.
4. (a) Gruen, H.; Görner, H. J. Phys. Chem. 1989, 93, 7144–7152; (b) Gurzadyan, G.;
Görner, H. Chem. Phys. Lett. 2000, 319, 164–172; (c) Bolduc, A.; Dong, Y.; Guérin,
A.; Skene, W. G. Phys. Chem. Chem. Phys. 2012, 14, 6946–6956; (d) Lapouyade,
R.; Kuhn, A.; Letard, J.-F.; Rettig, W. Chem. Phys. Lett. 1993, 208, 48–58; (e)
Malval, J.-P.; Morlet-Savary, F.; Chaumeil, H.; Balan, L.; Versace, D.-L.; Jin, M.;
Defoin, A. J. Phys. Chem. C 2009, 113, 20812–20821; (f) Megyesi, M.; Biczók, L.;
Görner, H.; Miskolczy, Z. Chem. Phys. Lett. 2010, 489, 59–63; (g) Qian, F.; Zhang,
C.; Zhang, Y.; He, W.; Gao, X.; Hu, P.; Guo, Z. J. Am. Chem. Soc. 2009, 131, 1460–
1468; (h) Ueda, Y.; Tanigawa, Y.; Kitamura, C.; Ikeda, H.; Yoshimoto, Y.; Tanaka,
M.; Mizuno, K.; Kurata, H.; Kawase, T. Chem. Asian J. Early View. doi:10.1002/
asia.201200976.
Figure 2. UV–vis absorption and fluorescence spectra of BNP2T in various solvents.
Excitation wavelength for fluorescence measurements was absorption maxima.
observed in the case of BNPEnT. These results suggested that
p-
extension dramatically affects the solvent-specific fluorescence of
nitro-phenyl-containing compounds. BNP2T showed fluorescence
in various polar solvents and strong fluorescence even in weakly po-
lar solvents, which is a very unique environment-responsive fluo-
rescence characteristic.
The fluorescence rate kf and nonradiative relaxation rate knr
were calculated from UF and the fluorescence lifetime s 16
In all
.
the compounds except BNP1T, the value of knr increased with an
increase in the solvent polarity because of the nonradiative
relaxation process through ICT, induced by the strong electro-
withdrawing property of the nitro group.17 In general, a fluores-
cence dye showing ICT did not fluoresce in polar solvents but
exhibited strong fluorescence in non-polar solvents.17 On the
other hand, the knr value of BNP1T, BNP2T, and BNPE1T,
which show weak ICT, increased with a decrease in the solvent
polarity. Since the main mode of relaxation is IC through ISC in
the nitro-group-containing compounds,9 ISC might be the main
relaxation mode in nonpolar solvents. Thus, there are two nonradi-
ative relaxation processes, ISC and ICT, whose rates depend on the
solvent polarity. As a result, nitrophenyl oligothiophene deriva-
tives BNPnT and BNPEnT showed unique environment-responsive
multicolor fluorescence (see Fig. 2).
In conclusion, we designed unique environment-responsive
fluorescent dyes based on oligothiophene with a nitrophenyl or
nitrophenylethynyl group. We investigated the influence of
p-conjugation length on the fluorescence behavior of oligothioph-
ene derivatives having a nitrophenyl moiety and successfully
developed nitro-group-containing dyes that do not have any strong
donor moiety but show multicolor fluorescence. With an increase
in the number of thiophene rings, a solvent-polarity-dependent
maximum UF of BNPnT and BNPEnT was decreased. Nonradiative
relaxation through ISC and ICT was predominant in nonpolar
and polar solvents, respectively. These two relaxation processes
caused unique environment-responsive fluorescence. BNP2T, a
nitro-containing fluorescence dye without a strong donor moiety,
showed multicolor fluorescence in various solvents and a large
fluorescence quantum yield. These unique environment-
responsive solvatochromic fluorescent compounds may find
applications as sensors for bioimaging.18 In particular, fluorescence
probes with the nitro group can be used to detect nitro group
reduction, an important in vivo reaction, on the basis of fluores-
cence intensity changes.19 Further investigation of the effect of
5. (a) Neeraj, A.; Pabitra, K. N.; Periasamy, N. J. Chem. Sci. 2008, 120, 355–362; (b)
Samori, S.; Tojo, S.; Fujitsuka, M.; Spitler, E. L.; Haley, M. M.; Majima, T. J. Org.
Chem. 2007, 72, 2785–2793; (c) Plaza-Medina, E. F.; Rodríguez-Cárdoba, W.;
Morales-Cueto, R.; Peon, J. J. Phys. Chem. A 2011, 115, 577–585; (d) Flamini, R.;
Tomasi, I.; Marrocchi, A.; Calotti, B.; Spalletti, A. J. Photochem. Photobiol. A 2011,
223, 140–148; (e) Singh, A. K.; Darshi, M.; Kanvah, S. J. Phys. Chem. A 2000, 104,
464–471; (f) Zugazagoitia, J. S.; Almora-Díaz, C. X.; Peon, J. J. Phys. Chem. A
2008, 112, 358–365.
p-conjugation length on the fluorescence properties by quantum
6. Madhura, V.; Kulkarnia, M. V.; Badamib, S.; Yenagib, J.; Tonannavar, J.
Spectrochim. Acta A 2011, 84, 137–143.
chemical calculations is in progress.
Please cite this article in press as: Hachiya, S.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.03.054

4
S. Hachiya et al. / Tetrahedron Letters xxx (2013) xxx–xxx
7. (a) Crespo-Hernández, C. E.; Burdzinski, G.; Arce, R. J. Phys. Chem. A 2008, 112,
(BNP3T). Red needle; yield 16%; mp: decomp. (350 °C); FT-IR (KBr): 3095,
6313–6319; (b) Arce, R.; Pino, E. F.; Valle, C.; Ágreda, J. J. Phys. Chem. A 2008,
112, 10294–10304; (c) Collado-Fregoso, E.; Zugazagoitia, J. S.; Plaza-Medina, E.
F.; Peon, J. J. Phys. Chem. A 2009, 113, 13498–13508; (d) Mohammed, O. F.;
Vauthey, E. J. Phys. Chem. A 2008, 112, 3823–3830; (e) Zugazagoitia, J. S.;
Collado-Fregoso, E.; Plaza-Medina, E. F.; Peon, J. J. Phys. Chem. A 2009, 113, 805–
810.
3069, 1590, 1509, 1484, 1444, 1374, 1331, 1277, 1186, 1110, 1070, 852, 781,
748 cmꢀ1 1H NMR (CDCl3, 400 MHz) d (ppm): 7.19 (2H, s), 7.23 (2H, d,
;
J = 4.0 Hz), 7.40 (2H, d, J = 4.0 Hz), 7.72 (4H, d, J = 9.0 Hz); 8.24 (4H, d,
J = 9.0 Hz); HRMS (EI): calcd for C24H14N2O4S3 [M]+, 490.0116; found 490.0109.
14. (a) Sonogashira, K. J. Organomet. Chem. 2002, 653, 46–49; (b) Sonogashira, K.;
Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 50, 4467–4470.
8. (a) Foster, R.; Hammick, D. Ll; Hood, G. M.; Sanders, A. . E. J. Chem. Soc. 1956,
4865–4868; (b) Corkill, J. M.; Graham-Bryce, I. J. J. Chem. Soc. 1961, 21, 3893–
3897; (c) Mesaros, M.; Bonesi, S. M.; Ponce, M. A.; Erra-Balsells, R.; Bilmes, G. M.
Photochem. Photobiol. Sci. 2003, 2, 808–816.
9. Seliskar, C. J.; Khalil, O. S.; McGlynn, S. P. In Excited States; Lim, E. C., Ed.;
AcademicPress: New York, 1974; pp 232–294.
10. (a) Kotaka, H.; Konishi, G.; Mizuno, K. Tetrahedron Lett. 2010, 51, 181–184; (b)
Niko, Y.; Konishi, G. J. Synth. Org. Chem. Jpn. 2012, 70, 918–927; (c) Hachiya, S.;
Asai, K.; Konishi, G. Tetrahedron Lett. doi:10.1016/j.tetlet.2013.01.096.
11. (a) Bolívar-Marinez, L. E.; dos Santos, M. C.; Galvão, D. S. J. Phys. Chem. 1996,
100, 11029–11032; (b) Melo, J. S.; Silva, L. M.; Arnaut, L. G. J. Chem. Phys. 1999,
111, 5427–5433; (c) Fin, A.; Jentzsch, A. V.; Sakai, N.; Matile, S. Angew. Chem.,
Int. Ed. 2012, 51, 12736–12739; (d) Siddle, J. S.; Ward, R. M.; Collings, J. C.;
Rutter, S. R.; Porrès, L.; Applegarth, L.; Beeby, A.; Batsanov, A. S.; Thompson, A.
L.; Howard, J. A. K.; Boucekkine, A.; Costuas, K.; Halet, J.-F.; Marder, T. B. New J.
Chem. 2007, 31, 841–851; (e) Promarak, V.; Punkvuang, A.; Jungsuttiwong, S.;
Saengsuwan, S.; Sudyoadsuk, T.; Keawin, T. Tetrahedron Lett. 2007, 48, 3661–
3665.
15. General procedure for synthesis of BNPEnT: To
a
solution of
dibromooligothiophene, 4-nitrophenylacethylene (2.4 equiv), Pd(PPh3)4
(5 mol %), and CuI (4 mol %) in THF, triethylamine (5 equiv) were added, and
the reaction mixture was stirred at 50 °C under air overnight. The reaction
mixture was diluted with water and the product was extracted with
chloroform. The organic layer was dried over MgSO4, and concentrated in
vacuo. The residue was purified by silica gel column chromatography and
recrystallization to give BNPEnT. (2,5-Bis((4-nitrophenyl)ethynyl)thiophene
(BNPE1T)). Yellow needle; yield 51% mp: 194–196 °C; FT-IR (KBr): 3084,
2839, 2199, 1592, 1508, 1342, 1108, 1098, 850, 811, 748, 696 cmꢀ1 1H NMR
;
(CDCl3, 400 MHz) d (ppm): 7.28 (2H, s), 7.67 (4H, d, J = 9.0 Hz); 8.24 (4H, d,
J = 9.0 Hz); MS (DART): m/z 375.0 ([M+H]+); Anal. Calcd for C20H10N2O4S: C,
64.16; H, 2.69; N, 7.48; Found C, 64.16; H, 2.69; N, 7.37. 5,50-Bis((4-
nitrophenyl)ethynyl)-2,20-bithiophene (BNPE2T): Red solid; yield 43%; mp:
283–286 °C; FT-IR (KBr): 3094, 2191, 1591, 1506, 1449, 1341, 1285, 1226,
1194, 1172, 1105, 1040, 857, 791 cmꢀ1 1H NMR (CDCl3, 400 MHz) d (ppm):
;
7.16 (2H, d, J = 4.0 Hz), 7.29 (2H, d, J = 4.0 Hz) 7.65 (4H, d, J = 9.0 Hz), 8.23 (4H,
d, J = 9.0 Hz); HRMS (EI): calcd for
C
24H12N2O4S2 [M]+, 456.0239; found
12. (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483; (b) Miyaura, N.;
Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11, 513–519.
13. General procedure for synthesis of 2,5-bis(4-nitrophenyl)oligothiophene (BNPnT):
456.0228. 5,500-bis((4-nitrophenyl)ethynyl)-2,20:50,200-terthiophene (BNPE3T).
Red solid; yield 25%; mp: decomp. 350 °C; FT-IR (KBr): 3172, 2191, 1591,
1508, 1442, 1374, 1339, 1285, 1222, 1192, 1104, 1042, 849, 783, 747 cmꢀ1 1H
;
To
a
solution of dibromooligothiophene, Pd(PPh3)4 (5 mol %), and Cs2CO3
NMR (CDCl3, 400 MHz) d (ppm): 7.15, (2H, d, J = 4.0 Hz), 7.18 (2H, s), 7.30 (2H,
d, J = 4.0 Hz), 7.67 (2H, d, J = 9.0 Hz), 8.25 (2H, d, J = 9.0 Hz); HRMS (EI): calcd
for C28H14N2O4S3 [M]+, 538.0116; found 538.0124.
(6 equiv) in THF, 4-nitrophenylboronic acid (2.1 equiv) were added and the
reaction mixture was stirred at reflux under Ar for several hours. The reaction
mixture was diluted with water and the product was extracted with
chloroform. The organic layer was dried over MgSO4, and concentrated in
vacuo. The residue was purified by silica gel column chromatography and
recrystallization to give BNPnT. 2,5-Bis(4-nitrophenyl)thiophene (BNP1T).
Orange needle; yield 58%; mp: 270–272 °C; FT-IR (KBr): 3084, 2839, 2199,
16. Turro, N. J.; Ramamurthyl, V.; Scaiano, J. C. In Modern Molecular Photochemistry
of Organic Molecules; University Science Books: South Orange, 2010; pp 223–
230.
17. (a) Giordano, L.; Shvadchak, V. V.; Fauerbach, J. A.; Jares-Erijman, E. A.; Jovin,
T. M. J. Phys. Chem. Lett. 2012, 3, 1011–1016; (b) Vazquez, M. E.; Blanco, J. B.;
Imperiali, B. J. Am. Chem. Soc. 2005, 127, 1300–1306; (c) Soujanya, T.;
Fessenden, R. W.; Samanta, A. J. Phys. Chem. 1996, 100, 3507–3512; (d) Mes,
G. F.; Dejong, B.; Vanramesdonk, H. J.; Verhoeven, J. W.; Warman, J. M.;
Dehaas, M. P.; Horsmanvandendool, L. E. W. J. Am. Chem. Soc. 1984, 106,
6524–6528.
1592, 1508, 1342, 1108, 1098, 850, 811, 748, 696 cmꢀ1 1H NMR (CDCl3,
;
400 MHz) d (ppm): 7.28 (2H, s), 7.67 (4H, d,J = 9.0 Hz); 8.24 (4H, d, J = 9.0 Hz);
MS (DART): m/z 327.0 ([M+H]+); Anal. Calcd for C16H10N2O4S: C, 58.89; H, 3.09;
N, 8.58; Found C, 58.54; H, 3.12; N, 8.48. 5,50-Bis(4-nitrophenyl)-2,20-bithiophene
(BNP2T): Red solid; yield 59%; mp: 300–303 °C; IR (KBr): 3098, 3064, 2359,
1590, 1509, 1484, 1444, 1374, 1331, 1293, 1277, 1186, 1110, 1070, 852,
18. (a) Signore, G.; Nifosì, R.; Albertazzi, L.; Storti, B.; Bizzarri, R. J. Am. Chem. Soc.
2010, 132, 1276–1288.
781 cmꢀ1 1H NMR (CDCl3, 400 MHz) d (ppm): 7.29 (2H, d, J = 4.0 Hz), 7.44 (2H,
;
d, J = 4.0 Hz) 7.75 (4H, d, J = 9.0 Hz); 8.27 (4H, d, J = 9.0 Hz); MS (DART): m/z
409.0 ([M+H]+); Anal. Calcd for C20H12N2O4S2: C, 58.81; H, 2.96; N, 6.56; Found
C, 58.43; H, 2.96; N, 6.60. 5,500-Bis(4-nitrophenyl)-2,20:50,200-terthiophene
19. (a) Wang, R.; Yu, F.; Chen, L.; Chen, H.; Wang, L.; Zhang, W. Chem. Commun.
2012, 48, 11757–11759; (b) Montoya, L. A.; Pluth, M. D. Chem. Commun. 2012,
48, 4767–4769.
Please cite this article in press as: Hachiya, S.; et al. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.03.054