Precise synthesis of end-functionalized Oligo(2,5-dialkoxy-1,4-phenylene vinylene)s with controlled repeat units via combined olefin metathesis and wittig-type coupling

Article abstract of DOI:10.1021/ol400397p

The precise synthesis of chemically, analytically pure oligo(2,5-dialkoxy- 1,4-phenylene vinylene)s [OPVs, alkoxy = O(CH₂)₂OSi ⁱPr₃] with strictly controlled repeat units (up to 15 repeat units) and well-defined end groups has been achieved by a combined olefin metathesis reaction of 2,5-dialkoxy-1,4-divinylbenzene or their derivatives with a molybdenum-alkylidene complex and the subsequent Wittig-type cleavage with their dicarboxaldehyde analogues. The effects of the repeat units and the end functional groups toward their UV-vis and the fluorescence spectra have been clearly demonstrated.

Full text of DOI:10.1021/ol400397p

ORGANIC
LETTERS
2013
Vol. 15, No. 7
1618–1621
Precise Synthesis of End-Functionalized
Oligo(2,5-dialkoxy-1,4-phenylene
vinylene)s with Controlled Repeat Units
via Combined Olefin Metathesis and
Wittig-Type Coupling
Mohamed Mehawed Abdellatif† and Kotohiro Nomura*,†,‡
Department of Chemistry, Faculty of Science and Engineering, Tokyo Metropolitan
University, 1-1 minami Osawa, Hachioji, Tokyo 192-0397, Japan, and Advanced
Catalytic Transformation for Carbon Utilization (ACT-C), Japan Science and
Technology Agency (JST), Saitama 332-0012, Japan
ktnomura@tmu.ac.jp
Received February 9, 2013
ABSTRACT
The precise synthesis of chemically, analytically pure oligo(2,5-dialkoxy-1,4-phenylene vinylene)s [OPVs, alkoxy = O(CH2)2OSiiPr3] with strictly controlled
repeat units (up to 15 repeat units) and well-defined end groups has been achieved by a combined olefin metathesis reaction of 2,5-dialkoxy-1,4-
divinylbenzene or their derivatives with a molybdenumꢀalkylidene complex and the subsequent Wittig-type cleavage with their dicarboxaldehyde
analogues. The effects of the repeat units and the end functional groups toward their UVꢀvis and the fluorescence spectra have been clearly demonstrated.
Organic electronics have been recognized as important
emerging technologies, and conjugated polymers/oligomers
exemplified as poly(p-arylene vinylene)s are promising
semiconducting materials.1ꢀ4 The synthesis of structurally
regular, chemically pure materials by development of new
synthetic methods/methodology has attracted considerable
attention1 because their device performances are affected by
their structural regularity, chemical purity, and supramolec-
ular order.2,3 We recently demonstrated syntheses of defect-
free, stereoregular (all-trans), high molecular weight
poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs),5 poly(2,5-
dialkylphenylene-1,4-vinylene)s (PPVs),6 etc. by acyclic
diene metathesis (ADMET) polymerization.5ꢀ11 Since the
resultant polymers prepared by a Ru-carbene catalyst
† Tokyo Metropolitan University.
‡ Japan Science and Technology Agency (JST).
(1) (a) Special Issue in Organic Electronics: Chem. Mater. 2004, 16,
4381. (b) Organic Light Emitting Devices; M€ullen, K., Scherf, U., Eds.;
Wiley-VCH: Winheim, 2006. (c) Handbook of Conducting Polymers, 3rd
ed.; Skotheim, T. A., Reynolds, J., Eds.; CRC Press: Boca Raton, FL, 2007.
(3) Selected reviews: (a) Fumitomo, H.;Dıaz-Garcıa, M. A.; Schwartz,
´ ´
B. J.; Heeger, A. J. Acc. Chem. Res. 1997, 30, 430. (b) Kraft, A.; Grimsdale,
A. C.; Holmes, A. B. Angew. Chem., Int. Ed. 1998, 37, 402. (c) Friend, R. H.;
Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.;
€
(2) (a) Grimsdale, A. C.; Mullen, K. In Macromolecular Engineering;
ꢀ
€
Matyjaszewski, K., Gnanou, Y., Leibler, L., Eds.; Wiley-VCH: Weinheim,
2007; Vol. 4, p 2225. (b) Bielawski, C. W.; Wilson, C. G. In Macro-
molecular Engineering; Matyjaszewski, K., Gnanou, Y., Leibler, L., Eds.;
Wiley-VCH: Weinheim, 2007; Vol. 4, p 2263. (c) Laclerc, N.; Heiser, T.;
Brochon, C.; Hadziioannou, G. In Macromolecular Engineering;
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2007; Vol. 4, p 2369.
Bradley, D. C. C.; Dos Santos, D. A.; Bredas, J. L.; Logdlund, M.;
Salaneck, W. R. Nature 1999, 397, 121. (d) Grimsdale, A. C.; Chan,
K. L.; Martin, R. E.; Jokisz, P. G.; Holmes, A. B. Chem. Rev. 2009, 109,
€
897. (e) Li, C.;Liu, M.;Pschirer, N. G.; Baumgarten, M.;Mullen, K. Chem.
Rev. 2010, 110, 6817. (f) Zade, S. S.; Zamoshchik, N.; Bendikov, M. Acc.
Chem. Res. 2011, 44, 14. (g) Zhou, H.; Yang, L.; You, W. Macromolecules
2012, 45, 607.
r
10.1021/ol400397p
Published on Web 03/22/2013
2013 American Chemical Society

possessed well-defined chain ends (as vinyl group),5bꢀe,6 an
exclusive end-functionalization can be achieved by treating
the vinyl groups with Mo-alkylidene (Mo cat.) followed by
Wittig-type cleavage with aldehyde.5b,d,e,12,13 We thus dem-
onstrated precise syntheses of amphiphilic (multi)block
copolymers,5b,e and of PFV’s containing oligo(thiophene)s
in both chain ends which exhibit unique emission properties
by an energy transfer.5d
Mo-alkylidene species with aldehydes took place in quanti-
tative yields,5b,d,e here, we thus wish to present a precise,
exclusive synthesis of analytically pure OPVs with strictly
controlled repeat units and well-defined chain ends,
achieved by (repetitive stepwise) coupling of the “bis-alky-
lidene” species with OPV containing aldehyde at the both
chain ends (Scheme 1).14,15
Synthesis of oligo(2,5-dialkoxy-1,4-phenylene vinylene)s
(OPVs) by the ADMET technique was reported;9 however,
oligomers up to 7 (average 3) repeat units were prepared,9b
and synthesis of high molecular weight oligomers seemed
difficult due to coordination of an O-atom toward the
centered metal (Mo, Ru, etc.) and/or accompanied catalyst
decomposition.9g Since the above Wittig-type reactions of
Scheme 1. Synthesis of Analytically Pure OPVs
(4) (a) Stirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.;
Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen,
R. A. J.; Meijer, E. W.; de Leeuw, D. M. Nature 1999, 401, 685. (b)
Hoofman, J. O. M.; de Haas, M. P.; Siebbeles, L. D. A.; Warman, J. M.
Nature 1998, 392, 54. (c) Son, S.; Dodabalapur, A.; Lovinger, A. J.;
Galvin, M. E. Science 1995, 269, 376.
(5) (a) Nomura, K.; Morimoto, H.; Imanishi, Y.; Ramhani, Z.;
Geerts, Y. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 2463. (b)
Nomura, K.; Yamamoto, N.; Ito, R.; Fujiki, M.; Geerts, Y. Macro-
molecules 2008, 41, 4245. (c) Yamamoto, N.; Ito, R.; Geerts, Y.;
Nomura, K. Macromolecules 2009, 42, 5104. (d) Kuwabara, S.;
Yamamoto, N.; Sharma, P. M. V.; Takamizu, K.; Fujiki, M.; Geerts,
Y.; Nomura, K. Macromolecules 2011, 44, 3705. (e) Abdellatif, M. M.;
Nomura, K. ACS Macro Lett 2012, 1, 423.
(6) Synthesis of high molecular weight poly(2,5-dialkyl-1,4-phenyl-
ene vinylene)s (PPVs): Nomura, K.; Miyamoto, Y.; Morimoto, H.;
Geerts, Y. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 6166.
(7) Selected recent reviews concerning ADMET polymerization: (a)
Lehman, S. E. Jr.; Wagener, K. B. In Handbook of Metathesis; Grubbs,
R. H., Ed.; Wiley-VCH: Weinheim, 2003; Vol. 3, p 283. (b) Baughman,
T. W.; Wagener, K. B. In Metathesis Polymerization; Buchmeiser, M. R.,
Ed.; Springer: Heidelberg, 2005; p 1.
We have thus chosen a stepwise approach for synthesis
of conjugated oligomers (Scheme 1). The vinyl groups in
DVB were treated with Mo(CHCMe2Ph)(N-2,6-Me2C6H3)-
[OCCH3(CF3)2]2, (Mo cat., 2 equiv), to form the “bis-
alkylidene” species (expressed as Mo=DB=Mo) in situ,
and subsequent reaction with corresponding aldehyde
(2,5-dialkoxybenzene-1,4-dicarboxaldehyde, DBDA) in
a rather excess amount (2.2 equiv to DVB) afforded a
3-mer containing aldehyde as the end groups (expressed as
3PV-CHO). 3PV-CHO was isolated as an analytically pure
form by a simple fractional separation (yield 85.0%) and
(8) Another synthetic protocol for poly(arylene vinylene)s by
ADMET polymerization using RuCl2(PCy3)(IMesH2)(CHPh) (Ru):
Weychardt, H.; Plenio, H. Organometallics 2008, 27, 1479.
(9) Synthesis of oligo(2,5-dialkoxy-1,4-phenylene vinylene)s by
ꢀ
ADMET approach: (a) Thorn-Csanyi, E.; Kraxner, P. Macromol.
Rapid Commun. 1998, 19, 223. (b) Peetz, R.; Narwark, O.; Herzog, O.;
ꢀ
ꢀ
Brocke, S.; Thorn-Csanyi, E. Synth. Met. 2001, 119, 539. (c) Thorn-Csanyi,
E. In Ring Opening Metathesis Polymerization and Related Chemistry;
Khosravi, E., Szymanska-Buzar, T., Eds.; Kluwer Academic: Dordrecht, 2002;
ꢀ
p 295. (e) Narwark, O.; Meskers, S. C. J.; Peetz, R.; Thorn-Csanyi, E.;
Bassler, H. Chem. Phys. 2003, 294, 1. (f) Thorn-Csanyi, E.; Herzog, O.
J. Mol. Catal. A 2004, 213, 123. (g) Peetz, R. M.; Sinnwell, V.; Thorn-Csanyi,
€
ꢀ
ꢀ
E. J. Mol. Catal. A 2006,254, 165. (h) Pecher, J.; Mecking, S. Macromolecules
2007, 40, 7733. In ref 9b and 9c, no analysis data were given for the resultant
oligomers (only mass spectrometry).
(10) Synthesis of oligo(2,5-dialkyl-1,4-phenylene vinylene)s by
ꢀ
ADMET approach:6,8 (a) Thorn-Csanyi, E.; Kraxner, P. Macromol.
ꢀ
Rapid Commun. 1995, 16, 147. (b) Thorn-Csanyi, E.; Kraxner, P. J. Mol.
(13) For examples (end functionalization of ROMP polymers and
their application for further grafting), see: (a) Nomura, K.; Takahashi,
S.; Imanishi, Y. Macromolecules 2001, 34, 4712. (b) Murphy, J. J.;
Kawasaki, T.; Fujiki, M.; Nomura, K. Macromolecules 2005, 38, 1075.
(c) Murphy, J. J.; Nomura, K. Chem. Commun. 2005, 4080. (d) Murphy,
J. J.; Furusho, H.; Paton, R. M.; Nomura, K. Chem.;Eur. J. 2007, 13,
8985. (e) Nomura, K.; Abdellatif, M. M. Polymer 2010, 51, 1861.
(14) These results were partly introduced at the 12th International
Kyoto Conference on New Aspect of Organic Chemistry (IKCOC-12),
Kyoto, Japan, November 2012 (poster presentation).
(15) Detailed experimental procedures including syntheses and iden-
tifications of all oligo(2,5-dialkoxy-phenylene vinylene)s presented in
this paper, selected NMR spectra, GPC traces are shown in the
Supporting Information (SI). An attempted synthesis of high molecular
weight polymers by ADMET polymerization of 2,5-bis(20-triisopro-
ꢀ
Catal. A 1997, 115, 21. (c) Thorn-Csanyi, E.; Kraxner, P. Macromol.
Chem. Phys. 1997, 198, 3827. (d) Thorn-Csanyi, E.; Kraxner, P. In
ꢀ
Metathesis Polymerization of Olefins and Polymerization of Alkynes;
Imamoglu, Y., Ed.; Kluwer Academic: Dordrecht, 1998; p 297.
(11) Synthesis of poly(thienylene vinylene)s by ADMET approach:
(a) Qin, Y.; Hillmyer, M. A. Macromolecules 2009, 42, 6429. (b)
Delgado, P. A.; Liu, D. Y.; Kean, Z.; Wagener, K. B. Macromolecules
2011, 44, 9529. (c) Speros, J. C.; Paulsen, B. D.; White, S. P.; Wu, Y.;
Jackson, E. A.; Slowinski, B. S.; Frisbie, C. D.; Hillmyer, M. A.
Macromolecules 2012, 45, 2190. (d) Speros, J. C.; Paulsen, B. D.;
Slowinski, B. S.; Frisbie, C. D.; Hillmyer, M. A. ACS Macro Lett
2012, 1, 986.
(12) For example, see: (a) Schrock, R. R. In Alkene Metathesis in
Organic Synthesis; F€urstner, A., Ed.; Springer-Verlag: Berlin Heidelberg,
1998; p 1. (b) Schrock, R. R. In Metathesis Polymerization of Olefins and
Polymerization of Alkynes; Imamoglu, Y., Ed.; NATO ASI Series, Kluwer
Academic Publishers: 1998; pp 1 and 357. (c) Schrock, R. R. In Handbook
of Metathesis; Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, 2003; Vol. 1, p 8.
(d) Schrock, R. R. Chem. Rev. 2009, 109, 3211.
pylsilyloxyethoxy)-1,4-divinylbenzene (DVB) using
a Ru-carbene
catalyst, RuCl2(PCy3)(IMesH2)(CH-2-OiPr-C6H4) [Cy = cyclohexyl,
IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene], was
not successful [Mn(GPC) = 2.9 ꢁ 103, Mn(NMR) = 1.87 ꢁ 103, Mw/Mn =
1.27]. The result is also shown in the SI.
Org. Lett., Vol. 15, No. 7, 2013
1619

was identified by NMR spectra, GPC trace (unimodal
distribution, Mw/Mn = 1.0), and elemental analysis.15
1
The Mn value estimated by the H NMR spectrum (on
Scheme 2. Synthesis of OPVs with Well-Defined End Groups
the basis of integration ratio of aromatic protons in OPV vs
chain end group) was very close to the calculated value
(Table 1).
Moreover, 3PV-CHO was treated with <0.5 equiv of the
“bis-alkylidene” species to afford the 7-mer (7PV-CHO) as
the sole coupled product.15 Then, the resultant 7PV-CHO
was treated with <0.5 equiv of the “bis-alkylidene” species to
afford the 15-mer (15PV-CHO) exclusively.15 7PV-CHO
was isolated as an analytically pure form by a fractional
separation (isolated yield 80.0%) and identified by NMR
spectra, GPC trace (Mw/Mn = 1.0), and elemental analysis:15
15PV-CHO was also isolated as a pure form confirmed
by fractional GPC (in addition to ordinary GPC traces,
Mw/Mn = 1.0) and identified by NMR spectra (isolated
yield 82.0%). The Mn values in 7PV-CHO and 15PV-CHO
estimated by 1H NMR spectra were very close to the
calculated values. Note that a synthesis of high molecular
weight oligomers [ex. 15PV-CHO, Mn = 8.07 ꢁ 103] has
been achieved by adopting this methodology and that the
resultant oligomer possessed strictly repeat units with well-
defined end groups. Moreover, it should also be noted that
the olefinic double bond in the OPVs possessed high stereo-
regularity (highly trans) confirmed by 1H NMR spectra.15
1
elemental analysis.15 The Mn values estimated by H NMR
spectra in these 5PVs were very close to the calculated values
(Table 1). These results clearly indicate that a precise
synthesis of analytically pure oligomers that possess strictly
repeat units and various well-defined end groups has been
achieved by adopting this approach.
Figure 1 shows UVꢀvis (left) and fluorescence (right,
excitation wavelength at 450 nm) spectra (in THF, 1.0 ꢁ
10ꢀ6 M at 25 °C) for the resultant OPVs (3PV-CHO, 7PV-
CHO, 15PV-CHO) and starting divinylbenzene (DVB).
Different absorption bands observed were due to the
influence of the conjugation repeat units: the λmax values,
which have been known to be attributed to the πꢀπ*
transition of the conjugated backbone,9e,16 shifted to a
longer wavelength (the maximum of the S1 r S0 electronic
transition shifts toward lower energies) upon the increase
in the conjugation units [λmax: 276 and 432 nm (3PV-
CHO), 459 nm (7PV-CHO), 476 nm (15PV-CHO)]. In
contrast to the absorption, as reported previously,9e,16 the
recorded fluorescence spectra showed a vibronic splitting
where the relative intensity of the S1 f S0 0ꢀ0 compared
to the 0ꢀ1 electronic transition seems to increase upon
increasing conjugation length [λmax: 540 nm (3PV-CHO),
532 nm (7PV-CHO), 539 nm (15PV-CHO)]. Moreover,
photoluminescence quantum yields in the resultant 3PV-CHO,
7PV-CHO, and 15PV-CHO (in THF at 25 °C, excitation at
450 nm) were 0.83, 0.62, and 0.51, respectively. These values
Table 1. Synthesis of OPVs with Well-Defined End Functional
Groups [alkoxy (OR) = O(CH2)2OSiiPr3]a
Mn(NMR) Mn(calcd) Mw/ yielde/ absorptionf fluorescenceg
b
c
d
OPVs
ꢁ10ꢀ3
ꢁ10ꢀ3 Mn
%
λ
max/nm
λ
max/nm
3PV-CHO
7PV-CHO
1.63
3.76
1.63
3.78
8.07
3.29
2.84
3.03
1.0 85.0
1.0 80.0
1.0 82.0
1.0 85.0
1.0 85.0
1.0 95.0
276,432
459
540
532
539
527
535
531
15PV-CHO 8.04
476
5PV-3T
3.24
2.84
3.02h
463
5PV-C6H5
5PV-C6F5
470
450
a Conditions: Experimental details are shown in the Supporting
Information.15 b Estimated by 1H NMR spectra (on the basis of integra-
tion ratios of aromatic protons in OPV vs chain end group). c Calculated
on the basis of formula, molar ratios. d GPC data in THF vs polystyrene
standards. e Isolated yield. f On the basis of UVꢀvis spectra (in THF at
25 °C). g On the basis of fluorescence spectra (in THF at 25 °C). h Mn
value estimated on the basis of methylene protons in the alkoxy group vs
aromatic protons.
Importantly, 3PV-CHO was reacted with ca. 2.2 equiv
of the “bis-alkylidene” species, and subsequent addition of
2,20:50,200-terthiophene-5-carboxaldehyde (3T-CHO) afforded
the 5-mer of the oligo(2,5-dialkoxy-1,4-phenylene vinylene)
containing an oligo(thiophene) moiety at both chain ends
(expressed as 5PV-3T, Scheme 2). Similarly, the reaction
with C6F5CHO, PhCHO in place of 3T-CHO afforded the
5-mer containing C6F5 or C6H5 end groups (5PV-C6F5,
5PV-C6H5, respectively). The resultant oligomers (5PV-3T,
5PV-C6F5, 5PV-C6H5) were also isolated as analytically
pure forms by a simple fractional separation and were
identified by NMR spectra, GPC trace (Mw/Mn = 1.0), and
(16) For example: (a) Stalmach, U.; Kolshorn, H.; Brehm, I.; Meier,
H. Liebigs Ann 1996, 1449. (b) Oelkrug, D.; Tompert, A.; Egelhaaf,
H.-J.; Hannack, M.; Steinhuber, E.; Hohloch, M.; Meier, H.; Stalmach,
U. Synth. Met. 1996, 83, 231. (c) Peeters, E.; Marcos Ramos, A.;
Meskers, S. C. J.; Janssen, R. A. J. J. Chem. Phys. 2000, 112, 9445.
(17) (a) Effect of conjugation length toward the photoluminescence
quantum yields in R,ω-dimethyl-oligo{2,5-bis[2-(S)-methylbutoxy]-p-
phenylene vinylenes: Peeters, E.; Ramos, A. M.; Meskers, S. C. J.;
Janssen, R. A. J. Chem. Phys. 2000, 112, 9445. The yields (in CHCl3)
were 0.62 (OPV3, trimer), 0.49 (OPV5, pentamer), and 0.25 (OPV7,
heptamer), respectively. (b) The value (0.51 in 15PV-CHO) was also
higher than that reported (0.35) in poly(2-methoxy-5-(20-ethylhexoxy)-
1,4-phenylene vinylene). Samuel, I. D. W.; Rumbles, G.; Friend, R. H.
In Primary Photoexcitations in Conjugated Polymers; Sariciftci, N. S.,
Ed.; World Scientific: Singapore, 1997; Chapter 7, p 140.
1620
Org. Lett., Vol. 15, No. 7, 2013

Figure 1. UVꢀvis spectra (left) and the fluorescent spectra
(right, excitation at 450 nm) for DVB, 3PV-CHO, 7PV-CHO,
and 15PV-CHO in THF at 25 °C (concn 1.0 ꢁ 10ꢀ6 M).
Figure 2. (a) UVꢀvis spectra (left) and (b) fluorescent spectra
(right, excitation at 450 nm) for 5PV-Ar (Ar = 3T, C6F5, C6H5)
in THF at 25 °C (concn 1.0 ꢁ 10ꢀ6 M).
were somewhat higher than those for reported OPVs with
different side and end groups:17 significant decreases in the
values were not observed even with 15PV-CHO, which would
be an interesting contrast to those reported previously.17
Figure 2 shows UVꢀvis (left) and fluorescence (right,
excitation wavelength at 450 nm) spectra (in THF, 1.0 ꢁ
10ꢀ6 M at 25 °C) for the 5PVs with different end functional
groups (5PV-3T, 5PV-C6F5, 5PV-C6H5). The λmax values
in the UVꢀvis spectra were varied by the introduction of
end functional groups [λmax: 463 nm (5PV-3T), 450 nm
(5PV-C6F5), 470 nm (5PV-C6H5)], which would be as-
sumed, as the charge transfer band is shifted by an increase
of the electron-withdrawing power of the acceptor.18
Moreover, the fluorescence intensities were affected by the
end functional group probably due to a degree of energy
transfer, suggesting that the emission properties can be
modified by the introduction of an end functional group.
We have shown that a precise, exclusive synthesis of
oligo(2,5-dialkoxy-1,4-phenylene vinylene)s [OPVs, up to
15 repeat units, alkoxy (OR) = O(CH2)2OSiiPr3] with
strictly controlled repeat units and well-defined end func-
tional groups has been achieved by adopting a stepwise
coupling of the “bis-alkylidene” species with OPVs con-
taining an aldehyde at both chain ends (Schemes 1, 2).
Moreover, the resultant oligomers are structurally regular
(highly trans olefinic double bonds) and chemically pure
and were identified by NMR spectra and elemental
analysis. The optical properties (in their UVꢀvis and
fluorescence spectra) can be modified by both the conjuga-
tion repeat units and the end functional groups.
The methodology presented here is, as far as we know,
the rare demonstration of a precise synthesis of end-
functionalized oligo(arylene vinylene)s, and a wide appli-
cability of this methodology enables us to fine-tune various
conjugated oligomers/polymers with unique properties.
We highly believe that the methodology presented here
should be thus highly promising for designing precise
conjugated materials for the desired purposes. More de-
tails, including the effect of various conjugation lengths
and end functional groups toward basic optical properties
are now in progress.
Acknowledgment. M.M.A. expresses his thanks to the
Ministry of Education, Culture, Sports, Science and Tech-
nology (MEXT) for a Japanese government scholarship.
The project is partly supported by the Advanced Catalytic
Transformation for Carbon utilization (ACT-C), Japan
Science and Technology Agency (JST), Japan. K.N. ex-
ꢀ
presses his thanks to Prof. Dr. Yves Geerts (Universite
Libre de Bruxelles, Belgium) for fruitful discussions and
Prof. Akiko Inagaki (TMU) for help in measurement of
quantum yields.
Supporting Information Available. Experimental pro-
cedures for syntheses of monomers and oligomers includ-
ing their identification. This material is available free of
charge via the Internet at http://pubs.acs.org.
(18) It seems likely from Figure 2 (right) that the relative intensity
ascribed to the S1 f S0 0ꢀ0 and the 0ꢀ1 electronic transition were
affected by the end functional groups.5d The report for tunable optical
properties of chromophores in OPV (up to 3 mer): Guerlin, A.; Dumur,
F.; Dumas, E.; Miomandre, F.; Wantz, G.; Mayer, C. R. Org. Lett. 2010,
12, 2382.
The authors declare no competing financial interest.
Org. Lett., Vol. 15, No. 7, 2013
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