900
Bull. Chem. Soc. Jpn. Vol. 82, No. 7 (2009)
Highly Coplanar Polythiophenes
C10H21
C4H9
C12H25
C6H13
= 2860 cm-1
∆
= 11340 cm-1
∆
S
S
S
S
S
S
,
C6H13
λ
max = 242 nm
260 nm
248 nm
345 nm
C4H9
Chart 8. Comparison of the UV-vis absorption peaks of 3-alkylthiophenes and 3-alkynylthiophenes.
HT-P3HexTh.
when cooled to below about 0 °C,1,7e and it was assigned to
As shown in Figure 2a, HH-P3(C≡C-Hex)Th gives rise to
two sharp -C≡C- carbon signals at ¤ 77.3 and 99.7.18 CP/MAS
solid-state 13C NMR spectra of HH-PTh3, TT-PTh3, HH-PTh4,
TT-PTh4, HH-P3(C≡C-Ph)Th, and HH-P3(C≡C-Ph-Bu)Th
also show sharp Th- and -C≡C- carbon signals, as shown in
Figure S14. The two -C≡C- carbon signals are separated by
about 20 ppm for HH-P3(C≡C-alkyl)Ths, HH-PTh3, TT-PTh3,
HH-PTh4, and TT-PTh4, whereas they are separated by about
10 ppm for HH-P3(C≡C-Ph)Th and HH-P3(C≡C-Ph-Bu)Th
because of the attachment of an aromatic ring at both the
-C≡C- carbons. In the case of HH-P3(C≡C-Th-Dod)Th, the
two -C≡C- carbon signals seem to overlap each other as shown
in the synthetic part of HH-P3(C≡C-Th-Dod)Th in Supporting
Information.
self-assembly of HT-P3HexTh at temperatures below about
0 °C. Similar self-assembly of HH-P3(C≡C-Dec)Th and HH-
P3(C≡C-Th-Dod)Th at temperatures below 60 and 35 °C,
respectively, is conceivable, and the occurrence of spectral
changes at considerably higher temperatures than those of the
CHCl3 and CH2Cl2 solutions of HT-P3HexTh indicates that
HH-P3(C≡CR)Th has a stronger tendency to self-assemble than
HT-P3HexTh. The UV-vis spectra of the 1,2-dichlorobenzene
solutions of HH-P3(C≡C-Dec)Th and HH-P3(C≡C-Th-
Dod)Th at 25 °C showed no time-dependence after cooling to
25 °C from about 130 °C, indicating that the self-assembly took
place rapidly upon cooling the solution.
Temperature-dependent 1H NMR spectra of HH-P3(C≡C-
Dec)Th also showed signs of self-assembly at lower temper-
atures. As shown in Figure S16a, HH-P3(C≡C-Dec)Th shows
1
UV-Vis Spectra and H NMR. The UV-vis absorption
peak of 3-alkylthiophene is shifted to a wavelength longer by
a
1H NMR spectrum, with reasonable peak area ratios, at
¹1
18 nm or 2860 cm when the alkyl group is replaced by the
130 °C. However, the aromatic Th-H (¤ 7.1) and -C≡C-CH2-
(¤ 2.5) signals are weakened, compared with the terminal CH3
signal, at 110 °C and below the temperature in CDCl2CDCl2.
Similar weakening of Th-H and Th-CH2- peaks of
HT-P3HexTh at ¹20 °C in CDCl3 has been reported (cf.
Figure S16b),7e and it was considered to originate from loss of
motional freedom of the Th-H and Th-CH2- protons in stacked
colloidal particles of HT-P3HexTh at ¹20 °C. Similar loss of
motional freedom of the Th-H and -C≡C-CH2- protons of
HH-P3(C≡C-Dec)Th in the stacked colloidal particles formed
at lower temperatures accounts for the NMR data.
-C≡C-alkyl group, presumably because of certain expansion of
the ³-conjugation system.
As shown on the right of Chart 8, the HH-dimers of 3-
alkylthiophene and 3-alkynylthiophene show a larger ³-³*
transition energy difference of 11340 cm¹1, which is ascribed
to a twisted structure of the 3-alkylthiophene dimer and
coplanar structure of the 3-alkynylthiophene dimer.
When the dimer is formed, -max of 3-alkynylthiophene shifts
from 260 to 345 nm (cf. Chart 8) with a ³-³* transition energy
shift of ¦E = 9480 cm¹1. This ¦E is comparable to that
observed between nonsubstituted thiophene (-max = 231 nm)
UV-vis peaks of spin-coated and cast films of HH-P3(C≡C-
Dec)Th17f and HH-P3(C≡C-Th-Dod)Th on a quartz glass plate
(cf. Figures S17 and S18) are shifted, e.g., by about 80 nm, to a
longer wavelength from that of the 1,2-dichlorobenzene solu-
tion. Cast film showed a larger red shift than spin-coated film.
After annealed at 130 °C, the UV-vis spectrum of the spin-
coated film essentially agreed with that of the cast film. By
annealing, the XRD peak becomes sharper as shown in
Figure S17. Similar differences in optical and XRD data
between spin-coated film, its annealed film, and cast film of
³-conjugated polymers have been reported.19
As shown in Figure S17, both the spin-coated and cast films
of HH-P3(C≡C-Dec)Th show sub-structures with an energy
difference of about 1370 cm¹1. The energy difference essen-
tially agrees with the Raman spectrum of HH-P3(C≡C-Dec)Th,
which contains a peak at 1388 cm¹1, as depicted in Figure S19.
The Raman peak is assignable to an asymmetric C=C
vibration,20 and the higher frequency of the Raman peak of
HH-P3(C≡C-Dec)Th than that (1379 cm¹1; cf. Figure S19) of
HT-P3HexTh suggests a higher order of ³-conjugation in HH-
¹1
and 2,2¤-bithiophene (-max = 302 nm2a and ¦E = 10180 cm
)
and gives additional support for the coplanar structure of the
dimer of 3-alkynylthiophene.
HH-P3(C≡C-Dec)Th,12a HH-P3(C≡C-Th-Dod)Th, and HH-
P3(C≡C-Ph)Th were not soluble in organic solvents at room
temperature. However, they were soluble in 1,2-dichloroben-
zene at high temperature (e.g., 130 °C), and the soluble state
had some stability even when their solutions were cooled
to room temperature; temperature dependent UV-vis spectra
of HH-P3(C≡C-Dec)Th,17e,17f have been reported. Figure S15
shows temperature dependent UV-vis spectra of HH-P3(C≡C-
Dec)Th, HH-P3(C≡C-Th-Dod)Th, and HH-P3(C≡C-Ph)Th in
1,2-dichlorobenzene. At high temperature of about 130 °C, they
showed a UV-vis peak at about 500-520 nm, and the UV-vis
peak shifts to a longer wavelength upon cooling. HH-P3(C≡C-
Dec)Th and HH-P3(C≡C-Th-Dod)Th gave rise to new
shoulder peaks at 600 and 650 nm, respectively.
CHCl3 and CH2Cl2 solutions of HT-P3HexTh showed
similar temperature-dependent changes in their UV-vis spectra