Chemistry Letters Vol.33, No.2 (2004)
157
Table 1. Absorption maxima,a absorption edges,a HOMO–
and width of the new wave increased with repeated sweeps
(Figure 3). These observations are characteristic of polymer for-
mation.6 Polymeric black films were deposited on the glassy car-
bon electrode for 1. Compounds 2 and 3 also revealed similar
characteristics. After polymerization, the electrode was kept at
0 V potential for several minutes to keep the polymer in an un-
doped state. The polymer-adsorbed electrode was washed with
solvent and their redox potentials were determined in a monomer
free electrolyte solution (Table 2). The oxidation potentials for
these polymers, poly-1, poly-2, and poly-3, were +0.91,
+0.72, and +0.67 V. The reduction potential was also observed
as a broad peak at ꢁ0:95 for poly-2 and at ꢁ0:60 V for poly-3
but could not be observed for poly-1. The relatively high oxida-
tion potential and lack of a reduction wave for poly-1 are attrib-
utable to the instability of its p-benzoquinone skeleton under
polymerization conditions and the structure of poly-1 may be
different from other CPDT based polymers. Polymerization
caused a large shift (0.45–0.69 V) in oxidation potentials but on-
ly small shift (0.03–0.07 V) in reduction potentials. These poly-
LUMO gaps, and redox potentialsb of azines (1–3)
c
Compd ꢂmax
/nm
ꢂedge
/nm, (eV)
Eox
E1=2
E1=2
red2
red1
V vs SCE
1
2
3
378 ꢂ630 (1.97) +1.36
370 ꢂ590 (2.10) +1.36
ꢁ0:52
ꢁ0:88
ꢁ0:75
ꢁ1:01
-
375 ꢂ600 (2.07) +1.36 ꢁ0:63 (2e)
aIn dichloromethane. bIn 1,2-dichloroethane containing 0.1 mol/
dm3 TBAP. Irreversible, peak potentials.
c
10
3
1
2.5
3
5
2
2
ε
1.5
0
500
800
1
0.5
0
ε
Wavelength / nm
mer films, as compressed forms, had a conductivity of 10ꢁ7
–
10ꢁ8 S cmꢁ1
.
250
350
450
550
650
Wavelength / nm
Figure 2. UV–vis spectra of 1 (solid line) measured in
dichloromethane and calculated with ZINDO-CI (bar graph: rel-
ative intensity). The absorption edges for 1–3 are shown as an
inset.
merization.6 These findings indicate that the oxidation potentials
are controlled by the CPDT structure. Conversely, the reduction
potentials were strongly dependent on the electron-accepting na-
ture of quinoid groups and decreased in the order of 2 > 3 > 1 as
expected from the sequence of quinone acceptors, i.e., the reduc-
tion potentials, ꢁ0:50 V for p-benzoquinone, ꢁ0:94 V for an-
thraquinone, and ꢁ0:65 V for 2-(10H-anthracen-9-ylidene)ma-
lononitrile. The sequence in reduction potentials is exactly the
reverse with the sequence of ꢂedge values in absorption spectra.
Thus, both absorption and electrochemical studies indicate that
both the ꢀEgap and the redox potentials can be controlled by
the systematic choice of donors or acceptors in this system.
Polymerization or oligomerization of CPDTs at 2-positions
generally decreases oxidation potentials.2,6 Electrochemical
polymerization in the present system would lead to further de-
creases in ꢀEgap. Multiple potential-sweeps ranging from 0.00
to 1.50 V were applied to 1 in 1,2-dichloroethane containing
0.1 M tetrabutylammonium perchlorate (TBAP). A new oxida-
tion wave appeared between +0.50–+1.30 V. The intensity
0
0.5
1
1.5
(V vs SCE)
Figure 3. Successive cyclic voltammograms of 1 measured in
1,2-dichloroethane containing 0.1 M TBAP.
This work was partially supported by the Research Founda-
tion for Young Scientists (B) (No. 14740354) from Ministry of
Education, Culture, Sports, Science and Technology, Japan.
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4
5
6
Table 2. Redox potentialsa of polymers
Polymer
Eox/V vs SCE
E1=2red/V vs SCE
b
Poly-1
Poly-2
Poly-3
+0.91
+0.72
+0.67
-
ꢁ0:95
ꢁ0:60
aIn 1,2-dichloroethane containing 0.1 mol/dm3 TBAP.
bNot observed.
Published on the web (Advance View) January 14, 2004; DOI 10.1246/cl.2004.156