2398
K. R. Idzik et al. / Tetrahedron Letters 51 (2010) 2396–2399
Table 1
As the direction of the polarization potential is changed, a reduc-
tion process take place, as shown by two peaks located at 0.28
and À0.57 V. The sharp and reversible spike in the cyclic voltam-
mogram could indicate a phase transformation,11 or a transition
between hydroquinone and quinone-like states.12 The second
broad polymer oxidation peak indicates a variety of chain lengths.
The first cyclic wave differs significantly from the subsequent
ones. It is observed as shift of the first and second oxidation peak
potential and their peak current ratio, however total charge con-
sumed during oxidation process remains the same. During subse-
quent cycles the first peak current increases and the second peak
decreases. The electrochromical behavior of the polymeric film
was observed during doping process. As the potential reached
the first oxidation stage, a rapid change from black to colorless
occurred. Future studies are required to clarify nature of this unu-
sual oxidation behavior.
Poly(2d) is stable, as indicated by the lack of a significant
change in its anode current during multiple doping and dedoping
processes within the range between À1.1 and 0.8 V. Poly(2d) is
only p-doped. Different conditions were employed, like different
scan rates, solvents and electrolytes, in order to record an n-doping
process, however it was not successful.
In the case of 2d oxidation, changes in color from a colorless
monomer solution, through to a greenish, then brown solution,
was observed. The solution of 2e was yellow. These phenomena oc-
curred both in acetonitrile as well as dichloromethane. UV–vis
spectra, before and after electrooxidation, confirmed that much
of the initial products diffused from the electrode surface to the
solution. This indicates the formation of soluble oligomers in the
initial phase of electropolymerization.
Electrochemical and optical results
ox
onset ox
ox
Compound
Em
Ep
(V)
Ep (V)
kmax
Eg (eV)
2a
2b
2c
2d
2e
1.02
1.13
0.81
0.55
0.57
0,61
0,87
0,33
0.69
*
0.51
À0.37
0.16
307
291
318
484
363
2.80
3.34
2.64
2.00
2.73
À0,53
À0,005
Where Emox is the monomer oxidation, Eponset ox is the polymer oxidation onset, Ep
is the oxidation, kmax is the polymer absorption maximum, and Eg is the HOMO–
LUMO gap. *Ill-defined peak.
ox
meta position13 enable the creation of polymers with a definite
conjugated length. The incorporation of groups that enable cou-
pling between arms may lead to low bandgap CPs.
Based on an effective, iterative, palladium-catalyzed cross-cou-
pling protocol, a homologous series of triarylbenzene and triaryl-
phenol derivatives have been synthesized with good yields. All
monomers undergo electropolymerization, which resulted in thin
film formation directly on the electrode. In all cases the cyclic vol-
tammograms of compounds, as well as UV–vis spectra, and visual
observations of forming colored films confirm deposition of the
polymers on electrode surface. In addition, based on the data set
obtained from the optical and electrochemical measurements,
the structure–property relationships were established, which give
further information about the nature of the parent oligoarylenes.
Polymers produced in the process of electropolymerization con-
taining thienyl and EDOT groups demonstrated good conductivity.
The attachment of a hydroxyl group dramatically changed the
properties of both monomers and polymers by decreasing their
oxidation potentials and Eg values, as well as improving the stabil-
ity of films. Taken together, these data lay the foundation for fur-
ther research into the possible use of these materials in organic–
electronic devices such as organic light-emitting diodes (OLEDs),
organic field-effect transitors (OFETs), and organic solar cells.
Polymer films of compounds 2a, 2b, 2c, and 2e demonstrate
strong adhesion to the electrode surface, even in solvents, in
contrast to poly(2d), which under the influence of CH3CN, easily
diffused away from the surface.
The basic electrical and optical properties of the formed films
are collected in Table 1. As expected, the electron-donating effect
of the hydroxyl groups attached to benzene ring results in a
decreasing oxidation potential. In the case of the furan arms, the
hydroxyl substituent lowers the oxidation potential about 0.88 V.
An even greater decrease is observed for polymers with thiophene
moieties.
Acknowledgements
This work was supported by grant of Ministry of Science and
Higher Education NN205106935. This work was supported by the
European Community from the European Social Fund within the
RFSD 2 project. This work was also realized within the European
Union Project (SNIB, MTKD-CT-2005-029554).
The UV–vis absorption spectrum of the neutral form of the poly-
mer films confirms the high impact of the hydroxyl substituent.
The energy bang gaps (Eg), as determined from the onset of the
References and notes
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