Carbon-Bridged Oligo(phenylenevinylene)s: Stable π‑Systems with High Responsiveness to Doping and Excitation

The high responsiveness of π-conjugated materials
to external
stimuli, such as electrons and photons, accounts for both their utility
in optoelectronic applications and their chemical instability. Extensive
studies on heteroatom-stabilized π-conjugated systems notwithstanding,
it is still difficult to combine high performance and stability. We
report here that carbon-bridged oligo­(p-phenylenevinylene)­s
(COPV-n) are not only more
responsive to doping and photoexcitation but also more stable than
the conventional p-phenylenevinylenes and poly­(3-hexylthiophene),
surviving photolysis very well in air, suggesting that they could
serve as building blocks for optoelectronic applications. Activation
of the ground state by installation of bond angle strain toward the
doped or photoexcited state and the flat, rigid, and hindered structure
endows COPVs with stimuli-responsiveness and stability
without recourse to heteroatoms. For example, COPV-6 can
be doped with an extremely small reorganization energy and form a
bipolaron delocalized over the entire π-conjugated system. Applications
to bulk and molecular optoelectronic devices are foreseen.