  Optical absorption spectra of poly(thiophene vinylene) (PTV) conjugated
polymers have been studied at room temperature in the spectral range of 450 to
800 nm. A dominant peak located at 577 nm and a prominent shoulder at 619 nm
are observed. Another shoulder located at 685 nm is observed at high
concentration and after additional treatment (heat, sonification) only.
Equilibrium atomic geometries and optical absorption of PTV conjugated polymers
have also been studied by first principles density functional theory (DFT). For
PTV in solvent, the theoretical calculations predict two equilibrium geometries
with different interchain distances. By comparative analysis of the
experimental and theoretical data, it is demonstrated that the new measured
long-wavelength optical absorption shoulder is consistent with new optical
absorption peak predicted for most energetically favorable PTV phase in the
solvent. This shoulder is interpreted as a direct indication of increased
interchain interaction in the solvent which has caused additional electronic
energy structure transformations.
