PHOTOEXCITATIONS IN CONJUGATED COPOLYMERS

We report in this short paper a preliminary account on the optical cha racterization and photoexcitation of a class of novel conjugated polym ers consisting of regularly alternating thiophene and benzene sequence s, which might represent models for one-dimensional superlattices. Opt ical absorption and emission spectra suggest that the barriers produce d by the phenylene moieties do not interrupt the conjugation but can p roduce localization effects. Resonant Raman spectra indicate that a se lective response of the thiophene and phenylene moieties occurs by var ying the excitation energy from visible to ultraviolet. Moreover these measurements confirm the presence of a confinement on the thiophene b locks, while the biphenyl moiety does not appear to feel the energy ba rrier and behaves as a poly(paraphenylene) oligomer of 5-6 ring length . CW photomodulation spectra show that the formation of long-lived bip olarons takes place only if the thienylenic moiety is long enough to a ccomodate the lattice distortion.