Intramolecular delocalization of Π electrons in polythiophenes with fixed conformation: A spectroscopic study

The main feature of β,β′-bridge–α,α′-bithienyls is that their conformation is controlled by the bridge length. This class of molecules could be useful for the understanding of the intra and intermolecular processes which determine the conductivity of the corresponding polymers. In this work we have recorded and studied (i) the electronic spectra of the monomers, (ii) the vibrational spectra (IR, Raman λexc=514 nm, FT–Raman λexc=1064 nm) of the monomers and polymers in the pristine state, (iii) the IR spectra of the doped polymers, and (iv) the IR spectra (probe) of the polymers photoinduced by visible light (pump). The interpretation of the spectra is made in terms of the ‘‘effective conjugation coordinate’’ theory. Poly(cyclopentabithiophene) P(T+1) has the largest π-electron delocalization with a wide distribution of conjugation lengths. In poly(cycloheptabithiophene) P(T+3) π electrons are highly localized, while an intermediate situation is observed in poly(dihydrobenzobithiophene) P(T+2). The various aspects of intra and intermolecular hopping of charge carriers are discussed.