SMALL-BANDGAP CONDUCTING POLYMERS BASED ON CONJUGATED POLY(HETEROARYLENE METHINES) .1. PRECURSOR POLY(HETEROARYLENE METHYLENES)

A series of 20 new poly(heteroarylene methylenes) containing one to four a-thiophene rings alternating with an sp(3)-carbon atom in the main chain were synthesized and characterized. The 11 as-synthesized poly[(2,5-thienylene)methylenes] were found to be highly dehydrogenated, thus resulting in red materials with conjugated segments larger than a single thiophene ring. However, poly[(alpha- bithienylene)methylenes], poly[(alpha-terthienylene)methylenes], and poly[(alpha-quaterthienylene)methylenes] were obtained with optical absorption spectra and pi-conjugation lengths characteristic of the isolated thiophene oligomers. The chemical and physical properties of the poly(heteroarylene methylenes) such as the glass transition temperature (T-g) and solubility were significantly modified by the variation of the size of the oligomer in the main chain and by the side group substitution at the bridge carbon. The new polymers are useful precursors to small-bandgap polymers based on poly(heteroarylene methines) and are also useful model systems for the investigation of the effects of pi-conjugation length on the electronic and optical properties of conjugated polymers.