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 fo ur 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, th us resulting in red materials with conjugated segments larger than a s ingle thiophene ring. However, poly[(alpha- bithienylene)methylenes], poly[(alpha-terthienylene)methylenes], and poly[(alpha-quaterthienylen e)methylenes] were obtained with optical absorption spectra and pi-con jugation lengths characteristic of the isolated thiophene oligomers. T he chemical and physical properties of the poly(heteroarylene methylen es) such as the glass transition temperature (T-g) and solubility were significantly modified by the variation of the size of the oligomer i n the main chain and by the side group substitution at the bridge carb on. The new polymers are useful precursors to small-bandgap polymers b ased 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.