THE EFFECT OF SIDE-GROUP SUBSTITUTION ON THE ENERGY GAPS OF PHENYLENE AND THIENYLENE OLIGOMERS AND POLYMERS

Polymer properties were studied by band structure calculations on polymers and using large oligomers. MNDO semi-empirical energy band theory was used for determination of the fully optimized geometry of poly(thienylene vinylene), poly(p-phenylene), poly(phenylene vinylene) and their substituted derivatives. The optimized structures were used in extended Huckel energy band structure calculations to determine the variation of the bandgap caused by substitutions. Polymer properties were also modeled by CNDO/S calculations of the electronic spectra of large oligomers. Both these approaches explain the observed reduction of the energy gap induced by the methoxy side group.