Joint theoretical and experimental study of the UV absorption spectra of polybenzoxazoles

A series of conjugated rigid-rod polymers, poly(p-phenylene benzobisoxazole) (PBO), poly(benzobisoxazole-2,6-diylvinylene) (PBOV), poly(benzobisoxazole-2,6-diyldivinylene) (PBODV) have been synthesized. UV absorption spectroscopy has been used to investigate the optical properties of these polymers in methanesulfonic acid (MSA) or in films. The results show that the introduction of vinyl segments into the poly(benzobisoxazole)s backbone narrowed the optical bandgap of this class of polymers. The UV spectra of the polybenzoxazole can be well predicted with the polybenzoxazole models by the semiempirical method AM1/ZINDO (Austin Method 1/Zerner’s intermediate neglect of differential overlap), coupled to single configuration interaction. The UV spectra of polymers in MSA solution were red-shifted from that of the thin films and the theoretical UV spectra. The AM1/ZINDO-CI calculations of protonated PBO at N heteroatom suggest that the red shift is due to the protonation effect. q 2004 Elsevier B.V. All rights reserved