SYNTHESIS AND PROCESSING OF HETEROCYCLIC POLYMERS AS ELECTRONIC, OPTOELECTRONIC, AND NONLINEAR-OPTICAL MATERIALS .4. NEW CONJUGATED RIGID-ROD POLY(BENZOBIS(IMIDAZOLE))S

New conjugated rigid-rod poly(benzobis(imidazole))s incorporating varying lengths of trans-polyene segments and 1,4-phenylenebis(vinylene) linkages have been synthesized and characterized by infrared, H-1 MMR, and electronic absorption spectra. Thin films of the polymers were prepared from their soluble coordination complexes. The pi-pi* optical band gap of thin films of the new polymers was in the range 1.8-2.3 eV which is smaller than the corresponding poly(benzobis(thiazole))s. In spite of the structural modifications which ensure strong interchain interactions in the new polymers, they still exhibit significant moisture sensitivity, absorbing equilibrium moisture of similar to 6-9 wt % which is however smaller than the well-known poly(1,3-phenylenebibenzimidazole) (PBI) which absorbs similar to 15 wt %. It is suggested that the moisture sensitivity of the poly(benzobis(imidazole))s is intrinsic to the N-H group and also partly explains the luminescence quenching in thin films. However, the poly(benzobis(imidazole))s are highly fluorescent in dilute solution.