EFFECTS OF MOLECULAR-STRUCTURE ON THE ELECTROACTIVE AND OPTICAL-PROPERTIES OF CONJUGATED RIGID-ROD POLY(BENZOBISAZOLES)

The effects of molecular structure on the electronic structure and electrochemical and linear optical properties of a series of pi-conjugated rigid-rod poly(benzobisazoles), including three new polymers, were explored by cyclic voltammetry and measurement of the optical dispersion of the refractive index. The electrochemical reduction of the polymers was reversible, whereas oxidation was not reversible in accord with the electron-deficient nature of the benzobisazole ring. The observed variation of the reduction and oxidation potentials, electron affinity, and ionization potential of the series of polymers was related to the variation in backbone structure. The electron affinity of the polymers was 2.4-3.0 eV, which indicated that the LUMO energy level was tunable by up to 0.6 eV. The ionization potential (5.2-5.7 eV) and associated HOMO level of the polymers was tunable by up to 0.5 eV. The measured wavelength dispersion of the refractive index of the polybenzobisazoles showed that n(lambda = 1064 nm) and n(lambda = 2500 nm) were 1.74-2.03 and 1.55-1.95, respectively. The large refractive index variation with molecular structure was satisfactorily accounted for by the competing effects of polarizability and molar volume. These results provide a basis for understanding the electronic, optoelectronic, and optical properties of the conjugated poly(benzobisazoles) in terms of the underlying molecular and electronic structures.