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 ele ctrochemical and linear optical properties of a series of pi-conjugate d rigid-rod poly(benzobisazoles), including three new polymers, were e xplored by cyclic voltammetry and measurement of the optical dispersio n of the refractive index. The electrochemical reduction of the polyme rs 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 affinit y, and ionization potential of the series of polymers was related to t he variation in backbone structure. The electron affinity of the polym ers was 2.4-3.0 eV, which indicated that the LUMO energy level was tun able by up to 0.6 eV. The ionization potential (5.2-5.7 eV) and associ ated HOMO level of the polymers was tunable by up to 0.5 eV. The measu red wavelength dispersion of the refractive index of the polybenzobisa zoles showed that n(lambda = 1064 nm) and n(lambda = 2500 nm) were 1.7 4-2.03 and 1.55-1.95, respectively. The large refractive index variati on with molecular structure was satisfactorily accounted for by the co mpeting effects of polarizability and molar volume. These results prov ide a basis for understanding the electronic, optoelectronic, and opti cal properties of the conjugated poly(benzobisazoles) in terms of the underlying molecular and electronic structures.