STABILIZATION OF CARBAZOLE RADICAL CATION FORMED IN POLY(N-VINYLCARBAZOLE) BY CHARGE DELOCALIZATION

The transient absorption spectra (charge-resonance (CR) band) of poly(N-vinylcarbazole) (PVCz) and the copolymers of N-vinylcarbazole (VCz) with methyl methacrylate and vinyl acetate were measured by laser photolysis to investigate the charge delocalization in the polymers. For the copolymers in which the fraction of VCz (fvcz) is less than 0.4, the CR band appeared at ca. 1800 nm. In the case of fvcz > 0.5, the CR band was shifted to longer wavelengths with increasing fvcz and the copolymer with fvcz = 0.83 showed the same transient absorption spectrum as PVCz. By considering the sequential distribution of the copolymers, the charge formed in PVCz was found to be delocalized among more than two chromophores. For the copolymer (fvcz = 0.07) having no neighboring chromophore interaction, the radical-cation transfer to a series of amines was measured to investigate the free energy change (ΔG) dependence of an electron-transfer rate constant (ke). The result shows that there is a linear relationship between log ke and ΔG. By using this relationship, the stabilization energy of the carbazole radical cation in PVCz was estimated to be 0.5 ± 0.1 eV. This value is larger than that of the carbazole dimer radical cation, i.e., the stabilization by the charge delocalization among more than two chromophores is stronger than that of the dimer radical cation. © 1990, American Chemical Society. All rights reserved.