POLING BEHAVIOR OF OPTICAL-ABSORPTION SPECTRA IN CARBAZOLES WITH ONE-DIMENSIONAL AND 2-DIMENSIONAL CHARGE-TRANSFER CHARACTER

Spectral change in optical absorption due to molecular alignment induc ed by electric poling has been studied experimentally and theoreticall y, in one- and two-dimensional charge-transfer carbazole molecules. Af ter poling, an increase in absorbance at lambda(max) was observed in 3 ,6-dinitrocarbazoles which present a two-dimensional charge-transfer c haracter, while the absorbance at lambda(max) decreased in 3-monosubst ituted carbazoles which possess a one-dimensional charge-transfer char acter. From molecular-orbital calculations and evaluations of the mole cular polarizability spectra for random and uniaxial orientations of t he molecules, an explanation is provided for the poling behavior in te rms of the vector directions of the transition and ground-state dipole moments of the molecules. Theoretical investigation of various confor mers has been made, resulting in the suggestion that the poling behavi or of absorption spectra should be strongly affected by the conformati on of the acceptor groups in the case of disubstituted. carbazoles. (C ) 1996 American Institute of Physics.