Spectroscopic study of carbazole by photoselection

The polarization of transitions linking the ground state with the lower-lying electronic states of carbazole and its N-ethyl, N-isopropyl, N-vinyl, and N-phenyl derivatives is determined using photoselection techniques. The first absorption band as well as the fluorescence and phosphorescence emissions exhibit wavelength dependent polarizations, indicating the presence of a significant amount of forbidden character in these transitions. The second and third absorption bands of carbazole and its N-alkyl derivatives have been found to be uniformly polarized along the long in-plane molecular axis. The N-vinyl and the N-phenyl carbazoles are shown to exhibit new spectral features at wavelengths to the blue of the second electronic transition.