Investigation of carbazole derivatives and their van der Waals complexes in the jet by laser-induced fluorescence spectroscopy

Laser-induced fluorescence (LIF) spectra of jet-cooled carbazole, N-ethylcarbazole (EC), N-phenylcarbazole (PC), N-(4-cyanophenyl)carbazole (CPC) and N-anthrylcarbazole (AC) are presented and analysed. Perpendicularity is proposed in the ground state geometry of PC and CPC, in contrast with the twisted angle in AC, and these ground state configurations of PC and CPC are preserved on electronic excitation, but not in AC. The electron distribution on the nitrogen atom in the carbazole moiety is used as a basis to explain the differences in the spectral shifts of the substituted carbazoles with respect to the bare carbazole chromophore. PC complexes with argon atoms, non-polar and polar molecules were investigated and compared with those of CPC and EC. Intermolecular vibrational modes were observed in several PC complexes. The similarity of the spectral shifts of PC complexes to those of CPC indicates that they have very similar properties under jet conditions, in contrast with observations in acetonitrile solution. No twisted intramolecular charge transfer (TICT) took place for PC and CPC, where the perpendicularity is preserved on electronic excitation, which is in agreement with the fact that TICT fluorescence emission was not observed in the jet for CPC-acetonitrile complexes.