Rôle de la liaison hydrogène intra et intermoléculaire dans l'étude des propriétés spectroscopiques et photophysiques. Cas types: dérivés du carbazole

The absorption and fluorescence spectra along with the fluorescence quantum yields and lifetimes of the 1-cyano and 1-carboethoxy derivatives of carbazole in polar and non-polar fluids and in rigid solutions at 77 K have been investigated. The existence of the cyclic dimer has been confirmed for 1-cyanocarbazole in 3-methylpentane. The enthalpy and entropy of complexation are evaluated to be −39 kJ mol−1 and −78 J mol−1 K−1 respectively. No tautomeric species has been observed following excitation of the dimer. On the other hand, the intramolecular hydrogen bonding system always predominates in the gas phase and in non-polar solvents in the ground electronic state. This intramolecular hydrogen bonding has been shown to be broken in ethanol, where intermolecular hydrogen bonding to the solvent takes place. 1-Cyano carbazole follows the same behaviour in ethanol. All the 1-substituted derivatives of carbazole show exciplex fluorescence in ethanol and the formation of these exciplexes has been explained by the strong charge transfer character involved in the excited 1Lb states of these molecules.