Bichromophores symétriques: torsion intramoléculaire sans transfert de charge à l'état électronique excité S 1 dans le dicarbazyle- N,N′

Abstract

N,N′-dicarbazyl (NNDC) was investigated in the gas phase and in fluid and rigid solutions of non-polar and polar protic and aprotic solvents over a wide temperature range (77 – 300 K). A comparison of the spectral and photophysical parameters in a series of N-substituted carbazole derivatives allows us to conclude that the symmetry of the relaxed excited singlet S 1 state in NNDC has been lowered compared with that in the electronic ground state. We have shown that the 90° geometry in the excited Franck—Condon state is transformed to an oblique geometry through intramolecular interaction processes only. This is in contrast with the only other well-studied symmetrical bichromophoric system, 9,9′-bianthryl, where a polar-solvent-induced charge transfer operates in the Franck—Condon excited state relaxation process.