Intramolecular relaxation processes in a singlet excited naphthalene–acridine bichromophoric molecule in solution and in a supersonic jet expansion

Intramolecular electronic relaxation processes in a flexible naphthalene–acridine bichromophoric molecule I were studied in solution and in a supersonic jet expansion. Intramolecular electronic energy transfer (intraEET) from the electronically excited naphthalene unit to the acridine moiety and an additional non-radiative decay process, probably intramolecular electron transfer (intraELT) to the acridine unit, of the excited naphthalene group was observed in solution. In a supersonic jet expansion, no indication for intraEET or other interchromophoric interactions was found. The relaxation of the excited naphthalene chromophore in I, under the conditions of supersonic jet expansion, is dominated by intrachromophoric radiationless transitions. The dependence of single vibronic fluorescence lifetimes of jet-cooled I on the excitation frequency is discussed.