Spectra and nature of the electronic excited states of 2,3-dibromonaphthalene single crystals

Abstract

Absorption and emission spectra of single crystals of 2,3-dibromonaphthalene (23DBN) were measured at 5 K. Stokes shift between the absorption edge and the onset of weak fluorescence indicated intermolecular charge transfer (CT) character of the electronic transition between the singlet states. Theoretical analysis performed with the aid of quantum chemistry methods showed that CT operated between 23DBN molecules belonging to two subgroups within the crystal unit cell. Structured phosphorescence, enhanced by the heavy-atom (Br) effect, had a local character. Vibronic structure of this emission, in the first approximation, was described by the spectrum calculated for an isolated 23DBN molecule. Simulation of the spectrum details required more advanced computations taking into account the whole crystal unit cell with 8 molecules of 23DBN.