Spectra of dimers of anthracene and its derivatives. I. Sandwich dimers

Abstract

Sandwich dimers are obtained by photochemical cleavage of dianthracene and related compounds in a rigid glass matrix at 77 K. Detailed studies of the absorption spectra, fluorescence spectra, and fluorescence lifetimes of symmetric dimers of anthracene and 9-substituted anthracenes (both molecules the same) and dissimilar dimers (one molecule anthracene, the other 9- or 9,10-substituted anthracene) have been made. Particular attention has been paid to these properties during dissociation of the dimers as the glass is allowed to soften. The fluorescence properties show a discontinuity during this dissociation. The excimer emission maxima (lifetimes about 200 ns) move a little to higher energy (lifetimes decrease to about 100 ns) then broad structure is observed in the spectra and lifetimes drop to about 5 ns. The fluorescence spectra of the dissimilar dimers are of the excimer type with lifetimes of about 100 ns. These values do not appear to be compatible with existing theories of the excimer state.