Concentration effect on delayed emissions: 1,4 dibromonaphthalene host-pyrene guest mixed crystal system

Abstract

In 1,4 dibromonaphthalene (DBN) crystal, phosphorescence emission is observed in conformity with quasi-one-dimensional exciton motion. In pyrene doped DBN crystal, fairly intense delayed fluorescence (DF) and delayed excimer fluorescence (DEF) are observed on host singlet excitation though prompt excimer fluorescence (EF) is absent. EF emission, however, is observed on pyrene singlet excitation. These results suggest that host triplet excitons are trapped more efficiently at monomeric pyrene sites than at nascent excimeric pyrene sites. From temperature and guest concentration dependence studies of delayed emission intensities and lifetimes it is concluded that homofusion of an adventitious defect triplet and heterofusion of this defect with guest triplets produce DF and DEF at low temperature but at high temperature homofusion of guest triplets is the generative event of these delayed emissions.