Photophysical study of two carbostyril dyes: investigation of the possible role of a rotary decay mechanism

The photophysical behaviour of two carbostyrils used as layer dyes has been investigated. From a study of the solvent polarity dependence of the fluorescence properties we have shown that twisting of the amino or dimethylamino group does not affect the photophysical behaviour of carbostyrils. The results of AM1 calculations clearly show unfavourable energetics for the rotary decay process in carbostyrils. The keto form of the carbostyrils is shown to be the only absorbing and emitting species. In light of the present results, a reinvestigation of the fluorescence properties of structurally similar coumarins seems to be necessary.