STUDY OF CARRIER GENERATION IN TITANYL PHTHALOCYANINE (TIOPC) BY ELECTRIC-FIELD-INDUCED QUENCHING OF INTEGRATED AND TIME-RESOLVED FLUORESCENCE

We have studied the influence of electric field and humidity on photoc onductivity and fluorescence in particles of highly photoconductive Y- form TiOPc dispersed in a poly(vinylbutyral) polymer matrix. Both inte grated and time-resolved fluorescence quenching by electric field were measured. Integrated fluorescence quenching showed a linear dependenc e at low applied fields and a linear correlation with carrier generati on efficiency. Time-resolved fluorescence decays were analyzed by fitt ing the data to a sum of two exponentials representing fast and slow f luorescence components. Qualitative features of fluorescence decay wer e the same for low and high humidity levels. The amplitude and lifetim e changes of the two fluorescence components upon the application of t he electric field are in agreement with theory which describes energy transfer between free and trapped exciton states. These results indica te that carrier generation in Y-TiOPc originates from both relaxed and nonrelaxed intrinsic excited singlet states, while the trapped excito ns do not lead to significant carrier production. The field dependence of integrated fluorescence quenching supports the existence of a carr ier precursor state with charge-transfer character.