Primary carrier-generation process in Y-form and phase I titanyl phthalocyanines

We have studied the primary process of the photocarrier generation in Y-form and phase I titanyl phthalocyanine (TiOPc) microcrystallites using the electric-field-modulated picosecond time-resolved fluorescence spectroscopy. The electric-field dependence of the fluorescence amplitudes and lifetimes of TiOPcs leads to a detailed understanding of excited-state charge-transfer (CT) character. We have concluded that only the shorter-lifetime singlet exciton of the Y-form has significant CT character. We regard the CT exciton as a key to the high photocarrier-generation quantum yield of the Y-form. The lack of a CT state in phase I TiOPc causes its low photosensitivity.