Ultrafast optical probes of electronic excited states in linear trans-quinacridone

Time-resolved photoluminescence and transient photobleaching studies in the γ-polymorph of linear trans-quinacridone (QAC) are reported. A dramatic change in the luminescence spectrum is observed with subnanosecond delays. Fluorescence excitation spectra support the hypothesis on the different origin of the time-resolved spectra. The observed spectra and temporal behaviour of excited states are reconciled by assuming the emitting states to be a mixture of neutral molecular excitons and charge-transfer states. Their role in the charge separation process is discussed in relation to electromodulation of optical response (absorption, emission) and photoconductivity in QAC.