Distortion of the fluorescence spectrum of anthracene with increasing laser pulse excitation energy

An anthracenc solution in cyclohexane was subjected to continuous 354 nm laser pulse excitation under conditions that lead to amplified spontaneous emission (ASE) laser spikes in strongly fluorescent molecules. Instead of ASE spike development, the fluorescence spectrum of anthracene undergoes distortion that becomes increasingly pronounced with increasing excitation laser-pulse energy (0.10-13 mJ/pulse). On the assumption that the distortion is due to absorption of the fluorescence by transient excited states, an effective transient absorption spectrum is derived that is primarily composed of a combination of the known T-n <-- T-1 and S-n <-- S-1 anthracene spectra. The filtering of the fluorescence by the Tn <-- T-1 absorption is prominently expressed in a splitting of the vibronic band at ca. 23 500 cm(-1) as predicted earlier.