KINETIC AND SPECTROSCOPIC STUDY OF TRIPLET-STATE AND IONIC PATHWAYS IN THE LASER-INDUCED PHOTOEXCITATION OF N-ETHYLCARBAZOLE IN FLUID SOLUTIONS

When fluid solutions of N-ethylcarbazole (NEC) are irradiated by 308-nm pulses from an excimer laser, transient triplets and ions may be observed in the microsecond time regime. The formation of ions is favored in more polar solvents such as acetonitrile (AcN) and that of triplets in nonpolar solvents such as paraffin oil. The quantum yield of triplet formation from initial excitation is 0.23. Triplet states decay through concurrent first- and second-order channels: the second-order process, triplet-triplet annihilation, leads to formation of excited singlet states with an efficiency of 0.12. Transient carbazolyl cations and anions display double-exponential decays. To account for this behavior, a mechanism involving initial electron donation by the multiply excited chromophore to a nearby NEC molecule or solvent molecule is proposed; subsequent decay occurs primarily by geminate recombination of the resulting ion pair. The quantum yield for cation production is 0.037. Delayed fluorescence in AcN also decays by a double-exponential decay curve with rate constants, suggesting that the emission arises mainly from ion recombination.