CHARACTERIZATION OF THE TRIPLET TRIPLET ANNIHILATION PROCESS OF PYRENE AND SEVERAL DERIVATIVES UNDER LASER EXCITATION

Under conditions of pulsed laser excitation, pyrene and several of its substituted derivatives readily show P-type delayed fluorescence originating from triplet-triplet annihilation (TTA); this emission shows high contributions from excimer emission under conditions where only monomer fluorescence is observed from singlet states formed by direct excitation by the laser pulse (prompt emission). The effect observed in the delayed fluorescence results from the formation via TTA of excited singlet states (monomer or excimer) in a solvent cage that always contains two pyrene molecules. TTA rate constants approach diffusion control when spin-statistics are taken into account. Substituted pyrenes show wide variations in the excimer-to-monomer ratio for the delayed fluorescence. In particular, the ratio for pyrenedodecanoic acid (PDA) in polar solvents is similar to dodecylpyrene (DPY) in cyclohexane, but the ratio is much higher for PDA in nonpolar solvents. The effect is attributed to carboxylic association during the TTA encounter that assists excimer formation. P-type delayed fluorescence in pyrenes may prove useful as a probe for mobility in organized systems. © 1990, American Chemical Society. All rights reserved.