'Excimer’ fluorescence II. Lifetime studies of pyrene solutions

Abstract Measurements have been made of the concentration dependence of the rise and decay time characteristics of the monomer and excimer fluorescence of deoxygenated solutions of pyrene in cyclohexane at temperatures from 293 to 340 °K. Two independent methods were employed, one using a pulsed light source and a pulse-sampling oscilloscope, and the other a modulated light source and a phase and modulation fluorometer. In conjunction with observations of the monomer and excimer fluorescence quantum efficiencies, the results have been analyzed to determine the six rate parameters which describe the behaviour of the system. Values of 6.8 x 10-7 and 0.9 x 10-7s are obtained for the radiative lifetimes of the monomer and excimer, respectively. Excimer formation is shown to be a diffusion-controlled collision process, in which every collision between excited and unexcited molecules is effective. From the difference in the activation energies for excimer dissociation and formation, the excimer binding energy is found to be 0.34eV.