Global compartmental analysis of the fluorescence decay surfaces of the excimer of 1-cyanopyrene and of the exciplex of 1-cyanopyrene with 1,2-dimethylindole in toluene

Abstract

Global compartmental analysis was used to analyze the kinetics of excimer formation of 1-cyanopyrene and of exciplex formation between 1-cyanopyrene and 1,2-dimethylindole in toluene at room temperature. The fluorescence decay surface of the exciplex between 1 -cyanopyrene and 1,2-dimethylindole was analyzed in terms of a bicompartmental model. The following values were obtained for the rate constants: k01 = (4.830 ± 0.004) × 107 s-1, k21 = (1.140 ± 0.003) × 1010 M-1s-1, k02 = (1.128 ± 0.001) × 107 s-1. The rate constant for exciplex formation (k21) was virtually diffusion controlled while that for exciplex dissociation (k12) was negligibly small. k01 and k02 are the first-order rate constants for deactivation of the locally excited state of 1-cyanopyrene and of the exciplex, respectively. There was no evidence for ground-state aggregates between 1-cyanopyrene and 1,2-dimethylindole in the concentration range used (up to 0.012 M). The rate constant values for excimer formation of 1-cyanopyrene were similarly obtained by global bicompartmental analysis yielding values for k01 = (4.820 ± 0.004) × 107 s-1, k31 = (6.43 ± 0.03) × 109 M-1 s-1, k03 = (2.054 ± 0.004) × 107 s-1. The rate constant for excimer dissociation (k13) was negligible. k03 is the rate constant for deactivation of the excimer whereas k31 is the rate constant for excimer formation. The fluorescence decay surface of excimer-forming solutions of 1-cyanopyrene was measured as a function of 1,2-dimethylindole concentration and then globally analyzed in terms of a tricompartmental model with additional quenching of the excimer by 1,2-dimethylindole. In this system there are three excited-state species: the locally excited state of 1-cyanopyrene, the excimer of 1-cyanopyrene and the exciplex between 1-cyanopyrene and 1,2-dimethylindole. The global analysis in terms of three excited-state compartments yielded values for the rate constants which agreed very well with those obtained from the separate bicompartmental analyses. The rate constant for quenching of the excimer by 1,2-dimethylindole was estimated to be (3.98 ± 0.07) × 109 M-1 s-1. The decay parameters obtained by global tricompartmental analysis were used together with the steady-state fluorescence spectrum to construct the three species-associated emission spectra. This represents the first application of global tricompartmental analysis in the field of photophysics. © 1993 American Chemical Society.