Vibronic Quantum Effects in Fluorescence and Photochemistry. Competition between Vibrational Relaxation and Photochemistry and Consequences for Photochemical Control

Abstract

In this paper we measured the fluorescence quantum yield (ΦF) and the reaction quantum yield (ΦPC) of a photochromic molecule (flindersine) as a function of the vibronic level (n) excited within a given sequence. We found that ΦF decreased and ΦPC increased with an increase in the quantum number of the vibronic level excited within a sequence. On the basis of a previously proposed model, this behavior was interpreted as resulting from competition between vibrational relaxation and photochemistry at each vibronic level. This model was broadened, and a new equation developed which, alone, or in combination with fluorescence data, permits determination of (1) the molar extinction coefficient of the partially produced colored form, (2) the quantum yield of vibrational relaxation, ΦV, and the complementary ΦPC at each vibronic level, (3) the photochemical reaction rate constant, kPC, (4) the nonradiative internal-conversion rate constant from S1 to S0, kNR, and (5) the vibrational relaxation rate constant amon...