Instantaneous fluorescence quantum yield of organic molecular systems: information content of its intensity dependence

Abstract

In pulse laser investigations of systems of fluorescent organic molecules (e.g. aggregates, light harvesting antennas) it is usual to derive from the intensity dependence of time-integrated fluorescence (fluorescence yield) conclusions on deactivation channels, bimolecular interaction and sizes of interacting units (“domains”), though the content of information of this type of measurement is restricted because the shape of this function is hardly structured. Especially when further processes take place (e.g. excited singlet absorption) problems of ambiguity arise. Based on analytical investigations of the adapted rate equation system of noncoherent nonlinear light-matter interaction, especially of the asymptotic behaviours of its solution with respect to the excitation intensity, we propose a new measuring quantity “instantaneous fluorescence quantum yield”, which in its intensity dependence reflects far more sensibly the several excited state processes and therefore should allow the characterization of absorption, relaxation, and annihilation quantitatively and in a unique way.