Fluorescence depolarization in organized media. Two-excited-state reactions controlled by orientation-dependent kinetic rates. I. Theory

Abstract

Articles you may be interested inTime-dependent density functional theory excited state nonadiabatic dynamics combined with quantum mechanical/molecular mechanical approach: Photodynamics of indole in water J. Chem. Phys. 135, 054105 (2011); 10.1063/1.3622563 Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a π σ reaction intermediate A model describing fluorescence depolarization of fluorophores undergoing the two-ground-and two-excited-state reactions in ordered systems, is discussed. It is assumed that the rates for state-to-state kinetic relaxation process are dependent on angular orientation of fluorophores, and that this process is controlled by fluorophore-matrix ground-and excited-state aligning interactions and by rotational dynamics. The evolution of the two-excited-state system is described by the equation of motion composed of a set of two differential equations for the Green functions, coupling state-dependent molecular ordering and rotational dynamics with the orientation-dependent kinetic relaxation. A method of solving the motion equation is outlined. The main properties of the solution to motion equation and its information content on angular alignment and potential-restricted rotational dynamics of fluorophores, are discussed in detail. An illustrative example manifesting the effect of orientation-dependent excited-state reversible interconversion process on fluorescence depolarization, is presented. Two experimental arrangements enabling the recovery of the model parameters are presented and discussed. Possible applications of the model to different cases important from the experimental point of view, are indicated and discussed.