Stochastic Cellular Automata Models of Molecular Excited-State Dynamics

A probabilistic asynchronous cellular automaton described previously [Seybold, Kier, and Cheng, J. Chem. Info. Comput. Sci. 1997, 37, 386-391] has been applied to the description of molecular excited-state dynamics. The model simulates in a visual, time-dependent fashion the variations in groundand excited-state populations that occur under stipulated probabilistic transition rules. Both pulse mode and steady-state conditions can be simulated. The deterministic values for the fluorescence lifetime (τf), the phosphorescence lifetime (τp), and the quantum yields of fluorescence (φf), triplet state formation (φT), and phosphoresence (φp) arise as limiting cases for large numbers of cells or large numbers of trials. Since each trial is an independent “experiment”, stochastic variations in the populations and properties can be estimated from repeated trials. Phenomena such as ground-state depletion and population inversion under high radiation intensity arise naturally within the model.