DIFFUSION-LIMITED EXCITON FUSION REACTION IN ONE-DIMENSIONAL TETRAMETHYLAMMONIUM MANGANESE TRICHLORIDE (TMMC)

We present results of an experimental study on the reaction kinetics o f a one-dimensional diffusion-reaction system, on a picosecond to mill isecond time scale. Tetramethylammonium manganese trichloride (TMMC) i s a perfect model system to study this problem. Time-resolved luminesc ence of TMMC has been measured over nine decades in time. The nonexpon ential shape of the luminescence decay curves depends strongly on exci ting laser power. This is shown to result from a fusion reaction (A A --> A) between photogenerated excitons, which is very well described by the diffusion-limited single-species fusion model for initial exci ton densities < 2 x 10(-3) (fraction of the number of sites). At highe r initial exciton densities the diffusion process, and thus the reacti on rate, is significantly influenced by the heat produced in the fusio n reaction. This is supported by Monte Carlo simulations.