Modelling of geminate annihilation in quasi-one-dimensional solids

Exciton migration processes in the liquid-crystal mesophase of phthalocyanines and porphyrins exhibit extreme anisotropy, so a diffusion-based analysis of the kinetics of annihilation may not be suitable, even if the appropriate three-dimensional diffusion tensor is used. A simulation technique incorporating the crystal structure of a quasi-one-dimensional phthalocyanine-like medium is developed and its predictions are contrasted with those of the conventional diffusion-based treatments. The kinetics obtained using the simulation model are very different from those given by conventional methods. For instance, the annihilation probability of a pair initially on the same stack is considerably larger. Approximate master-equation models for the annihilation kinetics in highly anisotropic media are also described.