Nonisotropic Excitation Energy Transport in Organized Molecular Systems: Monte Carlo Simulation-Based Analysis of Fluorescence and Fluorescence Anisotropy Decay

An improved application is presented of the Monte Carlo method including simultaneous parameter fitting to analyze the experimental time-resolved fluorescence and fluorescence anisotropy decay of two organized molecular systems exhibiting a number of different, nonisotropic energy transfer processes. Using physical models and parameter fitting for these systems, the Monte Carlo simulations yield a final set of parameters, which characterize the energy transfer processes in the investigated systems. The advantages of such a simulation-based analysis for global parametric fitting are discussed. Using this approach energy transfer processes have been analyzed for two porphyrin model systems, i.e., spin-coated films of zinc tetra(octylphenyl)-porphyrins (ZnTOPP) and the tetramer of zinc mono(4-pyridyl)triphenylporphyrin (ZnM(4Py)TrPP). For the ZnTOPP film energy transfer rate constants of 1 10 12 s -1 and 80 10 9 s -1 have been found, and are assigned to intra- and interstack transfer, respectively. For the tetramers, the transfer rate constants of 38 10 9 and 5 10 9 s -1 correspond to energy transfer to nearest and next nearest neighbor