Computer simulation of energy relaxation and -transport in organized porphyrin systems

This Thesis is devoted to the investigation of optical photophysical processes in organized porphyrin systems. These systems can serve as molecular antennas for organic solar cells, a field of research which recently has received increasing interest. Using a novel application of Monte Carlo computer simulation an improved analysis of the complex fluorescence and fluorescence anisotropy decay in the presence of energy transfer processes has been introduced.

Self-organized [Zn(4-Py)TrPP] ₄ tetramers in solution and in solid films as well as ZnTOPP domains in spin coated films have been studied experimentally by steady state and time-resolved spectroscopy. The results have been analyzed using the abovementioned Monte Carlo simu-lation, yielding the characteristic rate constants for energy transfer- and relaxation processes.

The results of these Monte Carlo simulations are: for [Zn(4-Py)TrPP] ₄ tetramers in solution the fluorescence lifetime is ~ 1.5 × 10 ^-9 s and nearest neighbor energy transfer rate constant is ~ 40 × 10 ⁹ s ^-1 ; ZnTOPP forms parallel porphyrin stacks within one domain in the films, whereas in each stack the porphyrin planes are perpendicularly oriented with respect to the substrate and make an angle of 45˚ with the long stack axis. As follows from the fit of simulated decay curves to the experimental fluorescence- and fluorescence anisotropy decay curves the rate constants for intra-stack and inter-stack energy transfer are ~ 1 × 10 ¹² s ^-1 and ~ 80 × 10 ⁹ s ^-1 , respectively, whereas the fluorescence lifetime is ~ 1.8 × 10 ^-9 s.