Exciton transfer dynamics in supramolecular semiconductor nanostructures

A simple model is developed to extract the intrinsic decay rates of excitonic states in chiral supramolecular assemblies of OPV derivatives and those rates are found to decrease significantly upon aggregation. In stacks of HBC derivatives, the photoluminescent anisotropy reveals the existence of two excited states with complex characteristics illustrating the subtle interplay between molecular structure, packing and optoelectronic properties. Ultrafast spectroscopy is used to probe the dynamics of excitonic states in a chiral supramolecular assembly of an OPV derivative. Fast exciton diffusion leads to diffusion to trap states, exciton depolarisation, dynamic photoluminescence red-shift and exciton-exciton annihilation. A Monte-Carlo model based on resonance energy transfer steps is presented and yields microscopic properties such as the diffusion coefficient. These excitonic properties are very similar to those of polymeric semiconductors and justify the term “supramolecular polymers”. The study of mixed assemblies of OPV derivatives gives evidence of efficient energy transfer from the short oligomers to longer ones. The results are analysed with a model based on one-step Förster transfers. The supramolecular assembly is shown to speed up dramatically the energy transfers. The transfer rate and dimensionality are controlled by the molecular configuration and external parameters such as the temperature. Thus, I show that the supramolecular assemblies possess polymeric properties while offering more control than organic polymers.EThOS - Electronic Theses Online ServiceGBUnited Kingdo