Localization and transport of excitation energy in inhomogeneous supramolecular arrays

Promotie: dhr. S.M. Vlaming, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen
Proefschrift: Localization and transport of excitation energy in inhomogeneous supramolecular arrays
Promotor(s): prof.dr. J. Knoester
Faculteit: Wiskunde en Natuurwetenschappen
Contact: Sebastiaan Vlaming, tel. 050-363 8691, e-mail: s.m. vlaming@rug.nl

Localization and transport of excitation energy in inhomogeneous supramolecular arrays

Biological systems, such as for example photosynthesis complexes of plants and bacteria, perform a large number of functions with an impressive efficiency. As such, they form a considerable source of inspiration for nanotechnology, where one intends to fabricate functional structures on the nanoscale. Two applications we are particularly interested in are efficient light absorption, where fabrication of solar cells based on natural light harvesting systems is a promising target, and the efficient transport of energy. Inspired by similarly functioning biological structures, we consider the properties of so called supramolecular structures: complexes of molecules that collectively absorb light and transport energy.

In this thesis, I study the optical and transport properties of these types of complexes, where specifically the effect of interactions with the unavoidable (disordered) environment of these complexes is studied. It is shown that, in such a chain, a larger excitation energy gradient does not necessarily accelerate the transport over the chain, and an optimal gradient can be calculated. Furthermore, a study has been performed on the consequences of a strongly disordered environment on such complexes, where there is a relatively large probability of obtaining strong fluctuations in the system parameters. It turns out that such types of disorder lead to large changes, both qualitatively and quantitatively, in the optical properties of such chains. Finally, the calculation of the theoretical optical spectra of porphyrin-based nanocylinders and subsequent comparison with experiment allows for a determination of the microscopic structure of such cylinders.