Formation Principles and Exciton Relaxation in Semiconductor Quantum Dot–Dye Nanoassemblies

Abstract

In this chapter we discuss “bottom-up” non-covalent self-assembly principles which define a strategy for the formation of organic–inorganic nanoassemblies containing colloidal semiconductor quantum dots (QD) of different types (based on a CdSe core) and various heterocyclic molecules (dyes) with functionalized anchoring side substituents (meso-pyridyl substituted porphyrins and perylene diimides). Using a combination of ensemble and single molecule spectroscopy of “QD–Dye” nanoassemblies, we show that single functionalized molecules can be considered as extremely sensitive probes for studying the complex interface physics and chemistry (influence of the embedding environment and temperature) and related exciton relaxation processes in QDs. It will be quantitatively laid out that the major part of the observed QD photoluminescence (PL) quenching in nanoassemblies can be understood, on the one hand, in terms of exciton wave function tunneling under the condition of quantum confinement and, on the other hand, by the influence of ligand dynamics. In nanoassemblies, photoinduced Foerster-type energy transfer (FRET) QD → Dye is often only a small contribution to the PL quenching and is effectively suppressed already in slightly polar solvents which is often overlooked in literature. Finally we would like to point out that properties of “QD–Dye” nanoassemblies are not only interesting in themselves but also provide a valuable tool to study surface-related phenomena in QDs on an extremely low level of surface modification, thus providing the data for a further development of defined multi-component structures for exploitation as artificial light-harvesting complexes, electro- and photochemical devices or nanosensors.