Identification of different donor-acceptor structures via Förster Resonance Energy Transfer (FRET) in quantum-dot-perylene bisimide assemblies.

Danny Kowerko,Stefan Krause,Mohamed Abdel-Mottaleb,Nicole Amecke,Christian Von Borczyskowski,Jörg Schuster

doi:10.3390/ijms10125239

Abstract

Nanoassemblies are formed via self-assembly of ZnS capped CdSe quantum dots (QD) and perylene bisimide (PBI) dyes. Upon assembly formation the QD photoluminescence is quenched, as can be detected both via single particle detection and ensemble experiments in solution. Quenching has been assigned to FRET and NON-FRET processes. Analysis of FRET allows for a distinction between different geometries of the QD dye assemblies. Time-resolved single molecule spectroscopy reveals intrinsic fluctuations of the PBI fluorescence lifetime and spectrum, caused by rearrangement of the phenoxy side groups. The distribution of such molecular conformations and their changed dynamics upon assembly formation are discussed in the scope of FRET efficiency and surface ligand density.

Highlights

Much of the current research related to colloidal semiconductor quantum dots (QD) has been focused on photoinduced excitation energy transfer [7] processes
In this paper we report how Förster-type resonant excitation energy transfer (FRET) can be used as a tool to provide insight into aggregate geometry of QD-dye assemblies, and discuss typical FRET efficiencies affecting mechanisms like spectral shifts of the dye and the QD caused by conformational dynamics [6] or photooxidation, respectively
Tentative assembly structures are shown in Similar to previous experiments [3,4,31,32,43] we could show that QD-dye nanoassemblies can be formed via self-aggregation processes, in case that suitable functional pyridyl groups are able to coordinate the dye to the QD surface

Summary

Introduction

Much of the current research related to colloidal semiconductor quantum dots (QD) has been focused on photoinduced excitation energy transfer [7] processes. (3) The third approach is related to self-organized QD-dye assemblies via suitable functional groups of the dyes, which can anchor via “ligand-type” bonds to surface atoms of the QD This approach is related to a dynamic process [3,4,25], which takes place as a competition between ligand bonding (e.g., of TOPO) and dye bonding This implies that QD-dye assemblies are not permanent in time, but might be effective FRET systems on a single dye/single QD level. The outcome of previous analysis is that for exact discrimination of FRET and Non-FRET mechanism, such assemblies need simultaneous quantitative investigation of QD PL quenching and dye fluorescence enhancement This is often missing in published reports repeatedly resulting in incorrect assignments of processes and erroneous data evaluation. We demonstrate how Förster theory based calculations of FRET efficiencies are used (i) to obtain information about surface geometry and (ii) to explain reduced FRET efficiencies at a single emitter level

Ensemble Experiments

Discussion

Experimental Section

Conclusions