Nanoassemblies are formed via self-assembly of ZnS capped CdSe quantum dots (QD) and perylene bisimide dyes (PBI). Upon assembly formation with functionalized dye molecules the QD photoluminescence (PL) is quenched. Quenching has been assigned partly to FRET (fluorescence resonance energy transfer) and NON-FRET processes. By means of time resolved single particle spectroscopy of immobilized QD-dye assemblies, it is demonstrated that NON-FRET processes are due to new non-radiative decay channels caused by the assembly formation process itself. Immobilized (single) assemblies exhibit the same processes as ensembles of assemblies in toluene solution. Only one dye molecule on a QD quenches the PL up to 50%, which is much stronger than is expected when replacing a volume related number of ligands. NON-FRET processes are distinct from photoinduced charge and/or energy transfer. A combination of a Stern-Volmer and FRET analysis of ensemble experiments supports the investigation of the dynamics of assembly formation at extremely low concentration ratios of PBI to QD. This allows us to distinguish between the effects of PBI and ligands on PL quenching on a single molecule level which is not possible in conventional ligand dynamic experiments.

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.

Fluorescence intermittency is a random switching between emitting (on) and non-emitting (off) periods found for many single chromophores such as semiconductor quantum dots and organic molecules. The statistics of the duration of on- and off-periods are commonly determined by thresholding the emission time trace of a single chromophore and appear to be power law distributed. Here we test with the help of simulations if the experimentally determined power law distributions can actually reflect the underlying statistics. We find that with the experimentally limited time resolution real power law statistics with exponents α(on/off) ≳ 1.6, especially if α(on) ≠ α(off) would not be observed as such in the experimental data after binning and thresholding. Instead, a power law appearance could simply be obtained from the continuous distribution of intermediate intensity levels. This challenges much of the obtained data and the models describing the so-called power law blinking.

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