Quantifying the number of chromophores and the kinetics of exciton diffusion in nanoparticles with picosecond time-resolved photon antibunching (psTRAB)

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The particle nature of light becomes most evident by studying the fluorescence of single quantum systems, such as organic chromophores or quantum dots. Provided that there is no biexcitonic species formed, not more than one single photon is emitted in one excitation cycle, i.e. photon antibunching appears in the photon statistics. In multichromophoric particles, such as light-harvesting complexes and conjugated polymers, the photon statistics hides important information regarding energy transfer and subsequent exciton annihilation processes but is impossible to interpret without further knowledge about the particles, e.g. the size or number of chromophores. However, energy transfer is a time-dependent process and therefore the signatures thereof must be hidden in the photon stream. We will employ and further develop our technique of picosecond time-resolved photon antibunching (psTRAB) to unravel such signatures and demonstrate on well-defined multichromophoric DNA-origami structures and well-defined multichromophoric molecules that energy transfer processes between multiple dye molecules can indeed be measured. In a second step, we will apply this technique to various poorly defined multichromophoric nanoparticles, such as single conjugated polymer chains and mesoscopic conjugated polymer aggregates with distinct electronic aggregation behaviour, e.g. H- and J-type aggregation, and with different sizes to unravel the nature and efficiency of energy transfer in this important class of materials. Finally, we also want to venture into the interesting class of monolayer transition metal dichalcogenides (TMDCs) and investigate the possibility of using psTRAB to study exciton-exciton annihilation in 2D materials. Single-molecule spectroscopy, or rather single-particle spectroscopy, is the obvious technique for this because both static and dynamic heterogeneities can be resolved.