Single-molecule interfacial electron transfer in donor-bridge-nanoparticle acceptor complexes

Photoinduced interfacial electron transfer (IET) in sulforhodamine B (SRhB)-aminosilane-Tin oxide (SnO₂) nanoparticle donor-bridge- acceptor complexes has been studied on a single molecule and ensemble average level. On both SnO₂ and ZrO₂, the sum of single molecule fluorescence decays agree with the ensemble average results, suggesting complete sampling of molecules under single molecule conditions. Shorter fluorescence lifetime on SnO₂ than on ZrO₂ is observed and attributed to IET from SRhB to SnO₂. Single molecule lifetimes fluctuate with time and vary among different molecules, suggesting both static and dynamic IET heterogeneity in this system. Computational modeling of the complexes shows a distribution of molecular conformation, leading to a distribution of electronic coupling strengths and ET rates. It is likely that the conversion between these conformations led to the fluctuation of ET rate and fluorescence lifetime on the single molecule level.