Professor Kristin Wustholz of the College of William and Mary will present:
"Elucidating the Excited-State Dynamics of Eosin Y Photosensitizers using Single-Molecule Spectroscopy"
Dye-sensitized photocatalysis (DSP) is a promising strategy to meet surging energy demands via the direct conversion of solar energy into renewable fuels. In this approach, a photosensitizer that undergoes fast photoinduced charge generation is coupled to an electrocatalyst for fuel production, which occurs on relatively slow timescales. To minimize charge recombination losses and kinetic redundancy in DSP, the lifetime of charge carriers can be prolonged by using chromophores like eosin Y (EY) that exhibit enhanced intersystem crossing (ISC) to a long-lived triplet state prior to electron injection. However, minimizing kinetic redundancy requires understanding the extent and origin of kinetic dispersion in the electron injection, recombination, and ISC dynamics - information that is not accessible at the ensemble-averaged level. This study examines the heterogeneous excited-state dynamics of EY photosensitizers in complex, condensed phase environments using single-molecule spectroscopy (SMS). Using a combination of SMS measurements, robust statistical analysis, and Monte Carlo simulations, we demonstrate that both triplet state decay and dispersive electron transfer are operative. Furthermore, both static and dynamic heterogeneity in the electron-transfer dynamics are observed. These results provide new insights that are relevant to the design of next-generation materials for DSP.