Speaker
Description
Intersystem crossing (ISC) is a photophysical process which is essential for triplet-state formation, with profound implications for photocatalysis, photodynamic therapy, and optoelectronic devices. Our research combines ultrafast and steady state spectroscopy, and quantum chemical calculations to unravel how molecular structure, vibrational dynamics, and environmental factors govern ISC efficiency. Across diverse systems including aromatic carbonyls, nitroaromatic compounds, thiocarbonyls, heavy atom substituted organoboron compounds we have demonstrated that ISC is not dictated solely by static spin-orbit coupling (SOC) strength. Our findings suggest that specific bond associated vibrational modes can modulate the singlet-triplet conversion in all these compounds. For example, ISC in positional isomers in heavy-atom-substituted chromophores reveals that vibrational mixing and heavy-atom participation in key orbital transitions can influence or take precedence over SOC magnitude. Intermolecular interactions, such as hydrogen bonding, and medium viscosity further modulate ISC by reshaping nuclear motion and altering access to the singlet-triplet crossing. Collectively, these findings establish a detailed mechanistic understanding in which ISC efficiency emerges from a synergy of electronic structure, nuclear coordinates, and environmental constraints offering actionable design principles for next-generation triplet photosensitizers and photochemical systems.