Photophysics of First-Generation Photomolecular Motors: Resolving Roles of Temperature, Friction, and Medium Polarity

Light-driven unidirectional molecular rotary motors have the potential to power machines. Consequently, optimizing their speed and efficiency is an important objective. Here, we investigate factors controlling photochemical yield of prototypical motor, a sterically overcrowded alkene, through detailed investigation its excited-state dynamics. An isoviscosity analysis ultrafast fluorescence decay data resolves friction from barrier effects reveals 3.4 ± 0.5 kJ mol–1 in nonpolar media. Extension this polar solvents shows that height strong function medium polarity pathway becomes near barrierless more Thus, properties can be used as route for motor’s The connection between these dynamics quantum isomerization probed. shown much weaker solvent polarity, most efficient does not lead strongly enhanced isomerization. These results are discussed terms dependence complex multidimensional reaction coordinate.