Ultrafast Isomerization Dynamics of a Unidirectional Molecular Rotor Revealed by Femtosecond Stimulated Raman Spectroscopy (FSRS)

Unidirectional molecular rotors based on chiral overcrowded alkenes operate via sequential photochemical- and thermal-activated steps. Over the last decade the rotation rate limiting thermal step has been optimized through modification of the molecular structure. In recent years we have shown the photochemical step proceeds on an ultrafast timescale via a barrierless isomerization reaction. Here we reveal for the first time the excited state vibrational structure and associated ultrafast dynamics for a unidirectional molecular rotor, providing insight into the structural and electronic evolution involved in the rotary motion.