Deciphering the Novel Photoreactivity of β‐Enaminones

The mechanism of a newly discovered photochemical reaction of β-enaminones is examined by femtosecond transient absorption spectroscopy and multistate multiconfigurational quantum chemical calculations. Our study reveals that this photochemical reaction features a previously undocumented excited-state-proton-transfer (ESIPT) process. We show that this process is structurally and dynamically gated, occurring in ultrafast time domain with complex progression of β-enaminone along three potential energy surfaces featuring two conical intersections and a singlet-triplet crossing.