Ultrafast transient absorption spectroscopy of the photo-induced Z–E isomerization of a photochromic furylfulgide

The photo-induced Z–E isomerization of a photochromic furylfulgide following excitation at 387 nm was studied using time-resolved transient absorption spectroscopy with probing from 410 to 690 nm in ethanol as solvent. The excited-state absorption decayed dominantly on a time scale of 220 fs. An oscillatory behavior was interpreted as vibrational coherence involving a low-frequency torsional motion. A slow component with a decay time of 4.1 ps was assigned to hot ground state absorption. At 25 ps, the transient absorption resembled the stationary E-Z difference spectrum. The results indicate that the Z–E photoisomerization proceeds on a sub-ps time scale.