Photochemical cis−trans Isomerization of cis-(η6-1,2-Diphenylethene)Cr(CO)3 and the Molecular Structure of trans-(η6-1,2-Diphenylethene)Cr(CO)3

Visible irradiation of cis-(η6-1,2-diphenylethene)Cr(CO)3 results in an efficient conversion to the trans isomer as confirmed by NMR, room-temperature UV−vis spectroscopy, and low-temperature matrix isolation studies. Laser flash photolysis of trans-(η6-1,2-diphenylethene)Cr(CO)3 at 355 nm forms a solvated dicarbonyl species, (η6-1,2-diphenylethene)Cr(CO)2. Matrix isolation studies confirm that cis to trans isomerization occurs under low-energy irradiation (λexc > 400 nm), while photolysis with λexc = 313 nm is required to induce CO loss. Time-dependent density functional theory (TDDFT) calculations predict wavelength-dependent photochemical cis to trans isomerization for low-energy (λexc > 400 nm) irradiation, while high-energy irradiation (λexc > 300 nm) populates excited states that are labile to CO loss.