The photochemistry of fac-[Re(bpy)(CO)3Cl] (1 a; bpy=2,2'-bipyridine) initiated by irradiation using <330 nm light has been investigated. Isomerization proceeded in THF to give the corresponding mer-isomer 1 b. However, in the presence of a small amount of MeCN, the main product was the CO-ligand-substituted complex (OC-6-24)-[Re(bpy)(CO) 2Cl(MeCN)] (2 c; bpy=2,2'-bipyridine). In MeCN, two isomers, 2 c and its (OC-6-34) form (2 a), were produced. Only 2 c thermally isomerized to produce the (OC-6-44) form 2 b. A detailed investigation led to the conclusion that both 1 b and 2 c are produced by a dissociative mechanism, whereas 2 a forms by an associative mechanism. A comparison of the ultrafast transient UV-visible absorption, emission, and IR spectra of 1 a acquired by excitation using higher-energy light (e.g., 270 nm) and lower-energy light (e.g., 400 nm) gave detailed information about the excited states, intermediates, and kinetics of the photochemical reactions and photophysical processes of 1 a. Irradiation of 1 a using the higher-energy light resulted in the generation of the higher singlet excited state with τ<fs, from which intersystem crossing proceeded to give the higher triplet state (;bsupesup&HES(1)). In THF, ;bsupesup&HES(1) was competitively converted to both the triplet ligand field (;bsupesup&LF) and metal-to-ligand charge transfer (;bsupesup&MLCT) with lifetimes of 200a;fs, in which the former is a reactive state that converts to [Re(bpy)(CO);bsubesub (1 c) within 10a;ps by means of a dissociative mechanism. Re-coordination of CO to 1 c gives both 1 a and 1 b. In MeCN, irradiation of 1 a by using high-energy light gives the coordinatively unsaturated complex, which rapidly converted to 2 c. A seven-coordinate complex is also produced within several hundred femtoseconds, which is converted to 2 a within several hundred picoseconds. Time on our side: Photochemical ligand substitution and isomerization of fac-[Re(bpy)(CO) ;bsubesub&Cl] (bpy=2,2'-bipyridine) with high-energy light are reported. The combination of steady-state irradiation, time-resolved (TR)-UV-visible, TR-IR, and TR-emission experiments gave detailed information on not only various excited states but also short-lived intermediates (see scheme).
All Science Journal Classification (ASJC) codes
- Organic Chemistry