Excited State Competition in fac-[ReI(dppz)(CO)3(py-PTZ)]+

Abstract

Following ReI → dppz (dppz is dipyrido[3,2-a:2‘,3‘-c]phenazine) metal-to-ligand charge transfer (MLCT) excitation of fac-[Re(dppz)(CO)3(py-PTZ)]+ (py-PTZ is 10-(4-picolyl)phenothiazine), there is a dynamic competition between intramolecular electron and energy transfer. Laser flash photolysis at 420 nm in 1,2-dichloroethane produces the MLCT excited state fac-[ReII(dppz.-)(CO)3(py-PTZ)]+*. It undergoes intramolecular energy transfer to give the dppz-localized ππ* excited state [ReI(3dppz)*(CO)3(py-PTZ)]+ (3ππ*) in competition with electron transfer to give the redox-separated state (RS) [ReI(dppz.-)(CO)3(py-PTZ.+)]+. The ππ* state decays to the ground state with k = 1.7 × 104 s-1 (τ = 60 ± 15 μs) and the RS state decays with k = 9.1 × 106 s-1 (τ = 110 ± 10 ns). The competition ratio for formation of the two is [RS]/[3ππ*] ∼ 2.4. Subsequent 3ππ* → RS interconversion is slow even though the process is favored by 0.43 eV.