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

Following Re I → 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 -[Re II (dppz .- )(CO) 3 (py-PTZ)] + *. It undergoes intramolecular energy transfer to give the dppz-localized ππ* excited state [Re I ( 3 dppz)*(CO) 3 (py-PTZ)] + ( 3 ππ*) in competition with electron transfer to give the redox-separated state (RS) [Re I (dppz .- )(CO) 3 (py-PTZ .+ )] + . The ππ* state decays to the ground state with k = 1.7 × 10 4 s -1 (τ = 60 ± 15 μs) and the RS state decays with k = 9.1 × 10 6 s -1 (τ = 110 ± 10 ns). The competition ratio for formation of the two is [RS]/[ 3 ππ*] ∼ 2.4. Subsequent 3 ππ* → RS interconversion is slow even though the process is favored by 0.43 eV.