Electron Transfer Triggered by Optical Excitation of Phenothiazin-tris(meta-phenylene-ethynylene)-(tricarbonyl)(bpy)(py)rhenium(I)

We have investigated excited-state electron transfer in a donor-bridge-acceptor complex containing phenothiazine (PTZ) linked via tris(meta-phenylene-ethynylene) to a tricarbonyl(bipyridine)(pyridine)Re(I) unit. Time-resolved luminescence experiments reveal two excited-state (*Re) decay regimes, a multiexponential component with a mean lifetime of 2.7 ns and a longer monoexponential component of 530 ns in dichloromethane solution. The faster decay is attributed to PTZ → *Re electron transfer in a C-shaped PTZ-bridge-Re conformer (PTZ–Re ≈ 7.5 Å). We assign the longer lifetime, which is virtually identical to that of free *Re, to an extended conformer (PTZ–Re > 20 Å). The observed biexponential *Re decay requires that interconversion of PTZ-bridge-Re conformers be slower than 10^6 s^(–1).