Photoinduced intramolecular tryptophan oxidation and excited-state behavior of [Re(L-AA)(CO)3(α-diimine)](+) (L = pyridine or imidazole, AA = tryptophan, tyrosine, phenylalanine).

ReI carbonyl-diimine complexes [Re(L-AA)(CO)3(N,N)]+ (N,N = bpy, phen) containing an aromatic amino acid (AA), phenylalanine (Phe), tyrosine (Tyr), or tryptophan (Trp), linked to Re by a pyridine-amido or imidazole-amido ligand L have been synthesized and their excited-state properties investigated by nanosecond time-resolved IR (TRIR) and emission spectroscopy. Near-UV optical excitation populates a ReI(CO)3→N,N 3MLCT excited state *[ReII(L-AA)(CO)3(N,N•–)]+. Decay to the ground state (50–300 ns lifetime) is the only excited-state deactivation process observed in the case of Phe and Tyr complexes, whereas the Trp-containing species undergo a Trp(indole)→*ReII electron transfer (ET) producing a charge-separated (CS) state, [ReI(L-Trp•+)(CO)3(N,N•–)]+. The ET occurs with a 8–40 ns lifetime depending on L, N,N, and the solvent. The CS state is characterized by ν(CO) IR bands shifted to lower wavenumbers from their respective ground-state positions and two bands at 1278 and 1497 cm–1 tentatively attributed t...