Synthesis, characterization, crystal structure, and electrochemical, photophysical, and protein-binding properties of luminescent rhenium(I) diimine indole complexes

We report the synthesis, characterization, and photophysical and electrochemical properties of a series of luminescent rhenium(I) diimine indole complexes, [Re(N-N)(CO)₃(L)](CF₃SO₃) (N-N = 3,4,7,8-tetramethyl-1,10-phenanthroline (Me₄-phen), L = N-(3-pyridoyl)tryptamine (py-3-CONHC₂H₄-indole) (1a), N-[N-(3-pyridoyl)-6-aminohexanoyl]tryptamine, (py-3-CONHC₅H ₁₀CONHC₂H₄-indole) (1b); N-N = 1,10-phenanthroline (phen), L = py-3-CONHC₂H₄-indole (2a), py-3-CONHC₅H₁₀CONHC₂H₄-indole (2b); N-N = 2,9-dimethyl-1,10-phenanthroline (Me₂-phen), L = py-3-CONHC₂H₄-indole (3a), py-3-CONHC₅H ₁₀CONHC₂H₄-indole (3b); N-N = 4,7-diphenyl-1,10-phenanthroline (Ph₂-phen), L = py-3-CONHC ₂H₄-indole (4a), py-3-CONHC₅H ₁₀CONHC₂H₄-indole (4b)), and their indole-free counterparts, [Re(N-N)(CO)₃(py-3-CONH-Et)](CF₃SO ₃) (py-3-CONH-Et = N-ethyl-(3-pyridyl)formamide; N-N = Me ₄-phen (1c), phen (2c), Me₂-phen (3c), Ph₂-phen (4c)). The X-ray crystal structure of complex 3a has also been investigated. Upon irradiation, most of the complexes exhibited triplet metal-to-ligand charge-transfer (³MLCT) (dπ(Re) → π*(diimine)) emission in fluid solutions at 298 K and in low-temperature glass. However, the structural features and long emission lifetimes of the Me₄-phen complexes in solutions at room temperature suggest that the excited state of these complexes exhibited substantial triplet intraligand (³IL) (π → π*) (Me₄-phen) character. The binding interactions of these complexes to indole-binding proteins including bovine serum albumin and tryptophanase have been examined. © 2005 American Chemical Society.