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-CONHC5H10CONHC2H4-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-CONHC5H10CONHC2H4-indole (3b); N−N = 4,7-diphenyl-1,10-phenanthroline (Ph2-phen), L =
py-3-CONHC2H4-indole (4a), py-3-CONHC5H10CONHC2H4-indole (4b)), and their indole-free counterparts,
[Re(N−N)(CO)3(py-3-CONH-Et)](CF3SO3) (py-3-CONH-Et = N-ethyl-(3-pyridyl)formamide; N−N = Me4-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.