Luminescent Tricarbonylrhenium(I) Polypyridine Estradiol Conjugates: Synthesis, Crystal Structure, and Photophysical, Electrochemical, and Protein-Binding Properties

A series of luminescent tricarbonylrhenium(I) polypyridine estradiol complexes [Re(N−N)(CO)3(L)](CF3SO3) (N−N = 1,10-phenanthroline (phen), L = 4-(17α-ethynylestradiolyl)pyridine (py-est) (1a),
4-(N-(6-(4-(17α-ethynylestradiolyl)benzoylamino)hexanoyl)aminomethyl)pyridine (py-C6-est) (1b); N−N
= 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4-phen), L = py-est (2a), py-C6-est (2b); N−N = 4,7-diphenyl-1,10-phenanthroline (Ph2-phen), L = py-est (3a), py-C6-est (3b)) have been synthesized and
characterized. The X-ray crystal structure of complex 1a has also been investigated. The photophysical
and electrochemical properties of all the complexes have been studied. Upon irradiation, most of the
complexes exhibited intense and long-lived triplet metal-to-ligand charge-transfer (3MLCT) (dπ(Re) →
π*(N−N)) emission in fluid solutions at 298 K and in low-temperature glass. The excited states of the
Me4-phen complexes possessed some triplet intraligand 3IL character. The lipophilicity of all the complexes
has been determined by reversed-phase HPLC. In addition, the binding of these complexes to estrogen
receptor α has been investigated by emission titrations.