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)](CF 3 SO 3 ) (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 (Me 4 -phen), L = py-est ( 2a ), py-C6-est ( 2b ); N−N = 4,7-diphenyl-1,10-phenanthroline (Ph 2 -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 ( 3 MLCT) (dπ(Re) → π*(N−N)) emission in fluid solutions at 298 K and in low-temperature glass. The excited states of the Me 4 -phen complexes possessed some triplet intraligand 3 IL 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.