Synthesis, Photophysical Properties, and Biomolecular Labeling Studies of Luminescent Platinum(II)-Terpyridyl Alkynyl Complexes

Three luminescent alkynylplatinum(II) terpyridyl complexes, [Pt( t Bu 3 tpy)(C⋮C−C 6 H 4 −X-4)](OTf) (X = NH 2 1, NCS 2, NHCOCH 2 I 3 ), have been synthesized and characterized. Their electrochemical and photophysical properties have been studied, and the molecular structure of 2 has also been determined by X-ray crystallography. Complexes 2 and 3 exhibit strong luminescence in various media, the origin of which has been tentatively assigned as a dπ(Pt) → π*( t Bu 3 tpy) 3 MLCT excited state, with some mixing of a π(C⋮CR) → π*( t Bu 3 tpy) 3 LLCT character. Human serum albumin (HSA) has been labeled by the ready reaction of the isothiocyanate and iodoacetamide functional groups in 2 and 3, to afford the respective bioconjugates, 2-HSA and 3-HSA . Both bioconjugates in 50 mM Tris-Cl buffer (pH 7.4) are highly colored and exhibit luminescence in the visible region upon photoexcitation.