Three luminescent alkynylplatinum(II) terpyridyl complexes, [Pt( ^tBu₃tpy)(C≡C-C₆H_4- X-4)](OTf) (X = NH₂ 1, NCS 2, NHCOCH₂I 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*(^tBu₃tpy) ³MLCT excited state, with some mixing of a π(C≡CR) → π*(^tBu ₃tpy) ³LLCT 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.