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)(CdropC-C6H4- 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 dpi(Pt) --> pi*(Bu-t(3) tpy) (MLCT)-M-3 excited state, with some mixing of a pi(CdropCR) --> pi*((t)Bu(3)tpy) (LLCT)-L-3 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.