Electrogenerated Chemiluminescence of Platinum(II) Alkynyl Terpyridine Complex with Peroxydisulfate as Coreactant

A Pt(II) alkynyl terpyridine complex containing a carbazole moiety, [Pt(tBu3tpy)(CC−C6H4-4-carbazole-9)]+ (tBu3tpy = 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine) 1, has been synthesized and characterized. The photophysical behavior has been studied, and the molecular structure has been determined by X-ray crystallography. The complex was found to exhibit intense electrogenerated chemiluminescence (ECL) using peroxydisulfate (S2O82−) as coreactant in acetonitrile/water (1−25%, v/v) mixture at both glassy carbon and gold electrodes, representing the first ECL example of the Pt(II) alkynyl family. The ECL was produced at potential corresponding to the first reduction wave (−0.90 V vs SCE), significantly shifted by ∼0.65 V toward more positive potential compared with that of [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine). The ECL spectrum was found to be identical to the photoluminescence spectrum recorded in the same medium, indicating the formation of the same excited state of dπ(Pt) → π*(tBu3tpy) 3MLCT mixed with π(CCR) → π*(tBu3tpy) 3LLCT in both cases. The ECL mechanism was proposed involving the formation of the strongly oxidizing intermediate, SO4•−, mainly generated during the catalytic reduction of S2O82− by the electrogenerated 1−. Chemiluminescence of 1/S2O82− based on reduction with Al metal is also described.