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.

本研究合成并表征了一种含咔唑基团的二价铂炔基三联吡啶配合物[Pt(tBu3tpy)(C≡C−C6H4-4-咔唑-9)]⁺（其中tBu3tpy=4,4′,4′′-三叔丁基-2,2′:6′,2′′-三联吡啶，记为配合物1），并对其光物理行为开展了系统研究，同时通过X射线晶体学（X-ray crystallography）确定了该配合物的分子结构。研究发现，在乙腈/水（体积比1~25%）混合溶剂中，以过二硫酸根（S2O8²−）作为共反应物时，该配合物在玻碳电极与金电极上均展现出强烈的电致化学发光（electrogenerated chemiluminescence，ECL）信号，这是二价铂炔基类配合物领域首例电致化学发光体系。该ECL信号产生于对应第一还原波的电位（相对于饱和甘汞电极（SCE）为−0.90 V），相较于三(2,2'-联吡啶)合钌(II)阳离子([Ru(bpy)3]²+，其中bpy=2,2'-联吡啶)的ECL电位，正移了约0.65 V。经检测，该配合物的ECL光谱与同一介质中测得的光致发光光谱完全一致，表明两种测试条件下均形成了相同的激发态：即dπ(Pt)→π*(tBu3tpy)的三重态金属到配体电荷转移（³MLCT）与π(C≡CR)→π*(tBu3tpy)的三重态配体到配体电荷转移（³LLCT）的混合激发态。本研究提出了该ECL的反应机理：电还原生成的配合物阴离子自由基(1⁻)催化还原过二硫酸根(S2O8²−)，主要生成强氧化性中间体硫酸根自由基阴离子(SO4•−)。此外，本研究还报道了以金属铝作为还原剂时，配合物1/过二硫酸根(S2O8²−)体系的化学发光行为。