Electrochemiluminescence Properties of [Pt2Ag4(CCC6H4R)8]n (R = CH3, n = 1; R = H, n = 1 and 2) with Amine (TPrA and DBAE) as the Coreactant and Determination of Sudan I

Two hexanuclear clusters, [Pt2Ag4(CCC6H4R)8] (R = CH3, 1; R = H, 2), together with dimer [Pt2Ag4(CCC6H5)8]2 (3), have been synthesized and characterized by elemental analyses, electrospray ionization mass spectrometry, and 1H NMR spectroscopy and by X-ray crystallography for 1 and 3. A considerable enhancement of photoluminescence (PL) and a notable red shift in the emission maximum of 1 (λmax 600 nm) relative to 2 (λmax 545 nm) are observed. Electrogenerated chemiluminescence (ECL) of 1 and 2 in the absence or presence of coreactant tri-n-propylamine (TPrA) or 2-(dibutylamino)­ethanol (DBAE) at different working electrodes in different solvents (CH2Cl2, CH2ClCH2Cl, or CH3CN) has been studied. The ECL spectra are identical with the PL spectra, indicating that ECL emissions are also due to a MLM′CT [Pt­(d)/π (CCC6H4R-4) → Pt­(pz)/Ag­(sp)/π* (CCC6H4R-4)] state modified by Pt···Ag and Ag···Ag contacts. ECL of 1- and 2/amine systems in CH2ClCH2Cl was produced at the potentials of 1.14–1.19 V vs SCE, notably negatively shifted by about 0.38 V compared to those of the Ru­(bpy)32+/amine system. In all cases, ECL quantum efficiencies of 2 are higher than those of 1 and on the same order of magnitude as that of the [Ru­(bpy)3]­(PF6)2/amine system. It is noted that Sudan I tends to decrease the ECL intensity of the 1/DBAE system in CH2ClCH2Cl at a platinum working electrode. A new ECL method for the determination of Sudan I was developed with a linear range of 2.5 × 10–5–1.0 × 10–3 M and a detection limit of 8.0 × 10–6 M based on 3 times the ratio of signal-to-noise.