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 H-1 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 (lambda(max) 600 nm) relative to 2 (lambda(max) 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)/pi (C CC6H4R-4) -> Pt(p(z))/Ag(sp)/pi* (C CC6H4R-4)] state modified by Pt center dot center dot center dot Ag and Ag center dot center dot center dot 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)(3)(2+)/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 x 10(-5)-1.0 x 10(-3) M and a detection limit of 8.0 x 10(-6) M based on 3 times the ratio of signal-to-noise.