The synthesis, characterization, and photophysical properties of several Pt(II) complexes of quinoxaline-2,3-dithiolate (qdt) and 6,7-dimethylquinoxaline-2,3-dithiolate (dmqdt) are described. Specifically, (TBA)(2)[Pt(qdt)(2)], where TBA = tetra-n-butylammonium, Pt(COD)(qdt), where COD = 1,5-cyclooctadiene, and Pt(phen)(qdt), where phen = 1,10-phenanthroline, and their dmqdt analogs have been prepared and examined with respect to their photophysical properties. Highly structured emission from Pt(COD)(qdt) in frozen glass solution at 77 K has been detected, having a major vibrational progression of 1370 cm(-1) corresponding to a C=C stretching frequency of the quinoxalinedithiolate backbone. Solution luminescence from (TBA)(2)[Pt(qdt)(2)] and Pt(phen)(qdt) has been detected with quantum yields, Phi(em), of 10(-5) and 10(-3), respectively, although the latter is highly sensitive to solvent effects. The complex Pt(phen)(qdt) possesses a low-energy (lambda(max) = 497 nm in CHCl3) absorption band assigned to a charge-transfer-to-diimine transition which exhibits a high degree of negative solvatochromism. Through both emission quantum yield and excited state lifetime measurements, the emissive excited state of Pt(phen)(qdt) is shown to undergo increasing degrees of nonradiative deactivation with increasing solvent polarity. Reductive quenching of the excited state of Pt(phen)(qdt) has been examined using the aromatic amines N,N-dimethylaniline (DMA) and N,N,N’,N’-tetramethylphenylenediamine (TMPD). From a Stern-Volmer analysis of the emission quenching data, quenching rate constants of 2.8 x 10(9) s(-1) (DMA) and 6.9 x 10(9) s(-1) (TMPD) were calculated, Cyclic voltammetry was conducted on each of the complexes in order to probe further the nature of the HOMO and LUMO. From a simple thermochemical analysis, an excited state reduction potential of 1.14 V (vs NHE) has been estimated for Pt(phen)(qdt).