The solvent and temperature dependence of the emission of Pt(diimine)(dithiolate) complexes is reported where diimine = 4,4[prime]-dimethyl-2,2[prime]-bipyridine (dmbpy) or 4,7-diphenyl-1,10-phenanthroline (dpphen) and dithiolate = 1-(ethoxycarbonyl)-1-cyanoethylene-2,2-dithiolate (ecda) or 1-(tert-butoxycarbonyl)-1-cyanoethylene-2,2-dithiolate (tbcda). In fluid solution at room temperature, a single emission band is observed at [approximately] 16,670 cm[sup [minus]1] (600 nm) for the complexes Pt(dmbpy)(ecda) (1), Pt-(dpphen)(ecda) (2), and Pt(dpphen)(tbcda) (3), which are studied in detail. The radiative quantum yields and lifetimes of the emission decrease with increasing solvent polarity for the three complexes. In DMF/CH[sub 2]Cl[sub 2]/MeOH the emission intensity for the complexes increases between 298 and 175 K with no change in the emission energy. Between 175 and 165 K the emission undergoes a red shift to [approximately] 15,625 cm[sup [minus]1] (640 nm), corresponding to a rigidochromic effect, and below 140 K two new bands appear at higher energies (17,000-18,500 and 18,600-19,900 cm[sup [minus]1]). The latter bands have a relative separation of 1,360 cm[sup [minus]1] and are assigned to a [pi]-[pi]* diimine transition on the basis of their observed lifetime and comparison with PtCl[sub 2](diimine) analogues. Between 80 and 6 K, the lifetime of the 15,625-cm[sup [minus]1] (640-nm) emission band increases, while, below 50 K, its emission intensity decreases with decreasingmore » temperature, suggesting the presence of closely spaced excited states. From a kinetic analysis of the radiative quantum yield and lifetime data, the low-energy emission is assigned to a charge-transfer manifold of two emitting states separated by 50-60 cm[sup [minus]1].« less