This report outlines progress to date in preparing Pt(trpy)Cl⁺ derivatives that exhibit long-lived photoluminescence in solution (trpy=2,2′;6′,2″-terpyridine). The trpy complex itself is a versatile binding agent/reporter probe for biological macromolecules but is non-emissive, except in solids or low-temperature glasses. Derivatives investigated are of the type Pt(4′-R-T)Y⁺, where 4′-R-T denotes a 4′-substituted form of the trpy ligand and Y is a pseudohalide co-ligand. Simple halide replacement yields the Pt(trpy)OH⁺ derivative which has facilitated luminescence-based DNA-binding studies. Other complexes with long-lived excited states in fluid solution include Pt(4′-NMe₂-T)Cl⁺ and Pt(4′-Pyre1-T)Cl⁺, where Pyre1 designates a 1-pyrenyl substituent. Due to intra-ligand charge-transfer character, Pt(4′-NMe₂-T)Cl⁺ and Pt(4′-Pyre1-T)Cl⁺ each exhibit relatively low energy absorption maxima. Open coordination sites support quenching by Lewis bases, however, the effect is less evident with increased intra-ligand orbital parentage in the excited state.