Dinuclear platinum(<sc>ii</sc>) complexes emitting through TADF: new ligand design to minimise aggregation and the S1-T1 energy gap

Dinuclear platinum(ii) complexes of a new, ditopic, bis-tridentate NCN-NCN-coordinating ligand, appended with four mesityl groups, are reported. The high radiative rate constants and correspondingly efficient luminescence of the complexes involves thermally activated delayed fluorescence (TADF), thanks to a near-zero energy gap between the S-1 and T-1 states. The mesityl groups also serve to hinder the aggregation that was detrimental to electroluminescence efficiency in previous studies, allowing a similar to 4-fold increase in OLED efficiency to be achieved (i.e. from 2.3% previously to 10% in this work). Oxidation of one of the Pt(ii) complexes led to a dinuclear Pt(iv) complex of unprecedented structure.