Dinuclear platinum(II) 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 S₁ and T₁ states. The mesityl groups also serve to hinder the aggregation that was detrimental to electroluminescence efficiency in previous studies, allowing a ∼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.