Bimetallic Coinage Metal Complexes of Tetradentate ortho ‐Ter‐arylene Ligands

Abstract

ABSTRACT We report a series of photoluminescent bimetallic Cu(I), Ag(I), and Au(I) complexes supported by tetradentate donor‐acceptor ligands containing two monoanionic amide donors (D) and two aza‐arene acceptors (A). The metal complexes of the ligand containing carbazolide and pyridyl ligating groups possess high photoluminescence quantum yields (up to 65% in solution) and emission properties consistent with thermally‐activated delayed fluorescence (TADF). Bimetallic Cu(I) complexes of similar ligands containing benzannulated donor (benzo[a]carbazolide) or acceptor (isoquinoline) moieties demonstrate that absorption/emission properties are tunable by modification of D/A groups. Single‐crystal x‐ray diffraction of the bimetallic complexes reveals metal–metal distances shorter than the sum of their van der Waals radii, suggesting metallophilic interactions between the d 10 metal centers. Ultrafast excited‐state kinetic analysis reveals nearly equal exergonic intersystem crossing rates between Cu(I) and Au(I) complexes, contrary to what is expected from each metal's spin–orbit coupling contributions. These findings are corroborated with theoretical modeling, which suggests that the optical transitions of these bimetallic complexes are characterized as metal–ligand‐to‐ligand charge transfer (MLLCT) states.