Strongly Luminescent Cyclometalated Gold(III) Complexes Supported by Bidentate Ligands Displaying Intermolecular Interactions and Tunable Emission Energy

Abstract

A series of charge-neutral AuIII complexes, which comprise a dicarbanionic C-deprotonated biphenyl ligand and bidentate ancillary ligands ([Au(C^C)(L^X)]; L^X=β-diketonate and relatives (O^O), quinolinolate and relatives (N^O), and diphosphino (P^P) ligands), were prepared. All the complexes are emissive in degassed CH2Cl2 solutions and in thin-film samples with Φem up to 18 and 35 %, respectively, except for 5 and 6, which bear (N^O)-type ancillary ligands. Variation of the electronic characteristics of the β-diketonate ancillary ligand was demonstrated to be a viable route for tuning the emission color from blue-green (peak λem at ca. 466 nm for 1 and 2; 501 nm for 4 a and 4 b) to orange (peak λem at 585 nm for 3), in contrast to the common observations that the ancillary ligand has a negligible effect on the excited-state energy of the AuIII complexes reported in the literature. DFT/time-dependent (TD) DFT calculations revealed that the energies of the 3ππ*(C^C) and the 3ILCT(O^O) excited states (ILCT=intraligand charge transfer) switch in order on going from O^O=acetylacetonate (acac) to aryl-substituted β-diketonate ligands. Solution-processed and vacuum-deposited organic light-emitting diode (OLED) devices of selected complexes were prepared. The vacuum-deposited OLED fabricated with 2 displays a sky-blue emission with a maximum external quantum efficiency (EQE) of 6.71 % and CIE coordinates of (0.22, 0.40). The crystal structures of 7 and 9 reveal short intermolecular AuIII⋅⋅⋅AuIII contacts, with intermetal distances of 3.408 and 3.453 Å, respectively. DFT/TDDFT calculations were performed on 7 and 9 to account for the noncovalent interactions. Solid samples of 1, 3, and 9 exhibit excimeric emission at room temperature, which is rarely reported in AuIII complexes.