Heteroleptic C^N Cyclometalated Iridium Complexes Enabling Photochemical Isomerization To Remarkably Enhance Luminescent Performance Using 2-(Diphenylphosphino)phenol Auxiliary Ligand

A series of stable heteroleptic Ir complexes bearing a pair of 2-phenylpyridine as main ligands and 2-(diphenylphosphino)phenol as an auxiliary ligand were synthesized to achieve efficient luminescence upon photochemical isomerization. Photoisomerization of an N,N-trans isoform, where a pair of nitrogen atoms of 2-phenylpyridine ligands were located at the trans position, using a high-pressure Hg lamp successfully produced its N,N-cis isomer in solution. A fluorine substituent on 2-phenylpyridine accelerated photoisomerization, whereas a methyl group deactivated the photochemical reaction. Photoluminescence efficiencies of the obtained N,N-cis isomers were significantly higher than those of the N,N-trans isomers.