Cyclometalated cinchophen ligands on iridium(iii): Towards water-soluble complexes with visible luminescence

Abstract

Eight cationic heteroleptic iridium(iii) complexes, [Ir(epqc) 2(N^N)]+, were prepared in high yield from a cyclometalated iridium bridged-chloride dimer bearing two ethyl-2- phenylquinoline-4-carboxylate (epqc) ligands. Two X-ray crystallographic studies were undertaken on selected complexes (where the ancillary ligand N^N = 4,4′-dimethyl-2,2′-bipyridine and 4,7-diphenyl-1,10-phenanthroline) each confirming the proposed formulations, showing an octahedral coordination at Ir(iii). In general, the complexes are luminescent (620-630 nm) with moderately long lifetimes indicative of phosphorescence. Hydrolysis of the ethyl ester moieties of the epqc ligands gave the analogous cinchophen-based complexes, which were water-soluble and visibly luminescent (568-631 nm). The spectroscopic and redox characterisation of the complexes was complemented by DFT and TD-DFT calculations, supporting the assignment of dominant 3MLCT to the emissive character. © 2013 The Royal Society of Chemistry.