The shiny side of copper: bringing copper(i) light-emitting electrochemical cells closer to application.

Heteroleptic [Cu(P^P)(N^N)][PF] complexes, where N^N is 5,5'-dimethyl-2,2'-bipyridine (5,5'-Mebpy), 4,5,6-trimethyl-2,2'-bipyridine (4,5,6-Mebpy), 6-(-butyl)-2,2'-bipyridine (6-Bubpy) and 2-ethyl-1,10-phenanthroline (2-Etphen) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP, PIN [oxydi(2,1-phenylene)]bis(diphenylphosphane)) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos, PIN (9,9-dimethyl-9-xanthene-4,5-diyl)bis(diphenylphosphane)) have been synthesized and their NMR spectroscopic, mass spectrometric, structural, electrochemical and photophysical properties were investigated. The single-crystal structures of [Cu(POP)(5,5'-Mebpy)][PF], [Cu(xantphos)(5,5'-Mebpy)][PF], [Cu(POP)(6-Bubpy)][PF], [Cu(POP)(4,5,6-Mebpy)][PF]·1.5EtO, [Cu(xantphos)(4,5,6-Mebpy)][PF]·2.33CHCl, [Cu(POP)(2-Etphen)][PF] and [Cu(xantphos)(2-Etphen)][PF] are described. While alkyl substituents in general exhibit electron-donating properties, variation in the nature and substitution-position of the alkyl group in the N^N chelate leads to different effects in the photophysical properties of the [Cu(P^P)(N^N)][PF] complexes. In the solid state, the complexes are yellow to green emitters with emission maxima between 518 and 602 nm, and photoluminescence quantum yields (PLQYs) ranging from 1.1 to 58.8%. All complexes show thermally activated delayed fluorescence (TADF). The complexes were employed in the active layer of light-emitting electrochemical cells (LECs). The device performance properties are among the best reported for copper-based LECs, with maximum luminance values of up to 462 cd m and device half-lifetimes of up to 98 hours.