Thermally activated delayed fluorescence (TADF) and enhancing photoluminescence quantum yields of [Cu(I)(diimine)(diphosphine)](+) complexes-photophysical, structural, and computational studies.

The complexes [Cu(I)(POP)(dmbpy)][BF4] (1) and [Cu(I)(POP)(tmbpy)][BF4] (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl; tmbpy = 4,4',6,6'-tetramethyl-2,2'-bipyridyl; POP = bis[2-(diphenylphosphino)-phenyl]ether) have been studied in a wide temperature range by steady-state and time-resolved emission spectroscopy in fluid solution, frozen solution, and as solid powders. Emission quantum yields of up to 74% were observed for 2 in a rigid matrix (powder), substantially higher than for 1 of around 9% under the same conditions. Importantly, it was found that the emission of 2 at ambient temperature represents a thermally activated delayed fluorescence (TADF) which renders the compound to be a good candidate for singlet harvesting in OLEDs. The role of steric constraints within the complexes, in particular their influences on the emission quantum yields, were investigated by hybrid-DFT calculations for the excited triplet state of 1 and 2 while manipulating the torsion angle between the bipyridyl and POP ligands. Both complexes showed similar flexibility within a ±10° range of the torsion angle; however, 2 appeared limited to this range, whereas 1 could be further twisted with little energy demand. It is concluded that a restricted flexibility leads to a reduction of nonradiative deactivation and thus an increase of emission quantum yield.

Substituted [Cu(I)(POP)(bipyridyl)] and related complexes: synthesis, structure, properties and applications to dye-sensitised solar cells.

The synthesis and subsequent spectroscopic, electrochemical, photophysical and computational characterisation of a series of heteroleptic Cu(I) complexes of general formula: [CuPOP{4,4'(R)-bipyridyl}][BF(4)] and [CuPOP{4,4',6,6'(R)-bipyridyl}][BF(4)] is described (POP = bis{2-(diphenylphosphanyl)phenyl} ether; R = Me, CO(2)H, CO(2)Et. The steric constraint imposed by the POP ligand can impede distortion towards square planar geometry upon MLCT excitation or oxidation and this is explored in the context of varying substituents on the bipyridyl ligand. The insight gained opens new avenues for design of functional Cu(I) systems suitable for photophysical and photoelectrochemical applications such as sensitisers for dye-sensitised solar cells (DSSCs).