Novel Red-Emitting Copper(I) Complexes with Pyrazine and Pyrimidinyl Ancillary Ligands for White Light-Emitting Electrochemical Cells

The synthesis, photophysical/electrochemical characterization, and implementation in light-emitting electrochemical cells (LECs) of three novel red-emitting heteroleptic [Cu((NN)-N-<^>)((PP)-P-<^>)]PF6 complexes are reported. The complex design consists in combining i) the bridged di(pyrazin-2-yl)sulfane (NN)-N-<^> ligand with expanded pi-conjugation and electro-withdrawing 4-(trifluoromethyl)pyrimidine moieties and ii) the [(diphenylphosphino)phenyl] ether (DPEphos) (PP)-P-<^> ligand. The effect of the (NN)-N-<^> ligand substitution on the photophysical, electrochemical, ion conductivity, and morphological features in their respective powders and thin films is thoughtfully rationalized. This is rounded by the trends noted in single-layered red-emitting LECs (lambda(max) = 630-660 nm) featuring moderate performances with irradiances of around 60-90 mu W cm(-2) and total emitted energies in the range of 4-12 mJ. A further optimization using a multilayered architecture, in which hole injection/transport and exciton formation processes are decoupled, leads to a significant enhancement of the irradiance up to approximate to 150 mu W cm(-2) and total emitted energies of 91 mJ without affecting device chromaticity. Finally, the best red-emitting complex in LECs is used to fabricate host:guest white devices, achieving luminances of 12 cd m(-2) in concert with an excellent white color quality (x/y CIE color coordinates of 0.31/0.32; color rendering index of 90) stable over lifespan.