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(N^N)(P^P)]PF6 complexes are reported. The complex design consists in combining i) the bridged di(pyrazin-2-yl)sulfane N^N ligand with expanded π-conjugation and electro-withdrawing 4-(trifluoromethyl)pyrimidine moieties and ii) the [(diphenylphosphino)phenyl] ether (DPEphos) P^P ligand. The effect of the N^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 (λmax = 630–660 nm) featuring moderate performances with irradiances of around 60–90 µW 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 ≈150 µW 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.