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

Abstract The synthesis, photophysical/electrochemical characterization, and implementation in light‐emitting electrochemical cells (LECs) of three novel red‐emitting heteroleptic [Cu(N ^ N)(P ^ P)]PF 6 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 (λ max = 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.