Organophosphides: A New Class of Luminophore Ligands for Copper(I) Carbene Based TADF Emitters and Photocatalysts

Luminescent carbene copper(I) charge transfer complexes are promising candidates as molecular materials for photonic applications. Apart from steric and electronic modification of the acceptor carbene, most of the research has been dedicated to amide donor ligands to control the luminescence properties, while the remaining pnictogen group as anionic electron donating ligands is photophysically underrepresented. Herein, we demonstrate that dimesityl phosphide (Mes₂P-) as a heavier homologue in [Cu(cAAC)(PMes₂)] (cAAC = cyclic amino(alkyl) carbene) gives rise to orange emission with quantum yields of up to ϕ_max = 0.52 in the solid state that is bathochromically shifted by ∼3000 cm^-1 in comparison to related amide complexes due to the lower electronegativity of phosphorus. Time-resolved variable temperature studies reveals that the µs-lifetimes and radiative rate constants of ca. k_r = 5 ⋅ 10⁴ s^-1 are due to thermally activated delayed fluorescence (TADF) as the dominating emission mechanism at room temperature. In polystyrene matrices, the complexes exhibit environment dependent chiroptical properties (up to g_lum = 10^-2, B_CPL = 1.31 M^-1 cm^-1, k_CPL = 41.5 s^-1) and are efficient blue light photocatalysts for hydrophosphination of alkynes in solution, highlighting the potential of heavier pnictogen ligands for photonic materials.