Designing diphosphines towards photo- and electro-luminescent homoleptic Cu(i)/Ag(i) complexes

Abstract

While luminescent heteroleptic d¹⁰ complexes have been widely studied, their homoleptic counterparts have been barely explored. Herein, we demonstrate how to tune the emission colour of homoleptic diphosphine Cu(I)/Ag(I) complexes by introducing N-heteroaromatic rings and extended π-systems in the diphosphine backbone (λ_em = 455–610 nm). In crystalline powder, photoluminescence quantum yields (PLQYs) of up to 48% and thermally activated delayed fluorescence for both Cu(I) and Ag(I) series were found. However, their photoluminescent behaviour in thin films resulted, for example, in large bathochromically shifted emission maxima and unexpected changes in PLQYs. Besides the presence of aggregation, these findings could also be tentatively attributed to structural distortion of the coordination sphere (i.e., different conformers) upon film formation as suggested by powder X-ray diffraction and theoretical studies. Finally, the best films were also tested in light-emitting electrochemical cells, showing moderate performance, yet comparable to that of devices based on heteroleptic complexes.