This work studies the effect of the σ-Hammett parameter (σ_p) – i.e., the σ-donation effect caused by substitution at the para position of a bipyridine ligand (4,4′-R₂bipy, where R is MeO, Me, H, NO₂) – on both the photo- and electro-luminescence features of a series of heteroleptic copper(I) complexes – i.e., [Cu(N^N)(P^P)]⁺ where N^N and P^P ligands are R₂bipy and Xantphos, respectively. By virtue of a comprehensive photophysical, theoretical, and thin-film lighting device – i.e., light-emitting electrochemical cells (LECs) – investigation, we note a clear relationship between the σ_p and the photo- and electro-luminescence parameters, such as photoluminescence quantum yields, excited-state lifetimes, and emission maxima, as well as device brightness, stability, and efficacy, respectively. As the most relevant finding, the substitution with the group featuring the most negative σ_p – i.e., MeO – provides a ca. five-fold enhancement of all of the aforementioned figures-of-merit upon comparison within the series of complexes. As such, this work provides a new guideline for a device optimization through a rational ligand design for heteroleptic copper(I) complexes.

This work describes the synthesis, and structural, spectroscopic, and theoretical studies of a mononuclear silver(I) complex with the formula [Ag(Xantphos)(4,4′-(MeO)₂-2,2′-bipy)]BF₄·DCM (1·BF₄) [Xantphos: 4,5-bis(diphenylphosphino)-9,9′-dimethylxanthene]. We provide meaningful insights into the enhancement of the photoluminescence features of this silver(I) complex compared to its copper(I) analogue.

Two novel mixed valence di/tri nuclear Co^II–Co^III complexes were synthesized and characterized by single crystal X-ray diffraction. Magnetic studies at low temperature revealed that both complexes show slow magnetic relaxation.