Improved Photostability of a Cu I Complex by Macrocyclization of the Phenanthroline Ligands

The development of molecular materials for conversion of solar energy into electricity and fuels is one of the most active research areas, in which the light absorber plays a key role. While copper(I)-bis(diimine) complexes [Cu$^{l}$ (L) $_{2}$] $^{+}$ are considered as potent substitutes for [Ru$^{ll}$ (bpy) $_{3}$] $^{2+}$, they exhibit limited structural integrity as ligand loss by substitution can occur. In this article, we present a new concept to stabilize copper bis(phenanthroline) complexes by macrocyclization of the ligands which are preorganized around the Cu$^{l}$ ion. Using oxidative Hay acetylene homocoupling conditions, several Cu$^{l}$ complexes with varying bridge length were prepared and analyzed. Absorption and emission properties are assessed; rewardingly, the envisioned approach was successful since the flexible 1,4-butadiyl-bridged complex does show enhanced MLCT absorption and emission, as well as improved photostability upon irradiation with a blue LED compared to a reference complex.