Diversity of supramolecular assemblies based on photoactive Cu(I) trimetallic building blocks and N donor ditopic ligands: from 1D coordination polymers to metallacycles

A series of polymetallic Cu(I) assemblies C1-4 was selectively obtained by self-assembly of a preorganized trimetallic precursor B with 3,3'-bipyridine ligand L1 and structurally related longer ligands L2-4, respectively, allowing to investigate the impact of ligands’ backbones on architectures on the derivatives C1-4. While linkers L1 and L2 led to the formation of 1D coordination polymers (C1,2), the newly prepared alloxazine-functionalized ligands L3 and L4, promoting the appearance of steric constraints and π–π interactions, led to the formation of discrete hexametallacycles (C3,4). Structural characterization via X-ray diffraction confirmed the role of ligand design in determining the final architectures. The solid-state photophysical properties of ligands L3 and L4, trimetallic precursor B and derivatives C1-4. are reported. L3 and L4 exhibit weak yellow fluorescence at room temperature (RT), while the trimetallic precursor B displays intense yellow 3MLCT phosphorescence at RT. Assemblies C1-4 show varied photophysical behaviors including 3MLCT phosphorescence for C1, ligand centered phosphorescence and fluorescence for C2 and C4, respectively, while C3 is non-emissive. This study provides new insights into the steric and electronic factors governing Cu(I)-based luminescent materials’ preparation, highlighting diverse photophysical behaviors including efficient RT emission performances.