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

Abstract

A series of polymetallic Cu(I) assemblies C_1–4 was selectively obtained by self-assembly of a preorganized trimetallic precursor B with 3,3′-bipyridine ligand L₁ and structurally related longer ligands L_2–4, respectively, allowing to investigate the impact of ligands’ backbones on architectures on the derivatives C_1–4. While linkers L₁ and L₂ led to the formation of 1D coordination polymers (C_1,2), 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 (C_3,4). 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 C_1–4. 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 C_1–4 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.