From Mono- to Tetranuclear: A Silsesquioxane-Anchored Cu(I) Chromophore Array with Additive Absorption and Preserved Excited-State Properties

Abstract

Multichromophoric assemblies provide a practical route to increase light absorption without fundamentally altering the electronic structure of the individual chromophores. Here we report a tetranuclear heteroleptic Cu(I) complex in which four [Cu(N∧N)(P∧P)] units are covalently attached to a double-decker silsesquioxane (DDSQ) scaffold. A structurally related mononuclear [Cu(N∧N)(P∧P)]+ complex (with N∧N = pyridyl-triazole; P∧P = DPEPhos) was used as a reference. The absorption and emission profiles of the tetranuclear assembly closely match those of the monomer, indicating that the local Cu(I) chromophore properties are largely preserved upon attachment to the DDSQ scaffold. At the same time, the MLCT absorption intensity increases approximately 4-fold (ε ≈ 17.3 vs. 4.1 · 103 M–1 cm–1 at 340 nm), consistent with chromophore multiplication and additive light harvesting. Electrochemical studies indicate that the tetranuclear scaffold largely preserves the mononuclear Cu(I)/ligand redox motif, with no clear evidence for electrochemical communication between the Cu(I) chromophores. Overall, DDSQ emerges as a versatile platform for constructing Cu(I) chromophore arrays that boost absorption cross sections while retaining monomer-like excited-state signatures.