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

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.