Bulky (Imino)phosphide and Mixed Bis-dimethyl-siloxane /(Imino)phosphide-supported Redox-Active Cu5 and Cu6 Nanoclusters: Luminescence and Photocatalytic Studies.

Herein, we depict isolation of neutral air-stable atomically precise Cu5 [((R2-cAI)P(Dipp))3Cu5Cl2] (cAI = cyclic alkyl(imino); Dipp = 2,6-diisopropylphenyl; R2 = Cy (2a) and Et2 (2b)) and Cu6 [((Et2-cAI)P(Dipp))2Cu6(OSiMe2OSiMe2O)2] (3) nanoclusters, stabilized by bulky (imino)phosphide and mixed bis-dimethyl-siloxane/(imino)phosphide ligands. 2a-2b and 3 are structurally characterized by X-ray single-crystal diffraction and studied by XPS, FT-IR, and NMR spectroscopy. 2a-2b exhibit yellow emission at ambient temperature with photoluminescence quantum yields (ϕPL) up to 11% and significantly high average lifetimes (τav = 38-110 μs). At 80 K, 2a-2b exhibit red emission with 5-fold to ∼80-fold increased τav values (191 μs-8.32 ms). Time-dependent density functional theory calculations, along with natural transition orbital analyses, reveal that the singlet-triplet energy gap, ΔE(S1-T1) for 2a-2b lies in the order of ∼0.2 eV, which is comparable with the experimentally obtained value of 0.16 eV, suggesting thermally activated delayed fluorescence (TADF). The spin-orbit coupling matrix (SOCM) calculations between different excited singlet and triplet states reveal significantly larger values (∼10-14 cm-1), which, along with lower ΔE(S1-T1) values, possibly facilitate an efficient spin-flipping process, enabling TADF. 2a is fabricated to a converted-LED and utilized as an excellent photocatalyst for regioselective [2 + 3] cycloaddition of aromatic alkynes and azides in the presence of a white LED, affording substituted triazoles (6) in good yields.