Double-Helical Assembly of a Copper-Silver Hydride Cluster Exhibiting Thermally Activated Delayed Fluorescence

Abstract

The synthesis of helical nanostructures with advanced functions from atomically precise building blocks is attractive, but remains a significant challenge. In this work, we report two atomically precise metal hydride clusters, Cu₂₄H₆L₁₂(PPh₃)₂Pz₆ ( Cu@Cu₂₃H₆,) and Cu_24-xAg_xH₆L₁₂(PPh₃)₂Pz₆ (0 > x > 1) ( Ag@Cu₂₃H₆) (L= CH₃OPhC≡C⁻, Pz = 3,5-(CF₃)₂-pyrazolate), containing M@Cu₂₃ (M=Cu/Ag) kernels with D₃-symmetry. Single crystal X-ray diffraction results reveal that the DNA-like double-helical nanostructures driven by intrastrand and interstrand supramolecular interactions, including weak hydrogen bonds (i.e., C–H···F/O/C) and van der Waal’s interactions (i.e., C···F and F···F), are formed through the self-hierarchical assembly of Cu@Cu₂₃H₆ and Ag@Cu₂₃H₆. In addition, Cu@Cu₂₃H₆ is nonemissive. After doping with Ag, Ag@Cu₂₃H₆ exhibits thermally activated delayed fluorescence (TADF) both in the solid state and in solution, which was seldom presented in high-nuclear clusters. Experimental and theoretical calculations suggest that the efficient separation of highest occupied molecular orbital and lowest unoccupied molecular orbital as well as larger spin–orbit coupling of Ag@Cu₂₃H₆ than Cu@Cu₂₃H₆ are responsible for the TADF. This work not only provides a platform to facilitate the in-depth investigation of self-hierarchical assembly mechanisms of double-helical nanostructures but also demonstrates that the doping strategy can endow helical nanostructures with interesting luminescent behavior.