Isomeric Ag₁₄ Nanoclusters With Distinct Photophysical and Nanomechanical Properties

Atomically precise luminescent nanoclusters (NCs) with positional isomerism originating from the coordinating ligand shell represent an important group of functional nanomaterials. We report the synthesis of two neutral isomeric [Ag₁₄(CBDT)₆(TPP)₄] NCs (where CBDT-H₂ = ortho-carborane-9,12-dithiol, TPP = triphenylphosphine) having a stable 2e^- superatomic configuration with face-centered cubic (fcc) Ag₆@Ag₈ core-shell geometry, where TPP ligand coordination makes the structural distinction. The positioning of four TPP ligands on the outer four Ag atoms results in distinct distortions of the Ag₈ cubic shell and yields two Ag₁₄ isomeric NCs: Ag₁₄T (tetrahedral TPP binding) and Ag₁₄S (square-planar TPP binding). Density functional theory (DFT) calculations confirm a narrowed HOMO-LUMO gap for Ag₁₄S. The isomeric NCs exhibit markedly distinct photoluminescence (PL) properties, with room-temperature green and red phosphorescence for Ag₁₄T and Ag₁₄S, respectively. The former NC shows an especially complex PL behavior with multi-band emission at low temperatures. Furthermore, nanoindentation studies reveal slightly higher stiffness and hardness for Ag₁₄S crystals than the other isomer. These findings establish phosphine binding as a versatile strategy to tune structure, luminescence, and mechanical characteristics in atomically precise NCs, enabling tailored platforms for optoelectronics and nanomechanics applications.