Heterometal-Doped M₂₃ (M = Au/Ag/Cd) Nanoclusters with Large Dipole Moments

Dipole moment (μ) is a critical parameter for molecules and nanomaterials as it affects many properties. In metal-thiolate (SR) nanoclusters (NCs), μ is commonly low (0-5 D) compared to quantum dots. Herein, we report a doping strategy to give giant dipoles (∼18 D) in M₂₃ (M = Au/Ag/Cd) NCs, falling in the experimental trend for II-VI quantum dots. In M₂₃ NCs, high μ is caused by the Cd-Br bond and the arrangement of heteroatoms along the C₃ axis. Strong dipole-dipole interactions are observed in crystalline state, with energy exceeding 5 kJ/mol, directing a "head-to-tail" alignment of Au_22-AgCd₁(SR)₁₅X (SR = adamantanethiolate) dipoles. The alignment can be controlled by μ via doping. The optical absorption peaks of M₂₃ show solvent polarity-dependent shifts (∼25 meV) with negative solvatochromism. Detailed electronic structures of M₂₃ are revealed by density functional theory and time-dependent DFT calculations. Overall, the doping strategy for obtaining large dipole moments demonstrates an atomic-level design of clusters with useful properties.