IrAu12 superatom modified by chiral diphosphines: doping-induced enhancement of chiroptical activity

Gold superatoms modified by chiral ligands are a new class of chiroptical nanomaterials, but improvement of their chiroptical properties, such as circular dichroism (CD) and circularly polarized luminescence (CPL), remains a challenge. In this work, we studied the effects of single-atom doping on the chiroptical properties of a representative Au-13 superatom using [Au-13((R,R)-DIPAMP)(5)Cl-2](3+) and [Au-13((S,S)-DIPAMP)(5)Cl-2](3+) (Au-13-R/S; DIPAMP = 1,2-bis[(2-methoxyphenyl)phenylphosphino]ethane). We synthesized an enantiomeric pair of superatoms: [IrAu12((R,R)-DIPAMP)(5)Cl-2](+) and [IrAu12((S,S)-DIPAMP)(5)Cl-2](+) (IrAu12-R/S). Single-crystal X-ray diffraction analysis revealed that the icosahedral Ir@Au-12 core of IrAu12-R/S was more twisted along the Cl-Au-Ir-Au-Cl axis compared with the Au-13 core of Au-13-R/S, leading to a larger absorption anisotropy factor. IrAu12-R/S exhibited a much higher photoluminescence quantum yield (similar to 70%) compared with Au-13-R/S (15%) due to a larger energy gap between the highest occupied and the lowest unoccupied molecular orbitals. Although Ir doping did not appreciably enhance the photoluminescence anisotropy factors, the brightness of the CPL of IrAu12-R/S was five times higher than that of Au-13-R/S. This work provides a rational guide for improving the chiroptical activity of Au superatoms via the doping-mediated manipulation of the geometric and electronic structures.