Chiral Au25 Nanospheres and Nanorods: Synthesis and Insight into the Origin of Chirality

Chirality in nanoparticles is an intriguing phenomenon. Herein, we have devised a well-defined gold nanoparticle system for investigating the origin of chirality in nanoparticles. We have designed chiral thiols (R- and S-isomers) and synthesized chiral gold nanoparticles composed of 25 gold atoms and 18 ligands, referred to as Au-25(pet*)(18), where pet* represents chirally modivied phenylethylthiolate -SCH2C*H-(CH3)Ph at the 2-position. These optically active nanoparticles are dose analogues of the optically nonactive phenylethylthioalte-capped Au-25 (pet)(18) nanoparticles, and the latter's crystal structure is known. On the basis of the atomic and electronic structures of these well-defined Au-25 nanoparticles, we have explicitly revealed that the ligands and surface gold atoms of Au-25 (pet*)(18) play a critical role in effecting the circular dichroism responses from the nanoparticles. Similar effects are also observed in chiral Au-25 rods. The mixing of electronic states of ligands with those of surface gold atoms constitutes the fundamental origin of chirality in such nanoparticles.