Chiroptical Activity Enhancement via Structural Control: The Chiral Synthesis and Reversible Interconversion of Two Intrinsically Chiral Gold Nanoclusters.

We report the synthesis and crystal structure determination of two novel chiral gold nanoclusters. By utilizing BINAP, we isolate atomically precise intrinsically chiral Au nanoclusters [Au9( R-/ S-BINAP)4](CF3COO)3 and [Au10( R-/ S-BINAP)4( p-CF3C6H4C≡C)](CF3COO)3 in high yield with one-pot synthesis. Au9 has C2 geometry, while Au10 is C1 symmetric. Interestingly, reversible interconversion between Au9 and Au10 can be realized by the addition or removal of a RC≡CAu component. The transformation from Au9 to Au10 leads to significant enhancement of CD signals. The maximum anisotropy factor in the visible region of [Au10(BINAP)4( p-CF3C6H4C≡C)]3+ is the hitherto largest (up to 6.6 × 10-3) among gold nanoclusters, which is approximately twice of that of [Au9(BINAP)4]3+. This work demonstrates that the chiroptical activity of gold nanoclusters can be modulated by structural control through the introduction of second ligands.