Temperature-modulated inversion and switching of chiroptical responses in dynamic side-by-side oligomers of gold nanorods

Herein, a new strategy is proposed for achieving dynamic chiral controls in self-assembly systems of plasmonic nanorods based on temperature-modulation. Via enlarging Au{100} side facets of Au nanorod (AuNR) building block and changing surface ligand from often-used cetyltrimethylammonium bromide (CTAB) to cetylpyridinium chloride (CPC), inversion of chiroptical signal in side-by-side (SS) oligomers is realized. Under the guide of chiral cysteine (Cys), Au{100} side facet-linked SS rods twist in the opposite direction compared with Au{110} side facet-linked counterparts. At high CPC concentration, by controlling the incubation temperature of chiral Cys, the dominant twist mode can be regulated. Finite-difference time-domain (FDTD) simulations indicate the key role of the twisting dihedral angle of the oligomers in driving chiral signal inversion. At low CPC concentration, a temperature-sensitive chiral switching is observed owing to the conformation change of the CPC ligand layer. The temperature-modulated chiral responses are based on the interactions of chiral molecules, achiral surface ligands, and exposed facets of the building block. The rich dynamic tunability of chiroptical responses of plasmonic assemblies may find applications in stimulus-responsive nanodevices.