Unraveling\nthe Origin of Reverse Plasmonic Circular\nDichroism from Discrete Bichiral Au Nanoparticles

Bichiral plasmonic nanoparticles exhibited intriguing\ngeometry-dependent\ncircular dichroism (CD) reversal; however, the crucial factor that\ndominates the plasmonic CD is still unclear. Combined with CD spectroscopy\nand theoretical multipole analysis, we demonstrate that plasmonic\nCD originates from the excitation of electric quadrupolar plasmons.\nMoreover, a comparative study of two distinct quadrupolar modes reveals\nthe correlation between the sign of the CD and the local geometric\nhandedness at the plasmonic hotspots, thereby establishing a structure–property\nrelationship in bichiral nanoparticles. The reverse CD is attributed\nto the opposite directions of the wavelength shift of the two plasmon\nmodes upon changing the particle geometry. By finely tuning the size\nof bichiral nanoparticles, we can further reveal that the dependence\nof plasmonic CD on the electric quadrupolar plasmons. Our work sheds\nlight on the physical origin of plasmonic CD and provides important\nguidelines for the design of chiral plasmonic nanoparticles toward\nchirality-dependent applications.