Optical response measurements. Sinusoidal AC electric fields were applied across colloidal dispersions of CdSe/CdS NRs using a function generator (RIGOL DG1032) coupled with a high-voltage amplifier (Trek Model 2220). Concurrent changes in optical transmission of a 405 nm laser (RGBLase FBB-405-200-FS-C-1-0) were measured using a photoreceiver (2007 Nirvana Auto-Balanced Optical Receiver) and a digital oscilloscope (RIGOL DS2302A). Sample cells were prepared by adhering pairs of patterned ITO glass slides (MSE Supplies) using a mixture of optical adhesive (Norland NOE81) and 50 µm spacer beads (Cospheric). Detailed schematics of the experimental setup and sample cell design are included in the Supporting Information.