Chiral plasmonic nanostructures have promising applications in optoelectronics due to their chiroptical responses. However, achieving active tuning of optical chirality remains challenging. Here, we develop stretchable chiroptical films with mechanically tunable extrinsic chirality by assembling hexagonal magnetic/plasmonic hybrid nanodisks in magnetic fields. The nanodisks, synthesized using a space-confined growth method, display three distinct plasmonic resonance modes at the UV-vis-NIR region, which red shift with increasing size as demonstrated by simulation and experimental results. The coupled magnetic and plasmonic anisotropy allows convenient control over the plasmonic resonance modes by altering the strength or direction of external magnetic fields. Further, magnetically aligning the nanodisks in a stretchable polymer film produces superstructures with extrinsic chirality, displaying selective absorption of circularly polarized light and inverted circular dichroism due to the linear dichroism-linear birefringence effect. Reversible mechanical stretching allows for continuous switching of circular dichroism in a wide range (from -1° to +1°). The efficient magnetic alignment of hybrid nanodisks in the hydrogel provides a simple and effective strategy for designing stretchable optical devices with tunable extrinsic chirality.
Keywords: circular dichroism; localized surface plasmon resonance; magnetic assembly; optical chirality; plasmonic nanodisk; space-confined growth.