Dynamic mechanical modulation of chiroptical structures via linearly assembled plasmonic nanoparticles on birefringent polymer films

Plasmonic chiral materials exhibiting strong dynamic circular dichroism (CD) with a high asymmetric g-factor are desired for diverse optical applications such as optical communication, especially in near infrared (NIR) spectral range but rarely achieved. Here, we show a chiroptical flexible film composed of an array of linearly aligned plasmonic nanosphere chains with an elastic polymer substrate. These nanomaterials are capable of light polarization rotation up to 40° and a g-factor of 1.71 in NIR wavelength. Such high ellipticity stems from the interplay of high linear dichroism (LD) and linear birefringence (LB). The nanoparticle chains manifest LD at plasmonic resonance, which, combined with the stretching-induced LB of the elastic substrate providing phase retardance, as confirmed by simulation. The configuration offers dynamical and reversible tuning of all critical chiroptical characteristics, including handedness, magnitude, and frequency, via the assembly angle of plasmonic chains, chain length, and the stretching degree of substrates. This strategy is universally applicable to various polymer substrates by combining with plasmonic nanoparticle assembly, enabling the design of flexible chiroptical materials with strong and dynamically tunable chiroptical performance.