Dual-mode switchable and tunable broadband UV shielding via azobenzene-loaded shape memory films

Smart UV filtering materials that can dynamically respond to environmental stimuli are crucial for applications in agriculture, defense, cosmetics, and preservation, especially under low-temperature conditions, where UV exposure is amplified. This work introduces a dual-mode, thermally switchable, and optically tunable broadband UV filter based on what we believe to be a novel polyurethane-azobenzene-carbon black (PAC) composite. The composite demonstrates a significant enhancement in UV absorption upon cooling, with switching observed around 24°C and tunable spectral broadening upon visible and UV light exposure. Structural and vibrational analyses via XRD and Raman spectroscopy reveal that the observed optical switching is associated with temperature-induced conformational changes in the PU matrix and light-triggered isomerization of azobenzene, leading to modulation in the local refractive index and absorption characteristics. The study reveals how shape memory-driven refractive index modulation and azobenzene photoisomerization synergistically enable adaptive UV shielding below room temperature. These findings establish PAC as a scalable, low-cost smart material for next-generation UV protection in cold-environment applications.