Bidirectionally Thermochromic Nanocolloid System for on‐Demand Optical Switching and Agricultural Energy Management

Extreme weather and massive energy demands in facility agriculture threaten food security. However, the current optical switching strategy fails to provide adequate crop climate management, since creating thermochromic materials capable of reversible and temperature-bidirectional optical modulation across a wide temperature range remains a formidable challenge. Here, a nanocolloid system comprising two tailored thermoresponsive copolymers that achieve optical-thermal regulation by a temperature-bidirectional phase transition is reported. Adopting the cononsolvency in a binary solvent, the nanocolloid exhibits a widely tunable transition from 27-85 °C (heat-induced) and -9-36 °C (cold-induced). In the transparent state, the nanocolloid-based smart window achieves a high photosynthetically active radiation (PAR) transmittance (>91%). Upon heating, it shows remarkable solar modulation ability (ΔT_sol up to 65.43%), while upon cooling, it provides a high PAR diffuse reflectance of 27.92% and enhances supplemental lighting efficiency by 33.91%. As a proof of concept in climate-resilient agriculture, nanocolloid-based smart windows reduce energy consumption by 11.61 kJ·m^-3 (cooling) and 2.96 kJ·m^-3 (heating), while boosting photosynthetic rates of specific crops by 222.19% and 126.07% under heat and cold stress, respectively. The bidirectional optical-thermal regulation by nanocolloid-based smart windows enables low-energy agriculture through higher light use efficiency, thereby reducing the carbon footprint in sustainable agriculture.