Integrated Multiband Smart Windows From UV to LWIR Based on Molecularly Engineered Thermochromic Hydrogels

ABSTRACT Smart windows offer energy‐saving potential for buildings, while challenges remain in achieving multi‐band design across ultraviolet‐visible‐near infrared‐long wavelength infrared (UV–VIS‐NIR‐LWIR). Here we present a smart window integrating a thermochromic poly (EEEA‐co‐NIPAM) (PEN) hydrogel with an anti‐UV layer and an indium tin oxide layer, enabling dynamic VIS‐NIR solar modulation alongside UV shielding and low LWIR emissivity ( ɛ LWIR ). Combined experimental and theoretical analyses reveal that 2‐(2‐ethoxyethoxy) ethyl acrylate (EEEA) comonomer strengthens the polymer network and forms favorable hydrogen‐bonding interactions with N‐isopropylacrylamide (NIPAM), promoting rapid dehydration‐driven chain collapse above a reduced lower critical solution temperature, and accelerating the optical response during heating. The produced window achieves a solar modulation (Δ Т sol ) of 42.7%, nearly complete UV shielding ( T UV = 0.1%), and low indoor‐facing ɛ LWIR = 0.31, with stable performance after 100‐h UV exposure and 100 thermal cycles. Outdoor tests demonstrate a 7.7°C cooling effect compared with ordinary glass, while EnergyPlus simulations demonstrate up to 62.6% savings in building heating/cooling energy in Singapore, San Francisco, and Brisbane. This work provides an effective multiband strategy for smart windows together with an in‐depth understanding of thermochromic hydrogel, and is expected to inspire future efforts toward spectrally selective, energy‐efficient building glazing.