Bright‐and‐Cool Smart Windows: Visually Silent and Near‐Infrared Modulation via Quinoid Donor–Acceptor Polymers

ABSTRACT Smart window technologies require precise control of solar heat gain without sacrificing daylight quality. However, most electrochromic materials intrinsically couple near‐infrared (NIR) attenuation with visible light absorption, leading to undesired dimming. Herein, we report a quinoid donor–acceptor polymer, P(EDOT–TQ–EDOT–ProDOT), that achieves “spectral decoupling”—strong NIR‐selective modulation with minimal visible variation. By integrating electron‐rich 3,4‐ethylenedioxythiophene (EDOT) spacers and a strong [1,2,5]thiadiazolo[3,4‐ g ]quinoxaline (TQ) acceptor, the polymer exhibits stabilized polaronic states with optical transitions confined to the NIR region. The resulting film delivers a remarkable NIR transmittance change of 78.7% at 1252 nm while keeping visible modulation under 10%. Assembled into a solid‐state electrochromic device with a Prussian Blue counter electrode, it demonstrates negligible visible transmittance change (Δ T _vis < 5%), a high general color rendering index ( R _a > 85), ultra‐high coloration efficiency (1319 cm ² C ⁻¹ ), fast response (<4 s), and excellent durability over 10 000 cycles. Building energy simulations confirm that this “bright‐and‐cool” modulation mode achieves a net annual energy saving of 3.41 kWh m ⁻² by avoiding the lighting penalty (11.71 kWh m ⁻² savings) typical of conventional tinting systems. This work provides a new strategy for designing visually transmissive, thermally adaptive electrochromic materials that advance next‐generation energy‐efficient building envelopes.