Heteroaromatic π-stacking engineered near-infrared absorption for highly stable near-zero transmittance electrochromic window

Electrochromic (EC) devices based on structurally designable and color-tunable EC molecules can dynamically regulate light-heat transmittance via the charge-transfer mechanism, yet face challenges of limited near-infrared (NIR) absorption, long-term instability, and restricted modulation modes. Here, we show that π-stacking of heteroaromatic tri-pyridine molecules with a 1,3,5-triazine core (H-TriPy) enhances molecular conjugation, significantly augments NIR absorption, and enables dual-band modulation with improved visual comfort. The three pyridine-based redox centers facilitate multi-step electron transfer, enabling multi-modal EC regulation, including bright, cool, and dark modes. Incorporation of a fluorinated ionic liquid into EC organogels inhibits irreversible π-stacking of high-concentration H-TriPy. Consequently, H-TriPy-based EC devices achieve neutral-colored states with near-zero transmittance as low as 3.7% in both visible and NIR ranges and maintain high switching stability of over 89.1% retention after 100,000 cycles. Furthermore, large-area EC devices exhibit uniform tinting and reliable stability, underscoring their potential for energy-efficient green buildings.