Fig. 2: Strong near-infrared absorption of H-TriPy engineered via π-stacking.

a Cyclic voltammetry (CV) curve of the H-TriPy-based EC devices at a scan rate of 5 mV s⁻¹ (active area: 3.14 cm²). b UV-Vis-NIR transmittance spectra of H-TriPy-based EC devices under different voltages, measured with air as the baseline. Digital photographs were captured using regular and NIR cameras (700–1100 nm). Scale bars: 10 cm. c Time-dependent density-functional theory (TD-DFT) calculated absorption spectra of the non-stacked H-TriPy³⁺/H-TriPy³⁺ (grey line), π-stacked H-TriPy^2+▪ (blue line), and π-stacked H-TriPy^+▪▪ (red line). d Absorption spectra of H-TriPy-based EC devices under bright (grey line), cool (blue line), and dark modes (red line), measured with air as the baseline (active area: 3.14 cm²). e Calculated binding energy of the non-stacked H-TriPy³⁺/H-TriPy³⁺ (grey), π-stacked H-TriPy^2+▪ (blue), and π-stacked H-TriPy^+▪▪ (red). f Small-angle X-ray scattering (SAXS) spectra of H-TriPy/NMP under bright (blue) and dark modes (red). The inset shows the corresponding 2D scattering patterns, with the upper image for bright mode and the lower image for dark mode.