Phenothiazine–Diphenylamine-Based Polyamides: Linking Diacid Structure to NIR Electrochromism and Energy-Storage Characteristics

A series of phenothiazine–diphenylamine (PTZ–DPA)-based polyamides were developed and evaluated as multifunctional electrochromic energy storage (EES) materials. The polymers were synthesized using a freshly designed diamine bearing a T-shaped PTZ–DPA donor core, with various acids, including thiophene (PA1), meta-phenylene (PA2), and pyridine (PA3) cycles. Structural confirmation was achieved by FT-IR and NMR, while TGA showed decomposition temperatures above 350 °C. UV–vis spectra revealed high optical transparency, and cyclic voltammetry showed two-step reversible oxidations. The polymers exhibited two-color switching (green and blue) with optical contrasts of 69.86–77.64% and 90.37–92.09%. Coloration efficiencies reached 162–212 cm2·C–1, with PA2 showing the highest values. PA1 demonstrated superior stability, with a decay of 8.24% (Δ%TT) and 9.36% (CE, η) after 1000 cycles. Galvanostatic charge–discharge analysis confirmed specific capacitances of 167.7 F·g–1 (PA1), 206.2 F·g–1 (PA2), and 193.3 F·g–1 (PA3), with PA2 delivering the highest energy density (46.4 Wh·kg–1) and PA1 exhibiting the best power density (10 103 W·kg–1). For practical purposes, a laboratory-scale EES prototype was fabricated by using PA2. The prototype exhibited color switching (green-gray and deep blue), while two prototypes were able to power an LED for ∼30 s.