Poly(ethylene oxide)-Azopyridine Block Copolymers for Photothermal Energy Storage and Release

Solar thermal fuel materials are promising for light-energy storage and on-demand heat release. However, simultaneously balancing energy-storage capacity, storage lifetime, and condensed-state heat-release behavior is challenging for these materials. Herein, azopyridine was used as a core photoresponsive unit to design and synthesize a series of monomers with different flexible alkyl chain lengths (M-Cn), followed by the synthesis of block copolymers with different azopyridine block lengths (E₁₁₄-M_n). The effects of the molecular structure, block composition, and aggregated-state behavior on photothermal energy storage and heat release performance were systematically investigated. The designed monomers exhibited pronounced photoinduced phase-transition behavior, among which M-C8 favorably balanced between the photoisomerization behavior, energy-storage performance, and storage lifetime. With an increasing azopyridine block length, the photochemical energy-storage capability and storage lifetime of the block copolymers were significantly enhanced, while poly(ethylene oxide) (PEO) crystallization was progressively suppressed. E₁₁₄-M₄₉ exhibits the highest total energy density, reaching 108 J g^-1, and shows a markedly enhanced heat-release response under visible-light stimulation. This study provides new insights into the design and application of flexible solar thermal fuel materials.