Stable Ultrabroad‐Absorbing Radical Achieves Efficient NIR‐II Photothermal Conversion via Facile Synthesis

Inspired by the electron‐withdrawing ability of nitroxide radicals, a novel open‐shell material, EDOT‐TPAO 4 is reported, synthesized via one‐step demethylation and oxidation of its closed‐shell precursor, EDOT‐TPAOMe 4 . Time‐dependent density functional theory calculations confirm an acceptor–donor–acceptor configuration of EDOT‐TPAO 4 where radical termini act as electron acceptors. This structural transformation narrows the optical bandgap from 2.74 eV of EDOT‐TPAOMe 4 to 1.26 eV of EDOT‐TPAO 4 and endows EDOT‐TPAO 4 high electrical conductivity of 0.02 S cm −1 and unexpected electrochemical stability in air. The reduced bandgap enables ultrabroad absorption in powder (300–2500 nm), driving exceptional photothermal conversion. Under 1064 nm laser irradiation (0.9 W cm −2 ), EDOT‐TPAO 4 heats rapidly to 290 °C within 60 s, outperforming most reported pure organic photothermal materials. Femtosecond spectroscopy confirms ultrafast excited‐state nonradiative quenching in picosecond timescale, underlying the efficient photothermal conversion. Leveraging both its optical properties and thermal responsiveness, EDOT‐TPAO 4 achieves outstanding solar‐driven water evaporation of 1.433 kg m −2 h −1 . This study not only presents one of the most efficient and readily synthesized organic photothermal materials to date, but also establishes a new molecular design strategy that expands the functional landscape of next‐generation radical‐based electron acceptor building blocks and open‐shell radical semiconductors for electronics, challenging conventional closed‐shell strategies in organic electronics.