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-TPAO₄ is reported, synthesized via one-step demethylation and oxidation of its closed-shell precursor, EDOT-TPAOMe₄. Time-dependent density functional theory calculations confirm an acceptor-donor-acceptor configuration of EDOT-TPAO₄ where radical termini act as electron acceptors. This structural transformation narrows the optical bandgap from 2.74 eV of EDOT-TPAOMe₄ to 1.26 eV of EDOT-TPAO₄ and endows EDOT-TPAO₄ 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-TPAO₄ 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-TPAO₄ 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.