Abstract
Phototheranostics within the second near-infrared (NIR-II, 1000-1700 nm) window offer considerable advantages compared to those operating in the visible and first near-infrared region (NIR-I, 700-900 nm). Herein, a donor-acceptor-donor (D-A-D) structured NIR-II absorbing Boron Difluoride Formazanate (BDF) dye FBDFDPA is developed through a donor engineering strategy for 1060 nm laser-excited photoacoustic imaging (PAI)-guided photothermal therapy (PTT). By replacing the donor unit from alkoxy-substituted triphenylamine with alkoxy-substituted diphenylamine, the planarity of the molecular conjugated skeleton is enhanced, thus promoting the intramolecular charge transfer (ICT) effect, leading to a 138 nm redshift in absorption and extending it into the NIR-II region. FBDFDPA NPs show excellent molar extinction coefficient (ε = 7.66 × 10(3) M(-1) cm(-1)) at 1060 nm and significant photothermal conversion efficiency (η = 54.4%), enabling effective NIR-II PTT for tumor ablation under the guidance of NIR-II PAI. This work establishes a donor planarization engineering strategy for designing NIR-II absorbing dyes, offering a promising avenue for advanced cancer photothermal theranostics.