Boron Difluoride Formazanate Dye With Donor Planarization Engineering for 1060 nm Laser Activated Photothermal Theranostics

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.