Transparent Single‐Dye NIR Photonic Platform for Multimodal Optical Authentication

ABSTRACT Multifunctional near‐infrared (NIR)‐responsive materials are essential for advanced anti‐counterfeiting (ACF). Here, we present a highly transparent squarylium (SQ) dye that integrates triple NIR responses—absorption, fluorescence, and photothermal conversion—within a single molecular system. The 2,3‑dihydroperimidine structure enables strong NIR absorption (811–823 nm) and fluorescence (834–857 nm) with > 97% visible transparency (0.1 wt.%) and thermal stability (T d = 208°C). The dye exhibits ∼13‐fold higher photostability than indocyanine green (ICG) and repeatable photothermal response under 808 nm irradiation. Screen‐printed NIR‐emitting inks on diverse substrates (films, textiles, glass, plastic bottles) show washing/solvent durability and enable QR code authentication under 832 nm excitation, maintaining no visible contrast under daylight. This work establishes a transparent single‐component NIR photonic platform for multimodal, instrument‐assisted authentication of visually imperceptible security patterns through orthogonal optical readout modes.