Zn2+-triggered excited-state intramolecular proton transfer: a sensitive probe with near-infrared emission from bis(benzoxazole) derivative

Near-infrared (NIR) emission can offer distinct advantages for biological applications. A fluorescent sensor, Zinhbo-1, based on bis(benzoxazole) ligand with 2,2'-dipicolylamine (DPA) as receptor, was synthesized. In aqueous solution, Zinhbo-1 demonstrates high sensitivity and selectivity for sensing Zn2+ with about 10-fold enhancement and nanomolar sensitivity (K-d = 0.29 nM). Moreover, sensor Zinhbo-1 can detect Zn2+ in near-infrared region (over 700 nm) with large Stokes shift (ca. 230 nm) attributing to the Zn2+-induced excited state intramolecular proton transfer (ESIPT).