A New Phenolate-Ion-Typed Two-Photon Near Infrared Fluorophore Based Biosensor for High-Performance Detection of HNO.

While ( E )-4-(2-(4-(dicyanomethylene)-4 H -chromen-2-yl)vinyl)phenolate anion ( DCPO - ) has emerged to be a potential near infrared (NIR) biosensor signaling unit recently, the p K a value of its conjugative acid of DCPOH (~9) was relatively high, which will lead to relatively low concentrations of DCPO - in physiological conditions and hence unsatisfactory sensitivity of DCPO - -based bio-probes. Herein, by difluoro-substitution on DCPO - , we exploit a novel fluorophore of o -FDCPO - whose conjugate acid has a much lowered p K a value of 7.42. Meanwhile, o -FDCPO - is NIR-emissive with λ em of 693 nm, together with a 0.76 time higher fluorescence efficiency than that of DCPO - . The significant superiority of o -FDCPO - over DCPO - in sensitivity for NIR bio-sensor applications has been confirmed by comparative studies on two HNO probes, namely o -FDCPO-P and DCPO-P bearing signaling units of o -FDCPO - and DCPO - , respectively. Moreover, o -FDCPO-P has been demonstrated to be a high-performance HNO probe with high selectivity, high sensitivity (detection limit: 50 nM) and rapid response, together with a two-photon NIR-excitation imaging capability.