Coumarin-Quinazolinone conjugate with large two photon action cross-section assisted by intramolecular hydrogen bond for bioimaging

[Display omitted] •A novel quinazolinone-based TP fluorescent platform (CQ) has been developed.•CQ exhibits large two-photon action cross-section value (299 G M).•Easily modification of CQ via amide group modification-deprotection strategy.•NBCQ from CQ as new “turn-on” nitroreductase (NTR) sensor for bioimaging.•NBCQ as a promising molecular tool for elucidating NTR activity in mitochondria for varying applications. Two photon (TP) fluorescence bioimaging proves to be a powerful tool for biomarker detection and disease diagnosis. However, the probes possessing both good optical properties and biocompatibility are limited. Herein a novel scaffold based on the conjugate of coumarin and quinazolinone (CQ) exhibited brilliant TP fluorescence properties (action cross-section value Φδmax = 299 GM and TP action cross section per molecular weight Φδmax/MW = 0.83) in water. The fluorescence properties are mainly attributed to the enlarged conjugate structure by intramolecular hydrogen bond. The TP fluorescence can be easily switched via amide group modification-deprotection strategy to regulate the formation of hydrogen bond. As a proof of concept, CQ was further engineered with p-nitrobenzyl moiety to afford 2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)-3-(4-nitrobenzyl) quinazolin-4(3H)-one (NBCQ) for mitochondria nitroreductase (NTR) imaging in normoxia and hypoxia, which proved to be a sensitive and selective “off-on” NTR fluorescent probe.