A near infrared singlet oxygen probe and its applications in in vivo imaging and measurement of singlet oxygen quenching activity of flavonoids

•A near infrared fluorescent probe is synthesized for detection of singlet oxygen.•The probe is highly sensitive and selective towards singlet oxygen.•An assay for quantifying singlet oxygen scavenging activity is developed based on the probe.•The NIR probe is able to Image 1O2 in vivo.•Morin is a potent singlet oxygen scavenger while other flavonoids are not. The synthesis, characterization, and application of a near infrared (NIR) fluorescent singlet oxygen (1O2) probe was reported. The probe employs an IR-780 as the fluorophore, and a dimethylhomoocoerdianthrone (HOCD) moiety as the fluorescence quencher as well as the reaction center for 1O2. At its original state, the fluorescence is quenched due to photo-induced electron transfer, while when reacted with 1O2, the quenching is abolished, and fluorescence turns on for nearly 30 folds. The probe showed good selectivity and sensitivity towards 1O2 and was able to Image 1O2in vivo in simulated photo dynamic therapy in mice carcass. Besides, a fluorescent method for quantifying 1O2 quenching capacity was established and was applied to measure the 1O2 quenching of flavonoids. The 1O2 scavenging activity is dependent on the structures of the flavonoids and morin is the most active singlet oxygen scavenger among the flavonoids measured and the rest of the compounds show only moderate activity.