– CAY10737 is a turn-on fluorescent probe for the detection of carbon monoxide (CO). It is selective for CO over a variety of anions, amino acids, amines, biothiols, and reactive species. In the presence of palladium (Pd) and CO, CAY10737 undergoes the Pd0-mediated Tsuji-Trost reaction to release a fluorescent compound that has absorption and emission maxima of 678/714 nm, respectively. This fluorescence can be used to detect CO production in vitro and in vivo. CAY10737 has low cytotoxicity, decreasing viability of HeLa cells by less than 25% when used at a concentration of 50 μM with PdCl2 for 24 hours.