A new CO-releasing terpyridine based manganese(I) tricarbonyl complex, [MnBr(CO)(3)(terpy-C6H4OH)] (1 center dot Mn-OH) functioning via light has been reported. For the first time, we have demonstrated the allosteric regulation concept to control the CO-releasing properties of a CO-releasing molecule (CORM). Fluoride ion is reported to function as an allosteric activator to control the rate of CO release in the CORM. Complex 1 center dot Mn-OH represents an interesting new class of CO-releasing system that releases CO upon irradiation with blue light (410 nm) over a period of 40 min with the half-time of 9.8 min. Fluoride ion selectively binds to the phenol moiety of the complex through hydrogen bonding and deprotonates to phenolate with a color change. Interestingly in the presence of fluoride ion, the rate of CO release is fast with the half-time of less than a minute. The rate of CO release is allosterically regulated by fluoride anion and can be monitored through a color change, fluorescence, and absorption based spectral changes along with IR studies and myoglobin assay.