Carbon monoxide (CO) is a gasotransmitter, which has shown therapeutic effects in recent studies. Photo carbon monoxide releasing molecules (PhotoCORMs) allow the delivery of CO to be controlled by light. In this work, a new organic photoCORM DK4 is studied. DK4 is a diketone type photoCORM, which releases two CO molecules under visible light and simultaneously generates a fluorescent anthracene derivative. However, this type of CORM suffers from a deactivating hydration reaction and often needs to be incorporated in polymers or micelles. The two highly hydrophobic tert-butyl groups of DK4 protect it from the hydration reaction. DK4 functions in 1% DMSO aqueous solution, in which other DKs are deactivated. DK4 was incorporated in a poly(butyl cyanoacrylate) (PBCA) nanoparticle. PBCA has been used as a tissue adhesive and has been extensively studied for delivery of drugs to the brain. The PBCA/DK4 nanoparticle showed good photoactivity and low cytotoxicity, and thus is a promising material for studying the biomedical effects of CO.