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Cobalamins are known to react with thiols to yield stable β-axial Co^III–S bonded thiolato-cobalamin complexes. However, in stark contrast to the Co–C bond in alkylcobalamins, the photolability of the Co–S bond in thiolato-cobalamins remains undetermined. We have investigated the photolysis of N-acetylcysteinyl cob(III)alamin at several wavelengths within the ultraviolet and visible spectrum. To aid in photolysis, we show that attaching fluorophore “antennae” to the cobalamin scaffold can improve photolytic efficiency by up to an order of magnitude. Additionally, electron paramagnetic resonance confirms previous conjectures that the photolysis of thiolato-cobalamins at wavelengths as long as 546 nm produces thiyl radicals.