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Vitamin B₁₂ (cyanocobalamin) is an essential nutrient with very low bioavailability. Compared with normal cells, tumor cells show an increased demand for vitamin B₁₂ to support their abnormal proliferation, which is a feature that can be exploited for the tumor-specific delivery of therapeutic and/or diagnostic agents by functionalizing vitamin B₁₂ with suitable metallodrugs and/or luminescent probes. In this context, we report on the design of fluorescent vitamin B₁₂–metal conjugates of the type [FLUO–B₁₂–{M}] in which cyanocobalamin is functionalized at the 5′-site of the ribose unit with a fluorophore (FLUO: rhodamine 6G), whereas the Co(III)–cyano moiety is <i>N</i>-coordinated to a metal-based anticancer scaffold ({M}: Pt(II) substrate bearing enantiopure phenylamino-oxime ligands derived from <i>R</i>- or <i>S</i>-limonene). Two novel fluorescent cyanocobalamin–platinum(II) derivatives and their corresponding non-fluorescent counterparts were successfully generated and fully characterized, including the evaluation of their lipophilicity and luminescent properties. Although they exhibit low antiproliferative activity (IC₅₀ = 40–70 μM), both fluorescent vitamin B₁₂–platinum(II) conjugates showed an enhanced capability to inhibit cell viability compared with the inactive metal precursors and the non-fluorescent vitamin B₁₂–platinum(II) analogues, confirming the beneficial effect of functionalization with the rhodamine 6G scaffold not only for imaging purposes but also with the aim of improving their biological activity.