Ring Closure Reaction of 19-Substituted Bilinones to 5-Oxaporphyrin Metal Complexes Induced by Zn2+ and Cu2+ —Application to Turn-on Red Fluorogenic Probes for Zinc Ions—

The reaction of 19-phenoxybilinones with Zn2+ caused ring-closure to afford the 5-oxaporphyrin zinc complex under ambient conditions. While bilinones are non-fluorescent, the 5-oxaporphyrin zinc complex fluoresced red light. 19-Phenoxybilinone can be employed as a fluorogenic zinc ion sensor. Among various metal ions, only Zn2+, Cu2+ and Co2+ can induce the ring closure reaction to yield 5-oxaporphyrin metal complexes, and only the zinc complex was fluorescent. Submicromolar Zn2+ can be detected by 19-phenoxybilinone both in organic solvents and aqueous solvents. Ring closure reaction of 19-phenoxybilinone to 5-oxaporphyrin metal complexes occurs upon addition of Zn2+, Cu2+, and Co2+ at room temperature in both organic solvent and an aqueous solution. Only the zinc complex of 5-oxaporphyrin fluoresced red light. Therefore, 19-phenoxybilinone can be used as a zinc specific fluorogenic sensor.