A porphyrin derivative containing 2-(oxymethyl)pyridine units showing unexpected ratiometric fluorescent recognition of Zn2+ with high selectivity

A porphyrin derivative (1), containing two 2-(oxymethyl)pyridine units has been designed and synthesized as chemosensor for recognition of metal ions. Unlike many common porphyrin derivatives that show response to different heavy metal ions, compound 1 exhibits unexpected ratiometric fluorescence response to Zn²⁺ with high selectivity. The response of the novel chemosensor to zinc was based on the porphyrin metallation with cooperating effect of 2-(oxymethyl)pyridine units. The change of fluorescence of 1 was attributed to the formation of an inclusion complex between porphyrin ring and Zn²⁺ by 1:1 complex ratio (K = 1.04 × 10⁵), which has been utilized as the basis of the fabrication of the Zn²⁺-sensitive fluorescent chemosensor. The analytical performance characteristics of the proposed Zn²⁺-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Zn²⁺ with a linear range covering from 3.2 × 10⁻⁷ to 1.8 × 10⁻⁴ M and a detection limit of 5.5 × 10⁻⁸ M. The experiment results show that the response behavior of 1 to Zn²⁺ is pH-independent in medium condition (pH 4.0-8.0) and show excellent selectivity for Zn²⁺ over transition metal cations.