Highly Reversible "On-Off-On" Fluorescence Switch Governed by pH, Utilizing Bis(Benzimidazole) Derivatives with Varied Link Groups.

In this work, a series of dibenzimidazole derivatives 1-4, act as highly reversible colorimetric and fluorescent pH chemosensor, were designed and synthesized. Excellent reversible pH response of these sensors could be found by a specific pH change through obvious fluorescent color changes. The response is not affected by common cations (including Al³⁺, Cu²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Mg²⁺, Na⁺, K⁺, Ni²⁺, Pb²⁺ and Zn²⁺) and anions (including F^-, Cl^-, Br^-, I^-, ClO₄^-, H₂PO₄^-, HSO₄^-, HCO₃^- and CH₃COO^-). Notably, these sensors can be reused more than 10 times without losing functionality. Unlike previous reports, the distinct properties of 1-4 are attributed to the varied link groups. Based on comprehensive experimental data and mechanistic analyses, it is concluded that sensors 1-4 are promising candidates for use as highly reversible "on-off-on" fluorescence switches under precise pH control.