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.