Excited state intramolecular proton transfer (ESIPT) termination enables “one-to-two” sensing property of an indolocarbazole-based Schiff base

Abstract

Detections towards multiple analytes by one sensor remain a significant challenges. Herein, a high-sensitivity chemo-sensor ICZ-o-XFJ is designed and synthesized for the simultaneous detection of F⁻ and Al³⁺. Suffering from the ESIPT process, this sensor is colorless and almost non-emissive in solutions. Once it interacts with F⁻ or Al³⁺, its solution becomes colored and bright emissive. This proves its high sensitivity and selectivity to F⁻ and Al³⁺, rendering its feasibility in colorimetric and fluorometric sensing of these ions. Accordingly, the full sensing studies of this sensor towards F⁻ and Al³⁺ including the ion response, anti-interference ability, limits of detection (LOD) and sensing mechanism have been conducted. The LOD of F⁻/Al³⁺ can be as low as 10^-7 M, suggesting the potential of this sensor in low concentration of these ions. Most importantly, by combining the results of stoichiometry, ¹H NMR titration and theoretical calculations, the sensing mechanisms have been revealed as deprotonation-induced and coordination-induced ESIPT termination for F⁻ and Al³⁺, respectively. Also, the potential applications of paper strips-based test kit and fluorescence RGB-based analysis method are tentatively explored, aiming to achieve fast, low-cost and convenient detection towards F⁻/Al³⁺. It’s expected that these results can provide valuable information for developing high performance “one-to-more” type chemo-sensor.