Dual-Mode Methanol Sensing via Smartphone-Assisted Intelligent Sensor Based on Benzothiazole Donor-Acceptor Fluorophores.

Methanol, an alcohol solvent with significant roles in biology, industry, and the environment, can exert negative impacts on organisms and the environment when it is present in excess. Therefore, developing efficient and easy-to-operate methanol detection methods is essential for providing timely information on its concentration. In this work, four novel small molecule probes (DBZ-H, DBZ-Me, DBZ-Bu, and DBZ-OMe) with a D-A-A-D structure are developed with distinct fluorescence emission and large Stokes shifts in different organic solvents because of their conjugated push-pull system. Furthermore, with the nitrogen atom in benzothiazole as the anchor point, all the dyes can quantitatively detect methanol through intensity and wavelength modes. This specific ability to distinguish methanol from other alcohols is attributed to the strong hydrogen-bonding interaction between the nitrogen atom and methanol, as well as the small molecular size of methanol. The detection limits for methanol are 0.054%, 0.048%, 0.047%, and 0.044% for DBZ-H, DBZ-Me, DBZ-Bu, and DBZ-OMe, respectively. The sensing mechanism of methanol is confirmed through emission spectroscopy and theoretical calculations. Additionally, these dyes are applied for methanol detection in biodiesel. Finally, a dual-mode convenient detection of methanol is achieved with the assistance of a smartphone.