Pattern Recognition and Visual Detection of Aldehydes Using a Single ESIPT Dye.

The accurate discrimination and quantification of aldehydes is a worthy objective made challenging by their similar chemical reactivities. Considering the nucleophilic reaction mechanism between an aldehyde and a primary amine, it is reasonable to vary the reaction pH to manipulate the reactivity of aldehydes and the stability of the resulting Schiff base for analytical purposes. We have designed and synthesized three benzothiazole-based fluorescent molecules (-) containing an amino group substituted at the ortho-, meta-, and para-positions for aldehyde sensing. It was determined that only having an amino group at the ortho-position exhibits a significant fluorescence response in the presence of formaldehyde at a particular pH, whereas and gave negligible responses, indicating that the ESIPT process in should be responsible for the changes in its fluorescence. Accordingly, a pH-mediated sensor array was constructed by dissolving in aqueous solvents with different pH values. was found to be reliable for the discrimination of seven different aldehydes and identification of unknown aldehyde samples. Moreover, was successfully applied to prepare a fluorescent test paper for the visual detection of formaldehyde vapor.