A novel DHP-NH2 fluorescent dye for the determination of water content in organic solvents, rice, and aspirin: DFT calculations

A novel aminodihydropyridine derivative ( DHP-NH 2 ) was synthesized from hydrazine via a tandem cyclotrimerization of methyl propiolate. DHP-NH 2 distinguishably exhibited either strong fluorescence in aprotic solvents or weak fluorescence in protic solvents. Its fluorescence quenching in THF and MeCN was quantitatively determined in the presence of water content, demonstrating the limit of detection (LOD) of 0.036 %wt and 0.014 %wt in THF and MeCN, respectively. The critical hydrogen-bonding interactions between water molecules and the amino group of DHP-NH 2 were found to stabilize its excited state, supporting a quenching mechanism as confirmed by DFT/TDDFT calculations. To apply this DHP-NH 2 probe for on-site analysis, smartphone-based photography together with the ImageJ program was employed for the moisture detection with the LOD of 0.28 %wt in MeCN. Moreover, the trace amount of moisture in organic solvents and solid samples (rice and aspirin) was successfully detected by using this developed method. In addition, we successfully immobilized the DHP derivative onto the cellulose paper to be used as a portable test strip for determining water content in MeCN by naked-eye detection. • A novel aminodihydropyridine ( DHP-NH 2 ) shows fluorescence quenching in the presence of moisture. •The classification of protic and aprotic solvents can be differentiated by the fluorescence emission of DHP-NH 2 . •The water-stabilized excited state of DHP-NH 2, as strong evidence of the quenching mechanism, was confirmed by using the DFT/TDDFT calculations. •The moisture in real samples was easily determined using smartphone-assisted fluorescence detection. • DHP-NH 2 was successfully immobilized onto paper to be used as a paper test strip for water.