Monitoring of reaction kinetics and determination of trace water in hydrophobic organic solvents by a smartphone-based ratiometric fluorescence device.

A smartphone-based ratiometric fluorescence device was designed to monitor the reaction kinetic process under vigorous mixing conditions, demonstrated by the hydrolysis of Cs4PbBr6 nanocrystals (NCs). In the presence of trace water, part of Cs4PbBr6 NCs (non-fluorescent) was converted to CsPbBr3 NCs (strong fluorescent). Using anthracene as the reference fluorophore, the brightness ratio of the green (from CsPbBr3 NCs) to blue (from anthracene) components in the fluorescence image which was recorded in situ by the smartphone camera was measured as the signal for kinetic analysis. It was shown that the water-triggered conversion reaction from Cs4PbBr6 NCs to CsPbBr3 NCs follows the pseudo-second-order kinetic model in the early rapid hydrolysis stage (up to 4 min). With increasing water content, the hydrolysis of Cs4PbBr6 NCs is promoted to yield more CsPbBr3 NCs, which was used to determine trace water in n-hexane, dichloromethane, and toluene with detection limits of 0.031, 0.043, and 0.057 μL mL-1, respectively. The device offers the advantages of portability and low cost for rapid field determination of trace water in hydrophobic organic solvents. Graphical abstract.