Smartphone assisted chromogenic sensing of halogenated solvents and monoaromatic hydrocarbons*

Because of the frequent use in industry and commerce, each year million tons of organic solvents have been released to the environment without any prior treatment. Prolonged exposure of the hazardous solvents to humans have already triggered different health issues. As a result, development of off-laboratory and easy-tohandle analytical techniques to detect the harmful solvents are receiving paramount attention. The focus of this article is the development of naked eye observable colorimetric technique for the detection of halogenated solvents and monoaromatic hydrocarbons as well. Two divanadium(V) compounds (probes 1 and 2) were found to show distinct and instant color change to blue when a pinch of the probe is added to a large varieties of colorless solvents of monoaromatic hydrocarbons and halogenated organic compounds as well. The intense blue coloration is presumably due to the ligand-to-metal-charge-transfer (LMCT) and ligand-to-ligand-charge-transfer (LLCT) processes, as concluded from molecular orbital energy level diagrams generated from TD-DFT calculations. Practical applicability of the sensors has been tested by investigating the colorimetric response of the probes in organic solvent mixtures. We also have developed smartphone RGB color value based colorimetric sensing of halogenated and monocyclic aromatic hydrocarbon solvents in various nonpolar organic solvent mixtures, which might be useful for on-site naked eye sensing.

Automated summary

This study focuses on the development of a naked eye observable colorimetric technique for the detection of halogenated solvents and monoaromatic hydrocarbons. Two divanadium(V) compounds were found to show distinct and instant blue color change when added to various colorless solvents, presumably due to ligand-to-metal-charge-transfer and ligand-to-ligand-charge-transfer processes. The practical applicability of the sensors was tested by investigating the colorimetric response in organic solvent mixtures, as well as smartphone RGB color value based colorimetric sensing for on-site detection.