Imidazole-2-thiohydantoin conjugates for trace water detection in organic solvents and visual colour recognition for real-time monitoring

Abstract

Trace water is a detrimental impurity present in organic solvents that negatively impacts various organic reactions, necessitating the development of new sensitive and selective methods for its detection. In this study, we develop two novel donor–acceptor molecules, Im-2TH and Di-OMeIm-2TH, using a Knoevenagel condensation reaction between imidazole-based aldehydes and 2-thiohydantoin. Im-2TH and Di-OMeIm-2TH show intramolecular charge transfer (ICT) bands at 414 and 425 nm, along with strong green and yellow emissions at 550 and 585 nm in THF, respectively. Both compounds exhibit strong solvatochromic behaviour with changes in the polarity of the solvent and show aggregation-induced emission (AIE) characteristics with distinct variations in their surface morphology (spheres, fibers, and needle-shaped flakes) as the fraction of water varies in THF, ACN and DMSO mixtures. Consequently, tuning their surface morphology and change in their emission behaviour offer potential for trace water detection in organic solvents. Di-OMeIm-2TH exhibits superior sensitivity compared with Im-2TH, as evident from its higher K_sv values of 1.3945, 3.117, and 0.6787 M⁻¹ with limit of detection (LOD) of 0.060, 0.034 and 0.124 ppm in THF, ACN, and DMSO, respectively. Furthermore, Im-2TH and Di-OMeIm-2TH were employed for trace water detection in real samples such as cement, sand, sugar, salt and detergent powder. A smart phone-based fluorometric assay is developed for the recognition of colour variation and RGB array profiles to facilitate the detection of water content in organic solvents for real-time monitoring.