Fluorescent dyes for moisture detection in organic solvents: Push-pull based phenothiazine aldehydes with large Stokes shifts

摘要

In an effort to develop probes for efficient detection of traces of water, a series of push-pull based donor (D)-acceptor (A) phenothiazine aldehydes displaying large Stokes shifts (115-156 nm) was designed and synthesized. Several aryl groups with hydrogen bonding ability were appended on the phenothiazine ring with an aim of enhancing moisture sensitivity and surrounding solvent environment dependency. The solvatochromic studies and Lippert-Mataga plots indicated the presence of positive solvatochmmism in all the compounds. The maximum ICT character was displayed by compound in which phenothiazine ring was appended with 4-formylphenyl ring. The possibility of twisted intramolecular charge transfer (TICT) states in this compound was revealed by Rettig plot. The regression analysis of Kamlet-Taft equations and the values of their correlation coefficients indicated that solvatochromic effect was influenced by solvent polarity and hydrogen bonding interactions. Among common organic solvents, water detection by all the compounds was found to be most sensitive in acetonitrile with detection limits 0.003-0.006 v/v %, suggesting their potential as low-cost moisture detecting probes for industrial applications.