Molecular sensing behavior of di-2-pyridylketone-2-thenoylhydrazone (dpktah) in non-aqueous media

Abstract

Optical measurements performed on di-2-pyridylketone-2-thenoylhydrazone (dpktah) in dimethylsulfoxide (dmso) and N, N-dimethylformamide (dmf) media disclosed two intraligand charge transfer (ILCT) transitions that are sensitive to changes in their environment. Variation in the chemical surroundings of dpktah demonstrate reversible interconversion between the two conformations (α-dpktah associated with the low-energy electronic transition observed at 400 nm and β-dpktah with the electronic transition observed at 326 nm), and allowed for calculation of their extinction coefficients. Thermo-optical measurements confirmed the reversible interconversion between the α- and β-dpktah, and gave Δ H ø = −39.57, −36.58 kJ mol −1, Δ S ø = −145.37, +108.57 J mol −1, Δ G ø = +3.77, +4.22 kJ mol −1 and K = +0.22, +0.38 at 298.15 K in dmf and dmso, respectively. The high values for the extinction coefficients, and low values for the thermodynamic parameters for the interconversion between the β- and α-forms of dpktah demonstrate the facile interconversion between the two forms and possible use of dpktah in dmf and dmso as a molecular sensor. Group 12 metal dichlorides in concentration as low as 1.00 × 10 −5 M can be detected and determined using dpktah in dmf. 1H NMR spectra measured in different solvents confirmed the sensitivity of dpktah to changes in its surroundings. At low temperatures, the spectral signature of two isomers appeared, and as the temperature increased, the spectral signature of a monomer prevails.