X-ray crystallographic, spectroscopic and electrochemical properties of a bi-stable di-2-thienyl ketone 2,4-dinitrophenyl hydrazone (dtkdnph)

Abstract

Di-2-thienyl ketone 2,4-dinitrophenyl hydrazone (dtkdnph), obtained from the acid-catalyzed condensation of di-2-thienyl ketone (dtk) with 2,4-dinitrophenylhydrazine, exhibits rich phyisco-chemical properties. X-ray structural analysis on a single crystal of dtkdnph grown from a dmso solution confirmed its identity, revealed non-coplanar thienyl rings, and a web of non-covalent interactions. Spectroscopic measurements in protophilic solvents, hydrogen bond acceptors, such as dmso or dmf, disclosed high sensitivity of dtkdnph to its surrounding, established an equilibrium between dtkdnph and dtkdnph.S (S = solvent) and showed substrates in concentrations as low as 1 × 10−9 M can be detected using protophilic solutions of dtkdnph. Variable temperature studies confirmed the facile inter-conversion between dtkdnph and dtkdnph.S and changes in enthalpy (ΔHø) of −11.77 ± 0.66, 13.55 ± 0.66 kJmol−1, entropy (ΔSø) of −37.21 ± 2.00 and 33.55 ± 2.00 JK−1mol−1 and free energy (ΔGø) of −0.68 and 3.5 kJmol−1 were calculated in dmf and dmso, respectively. Electrochemical measurements divulged solvent dependence, and electrochemical decomposition following the first electron transfer.