Optosensing behavior of the first Ru(II)-compound of di-2-pyridylketone-p-nitrophenylhydrazone (dpknph), [Ru(bpy)2(dpknph)]Cl2

Abstract

The reaction between Ru(bpy)2Cl2 (bpy=2,2′-bipyridine) and di-2-pyridylketone-p-nitrophenylhydrazone (dpknph) in refluxing ethanol gave [Ru(bpy)2(dpknph)]Cl2 in good yield. Optical measurements on [Ru(bpy)2(dpknph)]Cl2 in non-aqueous media revealed the presence of two interlocked electronic states due to conformational changes associated with the hydrazone moiety of [Ru(bpy)2(dpknph)]Cl2. The equilibrium distribution of the high-energy β-conformation associated with the high-energy electronic state and the low-energy α-conformation associated with the low-energy electronic state is solvent and solute dependent controlled by the solvent–solute and solute–solute interactions. The interplay between the α- and β-conformations of [Ru(bpy)2(dpknph)]Cl2 allowed calculations of the extinction coefficients of electronic states by forcing the equilibrium to shift to one conformation using chemical stimuli. Extinction coefficients of 56 000±2000 and 48 500±2000 M−1 cm−1 were calculated in DMSO for the β- and α-conformations of [Ru(bpy)2(dpknph)]Cl2, respectively, using excess HgCl2 in DMSO. Thermo-optical measurements on [Ru(bpy)2(dpknph)]Cl2 in DMSO confirmed the interconversion between the α- and β-conformations of [Ru(bpy)2(dpknph)]Cl2 and gave changes in enthalpy (ΔHø) of −35.5±4.0 and 13.0±0.5 kJ mol−1, entropy (ΔSø) of –126.9±20 and 45.2±4.5 kJ mol−1, and free energy (ΔGø) of 2.31±0.2 and −0.48±0.2 kJ mol−1 in the absence and presence of NaBH4 at 295 K. The high values for the extinction coefficients and low values and sensitivity of the activation parameters for the interconversion between the α- and β-conformations of [Ru(bpy)2(dpknph)]Cl2 in DMSO to solution composition allowed for the use of this system ([Ru(bpy)2(dpknph)]Cl2 and surrounding solvent or solute molecules) as a spectrophotometric sensor for a variety of chemical stimuli that include metal ions. Group 12 metal ions in concentrations as low as 1.00×10−8 M can be detected and determined using [Ru(bpy)2(dpknph)]Cl2 in DMSO in the presence and absence of NaBH4.