Optosensing properties of fac-Re(CO)3(dpknph)Cl (dpknph = di-2-pyridyl ketone p-nitrophenyl hydrazone)

Optical and thermodynamic measurements on fac-Re(CO)(3)(dpknph)Cl in polar non aqueous solvents revealed the existence of two interlocked conformational forms for fac-Re(CO)(3)(dpknph)Cl. The equilibrium distribution of the low (alpha-) and high (beta-) energy conformations is solvent dependent, controlled by the dipole moment of the solvent molecules and their orientation around the total dipole of fac-Re(CO)(3)(dpknph)Cl. The interplay between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, allowed calculations of their extinction coefficients, by forcing the equilibrium to shift to one conformation, using chemical stimuli. In DMSO and DMF extinction coefficients of 87 000 +/- 2000 and 35 000 +/- 2000 M-1 cm(-1) were calculated for the beta- and alpha-conformations of fac-Re(CO)(3)(dpknph)Cl at lambda(max), respectively. Thermo-optical measurements on fac-Re(CO)(3)(dpknph)Cl, allowed calculations of the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl. In DMSO and DMF changes in enthalpy (Delta H degrees) of - 11.2 +/- 1.3 and 10.9 +/- 0.5 kJ mol(-1), entropy (Delta S degrees) of - 12.7 +/- 4.3 and 29.4 +/- 1.7 JK(-1) mol(-1), and free energy (Delta G degrees) Of - 7.5 +/- 0.2 and + 2.2 +/- 0.2 kJ mol(-1) and hence equilibrium constants of 20.9 +/- 1.7 and 0.4 +/- 0.1 were calculated for fac-Re(CO)(3)(dpknph) at 295 K. The high values for the extinction coefficients End low values for the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, in polar non aqueous solvents allowed the use of these systems as molecular sensors to probe their structural relaxation and interactions with their surroundings. These systems (fac-Re(CO)(3)(dpknph)Cl and surrounding solvent molecules) optically sense chemical and physical stimuli and their sensing power depends on the intensity and nature of these stimuli, i.e. the systems exhibit a high degree of sensitivity and selectivity. (C) 2000 Elsevier Science B.V. All rights reserved.