Bakir, Mohammed, A.; Abdur-Rashid, Kamaluddin; Mulder, Willem H.
Author Affiliation, Ana.
Department of Chemistry
Optosensing properties of fac-Re(CO)3(dpknph)Cl (dpknph = di-2-pyridyl ketone p-nitrophenyl hydrazone)
Date of Publication
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 equilbrium distribution of the low (a-) and high (b-) energy conformations is solvent dependent, controlled by the dipole moment of the solvent molecules and their orintation around the total dipole of fac-Re(CO)3(dpknph)Cl. The interplay betwwen the a- and b-conformations of fac-Re(CO)3(dpkph)Cl, allowed calculations of their extinction cofficients, by forcing the equilbrium to shift to one conformation, using chemical stimuli. In DMSO and DMF extinction cofficients of 87 000± 2000 and 35 000± 2000 M-1 cm-1 were calculated for the b- and a-conformations of fac-Re(CO)3(dpknph)Cl at lmax., respectively. Thermo-optical measurements on fac-Re(CO)3(dpknph)Cl, allowed calculations of the activation parameters for the interconversion between the a- and b-conformations of fac-Re(CO)3(dpkph)Cl. In DMSO and DMF changes in enthalpy (DH ø)of –11.2± 1.3 and 10.9± 0.5 kJmol-1, entropy (DSø) of –12.7± 4.3 and 29.4± 1.7 JK-1 mol-1, and free energy (DGø) of –7.5± 0.2 and +2.2± 0.2 kJmol-1 and hence equilibruim constants of 20.9 ±1.7 and 0.4± 0.1 were calculated for fac-Re(CO)3(dpkph) at 295 K. The high values for the extenction coefficients and low values for the activation parameters for the interconversion betwwen the a- and b-conformations of fac-Re(CO)3(dpkph)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(dpkph)Cl and surroundings 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.....