The effects of hydrostatic pressure on the metal to ligand charge-transfer (MLCT) excited-state emission lifetimes for the copper® complexes Cu(dmp)2+ and Cu(dpp)2+ (dmp = 2,9-dimethyl-1,10-phenanthroline, dpp = 2,9-diphenyl-1,10-phenanthroline) have been determined in CH2C12 solution. In the absence of added quenchers, volumes of activation * for the nonradiative decay pathway have been determined to be -3.4 and -1.6 cm3/mol, respectively. For the previously reported quenching of [Cu(dmp)2+] * by the cosolvents CH3CN and CH3OH, * values of-6.2 and -5.4 cm3 5/mol were measured. These data are consistent with the proposal that an associative mechanism plays a role in the nonradiative deactivation of the MLCT excited state of the less sterically crowded (dmp)2 complex.
Volumes of activation for the photosubstitution of the nitrogen donor ligand by triethyl phosphite in W(CO)5(pyridine), W-(C0)5(4-cyanopyridine), and W(C0)5(4-acetylpyridine) were determined in toluene as solvent and have the values 5.7,6.3, and 9.9 cm3 mol-', respectively. The effect of pressure on the luminescence lifetimes of the two latter complexes, for which the lowest energy electronic excited states are metal-to-ligand charge transfer, was also studied. The larger volumes of activation for photosubstitution of these compounds are interpreted in terms of the volume increase during the dissociative reaction of the ligand field excited state and the difference in volume between this state and the lowest exicted CT state.
IntroductionPressure effects on reaction rates and quantum yields and the volumes of activation A P estimated from these constitute important phenomena that help to complete our comprehension of thermal and photochemical mechanisms."The photosubstitution reactions resulting from the ligand field (LF) excitations of d3 and d6 Werner-type transition-metal complexes were the first for which systematic studies on the pressure effects were conducted. We performed a series of detailed investigations on the mechanisms
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