PHOTOPHYSICAL STUDIES OF SEVERAL COPPER(I) SYSTEMS
Abstract
A least-squares algorithm for obtaining stability constants and molar absorptivities from absorbance data is described. The stability constants are refined by a numerical search method. At each stage in the refinement of the stability constants, conditionally optimum values of the molar absorptivities are estimated by a standard linear least-squares procedure. The method is used to characterize a pentakis complex of imidazole with copper(II) in aqueous solution that exhibits $\epsilon$ = 118 M$\sp{-1}$ cm$\sp{-1}$ at $\lambda\sb{\rm max}$ = 650 nm. In a second study the mono- and bis-ligand complexes of 2,9-dimethyl-1,10-phenanthroline (dmp) with copper(I) are characterized in acetonitrile. The mono- and bis-ligand complexes exhibit charge transfer absorption maxima at different wavelengths and the two intensities are not simply related. Picosecond flash photolysis studies of Cu(dmp)$\sb2\sp+$ and Cu(bcp)$\sb2\sp+$ have been carried out, where bcp is 2.9-dimethyl-4,7-diphenyl-1,10-phenanthroline. In each case the excited state absorption spectrum resembles that of the radical anion of 1,10-phenanthroline, consistent with the charge transfer nature of the excited state. The quenching kinetics of photoexcited Cu(dmp)$\sb2\sp+$ by acetonitrile, acetone, and p-dioxane in CH$\sb2$Cl$\sb2$ solution have been determined from studies of the luminescence lifetime. An exciplex mechanism in which a Lewis base (quencher) serves as a fifth donor for the copper center is proposed. The temperature-dependent emission behavior of several Cu(NN)(PPh$\sb3$)$\sb2$+ complexes is reported. The emission intensity of Cu(phen)(PPh$\sb3$)$\sb2$BF$\sb4$, where phen is 1,10-phenanthroline, increases with increasing temperature in methylene chloride, behaving in an analogous fashion to Cu(dmp)$\sb2\sp+$. In methanol, however, the converse is observed. This inverted behavior, also observed for Cu(dmp)(PPh$\sb3$)$\sb2$BF$\sb4$ in methanol, is rationalized in terms of a solvent-induced exciplex quenching mechanism. Steric demands around the metal center determine the ability of the quenching mechanism to compete with other deactivation pathways.
Degree
Ph.D.
Subject Area
Chemistry
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