Salting open-shell organic molecules

Christine Ann Mitchell, Purdue University

Abstract

Studies are presented that describe the behavior of open-shell molecules in the presence of alkali metal ions using two methods of matrix isolation: low temperature glasses and single salt crystals. It was previously reported that spin-labeled benzo-15-crown-5 derivatives gave triplet EPR spectra in ethanol glasses in the presence of alkali metal salts, supposedly resulting from a 2:1 complexation of the molecules with a metal ion. However, our control experiments demonstrate that a simple ion binding mechanism is not sufficient to explain the high-spin species observed. The ion binding properties of alkali metal ketyl radical ions in glasses were also studied to determine if the high-spin dimers formed could be used as molecular building blocks for magnetic materials. The zero field splitting parameters show that the behavior of the radical pairs is unaffected by a variety of substituents. Single crystals of K2SO4 grown in the presence of millimolar quantities of 2-aminonaphthalene-1,5-disulfonate encapsulate and orient the molecules within specific growth sectors. These mixed crystals show an intense fluorescence upon irradiation with UV light, and phosphoresce at room temperature with a lifetime of about a second. The anisotropic photophysical and magnetic properties of the molecules within the crystal were studied at ambient temperatures to determine how encapsulation affects the properties of the guest, and to model the orientation of the molecules in the lattice. It was found that these crystals incorporate different conformers of the guest in different growth sectors: in the {021} sectors the guest behaves as if the amine lone pair is in conjugation with the π system, and in the {110} sectors as if the lone pair were orthogonal to the π system. Single crystal EPR and polarized emission spectroscopies were used in conjunction with semiempirical quantum mechanical calculations to determine the orientation of the molecules in the crystal. The resulting model supports our proposed mechanism for incorporation, whereby substitution of a sulfonate group for a sulfate ion in the crystal orients the molecules within the lattice.

Degree

Ph.D.

Advisors

Kahr, Purdue University.

Subject Area

Organic chemistry|Physical chemistry|Chemistry

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