Photochemical Sciences Ph.D. Dissertations

Photochemistry of Vanadium Clusters and Applications For Responsive Materials

Date of Award

2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Alexis D. Ostrowski (Committee Chair)

Second Advisor

Nathan S. Hensley (Other)

Third Advisor

Malcolm D.E. Forbes (Committee Member)

Fourth Advisor

George S. Bullerjahn (Committee Member)

Abstract

A new, reversible photochemical transformation of V(V) tartrate clusters into V(IV) tartrate is described. While the initial V(V) tartrate cluster and photoproduct are known, this research uncovers a previously unreported photochemical transformation. Irradiation of V(V) tartrate in buffer at pH 5.8 showed color changes from orange yellow through a green intermediate to purple, developing a UV-vis spectrum characteristic of V(IV) tartrate. X–ray crystallography revealed an initial tetranuclear Na5[V4O8(2R,3R–tart) (2S,3S–tart)] •11H2O, and final photoproduct in solution which crystallized to a Na4[(VO)2(2R,3R–tart) (2S,3S–tart)] •12H2O dimer. EPR spectroscopy confirmed the reduction from diamagnetic V(V) to paramagnetic V(IV) photoproduct. CO2 was also produced during photolysis, indicating oxidation of the tartrate ligand during photolysis. These results highlight how light irradiation tunes the oxidation state of V(V/IV) clusters and thus these species have the potential to control the reactivity of these vanadium-based catalysts using light. Incorporation of the transition metal V(V) into hydrogels has been used to impart photo-responsive behavior which was used to tune materials properties during light irradiation. The photoreaction in the cellulose-agarose hydrogels coordinated with vanadium was evidenced by a clear color change of yellow to blue through a green intermediate. This color change was attributed to the reduction of V(V) to V(IV) as described above. A concomitant oxidative breakdown of the polysaccharide chain was noticeable upon the reduction of V(V) with a decrease in stiffness (G’) of the hydrogel material. This reduction of the metal ion and breakdown of polysaccharide chain induce irreversible changes in the microstructure of the hydrogel which enables the controlled delivery of V(IV) and/or encapsulated cargo. Polyaniline (PANI) is a famous conductive polymer. When V(V) was reduced to V(IV) upon irradiation, this ultimately causes an oxidative polymerization for polyaniline on hydrogels. Thus, we have developed conductivity in cellulose-agarose hydrogels with the light responsive properties of vanadium. Thus, we explained the photochemistry in vanadium tartrate clusters and developed interesting macroscopic effects with the light responsive properties of vanadium at the molecular level.

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