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Visible Light Photorelease of Carboxylate Anions by Mediated Photoinduced Electron Transfer to Pyridinium-based Protecting Groups

dc.contributor.advisorFalvey, Daniel Een_US
dc.contributor.authorBorak, John Brianen_US
dc.description.abstractThe use of sensitized photoinduced electron transfer (PET) to trigger release of redox-active photoremovable protecting groups (PRPGs) allows a broad range of chromophores to be selected that absorb in difference wavelength ranges. Mediated electron transfer (MET) is particularly advantageous as sub-stoichiometric amounts of the often costly sensitizer (relative to the amount of protected substrate) can be combined with an excess amount of an inexpensive electron donor. Thus, the sensitizer acts as an electron shuttle between the donor and the protecting group to initiate release. The development of improved MET release systems using visible light as the trigger is the focus of the current work. The <italic>N</italic>-alkylpicolinium (NAP) group has demonstrated its utility as an aqueous-compatible PET-based PRPG, releasing protected substrates upon one electron reduction. Adaptation of MET PRPG release to visible light absorbing mediators began with employing ketocoumarin dyes that primarily form excited triplet states. These chromophores demonstrated high rates of release of NAP-protected carboxylates using sub-stoichiometric concentrations of mediator. Subsequently, nanomolar concentrations of gold nanoparticles were used to mediate electron transfer to NAP-protected compounds. This system exhibited rapid deprotection with very high release quantum efficiencies. In an effort to use highly stable visible-light-absorbing metal-centered dyes with modest redox properties, the NAP group has been synthetically modified to adjust its reduction potential to more positive values. Photolysis of solutions containing the protected substrate, a large excess of an electron donor, and substoichiometric amounts of the dye tris(bipyridyl)ruthenium(II) released the free carboxylates in high yields while photodegradation of the chromophore was minimal. To demonstrate the utility of the NAP group, a quasi-reversible photorheological fluid has been developed based on the formation and disruption of aqueous micelles. In solutions containing the surfactant cetyltrimethylammonium bromide, visible light photorelease of a carboxylate additive from the NAP-ester derivative induces a 10<super>5</super> increase in solution viscosity due to the formation of an interpenetrating micelle network. Subsequent irradiation of the viscoelastic fluid with UV light induces a cis-trans isomerization within the released carboxylate thereby disrupting the micelle network and decreasing solution viscosity by 10<super>2.5</super>.en_US
dc.titleVisible Light Photorelease of Carboxylate Anions by Mediated Photoinduced Electron Transfer to Pyridinium-based Protecting Groupsen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.subject.pqcontrolledChemistry, Organicen_US
dc.subject.pqcontrolledChemistry, Physicalen_US
dc.subject.pqcontrolledPhysics, Opticsen_US
dc.subject.pquncontrolledgold nanoparticleen_US
dc.subject.pquncontrolledphotoinduced electron transferen_US
dc.subject.pquncontrolledphotorheological fluiden_US
dc.subject.pquncontrolledprotecting groupen_US

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