Enhancing thermal isomerization rates of redox auxiliary-appended azobenzenes via redox auxiliary catalysis

dc.contributorJennings, Michael P.
dc.contributorLeClair, Patrick R.
dc.contributorPan, Shanlin
dc.contributorShaughnessy, Kevin H.
dc.contributor.advisorBlackstock, Silas C.
dc.contributor.authorWarner, David James
dc.contributor.otherUniversity of Alabama Tuscaloosa
dc.descriptionElectronic Thesis or Dissertationen_US
dc.description.abstractAzobenzene exists in E or Z isomeric forms having different three-dimensional structures, chemical properties, optical properties and electronic properties. Azobenzene can switch between E and Z conformations using light and has been incorporated in chemical systems to impart photoswitchable characteristics. Thermal conversion from the Z to E often occurs slowly and is unideal when fast dynamics is desired. ZE photoswitching is typically incomplete, leaving a significant percentage of molecules in the Z conformation. The Blackstock group has covalently attached an easily oxidized aryl amine “redox auxiliary” (RA) to the azobenzene scaffold to facilitate rapid and complete ZE conversion by adding a catalytic amount of oxidant. We hypothesize that the oxidized Z isomer of a RA-appended azobenzene (RA-azo) will rapidly isomerize to the E conformation because oxidizing the RA greatly reduces the energetic barrier to ZE isomerization. The newly formed (E) RA•+ azo molecule will oxidize a neutral (Z) RA azo, generating a (Z) RA•+ azo radical cation. This (Z) RA•+ azo will undergo rapid ZE isomerization to yield another (E) RA•+ azo molecule, which will oxidize another neutral (Z) RA azo. To increase the electron catalysis turnover number, we incorporated a new RA. This new RA-azo underwent complete and rapid ZE switching using a lower electrocatalytic loading than other RA-azos previously studied. Rapid ZE conversion was also achieved in a photo-electrical cell device (PED), and several EZE switching cycles were achieved using light and voltage in tandem. Attaching two azobenzene moieties to the new RA allowed for electrocatalytic ZE switching of both moieties. The azobenzene ZE thermal isomerization half-life is ~2 days, but adding the RA (or most other substituents) reduces this half-life to hours or minutes. By developing an RA-azo with ortho fluorines, we produced an RA-azo exhbiting an exceptionally long half-life (t1/2 = 40 days) and the capability to undergo rapid and complete ZE switching upon addition of 0.11 mol% oxidant. This results in a 6,900,000 fold ZE rate acceleration. Extrapolating to the case of 100 mol% oxidant gives a 6,300,000,000 fold ZE rate acceleration, which is by far the greatest RA-facilitated ZE rate acceleration observed for any RA-azo studied by the Blackstock group to date.en_US
dc.format.extent213 p.
dc.publisherUniversity of Alabama Libraries
dc.relation.hasversionborn digital
dc.relation.ispartofThe University of Alabama Electronic Theses and Dissertations
dc.relation.ispartofThe University of Alabama Libraries Digital Collections
dc.rightsAll rights reserved by the author unless otherwise indicated.en_US
dc.subjectOrganic chemistry
dc.titleEnhancing thermal isomerization rates of redox auxiliary-appended azobenzenes via redox auxiliary catalysisen_US
etdms.degree.departmentUniversity of Alabama. Department of Chemistry and Biochemistry
etdms.degree.grantorThe University of Alabama
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