| Autor: |
Saint-Louis CJ; Department of Chemistry & Biochemistry, Kennesaw State University, Kennesaw, Georgia 30144, United States., Warner DJ; Department of Chemistry & Biochemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States., Keane KS; Department of Chemistry & Biochemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States., Kelley MD; Department of Physical Science, Perimeter College at Georgia State University, Atlanta, Georgia 30303, United States., Meyers CM; Department of Chemistry & Biochemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States., Blackstock SC; Department of Chemistry & Biochemistry, The University of Alabama, Tuscaloosa, Alabama 35487, United States. |
| Abstrakt: |
Azobenzenes appended with a redox-active arylamino group (redox auxiliary, RA) are prepared and shown to undergo fast, complete, and catalytic Z → E azo isomerization upon electron loss from the RA unit of the azobenzene. The RA-azo structures can be reversibly ( E → Z → E ) n cycled by sequential photo- and electrostimulation. Due to the robust nature of the RA •+ -azo radical cation chain carrying species, initiation of electron transfer (ET) catalysis occurs at low levels (1.0-0.04 mol %) of catalytic loading and is effective even at Z -RA-azo concentrations of 10 -4 -10 -5 M, yielding TONs (turnover numbers) of 100-2300 under such dilute conditions. The RA-azo Z → E conversion is demonstrated using chemical oxidation (redox switching), electrochemical oxidation (electro switching), and photochemical oxidation (photoredox switching). The Z → E acceleration is shown to be at least 2 × 10 9 -fold for RA-azo 5 . DFT calculations on methyl yellow suggest that a N-centered radical cation of the RA group stabilizes the Z → E N-N twist transition state of the RA •+ -azo, yielding a large reduction in the barrier for RA •+ -azo compared to neutral RA-azo. The RA-azo structure class has nanomechanical features that can be toggled with photo- and electrostimulation, the latter offering a quick switch for complete Z→E conversion. |
