Chemistry and Biochemistry
Azobenzenes appended with a redox-active arylamino group (redox auxiliary, RA) are prepared and shown to undergo fast, complete, and catalytic → azo isomerization upon electron loss from the RA unit of the azobenzene. The RA-azo structures can be reversibly (→→) 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 -RA-azo concentrations of 10-10 M, yielding TONs (turnover numbers) of 100-2300 under such dilute conditions. The RA-azo → conversion is demonstrated using chemical oxidation (redox switching), electrochemical oxidation (electro switching), and photochemical oxidation (photoredox switching). The → acceleration is shown to be at least 2 × 10-fold for RA-azo . DFT calculations on methyl yellow suggest that a N-centered radical cation of the RA group stabilizes the → 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.
The Journal of organic chemistry
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