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Photo-Electroswitchable Arylaminoazobenzenes

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journal contribution
posted on 2021-08-03, 21:13 authored by Carl Jacky Saint-Louis, David J. Warner, Katie S. Keane, Melody D. Kelley, Connor M. Meyers, Silas C. Blackstock
Azobenzenes appended with a redox-active arylamino group (redox auxiliary, RA) are prepared and shown to undergo fast, complete, and catalytic ZE azo isomerization upon electron loss from the RA unit of the azobenzene. The RA-azo structures can be reversibly (EZE)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 ZE conversion is demonstrated using chemical oxidation (redox switching), electrochemical oxidation (electro switching), and photochemical oxidation (photoredox switching). The ZE acceleration is shown to be at least 2 × 109-fold for RA-azo 5. DFT calculations on methyl yellow suggest that a N-centered radical cation of the RA group stabilizes the ZE 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.

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