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. Article pubs.acs.org/joc

The ability of azobenzene and its derivatives to undergo reversible and rapid light‐induced isomerization has led to its incorporation in a wide variety of chemical systems that are photoswitchable between two or more states. Following a brief introduction to azobenzene properties and a section describing new methods for azobenzene switching, this chapter summarizes selected recent reports on a wide range of chemical applications of bridged azobenzene. New switchable materials and their applications include molecular machines, triggered catalysis, porous metal‐organic structures, phase‐change materials, and responsive surfaces. The chapter describes how researchers have tailored the azobenzene function and its environment to fine‐tune absorption characteristics, photophysics, isomerization dynamics, and energetics to enhance function. Collectively, the works reported in this chapter illustrate the broad utility of photochemical and molecular control of function afforded by the cis–trans isomerization of azobenzene.

Capable of rapid and reversible conformational change in response to irradiation, azobenzene (AB) derivatives have been used in chemical systems to introduce on/off switchability and allow for photoregulation of the properties of such systems. Following a brief introduction of tuning AB absorption via substitution, this chapter summarizes the selected recent reports of applications of bridged ABs in biological systems or systems having potential biomedical utility. ABs have been used to achieve photocontrol of drug‐delivery systems, molecular actuators, deoxyribonucleic acid (DNA) nanomachines, enzyme activity, peptide structure and activity, and ion channels. This chapter describes how researchers have incorporated AB into biological systems as a photoresponsive switch to afford photocontrol of the chemical activity in such systems. The various works detailed in this chapter showcase the versatility of AB for use as a light‐responsive molecular switch in the photoregulation of biological processes. Additionally, light‐responsive AB‐derived macroscopic materials are also discussed, given their biomedical potential for use as artificial muscle.