Photo-Electroswitchable Arylaminoazobenzenes

Abstract

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

Inclusion-Activated Reversible E/Z Isomerization of a Cyanostilbene Derivative Based on Cucurbit[8]uril under 365 nm Ultraviolet Irradiation

“…In addition, we changed CB [8] to CB [7] to compare the effects of different assembly modes on the photoisomerization process. Job's plot of E,E-1⊂CB [7] showed that the binding ratio was 1:2, which was different from that of E,E-1⊂CB [8] due to the smaller cavity of CB [7] (Figure S9). The absorption peak red-shifted from 380 to 388 nm with a slight decrease in intensity.…”

“…Although there was a tendency to reverse the transformation, the change was very small after 120 s illumination, and it was still a large difference from the initial state. Therefore, the photoisomerization process of E,E-1 could not be realized by using CB [7].…”

“…The phenomenon of E / Z isomerism is ubiquitous in molecules with double bonds, but Z - and E -isomers usually have different properties, especially for the biological activity, luminous state, and topological morphology . Until now, carbon–carbon double bonds, − imines, and azobenzene , have been widely used in photoisomerization of supramolecular topography control, and many studies have been reported for the photoisomerization between different configurations under the stimulation of light or heat. , …”

“…The phenomenon of E/Z isomerism is ubiquitous in molecules with double bonds, but Z-and E-isomers usually have different properties, especially for the biological activity, 1 luminous state, 2 and topological morphology. 3 Until now, carbon− carbon double bonds, 4−6 imines, and azobenzene 7,8 have been widely used in photoisomerization of supramolecular topography control, 9 and many studies have been reported for the photoisomerization between different configurations under the stimulation of light or heat. 10,11 Cyanostilbene molecules, as a commonly used photoisomerization group, not only contain double bonds that can carry out the isomerization process but also enable aggregation-induced emission because of the existence of cyano groups.…”

“…High-resolution mass spectrometry (HRMS) and NMR tests demonstrate that this process is photoisomerization rather than photodimerization. As a comparison, CB [7] can also assemble with Z,Z-1 but cannot facilitate configuration reversal from the E,E-isomer to the Z,Zisomer. This work could provide a new strategy for the supramolecular macrocyclic-activated configuration switch of cyanostilbene derivatives under the same light source.…”