Arylazo‐3,5‐dimethylisoxazoles: Azoheteroarene Photoswitches Exhibiting High Z‐Isomer Stability, Solid‐State Photochromism, and Reversible Light‐Induced Phase Transition

Abstract

Reversibly photoswitchable phenylazo‐3,5‐dimethylisoxazole and 37 aryl‐substituted derivatives were synthesized. Excellent photoswitching ability of these compounds in solution and the solid state was demonstrated. Through kinetics studies by means of NMR spectroscopy, high Z‐isomer stability was demonstrated. Interestingly, the majority of the derivatives showed light‐induced contrasting color changes in solution and the solid state. Besides, many of the derivatives exhibit partial phase transition upon UV irradiation. The highlight of this class of photoswitches is the reversible light‐induced phase transition between solid and liquid phases in the parent compound, which can be used in patterned crystallization. These results show that this new class of azoheteroarene based photoswitches has opportunities to be useful in various domains.

Acid-catalysed liquid-to-solid transitioning of arylazoisoxazole photoswitches

“…Owing to mesomerism, 46 the uncatalysed half-life of the 4alkoxy-substituted Z-AIZs 2 and 3 in solution was determined to be 7 d 44 rather than the 45 d for Z-AIZ 1. 43 Although we observe no reactivity of Z-AIZ 2 and 3 to a large excess of acetic acid (CH3COOH, 5000 equivalents in acetonitrile, Figure S8), addition of CF3COOH and HCl cause the half-life to diminish to the (sub)second timescale at near-stoichiometric amounts already (Figure S9 and S10). DFT calculations of activation free energies confirm that the Zto E-barrier is substantially reduced in the azonium species from 1.29 eV (versus 1.11 eV experimentally 44 ) to 0.86 eV (Figure 2A).…”

Tuning of Bistability, Thermal Stability of the Metastable States, and Application Prospects in the C3‐Symmetric Designs of Multiple Azo(hetero)arenes Systems

“…For accessing the amide derivatives 1 a – c and 2 a – c , their corresponding amino azobenzenes ( 11 a – c ) or the N ‐methylated aminoazobenzene analogs ( 12 a – c ) have been treated with the in situ generated trimesoylchloride 10 , derived from trimesic acid 9 [3c, 10, 15] . In a similar procedure, 3 a – c and 4 a – c have been synthesized using the corresponding amine derivatives or their N ‐methylated analogs of phenylazo‐3,5‐dimethylisoxazoles ( 13 a – c and 14 a – c ) [6b, 14c] . For the synthesis of triazine derivatives 5 a – c , aromatic nucleophilic substitution has been exploited using the corresponding aminoazobenzene derivatives 11 a – c and cyanuric chloride 16 [16] .…”

Azobispyrazole Family as Photoswitches Combining (Near‐) Quantitative Bidirectional Isomerization and Widely Tunable Thermal Half‐Lives from Hours to Years**

“…[10] Thediversity of heterocycles and their distinct nature from benzene provide tremendous opportunities to regulate the performance of azo switches.Six-membered rings such as pyridine [11] and pyrimidine [12] afforded heteroaryl azo switches in which coordination interactions and hydrogen bonding could be utilized. Significantly,mono-heteroaryl azo molecules (Ph-N=N-Het) based on five-membered rings (imidazole, [13] pyrazole, [14] pyrrole, [14] thiophene, [15] isoxazole, [16] etc.) showed some unusual features.Herges group [13b] and Fuchter group [14a] reported that Z-isomers of phenylazoimidazoles and phenylazopyrazoles could adopt aTshaped geometry (where the phenyl ring was orthogonal to the azo-heterocycle moiety) not accessible by azobenzenes.…”