Control of the Helical Chirality of Enantiopure Sulfinyl (Z)‐Azobenzene‐Based Photoswitches

Abstract

A new class of enantiopure ortho,ortho-disubstituted azobenzene photoswitches has been synthesized from (S)-2-(p-tolylsulfinyl)benzoquinone and arylhydrazines. The sulfoxide acts as a unidirectional controller of the helical chirality that arises in the Z isomer after photoisomerization. Highly congested E-azobenzenes 5 c showed two atropisomeric diastereoconformers in the solid state that converged upon irradiation into a unique Z isomer with defined helicity (M), as evident in the X-ray structure. The chiroptical properties of this three-state enantiopure switch can be externally tuned both photochemically and/or thermally. Theoretical CD spectra calculated by using time-dependent DFT methods support the existence of two atropoisomeric E isomers and only one Z isomer with (M) helicity. Complementary to the classical azobenzene-based switches, the photoswiching event is promoted under green/blue light and do not occur under UV irradiation.

Sulfoxide‐Induced Homochiral Folding of ortho‐Phenylene Ethynylenes (o‐OPEs) by Silver(I) Templating: Structure and Chiroptical Properties

“…The known compound (S)-1-bromo-2,5-dimethoxyphenyl-4-(ptolylsulfinyl)benzene ((S)-A) [27,28] was chosen as the homochiral startingm aterial due to its availability and ability to freeze a sulfoxide conformation thanks to the vicinal disposition of methoxy and sulfinyl groups at the aryl ring. AS onogashira reaction between (S)-A and trimethylsilylacetylene, with catalytic amountso f[ Pd(CH 3 CN) 2 Cl 2 ], tBu 3 P·HBF 4 ,a nd CuI (3 mol %) in iPr 2 NH/THF( 1:1) as as olvent, was followed by desilylation to give p-tolylsulfinyl aryl-substituted acetylene derivative (S)-I in 75 %y ield (Scheme 1).…”

“…[26] This group has already been used to control, in av ery efficient manner, the conformationa nd configurationo f sulfinyl-containing azobenzene photoswitches. [27] In that case, a p-tolylsulfoxide situated in an aromatic ring adopted af ixed conformation in both E and Z isomerso fa zobenzenes andw as able to transfer the central chirality to the azobenzene core. [27] On this basis, we expecteda ne ffective transfer of chirality from the stereogenic sulfur of chiral sulfoxides to ah elically folded o-OPE.…”

“…[27] In that case, a p-tolylsulfoxide situated in an aromatic ring adopted af ixed conformation in both E and Z isomerso fa zobenzenes andw as able to transfer the central chirality to the azobenzene core. [27] On this basis, we expecteda ne ffective transfer of chirality from the stereogenic sulfur of chiral sulfoxides to ah elically folded o-OPE. Herein, we presentt he synthesis of enantiopure sulfinyl-substituted o-OPE foldamers and metallofoldamers, and as tudy of the structural and chiroptical properties of the resultings ystems ( Figure 1, acyclicc hiral enantiopure organic emitters).…”

Recent advances and potential applications of the photo‐induced macroscopic response of self‐assembled azopolymer in aqueous media

“…As the most shiny one among various photochromic systems, the color of azobenzene has not faded after numerous investigations and research not only due to its intrinsic response to light stimulus but also because of its good photo‐fatigue resistance . In recent years the photo‐induced trans − cis or E − Z isomerization of azobenzene and the resulting birefringence and nonlinear optical behavior, microscopic and macroscopic motions and photo‐controllable properties have fascinated increasing research groups and continuously inspire them for scientific exploration in the field of liquid crystals, molecular recognition, photoswitches, biomaterials etc.…”

Azobenzene Container Showing a Definite Folding – Synthesis and Structural Investigation

“…A further advantage of the use of azobenzene as switching units is the fact that it is possible to control the conformation of the cis or the trans isomers by chiral bridges. [43][44][45][46][47][48] Up to now two artificial Lissoclinum cyclopeptides, which feature azobenzene to change the distance between the amino acid side chains, are described in the literature. [49][50] One example is the platform 4, which consists of two imidazole building blocks connected by two azobenzene units ( Figure 2).…”