Photoinduced Conformational Switch of Enantiopure Azobenzenes Controlled by a Sulfoxide

Abstract

Two series of enantiopure azobenzenes with a p-tolylsulfoxide at the ortho or meta position with respect to the azo group, have been regioselectively synthesized. Both can act as enantiopure molecular switches showing different structural features owing to the presence of the stereogenic sulfur. The photoisomerization process, studied by UV-vis, circular dichroism (CD), NMR, and chiral HPLC evidenced a double role of the sulfoxide. A transfer of chirality from the sulfoxide to the azo system was observed by CD in both cis and trans-isomers of the meta sulfinyl derivatives 3, whereas this perturbation was evident for the ortho sulfinyl series 7 only in the cis isomer. The NMR study evidenced that the s-cis rigid conformation of the bisaromatic sulfoxide was fixing a different orientation of the overall system in each series both in the trans and cis isomers, by forcing a final U-shaped structure in cis-3 and an S-shaped structure in cis-7. Very different values of specific optical rotations were measured in both trans and cis isomers, also reflecting the existence of distinct chiral entities in the photostationary states. The easy and reversible changes occurring between different conformational states could find applications in the photocontrol of several molecular switches.

Enantiopure Double ortho‐Oligophenylethynylene‐Based Helical Structures with Circularly Polarized Luminescence Activity

“…Enantiopure 1,4-dimethoxy aryl substituted bisaromatic sulfoxide (S)-5 was chosen as homochiral sulfinyl group due to its well established ability to adopt a rigid S-cis conformation which could be able to induce a defined orientation of the overall system. [24] Thus, we prepared precursors 4 and (S,S)-7 from simple and commercially available dihaloaryl derivatives with trimethylsilyl acetylene or phenylacetylene followed by removal of the protecting silyl group. Then, both intermediates were coupled with (S)-5, affording model compound (S,S)-2 and multipodal structure (S,S,S,S)-1 in 63 % and 40 % yield respectively (see SI for details).…”

Control over molecular motion using thecis–transphotoisomerization of the azo group

“…Recently, Carreño et al [132–133] synthesized different enantiomerically pure sulfinyl azobenzenes. The sulfinyl group is a key component in the design of a molecular sunflower, a device that by means of light can undergo phototropism with a given direction.…”

Diazocines on Molecular Platforms

“…The corresponding tetracyclic structures, upon irradiation, can only bend in one direction (left or right depending on the enantiomer, Figure 1). [15][16][17] Figure 1. Schematic representation of artificial cilia with diazocines as switching units.…”