Simple Azo Dyes Provide Access to Versatile Chiroptical Switches

Abstract

AbstractAzo dyes have played an important role in the development of the chemical industry for 150 years. The azo‐core of these dyes can undergo trans to cis photoisomerization, which allows azobenzene derivatives to act as light triggered molecular switches. Here, we showed that simple derivatization of Sudan I provides access to chiroptical molecular switches, and that the properties of these switches can be readily tuned by modification of the molecular structure. The synthesis, characterization, photoisomerization, thermal stability, chiral HPLC resolution, determination of absolute configuration and chiroptical properties of chiroptical switches based on Sudan I are reported. ortho‐difluorinated Sudan I derivatives have improved thermal stabilities and switching properties compared to switches based on Sudan I itself. Transfer of stereochemical information from a non‐racemic chiral unit to the π‐conjugated system of the dye and exciton‐coupled circular dichroism are both observed. The chiral unit influences the geometry and hence the spectra of cis and trans‐isomers differently, which is the mechanistic basis of chiroptical switching.