Cross-conjugation controls the stabilities and photophysical properties of heteroazoarene photoswitches

18 October 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Azoarene photoswitches are versatile molecules that interconvert from their E-isomer to their Z-isomer with light. Azobenzene is a prototypical photoswitch but its derivatives can be poorly suited for in vivo applications such as photopharmacology due to undesired photochemical reactions promoted by ultraviolet light and its relatively short half-life (t1/2) of the Z-isomer (2 days). Experimental and computational studies suggest that these properties (位max of the E isomer and t1/2 of the Z-isomer) are inversely related. We identified isomeric azobisthiophenes and azobisfurans from a high-throughput screening study of 1700 azoarenes as photoswitch candidates with improved 位max and t1/2 values relative to azobenzene. We used density functional theory to predict the activation free energies, reaction free energies, and vertical excitation energies of the E- and Z-isomers of 2,2- and 3,3-substituted azobisthiophenes and azobisfurans. The half-lives depend on whether the heterocycles are 饾湅-conjugated or cross-conjugated with the diazo 饾湅-bond. The 2,2-substituted azoarenes both have t1/2 values on the scale of 1 hour, while the 3,3-analogues have computed half-lives of 40 (thiophene) and 230 (furan) years. The 2,2-substituted heteroazoarenes have significantly higher 位max absorptions than their 3,3-substituted analogs: 76 nm for azofuran and 77 nm for azothiophene.


Computational Chemistry
Physical Organic Chemistry

Supplementary weblinks


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.