Issue 30, 2022

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

Abstract

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 the relatively short half-life (t1/2) of the Z-isomer (2 days). Experimental and computational studies suggest that these properties (λmax 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 1540 azoarenes as photoswitch candidates with improved λmax and t1/2 values relative to azobenzene. We used density functional theory to predict the activation 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 π-conjugated or cross-conjugated with the diazo π-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 and 230 years (thiophene and furan, respectively). The 2,2-substituted heteroazoarenes have significantly higher λmax absorptions than their 3,3-substituted analogues: 76 nm for azofuran and 77 nm for azothiophene.

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

Supplementary files

Article information

Article type
Paper
Submitted
15 10 2021
Accepted
24 12 2021
First published
28 12 2021

Org. Biomol. Chem., 2022,20, 5989-5998

Author version available

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

D. M. Adrion and S. A. Lopez, Org. Biomol. Chem., 2022, 20, 5989 DOI: 10.1039/D1OB02026A

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