Organic Chemistry

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

Authors

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 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.

Content

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Supplementary weblinks

Supporting information containing all optimized reactants, IRC calculations, and transition structures
The compressed folder attached contains all of the optimized output files for all structures used in this publication