A combinatorial approach to improving the performance of azoarene photoswitches

Abstract

Azoarenes remain privileged photoswitches - molecules that can be interconverted between two states using light - enabling a huge range of light addressable multifunctional systems and materials. Two key innovations to improve the addressability and <i>Z</i>-isomer stability of the azoarenes have been <i>ortho</i>-substitution of the benzene ring(s) or replacement of one of the benzenes for a pyrazole (to give arylazopyrazole switches). Here we study the combination of such high-performance features within a single switch architecture. Through computational analysis and experimental measurements of representative examples, we demonstrate that <i>ortho</i>-benzene substitution of the arylazopyrazoles drastically increases the <i>Z</i>-isomer stability and allows further tuning of their addressability. This includes the discovery of new azopyrazoles with a <i>Z</i>-isomer thermal half-life of ≈46 years. Such results therefore define improved designs for high performance azo switches, which will allow for high precision optically addressable applications using such components.