A combinatorial approach to improving the performance of azoarene photoswitches.

Joaquin Calbo,Matthew J Fuchter,Rosina S L Gibson,Andrew J P White,Aditya R Thawani

doi:10.3762/bjoc.15.266

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 Z-isomer stability of the azoarenes have been ortho-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 ortho-benzene substitution of the arylazopyrazoles drastically increases the Z-isomer stability and allows further tuning of their addressability. This includes the discovery of new azopyrazoles with a Z-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.

Highlights

Photoswitches are molecules that are capable of being reversibly interconverted between two states by means of light irradiation
Theoretical half-lives (t1/2) were calculated within the density functional theory (DFT) framework, according to the protocol reported in our prior paper [18]
The reliability of the singledeterminant Kohn–Sham DFT approach to describe correctly the transition state energy/geometry was assessed by calculating the energy difference between the lowest-lying singlet excited state and the ground state at the transition state geometry for 4pzH and 4pzMe

Summary

Introduction

Photoswitches are molecules that are capable of being reversibly interconverted between (at least) two states by means of light irradiation. The incorporation of photoswitches into multifunctional systems has huge relevance to next-generation materials, with a plethora of applications that range from photopharmacology [1,2] and optochemical genetics [3] to data storage [4]. Numerous classes of photochromic molecules exist, each with their own unique characteristics. Spiropyrans [5,6] may exhibit significant changes in solubility upon photoswitching, whilst the photoswitching of diarylethenes [7] is accompanied by large variations in their absorption spectra. Azobenzenes remain one of the most popular photoswitches owing to their stability, reliability and tunability: azobenzenes provide high extinction coefficients and quantum.

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Conclusion