Accessing a Diverse Set of Functional Red-Light Photoswitches by Selective Copper-Catalyzed Indigo N-Arylation

The ability to correlate the structure of a molecule to its properties is the key to a rational and accelerated design of new functional compounds and materials. Taking photoswitches as an example, the thermal stability of meta-stable state is a crucial property that dictates their application in molecular systems. Indigos have recently emerged as an attractive motif for designing photoswitchable molecules due to their red-light addressability, which can be advantageous in biomedical and material applications. The absence of comprehensive synthetic techniques and a thorough understanding of the impact of structural factors on the photochemical and thermal properties of this widely available dye hinders its broad application. Herein, we report an efficient copper-catalyzed indigo N-arylation that enables the installation of a wide variety of aryl moieties carrying useful functional groups. The exclusive selectivity for mono-arylation likely originates from a bimetallic cooperative mechanism through a binuclear copper-indigo intermediate. Functional N-aryl-N′-alkylindigos were prepared and shown to photoisomerize efficiently under red light. Moreover, this design allows for the modulation of thermal half-lives through N-aryl substituents, while the N′-alkyl groups enable the independent attach-ment of functional moieties without affecting the photochromic properties. Strong correlation between the structure of N-aryl moiety and the thermal stability of the photogenerated Z-isomers was achieved by multivariate linear regression models obtained through a straightforward data-science workflow. This work thus builds an avenue leading to versatile red-light photoswitches and a general method for structure-property correlation that is expected to be broadly applicable to the design of photoresponsive molecules.