Light-Responsive Pyrazine-Based Systems: Probing Aromatic Diarylethene Photocyclization

Here, we present an investigation of the photocyclization of novel aromatic diarylethene (DAE) systems 1-3 based on pyrazine, quinoxaline, and helicene scaffolds. These prospective photoswitches were designed using density functional theory calculations and analyzed in solution and in the solid state by cyclic and rotating disk voltammetry, UV-vis and transient absorption spectroscopy, as well as X-ray crystallography. Additionally, nucleus-independent chemical shift calculations were performed to investigate the influence of aromaticity on the photocyclization ability. While pyrazine-2,3-diyl-extended DAE system 1 demonstrated photoswitching ability with short lifetimes of the cyclized form, the more aromatic quinoxaline analogue 2 did not feature any photocyclization. Further extension of these aromatic systems into helicene-DAE 3 resulted in the stabilization of the cyclized form through the conserved backbone aromaticity, accompanied by enhanced photochromism. This study paves the way toward the generation of aromatic DAE photoswitches for light-controlled molecular systems in the future.