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.