Photoinstability of Aryl‐Functionalized Perylene Bisimides at Bay Positions in Ambient Environment

Dye molecules are widely used as active layers in optoelectronic devices, making their photostability crucial for long‐term device performance. In this study, we investigated the photostability of a typical class of dye molecules, aryl‐functionalized perylene bisimides (PBIs) at the bay position and observed significant color changes in their solutions upon exposure to visible light under ambient conditions within hours. UV–vis absorption spectra revealed a blueshift accompanied by changes in peak intensities. This spectral shift was more prominent for aryl‐functionalized PBI dyes with electron‐withdrawing bay substituents than with electron‐donating ones. Although the observed spectral shift resembled aggregation behavior, it is temperature‐independent, effectively ruling out aggregation as the underlying cause. Interestingly, the effect was more pronounced in diluted dye solutions, while concentrated dye solutions remained photostable. Mass spectrometric analysis indicated the formation of dehydrogenated species upon light exposure in solution, supporting the hypothesis of a photoinduced reaction. The isolated dehydrogenated products exhibited identical spectral features to those of the light‐exposed diluted solutions, confirming that spontaneous dehydrogenation under ambient light is responsible for the reduced photostability of aryl‐functionalized PBIs at the bay position in solution.