Achieving enhanced solid-state photochromism and mechanochromism by introducing a rigid steric hindrance group

For photochromic molecules, effective isomerization usually requires conformational freedom, which is usually unavailable under solvent-free conditions. In this work, we report a new method, which can realize the reversible switching of spiropyran molecules by introducing a rigid aromatic ring group and this method can provide the required free volume to transform from a closed-ring to an open-ring form. This new molecule can quickly change color in the solid state under ultraviolet light, and can be erased after being heated at 60 degrees C for about 5 minutes. Furthermore, this new compound presents mechanochromicity when a mechanical force is applied. What is more, it can be used for at least 30 cycles of print-erase operations without apparent fatigue. This new molecule exhibits improved photochromic and anti-fatigue properties in the solid state, which can promote its application in both ultraviolet printing and anti-counterfeiting materials.

Automated summary

A new method has been developed to achieve the reversible switching of spiropyran molecules by introducing a rigid aromatic ring group, providing the required free volume for transformation. This new molecule quickly changes color in the solid state under UV light and can be erased by heating. Additionally, it exhibits mechanochromicity and can be used for at least 30 print-erase cycles without fatigue, showing improved properties for UV printing and anti-counterfeiting materials applications.