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 °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.