Photoinduced Puffing with Large Volume Expansion and Photomechanical Motions induced by Topochemical [4+4] Reactions in Molecular Crystal Solvates.

In this work, we report the first example of two crystal solvates of an anthracene-benzhydrazide based molecule (Ant) that display very distinct photo-responsive behaviour when 365 or 405 nm or visible light is illuminated. For the first time, the crystal hydrate that has water molecule in the lattice (hereafter named as Ant-HO) display fascinating puffing behavior with large volume expansion upto 50 % accompanied with surface modulation when illuminated with 405 nm light, a phenomenon very much similar to the rice or popcorn puffing by thermal treatment. Utilizing the properties of photoconverted Ant-HO crystals, we have demonstrated their application in photoinduced enhanced liquid absorption using various liquids/solutions. The other crystal solvate having DMF in the crystal lattice (hereafter named as Ant-DMF) responds to 405 nm light by bending, twisting, chopping, jumping or splitting etc. The chopping of Ant-DMF crystal was also observed under ambient/white light but at a slower rate compared to 405 nm light. Single crystal X-ray diffraction study reveals that the photoinduced puffing and photomechanical effects of these materials are rooted to the topochemical [4+4] cycloaddition reaction between the anthracene moieties that facilitate molecular packing change assisted by the reconfiguration of intermolecular non-covalent interactions involving lattice trapped solvent molecules.