The Factor beyond Schmidt's Criteria Impacting the Photo‐Induced [2+2] Cycloaddition Reactivity and Photoactuation of Molecular Crystals Based on Cyclic Chalcone Analogues
Yuan Yue, Jiawei Dai, Liuyang Jin, Cheng Liu, Jingbo Sun, Kaiqi Ye, Ran Lu
Abstract
Abstract Generally, the potential reactive “olefin pairs” in the molecular crystals satisfying Schmidt's criteria could undergo topological [2+2] cycloaddition. In this study, another factor that affects the photodimerization reactivity of chalcone analogues was found. The cyclic chalcone analogues of ( E )‐2‐(2,4‐dichlorobenzylidene)‐2,3‐dihydro‐1 H ‐inden‐1‐one ( BIO ), ( E )‐2‐(naphthalen‐2‐ylmethylene)‐2,3‐dihydro‐1 H ‐inden‐1‐one ( NIO ), ( Z )‐2‐(2,4‐dichlorobenzylidene)benzofuran‐3(2 H )‐one ( BFO ), and ( Z )‐2‐(2,4‐dichlorobenzylidene)benzo[ b ]thiophen‐3(2 H )‐one ( BTO ) have been synthesized. While the geometrical parameters for the molecular packing of the above four compounds did not exceed Schmidt's criteria, [2+2] cycloaddition did not occur in the crystals of BIO and BTO . The single crystal structures and Hirshfeld surface analyses revealed that interactions of C=O⋅⋅⋅H (CH 2 ) existed between adjacent molecules in the crystal of BIO . Therefore, the carbonyl and methylene groups linked with one carbon atom in carbon‐carbon double bond were tightly confined in the lattice, acting as a tweezer to inhibit free movement of the double bond and suppressing [2+2] cycloaddition. In the crystal of BTO , similar interactions of Cl⋅⋅⋅S and C=O⋅⋅⋅H (C 6 H 4 ) prevented free movement of the double bond. In contrast, the intermolecular interaction of C=O⋅⋅⋅H only exists around the carbonyl group in the crystals of BFO and NIO , leaving the C=C double bonds to move freely and allowing the occurrence of [2+2] cycloaddition. Driven by photodimerization, the needle‐like crystals of BFO and NIO displayed evident photo‐induced bending behavior. This work demonstrates that the intermolecular interactions around carbon‐carbon double bond affect the [2+2] cycloaddition reactivity except for Schmidt's criteria. These findings provide valuable insights into the design of photomechanical molecular crystalline materials.