The Factor beyond Schmidt's Criteria Impacting the Photo‐Induced [2+2] Cycloaddition Reactivity and Photoactuation of Molecular Crystals Based on Cyclic Chalcone Analogues

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 (2H)-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 carboncarbon 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.

Shape Dependence of Photoresponsive Molecular Crystals Composed of Naphthyl Acrylic Acid Stimulated by Solid-State [2 + 2] Photocycloaddition

“…Because NA molecules entate along the (002) and (003) Miller planes, the microcrystal rods were exp a similar cracking motion as the microplates did upon light irradiation. Previous literature suggested that the intermolecular couplings were w ing the [2 + 2] photocycloaddition, enabling an increased fluorescence inten Previous literature suggested that the intermolecular couplings were weakened during the [2 + 2] photocycloaddition, enabling an increased fluorescence intensity [9,37,38]. We then measured the steady-state fluorescence spectra of the illuminated NA solids to investigate the intermediate fluorescence emission during the photochemical reaction.…”

Photocycloaddition of Zero-Dimensional Metal Halide Hybrids with Reversible Photochromism

“…Since [2 + 2] photocycloaddition brings about great variation in lattice strain and conjugation of π electrons, it has been widely employed in the fields of photomechanical motions and optoelectronic devices including optical writing and data storage without any physical contact. − In principle, parallelly aligned olefinic bonds within less than 4.2 Å can undergo [2 + 2] photocycloaddition according to Schmidt’s criteria. − To satisfy this prerequisite, metal–organic frameworks (MOFs) and coordination polymers (CPs) with wide structural tunability and good designability are often designed to bring olefin group into the required alignment or incorporate olefins in the confined space. ,− …”

Superelastic and Photomechanical Behavior of Acylhydrazone Derivative Crystals

“…Later, in 1964, Schmidt et al developed the concept of “topochemistry” by studying the solid-state photochemical reactions of cinnamic acid derivatives . Since then, the photomechanical effects of organic crystals have been extensively studied. − Many studies have described [2 + 2] cycloaddition reactions involving olefins, − isomerization processes such as trans ( E )– cis ( Z ) isomerization in diarylethenes or azobenzenes, − [4 + 4] photodimerization reactions occurring in anthracene, − and ring opening and closing of diarylethenes, − leading to photoinduced mechanical responses in organic molecular crystals.…”