Controllable photomechanical bending of metal-organic rotaxane crystals facilitated by regioselective confined-space photodimerization

Abstract

Molecular machines based on mechanically-interlocked molecules (MIMs) such as (pseudo) rotaxanes or catenates are known for their molecular-level dynamics, but promoting macro-mechanical response of these molecular machines or related materials is still challenging. Herein, by employing macrocyclic cucurbit[8]uril (CB[8])-based pseudorotaxane with a pair of styrene-derived photoactive guest molecules as linking structs of uranyl node, we describe a metal-organic rotaxane compound, U-CB[8]-MPyVB, that is capable of delivering controllable macroscopic mechanical responses. Under light irradiation, the ladder-shape structural unit of metal-organic rotaxane chain in U-CB[8]-MPyVB undergoes a regioselective solid-state [2 + 2] photodimerization, and facilitates a photo-triggered single-crystal-to-single-crystal (SCSC) transformation, which even induces macroscopic photomechanical bending of individual rod-like bulk crystals. The fabrication of rotaxane-based crystalline materials with both photoresponsive microscopic and macroscopic dynamic behaviors in solid state can be promising photoactuator devices, and will have implications in emerging fields such as optomechanical microdevices and smart microrobotics.

Photoresponsive Metal-Organic Frameworks as Adjustable Scaffolds in Reticular Chemistry

“…The incorporation of photoactive guests, such as styrylpyridinium derivatives, in the cavities of cucurbituril with a macrocycle-photoactive unit binding ratio of 1:2 has led to a cucurbituril-promoted photodimerization upon visible light irradiation (Figure 17) [129][130][131]. Professors Mei, Feng, Shi and colleagues reported the preparation of the uraniumorganic framework U-CB [8]-MPyVB by using cucurbit [8]uril-based pseudorotaxanes having a pair of carboxylic acid-functionalized styrylpyridinium linear components [53]. The synthesis of U-CB[8]-MPyVB proceeds via a one-pot solvothermal reaction through the assembly of uranium nitrate oxide, (E)-4-[2-(methylpyridine-4-yl) vinylbenzoic acid (16) and cucurbit [8]uril.…”

“…Favorable properties of these materials herald possible applications in other fields, such as Nanorobotics, Data Storage and Optoelectronics (Table 1, entries 5-7 and 9) [53,76,78,85,87].…”

“…However, there are two main limitations: (i) the postsynthetic conditions must not affect the integrity of the crystalline array; (ii) the functionalization with the photoresponsive units may not be homogeneous throughout the material. This short review aims to give an insight in the preparation and application of lightresponsive metal-organic frameworks by using different photoswitchable organic ligands (Figure 1), including azobenzenes [47], diarylethenes [48], spiropyrans [49], donor-acceptor Stenhouse adducts (DASA) [50], molecular motors [51], interlocked fumaramides [52] and interlocked styrylpyridinium derivatives [53]. For this purpose, some recent advances in the use of the abovementioned organic ligands will be highlighted in this manuscript.…”

The Role of Dethreading Process in Pseudorotaxanes and Rotaxanes towards Advanced Applications: Recent Examples

“…Mechanically interlocked molecules (MIMs) are a type of compounds constituted by components which are bonded together through noncovalent interactions, forming a mechanical bond [1–3] . Within the range of intertwined compounds, rotaxanes are postulated as ideal candidates for the design of molecular machines, developing applications in a wide range of fields, [4–6] such as catalysis, [7–14] materials science [15–24] or medicinal chemistry [25–27] …”

Light-driven flagella-like motion of coordination compound single crystals

“…Stimuli-responsive dynamic single crystals have been discovered to show mechanical motions, such as bending, curling, jumping, twisting, flipping, hopping, breaking, elongation, contraction, and explosion. [1][2][3][4] Most of these reports showed the triggering of these materials taking place through external stimuli such as light, heat, and magnetism. 5,6 Recently, light has been utilized as one of the best stimuli, mainly due to its remote action, non-invasive properties, target manipulation, control over input intensity and wavelength.…”