Cocrystal Strategy to Harmonize the Photochemical Reactivity of Styrylquinolines and the Photoactuation Performance of the Molecular Crystals

Abstract

In previous reports, the solid-state photo-induced [2 + 2] cycloaddition of styrylpyridine or styrylquinoline derivatives took place only assisted by templates. Herein, (E)-2-(2,4-difluorostyryl)quinoline (24FQL) and (E)-2-(3,5-difluorostyryl)quinoline (35FQL) have been synthesized and can undergo photodimerization in the pristine crystals. Interestingly, the photomechanical effects of the plate-like crystals are triggered by the photochemical reaction. Furthermore, the cocrystal approach was employed to harmonize the photochemical reactivity of 24FQL and 35FQL as well as the photoactuation performance of the molecular crystals. In the cocrystals of 24FQL/TFBA and 24FQL/TFPTA, the [2 + 2] cycloaddition reactivity of 24FQL decreased compared with that in a one-component crystal. However, the cocrystals showed more significant photoactuation. It was deduced that during the [2 + 2] cycloaddition, more intermolecular interactions would be broken in cocrystals, which might weaken the reactivity but enhance the photomechanical performance due to more strain being accumulated. On the contrary, the photochemical conversion of 35FQL was improved significantly in cocrystals of 35FQL/TFBA and 35FQL/TFPTA, leading to obvious photo-induced movement. Therefore, the cocrystal strategy can be a useful tool to harmonize the photochemical reactivity and photomechanical behaviors of the potentially photoactive molecular crystals.

Halogen effect in photomechanical molecular crystals

“…Lu's group synthesized ( E )-2-(2,4-difluorostyryl)quinoline ( 19 ) and ( E )-2-(3,5-difluorostyryl)quinoline ( 20 ), which could be templated by tetrafluoroterephthalic acid (TFA) or tetrafluorobenzoic acid (TA) to form co-crystals ( 19 –TA, 19 –TFA, 20 –TA and 20 –TFA). 114 The one-component crystals and co-crystals showed photo-induced mechanical behaviors, such as cracking, elongating, splitting and bending due to the [2+2] cycloaddition reactions of 19 or 20 (Fig. 9).…”

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.…”

Mechanical Effects of Elastic Crystals Driven by Natural Sunlight and Force

“…Most of the reported photoactuators require the use of artificial light sources emitting short wavelengths, and continuous deformation is achieved by actively controlling light irradiation. [23] However, the use of short-wavelength light significantly complicates the system, which in turn limits miniaturization and broad applicability. In addition to the engineering limitations involved with short wavelength light, they also pose increased health risks to humans (for example high-energy UV light).…”