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

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.