Beijing Key Laboratory of Energy Conversion and Storage Materials, College of Chemistry , Beijing Normal University , Beijing 100875 , P. R. China.
ACS Appl Mater Interfaces. 2018 Jul 5;10(26):22703-22710. doi: 10.1021/acsami.8b05804. Epub 2018 Jun 25.
Flexible molecular crystals with stimuli-responsive properties are highly desirable; however, uncovering them is still a challenging goal. Herein, we report a cocrystal approach to obtain elastic molecular crystals that exhibit light-induced fluorescence changes and dynamic mechanical responses at the macroscale level. Cocrystals of naphthylvinylpyridine and tetrafluoroterephthalic acid were fabricated in different stoichiometry ratios (2:1 and 1:1), which present different shapes [two-dimensional (2D) and one-dimensional (1D) morphologies], photoemission, and mechanical properties (rigidity and flexibility). Moreover, obviously different photomechanical energy conversions (light-driven cracking/popping and bending/motion) occur for the 2D and 1D cocrystals, respectively. Nuclear magnetic resonance (NMR) spectra show the occurrence of photoinduced [2 + 2] cycloaddition in both cocrystals, which is the primary mechanism for their photoactuating behaviors. Crystal structure analysis and theoretical calculation further reveal that protonation and the hydrogen-bonding network play important roles in light-stimulus-bendable 1D cocrystal. Thus, the transformation from rigidity to flexibility based on cocrystallization with different stoichiometry may offer an effective means to tune the dynamic light-driven responses for smart crystalline materials.
具有刺激响应特性的柔性分子晶体是人们非常期望得到的；然而，要揭示它们仍然是一个具有挑战性的目标。在此，我们报告了一种共晶方法，以获得弹性分子晶体，其在宏观尺度上表现出光诱导荧光变化和动态力学响应。萘基乙烯基吡啶和四氟对苯二甲酸以不同的化学计量比（2:1 和 1:1）制备共晶，呈现出不同的形状[二维（2D）和一维（1D）形态]、光发射和机械性能（刚性和柔性）。此外，2D 和 1D 共晶分别发生明显不同的光机械能量转换（光驱动开裂/爆裂和弯曲/运动）。核磁共振（NMR）谱表明，两种共晶中都发生了光诱导[2+2]环加成反应，这是它们光致动行为的主要机制。晶体结构分析和理论计算进一步表明，质子化和氢键网络在光刺激可弯曲的 1D 共晶中起着重要作用。因此，基于不同化学计量比的共晶化从刚性到柔性的转变可能为智能结晶材料的动态光驱动响应提供一种有效的调节手段。
