Highly-emissive mechanofluorochromic (MFC) organic solids changing their emission colors upon exposure to mechanical stimuli are highly demanded for various practical applications. In this work we introduced a planarizable by intramolecular N⋯H bond 2-((9H-fluoren-9-ylidene)methyl)pyridine fragment featuring an Aggregation-Induced Emission Enhancement and, particularly, MFC property for its bithiophene derivative. A two compounds, 2-((9H-fluoren-9-ylidene)methyl)-5-(5-phenylthiophen-2-yl)pyridine (FTP) and 2-((9H-fluoren-9-ylidene)methyl)-5-([2,2′-bithiophen]-5-yl)pyridine (FTT) were synthesized and fully characterized. In liquid solution both compounds are low emissive, however in the solid state they exhibit the photoluminescence quantum yield of 33% and 13% for FTP and FTT, respectively. Remarkably, the powder of FTT demonstrates a self-reversible mechanofluorochromism: the emission spectrum red-shifts after the grinding or pressurization and it recovers during one-day of storage without any treatment. The powder X-ray diffraction and differential scanning calorimetry revealed the reversible phase transition under temperature and mechanic stimuli. Analysis of molecular structure shows that in the gas phase FTT has a planar geometry while in the solid state it loses the flatness due to the crystal environment. Our results speak in favor of the increase of FTT planarity under the pressure to be responsible for the observed mechanofluorochromism.

对于各种实际应用，非常需要高度发射性的机械荧光致变色（MFC）有机固体，在受到机械刺激后会改变其发射颜色。在这项工作中，我们介绍了一个分子内的N⋯H键2-（（9H-芴-9-亚甲基）甲基）吡啶片段可平面化的化合物，该片段具有聚集诱导的发射增强，尤其是其联噻吩衍生物的MFC性能。两种化合物2-（（（9H-芴-9-亚甲基）甲基）-5-（5-苯基噻吩-2-基）吡啶（FTP）和2-（（9H-芴-9-亚甲基）甲基）-合成了5-（[2,2'-联噻吩] -5-基）吡啶（FTT）并进行了充分表征。在液态溶液中，这两种化合物的发射率均较低，但是在固态时，FTP和FTT的光致发光量子产率分别为33％和13％。值得注意的是 FTT粉末表现出自可逆的机械荧光致变色：研磨或加压后发射光谱发生红移，并且在一天的储存中无需任何处理即可恢复。粉末X射线衍射和差示扫描量热法显示在温度和机械刺激下可逆的相变。分子结构分析表明，在气相中，FTT具有平面几何形状，而在固态时，由于晶体环境，它失去了平面度。我们的结果表明，在负责观察到的机械荧光致变色的压力下，FTT平面度的增加是有利的。粉末X射线衍射和差示扫描量热法显示在温度和机械刺激下可逆的相变。分子结构分析表明，在气相中，FTT具有平面几何形状，而在固态时，由于晶体环境，它失去了平面度。我们的结果表明，在负责观察到的机械荧光致变色的压力下，FTT平面度的增加是有利的。粉末X射线衍射和差示扫描量热法显示在温度和机械刺激下可逆的相变。分子结构分析表明，在气相中，FTT具有平面几何形状，而在固态时，由于晶体环境，它失去了平面度。我们的结果表明，在负责观察到的机械荧光致变色的压力下，FTT平面度的增加是有利的。