Organic materials exhibiting mechano-fluorochromic behavior in their gel state are extremely rare in the literature. Similarly, examples of mechano-fluorochromic organic materials with crystal-to-crystal phase transitions have not been reported until date. Herein, we achieved these two remarkable properties in phenothiazine derivatives S1 and S2[(E)-N′-((10-ethyl-10H-phenothiazin-3-yl)methylene)-3,4,5-tris(hexadecyloxy)benzohydrazide and (E)-N′-((10-ethyl-10H-phenothiazin-3-yl)methylene)isonicotinohydrazide)], where S1 formed mechano-luminescent xerogel and S2 exhibited the rare feature of crystal-to-crystal phase transition with mechano-luminescence behavior. Study of the photophysical properties of S1 and S2 indicated the suppression of twisted intramolecular charge transfer (TICT) upon self-assembly, leading to blue-shifted emission from S1 and S2. While both S1 and S2 exhibited the propensity to aggregate and disclosed the aggregation induced emission (AIE) behavior in a binary solvent (THF/H₂O) mixture, only S1 resulted in a robust gel, which was further utilized for developing a superhydrophobic surface with a contact angle of 157.56°. Upon mechanical grinding, both pristine sample and xerogel of S1 showed an emission color change from light green (505 nm) to yellowish green (530 nm), whereas S2 exhibited an emission color change from cyan blue (480 nm) to green (535 nm). Furthermore, both fluorophores exhibited red-shifted emission under application of increased pressure. Mechanistic studies indicated that grinding resulted in crystal to amorphous phase transition in S1, whereas grinding in S2 demonstrated the rare feature of crystal-to-crystal phase transition. The mechano-fluorochromic (MFC) natures of S1 and S2 were supported by single point energy calculations using density functional theory (DFT).

中文翻译：

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基于吩噻嗪的机械荧光变色凝胶和固体：超疏水性表面形成和晶体到晶体的相变

在其凝胶状态下表现出机械荧光色行为的有机材料在文献中极为罕见。类似地，直到现在为止还没有报道具有晶体到晶体相变的机械-氟致变色有机材料的例子。在这里，我们在吩噻嗪衍生物S1和S2 [（E）-N '-（（10-乙基-10 H-吩噻嗪-3-基）亚甲基）-3,4,5-三（十六烷基氧基）中实现了这两个显着的特性苯并酰肼和（E）-N '-（（（10-乙基-10 H-吩噻嗪-3-基）亚甲基）异烟酰肼）），其中S1形成了机械发光干凝胶，S2表现出具有机械发光特性的晶体到晶体相变的罕见特征。对S1和S2的光物理性质的研究表明，自组装后分子内电荷转移（TICT）受到抑制，导致S1和S2发生蓝移发射。尽管S1和S2均表现出聚集倾向并公开了在二元溶剂（THF / H ₂ O）混合物中的聚集诱导发射（AIE）行为，但只有S1产生坚固的凝胶，将其进一步用于形成接触角为157.56°的超疏水表面。机械研磨后，S1的原始样品和干凝胶均显示出从浅绿色（505 nm）到黄绿色（530 nm）的发射颜色变化，而S2则显示出从青蓝色（480 nm）到绿色（535 nm）的发射颜色变化。 ）。此外，两种荧光团在施加增加的压力下均表现出红移发射。机理研究表明，在S1中进行研磨会导致晶体向非晶相变，而在S2中进行研磨则表明了晶体至晶体相变的罕见特征。S1和S1的机械-氟致变色（MFC）性质使用密度泛函理论（DFT）通过单点能量计算来支持S2。