A series of D-A typed phenothiazine derivatives functionalized by formyl group (PCAn, n = 1, 2, 4 and 6) with different lengths of N-alkyl chains have been designed and synthesized to systematically investigate the effect of chain length on their solid-state fluorescence properties. The results showed that these compounds emitted strong fluorescence in solutions and solid states with 52%, 42%, 49% and 45% solid-state absolute fluorescence quantum yield (Φ_F), respectively. Their emission wavelengths were strongly affected by solvent polarity, indicating intramolecular charge transfer (ICT) transitions. Interestingly, PCAn solids exhibit not only naked-eye visible and reversible mechanochromic behavior, but chain length-dependent emission properties. PCA1 shows smaller fluorescence spectrum shifts (22 nm) under mechanical force stimuli. Homologs with longer alkyl chains exhibit similar mechanochromic behaviors but larger fluorescence contrasts after grinding except for PCA6. Moreover, the fluorescence emission of ground solid PCA1 and PCA4 can recover at room temperature, PCA2 need high temperatures for fluorescence to be restored, and XRD and DSC revealed that the transformation between crystalline and amorphous states upon various external stimuli was responsible for the MFC behavior. This work demonstrates the feasibility of tuning the solid-state optical properties of fluorescent organic compounds by combining the simple alteration of chemical structure and the physical change of aggregate morphology under external stimuli.

设计并合成了一系列被甲酰基官能化的DA型吩噻嗪衍生物（PCAn，n = 1、2、4和6），具有不同的N-烷基链长度，以系统地研究链长对其固态的影响荧光性质。结果表明，这些化合物在发射溶液和固体状态的荧光强52％，42％，49％和45％的固态绝对荧光量子产率（Φ _˚F分别地）。它们的发射波长受溶剂极性的强烈影响，表明分子内电荷转移（ICT）跃迁。有趣的是，PCAn固体不仅表现出肉眼可见和可逆的变色行为，而且表现出与链长相关的发射特性。PCA1在机械力刺激下显示出较小的荧光光谱位移（22 nm）。具有较长烷基链的同源物表现出类似的机械变色行为，但除PCA6外研磨后的荧光对比度更大。此外，磨碎的固体PCA1和PCA4的荧光发射可以在室温下恢复，PCA2需要高温才能恢复荧光，XRD和DSC揭示了在各种外部刺激下晶态和非晶态之间的转变是MFC行为的原因。这项工作证明了通过结合化学结构的简单变化和外部刺激下聚集体形态的物理变化来调节荧光有机化合物的固态光学性能的可行性。