A Tri-state Fluorescent Switch with “Gated” Solid-state Photochromism Induced by an External Force

Mr. Chen Qian, Dr. Zhimin Ma, Mr. Jianwei Liu, Mrs. Xue Zhang, Prof. Shitao Wang and Prof. Zhiyong Ma. In this article, we report a newly designed molecule composed of a dihydroazulene (DHA) group and a phenothiazine (PTZ) moiety, which achieves aggregation-induced emission enhancement (AIEE), mechanochromism and “gated” solid-state photochromism upon stimulation by an external force. Grinding loosens intermolecular interactions in the crystal and causes a red-shift of fluorescence from 570 nm to 600 nm. Meanwhile, the ring-opening reaction of DHA unit is activated by grinding and a remarkable photochromism could be observed from the grinded powder. The reddish emission of the grinded powder peaked at 600 nm weakened gradually and finally became dark, and a new absorption band at 470 nm emerged in the absorption spectra. Time-dependent density functional theory (TD-DFT) calculation results reveal that the intramolecular intramolecular charge-transfer (ICT) process is replaced by a locally excited (LE) emission on the DHA group, which leads to the quenching of fluorescence. Its impressive photochromic property inspired us to a simple but effective way to develop an encryption system which can let the correct information be displayed upon external stimulation.     

Synthesis and characterization of an unexpected mechanochromicbistricyclic aromatic ene

An unexpected bistricyclic aromatic ene AF was synthesized in a tin(II) chloride-mediated reductive aromatization reaction. The obtained AF showed a highly overcrowded structural conformation as revealed by X-ray crystallography. Interestingly, AF exhibited reversible high-contrast mechanochromism and thermochromism between pale and red color. The obvious chromism is likely ascribed to the conformation transformation and trace amount of diradical species formation upon stimulus.     

Dimethylamine substituted bisbenzocoumarin amides with solvatochromic and mechanochromic properties

Stimuli responsive luminescent materials have attracted increasing attention for their potential application in many fields. In this work, dimethylamine substituted bisbenzocoumarins amides (DBCE and DBCP) are synthesized and their optical properties are investigated. These molecules show solvatochromic properties. The orange fluorescence emission of DBCE in crystalline state is blue-shifted to yellow emission upon grinding. The orange color could be recovered by recrystallization process. Powder wide-angle X-ray diffraction and DSC experiments reveal that the transformation from crystalline states to amorphous states under external stimuli is responsible for the mechanochromic properties. This work developed a new kind of binaphthane-type luminescent materials with blue-shifted mechanochromic properties.     

基于1,3,5-三嗪的具有力致变色性质的聚集诱导荧光化合物的合成及性质

以1,3,5-三嗪为核, 四苯基乙烯为端基, 合成了两种新型的星状结构分子2,4,6-三(4-(1,2,2-三苯基乙烯基)苯基)-1,3,5-三嗪(TTPE-Tr)和2,4,6-三(4-(1,2,2-三苯基乙烯基)-4-联苯基)-1,3,5-三嗪(TTPE-Ph-Tr), 并利用核磁共振(NMR)、离子化质谱(MALDI-MS)及元素分析等对其进行了结构表征. 通过混合溶剂四氢呋喃(THF)/水析出实验显示, 化合物TTPE-Tr和TTPE-Ph-Tr在纯THF溶剂中无荧光, 而在THF/水混合溶剂中, 当水体积分数增加时呈现荧光增强现象. 通过紫外-可见(UV-Vis)光谱、荧光(PL)光谱、扫描电子显微镜(SEM)证实荧光量子效率的提高是由于分子内电子旋转受限(RIR)导致的. 同时发现化合物TTPE-Tr具有力致变色性质, 简单的研磨使其发光颜色(蓝绿光到黄绿光)及发光强度(Φ_F, 24.4%到14.7%)发生了明显的改变. UV-Vis光谱、PL光谱、X射线衍射(XRD)、荧光寿命和荧光量子效率等测试结果显示, 这种现象是由于力刺激改变了TTPE-Tr的分子堆积形式导致的. 热分析结果显示化合物TTPE-Tr和TTPE-Ph-Tr的热分解温度分别为464和385℃, 具有良好的热稳定性.     

Vinylpyridine- and vinylnitrobenzene-coating tetraphenylethenes: Aggregation-induced emission (AIE) behavior and mechanochromic property

Two new functionalized tetraphenylethene-based dyes were synthesized, and the enhanced AIE and mechanochrmic properties were evaluated upon grinding-fuming with the transformation from crystal forms to irregular amorphous forms.     

Crystallization-induced phosphorescence,remarkable mechanochromism,and grinding enhanced emission of benzophenone-aromatic amine conjugates

Twisted pure organic luminogens based on benzophenone and aromatic amines exhibit both fluorescence and phosphorescence in crystals, while owning merely red-shifted fluorescence at ground amorphous solids. Some of them even demonstrate greatly enhanced emission upon grinding.     

Selective Expression of a Carbazole-Phenothiazine Derivative Leads to Dual-mode AIEE,TADF and Distinctive Mechanochromism

In this article, we report a newly designed D−A−D’ derivative (CNCzPTZ), which displays selective expression of chromophores. This enables CNCzPTZ with solvatochromism, rare dual-mode AIEE properties, solid-state dual-emissions with phosphorescence and distinctive mechanochromism.CNCzPTZ exhibits dual-mode AIEE properties, since the emission band abruptly shifts from 550 nm to 500 nm as the water fraction increases. In the crystalline state, CNCzPTZ demonstrated dual emission bands of 478 nm and 538 nm.CNCzPTZ shows distinctive mechanochromic property in the solid state due to the planarization.     

D-A-D type dinitriles with vapor-dependent luminescence in the solid state

D-A-D (Donor-Acceptor-Donor) type dinitriles linked by a styryl or phenylethynyl group have been prepared. These groups were introduced to increase the flexibility and the size of the π-conjugation in the chromophores. Both compounds showed strong emission in the solid state, AIE (aggregation-induced emission) behavior, and mechanochromism. The fluorescence color of ground powder changed by organic solvent vapor (vapochromism). Especially, the emission color of the styryl dinitrile after exposures depends on the solvent, while that of the phenylethynyl dinitrile is the same after exposure to different solvents. These results were explained by single crystal and powder XRD measurements, which revealed that the flexible styryl linker leads to a loose crystal packing, resulting in a dinitrile with multi-state microcrystalline structures. This methodology based on the flexible linker allows for the detection of small organic molecules without transition metals.     

Relationship between mechanochromic behavior and crystal structures in donor-π-acceptor compounds consisted of aromatic rings with ester moiety as an acceptor

We investigated the mechanochromic behavior of donor-π-acceptor compounds which consisted of diphenylaminophenylacetylene as a donor-π moiety and (hetero)aromatic ring bearing ester as an acceptor. The compounds with dicyanobenzoic ester gave the bathochromic shift by grinding, whereas the compounds consisted of the ester with benzene, imidazole, and thiazole rings showed the hypsochromic shift. From single-crystal X-ray analysis, we revealed that the compound with bathochromic shift gave the herringbone alignment with H-aggregate-like π-stacking in the crystal structure. On the contrary, the compounds with hypsochromic shift showed the structure with the alignment of long axis of the molecule in crystal structure.     

Stimuli-responsive organic chromic materials with near-infrared emission

Some organic chromic materials responding to external stimuli, mainly to mechanical forces, with a near-infrared (NIR) emission are discussed. In line with reported cases, there is a conclusion that subtle changes in conformations and packing modes are the primary elements contributing to the optical properties changes.