Sharber Seth A, Shih Kuo-Chih, Mann Arielle, Frausto Fanny, Haas Terry E, Nieh Mu-Ping, Thomas Samuel W
Department of Chemistry , Tufts University , 62 Talbot Avenue , Medford , MA 02155 , USA . Email:
Department of Chemical & Biomolecular Engineering , University of Connecticut , 97 North Eagleville Road, Storrs , CT 06269 , USA.
Chem Sci. 2018 May 24;9(24):5415-5426. doi: 10.1039/c8sc00980e. eCollection 2018 Jun 28.
Seven three-ring phenylene-ethynylene (PE) structural analogs, differing only in the lengths of alkyl chains on terminal aniline substituents, show 50-62 nm bathochromic shifts in emission maxima in response to mechanical force (mechanofluorochromism, MC). These shifts are fully reversible with heat or solvent fuming. Shearing of these solids yields a transition from green-emitting crystalline phases to orange-emitting amorphous phases as established by differential scanning calorimetry and X-ray diffraction. Molecules with shorter alkyl chain lengths required higher temperatures to recover the hypsochromically shifted crystalline phases after grinding, while the recovery with chain lengths longer than butyl occurred at room temperature. In addition to this structure-dependent thermochromism, these compounds retain their MC properties in polymer hosts to various extents. The crystalline phases of these materials have PE chromophores that are twisted due to non-covalent perfluoroarene-arene (ArF-ArH) interactions involving perfluorophenyl pendants and the terminal rings of the PE chromophore, resulting in interrupted conjugation and an absence of chromophore aggregation. The MC behavior of an analog without the perfluoroarene rings is severely attenuated. This work demonstrates the general utility of twisted PEs as stimuli-responsive moieties and reveals clear structure-property relationships regarding the effects of alkyl chain length on these materials.
七种仅在末端苯胺取代基上烷基链长度不同的三环亚苯基乙炔（PE）结构类似物，在受到机械力作用时（机械荧光变色，MC），其发射最大值出现50 - 62纳米的红移。这些位移可通过加热或溶剂熏蒸完全逆转。通过差示扫描量热法和X射线衍射确定，这些固体的剪切作用会导致从绿色发光的结晶相转变为橙色发光的非晶相。烷基链长度较短的分子在研磨后需要更高的温度才能恢复到蓝移的结晶相，而链长超过丁基的分子在室温下即可恢复。除了这种依赖结构的热致变色外，这些化合物在聚合物主体中在不同程度上保留了它们的MC特性。这些材料的结晶相具有PE发色团，由于涉及全氟苯基侧链和PE发色团末端环的非共价全氟芳烃 - 芳烃（ArF - ArH）相互作用而发生扭曲，导致共轭中断且不存在发色团聚集。没有全氟芳烃环的类似物的MC行为会严重减弱。这项工作证明了扭曲的PE作为刺激响应基团的普遍实用性，并揭示了关于烷基链长度对这些材料影响的明确结构 - 性质关系。
