Chromic materials, an important class of stimuli-responsive materials, have aroused extensive attention in recent years. Normally, their color is based on changes in morphology. Few examples of chromic material based on conformational isomerization, such as in overcrowded alkenes, have been reported previously. Furthemore, experimental thermodynamic studies of overcrowded bistricyclic aromatic enes have not been carried out to our knowledge. Here, we show that N-phenyl-substituted fluorenylidene-acridanes, with a properly modified fluorene moiety, performs chromisms originating from conformational changes. Thermodynamic studies determine equilibrium constants, changes in enthalpy, entropy, and free energy in solution, enabling in-depth understanding of the equilibrium behavior of overcrowded alkenes and providing useful information for designing functional chromic compounds. Single-crystal X-ray diffraction analysis of fluorenylidene-acridanes in this work clearly shows well-tuned charge transfer from the acridane to the fluorene moiety. Various chromic behaviors such as mechanochromism, thermochromism, solvatochromism, vapochromism, and proton-induced chromism also support understanding of conformational isomerism.

铬材料作为一类重要的刺激响应材料，近年来引起了广泛关注。通常，它们的颜色是基于形态的变化。之前已经报道了基于构象异构化的铬材料的几个例子，例如在过度拥挤的烯烃中。此外，据我们所知，尚未对过度拥挤的双三环芳烃进行实验热力学研究。在这里，我们证明N-phenyl-substituted fluorenylidene-acridanes, 具有适当修饰的 fluorene 部分, 执行源自构象变化的色差。热力学研究确定溶液中的平衡常数、焓变、熵和自由能，从而能够深入了解过度拥挤的烯烃的平衡行为，并为设计功能性铬化合物提供有用的信息。这项工作中亚亚芴基吖啶的单晶 X 射线衍射分析清楚地表明从吖啶到芴部分的电荷转移得到了很好的调整。机械致色、热致变色、溶剂化致色、蒸气致色和质子诱导致色等各种变色行为也支持对构象异构现象的理解。