Molecular rotors are an important class of dynamic molecules which have been studied not only for their possible uses as components of molecular machines but also because of potential applications as probes of local viscosity in biological media, especially self-assembled membranes. For the former, factors affecting rotational motility are critical while for the latter the rotor activity must be complexed with an output signal (often fluorescence) for reporting of local conditions. Molecular single stator-double rotor activity of an oxidized resorcinarene (fuchsonarene) macrocycle containing unsaturated hemiquinonoid groups at its meso positions was investigated. Fuchsonarenes contain two hemiquinonoid substituents at diagonally-opposed meso-positions with two electron rich phenol groups at the remaining meso-positions between the hemiquinonoid groups. All meso-substituents are in proximity at one side of the resorcinarene macrocycle (so-called rccc-type isomer) with rotational activity of the phenol meso-substituents. Rotation rates of the phenol moieties can be controlled by varying temperature, solvent polarity and acidity of the medium of study with rotation being thermally activated in neutral and acidic media and tunable in the range from 2 s⁻¹ to 20 000 s⁻¹. Experimental and computational data indicate that rotation of the mobile phenol meso-substituents is remotely affected by interactions with acidic solvents at the carbonyl CO groups of macrocyclic acetyloxy groups, which occurs with the emergence of a lower energy electronic absorption band whose intensity is correlated with both the acidity of the medium and the rotation rate of the phenol substituents. Time-dependent DFT calculations suggest that the low energy band is due to a molecular conformational adjustment affecting electronic conjugation caused by strong interaction of macrocyclic acetyloxy carbonyl groups with the acid medium. The work presents a molecular mechanical model for estimating solution acidity and also gives insight into a possible method for modulating rotor activity in molecular machines.

中文翻译：

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基于氧化间苯二酚的分子转子

分子转子是一类重要的动态分子，不仅因为它们可能用作分子机器的组件而被研究，而且还因为它们作为生物介质中局部粘度的探针的潜在应用，特别是自组装膜。对于前者，影响旋转运动的因素至关重要，而对于后者，转子活动必须与输出信号（通常是荧光）相结合，以报告当地条件。含有在其不饱和基团hemiquinonoid氧化间苯二酚杯芳烃（fuchsonarene）大环化合物的分子单定子-双转子活性内消旋位置进行了研究。Fuchsonarenes 在对角相对的中间位置含有两个半醌类取代基在半醌基团之间的剩余中间位置具有两个富电子苯酚基团的位置。所有内消旋取代基都靠近间苯二酚大环（所谓的rccc型异构体）的一侧，具有苯酚内消旋取代基的旋转活性。酚部分的旋转速率可以通过改变研究介质的温度、溶剂极性和酸度来控制，旋转在中性和酸性介质中被热激活并且在2 s ^-1到20 000 s ^-1的范围内可调。实验和计算数据表明，移动苯酚内消旋- 取代基受到与大环乙酰氧基羰基CO 基团处的酸性溶剂相互作用的远程影响，这种相互作用发生在低能量电子吸收带的出现时，其强度与介质的酸度和旋转速率相关苯酚取代基。时间相关的 DFT 计算表明，低能带是由于分子构象调整影响电子共轭，这是由大环乙酰氧基羰基与酸介质的强相互作用引起的。这项工作提出了一种用于估计溶液酸度的分子力学模型，并且还提供了一种可能的方法来调节分子机器中的转子活动。