Fluorescent molecular rotors find widespread application in sensing and imaging of microscopic viscosity in complex chemical and biological media. Development of viscosity-sensitive ultrafast molecular rotor (UMR) relies upon the understanding of the excited-state dynamics and their implications for viscosity-dependent fluorescence signaling. Unraveling the structure–property relationship of UMR behavior is of significance toward development of an ultrasensitive fluorescence microviscosity sensor. Herein we show that the ground-state equilibrium conformation has an important role in the ultrafast twisting dynamics of UMRs and consequent viscosity sensing efficiency. Synthesis, photophysics, and ultrafast spectroscopic experiments in conjunction with quantum chemical calculation of a series of UMRs based on dimethylaniline donor and benzimidazolium acceptor with predefined ground-state torsion angle led us to unravel that the ultrafast torsional dynamics around the bond connecting donor and acceptor groups profoundly influences the molecular rotor efficiency. This is the first experimental demonstration of conformational control of small-molecule-based UMR efficiencies which can have wider implication toward development of fluorescence sensors based on the UMR principle. Conformation-controlled UMR efficiency has been shown to exhibit commensurate fluorescence enhancement upon DNA binding.

中文翻译：

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超快分子转子特性的构象控制：通过扭转角变化来调节粘度传感效率

荧光分子转子广泛应用于复杂化学和生物介质中微观粘度的感测和成像。粘度敏感的超快分子转子（UMR）的开发依赖于对激发态动力学及其对粘度依赖性荧光信号的影响的理解。揭示UMR行为的结构-性质关系对于开发超灵敏的荧光微粘度传感器具有重要意义。在这里，我们表明，基态平衡构象在UMR的超快扭转动力学和由此产生的粘度感测效率中具有重要作用。合成，光物理，和超快光谱实验，以及基于二甲基苯胺给体和苯并咪唑鎓受体的，具有预定义基态扭转角的一系列UMR的量子化学计算，使我们发现，连接给体和受体基团的键周围的超快扭转动力学对分子产生了深远的影响。转子效率。这是对基于小分子的UMR效率进行构象控制的第一个实验演示，对基于UMR原理的荧光传感器的开发可能具有更广泛的意义。构象控制的UMR效率已显示出在DNA结合后显示出相应的荧光增强。