Fluorescent molecular rotors have been used for measurements of local mobility on molecular length scales, for example to determine viscosity, and for the visualization of contact between two surfaces. In the present work, we deepen our insight into the excited‐state deactivation kinetics and mechanics of dicyanodihydrofuran‐based molecular rotors. We extend the scope of the use of this class of rotors for contact sensing with a red‐shifted member of the family. This allows for contact detection with a range of excitation wavelengths up to ∼600 nm. Steady‐state fluorescence shows that the fluorescence quantum yield of these rotors depends not only on the rigidity of their environment, but – under certain conditions – also on its polarity. While excited state decay via rotation about the exocyclic double bond is rapid in nonpolar solvents and twisting of a single bond allows for fast decay in polar solvents, the barriers for both processes are significant in solvents of intermediate polarity. This effect may also occur in other molecular rotors, and it should be considered when applying such molecules as local mobility probes.

中文翻译：

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基于二氰基二氢呋喃基序的荧光接触式传感器的光物理

荧光分子转子已经用于在分子长度尺度上测量局部迁移率，例如确定粘度，以及用于可视化两个表面之间的接触。在当前的工作中，我们加深了对基于二氰基二氢呋喃的分子转子的激发态失活动力学和力学的认识。我们扩大了该系列用于接触感测的转子的使用范围，该家族已红移。这允许在高达约600 nm的激发波长范围内进行接触检测。稳态荧光表明，这些转子的荧光量子产率不仅取决于其环境的刚性，而且在某些条件下还取决于其极性。尽管在非极性溶剂中通过绕环外双键旋转引起的激发态衰减很快，而单键的扭曲使极性溶剂快速衰减，但在中间极性的溶剂中，这两个过程的障碍都很重要。此效应也可能在其他分子转子中发生，在将此类分子用作局部迁移探针时应予以考虑。