Howe Morgan E, Barbour Nicole A, Garcia Ronnie V, Garcia-Garibay Miguel A
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, United States.
J Org Chem. 2020 Jun 5;85(11):6872-6877. doi: 10.1021/acs.joc.9b03398. Epub 2020 May 21.
Herein, we report the use of fluorescence anisotropy decay for measuring the rotation of six shape-persistent molecular rotors with central naphthalene (), anthracene (, , and ), tetracene (), and pentacene () rotators axially linked by triple bonds to bulky trialkylsilyl groups of different sizes. Steady-state and time-resolved polarization measurements carried out in mineral oil confirmed that the vibrationally resolved lowest-energy absorption bands are characterized by a transition dipole moment oriented along the short acene axes, in the direction of the alkyne linkers. Fluorescence lifetimes increased significantly with increasing acene size and moderately with a decrease in the size of the trialkylsilyl group. The fluorescence anisotropy decay for all compounds in mineral oil with a viscosity of ca. 21.6 cP at 40 °C was completed within the fluorescence lifetime, so that the rotational time constants could be obtained via their rotational correlation times, which increased with silyl protecting group size rather than acene size, indicating that polarization decay is determined by tumbling of the molecular rotor about the long acene axis. These results suggest that monitoring the rotational motion of bis(silylethynyl)acenes in restricted media should be possible for media with viscosity values on the order of 21.6 cP or greater.
在此，我们报道了利用荧光各向异性衰减来测量六个形状持久的分子转子的旋转情况，这些转子的中心萘（）、蒽（、和）、并四苯（）和并五苯（）通过三键轴向连接到不同大小的庞大三烷基甲硅烷基上。在矿物油中进行的稳态和时间分辨极化测量证实，振动分辨的最低能量吸收带的特征是跃迁偶极矩沿短并苯轴方向取向，即炔烃连接基的方向。荧光寿命随着并苯尺寸的增加而显著增加，并随着三烷基甲硅烷基尺寸的减小而适度增加。在40℃下粘度约为21.6 cP的矿物油中，所有化合物的荧光各向异性衰减在荧光寿命内完成，因此可以通过它们的旋转相关时间获得旋转时间常数，旋转相关时间随着甲硅烷基保护基尺寸的增加而增加，而不是随着并苯尺寸增加，这表明极化衰减是由分子转子围绕长并苯轴的翻滚决定的。这些结果表明，对于粘度值在21.6 cP或更高量级的受限介质，监测双（硅乙炔基）并苯的旋转运动应该是可行的。
