Tavarone Raffaele, Charbonneau Patrick, Stark Holger
Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany.
Departments of Chemistry and Physics, Duke University, Durham, North Carolina 27708, USA.
J Chem Phys. 2016 Mar 14;144(10):104703. doi: 10.1063/1.4943393.
Recent experiments have demonstrated that in a dense monolayer of photo-switchable dye methyl-red molecules the relaxation of an initial birefringence follows a power-law decay, typical for glass-like dynamics. The slow relaxation can efficiently be controlled and accelerated by illuminating the monolayer with circularly polarized light, which induces trans-cis isomerization cycles. To elucidate the microscopic mechanism, we develop a two-dimensional molecular model in which the trans and cis isomers are represented by straight and bent needles, respectively. As in the experimental system, the needles are allowed to rotate and to form overlaps but they cannot translate. The out-of-equilibrium rotational dynamics of the needles is generated using kinetic Monte Carlo simulations. We demonstrate that, in a regime of high density and low temperature, the power-law relaxation can be traced to the formation of spatio-temporal correlations in the rotational dynamics, i.e., dynamic heterogeneity. We also show that the nearly isotropic cis isomers can prevent dynamic heterogeneity from forming in the monolayer and that the relaxation then becomes exponential.
最近的实验表明，在光开关染料甲基红分子的致密单层中，初始双折射的弛豫遵循幂律衰减，这是类玻璃动力学的典型特征。通过用圆偏振光照射单层，可以有效地控制和加速这种缓慢的弛豫，圆偏振光会引发反式-顺式异构化循环。为了阐明微观机制，我们开发了一个二维分子模型，其中反式和顺式异构体分别由直针和弯针表示。与实验系统一样，针可以旋转并形成重叠，但不能平移。针的非平衡旋转动力学是通过动力学蒙特卡罗模拟生成的。我们证明，在高密度和低温的情况下，幂律弛豫可以追溯到旋转动力学中时空相关性的形成，即动态不均匀性。我们还表明，近乎各向同性的顺式异构体可以防止单层中形成动态不均匀性，此时弛豫变为指数形式。
