Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 120-750, Republic of Korea.
Phys Chem Chem Phys. 2011 Sep 7;13(33):15227-32. doi: 10.1039/c1cp20835g. Epub 2011 Jul 18.
The trans-cis isomerization of an excited molecule converts light energy into mechanical motion, which interacts cooperatively with its surroundings. To understand such a photodynamic process in solids, we investigated the internal twisting motion of 1,1'-diethyl-2,2'-cyanine iodide (DCI) in a series of poly(alkyl methacrylate) (PAMA) polymers by measuring the Young's moduli of the polymers with atomic force microscopy nanoindentation and the fluorescence lifetimes of the dye with time-correlated single photon counting. We found that the isomerization rate constant obtained from the average lifetime correlated well with the mechanical property of the matrix. Our results show that the light-induced molecular motion lies in the modulus-controlled regime in which the polymer matrix not only provides a rigid environment for the dynamics of the molecules but also participates actively in the motion. The concept of elastic modulus may be applicable to molecular rotor dynamics in any synthetic polymer and, in principle, can be extended to biopolymers such as proteins or DNA.
激发态分子的顺反异构将光能转化为机械能，这种机械能与周围环境相互作用。为了在固体中理解这种光动力过程，我们通过原子力显微镜纳米压痕测量一系列聚（烷基甲基丙烯酸酯）（PAMA）聚合物中 1,1'-二乙基-2,2'-氰基碘化物（DCI）的内部扭曲运动，并用时间相关单光子计数测量染料的荧光寿命。我们发现，从平均寿命获得的异构化速率常数与基质的机械性能密切相关。我们的结果表明，光诱导的分子运动位于模量控制区域，其中聚合物基质不仅为分子的动力学提供了刚性环境，而且还积极参与运动。弹性模量的概念可能适用于任何合成聚合物中的分子转子动力学，并且原则上可以扩展到蛋白质或 DNA 等生物聚合物。
