Rury Aaron S, Sorenson Shayne, Dawlaty Jahan M
Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
J Chem Phys. 2016 Mar 14;144(10):104701. doi: 10.1063/1.4943047.
Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.
能够响应外部刺激产生相干晶格声子激发的有机材料，可能会在广泛的应用领域提供下一代解决方案。然而，要使这些材料应用于技术领域制成功能性器件，必须全面了解相干晶格声子产生的可能驱动力。为推动实现这一目标，我们对一种由常见的氧化还原对氢醌和对苯醌形成的有机电荷转移材料进行了光谱学研究。在用泵浦光激发这种称为醌氢醌的材料时，激发其分子间电荷转移共振以及对苯醌的分子内共振，我们发现了波数低于厘米-1的振荡，其随探测能量的色散类似于相干声子的色散，我们认为这是在醌氢醌电子密度变化后被相干激发的。利用这些超快泵浦-探测测量得到的动力学信息，我们发现无论在哪个能量下泵浦醌氢醌，我们能分辨的最快过程都不会改变。超快相干振动光谱和稳态共振拉曼光谱的电子-声子耦合，使我们能够确定对苯醌的分子内电子激发也驱动了醌氢醌中的电子转移过程。这些结果表明，许多功能性有机材料中发现的母体分子具有广泛的电子激发，可驱动对电子学、光子学和信息技术应用有用的相干晶格声子激发。
