Evidence for Ultralow-Energy Vibrations in Large Organic Molecules.
Evidence for Ultralow-Energy Vibrations in Large Organic Molecules.
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DOI：
10.1021/acs.nanolett.7b01963
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发表时间：
2017-07
期刊：
影响因子：
10.8
通讯作者：
Hui Chen;T. Pope;Zhuo-Yan Wu;Dongfei Wang;L. Tao;Deliang Bao;W. Xiao;Jun‐Long Zhang;Yu‐yang Zhang;S. Du;Song Gao;S. Pantelides;W. Hofer;Hongjun Gao
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文献类型：
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作者：
Hui Chen;T. Pope;Zhuo-Yan Wu;Dongfei Wang;L. Tao;Deliang Bao;W. Xiao;Jun‐Long Zhang;Yu‐yang Zhang;S. Du;Song Gao;S. Pantelides;W. Hofer;Hongjun Gao
已知光合作用中入射光子转化为自由电子的量子效率或速率极高。长期以来，人们一直认为这种效率的来源是分子振动，导致电子和空穴在所涉及的分子中非常快速地分离。然而，分子振动通常在100 meV以上的范围内，这对于周围环境中的激发来说太高了。在这里，我们分析实验光谱的金属表面上的单个有机分子在104 K，这往往表现出明显的下降。我们表明，测量铁（II）[四-（五氟苯基）]卟啉解决这个单一的下降在4 K到一系列的阶梯形非弹性激发在0.4 K。通过广泛的光谱图下施加的磁场和相应的理论分析，我们发现，下降是由于分子框架的超低能量振动，通常在20 meV以下的范围。结果表明，有机分子中的超低能量振动比目前认为的要普遍得多，并且可能对一定尺寸以上的分子无处不在。
The quantum efficiency or the rate of conversion of incident photon to free electron in photosynthesis is known to be extremely high. It has long been thought that the origin of this efficiency are molecular vibrations leading to a very fast separation of electrons and holes within the involved molecules. However, molecular vibrations are commonly in the range above 100 meV, which is too high for excitations in an ambient environment. Here, we analyze experimental spectra of single organic molecules on metal surfaces at ∼4 K, which often exhibit a pronounced dip. We show that measurements on iron(II) [tetra-(pentafluorophenyl)]porphyrin resolve this single dip at 4 K into a series of step-shaped inelastic excitations at 0.4 K. Via extensive spectral maps under applied magnetic fields and corresponding theoretical analysis we find that the dip is due to ultralow-energy vibrations of the molecular frame, typically in the range below 20 meV. The result indicates that ultralow energy vibrations in organic molecules are much more common than currently thought and may be all-pervasive for molecules above a certain size.