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Characteristic Molecular Structures of Electronically Excited Species Studied by Ultrafast Time-Resolved Infrared Spectroscopy in the Fingerprint Region.

通过超快时间分辨红外光谱研究指纹区域电子激发物质的特征分子结构。

基本信息

批准号：
09640597
负责人：
OKAMOTO Hiromi
金额：
$ 2.11万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

In this research we have tried to improve sensitivity of our apparatus for picosecond infrared spectroscopy in the fingerprint region and to measure several photochemically important electronically excited species to obtain their structural information. As for the sensitivity improvement, we have succeeded in proposing a novel method based on optically heterodyned detection of absorption anisotropy, in addition to many minor changes of apparatus. By this method amplitude of the absorption signal increases in nearly (or sometimes more than) one order of magnitude. We have then performed picosecond infrared measurements in the fingerprint region for several photochemically improtant excited species. Transient infrared spectra of S state of S^1 state of trans-stilbene are measured in acetonitrile and n-heptane solutions, and from the comparison between them and the Raman spectra of the same species, the excited molecular structures are discussed. It has been suggested that the S^1 species retains the center of symmetry in n-heptane, while the S^1 state in acetonitrile is slightly distorted from the centrosymmeric structure. A possible interpretation for this result is that the excited species is weakly polarized around the olefinic C=C bond in acetonitrle solution. As a related compound, we have also succeeded in obtaining an infrared spectrum of the excited diphenylacetylene. We have investigated transient infrared spectrum of S^1 state of 4-(dimethylamino)benzonitrile in an acetonitrile solution, which attracts much attention in relation to the TICT (twisted intramolccular charge transfer) structure. A strong band has been found in the single-bond stretching wavenumber region, which may be assigned to the C-N stretch of the bond between the C atom of the benzene ring and the N atom of the dimethylamino group. This result suggests that the C-N bond has a single-bond character in the S^1 state.

在这项研究中，我们试图提高指纹区域皮秒红外光谱仪的灵敏度，并测量几种光化学上重要的电子激发物质以获得它们的结构信息。至于灵敏度的提高，除了设备的许多微小变化之外，我们还成功地提出了一种基于吸收各向异性的光学外差检测的新方法。通过这种方法，吸收信号的幅度增加了接近（或有时超过）一个数量级。然后，我们在指纹区域对几种光化学重要的激发态物质进行了皮秒红外测量。测量了反式二苯乙烯S^1态在乙腈和正庚烷溶液中S态的瞬态红外光谱，并通过与同种物质的拉曼光谱的比较，讨论了激发的分子结构。有人认为，正庚烷中的 S^1 物质保留了对称中心，而乙腈中的 S^1 状态与中心对称结构略有扭曲。对该结果的可能解释是，在乙腈溶液中，激发态物质在烯属 C=C 键周围弱极化。作为相关化合物，我们还成功获得了激发态二苯乙炔的红外光谱。我们研究了乙腈溶液中 4-(二甲基氨基)苯甲腈 S^1 态的瞬态红外光谱，该光谱因其 TICT（扭曲分子内电荷转移）结构而备受关注。在单键伸缩波数区发现了强谱带，该谱带可能归属于苯环的C原子和二甲氨基的N原子之间的键的C-N伸缩。这一结果表明，C-N 键在 S^1 状态下具有单键特征。