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的picsecond红外光谱的敏感性，并测量几种具有光化学上重要的电子激发物种以获得其结构信息。至于灵敏度的提高，除了许多较小的设备变化外，我们还成功地提出了一种基于光学异化的吸收各向异性检测的新方法。通过这种方法，吸收信号的幅度几乎（或有时超过）一个数量级增加。然后，我们在指纹区域进行了几种光化学上不合理的激发物种的Picsecond红外测量。 s^1跨曲苯s状态的瞬态红外光谱在乙腈和N-己酯溶液中测量，从它们与同一物种的拉曼光谱之间的比较中，讨论了激发分子结构。有人提出，S^1物种保留在N heptane中的对称性中心，而乙腈中的S^1状态略微扭曲了中心对称结构。对此结果的一种可能的解释是，乙酰硝基溶液中的烯烃C = c键在烯烃C = C键周围弱极化。作为一种相关化合物，我们还成功地获得了激发二苯基乙二醇的红外光谱。我们已经研究了乙腈溶液中4-（二甲基氨基）苯甲腈的S^1状态的瞬态红外光谱，这引起了与TICT（扭曲的Omolccular电荷转移）结构的极大关注。在单键拉伸波数区域中发现了一个强带，可以将其分配到苯环的C原子和二甲基氨基基团的N原子之间的键的C-N延伸。该结果表明C-N键在S^1状态中具有单键字符。