Raman and ROA Spectra of (鈭?- and (+)-2-Br-Hexahelicene: Experimental and DFT Studies of a 蟺-Conjugated Chiral System
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- 作者：Christian Johannessen ; Ewan W. Blanch ; Claudio Villani ; Sergio Abbate ; Giovanna Longhi ; Nisha R. Agarwal ; Matteo Tommasini ; David A. Lightner
- 刊名：The Journal of Physical Chemistry B
- 出版年：2013
- 出版时间：February 21, 2013
- 年：2013
- 卷：117
- 期：7
- 页码：2221-2230
- 全文大小：587K
- 年卷期：v.117,no.7(February 21, 2013)
- ISSN：1520-5207
文摘
The Raman optical activity (ROA) spectra of both enantiomers of 2-Br-hexahelicene in chloroform solution have been measured in the range 1700鈥?00 cm鈥?. Density functional theory (DFT) calculations accurately reproduce the observed features. The most intense ROA features are also the most intense Raman features, in the region 1350鈥?400 cm鈥?, and correspond to the so-called D-modes, which play a major role in coronene and other PAHs (polycyclic aromatic hydrocarbons). Together with a detailed analysis of the normal mode structure, the polarizability tensors for the intense Raman features are investigated and related to the principal characteristics of helicene systems, namely, chirality and 蟺-conjugation. Through electron鈥損honon coupling analysis, we propose a mechanism that justifies the intense ROA signals.