The Raman Optical Activity (ROA) spectra of both enantiomers of 2-Br-hexahelicene in chloroform solution have been measured in the range 1700-300 cm-1. 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 1350-1400 cm-1, and correspond to the so-called D modes, which play a major role in coronene and other PAH’s (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 π-conjugation. Through electron-phonon coupling analysis we propose a mechanism that justifies the intense ROA signals.
Raman and ROA Spectra of (-)- and (+)-2-Br-Hexahelicene: Experimental and DFT Studies of a π-Conjugated Chiral System
TOMMASINI, MATTEO MARIA SAVERIO;
2013-01-01
Abstract
The Raman Optical Activity (ROA) spectra of both enantiomers of 2-Br-hexahelicene in chloroform solution have been measured in the range 1700-300 cm-1. 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 1350-1400 cm-1, and correspond to the so-called D modes, which play a major role in coronene and other PAH’s (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 π-conjugation. Through electron-phonon coupling analysis we propose a mechanism that justifies the intense ROA signals.File | Dimensione | Formato | |
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