Raman and ROA spectra of (-)- and (+)-2-Br-hexahelicene: experimental and DFT studies of a π-conjugated chiral system.
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 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 π-conjugation. Through electron-phonon coupling analysis, we propose a mechanism that justifies the intense ROA signals.
Faculty of Life Sciences and Manchester Institute of Biotechnology, John Garside Building, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
Christian
C
Johannessen
Ewan W
EW
Blanch
Claudio
C
Villani
Sergio
S
Abbate
Giovanna
G
Longhi
Nisha R
NR
Agarwal
Matteo
M
Tommasini
David A
DA
Lightner
D002725:Chloroform / Q000737:chemistry; D009904:Optical Rotation; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry; D011083:Polycyclic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman; D013237:Stereoisomerism
D011084:Polycyclic Aromatic Hydrocarbons; D011083:Polycyclic Compounds; C031660:helicenes; D002725:Chloroform; C012256:coronene