Raman spectra and DFT calculations of the vibrational modes of hexahelicene

We performed Raman spectra of the polycyclic aromatic molecule hexahelicene and compared the ≈ 50 identified vibrational modes with those of coronene. Hexahelicene has a similar structure to coronene but lower symmetry due to a cut of the molecule in the radial direction. Correspondingly, there are many more modes in the spectra. We calculated the eigenfrequencies and eigenvectors of both molecules with density-functional calculations and compared experiment and calculation, together with an assignment of the vibrational modes of hexahelicene, and we show parallels with the important modes in 2D-graphene.