Conceptions of Vibrational Signatures Based on Chiral/Helical Functionalized Helicenes Nanostructures: Analyzed of Normal and Identical Modes

Optoelectronics properties as helical molecular fingerprints have been investigated on a set of Helicenes molecules, which form a particular class of compounds and exhibit both π-electron delocalization and chiral properties. In this paper, we investigate the IR and Raman signatures of four representative Helicenes: Hexahilicene (Hexa-Helicene), tetrathia-[7]-helicene (Helicene-4S), and its pyrrole (Helicene-4N) and furan analogs (Helicene-4O), under the visible wavelength of 532 nm. Correctly, the impact of the method of calculation on these signatures has been pointed out. The simulation of the IR and Raman signatures involves two different steps: the evaluation of the vibrational frequencies and normal modes and the calculation of the Cartesian derivatives of electric properties. While most of the time, all the quantities are evaluated with a single method, we believe that this should not be the case since both steps have not the same requirements in terms of computational methods. Density functional theory has been then used with different exchange-correlation functional and Coupled Perturbed Time-Dependent Hartree-Fock (CP-TDHF) for the electric properties investigations. It comes out of the results that B3LYP, B3P86, and PBE0, reproduces better experimental spectra. The impact of the electron correlation as view one the XC functional on the evaluation of the Cartesian derivatives of the electric properties were found to be somewhat limited. Overall, the most crucial point is to have an accurate description of the normal vibrational modes via the choice of appropriate XC functionals, which describe the experiment results.