Conceptions of Vibrational Signatures Based on Chiral/HelicalFunctionalized Helicenes Nanostructures: Analyzed of Normaland Identical Modes

Abstract

Optoelectronics properties as helical molecularfingerprints have been investigated on a set of Helicenesmolecules, which form a particular class of compounds andexhibit both π-electron delocalization and chiral properties. Inthis paper, we investigate the IR and Raman signatures of fourrepresentative Helicenes: Hexahilicene (Hexa-Helicene),tetrathia-[7]-helicene (Helicene-4S), and its pyrrole (Helicene-4N) and furan analogs (Helicene-4O), under the visiblewavelength of 532 nm. Correctly, the impact of the method ofcalculation on these signatures has been pointed out. Thesimulation of the IR and Raman signatures involves twodifferent steps: the evaluation of the vibrational frequencies andnormal modes and the calculation of the Cartesian derivatives ofelectric properties. While most of the time, all the quantities are evaluated with a single method, we believe thatthis 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 CoupledPerturbed Time-Dependent Hartree-Fock (CP-TDHF) for the electric properties investigations. It comes out of theresults that B3LYP, B3P86, and PBE0, reproduces better experimental spectra. The impact of the electroncorrelation as view one the XC functional on the evaluation of the Cartesian derivatives of the electric propertieswere found to be somewhat limited. Overall, the most crucial point is to have an accurate description of the normalvibrational modes via the choice of appropriate XC functionals, which describe the experiment results