Theoretical calculation of the maximum absorption wavelength for Cyanidin molecules with several methodologies

Abstract Seven functionals, M06-L, M06, M06-2X, M06-HF, M11, PBE0 and B3LYP with two different basis set were used in the determination of the absorption spectrum in two chemical arrangements, Cyanidin (Cy) and Cyanidin-chloride (Cy-Cl). This second arrangement is studied trying to reproduce the ethanol/HCl environment of the experimental results. The main objective of this work is to find to find the influence of the electronic correlation and exchange in the absorption spectrum of Cy and Cy-Cl systems. The results of the calculated vertical excitation energies were affected by the Hartree–Fock exchange involved in the exchange–correlation functional. This can be clearly seen in the maximum absorption wavelength values found with the different methodologies applied, from which can be concluded that the best results are obtained with M06-L/6-31G(d) that predicts 547.93 nm followed by M06-L functional in combination with the 6-31G+(d,p) basis set with 544.3 nm. The experimental value is 547 nm. Also, a linear regression was performed comparing the calculated geometrical parameters with X-ray experimental data to define the best level of theory to reproduce with high precision the structural geometry, this is B3LYP/6-31+G(d,p).