Substituent effects on vibrational and electronic excitation spectra of pyridone tautomers and ions: The case of the cyano group

In this theoretical work, we computed the equilibrium geometries and a set of rotational and vibrational spectroscopic parameters for cyano substituted 2-pyridones neutral or cationic and their tautomers (cyano 2-hydroxypyridines). We examined also the effect of tautomerism equilibrium on those systems. In our analysis, we mostly focused on the perturbations induced by the CN group on the electronic structure and on the spectroscopy of 2-pyridone/2-hydroxypyridine block. Moreover, we investigated the pattern of their low lying electronic states at both the PBE0/aug-cc-pVDZ Density Functional Theory (DFT) and the CASSCF/aug-cc-pVTZ levels of theory. Vertical excitation spectra and both adiabatic and vertical ionization energies were performed.