title: Spectrothermodynamic relationship of cationic vs anionic species derived from protonation vs deprotonation of pyrrolo-aza-aromatic bases in homologous series.
abstract: Theoretical research on the spectroscopy and protonation energies of ionic species related to the neutral pyrrolo-aza-aromatic bases has been carried out, using Density Functional Theory (DFT) and its time dependent form (TDDFT). In the ionic species the skeleton localized (+) and (-) charge in the protonated and deprotonated species is shown to have a strong perturbation of the pi-electronic states. The lowest electronic S(0) --> S(1) (pi,pi*) transitions are shown to have near-coincidence for each cation and anion for the whole homologous series, in agreement with the Valle-Kasha-Catalán rule previously stated. It is further demonstrated that simultaneous dramatic changes, upon electronic excitation, in acidity and basicity at the pyrrolo- and aza-positions of the molecular skeleton are the driving force for the biprotonic phototransfer processes in these bases. This constitutes confirmation of the proton-transfer rather than H-atom transfer as the reaction mechanism.
authors.affiliation: Departamento de Química Física Aplicada, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Catalán
mesh_terms: D000838:Anions / Q000737:chemistry; D001372:Aza Compounds / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D007211:Indoles / Q000737:chemistry; D010777:Photochemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011522:Protons; D011687:Purines / Q000737:chemistry; D011758:Pyrroles / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000838:Anions; D001372:Aza Compounds; D002412:Cations; D007211:Indoles; D011084:Polycyclic Aromatic Hydrocarbons; D011522:Protons; D011687:Purines; D011758:Pyrroles