Electronic structure of excited states and spectroscopic properties of pyridine, quinoline, and their protonated forms

Modulation of Antimalarial Activity at a Putative Bisquinoline Receptor In Vivo Using Fluorinated Bisquinolines

“…These observations are consistent with previous studies on related heterocyclic compounds, in which a hypsochromic shift has been related to protonation at the endocyclic nitrogen whereas a bathochromic shift is associated with protonation at the exocyclic nitrogen . Protonation of the endocyclic nitrogen changes the effective electronegativity of this position, the change in the charge on the nitrogen atom upon excitation determines the magnitude of the bathochromic spectral shift upon protonation (or deprotonation of the cation) . The increase in extinction coefficients of 7 c ‐ trans on moving to an increased hydrogen‐bonding environment reflects the geometrical change involved on the torsion angles upon protonation and its subsequent interaction on the chromophore.…”

“…To determine the effect of protonation on 6-trans and 7c-trans,U Vs pectra were recorded in DMSO and in trifluoroacetic acid (TFA). [31] The increase in extinction coefficients of 7ctrans on movingt oa ni ncreased hydrogen-bonding environment reflectst he geometrical change involved on the torsion anglesu pon protonation and its subsequenti nteraction on the chromophore. Protonation of 6-trans in DMSO resultsi nar eduction of basicity,w hichc aused ah ypsochromic shift of a p to p* band in TFA, whereas the opposite was noted for 7c-trans (bathochromic shift).…”

“…[30] Protonation of the endocyclic nitrogen changes the effective electronegativity of this position, the change in the charge on the nitrogen atom upon excitation determines the magnitude of the bathochromic spectral shift upon protonation (or deprotonation of the cation). [31] The increase in extinction coefficients of 7ctrans on movingt oa ni ncreased hydrogen-bonding environment reflectst he geometrical change involved on the torsion anglesu pon protonation and its subsequenti nteraction on the chromophore. In the case of 6-trans,t he corresponding increase of the extinction coefficients from as lightly basic (DMSO)t oa na cidic mediumr eflects the change in geometry on protonation of the endocyclic nitrogen at position 1a sw ell as hydrogen bonding of the endocyclic nitrogen, which is known to add as ap roton donor.…”