The unusually strong effect of a 4-cyano group upon electronic spectra and dissociation constants of 3-substituted 7-hydroxycoumarins.

摘要: Synthesis, absorption and fluorescence spectra as well pKa values of 7-hydroxycoumarins with electron-withdrawing substituents in positions 3 are described. Introduction a 4-cyano group is achieved by oxidative cyanation coumarins using potassium cyanide elemental bromine. 7-Hydroxycoumarins without useful indicators for measuring physiological pH due to their intense fluorescences, longwave absorptions emissions, around 7. The presence gives rise dramatic shift (30–40 nm methanol) emission (55–80 nm). In water solution, the maxima at 570–600 nm, excitation between 410 510 depending on whether phenol or phenolate species excited. For all under investigation, from anion form even 2–7 range. This phenomenon interpreted terms excited state dissociation according Forster model. i...