Hydrogen Bonding Effect on the Fluorescence of Some Nitrogen Heterocycles. I

Abstract

1. The hydrogen bonding effect on the fluorescence of quinoline and acridine was studied in non-polar solvent mixed with various proton donors.2. The equilibrium constants of hydrogen bonding calculated from the absorption and fluorescence data were the same for these molecules, in contradistinction to the case of naphthols. Possible mechanisms for this experimental fact were proposed.3. The larger the relative fluorescenceyields of hydrogen bonded nitrogen heterocycles become, the stronger the donating powers of proton donors are, and from this fact, discussions were given on the role of non-bonding electrons in the inner-quenching of these molecules.4. The difference between quinoline and acridine in their fluorescence quenching caused by the existence of a halogen atom was ascribed to the different emitting π-electronic states in these molecules (1Lb in quinoline, 1La in acridine), and some considerations by means of analogy to the π-electronic structures of aromatic hydrocarbons were given.