Articles you may be interested inEstimation of the degree of hydrogen bonding between quinoline and water by ultraviolet-visible absorbance spectroscopy in sub-and supercritical water A purification scheme has been developed which is capable of separating the two isomers quinoline and isoquino1ine. The emission spectra of the purified compounds were measured at 77 K in a 3-methylpentane (3MP) glass and in a 3MP glass with small amounts of hydrogen bonder added. The hydrogen bonders used were hexafluoroisopropanol (HFIP), trifluoroethanol (TFE), and absolute ethanol (EtOH). An upper limit on the ratio of fluorescence to phosphorescence quantum yields has been set at 20 ppm for quinoline in 3MP, which is 1-2 orders of magnitude smaller than previously reported. Isoquinoline still fluoresces in 3MP, which we believe to be caused by a residual hydrogen bonder not removed by the purification scheme. The excitation and lifetime data obtained suggest that the phosphorescence in these compounds is originating in a non hydrogen-bonded species, while the fluorescence is originating in a hydrogen-bonded species, regardless of solvent. A new emission has also been detected in the presence of small amounts of hydrogen bonder. This violet fluorescence is believed to be the result of an excited state protonation of the heterocycle. The ground state is believed to be nonprotonated, but strongly or "closely" hydrogen bonded. A summary of impurity induced absorption and luminescence data obtained by other authors is included to help clarify the spectral properties of quinoline and isoquinoline.

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In the absence of a hydrogen bonder, quinoline only éxhibits phosphorescence in a 3-methypentane glass at 77 K. Under these conditions isoquinoline both fluoresces and phosphoresces weakly. The addition of a weak hydrogen bonder such as ethanol induces structured ultraviolet fluorescence originating from the lowest excited singlet state. More acidic alcohols such as trifluoroethanol and hexafluoro-2-propanol induce both the structured ultraviolet fluorescence, and a now broad, violet fluorescence. This new fluorescence resembles, but differs from, that of the corresponding protonated cation. An analysis of the excitation spectrum, which differs from the excitation spectrum of the structured fluorescence, leads to the conclusion that the proton has been displaced toward the nitrogen heterocycle in the excited state.

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