Fluorescence spectra of aromatic hydrocarbons of the biphenyl series and their oxygen- and sulfur-containing analogs

1. The fluorescence spectra of biphenyl, diphenylmethane, diphenylethane, diphenylpropane, diphenylpentane and dibeazyl ether and also diphenyl, dibenzyl and diphenyldiethyl sulfides at room temperature and at liquid-nitrogen temperature were studied. It was shown that the fluorescence of these compounds was very weakly expressed at room temperature. At low temperatures (liquid-nitrogen temperature) there was a considerable increase in the brightness of the luminescence spectra of these compounds and sharp, characteristic bands which could be used for analytical purposes appeared in the spectra. 2. If there was strong interaction of the π -electrons in the molecule between the two benzene rings, then the bands were displaced in the long, wave direction at low temperature in comparison with room temperature and with a weakening of the interaction of these parts of the molecule there was a displacement into the short wave region. 3. The introduction of an oxygen atom and especially a sulfur atom into the aliphatic bridge strongly changes the luminescence spectra of compounds of the biphenyl series. A probable explanation is given for the strong effect of the sulfur atom on the character of the luminescence spectra.