Knowledge Bank

Several absorption and emission spectra and decay lifetimes of phosphorescent states for compounds with triple bonds in conjugation have been observed. Using the wavelengths and intensities of bands it has been possible to relate the electronic energy levels to those of acetylene. It was found that compounds with less than four triple bonds phosphoresce but do not fluoresce. Compounds with four triple bonds fluoresce as well. The explanation offered points to the important role of the spacing of electronic energy levels in determining the relative efficiencies of fluorescence and phosphorescence.