The Phosphorescence Spectra of 1,4-Naphthoquinone and Its Alkyl Derivatives in Solutions at 77 K

The phosphorescence spectra of 1,4-naphthoquinone (NQ), 2-methyl-, 2,6-dimethyl-, 2,6-diisopropyl-, and 2,6-di-t-butyl-NQ’s in various kinds of solutions at 77 K were studied. The phosphorescence bands of NQ and 2,6-di-t-butyl-NQ in all the solutions and those of the other NQ’s in saturated hydrocarbon solutions are assigned to the n,π* band. In the ethanol solution, 2-methyl-NQ shows a dual phosphorescence, the lifetimes of which are different and which depends on the excitation wavelength. In the Daifloil solutions, 2-methyl- and 2,6-dimethyl-NQ’s also show a dual phosphorescence. In the toluene solutions, these two NQ’s show remarkably broad phosphorescence bands. These facts are discussed on the basis of the electronic structures at the excited states of these NQ’s.