The Long-wavelength nπ* Phosphorescence Spectra of p-Quinones in Polycrystalline Solutions at 77 K

Besides the usual nπ* phosphorescence spectra, broad, long-wavelength nπ* phosphorescence spectra are observed in normal paraffine solutions, such as a heptane solution, of 1,4-naphthoquinone, and in a benzene solution of 5,14 : 7,12-pentacenediquinone at 77 K. The energy difference between the two spectra are ca. 750 and 980 cm−1 respectively. The intensity of the long-wavelength spectra relative to the short-wavelength spectra becomes weaker with decreases in the concentrations of the quinones, and the lifetimes of the long-wavelength spectra are shorter than those of the short-wavelength spectra. These long-wavelength spectra are assigned to those of the quinone aggregates. The excitation spectra of these phosphorescences have also been obtained. An explanation of the above red-shift of the nπ* phosphorescence spectra of the aggregates is presented; in it, the phosphorescence state of the aggregates corresponds to the nπ* triplet excimer state.