Purification and Fluorescence Spectra of Phenanthrene

Abstract

Crude phenanthrene(C14H10), extracted from coal-tar pitch, contains a small amount of anthracene, fluorene and carbazole as impurities. The most effective purification method was as follows. The crude hydrocarbon (10g) was heated in boiling maleic anhydride (100g) with chloranil (8g) as an oxidizing aget for about 4hrs. Hot benzene (150ml) was added to the reactian mixture, and the solution was boiled further for 1 hr. The benzene Iayer was separated and was heated at 80C with potassium hydroxide solution for 30 min. Then the benzene layer was separated again and the phenanthrene contained was collected after the solvent was eliminated by vacuum distillation. The phenanthrene (13g) was heatd in boiling absolute alcohol (100ml) and metallic sodium (1.7g) was added to this solution, which was further boiled for 3 hrs. After this, reactioh mixture was obtained by eliminating the solvent from the filtrate by vacuum distillation. The obtained phenanthrene was further purified by repeated sublimation and zone melting.
The fiuorescence spectra and wave length dependence of fluorescence life-time of phenanthrene in its solid state were very effective to detect impurities contained in this hydrocarbon. The fluorescence maxima of the high-purity phenanthrene at room temperature were at 370, 380 nm, and at liquid nitrogen temperatureat 355, 370 and 390 nm. And the fluorescence maxima of the impure phenanthrene were observed at room temperature and also at liquid nitrogen temperature at 395, 409 and 430 nm, but not at 370 mn.
The average fluorescence life-time of the high-purity phenanthrene was 62.5 n sec at room temperature, and it decreased to10-44 n sec when the sample was contaminated with a small amount of impurities.