Anthracene as the origin of the red-shifted emission from commercial zone-refined phenanthrene sorbed on mineral surfaces

The origin of the red-shifted fluorescence emission spectra observed for co mmercial zone-refined phenanthrene (purity 99.5+%) in concentrated cyclohex ane solution and as sorbates on porous silica at high loading levels was st udied by absorption and fluorescence spectroscopy as well as fluorescence q uenching measurements, The absorption and fluorescence spectra indicate tha t a small amount of anthracene is present in the zone-refined phenanthrene. In concentrated phenanthrene solution and highly phenanthrene-loaded porou s silica, excitation energy transfer from phenanthrene to the anthracene: i mpurity results in the reduction of the phenanthrene fluorescence intensity and the appearance of the anthracene fluorescence emission at longer wavel ength. A Stern-Volmer plot for quenching of phenanthrene fluorescence by an thracene in cyclohexane indicates both dynamic and static energy transfer m echanisms. For phenanthrene sorbed on mineral surfaces, the dynamic pathway is limited. Therefore, the appearance of anthracene fluorescence due to en ergy transfer from excited phenanthrene can serve as a spectral probe for p olyaromatic hydrocarbon (PAH) aggregation and association on mineral surfac es.