Monomer Emission from Excimer Forming Crystals: Pyrene and Perylene

Abstract

The phenomenon of monomer emission from excimer forming crystals has been investigated for pyrene and perylene. A variety of spectroscopic techniques have been used to demonstrate that genuine monomer emission can be observed from pyrene crystals. The emitting monomers appear to be located in disordered regions of the crystal situated within 5 × 10² nm of the surface. Both delayed monomer and excimer emission have been observed at 4.2°K and information on the range of the monomer exciton migration has been obtained. The low temperature emission observed from the dimeric α-form of perylene crystals appears to be either from highly perturbed perylene monomers located in disordered regions of the crystal or from impurities. The unusual temperature dependence previously observed for the emission spectrum of the monomeric β-form of perylene crystals is shown to be due largely to reabsorption effects.