Abstract

Excimers in molecular crystals constitute an intriguing object of study in luminescence investigations. Basic questions have remained un-answered about their formation and about their migration. The latter presents particularly interesting challenges. The necessity of large distortions and considerable activation energies for their motion leads one to expect excimers to be relatively immobile. However, experimental evidence for their motion has been presented several times in the literature. Such evidence has been gathered both indirectly from the supposed mutual annihilation of excimers as in recent experiments on dichloroanthracene,⁽¹⁾ and more directly from their trapping by dopants as in earlier experiments on pyrene⁽²⁾ The two kinds of systems involved are representative of two different physical situations; stacks are involved in the former and preformed dimers in the latter. We have analyzed the motion observations from a general theoretical framework and found that considerable latitude exists in the interpretation of the reported observations. We examine the applicability of polaron transport concepts to excimer motion and comments on what further experiments are necessary to remove the considerable uncertainties that exist in our present understanding of excimers.

© 1984 Optical Society of America