A Theory of Excitons in Strained Molecular Crystals

This paper examines theoretically the effects of strain on the exciton properties of some molecular crystals. It is found that the parameters of exciton theory are relatively sensitive to changes in lattice parameters of the crystal, and thus strain can result in significant changes in the crystal spectrum. The method proceeds through strain derivatives of the exciton parameters, which are evaluated for the unstressed crystal geometries. In this way, the influence of pressure and temperature on the spectrum is examined. The strain derivatives are evaluated for anthracene and naphthalene for light incident on the ab-face, and the theory used to re-examine some of the features of the first singlet of anthracene. Good agreement with experiment is obtained.