Quantum size effects in the optical properties of organic superlattices containing 3, 4, 9, 10 perylene tetracarboxylic dianhydride (PTCDA)

Abstract

A Frenkel exciton model is applied to ultrathin films of PTCDA confined between layers of a material with electronic transitions in a different energetic region. This model accounts for the elongation of an effective internal vibration in the relaxed excited geometry of a molecule and for the transfer of an electronic excitation between different molecular sites. The comparison of the model calculations with experimental findings reveals that due to the modified conditions at the organic interfaces, boundary layers of the PTCDA films show blue-shifted transition energies with respect to inner molecular layers surrounded by the same material. The resulting changes of the lowest vibronic subband contribute further to the distinct absorption line shapes. © 2008 Springer.