Characteristic electronic structures of organic solids classified in terms of molecular electronic relaxation

Abstract

Organic molecular and polymeric solids can be grouped into three classes in accordance with their bonding nature. Ultraviolet photoelectron spectroscopy (UPS) is useful to study the electronic structure of each class of solids. The molecular identity is preserved in weakly bound solids, where the polarization energy as the electrostatic stabilization energy for an electric charge on a molecule works as a key parameter determining the energy levels in the solid. In mesoenergetically bound solids, including most of the interesting organic molecular solids, the molecular identity is reduced and quasi-delocalized electronic states can be studied by examining the electronic relaxation energy. In strongly bound solids consisting predominantly of organic polymeric solids, one-dimensional energy band formation is often observed in angle-resolved UPS, as in the case of long-chain alkanes.