The excited state properties of PT were theoretically studied with quantum chemical methods as well as 2D site and 3D cube representations. The theoretical results reveal that the 1(n→π*) and 1Ag-(π→π*) excited states are intramolecular charge transfer (ICT) excited states, while the 1Bu+(π→π*) excited state is the delocalized excited state. The orientation and strengths of the transition dipole moments of them are interpreted with 3D transition density (TD), and the excited state characters of the ICT or localized excitation are investigated with the 3D charge difference densities (CDD). The electron-hole coherence, delocalization and exciton sizes are studied with 2D site representation.作者简介：马凤才.E-mail: fcma@lnu.edu.cn.通讯作者