LAUSR

In this work, density functional theory is used to study organic molecules in a donor–acceptor (D–A) system centered on phenothiazine with strip and trigonal structures. The transition modes of the one-photon absorption (OPA) and two-photon absorption (TPA) processes of the two molecules are studied. The calculations show that the molar absorption coefficient of OPA for trigonal molecule TPPO and the cross section of TPA are both larger than those for strip molecule M1 due to the increase in the number of branches of the system. A special local excitation-enhanced charge-transfer excitation appears in strip-type molecule M1. In the charge-transfer process of trigonal D–A structure molecule TPPO, there are not only local excitation-enhanced charge-transfer excitation but also super-exchange charge transfer between the three branches that occurs due to the increase in the planarity of the system.