Enhancement of one- and two-photon absorption and visualization of intramolecular charge transfer of pyrenyl-contained derivatives

To further improve the pyrenyl-contained derivatives two-photon absorption (TPA) and third-order nonlinear optical (NLO) properties, three steps of optimization are employed based on experimental molecule PCVS-B: heteroatomic substitution, exchanging the position of double bonds and adding a branch. The contributions of π electrons to localized orbital locators and Mayer bond orders (LOL-π and I AB π ) show that the second step can enhance the chemical interaction between pyrenyl and the branched-chain. Two visual methods of charge density difference (CDD) and transition density matrix (TDM) are combined to intuitively analyze the intramolecular charge transfer (ICT) process of one (two) photon absorption; results show that both following two steps can increase the degree of ICT on the conjugated plane of the pyrenyl. The sum over state (SOS) model was used to find out the dominant two-photon transition process. The difference between the dipole moments obtained by the McRae equation is applied to the three-state model, revealing the inherent law of the second static hyperpolarizability. • Two visualization methods, CDD and TDM, are combined to reveal charge transfer process of one (two) photon absorption. • Exchange the position of carbonyl and vinyl can enhance the chemical interaction by π electrons between pyrenyl and the branched chain. • Visual analyses show that exchanging the position of double bonds and adding a branch can enhanced the rearrangement of electrons on the pyrenyl. • The difference of dipole moments obtained by McRae equation are applied to the three-state model, revealing the inherent law of the second hyperpolarizability well.