Quantum mechanical modelling and calculation of two-photon absorption properties of new class 'Λ'-shaped conjugated molecules

Organic material with high intensity of two-photon absorption (TPA)-induced fluorescence can be used as the up-converter material for photovoltaic devices. In this work, quantum mechanics modelling techniques were applied to theoretically investigate one-and two-photon absorption properties of new 'Lambda'-shaped conjugated molecules. Fluorene and diphenylmethylene analogues as the pi centres were chosen for building the pi-conjugated bridges to connect the two types of strong electron donors, N,N-diphenylamino and carbazole groups. In these molecular structures, cyano and ketone groups were also selected to modify the pi centres as electron acceptors. The TPA cross sections of these derivatives were calculated using two-state, three-state and sum-over-state models, respectively. Geometrical structures of these molecules were optimised using Hartree-Fock theory, and properties of excited states of these molecules were obtained based on configuration interaction with single excitations method. The effects of donor, acceptor and pi centre on the TPA behaviours of these designed molecules were investigated. Several of these molecules have attractive TPA properties, which may have potential for photovoltaic device applications.