The theoretical simulation for two-photon absorption properties of novel A-π-D-π-A two-photon carbazole compounds

The optical properties of three newly synthesized A-π-D-π-A compounds have been studied by use of analytical response theory at the density functional theory level. The theoretical results show that there exist three charge-transfer states for each compound in the low energy regime. The trends for both oscillator strengths and excitation energies among the three compounds as predicted by the numerical simulations are highly consistent with those given by measurement. Large two-photon absorption cross sections are predicted for the three compounds. Furthermore, the solvent effect on the optical properties of the compounds is investigated. It is found that the excitation energies in solvent DMF show a red-shift compared to those in gas case, and the two-photon absorption cross sections are highly enhanced. The optical properties of the compounds with experimental geometric parameters are also investigated. The oscillator strengths are found to be smaller due to the bent molecular structures. The calculated results predict that much higher two-photon absorption cross sections would be observed when a laser with a shorter wavelength is applied.