Theoretical studies of one- and two-photon absorption properties for two series of three-branched fluorenylene-vinylene compounds with different centers (B, N) and peripheral substituted groups

Two series of three-branched fluorenylene-vinylene compounds with different centers (B, N) and peripheral substituted groups were investigated. The equilibrium geometries and electronic structures were obtained by using the density functional theory B3LYP and 6-31G basis set. The one- and two-photon absorption properties of all the molecules were studied theoretically with a ZINDO-SOS method in detail. It can be seen that the maximum one-photon absorption (OPA) intensities and the maximum two-photon absorption (TPA) cross sections values δmax are gradually increased with the stronger electron-donating capability [H < OH < N(CH3)2] or electron-accepting one (H < CHO < NO2). This indicates that intramolecular charge transfer from the center to the peripheral substituted groups (or vice versa) plays a very important role on the TPA.