Theoretical studies on the one- and two-photon absorption properties of double-bis(styryl)benzene derivatives

Two series of bis(styryl)benzene derivatives (BSBD), namely the single-BSBD and the double-BSBD, were investigated. The equilibrium geometries and electronic structures were obtained by using the density functional theory B3LYP and 6-31G basis set. In succession, the one- and two-photon absorption properties of all the molecules were studied theoretically with a ZEN-DO-SOS (sum-over-states) method in detail. It can be seen that the double-BSBDs have larger two-photon absorption (TPA) cross sections in the visible-IR range than the corresponding single-BSBDs, demonstrating that increasing the molecular dimension is a very effective method to enhance the values of the TPA cross sections. On the other hand, it can be also noticed that the values of the TPA cross sections are correlative with the ability of donating (accepting) electrons of the terminal substiuent groups R [N(CH3)(2), CH3, H and CF3] in these molecules. That is, the intramolecular charge transfer is also a factor for the enhancement of the TPA efficiency. To sum up, the idea of increasing the molecular dimension to enhance the TPA cross section value is a helpful direction to explore better TPA materials for practical applications. And the double-BSBD molecules are promising TPA materials for the further investigation from the standpoint of the high transparency and the larger TPA cross sections.