The relationships study of structure-nonlinear optical property of two-dimensional charge transfer molecules substituted annulenes

The molecular first hyperpolarizabilities β and ultraviolet spectra of two-dimensional charge transfer (2DCT) substituted annulenes by employing MP2 and TD-DFT approach, respectively. It is found that these 2DCT molecules 2—6 possess larger β values and blue-shifted absorption spectra in comparison with 1DCT molecules 8 and 9. It is helpful to solve the nonlinearity-transparency trade-off. For 2DCT molecules 2—7, values of β depend on the band length alternation (BLA) and when the BLA increases, the values of β decrease. Moreover, there is not a relationship between β and HOMO-LUMO energy gap Δ E HL for 2DCT molecules. The maximum absorption wavelength λ max of 2DCT molecules originates from deeper energy level orbital transition than HOMO→LUMO transition.