Two-photon absorption property and excellent optical limiting response of three Schiff base derivatives with large conjugated system

In this work, three Schiff base derivatives with large conjugated system have been elaborately designed and synthesized, in which bithienyl (1), pyrenyl (2) and anthryl (3) connect an azo moiety (N = N) monomer through conjugation linkage (C = N), respectively. Their third-order nonlinear optical (NLO) properties are systematically investigated by performing the picosecond-pulsed Z-scan measurements at the wavelength of 532 nm and femtosecond-pulsed Z-scan measurements at the wavelength of 600 nm. The pump-probe measurements and the linear dependence between the amplitude of transmittance change and different laser energy indicate that the nonlinearity is originated from pure two-photon absorption (2PA) behavior. Among them, compound 1 with the bithiophene group has a larger two-photon absorption cross section up to 8.90 x 10(4) GM (ps). The reason may be that the electron-rich bithiophene group with lower delocalization energy improves electron transition. In addition, excellent optical limiting (OL) behaviors of the three Schiff base derivatives are observed under ps laser excitations at 532 nm wavelength, which resulted from 2PA induced reverse saturation absorption (RSA). All the experimental results manifest that these compounds could be used as potential NLO materials.