Light-adjustable third-order nonlinear absorption properties based on a series of hydrazone compounds

Recently, novel, predefined and adjustable third-order nonlinear optical (NLO) materials have attracted broad attention due to their widespread applications. In this work, a series of hydrazone compounds with third-order NLO performance have been synthesized, which can produce the configuration transformation from trans (E) to cis (Z) under stimulation of light. This structural transformation involves the reforming of electronic environment which leads to significant changes in the third-order nonlinear absorption properties (from the reverse saturation absorption (RSA) to the saturation absorption (SA)). The response progress is monitored and proved by UV-vis absorption spectra, ¹H NMR spectra and Z-scan measurement. In addition, the mechanism of third-order NLO variation (RSA→SA) are explored by pump-probe measurements, and the results indicate that the large changes take place in absorption cross-section of the ground state (σ₀) and the first excited state (σ₁), which dominate the response behavior. Combined with density functional theoretical (DFT) calculation, the relationships between molecular structures and nonlinear absorption behavior are revealed. This work may provide a new exploration for the preparation of optical materials with adjustable third-order NLO behaviors.