Third-order nonlinear optical adjusting behavior in azobenzene metal complexes

The third-order nonlinear optical (NLO) materials with stimuli-responsive properties have received extraordinary attention due to their controllable photophysical properties. In this work, two attractive metal complexes third-order NLO switches, which are far superior to congeneric optical switches in terms of their performance conversion, versatility, and fast response, were successfully designed and synthesized. The test of their third-order NLO properties proves that the metal complexes exhibit reverse saturable absorption and self-defocusing refraction. After light irradiation, the third-order NLO behavior turns quickly into self-focusing refraction. The relation between the molecular structures and the third-order NLO properties was investigated via1H nuclear magnetic resonance and ultraviolet-visible absorption. The results show that the metal ions have a significant influence on the NLO behavior and reveal the origin of third-order NLO properties via Z-scan determinations, pump-probe technology, and density functional theory calculations. These metal complexes can be used as third-order NLO switches with excellent fatigue resistance and broaden the application range of third-order NLO materials with adjustable performances.