Third-order nonlinear optical adjusting behavior in azobenzene metal complexes
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Published online 24 September 2020 | https://doi.org/10.1007/s40843-020-1429-9
Third-order nonlinear optical adjusting behavior in azobenzene metal complexes 1†
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Chang Xing , Jianxun Liu , Linpo Yang , Zhichao Shao , Wenjuan Xu , Yujie Zhao , Kai Li , 2 1* Yinglin Song and Hongwei Hou ABSTRACT 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 thirdorder 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 selffocusing refraction. The relation between the molecular structures and the third-order NLO properties was in1 vestigated via H nuclear magnetic resonance and ultravioletvisible 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. Keywords: third-order nonlinear optical, photo-controllable, reversible, signal inversion, metal complex
INTRODUCTION In recent years, along with the development of several optical technologies and optoelectronics, molecules with transformation nonlinear optical (NLO) functions have received extensive attention as optical switches [1–4]. Up to now, the NLO switch development is mainly focused on second-order NLO materials [5–9]. Third-order NLO materials show higher performance due to the presence of 1 2
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multiple optical fields which act simultaneously on the material. This makes the research on third-order NLO switches at the forefront [10–13]. Many organic thirdorder NLO switches with high laser damage thresholds and low dielectric constants have been investigated [14– 16]. However, their low NLO coefficients, single spatial structure, and common electronic property thresholds greatly limit their application prospects. Introducing metal ions into organic materials is an effective strategy to improve the performance of third-order NLO materials. Such metal complexes show the same advantages of organic molecules, while the central metal ions also effectively influences the electronic properties of the organic molecules, improving the response of the third-order NLO compounds [17–19]. More importantly, metal complexes usually exhibit diverse spatial structures and conjugated modes and can provide a wealth of electronic flow systems to enhance and extend NLO behaviors [20– 2
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