{'fraction_non_alphanumeric': 0.028921401837359646, 'fraction_numerical': 0.0027220142905750254, 'mean_word_length': 5.268656716417911, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Adjusting the Third-Order Nonlinear Optical Switch Performance Based on Azobenzene Derivatives

The photo-controllable third-order nonlinear optical (NLO) switches have drawn ever-increasing attention due to considerable research potential in the emerging field of nonlinear optics. A class of materials, which contain photosensitive groups but cannot express directly switching properties under light conditions, can also exhibit the characteristics of excellent photo-controllable NLO switches after external regulation. Azobenzene is a kind of classic photo-isomerized molecule and has good π coplanar property and excellent electron channel, which can engender third-order NLO response under push and pull electron action. It is a feasible strategy to design photo-controlled NLO switch materials by introducing azo groups. Nevertheless, the trans - cis isomerization behaviors of some azobenzene derivatives are interfered by other groups or external factors, further inhibiting the conversion of photo-controllable third-order NLO properties. Once these external interference factors are found and removed, the photo-controllable NLO behaviors of such azobenzene derivatives will be opened. In our work, a special azobenzene derivative was synthesized and reported, which was unable to produce cis - trans isomerization due to the H ＋ effect of self-dissociation, and the H ＋ effect could be shield by introducing organic groups or bases. The adjusted materials can easily undergo reversible cis - trans isomerization reaction, and the Z-scan test shows the complete inver-sions of third-order NLO properties before and after UV irradiation. The adjusted materials in trans configuration show the reverse saturation absorption (RSA) and self-defocusing properties. After UV irradiation, the materials convert into cis configuration and exhibit saturation absorption (SA) and strong self-focusing behaviors. To gain a deeper understanding of the light-adjusted third-order NLO switch behaviors, density functional theory (DFT) calculations of (CH 3 ) 2 L were carried out. For trans -(CH 3 ) 2 L, HOMO and LUMO are mainly localized on the azobenzene unit, where π - π * transition between the two orbitals is displayed. The azobenzene unit in the trans -(CH 3 ) 2 L is considered to have considerable contribution to the generation of third-order nonlinearity. For cis -(CH 3 ) 2 L, the electron cloud density of HOMO is mainly populated on the azobenzene unit, whereas the electron cloud density distribution of LUMO appears on the entire molecule, suggesting significant intra-molecular charge transfer (ICT) from azobenzene to the entire molecule. The effect of ICT in the cis structure dominants the generation of third-order nonlinearity. The remarkable third-order NLO transformation result from the rearrangement of the electronic structures, which makes them generate different response mechanisms under the laser stimulation.