Designing Strong Polarity and High Configurational Entropy Flexible Units toward Excellent Ultraviolet Nonlinear Optical Materials
Haotian Tian, Chensheng Lin, Bingxuan Li, Xin Zhao, Tao Yan, Ning Ye, Min Luo
Abstract
Abstract Polar materials play a crucial role in numerous essential fields; however, efficiently synthesizing them remains a significant challenge. In this study, a viable approach is proposed to enhance the probability of discovering polar materials by developing new functional basic units (FBUs) with strong polarity and high configurational entropy. To validate this approach, a site‐modification strategy is applied to the high configurational entropy flexible (C 3 H 2 O 4 ) 2− FBU, resulting in the development of four new polar‐enhancing FBUs: (C 3 (CH 3 ) 2 O 4 ) 2− , (C 3 F 2 O 4 ) 2− , (C 3 H(OH)O 4 ) 2− , and (C 3 HFO 4 ) 2− . Moreover, 11 new compounds through temperature‐driven conformational changes in FBUs are successfully synthesized. Among these, the proportion of polar structures reaches an impressive 54%. Remarkably, all of these novel polar compounds exhibit outstanding nonlinear optical (NLO) properties. The [Li 2 C 3 (CH 3 ) 2 O 4 ] 2 ·3H 2 O demonstrates the rare coexistence of a moderate birefringence (0.071@514 nm), short UV cutoff edge (210 nm), and the strongest second harmonic generation (SHG) effect (6.5 × KDP) among ionic‐organic fourth harmonic generation crystals. Preliminary laser experiments have also proven its potential practical value as a fourth harmonic generation crystal. This research not only discovers a variety of exceptional UV NLO crystals but also provides a feasible method to increase the likelihood of finding polar materials.