Boosted Second Harmonic Generation of a Chiral Hybrid Lead Halide Resonant to Charge Transfer Exciton from Metal Halide Octahedra to Ligand

• Published in: Angewandte Chemie International Edition 2024-05, Vol.63 (19), p.e202400644-n/a
• Main Authors: Cheng, Puxin, Jia, Xiaodi, Chai, Siqian, Li, Geng, Xin, Mingyang, Guan, Junjie, Han, Xiao, Han, Wenqing, Zeng, Shuming, Zheng, Yongshen, Xu, Jialiang, Bu, Xian‐He
• Format: Article
• Language: English
• Subjects: Charge transfer; charge transfer excitons; chiral hybrid lead halides; Energy levels; Excitons; Halides; Laser damage; Lead compounds; Ligands; Metal halides; Metals; Nonlinear optics; Nonlinear systems; Nonlinearity; Polyhedra; Resonance; resonance enhancement; Second harmonic generation; Urea; Yield point
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202400644

Chiral hybrid organic–inorganic metal halides (HOMHs) offer an ideal platform for the advancement of second‐order nonlinear optical (NLO) materials owing to their inherent noncentrosymmetric structures. The enhancement of optical nonlinearity of chiral HOMHs could be achieved by matching the free exciton and/or self‐trapped exciton energy levels with desired NLO frequencies. However, the current scarcity of resonance modes and low resonance ratio hamper the further improvements of NLO performance. Herein, we propose a new resonant channel of charge transfer (CT) excited states from metal halide polyhedra to organic ligand to boost the second‐order optical nonlinearity of chiral HOMHs. The model lead halide (C7H10N)PbBr3 (C7H10N=1‐ethylpyridinium) exhibits a drastically enhanced second harmonic generation in resonance to the deep CT exciton energy, with intensity of up to 111.0 times that of KDP and 10.9 times that of urea. The effective NLO coefficient has been determined to be as high as ~40.2 pm V−1, balanced with a large polarization ratio and high laser damage threshold. This work highlights the contribution of organic ligands in the construction of a resonant channel for enhancing second‐order NLO coefficients of metal halides, and thus provides guidelines for designing new chiral HOMHs materials for advanced nonlinear photonic applications. The metal octahedra to ligand charge transfer excitons of chiral metal halides have been demonstrated to serve as a new resonant channel with an appropriate resonant energy level to boost second‐order optical nonlinearity. Ultimately, these single crystals exhibit remarkably resonant enhanced SHG signals, of one order of magnitude higher than that of urea and two orders of magnitude higher than that of KDP.