Resonant Second-Harmonic Generation in a Hybrid Manganese Bromide: [3-Quinuclidinone]2MnBr4

Second-harmonic generation (SHG) is an upconversion process occurring in noncentrosymmetric crystals and can be used to transform near-infrared light to the visible region, hence fundamentally and technologically important for the development of lasing, sensing, and imaging. Herein, we report ketone-substituted [3-quinuclidinone] 2 MnBr 4 (QO-MnBr 4 ), derived from [quinuclidine] 2 MnBr 4 (space group P 2 1 / c ), which crystallizes in the noncentrosymmetric space group Pmn 2 1 . This compound exhibits green emission at about 520 nm upon UV excitation, attributed to the 4 T 1 → 6 A 1 radiative recombination of [MnBr 4 ] 2– tetrahedra. More importantly, QO-MnBr 4 shows a remarkable SHG response under 1064 nm excitation, which is 1 order of magnitude larger than that of y-cut quartz. Further wavelength-dependent SHG measurements reveal that the giant SHG response is ascribed to the excited state resonance. This work demonstrates symmetry-breaking engineering as a strategy to construct resonant channels for SHG enhancement in manganese-based bromides, offering a new design platform for high-performance SHG materials.