Giant Enhancement of Optical Nonlinearity by Manipulating Guest Molecular Stacking Modes in Metal–Organic Frameworks
Kangshuai Geng, Yupei Sun, Yujie Zhao, Zhichao Shao, Yi Wei, Jing Huang, Yang Cui, Xiaoyan Xu, Hongwei Hou
Abstract
The influence of guest stacking interactions in host–guest (H–G) MOF composites on third-order nonlinear optical (NLO) performance remains largely unknown. Herein, we propose for the first time a noncovalent aggregate confinement strategy for synthesizing H–G MOF composites with different guest stacking modes. And [perylene 2 ] n (α-Pe) and [perylene] n (β-Pe) were selected as guests and confined into a novel Ca-based MOF {[Ca(TBAPy)(DMA) 2 ]·3DMA·[N(CH 3 ) 2 ]·H 2 O} n (Ca-MOF-pts). The NLO results showed that compared to β-Pe@Ca-MOF-pts, the saturable absorption (SA) and self-defocusing properties of α-Pe@Ca-MOF-pts were increased by 2.71-fold and 3.82-fold, respectively. Interestingly, α/β-Pe@Ca-MOF-pts can be transformed into α/β-Pe@Ca-MOF-flu (Ca-MOF-flu = {[Ca 1.5 (TBAPy)(H 2 O) 2 ]·DMA·[N(CH 3 ) 2 ]·2H 2 O} n ) through self-adaptive topological evolution, and the corresponding NLO absorption signal change from SA to reverse saturable absorption (RSA). As expected, compared to β-Pe@Ca-MOF-flu, the RSA and self-defocusing properties of α-Pe@Ca-MOF-flu are improved by 2.94-fold and 4.07-fold, respectively, demonstrating the importance of guest stacking modes. Theoretical calculation and transient absorption spectra indicated the enhancement of NLO performance was attributed to the large π–π overlap of α-Pe, which promoted the electron delocalization/transfer and optimized the cross-sectional of the ground state and excited state. This study provides a new strategy for developing H–G MOF composites with excellent NLO properties.