Switchable Nonlinear Optical Absorption of Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are widely explored owing to their excellent nonlinear optical (NLO) properties. However, researchers have mainly focused on designing new structures of MOF crystals to adjust the NLO response while ignoring the influence of the number of metal-ligand coordination bonds on the NLO properties of MOFs. In this study, the influence of the coordination numbers of MOFs on their NLO properties is studied for the first time. Herein, MOFs with different coordination numbers, using trifluoroacetic acid as an auxiliary agent, are synthesized and their NLO properties are tested using the Z-scan technique. The results reveal that the NLO absorption properties of MOFs with high coordination numbers can be effectively modulated from saturable absorption to reverse saturable absorption by increasing the excitation intensity. First-principles calculations show that a change in the coordination numbers leads to a change in the charge transfer from metal to ligand, thereby resulting in different NLO responses. The MOFs with a high coordination number have potential applications in novel optical switches or logic gates. These results provide a reference for the precise adjustment of the NLO properties of MOFs.