Switchable Nonlinear Optical Absorption of Metal–Organic Frameworks

Abstract

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.

Postsynthetic Modification of NU-1000 for Designing a Polyoxometalate-Containing Nanocomposite with Enhanced Third-Order Nonlinear Optical Performance

“…The current work aimed to provide useful information on the structure–property relationships in MOF-POM hybrids, which would foster their exploration as novel nonlinear optical materials with greater hyperpolarizability. Because metal clusters contain delocalized dπ–pπ and conjugated dπ–dπ arrangements, they can perform well as nonlinear optical materials. , Besides, if metal–ligand and ligand–metal charge transfers are introduced, the nonlinear optical characteristics of these clusters can be improved. − The π-electron cloud delocalization mainly gives rise to the nonlinear optical characteristics even though a variety of procedures are applicable for the promotion of such characteristics in metal clusters. , Metal ions and organic ligands that construct the skeleton of MOFs are both of great importance in the NLO characteristics of NU-1000 as they primarily lead to the delocalization in metal clusters.…”

“… 65 , 66 Besides, if metal–ligand and ligand–metal charge transfers are introduced, the nonlinear optical characteristics of these clusters can be improved. 67 − 69 The π-electron cloud delocalization mainly gives rise to the nonlinear optical characteristics even though a variety of procedures are applicable for the promotion of such characteristics in metal clusters. 70 , 71 Metal ions and organic ligands that construct the skeleton of MOFs are both of great importance in the NLO characteristics of NU-1000 as they primarily lead to the delocalization in metal clusters.…”

Regulation of Third‐Order NLO Properties by Central Metal Exchange of Heterogeneous MOFs@CeO2

“…[12][13][14] Varying metal ions or clusters with d-electrons inside the frameworks also plays a dominant role in changing the level of d-p electron transition in the MOFs skeleton and expand the π-conjugate system to achieve the tuning effect of d-p transition band. [15][16][17][18] It is also known that exchanging/ introducing suitable metal elements into MOFs can increase carrier concentration, shorten the photon transition time of the MOFs, as well as extending electron transfer ability of the materials. [19,20] Most of the research focuses on the third-order nonlinearity of MOFs from the intrinsic structure perspective, as those metal centers generate strong electronic interaction and charge transfer between the ligand molecules, resulting in the delocalization of the intramolecular π-electron cloud.…”

Mass ratio-dependently tunable enhancement of the optical nonlinearities of SnO2/RGO composites

“…where w z is beam radius at z, I 0 is the average intensity at the focus (z=0). The normalized transmittance T against the incident light intensity I z was then plotted in figures 7 (c) and (d) respectively, and was fitted using the following formula [44]:…”