Transformation of SBUs and Synergy of MOF Host–Guest in Single Crystalline State: Ingenious Strategies for Modulating Third‐Order NLO Signals

Abstract

Central metal exchange can innovatively open the cavity of metal‐organic frameworks (MOFs) by alternating the framework topology. Here, the single‐crystal‐to‐single‐crystal (SC‐SC) transformation is reported from a Co‐based MOF {[Co1.25(HL)0.5(Pz‐NH2)0.25(µ3‐O)0.25(µ2‐OH)0.25(H2O)]·0.125 Co·0.125 L·10.25H2O}n (Co‐MOF, L = 5,5'‐(1H‐2,3,5‐triazole‐1,4‐diyl)diisophthalic acid) into two novel MOF materials, {[Cu1.75L0.75(Pz‐NH2)0.125(µ3‐O)0.125(µ2‐OH)0.25(H2O)0.375]•3CH3CN}n (Cu‐MOF) and {[Zn1.75L0.625(Pz‐NH2)0.25(µ3‐O)0.25(µ2‐O)0.25(H2O)1.25]•4CH3CN}n (Zn‐MOF), through exchanging the Co2+ in the MOF into Cu2+ or Zn2+, respectively. The free Co2+ and L4− in the Co‐MOF channels fuse with the skeleton during the Co→Cu and Co→Zn exchange processes, leading to the expansion of the channel space and the transformation of the secondary building units (SBUs) to form an adjustable skeleton. The nonlinear optical response results show that the MOFs generated by the exchange of the central metal exhibit different saturable absorption and the self‐focusing effect. In addition, loading polypyrrole (PPy) into the MOFs can not only improve the stability of the MOFs but also further optimize the nonlinear optical behavior. This work suggests that SC‐SC central metal exchange and the introduction of polymer molecules can tune the nonlinear optical response, which provides a new perspective for the future study of nonlinear optical materials.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs

“…The β value of ZnCu-MOF-1 is calculated as 1.8 × 10 –8 m W –1 , while the β value of ZnCd-MOF-1 is calculated as 1.0 × 10 –8 m W –1 . The comparison of experimental results of different bimetal ratios shows that the introduction of more Cu 2+ and Cd 2+ can further adjust the electron structure, thus amplifying the nonlinear optical absorption effect. , …”

“…shows that the introduction of more Cu 2+ and Cd 2+ can further adjust the electron structure, thus amplifying the nonlinear optical absorption effect. 25,28 In the closed aperture (CA) mode, Zn-MOF exhibits a valley followed by a peak, both equidistant from the focal point, indicating self-focusing behavior (n 2 > 0) (Figure 7b). It was demonstrated that Zn-MOF induces beam lateral beam distortion and manifests a self-focusing phenomenon under intense laser irradiation.…”

“…25,26 Meanwhile, they can effectively adjust the bandgap width of MOFs and reduce the photon energy required for electron transition, which can improve the electron transfer efficiency. 27,28 On this basis, the performance of third-order NLO can be further regulated by using external stimuli. 29−31 Viologen-based MOFs with photoresponsive behavior exhibit rapid photochromism when exposed to ultraviolet light, which mainly depends on the ligand-to-ligand charge transfer (LLCT) mechanism.…”

“…The synergistic effect of bimetals can regulate the charge density distribution, , thereby promoting charge separation and electron transfer. , Meanwhile, they can effectively adjust the bandgap width of MOFs and reduce the photon energy required for electron transition, which can improve the electron transfer efficiency. , On this basis, the performance of third-order NLO can be further regulated by using external stimuli. − Viologen-based MOFs with photoresponsive behavior exhibit rapid photochromism when exposed to ultraviolet light, which mainly depends on the ligand-to-ligand charge transfer (LLCT) mechanism. − The occurrence of photoinduced electron transfer (PET) can alter the distribution of charges within MOFs. , Therefore, by constructing viologen-based MOFs with bimetallic synergistic effects, the charge distribution of MOFs can not only be adjusted from the intrinsic structure perspective but can also be further adjusted through external stimuli so as to achieve diversified regulation of third-order NLO properties.…”

0D MXene quantum dots/2D MXene derived metal–organic frameworks for enhanced nonlinear optical absorption across spectral and temporal regimes

“…The efficient charge delocalization in the Ti 3 C 2 QD/V 2 C PMOF heterostructure imparts new linear optical spectroscopic features and expands the π-conjugate system, indicating a protruding NLO absorption, which can be observed in hybrid systems. 38,39,47,60,61 It holds great promise in nonlinear optics and other optoelectronic devices. 29,62,63 Overall, the systematic investigations of the energy alignment and electron transfer mechanisms in the Ti 3 C 2 QD/V 2 C PMOF heterostructure provide valuable insights into its optoelectronic properties, paving the way for the development of novel heterostructures with enhanced NLO functionalities.…”