Interpenetrated Structure Research Articles

Design of Three-Dimensional Mesoporous Adamantane-Based Covalent Organic Framework with Exceptionally High Surface Areas.

The development of three-dimensional (3D) covalent organic frameworks (COFs) with large pores and high specific surface areas is of critical for practical applications. However, it remains a tremendous challenge to reconcile the contradiction between high porosity and high specific surface areas, and increasing the length of building blocks leads to structural interpenetration in 3D COFs. Here, we report the preparation of mesoporous three-dimensional COF by a new steric hindrance engineering method. By incorporating adamantane into the monomers instead of carbon centers, we successfully achieve 2-fold interpenetrated diamondoid-structured 3D COFs, featuring permanent mesopores (up to 33 Å), exceptionally high surface areas (>3400 m2 g-1), and low crystal densities (0.123 g cm-3). These properties far surpass those of most conventional 3D COFs with similar topologies. This work not only aims to construct 3D COFs with low interpenetration but also to establish a foundation for the systematic design and structural control of 3D COFs.

Eco-friendly, highly interpenetrated and slightly swollen pHEMA hydrogel foam for durable underwater superoleophobicity and emulsion separation

Despite the emergence of hydrogels as ideal candidates for preparing the superhydrophilic materials for emulsion separation, their structural stability and swelling still hinder their long-term use, mainly due to structure defects after swelling. Herein, differing from the common modification, the eco-friendly poly 2-hydroxyethyl methacrylate (pHEMA) hydrogel foam was designed and synthesized via a one-step strategy by using the high internal phase emulsion (HIPE) template method, which endowed it with a highly interpenetrated porous structure. Unlike the normal swellable hydrogels such as poly(N-isoproplyacrylamide) (PNIPAM) hydrogel, or modified hydrogel coatings, the pHEMA hydrogel foam displayed stable structure and underwater superoleophobicity after 20 d of immersion in water. The pHEMA hydrogel foam could separate different kinds of highly surfactant-stabilized oil-in-water (O/W) emulsions with a high separation efficiency of 99.3% for liquid paraffin emulsion obtained solely under gravity-driven. Additionally, it exhibited excellent antifouling performance and long-term acid/alkali tolerance over 100 h without decrease in emulsion separation efficiency (98.0%, oil/water ratio of 99:1) and permeation flux (over 2000 L·m−2·h−1) attributed to its stable bulky structure. Moreover, the pHEMA hydrogel foam demonstrated high cell viability of 96.87% and 95.96% after culturing the 3T3 clone A31 cells in the pHEMA hydrogel foam for 24 h and 48 h, respectively, indicating good biocompatibility. Hence, our work provides a new design to develop an eco-friendly bulk hydrogel foam that achieves stable structure and performance for emulsion separation.

Interfacial reaction and strengthening mechanism of thermo-compression bonding foam Ni reinforced SAC105 and SAC105–0.3Ti solder joints

The foam Ni holds great potential as a reinforcement phase, attributed to its distinctive three-dimensional (3D) continuous structure. In this study, high-strength Cu connections were produced by vacuum thermo-compression bonding using Ni foam reinforced SAC105 and SAC105–0.3Ti solders. The microstructure, interfacial morphology and shear strength of the connections with different Ni foam composite solders were systematically examined. The results demonstrate that the incorporation of Ni foam as a reinforcing phase substantially enhances the strength of SAC105 solder. The introduction of foam Ni resulted in the formation of a prismatic (Cu, Ni)6Sn5 phase in the matrix and altered the composition of the IMC layer. As the bonding time increased, (Cu, Ni)6Sn5 further grew in the matrix and formed a double interpenetration structure with the foam Ni. The IMC layer, composed of (Cu, Ni)6Sn5 and Cu3Sn, exhibited a random orientation. The Cu/SAC105–0.3Ti-Foam Ni/Cu joints bonded for 10 min exhibited the highest shear strength of 70.23 MPa. Shearing failure predominantly occurs within the soldering seam. The double interpenetration structure and the random orientation of the interfacial IMC impeded crack propagation, thereby significantly enhancing the strength of the Cu joints.

Iron salicylaldehydate conjugated metal–organic framework for quasi solid-state supercapacitor

Conjugated metal–organic frameworks (c-MOFs) are potential candidates for excellent electro and photochemical activities such as energy storage and catalysis. However, the poor chemical stability of c-MOFs obstructs them from the practical utilities in acid or base-functioned energy storage devices. Herein, we have introduced a novel iron-based salicylaldehydate 3D-c-MOF (Fe-Tp) with high chemical stability in strong acid environments. The robust coordination bond between iron and C3 symmetric salicylaldehyde organic pockets results in a doubly interpenetrated 3D framework with ultra-high chemical stability. The biphasic doubly interpenetrated structure of Fe-Tp was elucidated using theoretical modeling with the assistance of single-crystal electron diffraction analysis. The Fe-Tp showed chemical stability even in 10 M H2SO4 for 24 h. Moreover, we have investigated the dynamic charge storages in Fe-Tp in varying concentrations of acid electrolyte (122 F g−1 at 0.1 M H2SO4 to 400 F g−1 at 5 M H2SO4 at 0.1 A/g). The Fe-Tp-based flexible quasi-solid-state supercapacitor was fabricated using proton-loaded PVA electrolyte gel. It showed an excellent electrode capacitance of 106.25 mF cm−2 (at 0.25 mA cm−2) with remarkable cyclic stability (36,000 cycles with 80 % capacitance retention at 5 mA cm−2).

Interpenetrated Lattices of Quaternary Chalcogenides Displaying Magnetic Frustration, High Na-Ion Conductivity, and Cation Redox in Na-Ion Batteries.

A series of quaternary selenides, NaxMGaSe4 (M = Mn, Fe, and mixed Zn/Fe), have been synthesized for the first time employing a high-temperature solid-state synthesis route through stochiometric or polychalcogenide flux reactions. Along with the selenides, a previously reported sulfide analogue, NaxFeGaS4, is also revisited with new findings. These compounds form an interpenetrated structure made up of a supertetrahedral unit. The electrochemical evaluations exhibit a reversible (de)intercalation of ∼0.6 and ∼0.45 Na-ions, respectively, from Na2.87FeGaS4 (1a) and Na2.5FeGaSe4 (2) involving Fe2+/Fe3+ redox when cycled between 1.5 and 2.5 V. Mössbauer spectroscopy of 1a shows the existence of a mixed oxidation state of Fe2+/3+ in the pristine compound and reversible oxidation of Fe2+ to Fe3+ during the electrochemical cycles. Na2.79Zn0.6Fe0.4GaSe4 possesses a reasonably high room temperature ionic conductivity of 0.077 ms/cm with an activation energy of 0.30 eV. The preliminary magnetic measurements show a bifurcation of FC-ZFC at 4.5 and 2.5 K, respectively, for 1a and Na3MnGaSe4 (4) arising most likely from a spin-glass like transition. The high negative values of the Weiss constants -368.15 and -308.43 K for 1a and 4, respectively, indicate strong antiferromagnetic interactions between the magnetic ions and also emphasize the presence of a high degree of magnetic frustration in these compounds.

Zn(II)-Coordination Polymers Constructed from Isomeric Bis(Imidazole) Derivative Ligands and Tetracarboxylic Acid for the Detection of Iron Ions

Three Zn(II)-coordination polymers, namely, {[Zn2(µ4-L)(µ-obix)2]·4DMF}n (1), {[Zn2(µ4-L)(µ-mbix)2]·6H2O}n (2) and {[Zn2(µ4-L)(µ-pbix)2]·5H2O}n (3), (L4−: 5,5’-(terephthaloylbis(azanediyl))diisophthalate and obix (y = 2), mbix (y = 3), pbix (y = 4): 1,y-bis((1H-imidazol-1-yl)methyl)benzene) were prepared with a tetracarboxylic acid and flexible isomeric bis(imidazole) linkers and characterized. The compounds displayed structural diversity depending on the rotation of imidazole rings around the –CH2- groups on bis(imidazole) ligands. Compounds 1–3 showed 2-fold interpenetrated 3D framework, 2D structure and 3D framework, respectively. The compounds showed high emissions in solid-state and solutions. Luminescence experiments showed that compounds 1–3 displayed sensitive detection towards Fe3+ ions with detection limits of 2.31 ppm, 5.17 ppm and 2.61 ppm, respectively. Moreover, the compounds could selectively detect Fe3+ ions over the other interfering metal ions via luminescence quenching. The detection mechanism could be ascribed to the competitive light absorption between Fe3+ ions and the compounds.

A stable 3D Sr-MOF as an efficient heterogeneous catalyst for the cycloadditions of CO2 and knoevenagel condensation reactions

The catalytic activity of MOF is determined not only by its unique structure but also by the active sites from metal sites and functional ligands. A sTable 3D strontium complex, {[Sr2(BTCB)Cl(H2O)2]}n (Sr-BTCB), was synthesized under solvothermal condition. It is assembled with an amide-functionalized tricarboxylic acid and a Sr(II)-based infinite chain, where Sr2 repeating units are arranged sequentially. Two such 3D structures are interwoven to create a two-folded interpenetrated structure. The interpenetrated structure is strengthened by π-π interstacking between the central phenyl rings of ligands from different 3D structures. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated Sr-BTCB is modified by unsaturated Sr2+ions. Complex Sr-BTCB has abundant Lewis acidic metal sites and Lewis basic sites of amide groups, as well as 1D rhombic channels. It exhibits excellent stability and heterogeneous catalysis on CO2 fixation reactions into cyclic carbonates and Knoevenagel condensation reactions of aldehydes and malononitrile.

A new 3D Cd-MOF with 2fold interpenetrated as “turn-on/turn-off” fluorescent sensor for selective and sensitive detection of Cu2+, Al3+ and Fe3+ ions

The quantitative research with high sensitivity of metal ions has been increasingly important due to the influence to the environment and human health. In this work, a new luminescent Cd-MOF has successfully been constructed by one-dimensional spiral chain-shaped CdO6 clusters, H2O and 1-(4-carboxyphenyl)-5-methyl-4-oxo-1,4-dihydropyridazine-3-carboxylic acid ligands (H2(4-PDCA)), namely [Cd2(H2O)(4-PDCA)2]n (SNUT-19), which were further characterized by single crystal X-ray diffraction, PXRD, FT-IR and TGA. Single crystal X-ray analysis revealed that SNUT-19 exhibits unique 1D [Cd–O–Cd]∞ chain, further bridging by the ligand to form a three-dimensional (3D) structure with a 2-fold interpenetrated structure. SNUT-19 exhibits excellent water stability and good solid luminescence properties. In addition, the luminescence sensing experiments show that SNUT-19 as a fluorescent sensor for “turn on” and “turn off” luminescence sensitive detection of Cu2+, Al3+ and Fe3+ ions in aqueous media, which sensing mechanisms also have been investigated.

AIE Ligand-Based Luminescent Ln-MOFs for Rapid and Selective Sensing of Tetracycline.

The design of highly stable and dual-emission lanthanide metal-organic frameworks (Ln-MOFs) is promising for practical chemical sensor applications. Rational design and synthesis of photoresponsive organic ligands provide a feasible approach to achieving highly fluorescent dual-emission Ln-MOFs. In this study, a tetraphenylpyrazine-based AIE ligand, H4L, was synthesized and combined with lanthanide ions (including Sm3+, Eu3+, Gd3+, and Tb3+) to fabricate a series of Ln-MOFs named Ln-L. The single-crystal analysis revealed that all Ln-L belonged to the tetragonal space group P4212 and featured a 2-fold interpenetrated 3D structure. Leveraging rational design, Eu-L exhibited a sensitive response to tetracycline, making it a promising fluorescence sensor for tetracycline detection. The experiments demonstrated that Eu-L could rapidly and quantitatively detect tetracycline and its analogs within 30 s. The lowest detection limits for tetracycline, oxytetracycline, and chlortetracycline were 0.43, 0.92, and 0.81 μM, respectively. Additionally, the probe displayed excellent reusability and exceptional selectivity. A plausible sensing mechanism was proposed, supported by both experimental and theoretical analyses. Furthermore, the study discovered that on-site and real-time determination of TCs in aqueous solutions could be achieved by using luminescence test papers and composite films derived from Eu-L.

Rational Regulation of Cu−Co Thiospinel Hierarchical Microsphere to Enhance the Supercapacitive Properties

AbstractMicro‐structure of the electrodes play significant role in regulating the supercapacitive properties. Herein, three‐dimensional hierarchical heterostructures (3DHHs) CuCo2S4 microspheres with regulated micro‐structure is constructed via a simple one‐step method. The 3DHHs CuCo2S4 microspheres experience two‐dimensional (2D) lamellar interpenetration structure→two‐dimensional (2D) lamellar interpenetration structure with nanoparticles embedded on the 2D lamellar→nanoparticles assembled lamellar interpenetration structure by simply tuning the reaction time. Typically, the transition state exhibits much higher specific surface area, which is conducive to electrochemical reaction by providing adequate electrochemical interfaces. As supercapacitor electrode, the 3DHHs CuCo2S4‐10 exhibits an excellent capacitance of 1060 F g−1 at 1 A g−1, and even superior capacity retention of 86.7 % at 5 A g−1 after 13000 cycles. Noteworthy, asymmetric supercapacitor assembles by 3DHHs CuCo2S4‐10 and active carbon can achieve high energy density of 56.3 Wh kg−1 at 750 W kg−1, which holds more than 150 % capacitance retention over 5000 cycles. This work provides simply micro‐structure regulation in materials synthesis, which has significant potential in renewable energy applications.

Poly[bis-[μ2-1,3-bis-(pyridin-4-yl)urea-κ2N4:N4']bis-(μ2-5-methyl-isophthalato-κ2O1:O3)dizinc(II)], a parallel inter-penetrated slab-like coordination polymer with {3.648}{326.728} 4,4-connected binodal topology.

In the title compound, [Zn2(C9H6O4)2(C11H10N4O)2]n, diperiodic coordination polymer slabs with {3.648}{326.728} 4,4-connected binodal topology are held into a parallel inter-penetrated triperiodic crystal structure by means of N-H⋯O hydrogen-bonding patterns.

Self-Assembled Cobalt–Nickel Bimetallic-Organic Framework Materials with High Supercapacitor Performance

Two new metal–organic frameworks (MOFs), [Co(bcpp)(bbip)]·H2O (Co-MOF) and [Ni(bcpp)(bbip)]·H2O (Ni-MOF), have been generated based on a V-type flexible carboxylic ligand 3,5-bis(4-carboxyl phenoxy) pyridine (H2bcpp) and a rigid N-donor ligand 1,1′-(1,4-phenylene)bis(1H-benzimidazole) (bbip) by a solvothermal method. Co-MOF and Ni-MOF are isostructural with a 2-fold interpenetrated layered structure. Moreover, a series of bimetallic CoxNiy-MOFs (x/y = 1:1, 2.5:1, 2.75:1, 3:1, 3.25:1, and 3.5:1) were obtained by using one-pot synthesis. Owing to their mixed metallic components and internal layered structure, the bimetallic CoxNiy-MOFs possess a remarkable electrochemical storage property. Significantly, the Co2.75Ni1-MOF has high specific capacitance (699 F g–1) at 0.5 A g–1 and good cycling durability (retained 72.7% over 3100 turns). Additionally, an asymmetrical ultra-capacitor based on Co2.75Ni1-MOF and activated carbon (AC) delivers a maximum energy density of 20.44 Wh kg–1 at 387.49 W kg–1 and a high cycle-to-cycle stability with 85.4% of the primary capacitance over 15,000 turns.

Pseudorotaxane Ligand‐Induced Formation of Copper(I) Iodide Cluster Based Assembly Materials: From Zero to Three Dimensional

Comprehensive SummaryIn this work, we have successfully obtained a series of novel copper(I)–iodide clusters (CuI NCs) based assembly materials by combining supramolecular pseudorotaxane ligands {[Mebpe+]PF6–@CB[6] (CB[6] = cucurbit[6]uril), L’·PF6} and linkers {BPHF@CB[6], [BPHF = C14H20N4(PF6)2], L·PF6}, including discrete cluster CuI 1 and extended cluster organic frameworks MORF 1 and MORF 2. CuI 1 can be described as a dumbbell‐shaped molecule with its body‐centered site and two vertexes respectively occupied by one [Cu5I6]– cluster and two CB[6] held together by two L’·PF6 ligands. The crystal structures of MORF 1 and MORF 2 are 1D anionic chain and four‐fold interpenetrated 3D cationic diamondoid structure, respectively, which all featured intriguing alternating CB[6] and CuI NCs. Furthermore, CuI 1 exhibits outstanding thermochromic and piezochromic luminescence. MORF 1 and MORF 2 also are detected pressure dependent luminescence properties with an enormous blue‐shift of the near‐infrared (NIR) emission band under high pressure compression. These exciting and smart materials possess great potential in the application field of novel temperature and pressure sensors.

Covalent organic framework atropisomers with multiple gas-triggered structural flexibilities.

Covalent organic frameworks (COFs) are emerging crystalline porous polymers, showing great potential for applications but lacking gas-triggered flexibility. Atropisomerism was experimentally discovered in 1922 but has rarely been found in crystals with infinite framework structures. Here we report atropisomerism in COF single crystals. The obtained COF atropisomers, namely COF-320 and COF-320-A, have identical chemical and interpenetrated structures but differ in the spatial arrangement of repeating units. In contrast to the rigid COF-320 structure, its atropisomer (COF-320-A) exhibits unconventional gas sorption behaviours with one or more sorption steps in isotherms at different temperatures. Single-crystal structures determined from continuous rotation electron diffraction and in situ powder X-ray diffraction demonstrate that these adsorption steps originate from internal pore expansion with or without changing the crystal space group. COF-320-A recognizes different gases by expanding its internal pores continuously (crystal-to-amorphous transition) or discontinuously (crystal-to-crystal transition) or having mixed transition styles, distinguishing COF-320-A from existing soft/flexible porous crystals. These findings extend atropisomerism from molecules to crystals and propel COFs into the covalently linked soft porous crystal regime, further advancing applications of soft porous crystals in gas sorption, separation and storage.

Insight into the complex coupled growth behavior of Al2O3/YAG eutectic ceramic based on the evolutions of microstructure and crystallographic texture

Clarifying the dependence of microstructure and crystallographic texture on growth kinetics is critical concerns for mechanical properties prediction in complex faceted eutectic growth. In this study, we present the comprehensive investigations of microstructure and crystallographic texture characteristic in directionally solidified Al2O3/YAG eutectic that rely on its coupled growth mechanism. The growth mechanism of eutectic spacing is also well depicted by the Magnin-Kurz (MK) model associated with morphological criteria for branching in faceted phase. As increasing the solidification rate (10 µm/s∼200 µm/s), the regularization tendency for irregular three-dimensional interpenetrated (TDI) structure in geometric category is stronger. Whereas, the enhanced kinetic undercooling increases the misorientation and interfacial energy, which is attributed to the fact that the growth kinetics is more dominant than the minimum interface energy in this work. Additionally, the fluctuation tendency of eutectic spacing and crystallographic orientation with the solidification rate is diametrically opposite. The colony structure consisting of coupled irregular eutectic is formed by the planar interface instability, and its formation mechanism is revealed by the misorientation distribution. This comprehensive research contributes to the design of high-performance eutectic ceramics considering the influence of microstructural features and crystallographic growth modes.

Numerical simulation of an entangled wire-silicone rubber continuous interpenetration structure based on domain meshing superposition method

The entangled metal wire/silicone rubber continuous interpenetrated phase composite (EMW-SRC) is a high-performance damping material with silicone rubber as matrix and metal wire turns as the reinforcement skeleton. EMW-SRC has good damping characteristics and significant load-bearing stiffness. This work first characterizes the fine interface morphology and macroscopic mechanical characteristics of the EMW-SRC and adopts a computer-aided preparation technology to accurately reconstruct the complex structure of the spatially random distribution of the entangled metal wire material. It develops a finite element model of the EMW-SRC with high-quality structured mesh based on the domain mesh superposition method cohesive cells to share and embed the surface nodes at the interface. Moreover, the composite interface bonding performance between metal wire and silicone rubber is investigated, the interfacial bonding parameters are determined, and the reliability of the mesh model is assessed by comparing the results of a single wire pull-out test and simulation analysis. Based on this, quasi-static compression test and simulation of the material are further performed, with the simulation results matching well with the experimental ones. The mesoscale simulation results show that the metal wire inside the EMW-SRC can overcome the silicone rubber restriction on micro-slip during the load-bearing process. The metal wire micro-element is subjected to torsional load. Under a compression displacement of 0.7 mm, the composite interface bonding remains intact without damage. In conclusion, the developed model can provide a prior guidance on the preparation and use conditions of the proposed material and offers an effective way to investigate the fine-mechanics of such materials with high damping and high load-bearing characteristics.

Genetic diversity and structure of the 4th cycle breeding population of Chinese fir (Cunninghamia lanceolata (lamb.) hook).

Studying population genetic structure and diversity is crucial for the marker-assisted selection and breeding of coniferous tree species. In this study, using RAD-seq technology, we developed 343,644 high-quality single nucleotide polymorphism (SNP) markers to resolve the genetic diversity and population genetic structure of 233 Chinese fir selected individuals from the 4th cycle breeding program, representing different breeding generations and provenances. The genetic diversity of the 4th cycle breeding population was high with nucleotide diversity (Pi ) of 0.003, and Ho and He of 0.215 and 0.233, respectively, indicating that the breeding population has a broad genetic base. The genetic differentiation level between the different breeding generations and different provenances was low (Fst < 0.05), with population structure analysis results dividing the 233 individuals into four subgroups. Each subgroup has a mixed branch with interpenetration and weak population structure, which might be related to breeding rather than provenance, with aggregation from the same source only being in the local branches. Our results provide a reference for further research on the marker-assisted selective breeding of Chinese fir and other coniferous trees.

Coordination-Induced NIR Photothermal Conversion and Laser Detonation Based on a Quasi-Diamond Interpenetrated Structure

In this work, a copper-based coordination polymer of [Cu3(dhba)2(OH)2(H2O)4] (Cu-dhba, H2dhba = 3,5-dinitro-4-hydroxybenzoic acid) has been constructed by the crystal-engineering approach, featuring a three-dimensional quasi-diamond interpenetrated structure. Impressively, due to the introduction of the d–d transition of the Cu2+ ion, Cu-dhba shows a broad absorption band with the maximum centered at the NIR section. As a result, Cu-dhba exhibits a remarkable photothermal conversion performance under 808 nm light; the temperature of the sample surface could be increased up to 115 °C within seconds. Benefiting from its high structure density and abundant hydrogen-bonding interactions, Cu-dhba shows no obvious performance decay after several photothermal cycling experiments. Moreover, due to the high density of energetic nitro groups periodically confined in its structure, Cu-dhba exhibits a drastic explosion under 808 nm laser irradiation, making Cu-dhba a promising laser-responsive energetic material.

The tail of imidazole regulated the assembly of two robust sandwich-type polyoxotungstate-based open frameworks with efficient visible-white-light-driven catalytic oxidation of sulfides

The tail of imidazole regulated the assembly of fascinating 2Dsqltopology and 3D 2-fold interpenetratedlvtstructure polyoxotungstate-based open frameworks with efficient visible-white-light-driven aerobic catalytic oxidation of sulfides.

Manipulating fluorescence by photo-switched spin-state conversions in an iron(ii)-based SCO-MOF.

Manipulating fluorescence by photo-switched spin-state conversions is an attractive prospect for applications in smart magneto-optical materials and devices. The challenge is how to modulate the energy transfer paths of the singlet excited state by light-induced spin-state conversions. In this work, a spin crossover (SCO) FeII-based fluorophore was embedded into a metal-organic framework (MOF) to tune the energy transfer paths. Compound 1 {Fe(TPA-diPy)[Ag(CN)2]2}·2EtOH (1) has an interpenetrated Hofmann-type structure, wherein the FeII ion is coordinated by a bidentate fluorophore ligand (TPA-diPy) and four cyanide nitrogen atoms and acts as the fluorescent-SCO unit. Magnetic susceptibility measurements revealed that 1 underwent an incomplete and gradual spin crossover with T1/2 = 161 K. Photomagnetic studies confirmed photo-induced spin state conversions between the low-spin (LS) and high-spin (HS) states, where the irradiation of 532 and 808 nm laser lights converted the LS and HS states to the HS and LS states, respectively. Variable-temperature fluorescence spectra study revealed an anomalous decrease in emission intensity upon the HS → LS transition, confirming the synergetic coupling between the fluorophore and SCO units. Alternating irradiation of 532 and 808 nm laser lights resulted in reversible fluorescence intensity changes, confirming spin state-controlled fluorescence in the SCO-MOF. Photo-monitored structural analyses and UV-vis spectroscopic studies demonstrated that the photo-induced spin state conversions changed energy transfer paths from the TPA fluorophore to the metal-centered charge transfer bands, ultimately leading to the switching of fluorescence intensities. This work represents a new prototype compound showing bidirectional photo-switched fluorescence by manipulating the spin states of iron(ii).