WO2021105759A1

WO2021105759A1 - New metal-organic frameworks and their use for encapsulation of fluorescent dyes

Info

Publication number: WO2021105759A1
Application number: PCT/IB2019/060328
Authority: WO
Inventors: Kirill SHUBIN; Andrei BARAN; Sergey BELYAKOV; Kristine KRUKLE-BERZINA; Anatolijs Misnovs
Original assignee: Latvian Institute Of Organic Synthesis
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2021-06-03
Also published as: DE112019007923T5; CA3158016A1

Abstract

Disclosed are new metal- organic frameworks (MOFs) based on tetradentate anthraquinone ligand and method of making and using the same. Disclosed is its ability to adsorb dye molecules from solution. In the formed host-guest complex dye is encapsulated inside MOF pores in such a way, that dye fluorescence is completely quenched. After liberation of the dye its fluorescence is fully restored.

Description

New metal-organic frameworks and their use for encapsulation of fluorescent dyes Field of the invention The present invention relates to new microporous metal-organic frameworks (MOFs), a new host-guest complexes of the said MOFs with dye molecules, as well as their fluorescent properties. Background of the art Synthesis and application of microporous metal-organic frameworks (MOFs) is a field of material science which have attracted a lot of attention in recent years. Compared to tradi- tional porous materials, like silica or zeolites, MOFs have open channels with a much wider variety of pore sizes, volume of internal cavities and nature of pores surface. Compared to other types of porous materials MOFs has one of the highest relative surface areas. Large va- riety of constituents together with a flexible design makes MOFs a versatile platform for nu- merous applications including gas storage or separation, catalysis, sensing, encapsulation of active compounds and many others (Cui, Y; Li, B.; He, H.; Zhou, W.; Chen, B.; Qian, G. Acc. Chem. Res. 2016, 49(3), 483-493). MOFs are coordination network compounds comprised of nodes, which are metal- containing inorganic groups, connected together with polydentate organic ligands. Ligand is connected to nodes through coordinating functional groups, such as carboxylates and amines. Together they form one-, two- or three-dimensional lattices, which often exhibit crystalline structure. In many instances they contain pores as channels and cavities of various diameters, which can contain solvent or other organic molecules. In many instances, if the size of a mol- ecule is comparable to the diameter of a channel, such molecules can be introduced to pores or extracted from them by diffusion (Cirujano, F. G.; Llabrés i Xamena, F. X. Metal Organic Frameworks as Nanoreactors and Host Matrices for Encapsulation. In Organic Nanoreactors; Elsevier, 2016; pp 305–340). Encapsulation of small organic molecules in MOFs and formation of host-guest com- plexes involves interaction of guests with walls of channels and cavities, where they are con- tained. Various modes of interaction between host and guest include sorption, coordination and chemical reaction. Understanding of the details of interaction between host MOF lattice and guest organic molecules is a prerequisite for the creation of new composite materials with useful functions. While coordination and chemical reaction often produce well-defined host- guest complexes, which can be characterized by a number of methods, sorption is reversible by nature and produce much weaker host-guest complexes. In one aspect it is advantageous to use fluorescent molecules as guests and to assess their interaction with hosts by changing of their fluorescent properties (Karmakar, A.; Samanta, P.; Desai, A. V.; Ghosh, S. K. Acc. Chem. Res. 2017, 50(10), 2457-2469). Sorption of various ions and molecules from solution by porous MOFs is described in a number of publications (Gao, Q.; Xu, J.; Bu, X.-H. Coordination Chemistry Reviews 2019, 378, 17–31). This effect is of interest for selective removal of certain pollutants from water streams (Cui, Z.; Zhang, X.; Liu, S.; Zhou, L.; Li, W.; Zhang, J. Inorg. Chem. 2018, 57(18), 11463–11473; Guo, H.; Sun, Y.; Zhang, F.; Ma, R.; Wang, F.; Sun, S.; Guo, X.; Liu, S.; Zhou, T. Inorganic Chemistry Communications 2019, 107, 107492) or for their degradation (Li, H.-P.; Dou, Z.; Chen, S.-Q.; Hu, M.; Li, S.; Sun, H.-M.; Jiang, Y.; Zhai, Q.-G. Inorg. Chem. 2019, 58(16), 11220–11230; Qiao, X.; Ge, Y.; Li, Y.; Niu, Y.; Wu, B. ACS Omega 2019, 4(7), 12402–12409). Efficiency of the sorption process is assessed by measurements of ultraviolet-visible spectra in solution. However, there is a lack of research and characteriza- tion of host-guest complexes, formed when a molecule is adsorbed inside MOF pores. Espe- cially interesting it would be to investigate properties of guest molecules, which have their own emission spectra. There is no literature data for solid-state fluorescence measurements of fluorescent molecules encapsulated in MOF pores. Detailed description Disclosed herein are novel metal-organic framework materials having tetradentate tetraphenylanthraquinone linking moieties and one or more secondary building units. In one embodiment a secondary building unit comprises metal ions which are selected from Cu or Ni. In another embodiment a secondary building unit comprises of the same metal ions (Cu or Ni) and atoms of oxygen with O/metal ratio is >0.5, preferably >0.6. In one aspect a schematic representation of Cu-Anth-MOF is illustrated by Fig. 1. In another aspect a schematic representation of Ni-Anth-MOF is illustrated by Fig. 2. In one embodiment the present disclosure is directed to preparation of a new MOF material, which may comprise of a compound represented by the formula (Formula 1): M_wL_xA_y*B_z*nSolv Formula 1 where M is selected from: Cu, Ni; L represents tetradentate tetraphenylanthraquinone ligand of formula L1;

A independently represents a ligand selected from (OH)-, H₂O, alkyl-(SO₃)-, aryl-(SO₃)-, (NO₂)-, halide anion; B independently represents a ligand selected from (OH)-, H₂O, alkyl-(SO₃)-, aryl-(SO₃)-, (NO₂)-, halide anion; Solv represents any solvent that can coordinate with the MOF metal ions. It may be a solvent, which participated in MOF formation selected from the list: water, dimethylformamide, di- ethylformamide, dimethylacetamide, diethylacetamide, dimethylsulfoxide. w represents the number of M atoms in the building unit; x represents the number of ligands L in the building units; y represents the number of ligands A in the building unit; z represents the number of ligands B in the building unit; n represents the average number of solvent molecules “Solv” coordinated to the metal centers M per building unit in the MOF material. Preferably, the ratio y/x is ≥1.0, more preferably ≥1.5. Preferably, the ratio z/x is in range ≥0 and ≤3. Ligand L1 was synthesized and used as the organic linker as it is described in Exam- ples section. There are no literature methods for preparation of ligand of L1 formula. Accord- ing to present invention a new and efficient synthetic method was developed for its prepara- tion, as it is indicated on Scheme 1. A short four-step sequence commence with a cross- coupling step, followed by oxidation of sulfur yielding substituted thiophene 1,1-dioxide 4. It was gratifying to found, that substance 4 is reactive in Diels-Alder cycloaddition and yields a corresponding tetrasubstituted anthraquinone 6. For the first time it was shown, that a thio- phene 1,1-dioxide substituted at positions 3 and 4 by phenyls with an electron-withdrawing group can undergo such transformation. Finally, hydrolysis of esters in 6 provided ligand L1. In one embodiment Cu(NO₃)₂·2.5H₂O salt was chosen to provide a metal node for the preparation of Cu-Anth-MOF. In another embodiment Ni(NO₃)₂·6H₂O salt was chosen to provide a metal node for the preparation of Ni-Anth-MOF. Experimental conditions for the preparation of Cu-Anth-MOF and Ni-Anth-MOF were optimized in such a way, that single crystals could be formed by the reaction of a metal salt and the organic ligand L1. Preferably, the crystal topology shall be related to a monoclin- ic crystal system and the P21/c or P2/m space group or a sub-group. Cell parameters and other data for Cu-Anth-MOF are represented in Table 1. Cell parameters and other data for Ni- Anth-MOF are represented in Table 2. Both Cu-Anth-MOF and Ni-Anth-MOF demon- strated excellent robustness upon isolation and storage. Together with a permanent porosity of the prepared MOFs it makes them ideal candidates for the preparation of host-guest complex- es with organic molecules. In one aspect the process of preparation of Cu-Anth-MOF the solvent, which is used for the preparation comprises a mixture of water and an organic solvent in ratio organic sol- vent/water from 90:10 to 65:35, expressed as a volume % of organic solvent. Organic solvent is preferably selected from the list: dimethylformamide, diethylformamide, dimethylacetam- ide, diethylacetamide, dimethylsulfoxide; preferably carboxylic acid dimethylamide; prefera- bly dimethylformamide. In another aspect the process of preparation of Ni-Anth-MOF the solvent, which is used for the preparation comprises a mixture of water, an organic solvent 1 and an organic solvent 2. Content of water in volume % is preferred to be less, than 50 vol%, preferably less than 30%. Ratio between organic solvent 1/organic solvent 2 is preferred to be 50:50, prefera- bly 60:40. Organic solvent 1 is preferably selected from the list: dioxane, tetrahydrofuran, preferably dioxane. Organic solvent 2 is preferably selected from the list: dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylsulfoxide; preferably car- boxylic acid diethylamide; preferably diethylformamide. According to the current disclosure MOFs based on tetraphenylanthraquinone ligand of formula L1 can be prepared in a form, where the coordination polymer is ordered, prefera- bly in a single-crystalline form. The structure of MOFs disclosed thereof was confirmed by single-crystal X-ray diffraction. In one embodiment a spatial arrangement of elements of Cu-Anth-MOF is exempli- fied by Fig. 3, which demonstrates a single-crystal X-ray structure of Cu-Anth-MOF. In another embodiment a spatial arrangement of elements of Ni-Anth-MOF is exem- plified by Fig. 4, which demonstrates a single-crystal X-ray structure of Ni-Anth-MOF. In another example crystalline nature of the prepared material is confirmed by powder X-ray diffraction as exemplified by Fig. 5 for Cu-Anth-MOF. In yet another example crystalline nature of the prepared material is confirmed by powder X-ray diffraction as exemplified by Fig. 6 for Ni-Anth-MOF. In one embodiment Cu-Anth-MOF and Ni-Anth-MOF are stable in water. Preferably, the three-dimensional structure of Cu-Anth-MOF incorporates channels having an internal diameter between 7.9 and 10.2 Å and are accessible through apertures with diameters 7.9 and 10.2 Å. Advantageously, the three-dimensional structure of Ni-Anth-MOF incorporates channels having an internal diameter between 6.4 to 8.5 Å and are accessible through apertures with diameters 6.4 to 8.5 Å. The present invention relates to a guest encapsulated in a host and a method of encap- sulation. The host comprises of a MOF and the guest comprise a molecule having a size smaller, than the aperture size of the MOF. In one embodiment a dye “Methylene Blue” (MB) is used as a guest. Molecular representation of MB is shown on Fig. 9. The size of MB mole- cule was estimated as a rectangular box of approximate dimensions 17.0 x 7.6 x 3.3 Å. Fluo- rescence of the solution of MB in water at a concentration c=1 µmol/L and pH 7 with excita- tion at 290 nm is indicated on Fig. 11. This emission spectrum is characterized by a strong peak in a range 650-750 nm with signal intensity higher that 100000 arbitrary units. In one aspect MOF materials disclosed herein, in particular Cu-Anth-MOF or Ni- Anth-MOF was characterized by fluorescence spectroscopy. Spectrum of solid-state fluores- cence emission characteristics of Cu-Anth-MOF is shown on Fig. 12. Spectrum of solid-state fluorescence emission characteristics of Ni-Anth-MOF is shown on Fig. 14. Both spectra are characterized by very low fluorescence intensity in 650-750 nm range. In particular, signals in this range are lower than 500 arbitrary units. In one embodiment the present invention provides a method for preparing of a host- guest complex. Scheme 200 of preparation of host-guest complexes of Cu-Anth-MOF and Ni-Anth-MOF with MB and measurement of its fluorescent properties is outlined on Fig. 10. At a step 205 the method can include mixing of a MOF with water. At a step 210 a solution of a guest in the same solvent is prepared. At a step 215 components obtained at steps 205 and 210 are mixed and incubated without stirring according to example provided in the current disclosure. In one embodiment, when MB is used as a guest and Cu-Anth-MOF is used as a host a new host-guest complex can be prepared at step 215. Fluorescence spectrum of the said complex is measured at step 220. A graph representing solid-state emission characteristics of a host-guest complex comprised of MB encapsulated in Cu-Anth-MOF (excited at 290 nm) is shown on Fig. 13. A graph representing solid-state emission characteristics of a host-guest complex comprised of MB encapsulated in Ni-Anth-MOF (excited at 290 nm) is shown on Fig. 15 for Ni-Anth- MOF. Both Fig. 13 and Fig. 15 demonstrate that fluorescence intensity in range 650-750 nm is below 2000 arbitrary units which means, that MB confined in pores of Cu-Anth-MOF or Ni-Anth-MOF does not exhibit fluorescence. This data demonstrates the unique property of the new MOFs described thereof. When a dye molecule is encapsulated inside the pores of the said MOFs, its fluorescence is completely quenched. At step 225 a digestion of a host-guest complex with encapsulated MB is carried out in aq. HCl solution. Under these conditions a complete decomposition of the polymeric struc- ture of a MOF to an initial ligand and a metal salt takes place. MB is liberated to the solution. At step 230 the solution after digestion is neutralized to pH 7 and its fluorescence is measured directly from the aqueous solution. In one aspect as demonstrated on Fig. 16 for Cu-Anth- MOF fluorescence of MB is restored after digestion and its emission spectrum contains a strong signal in 650-750 nm range with intensity higher than 30000 arbitrary units. In another aspect as demonstrated on Fig. 17 for Ni-Anth-MOF fluorescence of MB is restored after digestion and its emission spectrum contains a strong signal in 650-750 nm range with inten- sity higher than 15000 arbitrary units. The provided data demonstrates that interactions in the host-guest complex of the dye molecule inside the pores of the new MOFs quench dye fluo- rescence with an excellent efficiency. At the same time, the said interactions are reversible and once the dye is extracted from the pores its fluorescence is restored. Examples All reagents were obtained from commercial sources and used without further purifi- cation. The emission fluorescent spectra were recorded, at room temperature, using Edinburgh Instruments FS5 Spectrofluorometer. Scheme 1 demonstrates the reaction pathway for the preparation of ligand of formula L1 from starting materials. First, 3,4-dibromothiophene 1 was arylated by boronic acid 2 in a Suzuki-Miyaura cross-coupling reaction. Obtained diarylthiophene 3 was oxidized by Ox- one® to the appropriate thiophene 1,1-dioxide 4. Double Diels-Alder reaction between thio- phene 1,1-dioxide 4 and 1,4-benzoquinone 5 furnished tetrasubstituted anthraquinone 6. Fi- nally, hydrolysis of ethyl ester groups in 6 yields the target ligand L1.

Abbreviations AcOH Acetic acid CDCl₃ Chloroform-d Cu(NO₃)₂·2.5H₂O Cupric nitrate hemi(pentahydrate) DCM Dichloromethane DEF N,N′-Diethylformamide DMSO Dimethylsulfoxide EtOAc Ethyl acetate EtOH Ethanol HCl Hydrochloric acid KOH Potassium hydroxide Na₂CO₃ Sodium carbonate Na₂S₂O₃ Sodium thiosulfate NaHCO₃ Sodium bicarbonate Ni(NO₃)₂·6H₂O Nickel(II) nitrate hexahydrate Pd(OAc)₂ Palladium(II) acetate PPh₃ Triphenylphosphine Preparation of diethyl 4,4'-(thiophene-3,4-diyl)dibenzoate 3. In a 100 ml screw-cap vial under argon flow and stirring (4-(ethoxycarbonyl)phenyl)boronic acid 2 (7.0 g, 36.21 mmol, 4.0 equiv.), solid Na₂CO₃ (3.8 g, 36.21 mmol, 4.0 equiv.), Pd(OAc)₂ (0.2 g, 0.91 mmol, 10 mol%) and PPh₃ (0.6 g, 2.26 mmol, 25 mol%) were successfully introduced, and followed by 3,4-dibromothiophene 1 (1.0 mL, 2.19 g, 9.05 mmol), and the mixture was fur- ther purged with argon for 15 min at rt. Meanwhile, dry toluene and water were separately subjected to degassing sequence by connecting vacuum line and then purging with argon through rubber septum. The operation was repeated at least 3 times. Finally, degassed toluene (45 mL) and water (15 mL) were added into the reaction vessel, which was then sealed and heated to 100-110 °C for 24 h. Cooled to rt. The reaction mixture was diluted with EtOAc (100 mL), aq. layer was separated and further washed with EtOAc (3 x 30 mL). The organic phases were pooled together, washed with water (30 mL) and brine (50 mL), and evaporated onto 35 g of silica. Crude compound was purified with column flash chromatography, eluting with EtOAc/hexanes gradient from 0 to 30%. Yield of 3: 2.5 g (6.6 mmol, 72%), as a white solid. ¹H NMR (400 MHz, CDCl₃) δ: 7.94 (d, 2H), 7.41 (s, 2H), 7.23 (d, 2H), 4.37 (q, 2H), 1.39 (t, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 166.6, 140.9, 140.8, 129.7, 129.3, 129.0, 125.5, 61.1, 14.5; GC-MS (EI): m/z 380 [M]⁺. Preparation of diethyl 4,4'-(1,1-dioxidothiophene-3,4-diyl)dibenzoate 4. A solution of thiophene diester 3 (5.5 g, 14.5 mmol) in DCM/acetone/water (2:1:2) solvent mixture (500 mL total volume) was introduced into a 1000 ml round-bottom flask under ice-water cooling and intense stirring. Next, NaHCO₃ (59 g, 690 mmol, 45 equiv.) was added in one portion fol- lowed by Oxone® (96 g, 146 mmol, 10.0 equiv.) in small portions, 5-7 g each within 5 h, and the reaction mixture was left for overnight at rt. After that, the mixture was diluted with water (400 mL), organic layer was separated, aq. layer was further extracted with DCM (5 x 100 mL). The organic phases were pooled together, washed with 10% aq. soln. of Na₂S₂O₃ (2 x 50 mL), water (50 mL) and brine (50 mL), and evaporated onto 35 g of silica. Crude compound was purified with column flash chromatography, eluting with MeOH/DCM gradient from 0 to 5%. Yield of 4: 2.7 g (6.5 mmol, 45%), as a light-yellow foam, which solidify upon standing. ¹H NMR (300 MHz, CDCl₃) δ: 7.97 (d, 2H), 7.12 (d, 2H), 6.73 (s, 2H), 4.38 (q, 2H), 1.39 (t, 3H); LC-MS (ES⁺): m/z 413 [M+H]⁺. Preparation of tetraethyl 4,4',4'',4'''-(9,10-dioxo-9,10-dihydroanthracene-2,3,6,7- tetrayl)tetrabenzoate 6. In a 100 ml screw-cap vial under argon flow and stirring a solution of thiophene 1,1-dioxide 4 (2.0 g, 4.85 mmol) in glacial AcOH (25 mL) was introduced followed by 1,4-benzoquinone 5 (0.3 g, 2.78 mmol, 0.5 equiv.). The vessel was then sealed and heated to 110-120 °C for 48 h. After that, the reaction mixture was cooled to rt and poured into water (250 mL) and extracted with DCM (5 x 50 mL), organic layers were pooled together, washed with sat. aq. NaHCO₃ (2 x 50 mL), water (50 mL) and brine (50 mL), and evaporated onto 35 g of silica. Crude compound was purified with column flash chromatography, eluting with EtOAc/hexanes gradient from 0 to 30%. Yield of 6: 1.2 g (1.5 mmol, 31%) as a light-yellow solid. ¹H NMR (400 MHz, CDCl₃) δ: 8.42 (s, 4H), 7.99 (d, 8H), 7.31 (d, 8H), 4.41 (q, 8H), 1.42 (t, 12H); ¹³C NMR (100 MHz, CDCl₃) δ: 182.3, 166.2, 145.7, 143.7, 132.9, 130.1, 129.8, 129.8, 61.3, 14.5. Preparation of 4,4',4'',4'''-(9,10-dioxo-9,10-dihydroanthracene-2,3,6,7- tetrayl)tetrabenzoic acid L1. In a 25 ml screw-cap vial under stirring a solution of ester 6 (350 mg, 0.44 mmol) in EtOH (5.0 mL) was introduced followed by KOH (0.15 g, 2.65 mmol, 6.0 equiv.). The vessel was then sealed and heated to 100-110 °C for 24 h, showing complete conversion. The mixture was cooled to rt and poured into water (50 mL) and acidified with 1N aq. HCl to pH 3, precipitated solids were filtered, washed with water (5 x 10 mL), and dried under reduced pressure to constant weight. Yield of L1: 260 mg (0.37 mmol, 84%), as a light-yellow solid. ¹H NMR (400 MHz, DMSO-d₆) δ: 13.08 (br.s, 4H), 8.27 (s, 4H), 7.90 (d, 8H), 7.39 (d, 8H); LC-MS (ES^–): m/z 687 [M–H]^–. Synthesis of Cu-Anth-MOF. A mixture of L1 (10 mg, 0.015 mmol) and Cu(NO₃)₂·2.5H₂O (14 mg, 0.060 mmol) was dissolved in a mixed solvent of DEF (1.0 mL) and water (0.1 mL). Upon the addition of 10 µL of 6 M aq. HCl, the vial was capped and heated at 90 °C for 24 h. After cooling to room temperature the green crystals were formed. They were collected by filtration and dried at rt. Yield of Cu-Anth-MOF: 8 mg (65%). Synthesis of Ni-Anth-MOF. A mixture of L1 (17 mg, 0.025 mmol) and Ni(NO₃)₂·6H₂O (22 mg, 0.058 mmol) was dissolved in a mixed solvent of DEF (1.0 mL), wa- ter (0.5 mL) and dioxane (1.5 mL). Upon the addition of 30 µL of 1 M aq. HCl, the vial was capped and heated at 100 °C for 4 days. After cooling to room temperature greenish crystals were formed. They were collected by filtration and dried at rt. Yield of Ni-Anth-MOF: 10 mg (51%). Single-crystal XRD and crystal structure of Cu-Anth-MOF. SCXRD data of Cu- Anth-MOF were collected using XtaLAB Synergy, Dualflex, HyPix, diffractometer using Cu Κα (λ = 1.54178 Å) radiation. Data indexing, integration and reduction was performed using CrysAlis PRO 1.171.40.35a (Rigaku OD, 2018) software. Absorption correction was per- formed by multi-scan method. Structure was solved using Direct Methods (SHELXT 2014/4, Sheldrick, 2014) and refined using SHELXL2017/1 (Sheldrick, 2017) (full-matrix least- squares on F²). Crystal data and refinement conditions are shown in Table 1. All attempts to refine peaks of residual electron density of disordered solvent molecules were unsuccessful. Therefore the data were corrected for the contribution of a disordered solvent density using of the SQUEEZE procedure as implemented in PLATON. The total solvent accessible void vol- ume is 3141 Å. Table 1. Crystal data and structure refinement conditions for Cu-Anth-MOF

Single-crystal XRD and crystal structure of Ni-Anth-MOF. SCXRD data of Ni-Anth- MOF were collected using XtaLAB Synergy, Dualflex, HyPix, diffractometer using Cu Κα (λ = 1.54178 Å) radiation. Data indexing, integration and reduction was performed using CrysA- lis PRO 1.171.40.35a (Rigaku OD, 2018) software. Absorption correction was performed by multi-scan method. Structure was solved using Direct Methods (SHELXT 2014/4, Sheldrick, 2014) and refined using SHELXL2017/1 (Sheldrick, 2017) (full-matrix least-squares on F²). Crystal data and refinement conditions are shown in Table 2. All attempts to refine peaks of residual electron density of disordered solvent molecules were unsuccessful. Therefore the data were corrected for the contribution of a disordered solvent density using of the SQUEEZE procedure as implemented in PLATON. The total solvent accessible void volume is 1423 Å. Table 2. Crystal data and structure refinement conditions for Ni-Anth-MOF

The powder X-ray diffraction patterns for Cu-Anth-MOF and Ni-Anth-MOF were collected on a Bruker D8 Advance (Bruker AXS GmbH, Karlsruhe, Germany) diffractometer equipped with a LynxEye position sensitive detector, using copper radiation (CuK_α) at the wavelength of 1.54180 Å. The tube voltage and current were set to 40 kV and 40 mA, respec- tively. The divergence slit was set at 1.0 mm, and the antiscattering slit was set at 8.0 mm. The PXRD patterns were acquired using a scan speed of 0.25 s/0.02^◦ going from 3 to 35^◦ on the 2Θ scale. See Fig. 5 for PXRD of Cu-Anth-MOF. See Fig. 6 for PXRD of Ni-Anth- MOF. High-resolution dynamic thermal gravimetric analysis (TGA). Thermogravimetric analysis (TGA) was performed with TGA/DSC2 (Mettler Toledo). Open 100 µL aluminum pans were used. Heating of the samples: from 25 to 400 ^oC for Cu-Anth-MOF; from 25 to 600 ^oC for Ni-Anth-MOF. Heating rate: 10 °C·min^-1. Samples of ~3.3 mg mass were used, and the nitrogen flow rate was 100±10 mL·min^–1. See Fig. 7 for thermogravimetric curve for Cu-Anth-MOF. See Fig. 8 for thermogravimetric curve for Ni-Anth-MOF. Fluorescence in solution. Solution of MB in water was prepared with the final concentration 1 µmol/L, pH 7. Fluorescence emission spectrum was recorded with excitation at 290 nm (Fig. 11). Solid-state fluorescence. As-synthesized crystals were isolated by filtration, washed on filter, but not dried. Background fluorescence was measured with excitation at 290 nm (Fig. 12 for Cu-Anth-MOF and Fig. 14 for Ni-Anth-MOF). Crystals of MOF were soaked in aq. solu- tion of MB for 3 days at room temperature. The crystals were isolated by filtration and washed with water. Solid-state fluorescence emission spectrum was recorded with excitation at 290 nm (Fig. 13 for Cu-Anth-MOF and Fig. 15 for Ni-Anth-MOF). Then host-guest complexes of MOF with MB were suspended in water and equal amount of conc. aq. HCl was added. Mixture was incubated at 50 ºC for 8 h. All insolubles were filtered off, filtrate was neutralized to pH 7 with aq. satd. NaHCO₃ and fluorescence emission spectrum was recorded with excitation at 290 nm (Fig. 16 for Cu-Anth-MOF and Fig. 17 for Ni-Anth-MOF).

Claims

Claims 1. A microporous metal-organic framework (MOF) comprising tetradentate tetraphenylanthraquinone linking moieties and at least one secondary building unit (SBU) wherein secondary building unit comprises only metal ions or metal ions and oxygen atoms with O/metal ratio ˃0.5. 2. The metal-organic framework according to Claim 1 wherein metal ions are selected from Cu or Ni. 3. The metal-organic framework according to Claim 2 wherein the metal ion is Cu. 4. The metal-organic framework according to Claim 2 wherein the metal ion is Ni. 5. The metal-organic framework according to one of the preceding claims further comprising an encapsulated dye molecule. 6. The metal-organic framework according to Claim 1 wherein the O/metal ratio preferably is ˃0.6. 7. The metal-organic framework according to Claim 1 wherein the coordination polymer is ordered. 8. The metal-organic framework according to Claim 1 which encapsulates a dye molecule reversibly. 9. The metal-organic frameworks according to Claim 1 where pore apertures having an average diameter 1-10 Angstroms. 10. Use of MOF according to any of Claims 1-9 for quenching of fluorescence of encapsulated molecule.