•A thermostable Eu/Tb-codoped MOF exhibiting strong luminescent at elevated temperature is reported.•The high-temperature operating range of Eu0.37Tb0.63-BTC-a is 313–473 K.•The mechanism of Eu0.37Tb0.63-BTC-a used as thermometers are also discussed.Temperature measurements and thermal mapping using luminescent MOF operating in the high-temperature range are of great interest in the micro-electronic diagnosis. In this paper, we report a thermostable Eu/Tb-mixed MOF Eu0.37Tb0.63-BTC-a exhibiting strong luminescence at elevated temperature, which can serve as a ratiometric luminescent thermometer for high-temperature range. The high-temperature operating range (313–473 K), high relative sensitivity and accurate temperature resolution, make such a Eu/Tb-mixed MOF useful for micro-electronic diagnosis.A thermostable Eu/Tb-mixed MOF Eu0.37Tb0.63-BTC-a was developed as a ratiometric luminescent thermometers in the high-temperature range of 313–473 K.

•A water-stable metal-organic framework (MOF) EuNDC was synthesized.•The highly selective detection of picric acid with a detection limit of 37.6 ppb was realized.•The detection mechanism were also presented and discussed.A water-stable metal-organic framework (MOF) EuNDC has been synthesized for selective detection of the well-known contaminant and toxicant picric acid (PA) in aqueous solution. Due to the photo-induced electron transfer and self-absorption mechanism, EuNDC displayed rapid, selective and sensitive detection of PA with a detection limit of 37.6 ppb. Recyclability experiments revealed that EuNDC retains its initial luminescent intensity and same quenching efficiency in each cycle, suggesting high photostability and reusability for long-term sensing applications. The excellent detection performance of EuNDC makes it a promising PA sensing material for practical applications.A water-stable europium-based metal-organic framework has been reported for highly selective sensing of picric acid (PA) with a detection limit of 37.6 ppb in aqueous solution.

The precise and real-time monitoring of localized pH changes is of great importance in many engineering and environmental fields, especially for monitoring small pH changes in biological environments and living cells. Metal–organic frameworks (MOFs) with their nanoscale processability show very promising applications in bioimaging and biomonitoring, but the fabrication of nanoscale MOFs is still a challenge. In this study, we synthesized a nanoscale mixed-lanthanide metal–organic framework by a microemulsion method. The morphology and size of the NMOF can be simply adjusted by the addition of different amounts of the CTAB surfactant. This NMOF exhibits significant pH-dependent luminescence emission, which can act as a self-referenced pH sensor based on two emissions of Tb3+ at 545 nm and Eu3+ at 618 nm in the pH range from 3.00 to 7.00. The MTT assay and optical microscopy assay demonstrate the low cytotoxicity and good biocompatibility of the nanosensor.

A MOF thermometer, Dycpia, utilizing thermally coupled energy levels (TCELs) has been realized. Based on two emissions originating from two TCELs, Dycpia enables self-referenced temperature sensing in the range from 298 to 473 K with a high resolution of 0.05 K.

A tetracarboxylic acid ligand containing a highly polarized benzothiadiazole moiety was designed and used to construct the luminescent porous MOF ZJU-21, which can efficiently absorb the luminescent dye 4-[p-(dimethylamino)styryl]-1-methylpyridinium (DMASM) into the pores as well as sensitize it, yielding a dual-emitting MOF⊃dye composite ZJU-21⊃DMASM. The emission color of the resulting composite can be modulated by controlling the amount of dyes, and the intensity ratio of the two emissions can be used as a ratiometric thermometric parameter for temperature measurement. ZJU-21⊃DMASM also exhibits excellent temperature-dependent photoluminescence properties in the physiological temperature range, which, as well as the temperature and sensitivity ranges, can be tuned by controlling the concentration of DMASM in the pores of the host framework. Moreover, the proposed scheme can be readily applied to other luminescent porous MOFs and organic dyes, thereby providing a new perspective for the design of MOF⊃dye ratiometric temperature sensors.

•A triazole-based UiO-66-PSM is synthesized by the CuAAC click reaction.•The triazole unit can act as the metal binding sites to coordinate with Hg2+.•It is capable of detecting Hg2+ in environmental water samples.A novel metal-organic framework (MOF) fluorescent probe UiO-66-PSM is obtained by the copper-catalyzed azide-alkyne click (CuAAC) reaction of UiO-66-N3 with phenylacetylene. The click-generated triazole unit can act as the metal binding site to coordinate with Hg2+, which exhibits the most pronounced fluorescence response (rapid response, excellent selectivity, and high sensitivity) over other metal ions. Moreover, it is capable of detecting Hg2+ in environmental water samples without any structural disintegration of the framework, indicating its high potential in practical applications.A novel metal-organic framework (MOF) UiO-66-PSM is obtained by the copper-catalyzed azide-alkyne click (CuAAC) reaction of UiO-66-N3 with phenylacetylene. This MOF exhibits the high potential in detecting Hg2+ in environmental water samples.Download high-res image (152KB)Download full-size image

•We designed a new metal-organic framework UiO-66-CH=CH2 for biological H2S sensing.•The responsive time was 10 s and the detection limit was 6.46 μM.•This probe has anti-interference especially from cysteine and glutathione.•This biological H2S probe features low cytotoxicity, water-stability and nanoscale.Hydrogen sulfide (H2S) has been commonly viewed as a gas signaling molecule in various physiological and pathological processes. However, the highly efficient H2S detection still remains challenging. Herein, we designed a new robust nano metal-organic framework (MOF) UiO-66-CH=CH2 as a fluorescent probe for rapid, sensitive and selective detection of biological H2S. UiO-66-CH=CH2 was prepared by heating ZrCl4 and 2-vinylterephthalic acid via a simple method. UiO-66-CH=CH2 displayed fluorescence quenching to H2S and kept excellent selectivity in the presence of biological relevant analytes especially the cysteine and glutathione. This MOF-based probe also exhibited fast response (10 s) and high sensitivity with a detection limit of 6.46 μM which was within the concentration range of biological H2S in living system. Moreover, this constructed MOF featured water-stability, nanoscale (20–30 nm) and low toxicity, which made it a promising candidate for biological H2S sensing.A nanoscale Zr-based fluorescent metal-organic framework was synthesized for selective and sensitive biological detection of hydrogen sulfide.Download high-res image (179KB)Download full-size image

•A porous Zn-based metal-organic framework (MOF) Zn-TBDA was prepared exhibiting negligible cytotoxicity.•Zn-TBDA showed desirable drug Methotrexate loading.•Zn-TBDA showed sensitive pH and temperature dual-responsive controlled release of Methotrexate.A porous metal-organic framework Zn-TBDA (TBDA = 4′-(1H-tetrazol-5-yl) -[1,1′-biphenyl]-3,5-dicarboxylic acid) with one-dimensional channels has been synthesized from zinc ions and bifunctional ligands. The negligible cytotoxicity of Zn-TBDA is confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay and microscopy observation. The anticancer drug methotrexate (MTX) is loaded into Zn-TBDA successfully via in-situ encapsulation and the loading capability reaches about 12.59 wt% in resulting composite MTX-encapsulated Zn-TBDA. Under different physiological microenvironments, MTX-encapsulated Zn-TBDA exhibits sensitive pH and temperature dual-responsive release manners, revealing its practical value as a smart drug carrier with controlled release in certain site and improved therapeutic efficacy without any additional external fields.A porous metal-organic framework (MOF) Zn-TBDA has been synthesized. The negligible cytotoxicity, desirable drug loading capability and controlled release manners of Zn-TBDA shows it can be used as a drug vehicle. Especially, the pH and temperature dual-responsive drug release of material confirms the potential applications of Zn-TBDA as a smart drug carrier.Download high-res image (208KB)Download full-size image

•A novel MOF film was fabricated on porous α-Al2O3 ceramic plate.•The europium functionalized MIL-1244@Eu3+ exhibited excellent ammonia sensitivity.•MIL-1244@Eu3+ sensor showed good long-term stability and repeatability.•The mechanism of the ammonia sensing property was explored by FT-IR spectrum.A novel metal-organic framework film MIL-124 film was prepared on porous α-Al2O3 ceramic plate by in situ synthesizing. After introducing Eu3+ ions to the free -COOH sites of the MIL-124 ligand channels, a luminescent MOF film MIL-124@Eu3+ was obtained. Based on the chemical reaction between NH3 and the -COOH, the formation of -COONH4 which was demonstrated by FT-IR spectrum, affected the energy transfer between Eu3+ ions and ligand, quenching the characteristic emission of MIL-124@Eu3+ film. The limit of detection to ammonia was calculated as 26.2 ppm in ambient air. The XRD results demonstrated the long-term stability of this ammonia sensor. The excellent performance and economical synthesizing strategy of the MIL-124@Eu3+ film exhibited potential application of this sensor for detecting ammonia gas.Download high-res image (243KB)Download full-size image

The first luminescent two-dimensional MOF nanosheets NTU-9-NS Ti2(HDOBDC)2(H2DOBDC) (H2DOBDC = 2,5-dihydroxyterephthalic acid) fabricated via top-down delamination have been realized for the highly sensitive sensing of Fe3+ with a fast response. The highly dispersive nature and highly accessible active sites on the surface of the 2D NTU-9-NS nanosheets enable them to have close contact with targeted metal ions, which leads to the highly sensitive sensing of Fe3+ ions, with a fast response time within seconds and the best detection limit performance of 0.45 μM among MOF materials. The fast response and highly sensitive Fe3+ sensing based on the NTU-9-NS nanosheets sensor material highlights the promise of the two-dimensional MOF nanosheet approach for luminescent sensing applications. This work contributes to the development of research on two-dimensional MOF nanosheets materials with targeted and specific recognition for the application of biological and environmental luminescent sensors.

A near-infrared luminescent metal–organic framework Nd0.866Yb0.134BTB was developed as a self-calibrated thermometer in the physiological range. Its features include high sensitivity and resolution, and good biocompatibility, making such a material useful for biomedical applications.

Metal–organic frameworks (MOFs), self-assembled from metal ions with organic ligands, are well known for their intriguing framework topology, permanent porosity, and tunable optical properties and have shown great promise for a good number of applications. Over the past few years, luminescent MOFs have attracted growing attention, especially for developing various luminescent sensors, by virtue of their excellent selectivity and high sensitivity. In this feature article, we highlight some of the recent significant progress in this active research field, and provide a comprehensive review on luminescent MOFs as sensory materials for diverse sensing applications including for metal ions, anions, small molecules and gases, nitroaromatics and explosives, temperature, as well as other aspects.

Two series of cationic dyes, named DM-n and DP-n, were encapsulated in three anionic isostructural MOFs with a 1D channel. Ordered arrangement of the dyes in the channel was investigated by using the microscope polarized absorption spectra of different dye and MOF composites. Furthermore, the tunable second order nonlinear optical properties of these MOF⊃dye materials were observed.

•A ratiometric near infrared luminescent MOFs thermometer (Nd0.676Yb0.324BTC) was prepared via a simple solvothermal method.•The maximum relative sensitivity of Nd0.676Yb0.324BTC is determined to be 1.187% K−1 at 323 K.•Nd0.676Yb0.324BTC showed excellent repeatability in the physiological temperature range (288–323 K).A near infrared luminescent MOFs thermometer (Nd0.676Yb0.324BTC) was prepared via a simple solvothermal method using Ln3+ (Ln=Nd, Yb) ions and 1, 3, 5-benznenetricarboxylic acid (H3BTC), and characterized by PXRD, TGA, ICP, and photoluminescence (PL) spectrum. These results indicate that the Nd0.676Yb0.324BTC displays high relative sensitivity and excellent repeatability in the physiological temperature range (288–323 K), and the maximum relative sensitivity is determined to be 1.187% K−1 at 323 K. These NIR luminescent MOFs may have potential applications in physiological temperature sensing.A near infrared luminescent MOFs thermometer (Nd0.054Yb0.946BTC ) displays high relative sensitivity and excellent repeatability in the physiological temperature range (288–323 K).

The sensing of hydrogen sulfide (H2S) has become a long-time challenging task. In this work, we developed a general strategy for sensing of H2S utilizing postsynthetic modification of a nano metal–organic frameworks (MOF) UiO-66-(COOH)2 with Eu3+ and Cu2+ ions. The nano MOF Eu3+/Cu2+@UiO-66-(COOH)2 displays the characteristic Eu3+ sharp emissions and the broad ligand-centered (LC) emission simultaneously. Because H2S can strongly increase the fluorescence of Eu3+ and quench the broad LC emission through its superior affinity for Cu2+ ions, the MOF Eu3+/Cu2+@UiO-66-(COOH)2 exhibits highly sensitive turn-on sensing of H2S over other environmentally and biologically relevant species under physiological conditions. Furthermore, this approach for fluorescent turn-on sensing of H2S is expected to extend to other water-stable MOFs containing uncoordinated −COOH.Keywords: fluorescent probes; hydrogen sulfide; metal−organic frameworks; ratiometric sensing; turn-on;

A near infrared pumped luminescent metal–organic framework thermometer Nd0.577Yb0.423BDC-F4, with near infrared fluorescence and excellent sensitivity in the physiological temperature range (293–313 K), has been first realized, and might be potentially applied for biomedical systems.

An important result of research on mixed-lanthanide metal–organic frameworks (M′LnMOFs) is the realization of highly sensitive ratiometric luminescent thermometers. Here, we report the design and synthesis of the new M′LnMOF Tb0.80Eu0.20BPDA with high relative sensitivity in the physiological temperature regime (298–318 K). The emission intensity and luminescence lifetime were investigated and compared to those of existing materials. It was found that the temperature-dependent luminescence properties of Tb0.80Eu0.20BPDA are strongly associated with the distribution of the energy levels of the ligand. Such a property can be useful in the design of highly sensitive M′LnMOF thermometers.

•Novel porous Cr2O3@TiO2 yolk/shell structure constructed from MIL-101(Cr).•Multiple-core structure with small core size and moderate BET surface area.•Exhibiting improved lithium storage performance compared with bare Cr2O3 due to the yolk/shell structure.To make use of a metal–organic framework MIL-101(Cr3+) as template and core generator, we report synthesis of a novel nanoscale yolk/shell octahedron of Cr2O3@TiO2 and its high performance as the anode material for lithium ion battery. Nanoscale MIL-101(Cr3+) was coated with amorphous TiO2 shell and calcinated under Ar and then in air atmospheres to form nanoscale Cr2O3@TiO2. After heat treatment, the amorphous TiO2 coated MIL-101(Cr) was transformed into nanosized Cr2O3 crystals with crystalline TiO2 cover, forming multicore yolk/shell octahedrons, as demonstrated from their SEM and TEM morphologies. The resulting Cr2O3@TiO2 has moderate porosity with the BET surface area of 146 m2 g−1, and the diameter of its Cr2O3 cores is 10–40 nm. It has demonstrated a reversible capacity of 510 mA h g−1 after 500 cycles at 0.5 C charge/discharge rate, which is much better than the bare nano Cr2O3 without TiO2 shell, and is one of the best-performed Cr2O3 anode materials. The improved electrochemical performance of Cr2O3@TiO2 is attributed to its small particle size with moderate porosity for the infiltration of electrolyte and the fast diffusion of Li+ ions, its void space within yolk/shell structure to buffer volumetric variation of Cr2O3 and its TiO2 shell to restrain pulverized inner particles.

SnO2 nanoparticles have been immobilized inside MIL-101(Cr) crystals achieving the novel SnO2@MIL-101(Cr) anode material with a multiple-core/shell structure. Under the protection of MIL-101(Cr) shell, the pulverization and aggregation of SnO2 during cycling have been diminished. Both good cyclability and rate capability with a reversible capacity of ∼510 mA h g−1 at 0.1C after 100 cycles have revealed.

•Two microporous metal-organic frameworks have been synthesized and characterized.•The metal-organic frameworks exhibit high acetylene storage capacity.•The metal-organic frameworks exhibit high selectivities of C2H2/CH4 and C2H2/CO2.Two isostructural metal-organic frameworks (MOFs) Cu2TPTC-Me and Cu2TPTC-OMe have been synthesized and characterized. The as-synthesized MOFs show good thermal stability and hydrothermal stability. With open metal sites, suitable pore spaces and functional groups to confine acetylene molecules in frameworks, both MOFs exhibit high gravimetric acetylene storage capacities: Cu2TPTC-Me has a gravimetric capacity of 203 cm3 g−1 at 298 K and 1 bar, and Cu2TPTC-OMe has the highest gravimetric acetylene storage capacity ever reported with the capacity of 204 cm3 g−1 under the same conditions. Furthermore, Cu2TPTC-Me possesses both high separation selectivities of C2H2/CH4 and C2H2/CO2 with the Henry law's selectivity of 60 and 12.7 at room temperature, respectively.

Luminescent metal–organic framework films, CPM-5⊃Tb3+ and MIL-100(In)⊃Tb3+, have been constructed by postfunctionalization of two porous indium–organic frameworks with different structures, respectively. The MIL-100(In)⊃Tb3+ film shows high oxygen sensitivity (KSV = 7.59) and short response/recovery time (6 s/53 s).

A lanthanide coordination polymer Tb0.957Eu0.043cpda was synthesized as a ratiometric and colorimetric luminescent thermometer. The high triplet excited state energy of a linker enables Tb0.957Eu0.043cpda to detect and visualize temperature over a wide range from cryogenic to room temperature (40–300 K).

Microporous metal–organic frameworks (MOFs) represent a new family of microporous materials, offering potential applications in gas separation and storage, catalysis, and membranes. The engineering of hierarchical superstructured MOFs, i.e., fabricating mesopores in microporous frameworks during the crystallization stage is expected to serve a myriad of applications for molecular adsorption, drug delivery, and catalysis. However, MOFs with mesopores are rarely studied because of the lack of a simple, effective way to construct mesoscale cavities in the structures. Here, we report the use of a perturbation-assisted nanofusion technique to construct hierarchically superstructured MOFs. In particular, the mesopores in the MOF structure enabled the confinement of large dye species, resulting in fluorescent MOF materials, which can serve as a new type of ratiometric luminescent sensors for typical volatile organic compounds.

•A new Li–S cathode using MOFs as host material.•Effective elimination of dissolution problem with high reversible capacity.•Very small charge-transfer resistance using binders with excellent electrical conductivity.Through the melt-diffusion method, S@ZIF-8, a sulfur and metal–organic framework (MOFs) ZIF-8 composite material has been synthesized and utilized as cathode for lithium sulfur battery. Encapsulated into the matrix of ZIF-8, sulfur molecules are restricted in the cages with small apertures and the dissolution problem during the charge/discharge process has been alleviated. Owing to the strong confinement of ZIF-8 matrix to the sulfur molecules inside, the Li–S@ZIF-8 battery shows a reverse capacity of ∼510 mAh/g after 100 cycles at a 0.1 C charge/discharge rate, enabling the S@MOFs materials promising candidates for novel lithium–sulfur battery cathodes.Graphical abstract

•Two new phenyltetraene-based chromophores with alkylthio group were synthesized.•Inorganic–organic hybrid films are prepared through sol–gel process.•Incorporation of alkylthio group effectively improves the nonlinear optical property.Two new chromophores, CLDS1 and CLDS2, based on a similar D–π–A structure as the phenyltetraene chromophore CLD, but with an alkylthio group perpendicular to the direction of the long molecular axis as isolation spacer were synthesized. Through a urethane forming reaction between 3-isocyanatopropyltriethoxysilane (ICTES) and chromophores, the alkoxysilane dyes were synthesized. Subsequently, a series of transparent and homogeneous inorganic-organic hybrid films were prepared via a sol–gel process of the alkoxysilane dye with triethoxyvinylsilane. The molecular structures of the resultants were confirmed by 1H NMR, FTIR and UV–visible spectra. After electric poling, the nonlinear optical coefficients (d33) of the hybrid films F-CLDS1 and F-CLDS2 were determined to be 104.54 and 98.17 pm V−1, respectively, which are almost 3 times the d33 value of hybrid film containing CLD (37.78 pm V−1), indicating that the incorporation of alkylthio group can efficiently improve the macroscopic optical nonlinearities of hybrid materials.

•Continuous In-BTC films were prepared using in situ solvothermal synthesis method.•The Pt nanoparticles improve the heterogeneous nucleation and growth of In-BTC films.•Luminescent films were achieved by post-functionalizing In-BTC with lanthanide ions.•Luminescent films show good performance in fast detection of thiol vapors.Continuous and well-attached thin films of indium trimesate metal–organic framework (MOF) were prepared rapidly by in situ solvothermal synthesis method on silicon wafer modified with platinum nanoparticles. The film growth process and possible mechanism were studied in detail. Luminescent metal–organic framework thin films, In-BTC⊃Ln, were achieved by the post-functionalization of the resulted MOF film In-BTC with lanthanide ions (Eu3+, Tb3+, Dy3+ or Sm3+). The structure and morphology of the films were investigated by XRD and SEM. The luminescent properties of the In-BTC⊃Ln films indicate that lanthanide ions are sensitized by organic linker via the metal carboxylates in the pores. More interestingly, the luminescent In-BTC⊃Ln films show good performance in fast detection of volatile thiols such as 1,2-ethanedithiol and 1-butanethiol.Continuous luminescent MOF films, In-BTC⊃Ln were achieved by the post-functionalization of In-BTC films with lanthanide ions. And luminescent films show good performance in fast detection of vaporous thiols.

•A new metal–organic framework (ZJU-26) was synthesized.•ZJU-26 displays large adsorption enthalpies of 32.7 kJ/mol for C2H2.•ZJU-26 exhibited high separation selectivity for C2H2/CH4 and C2H2/CO2.A new three-dimensional micro-porous metal–organic framework Cu2(ADDI) (ZJU-26; H4ADDI = 5,5′-(anthracene-2,6-diyl) diisophthalic acid) with open metal sites and suitable pore space for their interactions with acetylene molecules was solvothermally synthesized and structurally characterized. ZJU-26 reveals a three-dimensional structure having hexagonal pores of about 5.0 Å along the c axis and irregular pores of about 3.4 × 8.5 Å2 along the a or b axis. Due to the introduction of anthracene ring do significantly enlarge pore size along a/b axis and enhance the interaction between MOF and acetylene, ZJU-26 indicates large adsorption enthalpies of 32.7 kJ/mol for C2H2 and moderately high acetylene uptake of 84 cm−1/g, highlighting ZJU-26 as the highly selective microporous metal organic framework for the C2H2/CH4 and C2H2/CO2 gas separation with separation selectivity of 45.9 and 12.5 at room temperature.

•Continuous indium metal-organic framework thin films are prepared.•The growth process and the possible growth mechanism of thin films are investigated.•Indium tin oxide glass promotes the homogeneous nucleation of thin films.Continuous indium metal-organic framework thin films of In12O(OH)12[(OH)4·(H2O)5)][BTC]6 (MIL-96(In)) (BTC = 1,3,5-benzenetricarboxylate) were prepared on indium tin oxide glass by in situ solvothermal growth method. The structure of the films was confirmed by X-ray diffraction. The growth process and the possible growth mechanism of MIL-96(In) films were investigated by a scanning electron microscopy. Furthermore, the influence of the reaction conditions on the morphology and thickness of films was studied. The best crack-free, continuous film with thickness of approximate 6 μm was obtained at the proper concentrations of InCl3 and H3BTC of 25.0 mmol·l− 1 at 100 °C for 12 h.

•Inorganic-organic hybrid films are prepared via sol-gel process of alkoxysilane dyes•Nonlinear optical properties of hybrid films are investigated•Fluorinated benzene group effectively improves the nonlinear optical propertyTwo azo chromophores containing fluorinated benzene and alkyl chain as isolation group were designed and synthesized, respectively, and the corresponding alkoxysilane dyes were obtained by coupling 3-isocyanatopropyltriethoxysilane with the chromophores. The molecular structures were verified by elemental analysis, hydrogen nuclear magnetic resonance, and Fourier transform infrared spectrum. Followed by a sol–gel process of the alkoxysilane dyes, inorganic–organic hybrid films were prepared by spin-coating. After electric poling, these hybrid films show the higher nonlinear optical (NLO) response than their analog containing chromophore DR1. Furthermore, the fluorinated benzene group exhibits better enhanced effect than the flexible alkyl group. The highest NLO coefficients (d33) of the hybrid film containing fluorinated benzene group was determined to be 140.5 pm V− 1 at the chromophore concentration of 40%.

Three new six-branched chromophores with different isolation groups were designed and synthesized by incorporating azo chromophores onto phenyl glycerol ester via an esterification reaction. The chemical structures were confirmed by 1H NMR, 13C NMR, FT-IR spectroscopy, mass spectrometry, element analysis and UV-visible absorption spectra. The six-branched dendritic chromophores can form thin films directly without adding any polymer matrix and show a quite high chromophore loading density. After electric poling, the nonlinear optical coefficients (d33) of the dendrimer films were determined to be around 113, 142 and 136 pm V−1, which are almost 3 times the maximum d33 value of the azo-chromophore doped polymer films. The further improvement in optical nonlinearity was successfully realized by mixing the six-branched chromophores containing different isolation groups.

A new six-branched chromophore GGQ1 is designed and synthesized via the incorporation of an FTC-type chromophore 1 with phenyl glycerol ester. The six-branched chromophore GGQ1 shows a large molecular weight of 3834 Daltons and can directly form thin films with quite high active chromophore loading density. For comparison, guest–host doped polymer films are fabricated by doping chromophore 1 and BF1 into poly(4-vinylphenol). All of these doped films show a saturated trend in second harmonic generation coefficient (d33) and a maximum d33 value between 50–70 pm V−1 around the doping concentration of 25 wt%, due to the strong interchromophore electrostatic interactions. In contrast, GGQ1 films display a d33 value of 192 pm V−1. The results indicate that the six-branched chromophore could efficiently reduce the interchromophore electrostatic interactions and enhance the macroscopic optical nonlinearity, showing promise for applications in nonlinear optical (NLO) materials.

A thiophene-vinyl conjugated FTC-type chromophore was synthesized and reacted with 3-isocyanatopropyltriethoxysilane to form alkoxysilane dye. The structure of alkoxysilane dye was confirmed via elemental analysis, FTIR and 1H NMR. Stable and transparent hybrid films were fabricated following sol–gel process of alkoxysilane dye and tetraethoxysilane. The second harmonic generation coefficients (d33) of the hybrid films were measured via in situ second harmonic generation measurement. The d33 value of hybrid films was calculated to be 43 pm V−1 when the chromophore loading density was 20 mol%. Furthermore, the thermal stability of optical nonlinearity was also investigated through a depoling experiment, showing a half decay temperature of 165 °C.

A new nonlinear optical (NLO) chromophore 4-dicyanomethylene-2-methyl-6- {4-[4-(N-ethyl-N-hydroxyethylamino)phenylazo]}styryl-4H-pyran (AZP), which features extended conjugated chain based on DCM laser dye, was synthesized and functionalized with alkoxysilane for materials processing. Hybrid films containing chromophore AZP and DCM were prepared via a sol–gel processing. The d33 values of films containing AZP are 39-48 pm/V varying with concentration of chromophores, which is similar to that containing DCM. By tuning the organic content, the thermal stability of d33 values can be significantly improved by about 30 °C, about 15 °C higher than those containing DCM. The residual rotational stress, along with cavity between chromophores and matrix, is proposed to contribute to the stability of NLO activity of hybrid films.

The structure of a novel bichromophore that comprised a readily hyperpolarisable chromophore with 3-phenoxypropane-1, 2-diol via esterification, was confirmed by elemental analysis, UV–visible absorption spectra and 1H NMR. Nonlinear optical polymer films were fabricated by doping the bichromophore and the corresponding monochromophore into poly(4-vinylphenol). In situ second harmonic generation measurements revealed that the bichromophore imparted a 2.2-fold enhancement in the second harmonic generation coefficients of the films, indicating that the novel 3-phenoxypropane-1, 2-diol derivative could be used in the design and synthesis of multi-chromophoric dendrimers with large macroscopic optical nonlinearity.

An alkoxysilane precursor based on imidazole chromophore, namely 2-((4-(ethyl(2-hydroxyethyl)amino)phenyl)diazenyl)-4,5-dicyano-1H-imidazole (IZ), has been successfully synthesized through a urethane forming reaction. Following a sol–gel process of the resultant precursor, inorganic–organic hybrid films were obtained by spin-coating. Their structures were verified by 1H NMR, FT-IR, UV–vis spectra and elemental analysis. After corona poling, the electro-optic (EO) properties of the hybrid films were characterized by a simple reflection technique, and the EO coefficient (r33) of a sample was determined to be 1.6 pm/V at a wavelength of 1310 nm.

A series of novel inorganic−organic hybrid materials with benzimidazole chromophores covalently bonded into the inorganic silica network as pendants has been designed and synthesized via the wet chemistry routes. The measurement results of solvatochromic method and UV−vis spectra indicate that these benzimidazole chromophores exhibit higher microscopic optical nonlinearity compared with their analogues with benzene ring and without undesirable red-shift of the absorption band. After corona poling, the macroscopic nonlinear optical activity and poling alignment stability of the hybrid films were investigated by in situ second harmonic generation measurement. These hybrid films exhibit enhanced nonlinear optical coefficient from 25 to 54 pm/V with chromophore concentration varied, improved optical transparency (λmax < 470 nm), as well as excellent polar orientation stability at 160 °C.

A new hetero-trichromophore (HT-1) was designed and synthesized by linking neutral-ground-state (NGS) chromophore 1 with zwitterionic (ZWI) chromophore 2, and their molecular structures were confirmed by elemental analysis, UV−vis absorption spectra, 1H NMR, etc. Theoretical calculations show that there is a decrease of molecular dipole moments in gas phase when chromophores 1 and 2 are linked together. The polymer films were fabricated by doping trichromophore HT-1, NGS chromophore 1, and ZWI chromophore 2 into poly(4-vinylphenol) (PVPh). The second harmonic generation coefficients (d33) of the films and the thermal stability of optical nonlinearities were measured by in situ second harmonic generation (SHG) measurement. The results show that almost a 5-fold enhancement in second harmonic coefficients (d33) is realized as the combination of NGS chromophore and ZWI chromophore. The results indicate that NGS and ZWI chromophore combined hetero-trichromophores can efficiently improve the macroscopic optical nonlinearities in poled polymer materials.

Two azole heterocycle-contained chromophores, named EBTC and EBOC respectively, were synthesized and then reacted with 3-isocyannatopropyltriethoxysilane (ICTES) to form functionalized alkoxysilane dyes (ASDs) which were named as ASD-EBTC and ASD-EBOC, respectively. Sol solutions were obtained after co-hydrolysis/condensation of ASD and tetraethoxysilane (TEOS). Second-order nonlinear optical (NLO) inorganic–organic hybrid films were successfully prepared via sol–gel process. The second harmonic coefficients (d33) of poled hybrid films were measured by a Maker fringe technique. The d33 values obtained for the EBTC and EBOC films are 23.7 and 9.3 pm/V, respectively. The hybrid film containing benzothiazole exhibited better NLO properties than its analogue containing benzoxazole.

The precise and real-time monitoring of localized pH changes is of great importance in many engineering and environmental fields, especially for monitoring small pH changes in biological environments and living cells. Metal–organic frameworks (MOFs) with their nanoscale processability show very promising applications in bioimaging and biomonitoring, but the fabrication of nanoscale MOFs is still a challenge. In this study, we synthesized a nanoscale mixed-lanthanide metal–organic framework by a microemulsion method. The morphology and size of the NMOF can be simply adjusted by the addition of different amounts of the CTAB surfactant. This NMOF exhibits significant pH-dependent luminescence emission, which can act as a self-referenced pH sensor based on two emissions of Tb3+ at 545 nm and Eu3+ at 618 nm in the pH range from 3.00 to 7.00. The MTT assay and optical microscopy assay demonstrate the low cytotoxicity and good biocompatibility of the nanosensor.

Microporous metal–organic frameworks (MOFs) represent a new family of microporous materials, offering potential applications in gas separation and storage, catalysis, and membranes. The engineering of hierarchical superstructured MOFs, i.e., fabricating mesopores in microporous frameworks during the crystallization stage is expected to serve a myriad of applications for molecular adsorption, drug delivery, and catalysis. However, MOFs with mesopores are rarely studied because of the lack of a simple, effective way to construct mesoscale cavities in the structures. Here, we report the use of a perturbation-assisted nanofusion technique to construct hierarchically superstructured MOFs. In particular, the mesopores in the MOF structure enabled the confinement of large dye species, resulting in fluorescent MOF materials, which can serve as a new type of ratiometric luminescent sensors for typical volatile organic compounds.

Two series of cationic dyes, named DM-n and DP-n, were encapsulated in three anionic isostructural MOFs with a 1D channel. Ordered arrangement of the dyes in the channel was investigated by using the microscope polarized absorption spectra of different dye and MOF composites. Furthermore, the tunable second order nonlinear optical properties of these MOF⊃dye materials were observed.

A tetracarboxylic acid ligand containing a highly polarized benzothiadiazole moiety was designed and used to construct the luminescent porous MOF ZJU-21, which can efficiently absorb the luminescent dye 4-[p-(dimethylamino)styryl]-1-methylpyridinium (DMASM) into the pores as well as sensitize it, yielding a dual-emitting MOF⊃dye composite ZJU-21⊃DMASM. The emission color of the resulting composite can be modulated by controlling the amount of dyes, and the intensity ratio of the two emissions can be used as a ratiometric thermometric parameter for temperature measurement. ZJU-21⊃DMASM also exhibits excellent temperature-dependent photoluminescence properties in the physiological temperature range, which, as well as the temperature and sensitivity ranges, can be tuned by controlling the concentration of DMASM in the pores of the host framework. Moreover, the proposed scheme can be readily applied to other luminescent porous MOFs and organic dyes, thereby providing a new perspective for the design of MOF⊃dye ratiometric temperature sensors.

A MOF thermometer, Dycpia, utilizing thermally coupled energy levels (TCELs) has been realized. Based on two emissions originating from two TCELs, Dycpia enables self-referenced temperature sensing in the range from 298 to 473 K with a high resolution of 0.05 K.

Three new six-branched chromophores with different isolation groups were designed and synthesized by incorporating azo chromophores onto phenyl glycerol ester via an esterification reaction. The chemical structures were confirmed by 1H NMR, 13C NMR, FT-IR spectroscopy, mass spectrometry, element analysis and UV-visible absorption spectra. The six-branched dendritic chromophores can form thin films directly without adding any polymer matrix and show a quite high chromophore loading density. After electric poling, the nonlinear optical coefficients (d33) of the dendrimer films were determined to be around 113, 142 and 136 pm V−1, which are almost 3 times the maximum d33 value of the azo-chromophore doped polymer films. The further improvement in optical nonlinearity was successfully realized by mixing the six-branched chromophores containing different isolation groups.

A lanthanide coordination polymer Tb0.957Eu0.043cpda was synthesized as a ratiometric and colorimetric luminescent thermometer. The high triplet excited state energy of a linker enables Tb0.957Eu0.043cpda to detect and visualize temperature over a wide range from cryogenic to room temperature (40–300 K).

A near-infrared luminescent metal–organic framework Nd0.866Yb0.134BTB was developed as a self-calibrated thermometer in the physiological range. Its features include high sensitivity and resolution, and good biocompatibility, making such a material useful for biomedical applications.

A new six-branched chromophore GGQ1 is designed and synthesized via the incorporation of an FTC-type chromophore 1 with phenyl glycerol ester. The six-branched chromophore GGQ1 shows a large molecular weight of 3834 Daltons and can directly form thin films with quite high active chromophore loading density. For comparison, guest–host doped polymer films are fabricated by doping chromophore 1 and BF1 into poly(4-vinylphenol). All of these doped films show a saturated trend in second harmonic generation coefficient (d33) and a maximum d33 value between 50–70 pm V−1 around the doping concentration of 25 wt%, due to the strong interchromophore electrostatic interactions. In contrast, GGQ1 films display a d33 value of 192 pm V−1. The results indicate that the six-branched chromophore could efficiently reduce the interchromophore electrostatic interactions and enhance the macroscopic optical nonlinearity, showing promise for applications in nonlinear optical (NLO) materials.

A near infrared pumped luminescent metal–organic framework thermometer Nd0.577Yb0.423BDC-F4, with near infrared fluorescence and excellent sensitivity in the physiological temperature range (293–313 K), has been first realized, and might be potentially applied for biomedical systems.

The first luminescent two-dimensional MOF nanosheets NTU-9-NS Ti2(HDOBDC)2(H2DOBDC) (H2DOBDC = 2,5-dihydroxyterephthalic acid) fabricated via top-down delamination have been realized for the highly sensitive sensing of Fe3+ with a fast response. The highly dispersive nature and highly accessible active sites on the surface of the 2D NTU-9-NS nanosheets enable them to have close contact with targeted metal ions, which leads to the highly sensitive sensing of Fe3+ ions, with a fast response time within seconds and the best detection limit performance of 0.45 μM among MOF materials. The fast response and highly sensitive Fe3+ sensing based on the NTU-9-NS nanosheets sensor material highlights the promise of the two-dimensional MOF nanosheet approach for luminescent sensing applications. This work contributes to the development of research on two-dimensional MOF nanosheets materials with targeted and specific recognition for the application of biological and environmental luminescent sensors.