Fluorescence anisotropy using highly polarized emitting dyes confined inside BNNTs

Polarized fluorescence emission of nanoscale emitters has been extensively studied for applications such as bioimaging, displays, and optical communication. Extending the polarization properties in large assemblies of compact emitters is, however, challenging because of self-aggregation processes, which can induce depolarization effects, quenching, and cancellations of molecular dipoles. Here we use α-sexithiophene (6T) molecules confined inside boron nitride nanotubes (6T@BNNTs) to induce fluorescence anisotropy in a transparent host. The experiments first indicate that individual 6T@BNNTs exhibit a high polarization extinction ratio, up to 700, at room temperature. Using aberration-corrected HRTEM, we show that the fluorescence anisotropy is consistent with a general alignment of encapsulated 6T molecules along the nanotube axis. The molecular alignment is weakly influenced by the nanotube diameter, a phenomenon ascribed to stronger molecule-to-sidewall interactions compared to intermolecular interactions. By stretching a flexible thin film made of transparent polymers mixed with 6T@BNNTs, we induce a macroscopic fluorescence anisotropy within the film. This work demonstrates that the dyes@BNNT system can be used as an easy-to-handle platform to induce fluorescence anisotropy in photonic materials.

Synthesis and characterization of phosphonated polybenzimidazole membranes with improved proton conductivity for high-temperature proton exchange membrane applications

The study has synthesized a novel dicarboxylic acid monomer with phosphonate group, 2-((diethoxyphosphoryl)methyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (PMDA), and then successfully prepared a series of polybenzimidazole polymers containing methyl-phosphonic acid group and ether group (POPBI-x) via the polycondensation between PMDA, 4,4′-oxybis (benzoic acid) (OBBA) and 3,3′-diaminobenzidine (DAB) in polyphosphoric acid (PPA)/phosphorus pentoxide (P2O5). Meanwhile, the smooth membranes were fabricated via the solution-casting method. Results of TGA, the Fenton’s reagent immersing test, and the tensile test showed that the POPBI-x membranes possessed good thermo-oxidative stability and mechanical properties. Moreover, compared to poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI), POPBI-x had a significant enhancement in the phosphoric acid doping level, PA retention ability, and proton conductivity after doped with phosphoric acid (PA) because the methyl-phosphonic acid groups on the backbones enriched the hydrogen bonding interactions between the polymer chain and phosphoric acid. Notably, the POPBI-19 exhibited a high phosphoric acid doping level of approximately 11.3 and excellent proton conductivity of approximately 0.0523 S cm−1 at 180°C under anhydrous conditions.

Interrogating Light-initiated Dynamics in Metal-Organic Frameworks with Time-resolved Spectroscopy

Time-resolved spectroscopy is an essential part of both fundamental and applied chemical research. Such techniques access light-initiated dynamics on time scales ranging from femtosecond to microsecond. Many techniques falling under this description have been applied to gain significant insight into metal-organic frameworks (MOFs), a diverse class of porous coordination polymers. MOFs are highly tunable, both compositionally and structurally, and unique challenges are encountered in applying time-resolved spectroscopy to interrogate their light-initiated properties. These properties involve various excited state mechanisms such as crystallographically defined energy transfer, charge transfer, and localization within the framework, photoconductivity, and structural dynamics. The field of time-resolved MOF spectroscopic studies is quite nascent; each original report cited in this review was published within the past decade. As such, this review is a timely and comprehensive summary of the most significant contributions in this emerging field, with focuses on the overarching spectroscopic concepts applied and on identifying key challenges and future outlooks moving forward.

Feasible polarised white-light emission based on conjugate plane-structured yellow/blue dye molecules encapsulated in metal-organic frameworks

We use a two-stage hierarchical growth method to encapsulate the blue KSN and yellow RhB molecules into a MOF crystal. By aligning these two conjugate plane-structured molecules in the MOF channel, a polarised white-light emission is obtained, with CIE coordinates of (0.3285, 0.3204) and a polarization ratio of 2.98.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.

Fluorine-Containing Triazole-Decorated Silver(I)-Based Cationic Metal-Organic Framework for Separating Organic Dyes and Removing Oxoanions from Water

Four new triazole-decorated silver(I)-based cationic metal-organic frameworks (MOFs), {[Ag(L1)](BF₄)}_n (1), {[Ag(L1)](NO₃)}_n (2), {[Ag(L2)](BF₄)}_n (3), and {[Ag(L2)](NO₃)}_n (4), have been synthesized using two newly designed ligands, 3-fluoro-5-(4H-1,2,4-triazol-4-yl)pyridine (L1) and 3-(4H-1,2,4-triazol-4-yl)-5-(trifluoromethyl)pyridine (L2). When the fluorine atom was changed to a trifluoromethyl group at the same position, tremendous enhancement in the MOF dimensionality was achieved [two-dimensional to three-dimensional (3D)]. However, changing the metal salt (used for the synthesis) had no effect. The higher electron-withdrawing tendency of the trifluoromethyl group in L2 aided in the formation of higher-dimensional MOFs with different properties compared with those of the fluoro derivatives. The fluoride group was introduced in the ligand to make highly electron-deficient pores inside the MOFs that can accelerate the anion-exchange process. The concept was proved by density functional theory calculation of the MOFs. Both 3D cationic MOFs were used for dye adsorption, and a remarkable amount of dye was adsorbed in the MOFs. In addition, owing to their cationic nature, the MOFs selectively removed anionic dyes from a mixture of anionic, cationic, and neutral dyes in the aqueous phase. Interestingly, the present MOFs were also highly effective for the removal of oxoanions (MnO₄^- and Cr₂O₇^2-) from water.

Antifungal activity of styrylpyridinium compounds against Candida albicans

We synthesized a set of 13 new and earlier described styrylpyridinium compounds (N-alkyl styrylpyridinium salts with bromide or tosylate anions) in order to evaluate antifungal activity against C. albicans cells, to assay the possible synergism with fluconazole, and to estimate cytotoxicity to mammalian cells. All compounds were synthesized according to a well-known two-step procedure involving alkylation of γ-picoline with appropriate alkyl bromide and further condensation with substituted benzaldehyde. Compounds with long N-alkyl chains (C₁₈ H₃₇ -C₂₀ H₄₁ ) had no antifungal activity against the cells of all tested C. albicans strains. Other styrylpyridinium compounds were able to inhibit yeast growth at the concentrations of 0.06-16 μg/ml. At fungicidal concentrations, the compound with the CN- group was least toxic to mammalian cells, showed the most effective synergism with fluconazole, and only slightly inhibited the respiration of C. albicans. The compound with the 4'-diethylamino group exhibited the strongest fungicidal properties and effectively blocked the respiration of C. albicans cells. However, toxicity to mammalian cells was also high. Summarizing, the results of our study indicate that styrylpyridinium compounds are promising candidates in the development of new antifungal drugs.

Encapsulation of stilbazolium-type dyes into layered metal–organic frameworks: solvent-dependent luminescence chromisms and their mechanisms

Dye@Cd-LMOCs composites exhibit interesting solvent-dependent chromismic fluorescence, in which a two step solvent exchange process and a new electron transfer route are proposed.

Nanovesicular MOF with Omniphilic Porosity: Bimodal Functionality for White-Light Emission and Photocatalysis by Dye Encapsulation

A new π-chromophoric and asymmetric bola-amphiphilic oligo-( p-phenylene ethynylene)-based tetracarboxylate (OPE-TC1) linker was designed, synthesized, and self-assembled with Zn(OAc)₂. The resulting nanoscale metal-organic framework (MOF) {Zn₂(OPE-TC1)} _n (NMOF-1) showed a vesicular morphology and permanent porosity with omniphilic pore surface. NMOF-1 showed cyan emission with high quantum efficiency (49%). The omniphilicity of the pore was utilized to incorporate ambipolar dye sulforhodamine G (SRG) to tune the band gap as well as to get pure white-light emission. Furthermore, the polar pore surface of NMOF-1 allowed facile diffusion of the substrate for efficient photocatalytic activity. The dye-encapsulated framework further showed enhanced dihydrogen production by 1.75-fold compared to that from the as-synthesized NMOF-1 because of the modulated band gap and high excited state lifetime. As a control experiment, we have synthesized a MOF (MOF-OMe) with an OPE-TC2 linker having -OMe functional groups that did not show nanoscale architecture. This suggested the important role of unsymmetrical bola-amphiphilicity in nanostructuring. This rational design of a chromophoric linker resulted in a nanoscale MOF with omniphilic porosity to achieve bimodal functionality in clean energy applications.

Tailoring adsorption induced phase transitions in the pillared-layer type metal-organic framework DUT-8(Ni)

Tailoring the characteristics of gating transitions in the porous network, Ni₂(ndc)₂dabco (ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane), also termed DUT-8(Ni) (DUT = Dresden University of Technology), was achieved by systematically adjusting the critical synthesis parameters. The impact of the starting composition and solvent mixtures in the synthesis was found to critically affect the guest-response properties of the obtained materials. A comprehensive set of physical characterization methods, namely thermal analysis, ¹H NMR of digested crystals, solid state ¹³C NMR, PXRD, SEM, IR and Raman spectroscopy shows that the crystallite size is a crucial factor, determining the differing characteristics such as "gate pressure" and adsorption capacity in the guest-responsive switching behaviour of DUT-8. Crystallites smaller than 500 nm in size retain the open form after removal of the guest molecules resulting in typical "Type Ia" isotherm, whereas crystallites larger than 1 μm transform into the "closed pore" form and therefore can show a characteristic "gate opening" behaviour during gas adsorption. The particle size distribution of DUT-8(Ni) can be tailored by changing the synthesis conditions and consequently the slope of the isotherm at the "gating step" is affected. The in depth analysis of synthesis conditions and switching behaviour is an important step towards a better understanding of the fundamental principles responsible for guest responsive porosity switching in the solid state.

Achieving Multicolor Long-Lived Luminescence in Dye-Encapsulated Metal-Organic Frameworks and Its Application to Anticounterfeiting Stamps

Long-lived luminescent metal-organic frameworks (MOFs) have attracted much attention due to their structural tunability and potential applications in sensing, biological imaging, security systems, and logical gates. Currently, the long-lived luminescence emission of such inorganic-organic hybrids is dominantly confined to short-wavelength regions. The long-wavelength long-lived luminescence emission, however, has been rarely reported for MOFs. In this work, a series of structurally stable long-wavelength long-lived luminescent MOFs have been successfully synthesized by encapsulating different dyes into the green phosphorescent MOFs Cd(m-BDC)(BIM). The multicolor long-wavelength long-lived luminescence emissions (ranging from green to red) in dye-encapsulated MOFs are achieved by the MOF-to-dye phosphorescence energy transfer. Furthermore, the promising optical properties of these novel long-lived luminescent MOFs allow them to be used as ink pads for advanced anticounterfeiting stamps. Therefore, this work not only offers a facile way to develop new types of multicolor long-lived luminescent materials but also provides a reference for the development of advanced long-lived luminescent anticounterfeiting materials.

Evaluating the component contribution to nonlinear optical performances using stable [Ni4O4] cuboidal clusters as models

Cuboidal [Ni₄O₄]-based clusters are systematically studied with the purpose of evaluating the component contribution to the overall nonlinear optical performances.

Acid- and base-stable porous mechanically interlocked 2D metal–organic polyrotaxane forin situorganochlorine insecticide encapsulation, sensing and removal

The encapsulation and removal of extremely toxic dieldrin by compound1.

Photonic functional metal–organic frameworks

The recent progress in photonic MOFs for luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, and biomedicine is summarized.

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal-Organic Framework for Fast White-Light Communication

A dye@metal-organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y₃Al₅O₁₂:Ce³⁺ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

Vibrational nonlinear optical properties of spatially confined weakly bound complexes

This study focuses on the theoretical description of the influence of spatial confinement on the electronic and vibrational contributions to (hyper)polarizabilities of two dimeric hydrogen bonded systems, namely HCNHCN and HCNHNC. A two-dimensional analytical potential is employed to render the confining environment (e.g. carbon nanotube). Based on the results of the state-of-the-art calculations, performed at the CCSD(T)/aug-cc-pVTZ level of theory, we established that: (i) the influence of spatial confinement increases with increasing order of the electrical properties, (ii) the effect of spatial confinement is much larger in the case of the electronic than vibrational contribution (this holds for each order of the electrical properties) and (iii) the decrease in the static nuclear relaxation first hyperpolarizability upon the increase of confinement strength is mainly due to changes in the harmonic term, however, in the case of nuclear relaxation second hyperpolarizability the anharmonic terms contribute more to the drop of this property.

Superlinear amplification of the first hyperpolarizability of linear aggregates of DANS molecules

A comprehensive study of optical properties of DANS in different environments explains the observed ∼30-fold enhancement of the hyper-Rayleigh signal of DANS@CNT vs. DANS in solution in terms of collective and cooperative phenomena occurring in aggregates of less than 10 aligned molecules.

Development of a viscosity sensitive fluorescent probe for real-time monitoring of mitochondria viscosity

Through rational design, two new mitochondria-targeted fluorescent viscosity probes were developed, which exhibited favorable properties such as large turn on fluorescence signal, good selectivity, low cytotoxicity, and high colocation coefficient (>0.90).

Single Fluorescent Probe for Dual-Imaging Viscosity and H2O2 in Mitochondria with Different Fluorescence Signals in Living Cells

Mitochondria, as essential and interesting organelles within the eukaryotic cells, play key roles in a variety of pathologies, and its abnormalities are closely associated with Alzheimer's disease (AD) and other diseases. Studies have shown that the abnormal of viscosity and concentration of hydrogen peroxide in mitochondria were all associated with AD. Accordingly, the detection of viscosity and hydrogen peroxide in mitochondria has attracted great attention. However, it remains a great challenge to explore a single probe, which can dual-detect the viscosity and H₂O₂ in mitochondria. Herein, in two ways to prevent the twisted internal charge transfer (TICT) process, we designed and sythesized the first dual-detection fluorescent probe Mito-VH that can visualize viscosity and H₂O₂ in mitochondria with different fluorescence signals in living cells.

A dye encapsulated terbium-based metal–organic framework for ratiometric temperature sensing

A ratiometric and colorimetric thermometer with high sensitivity and significant color change from 50 to 300 K has been developed by encapsulating the luminescent dye 7-diethylamino-4-methylcoumarin (C460) into the channels of a terbium-based MOFTbTATAB.