Guanidinium Cations Research Articles

The Dynamic Range of Acidity: Tracking Rules for the Unidirectional Penetration of Cellular Compartments.

Labeled ammonium cations with pK a∼7.4 accumulate in acidic organelles because they can be neutralized transiently to cross the membrane at cytosolic pH 7.2 but not at their internal pH<5.5. Retention in early endosomes with less acidic internal pH was achieved recently using weaker acids of up to pK a 9.8. We report here that primary ammonium cations with higher pK a 10.6, label early endosomes more efficiently. This maximized early endosome tracking coincides with increasing labeling of Golgi networks with similarly weak internal acidity. Guanidinium cations with pK a 13.5 cannot cross the plasma membrane in monomeric form and label the plasma membrane with selectivity for vesicles embarking into endocytosis. Self‐assembled into micelles, guanidinium cations enter cells like arginine‐rich cell‐penetrating peptides and, driven by their membrane potential, penetrate mitochondria unidirectionally despite their high inner pH. The resulting tracking rules with an approximated dynamic range of pK a change ∼3.5 are expected to be generally valid, thus enabling the design of chemistry tools for biology research in the broadest sense. From a practical point of view, most relevant are two complementary fluorescent flipper probes that can be used to image the mechanics at the very beginning of endocytosis.

A new bis(oxalato)ferrate(III) hybrid salt associated with guanidinium cations : Synthesis, crystal structure, magnetic properties and Hirshfeld surface analysis

A new organic-inorganic hybrid salt (CH6N3)2[Fe(C2O4)2(H2O)Cl] (1) (CH6N3+ = guanidinium cation) has been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction, EPR, SQUID magnetometry and Hirshfeld surface analysis. The asymmetric unit of salt 1 consists of one [Fe(C2O4)2(H2O)Cl]2– complex anion and two protonated guanidine molecules 2 CH6N3+. The FeIII ion in the complex anion shows a distorted octahedral coordination environment, with four O atoms from two chelating oxalate dianions, one O atom from a water molecule and one Cl− anion. A packing diagram of 1 highlights pillars of the [Fe(C2O4)2(H2O)Cl]2– complex anions and guanidinium CH6N3+ cations along the crystallographic a axis. These ionic entities are connected via intermolecular O–H···O, N–H···O and N–H···Cl hydrogen bonds into a three-dimensional network. Investigation of the thermal behavior of the compound confirmed its anhydrous character. The EPR spectrum of 1 corresponds to the Fe(III) oxidation state in an octahedral environment. The magnetic susceptibility measurements in the 2–300 K temperature range revealed weak antiferromagnetic interactions in salt 1. Hirshfeld surface analysis has also been evaluated to reveal various intermolecular interactions in 1.

Hybrid Antimicrobial Films Containing a Polyoxometalate-Ionic Liquid.

The increasing resistance of pathogenic microorganisms against common treatments requires innovative concepts to prevent infection and avoid long-term microbe viability on commonly used surfaces. Here, we report the preparation of a hybrid antimicrobial material based on the combination of microbiocidal polyoxometalate-ionic liquids (POM-ILs) and a biocompatible polymeric support, which enables the development of surface coatings that prevent microbial adhesion. The composite material is based on an antibacterial and antifungal room-temperature POM-IL composed of guanidinium cations (N,N,N′,N′-tetramethyl-N″, N″-dioctylguanidinum) combined with lacunary Keggin-type polyoxotungstate anions, [α-SiW11O39]8–. Integration of the antimicrobial POM-IL into the biocompatible, flexible, and stable polymer poly(methyl methacrylate) (PMMA) results in processable films, which are suitable as surface coatings or packaging materials to limit the proliferation and spread of pathogenic microorganisms (e.g., on public transport and hospital surfaces, or in ready-to-eat-food packaging).

Multifunctional Molecule Modification toward Efficient Carbon‐Based All‐Inorganic CsPbIBr2 Perovskite Solar Cells

AbstractFavorable stability is a big challenge for the commercialization of perovskite solar cells, and all‐inorganic perovskite semiconductors have attracted much attention due to their excellent performance in this field. In reality, the poor stability is mainly due to the high‐density defects in the perovskite films, which provide a channel for charge nonradiative recombination and ion migration. In this work, a multifunctional aminoguanidine hemisulfate (AG HSUL) is introduced into the CsPbIBr2 perovskite layer to achieve defect passivation. Guanidine cations (GA+) can form strong hydrogen bonds with under‐coordinated halogen ions to stabilize the crystal lattice; the nitrogen atom in the amino group can form a complex with the under‐coordinated lead ion; inorganic acids and ions can not only compensate for halogen anion vacancies, but also combine with lead clusters or capped lead ions to reduce defect density. The synergistic effect of anions and cations can effectively passivate the defects, and an energy conversion efficiency of 10.10% is obtained at the optimal concentration of modification. In addition, carbon electrodes are used instead of metal electrodes, which greatly reduces the cost. The results provide a new idea for the development of efficient all‐inorganic CsPbIBr2 perovskite solar cells.

NH4Br‐Assisted Two‐Step‐Processing of Guanidinium‐Rich Perovskite Films for Extremely Stable Carbon‐Based Perovskite Solar Cells in Ambient Air

The substitution of a portion of methylammonium (MA) for guanidinium (GA) has been verified to be able to enhance the stability of MA‐based devices. However, high‐dose guanidinium cation will introduce localized distortions to the perovskite lattice structure and destroy the microstructure of the perovskite films, impairing the stability and reproducibility of perovskite solar cells (PSCs) eventually. Herein, for the first time, the NH4Br‐assisted all‐atmospheric two‐step process is adopted to fabricate GA‐rich (20%) perovskite films. The NH4Br induces the formation of the intermediate phase NH4PbI3 and alleviates the disorder of the octahedron caused by the big GA. Consequently, the modified perovskite film shows increased tolerance for the roughness fluctuation and reduced risk of forming voids and pinholes. The fabricated compact GA‐rich perovskite films behave extremely well in photovoltaic performance when assembled as carbon‐based perovskite solar cells, delivering a high power conversion efficiency (PCE) of 16.19% and stability against moisture and sunlight. Especially, the unencapsulated devices in ambient air sustain 95.1%, 91.8%, and 95.7% of their initial PCEs after 2400 h of storage, after 1000 h of 65 °C heat environment, and after 800 h of sunlight illumination, respectively.

Surface Treatment of Inorganic CsPbI3 Nanocrystals with Guanidinium Iodide for Efficient Perovskite Light-Emitting Diodes with High Brightness

HighlightsA facile and effective surface passivation strategy was demonstrated to improve the optical and stability of CsPbI3 nanocrystals by using guanidinium iodide post-treatment.Guanidinium cations was shown to be compatible with CsPbI3 perovskite, leading to significantly improved surface properties of CsPbI3 nanocrystals.Performance of the CsPbI3 nanocrystal-based light-emitting device was enhanced by 3.6 folds.

Inhibiting Ion Migration by Guanidinium Cation Doping for Efficient Perovskite Solar Cells with Enhanced Operational Stability

Perovskite solar cells (PSCs) develop great potential to make photovoltaic power generation systems more cost‐effective due to the high power conversion efficiency (PCE), low material cost, and easy fabrication. Alloyed A‐site cations surrounded by PbI6 octahedra play decisive roles in the crystal structure, bandgap, and phase stability, as well as ion migration. Herein, based on the temperature‐dependent ion conductivity measurement, the activation energy for iodide ion migration is systematically studied with different proportions of guanidinium cation (GA+) substitution. It is found that partial GA+ doping could effectively suppress iodide ion migration. The triple‐cation perovskite (MA0.8FA0.1GA0.1PbI3) PSCs achieve a PCE of 22.17% with superior operational stability maintaining 90% of their initial efficiency after 1200 h under continuous light soaking. Furthermore, it is extended to mini perovskite solar modules, 14 cm2 active area, and achieves a PCE of 19.18%.

Internal Interactions between Mixed Bulky Organic Cations on Passivating Defects in Perovskite Solar Cells.

In perovskite solar cells (PSCs), bulky organic cation halide salt additions play a significant role in suppressing nonradiative recombination by passivating intrinsic defects in perovskites. Herein, a passivation treatment is developed by applying mixed bulky cations [guanidinium cation (GA+) and phenylethylammonium cations (PEA+)] as the additive for perovskite thin films. The internal interactions between the two bulky cations could result in lower carrier trap-state densities, a sharper Urbach tail, and better carrier transport in perovskite films in comparison with a control film. As a result, in comparison to the control device, which has a power conversion efficiency (PCE) of 18.92%, the mixed-cation-based device exhibits a dramatic enhancement of PCE of 20.64%. Importantly, after 720 h of storage in an ambient atmosphere with a relative humidity (RH) of 60-80% at room temperature, the mixed-cation-based device retains 62.7% of its original performance, whereas the control devices decay to less than 40% of their original performance.

Guanidinium-Pseudohalide Perovskite Interfaces Enable Surface Reconstruction of Colloidal Quantum Dots for Efficient and Stable Photovoltaics.

Complete surface passivation of colloidal quantum dots (CQDs) and their strong electronic coupling are key factors toward high-performance CQD-based photovoltaics (CQDPVs). Also, the CQD matrices must be protected from oxidative environments, such as ambient air and moisture, to guarantee air-stable operation of the CQDPVs. Herein, we devise a complementary and effective approach to reconstruct the oxidized CQD surface using guanidinium and pseudohalide. Unlike conventional halides, thiocyanate anions provide better surface passivation with effective replacement of surface oxygen species and additional filling of defective sites, whereas guanidinium cations promote the construction of epitaxial perovskite bridges within the CQD matrix and augment electronic coupling. Additionally, we replace a defective 1,2-ethanedithiol-treated CQD hole transport layer (HTL) with robust polymeric HTLs, based on a judicious consideration of the energy level alignment established at the CQD/HTL interface. These efforts collectively result in high-performance and stable CQDPVs with photocurrents over 30 mA cm-2, ∼80% quantum efficiency at excitonic peaks and stable operation under humid and ambient conditions. Elucidation of carrier dynamics further reveals that interfacial recombination associated with band alignment governs both the CQDPV performance and stability.

Eu(iii)-Functionalized HOFs based on machine learning-assisted fluorescence sensing: discrimination of quinolonesviaPCA and BPNN models

A Eu@HOF-GS-10 sensor has been preparedviaion exchange between Eu3+ions and guanidine cations, which can be utilized for fluorescence discrimination of quinolones based on PCA and BPNN models.

A combination therapy strategy for treating antibiotic resistant biofilm infection using a guanidinium derivative and nanoparticulate Ag(0) derived hybrid gel conjugate.

Bacteria organized in biofilms show significant tolerance to conventional antibiotics compared to their planktonic counterparts and form the basis for chronic infections. Biofilms are composites of different types of extracellular polymeric substances that help in resisting several host-defense measures, including phagocytosis. These are increasingly being recognized as a passive virulence factor that enables many infectious diseases to proliferate and an essential contributing facet to anti-microbial resistance. Thus, inhibition and dispersion of biofilms are linked to addressing the issues associated with therapeutic challenges imposed by biofilms. This report is to address this complex issue using a self-assembled guanidinium–Ag(0) nanoparticle (AD-L@Ag(0)) hybrid gel composite for executing a combination therapy strategy for six difficult to treat biofilm-forming and multidrug-resistant bacteria. Improved efficacy was achieved primarily through effective biofilm inhibition and dispersion by the cationic guanidinium ion derivative, while Ag(0) contributes to the subsequent bactericidal activity on planktonic bacteria. Minimum Inhibitory Concentration (MIC) of the AD-L@Ag(0) formulation was tested against Acinetobacter baumannii (25 μg mL−1), Pseudomonas aeruginosa (0.78 μg mL−1), Staphylococcus aureus (0.19 μg mL−1), Klebsiella pneumoniae (0.78 μg mL−1), Escherichia coli (clinical isolate (6.25 μg mL−1)), Klebsiella pneumoniae (clinical isolate (50 μg mL−1)), Shigella flexneri (clinical isolate (0.39 μg mL−1)) and Streptococcus pneumoniae (6.25 μg mL−1). Minimum bactericidal concentration, and MBIC50 and MBIC90 (Minimum Biofilm Inhibitory Concentration at 50% and 90% reduction, respectively) were evaluated for these pathogens. All these results confirmed the efficacy of the formulation AD-L@Ag(0). Minimum Biofilm Eradication Concentration (MBEC) for the respective pathogens was examined by following the exopolysaccharide quantification method to establish its potency in inhibition of biofilm formation, as well as eradication of mature biofilms. These effects were attributed to the bactericidal effect of AD-L@Ag(0) on biofilm mass-associated bacteria. The observed efficacy of this non-cytotoxic therapeutic combination (AD-L@Ag(0)) was found to be better than that reported in the existing literature for treating extremely drug-resistant bacterial strains, as well as for reducing the bacterial infection load at a surgical site in a small animal BALB/c model. Thus, AD-L@Ag(0) could be a promising candidate for anti-microbial coatings on surgical instruments, wound dressing, tissue engineering, and medical implants.

Insight into the Role of Guanidinium and Cesium in Triple Cation Lead Halide Perovskites

The overall impact of the partial replacement (5–15%) of methylammonium (MA) in the MAPbI3 perovskite by cesium or guanidinium (Gua) cations to fabricate thin films of triple cation Cs x Gua y MA1–x–y PbI3 perovskites is studied. The structural changes are investigated by using X‐ray diffraction measurements revealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation, respectively. The optoelectronic properties are characterized with photoluminescence (PL) time‐resolved spectroscopy and the space charge limited current (SCLC) method. Shorter PL time constants are obtained for the samples with only Cs, while longer PL decays are measured for the perovskites containing additional Gua cation. The SCLC measurements reveal a larger density of trap states in the Cs x MA1–x PbI3 perovskites compared to the MAPbI3 material. The PSCs fabricated with the different mixed cation Cs x Gua y MA1–x–y PbI3 perovskites reveal a good correlation with the measured optoelectronic properties. The power conversion efficiency (PCE) improves from an average value of 18.6% for the MAPbI3 to a value of 20.0% for the Cs0.05Gua0.05MA0.90PbI3 perovskite with a champion cell delivering 21.2%. On the opposite, the PCE decreases to a value of 17.3% for the double cation perovskite with Cs.

The mechanism of the isostructural phase transition in C(NH2)3PbI3 as a guide for understanding the properties of the new phase

Hybrid organic-inorganic perovskites (HOIPs) have attracted considerable attention, especially organometal trihalide perovskite, as promising materials for high-efficient solar cells. An interesting organic cation that can be incorporated in perovskite structure is the guanidinium (GUA) cation. Therefore, a number of investigations have been performed on the structure, stability and phase transitions of GUAPbI3. Herein, a study of the isostructural phase transition that is for the first time detected in GUPbI3, as well as some properties of the phase related to this transition, are presented. The existence of a new phase was deduced by the appearance of the temperature dependent isosbestic point at 47–48 °C in the infrared spectra, and the results obtained by the Raman spectroscopy. According to the powder X-ray diffraction (PXRD) patterns analysis, it was concluded that this phase transition is not accompanied by a change in the space group of the perovskite structure making it an isostructural one, and consequently, no additional peak at this temperature on differential thermal analysis (DTA) was detected. In order to relate the existence of this phase to the application of GUAPbI3 in solar cells, electrical measurements were undertaken from 24 to 71 °C. Thin films of GUAPbI3 on glass substrate were also prepared. The Ultra-violet and visible (UV/Vis) spectra of the corresponding phases were recorded and the band gaps were calculated.

Stiffening the Pb-X Framework through a π-Conjugated Small-Molecule Cross-Linker for High-Performance Inorganic CsPbI2Br Perovskite Solar Cells.

Inorganic CsPbI2Br perovskites have witnessed incredible advances as a promising representative for translucent and tandem solar cells, but unfortunately, they are still plagued by serious energy losses and undesired phase instability. Herein, a new type of π-conjugated small molecule of 4-guanidinobenzoic-acid-hydrochloride (4-GBACl) is demonstrated to effectively cross-link the Pb-X framework of perovskites. The strong coordination between 4-GBACl and the [PbX6]4- octahedron of perovskites effectively stiffens the Pb-X framework to suppress the ion migration, thus stabilizing the perovskite phase structure against light and thermal conditions. Apart from the physical barrier for phase instability resulting from the hydrophobic benzene ring at grain boundaries (GBs), guanidinium cations and -COOH and Cl- groups can simultaneously afford the passivation of positively and negatively charged defects at the GBs and surface, including undercoordinated halide species and undercoordinated Pb2+ ions, thereby effectively inhibiting the charge trapping/recombination centers. Two-dimensional confocal-fluorescence mapping images provide a visualized sight into the significantly suppressed nonradiative recombination and the prolonged carrier lifetime. It is suggested that the 4-GBACl additive plays multiple roles in grain cross-linking to regulate crystallization, distinctly reducing the trap-state density, ion migration inhibition, and moisture barrier in CsPbI2Br films. Consequently, the 4-GBACl-treated device exhibits a champion power conversion efficiency (PCE) of 15.59% accompanied with a considerably improved Voc of 1.28 V and maintains 88% of the initial PCE value after 1200 h aging under 20% relative humidity.

Guanidinium cation passivated Pb-Cu alloyed perovskite for efficient low-toxicity solar cells

Overcoming the toxicity of organic–inorganic perovskite materials is one of the main challenges in applying them to commercial optoelectronic devices, despite the amazing power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells (PSCs). In this work, we demonstrate a low-toxicity Pb-Cu alloyed perovskite film prepared by simple two-step methods and its integration in inverted PSCs. The formation of iodine defects was suppressed through the hydrogen bonding of guanidinium (Gua) cation (CH6N3+), which greatly improves the quality of the film. It is demonstrated that introduction of GuaI additives leads to stronger photoluminescence (PL) intensity, and lower defects state density. The open circuit voltage (Voc) and PCE of Pb-Cu alloyed PSCs reached 0.95 V and 9.69%, respectively. This work helps to guide the preparation of efficient low-toxicity Pb-Cu alloyed optoelectronic devices.

Development of N,N-disulfo-1,1,3,3-tetramethylguanidinium Chlorometallates as Heterogeneous Catalysts for One Pot Synthesis of 1,2-dihydro-1- aryl-3H-naphth[1, 2-e][1,3]oxazin-3-one Derivatives

Background: Four members of N,N-disulfo-1,1,3,3-tetramethylguanidinium chlorometallates [DSTMG]n[X], where n= 1 or 2; X= FeCl4 -, Zn2Cl6 2-, NiCl4 2-, MnCl4 2- were synthesized as solid Brønsted-Lewis acidic compounds and studied the catalytic activity with the most acidic salt for threecomponent synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2-e][1,3]oxazin-3-ones. Methods: N,N-disulfo-1,1,3,3-tetramethylguanidinium chlorometallates of the four transition metal cations such as Fe(III), Zn(II), Ni(II) and Mn(II) were prepared after treatment of the parent ionic liquid N,N-disulfo-1,1,3,3-tetramethylguanidinium chloride [DSTMG][Cl] with the respective metal chlorides in different mole fractions at 75 ºC. The synthesis of 1,2-dihydro-1-aryl-3H-naphth[1,2- e][1,3]oxazin-3-ones was carried out via three-component reaction of 2-naphthol, aromatic aldehydes and urea under neat condition at 90 ºC using 7 mol% of the [DSTMG][FeCl4] catalyst. Results: The characterization of synthesized chlorometallates was done using spectroscopic and other analytical techniques, including thermogravimetric analysis and Hammett acidity studies. Among the four salts, the salt of Fe(III) ion was observed as the strong Brønsted acidic hydrophobic salt and thus chosen for the catalytic study. Conclusion: A new type of chlorometallates of guanidinium cation with composition [DSTMG]n[X], where X= FeCl4-/Zn2Cl6 2-/NiCl4 2-/MnCl4 2- and n= 1 or 2 were developed as –SO3H functionalized solid acids with varied thermal stability (150-250 ºC) and physisorbed water (0-20%) as observed from the thermogravimetric study. From them, the most Brønsted acidic Fe(III) salt was employed as an efficient recyclable heterogeneous catalyst for the one-pot synthesis of 1,2-dihydro-1-aryl-3Hnaphth[ 1,2-e][1,3]oxazin-3-ones in neat condition.

Incorporating Guanidinium as Perovskitizer-Cation of Two-Dimensional Metal Halide for Crystal-Array Photodetectors.

Two-dimensional (2D) hybrid perovskites are recently emerging as a potential family of semiconductors for versatile optoelectronic applications. Currently, the "perovskitizer" moieties are rigidly limited to small-size cations, while few 2D metal-halides containing guanidinium cations inside perovskite cages have been studied for photodetection. Herein, we present a new 2D hybrid perovskite, (i-BA)2 (G)Pb2 I7 (where G is guanidinium and i-BA is isobutylammonium), which adopts a bilayered framework of {GPb2 I7 }. Single-crystal structure analyses disclose that G cations act as the perovskitizer, confined in the flexible perovskite cages formed by the distorted PbI6 octahedra. Such inorganic sheets are crucial to the superior semiconducting properties and optical bandgap, as verified by the density functional theory calculation. Furthermore, its planar crystal-array photodetector shows fascinating photoelectric performance, including a quite low dark current (∼4.6×10-11 A), a large current switching ratio (∼1.0×103 ), and a notable photo-responsivity of ∼0.72 A W-1 , suggesting great potential of (i-BA)2 (G)Pb2 I7 for photodetection.

The guanidinium t-diaqua-bis(oxalato)chromate(III) dihydrate complex: synthesis, crystal structure, EPR spectroscopy and magnetic properties

Abstract A new salt (CH6N3)[t-Cr(C2O4)2(H2O)2]·2H2O (1) (CH6N3 + = guanidinium cation) has been synthesized and characterized by single-crystal X-ray diffraction, FT-IR and UV–Vis spectroscopies, elemental and thermogravimetric analyses. In the crystal structure of 1, the chromate(III) ion lies on an inversion center in the form of an elongated octahedron. The coordination sphere consists of four oxygen atoms of two chelating oxalato ligands in the equatorial plane and two axial oxygen atoms of water ligands. The structural feature of focal interest in the structure of 1 is the formation of pillars of [Cr(C2O4)2(H2O)2]− complex anions and CH6N3 + guanidinium cations, with the next-neighbor cations rotated by an angle of 60° relative to each other. O–H···O and N–H···O hydrogen bonds play an important role in the construction of the three-dimensional network. The electron paramagnetic resonance (EPR) and magnetic properties of 1 have also been investigated.

Progress in High‐Performance Anion Exchange Membranes Based on the Design of Stable Cations for Alkaline Fuel Cells

AbstractSolid alkaline fuel cells with anion exchange membranes (AEMs) have drawn wide attention and have become an important focus in the field of renewable energy cells in recent years due to their high electrode activity, potential application of non‐precious metal catalysts, and relatively low requirements for fuel purity. AEM is the central component in solid alkaline fuel cells, and plays the role of conducting ions, blocking fuel crossover and providing catalyst support in fuel cells. Its performance directly affects the efficiency and service life of fuel cells. With some exceptions, the majority of AEMs have relatively low hydroxide conductivity and poor durability, which cannot meet the requirements of practical applications. The past decade has witnessed great progress in AEM designs and stability. Various kinds of AEMs with different cationic structures have been designed, and their properties and application in fuel cells are investigated. This review provides a comparative investigation and summary of highlights from the design of cationic structures for AEMs, including cyclic and spirocyclic quaternary ammonium cations, modified quaternary phosphonium, modified imidazoles, guanidinium, and metal cations. The authors’ perspective on the remaining challenges and directions of AEMs research for future development are also discussed.

C(NH2)3]3PO4·2H2O: A new metal-free ultraviolet nonlinear optical phosphate with large birefringence and second-harmonic generation response

[PO4]3− possesses small microscopic second-order susceptibility and polarizability anisotropy, which inherently result in weak second-harmonic generation (SHG) and small birefringence. Herein, a new noncentrosymmetric phosphate, [C(NH2)3]3PO4·2H2O, was successfully designed and synthesized by a solution evaporation method. [C(NH2)3]3PO4·2H2O without metal ions is composed of planar conjugated guanidine cations and PO4 tetrahedrons, which are connected by hydrogen bonds, forming a three-dimensional network. Physical property measurements indicate that the title compound displays an SHG response of 1.5 × KH2PO4 (KDP) and a larger birefringence (0.055@546.1 nm) compared with most reported ultraviolet nonlinear optical phosphates. Furthermore, first-principles calculations reveal that the π-conjugated planar [C(NH2)3]+ cations and [PO4]3− groups are responsible for its excellent linear and NLO properties.