Post-functionalization of triamino-phenazinium dyes to reach near-infrared emission

This study presents the synthesis and characterization of phenazinium dyes with absorption ranging from red to far-red, as well as emission extending into the far-red to near-infrared (NIR) region. The procedure involves the post-functionalization of a triamino-phenazinium that was recently reported as a theranostic agent. The introduction of electron-withdrawing moieties is accomplished through acylation or aromatic nucleophilic substitution. For one of the obtained products, a further substitution step could be achieved with primary amines to tune the electron density of the phenazinium core. The isolated dyes exhibit promising features that hold potential for future applications as biological markers or therapeutic agents.

Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

Like hydroquinones and quinones, aromatic compounds with multiple NH2 groups and the corresponding quinonediimines have the potential to serve as components of useful redox-active organic materials. Benzene-1,2,4,5-tetramine (BTA) and its oxidized form BTA-H2 offer a promising redox pair of this type, and the compounds have proven to be useful in many areas of chemistry. However, key aspects of their behavior have remained poorly studied, such as the nature of their protonated forms, their preferred molecular structures, their reactivity, and their organization in condensed phases. In the present work, we have used a combination of improved methods of synthesis, computation, spectroscopic studies, and structural analyses to develop a deeper understanding of BTA, BTA-H2, their salts, and related compounds. The new knowledge is expected to accelerate exploitation of the compounds in areas of materials science where desirable properties can only be attained by properly controlling the organization of molecular components.

7-Guanidinyl Coumarins: Synthesis, Photophysical Properties, and Application to Exploit the Pd-Catalyzed Release of Guanidines

Molecular manipulation of guanidino-containing biomolecules in a cellular environment is fundamental to exploiting protein function and drug release, but currently, there is a lack of suitable methods for reaction screening and monitoring. To exploit the potential of the fluorescent method in this respect, herein, we evaluated a novel array of 7-guanidinyl coumarins by incorporating different substituted guanidino moieties into a coumarin scaffold. These compounds were prepared by guanidinylation reagent S-methylisothiourea or TFA-protected pyrazole-carboxamidine. Examination of their photophysical properties revealed that the fluorescence emission of alkyloxycarbonyl-substituted guanidinyl coumarin was significantly enhanced as compared with the unsubstituted analogue. This dramatic fluorescence difference enabled preliminary exploitation of the Pd-catalyzed release of allyloxycarbonyl (Alloc)-caged guanidinyl coumarin-6 in living cells.

Organic Zinc-Ion Battery: Planar, π-Conjugated Quinone-Based Polymer Endows Ultrafast Ion Diffusion Kinetics

A novel poly(phenazine-alt-pyromellitic anhydride) (PPPA) has been successfully designed and synthesized via a condensation polymerization strategy as promising cathode material in organic zinc-ion batteries. Electrochemical quartz crystal microbalance (EQCM), FTIR and XPS characterizations verify a reversible Zn²⁺ -coordination mechanism in our PPPA cathode. Intriguingly, an ultrahigh Zn²⁺ diffusion coefficient of 1.2×10^-7  cm²  s^-1 was found in this large π-conjugated system, which is the highest one among all organic cathode materials for zinc-ion batteries. Theoretical calculations reveal the extended π-conjugated plane in our PPPA sample results in a significant reduction on energy gap, effectively accelerating intramolecular electron transfer during charge/discharge process. Our finding provides insights to achieve high zinc-ion transport kinetics by a design strategy on planar polymer system.

Novel Fluorescence Guanidine Molecules for Selective Sulfate Anion Detection in Water Complex Samples over a Wide pH Range

Quantitative analysis of sulfate anions in water still remains an important challenge for the society. Among all the methodologies, the most successful one is based on optical supramolecular receptors because the presence of small concentrations of sulfate anion modifies the photophysical properties of the receptor. In this case, fluorescence anion sensors have been designed by the incorporation of guanidine motifs into fluorenyl cores. The photophysical behaviors of the new mono- (M) and bis-guanidine (B) derivatives were studied through pH dependence, solvent effects, and ion sensing on steady-state spectra and time-resolved fluorescence spectroscopy. In more detail, the results demonstrate that M is a highly selective and sensitive sulfate ion receptor in real water samples and, even more importantly, its function remains unchanged at different ranges of pH. The reason behind this resides on the fluorescence quenching produced by an internal charge-transfer process when the sulfate anion is complexed with M. It is worth noting that the global and partial affinity constants (10¹⁰ M^-2 and 10⁵ M^-1, respectively) of complex formation are far above from the current sulfate sensors in water (10⁴ M^-1) which give an LOD of 0.10 μM in water with an analytical range of 2.5-10 μM. On the other hand, although it would seem, at first sight, that the B derivate will be the most promising one, the possibility of having two simultaneous protonation states reduces the complex formation and, therefore, its sensitivity to sulfate anions. The results presented here offer the possibility of using a new molecule in water environments, which opens the door to infinite applications such as the detection of trace amounts of sulfate ions in food or water.

Orthoamide und Iminiumsalze, IIC. Darstellung von N-(ω-Ammonioalkyl)-N,N′,N′,N″,N″-peralkylierten Guanidiniumsalzen und N-(ω-Aminoalkyl)-N′,N′,N″,N″-tetramethylguanidinen

N,N,N′,N′-Tetraalkylchlorformamidiniumchlorides 1a, b react with ω-dimethylaminoalkylamines 19, 20 to give mixtures of N-(ω-dimethylammonioalkyl)-guanidinium salts 12, 13 and N-(ω-dimethylaminoalkyl)-guanidinium salts 21, 22. These mixtures are transformed to mixtures of the ureas 15, 17 and N-(ω-dimethylaminoalkyl)-guanidines 23, 25 on treatment with aqueous sodium hydroxide. The reaction of N-(3-dimethylammoniopropyl)-guanidin 25a with dimethylsulfate in a molar ratio of 1:1 delivers a mixture of the N-(3-dimethylaminopropyl)-N,N,N′,N′,N″,N″-pentamethyl-guanidinium salt 29a and the N-(3-dimethylammoniopropyl)-N,N′,N′,N″,N″-pentamethyl-guanidinium-bis (methylsulfate) 33a. The action of dimethylsulfate on the guanidines 23a, 25a in a molar ratio of 2:1 affords the bisquarternary salts 32a, 33a. Alkylating reagents as methyliodide, benzylbromide, allylbromide and chloroacetonitrile attack N-(2-dimethylaminoethyl)-N′,N′,N″,N″-tetraethylguanidine (23b) in a molar ratio of 1:1 cleanly at the dimethylaminoethylgroup to give the ammonium salts 30a–d. As a strong base the guanidine 23b dehydrochlorinates β-Chlorpropionitrile and chloroacetone under formation of the guanidinium salt 21c. In contrast to this the reaction of ethyl bromoacetate with the N-(2-dimethylaminoethyl)guanidine 23b occurs at the guanidinogroup giving the guanidinium salt 28c. The methylation of the guanidinium chlorides 21a, 22a with dimethyl sulfate affords the bis-quaternary salts 35b, 36b with mixed anions. From the heterocyclic guanidines 14, 16 and the alkylating reagents benzylbromide and ethyl bromoacetate the heterocyclic guanidinium salts 37a, b, 39a, b can be obtained. The reactions with ethyl chloroformiate proceed in an analogous way giving the guanidinium salts 37c, 39c. The N-alkyl-N,N,N′,N′-tetramethyl-(3-ureidopropyl)guanidinium salts 41a, b can be prepared from the N′,N′,N″,N″-tetramethyl-N′′-(3-ureidopropyl) guanidine 17a and the alkylating compounds dimethyl sulfate and benzyl bromide. Several compounds obtained that way were transformed to the corresponding tetraphenyloborates and bis(tetraphenylborates), respectively.

1,2,4,5-Tetrakis(tetramethylguanidino)-3,6-diethynyl-benzenes: Fluorescent Probes, Redox-Active Ligands and Strong Organic Electron Donors

In this work, the change of reactivity induced by the introduction of two para-ethynyl substituents (CCSi(iPr)3 or CCH) to the organic electron-donor 1,2,4,5-tetrakis(tetramethylguanidino)-benzene is evaluated. The redox-properties and redox-state dependent fluorescence are evaluated, and dinuclear CuI and CuII complexes synthesized. The Lewis-acidic B(C6 F5 )3 substitutes the proton of the ethynyl -CCH groups to give new anionic -CCB(C6 F5 )3 - substituents, leading eventually to a novel dianionic strong electron donor in its diprotonated form. Its two-electron oxidation with dioxygen in the presence of a copper catalyst yields the first redox-active guanidine that is neutral (instead of cationic) in its oxidized form.

1,2,5,6-Tetrakis(guanidino)-Naphthalenes: Electron Donors, Fluorescent Probes and Redox-Active Ligands

New redox-active 1,2,5,6-tetrakis(guanidino)-naphthalene compounds, isolable and storable in the neutral and deep-green dicationic redox states and oxidisable further in two one-electron steps to the tetracations, are reported. Protonation switches on blue fluorescence, with the fluorescence intensity (quantum yield) increasing with the degree of protonation. Reactions with N-halogenosuccinimides or N-halogenophthalimides led to a series of new redox-active halogeno- and succinimido-/phthalimido-substituted derivatives. These highly selective reactions are proposed to proceed via the tri- or tetracationic state as the intermediate. The derivatives are oxidised reversibly at slightly higher potentials than that of the unsubstituted compounds to dications and further to tri- and tetracations. The integration of redox-active ligands in the transition-metal complexes shifts the redox potentials to higher values and also allows reversible oxidation in two potentially separated one-electron steps.

Fluorenone based fluorescent probe for selective "turn-on" detection of pyrophosphate and alanine

To sense biologically important entities with different size and dimensions, a fluorenone based fluorescent receptor was designed and synthesized. Probe 1 displayed a distinct fluorescence enhancement emission at 565nm for pyrophosphate and 530nm for alanine in polar solvent. The fluorescence titration experiments confirm 1:1 stoichiometric ratio with high-binding constant and very low limit of detection (LoD) values. Receptor 1 showed a highly selective and sensitive recognition to HP₂O₇^3- and to alanine over other competitive anions and amino acids. In addition, the fluorescence lifetime measurement and reversible binding study results support the practical importance of 1.

Integrating the fluorene substructure into azaacenes: syntheses of novel fluorophores

In this study, we report on the syntheses of novel angular fused azaacenes. For this purpose, the synthesis of the bis-diamine 2 (TABEF) could be shortened and optimized. The condensation reaction of 2 with different types of 1,2-diketones yielded new azaacene derivatives of types 10, 11 and 12. Analogously, 2 was cyclized with thionyl chloride to give the piazthiol derivative 13. The optical and electrochemical properties of all new compounds were investigated by UV/Vis absorption, fluorescence emission spectroscopy and cyclovoltammetric measurements.

Di- and tetranuclear transition metal complexes of a tetrakisguanidino-substituted phenazine dye by stepwise coordination

Coordination of a tetrakisguanidino-substituted phenazine dye in two steps provides rational access to tetranuclear homo- and heterobimetallic complexes.

Acid-Responsive Absorption and Emission of 5-N-Arylaminothiazoles: Emission of White Light from a Single Fluorescent Dye and a Lewis Acid

Solutions of 5-N-arylaminothiazoles containing pyridyl groups exhibited clear halochromism and halofluorism upon addition of Brønsted and Lewis acids. The addition of triflic acid to solutions of 5-N-arylaminothiazoles in Et2O induced bathochromic shifts of the absorption and emission bands. DFT calculations suggested that the spectral changes arise from the protonation of the pyridyl group of the thiazoles in Et2O. Single-crystal X-ray diffraction analysis of a thiazole and its protonated form revealed the change of the conformation around the thiazole ring. The emission of white light was accomplished from a single fluorescent dye by adjusting the ratio of dye and B(C6F5)3, whereby the International Commission on Illumination coordinates showed a linear change from blue to orange.

Construction of copper chains with new fluorescent guanidino-functionalized naphthyridine ligands

A high charge and a low coordination number are the characteristics of fluorescent Cu₄ chain complexes with 2,7-bisguanidino-naphthyridine ligands.

A phenazine-based near-infrared (NIR) chemodosimeter for cysteine obtained via a carbonyl-assisted cycloaddition process

A NIR phenazine-based chemodosimeter (PHS) is developed for sensing cysteine with high sensitivity, good selectivity and rapid response. The α,β-unsaturated carbonyl NHS-ester was employed as an recognition unit through a cycloaddition mechanism.

pH-Dependent supramolecular self-assemblies of copper(ii) (fluorene-9,9-diyl)dipropanoic acid complexes

Four supramolecular assemblies from 0D, 1D to 2D were obtained by reacting (fluorene-9,9-diyl)dipropanoic acid with cupric ion under media with different pH values of 4.0–8.0.