Visual sensing of picric acid in 100% aqueous media based on supramolecular polythiophene assemblies with colorimetric and fluorescent dual response

A colorimetric and fluorometric dual probe based on a water-soluble polythiophene derivative (PMTPBA) was designed and synthesized. It can be applied to determination of picric acid (PA) in 100% aqueous solution. The approach relies on the formation of supramolecular polythiophene assemblies in the presence of PA through electrostatic, charge transfer and π-π stacking interactions. This probe could be utilized for the rapid and visual detection of PA both in aqueous solution and solid support with high specificity and sensitivity. The detection limit of this sensor is as low as 5.0 × 10^-8 mol/L.     

Assembly-enhanced triplet-triplet annihilation upconversion in the aggregation formed by Schiff-base Pt(Ⅱ) complex grafting-permethyl-β-CD and 9,10-diphenylanthracence dimer

Water-soluble triplet sensitizer with permethyl-β-cyclodextrin(PMCD) grafting on a Schiff-base Pt(Ⅱ)complex(Pt-2),in which PMCD unit serves as a host for binding the acceptors and the Schiff-base Pt(Ⅱ)complex serves as a triplet sensitizer,was synthesized to investigate the effect of supramolecular complexation and assembly on the triplet-triplet annihilation upconversion emission in water.9,10-Diphenylanthracence(DPA) carboxylate(A-1) and its dimer(A-2) in which two DPA carboxylate were covalently linked with an alkyl chain were synthesized as triplet acceptors which also play a role of guest molecules for PMCD.A-1 and A-2 showed high affinity with PMCD,and A-2 can readily aggregate in water and form micron sized assemblies due to the hydrophobic effect and π-π stacking of anthracene core in A-2.The efficiency of TTA-UC was demonstrated to be enhanced by a synergistic effect of host-guest complexation of Pt-2 with A-2 and the self-aggregation of the acceptor A-2,which facilitated the energy transfer and energy fusion among donor and acceptor.     

Bodipy–C60 triple hydrogen bonding assemblies as heavy atom-free triplet photosensitizers: preparation and study of the singlet/triplet energy transfer

Supramolecular triplet photosensitizers based on hydrogen bonding-mediated molecular assemblies were prepared. Three thymine-containing visible light-harvesting Bodipy derivatives (B-1, B-2 and B-3, which show absorption at 505 nm, 630 nm and 593 nm, respectively) were used as H-bonding modules, and 1,6-diaminopyridine-appended C₆₀ was used as the complementary hydrogen bonding module (C-1), in which the C₆₀ part acts as a spin converter for triplet formation. Visible light-harvesting antennae with methylated thymine were prepared as references (B-1-Me, B-2-Me and B-3-Me), which are unable to form strong H-bonds with C-1. Triple H-bonds are formed between each Bodipy antenna (B-1, B-2 and B-3) and the C₆₀ module (C-1). The photophysical properties of the H-bonding assemblies and the reference non-hydrogen bond-forming mixtures were studied using steady state UV/vis absorption spectroscopy, fluorescence emission spectroscopy, electrochemical characterization, and nanosecond transient absorption spectroscopy. Singlet energy transfer from the Bodipy antenna to the C₆₀ module was confirmed by fluorescence quenching studies. The intersystem crossing of the latter produced the triplet excited state. The nanosecond transient absorption spectroscopy showed that the triplet state is either localized on the C₆₀ module (for assembly B-1·C-1), or on the styryl-Bodipy antenna (for assemblies B-2·C-1 and B-3·C-1). Intra-assembly forward–backward (ping-pong) singlet/triplet energy transfer was proposed. In contrast to the H-bonding assemblies, slow triplet energy transfer was observed for the non-hydrogen bonding mixtures. As a proof of concept, these supramolecular assemblies were used as triplet photosensitizers for triplet–triplet annihilation upconversion.     

Blue two-photon excited fluorescence of several D-π-D, A-π-A, and D-π-A compounds featuring dimesitylboryl acceptor

Several donor-π-donor (D-π-D), acceptor-π-acceptor (A-π-A), and donor-π-acceptor (D-π-A) types of organic compounds with fluorene as π bridge and dimesitylboryl group as electron acceptor, which show strong two-photon excited blue fluorescence, have been synthesized and structurally investigated. The symmetric A-π-A type of compound exhibits the shortest wavelength of two-photon excited fluorescence (TPEF) at λ_em=405 nm under the excitation of λ_ex=730 nm; the unsymmetric D-π-A type of compound with diphenylamino as donor exhibits the most intense TPEF at blue region (λ_em=484 nm) with a two-photon absorption cross-section of 425 GM under λ_ex=800 nm.     

Complete Quenching of the Pd3(dppm)3(CO)2+ Cluster Emission Via Electrostatic Host–Guest Assemblies with Carboxylate-Containing Tetraphenylporphyrins of Ni(II) and Fe(III)

The title cluster is luminescent at 77?K and exhibits an unsaturated site for binding anions when the counter ion is PF₆ ^?. A series of five non-luminescent metalloporphyrins exhibiting carboxylate anchoring groups were synthesized and characterized. These are the sodium salts of the 5-carboxyphenyl-tri-10,15,20-tolyl-, trans-di-5,10-carboxyphenyl-di-15,20-tolyl-, and tetra-5,10,15,20-carboxyphenyl(metallo)porphyrin (metallo?=?chloroiron(III), nickel(II)) anions. Evidence for supramolecular assemblies between the carboxylates and the cluster is provided by ³¹P NMR and UV?Cvis spectroscopy. The binding constant, K_1n, extracted from the UV?Cvis data via Benesi-Hildebrand, Scott and Scatchard plots are approximately 21,000?±?5,000?M^?1 for the nickel(II) species, in agreement with the previously reported zinc(II) ones (K₁₁?=?20,000?±?2,000?M^?1), but those for the chloroiron(III) are measured to be lower (12,500?±?3,500?M^?1). This association is accompanied by a complete quenching of the luminescence of the cluster which can only be due to an efficient energy transfer to the d?Cd states of the chloroiron(III) and nickel(II) species but an electron transfer from the nickel(II)-containing chromophore to the cluster is also possible. This work demonstrates the profound effect that supramolecular interactions may have on the photophysical properties despite the long donor?Cacceptor separation.     

Magnetic chains formed from tetra-coordinate Co(II) complexes

Two tetra-coordinate Co(II) complexes, [CoCl₂(bzfupy)₂] and [CoCl₂(p-tol)₂] with N-donor ligands, are apparently mononuclear systems. The magnetic susceptibility at low temperature attains a maximum which is a fingerprint of the exchange interaction. The exchange coupling constant fitted to a model of 1D-magnetic chain yields J/hc = ?0.50 cm^?1 and ?0.57 cm^?1, respectively. The magnetic interaction is mediated by the π-π stacking in the first complex, and the short Cl…Cl contacts in the second.     

Viologen derivatives with extended π-conjugation structures: From supra-/molecular building blocks to organic porous materials

Recently, increasing attention has been paid on extending the π-conjugation structures of viologens (1,1′-disubstituted-4,4′-bipyridylium salts) by incorporating planar aromatic units into the bipyridinium backbones. Various viologen derivatives with extended π-conjugation structures have been synthesized, including the N-termini aromatic substituted viologens, the extended π-conjugated viologens (denoted as ECVs) as well as the π-conjugated oligomeric viologens (denoted as COVs). These compounds typically exhibit interesting properties distinguished from those of an isolated viologen unit, which make them as new class of electron deficient supra-/molecular building blocks in supramolecular chemistry and materials science. In this review, we would like to highlight the recent advances of viologen derivatives with extended π-conjugation structures in versatile applications ranging from electrochromic and energy storage materials, the ECV/COV-based supramolecular self-assembly systems including the linear supramolecular polymers and 2D/3D supramolecular organic frameworks (SOFs), to the viologen-based covalent organic frameworks (COFs)/networks. We hope this review will serve as an in-time summary worthy of referring, more importantly, to provide inspiration in the rational design of novel molecules with unexplored properties and functions.     

Tetrapyridoxycalix[4]arene and its copper(II) complex: an ionic crystal engineering tecton for self-inclusion polymers

The crystal structures of a tetradentate pyridylcalix[4]arene ligand and its first copper(II) complex are discussed. The metal free ligand is mainly self-assembled by dipole–dipole interactions and a combination of CH–N bonds and CH–π interactions. The corresponding copper(II) perchlorate complex exhibits a self-inclusion behaviour to supramolecular zig-zag polymers.     

Interaction of Halogenoantimonates with Aromatic Compounds in organic solvents

The interaction of SbCl_nBr_6-n^? (n = 1—6) with various bπ-donors has been investigated by means of UV spectroscopy, conductometry, and polarography. The influence of the bπ-donor structure, of the corresponding cation, the ligands of the antimonates, and the solvent on the behaviour of complex formation is discussed. With increasing ionization potential of the bπ-donor the CT absorption shifts to higher energies. Derivatives of aminobenzene lead to the formation of radical cations. The influence of 18-crown-6 on the radical cation formation is also discussed. With increasing content of bromine in the antimonate the overall acceptor strength increases as well. The influence of the solvent on CT energy depends on both the specific solvation of the ground state of the electron donor-acceptor complex and the dielectric solvation of the excited state of the complex.     

Crystal structures and electrochemical properties of two Mn(II) 2-sulfoterephthalate complexes with N-donor ligands

Two Mn(II) sulfoterephthalate complexes, [Mn(HStp)(o-Phen)₂] (I) and [Mn(HStp)(2,2′-Bipy)₂] (II) (H₃Stp = 2-sulfoterephthalic acid, o-Phen = 1,10-phenanthroline, 2,2′-Bipy = 2,2′-bipyridine), were synthesized under hydrothermal condition. Single crystal X-ray diffraction analyses reveal that complexes I and II possess similar structure, in which the center Mn²⁺ ions are hexa-coordinated with one Hstpanion and two N-donor ligands. For both of them, the formation of 3D supramolecular structures are based on both H-bonds and π...π/C-H...π stacking interactions. Electrochemical properties of complexes I and II have been investigated by means of cyclic voltmetry, which shows that electron transfer between Mn(III) and Mn(II) in electrolysis is quasi-reversible process.     

A Concerted Enzymatic and Bioorthogonal Approach for Extra- and Intracellular Activation of Environment-Sensitive Ruthenium(II)-Based Imaging Probes and Photosensitizers

In this article, we report a novel targeting strategy involving the combination of an enzyme-instructed self-assembly (EISA) moiety and a strained cycloalkyne to generate large accumulation of bioorthogonal sites in cancer cells. These bioorthogonal sites can serve as activation triggers in different regions for transition metal-based probes, which are new ruthenium(II) complexes carrying a tetrazine unit for controllable phosphorescence and singlet oxygen generation. Importantly, the environment-sensitive emission of the complexes can be further enhanced in the hydrophobic regions offered by the large supramolecular assemblies, which is highly advantageous to biological imaging. Additionally, the (photo)cytotoxicity of the large supramolecular assemblies containing the complexes was investigated, and the results illustrate that cellular localization (extracellular and intracellular) imposes a profound impact on the efficiencies of photosensitizers.     

Ligand-controlled assembly of Cd(II) coordination polymers based on mixed ligands of naphthalene-dicarboxylate and dipyrido[3,2-d:2′,3′-f]quinoxaline: From 0D+1D cocrystal, 2D rectangular network (4,4), to 3D PtS-type architecture

Three novel Cd(II) coordination polymers, namely, [Cd(Dpq)(1,8-NDC)(H₂O)₂][Cd(Dpq)(1,8-NDC)]·2H₂O (1), [Cd(Dpq)(1,4-NDC)(H₂O)] (2), and [Cd(Dpq)(2,6-NDC)] (3) have been obtained from hydrothermal reactions of cadmium(II) nitrate with the mixed ligands dipyrido [3,2-d:2′,3′-f]quinoxaline (Dpq) and three structurally related naphthalene-dicarboxylate ligands [1,8-naphthalene-dicarboxylic acid (1,8-H₂NDC), 1,4-naphthalene-dicarboxylic acid (1,4-H₂NDC), and 2,6-naphthalene-dicarboxylic acid (2,6-H₂NDC)]. Single-crystal X-ray diffraction analysis reveals that the three polymers exhibit novel structures due to different naphthalene-dicarboxylic acid. Compound 1 is a novel cocrystal of left- and right-handed helical chains and binuclear complexes and ultimately packed into a 3D supramolecular structure through hydrogen bonds and π-π stacking interactions. Compound 2 shows a 2D rectangular network (4,4) bridged by 1,4-NDC with two kinds of coordination modes and ultimately packed into a 3D supramolecular structure through inter-layer π-π stacking interactions. Compound 3 is a new 3D coordination polymer with distorted PtS-type network. In addition, the title compounds exhibit blue/green emission in solid state at room temperature.     

A host–guest strategy for converting the photodynamic agents from a singlet oxygen generator to a superoxide radical generator

Type-I photosensitizers (PSs) generate cytotoxic oxygen radicals by electron transfer even in a hypoxic environment. Nevertheless, the preparation of type-I PSs remains a challenge due to the competition of triplet–triplet energy transfer with O₂ (type-II process). In this work, we report an effective strategy for converting the conventional type-II PS to a type-I PS by host–guest complexation. Electron-rich pillar[5]arenes are used as an electron donor and macrocyclic host to produce a host–guest complex with the traditional electron-deficient type-II PS, an iodide BODIPY-based guest. The host–guest complexation promotes intermolecular electron transfer from the pillar[5]arene moiety to BODIPY and then to O₂ by the type-I process upon light-irradiation, leading to efficient generation of the superoxide radical (O₂⁻˙). The results of anti-tumor studies indicate that this supramolecular PS demonstrates high photodynamic therapy efficacy even under hypoxic conditions. This work provides an efficient method to prepare type-I PSs from existing type-II PSs by using a supramolecular strategy.

A supramolecular strategy is reported for converting the conventional photodynamic agents from a singlet oxygen generator to a superoxide radical generator by the host–guest interaction enhanced electron transfer.     

Synthesis and supramolecular features of hybrid POM/onium solid-state assemblies

Abstract

Polyoxomolybdate-based organic?inorganic hybrid architectures were synthesised and characterised by X-ray crystallography. The supramolecular assemblies present rows of metallic clusters H-bonded by ammonium cations, with a 1:2 molybdate/ammonium ratio. The organic moieties of the ammonium cations establish hydrophobic contact among them such as van der Waals, C–H?π and π?π interactions that stabilise the supramolecular architectures. In particular, for compound 5 the n-alkyl tails pack closely together giving a lipid-like bilayer. In compound 6, the aromatic phenyl rings of the organic cation allow the stabilisation of the supramolecular architecture by C–H?π and π?π interactions. Regarding the X-ray structure of the compound 11, the tetraanionic octa-molybdate [Mo₈O₂₆]^4? cluster is surrounded by four ethyl-triphenyl-phosphonium cations. Running along the b-axis open channels are occupied by DMF solvent molecules. Interestingly, a soaking experiment in n-pentane with the corresponding crystals of compound 11 afforded to a crystal structure very different from the native one.     

2D and 3D supramolecular assemblies of double cyclopalladated azobenzenes realized by C-H?Cl-Pd, π?π and C-H?π interactions

The double cyclopalladated complex with azobenzene, μ-[(E)-1,2-diphenyldiazene-C^2,8, N^1,2]-di-[chloro(dimethylsulfoxide)palladium(II)]; (DMSO)PdCl(μ-C₆H₄NNC₆H₄)(DMSO)PdCl (1) and its analogous complex with DMF as ancillary ligand, (DMF)PdCl(μ-C₆H₄NNC₆H₄)(DMF)PdCl; μ-[(E)-1,2-diphenyldiazene-C^2,8,N^1,2]-di-[chloro(dimethylformamide)palladium(II)] (2a) were synthesized and the function of cyclopalladated moiety in molecular assembling in the solid state is illustrated by their crystal packings. The polymorphism of 2a and 2b is discussed. The crystal structures reveal assemblies with molecular components self-organized by C-H?Cl-Pd hydrogen bonds, π?π, and C-H?π interactions. The double cyclopalladated complexes of azobenzene, with two Pd-Cl moieties participating in the hydrogen bond formation and π-conjugated system involved in the π?π or C-H?π interactions, represent a new class of building blocks for construction of solid state supramolecular assemblies.     

Integrating proton coupled electron transfer (PCET) and excited states

In many of the chemical steps in photosynthesis and artificial photosynthesis, proton coupled electron transfer (PCET) plays an essential role. An important issue is how excited state reactivity can be integrated with PCET to carry out solar fuel reactions such as water splitting into hydrogen and oxygen or water reduction of CO₂ to methanol or hydrocarbons. The principles behind PCET and concerted electron–proton transfer (EPT) pathways are reasonably well understood. In Photosystem II antenna light absorption is followed by sensitization of chlorophyll P₆₈₀ and electron transfer quenching to give P₆₈₀⁺. The oxidized chlorophyll activates the oxygen evolving complex (OEC), a CaMn₄ cluster, through an intervening tyrosine–histidine pair, Y_Z. EPT plays a major role in a series of four activation steps that ultimately result in loss of 4e^?/4H⁺ from the OEC with oxygen evolution. The key elements in photosynthesis and artificial photosynthesis – light absorption, excited state energy and electron transfer, electron transfer activation of multiple-electron, multiple-proton catalysis – can also be assembled in dye sensitized photoelectrochemical synthesis cells (DS-PEC). In this approach, molecular or nanoscale assemblies are incorporated at separate electrodes for coupled, light driven oxidation and reduction. Separate excited state electron transfer followed by proton transfer can be combined in single semi-concerted steps (photo-EPT) by photolysis of organic charge transfer excited states with H-bonded bases or in metal-to-ligand charge transfer (MLCT) excited states in pre-associated assemblies with H-bonded electron transfer donors or acceptors. In these assemblies, photochemically induced electron and proton transfer occur in a single, semi-concerted event to give high-energy, redox active intermediates.     

A chiral SrSi2 (srs) superstructure constructed by a dual interaction system showing isotropic electrical conductivity

Most porous conductive frameworks are highly anisotropic in their structures thus leading to anisotropic charge transport. Here we report a supramolecular self-assembly which is constructed by intermolecular hydrogen bonding and π ···π interactions. This material features a chiral, porous, cubic framework structure with π-stacked helical columns along all of the three Cartesian coordinates. As a result, isotropic charge transport with an electrical conductivity(σ) of 2.1 × 10^–7S/cm is...     

Synthesis of new luminescent supramolecular assemblies from fluorenyl porphyrins and polypyridyl isocyanurate-based spacers

Two new dendrimeric supramolecular assemblies bearing twelve and twenty-four fluorenyl peripheral donor groups surrounding an organic core have been prepared and studied. These assemblies are composed of three zinc porphyrins possessing each four (ZnTFP) and eight fluorenyl chromophores (ZnOOFP) linked together by a central tris-pyridyl organic ligand. Due to efficient energy transfer between the fluorenyl arms, which act as antennas, and the Zn centres, which act as emitters; these assemblies behave as red emitters after selective UV or visible irradiation. The kinetic stability of these supramolecular assemblies and its impact on their photophysical properties are discussed.     

Assembly of Palladium(II) and Platinum(II) Metallo‐Rectangles with a Guanosine‐Substituted Terpyridine and Study of Their Interactions with Quadruplex DNA

Two novel [2+2] metallo‐assemblies based on a guanosine‐substituted terpyridine ligand ( 1 ) coordinated to palladium(II) ( 2 a ) and platinum(II) ( 2 b ) are reported. These supramolecular assemblies have been fully characterized by NMR spectroscopy, ESI mass spectrometry and elemental analyses. The palladium(II) complex ( 2 a ) has also been characterized by single crystal X‐ray diffraction studies confirming that the system is a [2+2] metallo‐rectangle in the solid state. The stabilities of these [2+2] assemblies in solution have been confirmed by DOSY studies as well as by variable temperature ¹H NMR spectroscopy. The ability of these dinuclear complexes to interact with quadruplex and duplex DNA was investigated by fluorescent intercalator displacement (FID) assays, fluorescence resonance energy transfer (FRET) melting studies, and electrospray mass spectrometry (ESI‐MS). These studies have shown that both these assemblies interact selectively with quadruplex DNA (human telomeric DNA and the G‐rich promoter region of c‐myc oncogene) over duplex DNA, and are able to induce dimerization of parallel G‐quadruplex structures.     

Synthesis of novel α-CF3-trifluoroalanine derivatives containing N-(diethoxyphosphoryl)difluoroacetyl group

An efficient synthesis of biologically interesting α-CF₃-trifluoroalanine derivatives bearing N-(diethoxyphosphoryl)difluoroacetyl moiety in good yields has been elaborated. The key substrate, α-TFM-imino ester, prepared from methyl trifluoropyruvate and (diethoxyphosphoryl)difluoroacetamide, followed by dehydration, was subjected to regiospecific reactions with various nucleophiles, including organometallic, π-donor compounds and sodium borohydride. These novel products may find a viable application in the modification of peptides or serve as potential drug candidates.