Highly Conductive Covalent-Organic Framework Films.

Chemically inert organic networks exhibiting electrical conductivity comparable to metals can advance organic electronics, catalysis, and energy storage systems. Covalent-organic frameworks (COFs) have emerged as promising materials for those applications due to their high crystallinity, porosity, and tunable functionality. However, their low conductivity has limited their practical utilization. In this study, copper-coordinated-fluorinated-phthalocyanine and 2,3,6,7-tetrahydroxy-9,10-anthraquinone-based COF (CuPc-AQ-COF) films with ultrahigh conductivity are developed. The COF films exhibit an electrical conductivity of 1.53 × 103 S m-1 and a Hall mobility of 6.02 × 102 cm2 V-1 s-1 at 298 K, reaching the level of metals. The films are constructed by linking phthalocyanines and anthraquinones through vapor-assisted synthesis. The high conductivity properties of the films are attributed to the molecular design of the CuPc-AQ-COFs and the generation of high-quality crystals via the vapor-assisted method. Density functional theory analysis reveals that an efficient donor-acceptor system between the copper-coordinated phthalocyanines and anthraquinones significantly promotes charge transfer. Overall, the CuPc-AQ-COF films set new records of COF conductivity and mobility and represent a significant step forward in the development of COFs for electronic, catalytic, and electrochemical applications.

Supramolecular Control of the Temperature Responsiveness of Fluorescent Macrocyclic Molecular Rotamers.

To fully harness the potential of molecular machines, it is crucial to develop methods by which to exert control over their speed of motion through the application of external stimuli. A conformationally strained macrocyclic fluorescent rotamer, CarROT, displays a reproducible and linear fluorescence decrease towards temperature over the physiological temperature range. Through the external addition of anions, cations or through deprotonation, the compound can access four discreet rotational speeds via supramolecular interactions (very slow, slow, fast and very fast) which in turn stop, reduce or enhance the thermoluminescent properties due to increasing or decreasing non-radiative decay processes, thereby providing a means to externally control the temperature sensitivity of the system. Through comparison with analogues with a higher degree of conformational freedom, the high thermosensitivity of CarROT over the physiological temperature range was determined to be due to conformational strain, which causes a high energy barrier to rotation over this range. Analogues with a higher degree of conformational freedom display lower sensitivities towards temperature over the same temperature range. This study provides an example of an information rich small molecule, in which programable rotational speed states can be observed with facile read-out.

14-Membered Macrocyclic ß-Diiminato Gold(II) - A New Member for the Gold(II) Complex Family?

The chemistry of molecular gold compounds is dominated by the oxidation states +I and +III. For the intermediate oxidation state +II with 5d9 electron configuration, dimerization or disproportionation of the gold(II) radicals is favored, so that only a few mononuclear gold(II) complexes have been isolated to date. The present study addresses the one-electron reduction of the macrocyclic gold(III) complex [AuIIIL]+ of the innocent ß-diiminato ligand L2- with a 14-membered macrocycle (L2-=5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-5,7,12,14-tetraenato). Electrochemistry, spectroelectrochemistry and chemical reduction of [AuIIIL]+ monitored by UV/Vis, NMR and EPR spectroscopy together with density functional theory calculations reveal disproportionation of the initially generated but elusive gold(II) complex AuIIL and provide guidelines for prospective stable mononuclear tetraazamacrocyclic gold(II) complexes.

In2Q2: A New Entry of 16-Membered Tetraazamacrocycle Concatenating Indole and Quinoline Units.

A new family of 16-membered macrocycles comprising two indole (In) and two quinoline (Q) units, coined In2Q2, was synthesized. Each unit is diagonally located and concatenated in a head-to-tail fashion, furnishing a non-flat saddle-shaped architecture with C2 symmetry. The synthetic protocol utilizing macrocyclic diamide as a pivotal precursor allowed us to access a series of In2Q2 derivatives bearing various substituents on the periphery. The In2Q2 derivatives and their Zn2+ complexes were emissive in both solution phase and solid state. While the entire architecture of In2Q2 is similar to that of quinoline tetramer TEtraQuinoline, a couple of contrasting physicochemical properties were revealed.

Ether Naphthotube Host-Guest Complexes and [2]Rotaxanes with Dications.

The interactions between ether naphthotube and a series of dication guests in organic solution were investigated. It was found that ether naphthotube formed stable host-guest complexes selectively with these guests in a 1 : 1 stoichiometric ratio with association constants ranging from 102 to 106 M-1, which were confirmed by 1H-NMR spectra and ITC experiments. The host-guest interactions are driven by enthalpy change as the entropic factors are unfavorable. Positive correlations between ΔH and ΔS have been observed in the host-guest complexes. Furthermore, the para-substitution of the guests can significantly affect the binding affinities through a combination of field/inductive and resonance effects by following a linear free energy relationship. Based on the host-guest complexes composed of ether naphthotube and organic cations, two interlocked [2]rotaxanes were prepared by cationization reaction and Huisgen cycloaddition between the cations and the stopper components. The ether naphthotube-based host-guest complexes are useful for creating sophisticated interlocked molecules.

A Cycloparaphenylene Acetylene as Potential Precursor for an Armchair Carbon Nanotube.

The bottom-up synthesis of carbon nanotubes (CNTs) is a long-standing goal in synthetic chemists. Producing CNTs with defined lengths and diameters would render these materials and thus their fascinating properties accessible in a controlled way. Inspired by a recently reported synthesis of armchair graphene sheets that relied on a benzannulation and Scholl oxidation of a poly(p-phenylene ethynylene), the same strategy is applied on a cyclic substrate with a short, but well defined CNT as target structure. Herein we report the synthesis of a derivatized [12]cyclo-para-phenylene acetylene ([12]CPPA) that was accessible employing a Sonogashira macro-cyclization. The obtained macrocycle is the largest [n]CPPA reported to date and displays bright turquoise fluorescence with a large quantum yield of 77%. The [12]CPPA can be transformed by a 12-fold benzannulation that converts each alkyne to a naphthalene and therefore allows formation of an armchair [12,12] CNT precursor. The final 72-fold Scholl oxidation to the [12,12] CNT turned out to be challenging and its optimization requires an improved synthetic strategy to produce large quantities of the final precursor. The developed approach poses a potential break through strategy for the production of CNTs and certainly incentivizes synthetic chemists to apply the same methodology for various conjugated macrocycles.

Isolation, Structure Elucidation, and Biological Activity of the Selective TACR2 Antagonist Tumonolide and its Aldehyde from a Marine Cyanobacterium.

The macrocyclic tumonolide (1) with enamide functionality and the linear tumonolide aldehyde (2) are new interconverting natural products from a marine cyanobacterium with a peptide-polyketide skeleton, representing a hybrid of apratoxins and palmyrolides or laingolides. The planar structures were established by NMR and mass spectrometry. The relative configuration of the stereogenically-rich apratoxin-like polyketide portion was determined using J-based configuration analysis. The absolute configuration of tumonolide (1) was determined by chiral analysis of the amino acid units and computational methods, followed by NMR chemical shift and ECD spectrum prediction, indicating all-R configuration for the polyketide portion, as in palmyrolide A and contrary to the all-S configuration in apratoxins. Functional screening against a panel of 168 GPCR targets revealed tumonolide (1) as a selective antagonist of TACR2 with an IC50 of 7.0 µM, closely correlating with binding affinity. Molecular docking studies established the binding mode and rationalized the selectivity for TACR2 over TACR1 and TACR3. RNA sequencing upon treatment of HCT116 colorectal cancer cells demonstrated activation of the pulmonary fibrosis idiopathic signaling pathway and the insulin secretion signaling pathway at 20 µM, indicating its potential to modulate these pathways.

Linear, Planar, Orbicular, and Macrocyclic Multinuclear Zinc (Meth)acrylate Complexes.

Zinc carboxylate complexes are widely utilized as artificial models of metalloenzymes and as secondary building units of PCPs/MOFs. However, the relationship between the structure of the monodentate carboxylato ligand and the molecular arrangement of multinuclear zinc carboxylate complexes is not fully understood because of the coordination flexibility of the Zn ion and carboxylato ligands. Herein, we report the structural analysis of a series of complexes derived from zinc (meth)acrylate which has a linear infinite chain structure. The molecular structure of µ4-oxido-bridged tetranuclear complexes [Zn4(µ4-O)(OCOR)6] revealed a distorted Zn4O core. Crystallization of zinc acrylate under aqueous conditions afforded a µ3-hydroxido-containing pentanuclear complex [Zn5(µ3-OH)2(OCOR)8] as the repeating unit of an infinite sheet-like structure in the solid state. It was also obtained by the hydrolysis of the µ4-oxido-bridged tetranuclear complex. In sharp contrast, the methacrylate analog retained the methacrylato ligands under aqueous crystallization conditions to form a macrocyclic dodecanuclear complex with methacrylato as the sole ligand.

[2,2]Paracyclophane Bridged, Thiophene Based Macrocycles: Synthesis and Electronic Properties in Different Redox States.

The study of through-space electronic coupling in π-conjugated systems remains an underexplored area. In this work, we present the facile synthesis of two isomeric macrocycles (1 and 2) bridged by [2,2]paracyclophane (pCp) and based on thiophene. The structures of these macrocycles have been confirmed through X-ray crystallographic analysis. Our investigation centers on their electronic properties across various redox states, with a specific focus on potential through-space electronic coupling and global aromaticity. Experimental measurements, including UV-vis-NIR electronic absorption, NMR, ESR spectra, and X-ray diffraction, combined with theoretical calculations, reveal that both the neutral compounds and their tetracations exhibit a closed-shell ground state. However, their dications manifest as diradical dications with a subtle magnetic exchange interaction. Consequently, the through-space electronic coupling facilitated by the pCp unit in their respective ground states appears to be weak.

Dynamics of Coordinated Phosphonate Group Directly Observed by 17O-NMR in Lanthanide(iii) Complexes of a Mono(ethyl phosphonate) DOTA Analogue.

Biological phosphates can coordinate metal ions and their complexes are common in living systems. Dynamics of mutual oxygen atom exchange in the tetrahedral group in complexes has not been investigated. Here, we present a direct experimental proof of exchange ("phosphonate rotation") in model Ln(III) complexes of monophosphonate H4dota analogue which alters phosphorus atom chirality of coordinated phosphonate monoester. Combination of macrocycle-based isomerism with P-based chirality leads to several diastereoisomers. (Non)-coordinated oxygen atoms were distinguished through 17O-labelled phosphonate group and their mutual exchange was followed by various NMR techniques and DFT calculations. The process is sterically demanding and occurs through bulky bidentate (κ2-PO2)- coordination and was observed only in twisted-square antiprism (TSA) diastereoisomer of large Ln(III) ions. Its energy demands increase for smaller Ln(III) ions (298ΔG≠(exp./DFT)=51.8/52.1 and 61.0/71.5 kJ mol-1 for La(III) and Eu(III), respectively). These results are helpful in design of such complexes as MRI CA and for protein paramagnetic NMR probes. It demonstrates usefulness of 17O NMR to study solution dynamics in complexes involving phosphorus acid derivatives and it may inspire use of this method to study dynamics of phosphoric acid derivatives (as e. g. phosphorus acid-based inhibitors of metalloenzymes) in different areas of chemistry.