Phosphine-Promoted Synthesis of Naphthoquinones Fused with Cyclopentadienyl Moiety Via Ring Expansion: Synthesis, Reactivity, and Ring Contraction Via [1,5] Sigmatropic Rearrangement.

Phosphine-promoted unprecedented [3 + 2] annulation reactions via ring expansion by using 2-benzylidene-indane-1,3-diones and diynoates for the synthesis of biologically interesting novel naphthoquinones fused with a five-membered ring bearing a phosphorus ylide up to 78% yield are described. Further ring contraction through [1,5] sigmatropic rearrangement to the spiro indan-1,3-diones by CPBA oxidation was revealed and inferred through oxidation, followed by protonation. The relevant structures were confirmed by single-crystal X-ray diffraction.

Isomerism tunes the diradical character of difluorenopyrroles at constant Hückel-level anti-aromaticity.

A new diradical based on diindenocarbazole or difluorenopyrrole was synthesized and experimentally characterized by optical, electrochemical, and magnetic techniques, as well as quantum chemical calculations. The isomerism of these structures tunes the diradical character and the associated properties, representing a unique case of such important modulation. A full study of the electronic structure was carried out considering the perturbative interactions between different canonical forms as well as the anti-aromatic character of the molecular cores.

A Highly Conductive n-Type Coordination Complex with Thieno[3,2-]thiophene Units: Facile Synthesis, Orientation, and Thermoelectric Properties.

An organometallic nickel complex containing thieno[3,2-]thiophene units was designed and synthesized. Composite films of the resulting nickel complex and polyvinylidene difluoride, which can be fabricated via a simple solution process under atmospheric conditions, exhibit remarkably high n-type conductivity (>200 S cm). Moreover, the thermoelectric power factor of the n-type composite film was proven to be air stable.

Promoting the Efficiency and Stability of Nonfullerene Organic Photovoltaics by Incorporating Open-Cage [60]Fullerenes in the Nonfullerene Nanocrystallites.

The device efficiency of :-based nonfullerene organic solar cells is fast advanced recently. To maintain organic solar cells (OSCs) with high power conversion efficiency over 16% in long-term operation, however, remains a challenge. Here, a novel non-volatile additive, an open-cage [60]fullerene (), is incorporated into -based OSCs for high-performance with high durability.

-Tetrafluorophenylene Divinylene-Bridged Nonfullerene Acceptors as Binary Components or Additives for High-Efficiency Organic Solar Cells.

In this study, we designed, synthesized, and characterized an A-D-A'-D-A-type indacenodithienothiophene ()-based molecular acceptor that exhibited a broader absorption range and higher lowest unoccupied molecular orbital energy level with a nearly comparable band gap compared to a well-known electron acceptor . The designed electron-deficient molecular acceptor with a fluorinated benzene tether (), that is, -tetrafluorophenylene divinylene, demonstrated long-wavelength absorption and high hole and electron charge mobility in the thin films blended with the electron donor for an inverted organic photovoltaic (OPV) binary device, resulting in a maximum power conversion efficiency (PCE) of 11.4%.

Open-shell singlet diradicaloid difluoreno[4,3-b:3',4'-d]furan and its radical cation and dianion.

Difluoreno[4,3-b:3',4'-d]furan (DFFu) was prepared via a short, scalable, multi-step synthesis, and characterized by crystallography, spectroscopic measurements, and theoretical calculations. Even though the results revealed an open-shell singlet diradical character, DFFu is stable under ambient conditions. The radical cationic and dianionic species of DFFu were also synthesized and characterized.

Near- and Mid-IR Gas-Phase Absorption Spectra of H@C-He.

Near- and mid-IR absorption spectra of endohedral H@C have been measured using He-tagging. The samples have been prepared using a "molecular surgery" synthetic approach and were ionized and spectroscopically characterized in the gas phase. In contrast to neutral C and H@C, the corresponding He-tagged cationic species show distinct spectral differences.

Palladium-Catalyzed Cyclization: Regioselectivity and Structure of Arene-Fused C Derivatives.

The palladium-catalyzed cyclization on the fullerene C cage has been achieved using several aryl halides and C. This reaction was found to be accelerated by the addition of pivalic acid, which can be rationally explained by the computational study based on the concerted metalation-deprotonation mechanism. We also demonstrated the regioselective π-functionalization using prefunctionalized designed molecules possessing the same substructure on the C cage.

Fullerene C as a Nanoflask that Reveals the Chemical Reactivity of Atomic Nitrogen.

To investigate the intrinsic reactivity of atomic nitrogen, which had previously been accomplished only by examining its decay in the gas phase using special equipment, a nitrogen atom was inserted into a series of molecule-encapsulating C and C fullerenes. Among the studied endofullerenes, H @C was able to encapsulate an additional nitrogen atom within the fullerene cage under radiofrequency plasma conditions. The product was analyzed by ESR spectroscopy and mass spectrometry in solution, which revealed that the nitrogen atom with a quartet ground state does not react but weakly interact with the H molecule, thus demonstrating the utility of such fullerenes as "nanoflasks".

Isolation of the simplest hydrated acid.

Dissociation of an acid molecule in aqueous media is one of the most fundamental solvation processes but its details remain poorly understood at the distinct molecular level. Conducting high-pressure treatments of an open-cage fullerene C derivative with hydrogen fluoride (HF) in the presence of HO, we achieved an unprecedented encapsulation of HO·HF and HO. Restoration of the opening yielded the endohedral Cs, that is, (HO·HF)@C, HO@C, and HF@C in macroscopic scales.

Orientation of a Water Molecule: Effects on Electronic Nature of the CN Cage.

A hydrogen-bonding network is a key impelling force for an assembly in bulk water. The fullerene cage can incarcerate a water molecule without hydrogen-bonding. Herein, we focused on spin system HO@CN.

Unsymmetric Twofold Scholl Cyclization of a 5,11-Dinaphthyltetracene: Selective Formation of Pentagonal and Hexagonal Rings via Dicationic Intermediates.

Even though the Scholl reaction is one of the most powerful processes for the synthesis of polycyclic aromatic hydrocarbons (PAHs), its mechanism still remains a subject of discussion. Herein, we report a unique twofold Scholl cyclization of a 5,11-dinaphthyltetracene. Single-crystal X-ray diffraction analysis of the cyclization product revealed that unsymmetric cyclizations of the two naphthyl groups resulted in the formation of fully unsaturated pentagonal and hexagonal rings.

A Stable, Soluble, and Crystalline Supramolecular System with a Triplet Ground State.

A supramolecular complex was constructed by encapsulation of a O molecule inside an open-cage C derivative. Its single-crystal X-ray diffraction analysis revealed the presence of the O at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated O after two-electron reduction.

Encapsulation and Dynamic Behavior of Methanol and Formaldehyde inside Open-Cage C Derivatives.

Methanol (CH OH) and formaldehyde (H CO) molecules were inserted into an open-cage C derivative with a large opening, under high-pressure and high-temperature conditions in solution. Isolation of their molecular complexes in pure form was achieved by the use of recycling HPLC with Buckyprep columns. H NMR spectroscopy, single-crystal X-ray diffraction studies, and DFT calculations revealed the orientation of the encapsulated CH OH and H CO, both in solution and in the solid state, and the results show that the CH group of the CH OH and the carbonyl group of the H CO point to the bottom of the cages.

Dithieno-Fused Polycyclic Aromatic Hydrocarbon with a Pyracylene Moiety: Strong Antiaromatic Contribution to the Electronic Structure.

A synthetic route to dithieno-fused CP-PAHs with a pyracylene segment is reported. A combination of experimental and theoretical studies revealed a strong contribution of antiaromatic character to the electronic structure of this dithieno-fused CP-PAH. Anisotropy of current-induced density (ACID) calculations indicated a significantly increased paramagnetic ring current on the two pentagonal rings, which is more prominent than that of the dibenzo-fused analogue.

Unprecedented photochemical rearrangement of an open-cage C derivative.

Upon irradiation of a sulfoxide C derivative with a 17-membered-ring opening, rearrangement of the carbon framework took place to give an unprecedented lactone C derivative with a 14-membered-ring opening, whose structure was unambiguously determined by single crystal X-ray analysis. This reaction is completely different from that of the previously reported sulfoxide C and C derivatives with a 13-membered-ring opening.

4,7-Bis[3-(dimesitylboryl)thien-2-yl]benzothiadiazole: Solvato-, Thermo-, and Mechanochromism Based on the Reversible Formation of an Intramolecular B-N Bond.

4,7-Bis-[3-(dimesitylboryl)thien-2-yl]benzothiadiazole (1) and monoborylated derivative 2 were synthesized and their chromic behavior was investigated. Photophysical measurements, single-crystal XRD analysis, and theoretical calculations revealed that an intramolecular B-N coordination bond formed reversibly. The equilibrium of this reversible bond formation depends on the solid-state structure, solvent, temperature, and mechanical forces, and leads to significant changes in the electronic structure and chromic behavior of these molecules.

Co(I)-Mediated Removal of Addends on the C Cage and Formation of the Monovalent Cobalt Complex CpCo(CO)(η-C).

The removal of addends on the fullerene C cage plays an important role in the final stage for synthesizing endohedral fullerenes by the molecular surgery method. We developed a cobalt-mediated reaction to regenerate C from N-substituted C derivatives (aziridinofullerene and azafulleroid). In these reactions, we found the formation of a green monovalent-cobalt complex of C, and its structure was unambiguously determined by X-ray analysis.

Water Entrapped inside Fullerene Cages: A Potential Probe for Evaluation of Bond Polarization.

The concept of the bond polarization is a useful tool to understand chemical reactions and fundamental properties of compounds. However, experimental considerations are limited owing to its difficulty of reliable description. We demonstrated that geometrically isolated H O inside the cage of fullerene C is a possible probe to evaluate the polarization degree of covalent bonds C(C )-X (X=heteroatom) on the C cage.

Synthesis of a distinct water dimer inside fullerene C70.

The water dimer is an ideal chemical species with which to study hydrogen bonds. Owing to the equilibrium between the monomer and oligomer structure, however, selective generation and separation of a genuine water dimer has not yet been achieved. Here, we report a synthetic strategy that leads to the successful encapsulation of one or two water molecules inside fullerene C70.

Synthesis and Properties of Endohedral Aza[60]fullerenes: H₂O@C₅₉N and H₂@C₅₉N as Their Dimers and Monomers.

The macroscopic-scale syntheses of the first endohedral aza[60]fullerenes X@C59N (X = H2O, H2) were achieved in two different ways: (1) synthesis from endohedral fullerene H2O@C60 as a starting material and (2) molecular surgical synthesis from a C59N precursor having a considerably small opening. In the neutral state of H2O@C59N, we expected the H-bonding interaction or repulsive N-O interaction between entrapped H2O and a nitrogen atom on the C59N cage. However, an attractive electrostatic N-O interaction was suggested from the results of variable temperature NMR, nuclear magnetic relaxation times (T1, T2), and density functional theory (DFT) calculations.

Trapping N2 and CO2 on the Sub-Nano Scale in the Confined Internal Spaces of Open-Cage C60 Derivatives: Isolation and Structural Characterization of the Host-Guest Complexes.

An open-cage C60 tetraketone with a large opening was able to encapsulate N2 and CO2 molecules after its exposure to high pressures of N2 and CO2 gas. A subsequent selective reduction of one of the four carbonyl groups on the rim of the opening induced a contraction of the opening (→2) and trapped the guest molecules inside 2. The thus-obtained host-guest complexes N2@2 and CO2@2 could be isolated by recycling HPLC, and were found to be stable at room temperature.

Electron-Deficient Tetrabenzo-Fused Pyracylene and Conversions into Curved and Planar π-Systems Having Distinct Emission Behaviors.

Polycyclic aromatic compounds containing fully unsaturated five-membered ring(s) have been intensively studied because of their unique properties, which include high electron affinity and reactivity. Reported herein is an efficient route for the synthesis of tetrabenzo-fused pyracylene, which comprises pyracylene and tetracene segments, using intramolecular oxidative C-H coupling. It was shown to possess high electron affinity and was found to undergo addition reactions with n-butyllithium or benzyne.