Youzhi

A carbon-rich geodesic dome has been synthesized by linking 20 trigonal planar 1,3,5-linked phenylenes through 25 biaryl linkages. H. Isobe et al. describe in their Communication (DOI: 10.1002/anie.201702063) how the geodesic, corannulenoidal combination of one pentagon and five hexagons leads to the nanometer-sized bowl. Concave–convex molecular recognition results in the formation of a bowl-in-bowl dimer in both the crystalline state and in solution.

Nanoscale carbon-rich molecular architectures are not only aesthetically appealing but also of practical importance for energy and biomedical technologies. Herein, we report the synthesis of cyclic-oligophenylene-based nanopropeller 1 by using an efficient synthon strategy involving sequential intramolecular bisboronate homocoupling and reductive aromatization by H₂SnCl₄. The nanopropeller molecules pack into a layered hexagonal lattice featuring long-ranged nano-sized channels and a total guest-accessible volume of 48 %, as revealed by X-ray diffraction studies. We suggest that such a solid-state arrangement is determined by the interplay between the propeller architecture and the intermolecular van der Waals interactions.

Nanohoops propel ahead: A triptycene-based molecular propeller with three nanohoop blades was synthesized by a three-fold intramolecular bisboronate homocoupling and subsequent reductive aromatization. Such nanopropeller molecules pack into a lamellar hexagonal structure with 11 Å-diameter channels that run perpendicularly to the layers.

A facile two-step synthesis of aza[7]helicenes possessing a 6-5-6-6-6-5-6 skeleton from commercially available 2,9-dichloro-1,10-phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent-mediated intramolecular double-NH/CH couplings was developed. Single-crystal X-ray analyses of the helicenes revealed unique structures, including both a significantly twisted center and planar terminals of the skeleton. The azahelicenes show high fluorescent quantum yields (Φs) under both neutral (Φ: 0.25–0.55) and acidic conditions (Φ: up to 0.80). An enantiomerically pure aza[7]helicene showed high circularly polarized luminescence (CPL) activity under both neutral and acidic conditions (g_lum: up to 0.009).

A two-step synthesis of polyaza[7]helicene from a commercially available compound by hypervalent iodine reagent-mediated NH/CH double coupling is described. The azahelicenes show high fluorescent quantum yield (Φ up to 0.80) and a enantiomerically pure tetraazahelicene emits strong circularly polarized luminescence (CPL) with high g_lum values (up to 0.009) under both neutral and acidic conditions.

We report on a series of electron donor–acceptor conjugates incorporating a Zn^II–porphyrin-based electron donor and a variety of non-conjugated rigid linkers connecting to push–pull chromophores as electron acceptors. The electron acceptors comprize multicyanobutadienes or extended tetracyanoquinodimethane analogues with first reduction potentials ranging from −1.67 to −0.23 V vs. Fc⁺/Fc in CH₂Cl₂, which are accessible through a final-step cycloaddition–retroelectrocyclization (CA-RE) reaction. Characterization of the conjugates includes electrochemistry, spectroelectrochemistry, DFT calculations, and photophysical measurements in a range of solvents. The collected data allows for the construction of multiple Marcus curves that consider electron-acceptor strength, linker length, and solvent, with data points extending well into the inverted region. The enhancement of electron–vibration couplings, resulting from the rigid spacers and, in particular, multicyano-groups in the conformationally highly fixed push–pull acceptor chromophores affects the charge-recombination kinetics in the inverted region drastically.

Molecular photovoltaics: A series of electron donor–acceptor conjugates incorporating a Zn^II–porphyrin-based electron donor and multicyanobutadienes or extended tetracyanoquinodimethane analogues as electron acceptors with first reduction potentials ranging from −1.67 to −0.23 V vs. Fc⁺/Fc. As such, the rich redox chemistry, broad absorption in the visible and near infrared region, and electron-transfer behavior upon photoexcitation with charge recombination kinetics in the inverted region render these systems promising materials for applications in the field of molecular photovoltaics.

A ruthenium complex, porphyrin sensitizer, fullerene acceptor molecular pentad has been synthesized and a long-lived hole–electron pair was achieved in aqueous solution by photoinduced multistep electron transfer: Upon irradiation by visible light, the excited-state of a zinc porphyrin (¹ZnP*) was quenched by fullerene (C₆₀) to afford a radical ion pair, ^1,3(ZnP^.+-C₆₀^.−). This was followed by the subsequent electron transfer from a water oxidation catalyst unit (Ru^II) to ZnP^.+ to give the long-lived charge-separated state, Ru^III-ZnP-C₆₀^.−, with a lifetime of 14 μs. The ZnP worked as a visible-light-harvesting antenna, while the C₆₀ acted as an excellent electron acceptor. As a consequence, visible-light-driven water oxidation by this integrated photosynthetic model compound was achieved in the presence of sacrificial oxidant and redox mediator.

Pent-up energy: A ruthenium-based water oxidation catalyst linked to porphyrin–fullerene units in a molecular pentad has been synthesized. Transient absorption indicated the photoinduced multistep electron transfer afforded a long-lived hole–electron pair, and photocatalytic water oxidation by the pentad was achieved in the presence of sacrificial oxidant.

The enantiomers of a new cyclic oligothiophene, bridged by two pseudo-ortho[2.2]paracyclophanes, were synthesized as a new class of the chiral π-conjugated system. Single-crystal X-ray diffraction analysis revealed a twisted structure for these oligothiophenes induced by a torsion of the cyclophane moieties. The embedding oligothiophenes into the inherent planar chirality provided a significant enhancement in circular dichroism (CD) spectra thanks to the large magnetic/electric transition dipole moments. In the dicationic state, an intramolecular π dimer was formed due to the strong interactions of the oligothiophenes. We further recorded unprecedented wide ranges of CD spectra in 250–1800 nm region. The transitions are reasonably described by the exciton coupling of the oligothiophenes.

Cyclophanes: The enantiomers of a new cyclic oligothiophene derived from planar chiral [2.2]paracyclophanes were synthesized. Intense circular dichroism (CD) was observed due to the large magnetic/electric transition dipole moments. In the dicationic state, an intramolecular π dimer, which exhibited a pronounced CD response up to 1900 nm, was formed (see figure).

The insoluble product mixture obtained from cycloparaphenylene (CPP) synthesis from Suzuki coupling and reductive aromatization was analyzed. Traditional mass spectrometry suggests a homologous series of macrocycles with 12 to 84 phenylene units. Ion-mobility mass spectrometry, however, unravels an unexpected complexity of isomers with identical chemical formula, but different topologies. Whereas macrocycles containing up to 30 phenylene units show only one structure, the homologue with 36 phenylene units forms at least four different isomers with significant molecular size differences. They can be assigned to catenanes composed of CPPs with 2×18 and 12+24 phenylene units together with the ordinary [36]CPP macrocycle. Most likely, a trefoil knot of the CPP with 36 moieties is also present. For the first time, catenanes can be elucidated in a simple reaction mixture by analyzing their ions in the gas phase, an analysis which lies beyond the scope of traditional analytical methods.

Cycle upon cycle: Solvent-free MALDI ion-mobility mass spectrometry is used to analyze an insoluble product mixture of cycloparaphenylenes. For the first time, monocycles and isomeric catenanes can be detected in a simple reaction mixture, where only monocycles could be expected.

Methanol (CH₃OH) and formaldehyde (H₂CO) molecules were inserted into an open-cage C₆₀ 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. ¹H NMR spectroscopy, single-crystal X-ray diffraction studies, and DFT calculations revealed the orientation of the encapsulated CH₃OH and H₂CO, both in solution and in the solid state, and the results show that the CH₃ group of the CH₃OH and the carbonyl group of the H₂CO point to the bottom of the cages. Furthermore, the dynamic behavior of the CH₃OH and H₂CO were studied at the molecular level.

One and only: Molecular complexes encapsulating CH₃OH and H₂CO inside open-cage C₆₀ derivatives were synthesized. The orientations of the encapsulated species in solution and in the solid state were revealed by NMR analysis, single crystal X-ray analysis, and DFT calculations. Each species shows only one orientation: the CH₃ group of the CH₃OH sits on the curve of the carbon cage, whereas the CH₂ group of the H₂CO is directed toward the opening.