Sebastian Beil

Carbonaceous and curvaceous: A new strategy is described for the synthesis of heptagon‐containing all‐sp²‐hybridized carbon scaffolds from unfunctionalized alkene precursors. This direct approach is applied for the synthesis of a flexible, negatively‐curved polyaromatic hydrocarbon that exhibits excellent solubility, visible range absorption and fluorescence, and two reversible one‐electron oxidations at mild potentials.

Abstract

A new strategy is demonstrated for the synthesis of warped, negatively curved, all‐sp²‐carbon π‐scaffolds. Multifold C−C coupling reactions are used to transform a polyaromatic borinic acid into a saddle‐shaped polyaromatic hydrocarbon (2) bearing two heptagonal rings. Notably, this Schwarzite substructure is synthesized in only two steps from an unfunctionalized alkene. A highly warped structure of 2 was revealed by X‐ray crystallographic studies and pronounced flexibility of this π‐scaffold was ascertained by experimental and computational studies. Compound 2 exhibits excellent solubility, visible range absorption and fluorescence, and readily undergoes two reversible one‐electron oxidations at mild potentials.

Cards on the table: Cyclopenta[hi]aceanthrylenes (CPAs) functionalized at two of the peripheral positions with trimethylsilylethynyl, as well as with electron‐donating 4‐ethynyl‐N,N‐dimethylaniline, ethynyl Zn^II phthalocyanine, and ethynyl Zn^II porphyrin units have been prepared and investigated by means of photophysical, electrochemical, and spectro‐electrochemical techniques.

Abstract

Cyclopenta[hi]aceanthrylenes (CPAs) have been functionalized at two of the peripheral positions with electronically inert trimethylsilylethynyl (1), as well as with electron‐donating 4‐ethynyl‐N,N‐dimethylaniline (2), ethynyl Zn^IIphthalocyanine (3), and ethynyl Zn^IIporphyrin (4) units. Consistent with X‐ray crystal structures of 2 and 4, analyses of absorption and fluorescence of 2–4 point to strong electronic communication between the CPA and the peripheral units, affording quadrupolar electron donor‐acceptor‐donor charge‐transfer conjugates. By virtue of their quadrupolar/dipolar charge‐transfer characters in the excited state, 2–4 exhibit fluoro‐solvatochromism. Transient absorption spectroscopy confirmed delocalized quadrupolar ground states and formation of weakly solvent stabilized quadrupolar singlet excited states. The latter transform into strongly stabilized dipolar excited states before deactivating to the ground state in 2 and give rise to a fully charge separated state in 3 and 4.

Under strain: 1,3‐dithiolium‐4‐olates reacted with strained alkynes, affording polyaromatic thiophene structures in high yields. Their use for ligation applications has also been investigated with cyclooctynes, offering a new orthogonal reaction to the strain‐promoted azide–alkyne reaction.

Abstract

Reported here is the reactivity of mesoionic 1,3‐dithiolium‐4‐olates towards strained alkynes, leading to thiophene cycloaddition products. In the process, the potential of these dipoles towards orthogonal reaction with azides, allowing efficient double ligation reactions, was discovered. A versatile process to access benzo[c]thiophenes, in an unprecedented divergent fashion, was developed and provides a new entry to unconventional polyaromatic thiophenes.

Nature, Published online: 20 September 2019; doi:10.1038/d41586-019-02830-y

Nature Communications, Published online: 10 September 2019; doi:10.1038/s41467-019-11690-z

Nature, Published online: 09 September 2019; doi:10.1038/s41586-019-1539-y

Conjugated carbon cyclic nanoring compounds are used as molecular additives to enhance the stretchability of semiconducting polymers without compromising mobility. The additives are shown to significantly decrease long‐range crystalline order, while short‐range ordered aggregates are well‐maintained. Fully stretchable transistors fabricated with the newly established polymer semiconductor/molecular additive blend films exhibit improved mobility retention under strain and after repeated applied strain.

Abstract

Molecular additives are often used to enhance dynamic motion of polymeric chains, which subsequently alter the functional and physical properties of polymers. However, controlling the chain dynamics of semiconducting polymer thin films and understanding the fundamental mechanisms of such changes is a new area of research. Here, cycloparaphenylenes (CPPs) are used as conjugated molecular additives to tune the dynamic behaviors of diketopyrrolopyrrole‐based (DPP‐based) semiconducting polymers. It is observed that the addition of CPPs results in significant improvement in the stretchability of the DPP‐based polymers without adversely affecting their mobility, which arises from the enhanced polymer dynamic motion and reduced long‐range crystalline order. The polymer films retain their fiber‐like morphology and short‐range ordered aggregates, which leads to high mobility. Fully stretchable transistors are subsequently fabricated using CPP/semiconductor composites as active layers. These composites are observed to maintain high mobilities when strained and after repeated applied strains. Interestingly, CPPs are also observed to improve the contact resistance and charge transport of the fully stretchable transistors. ln summary, these results collectively indicate that controlling the dynamic motion of polymer semiconductors is proved to be an effective way to improve their stretchability.

Nature, Published online: 30 August 2019; doi:10.1038/d41586-019-02607-3

Nucleophilic substitution reactions of alcohols are among the most fundamental and strategically important transformations in organic chemistry. For over half a century, these reactions have been achieved by using stoichiometric, and often hazardous, reagents to activate the otherwise unreactive alcohols. Here, we demonstrate that a specially designed phosphine oxide promotes nucleophilic substitution reactions of primary and secondary alcohols in a redox-neutral catalysis manifold that produces water as the sole by-product. The scope of the catalytic coupling process encompasses a range of acidic pronucleophiles that allow stereospecific construction of carbon-oxygen and carbon-nitrogen bonds.

Circulatory phase transfer was demonstrated based upon a stimuli‐responsive coordination cage with two different anion binding modes. The direction of cage circulation in a triphasic system of three immiscible solvents can be controlled by the order of addition of three different anions.

Abstract

Controlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.

Iron and cyanide: A new role is proposed for cyanide as a geochemical agent in promoting prebiotic phosphorylation. Cyanide and its metal complexes can transform and mobilize phosphate from its insoluble iron and calcium minerals, suggesting that phosphate could have been more mobile and prebiotic phosphorylation not as challenging as previously believed on the early Earth.

Abstract

Organophosphates were likely an important class of prebiotic molecules. However, their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals, is widely viewed as a major barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea‐based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a “warm little pond” scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes, urea, ammonium formate, and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allow us to propose a holistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals, allowing significant organic phosphorylation under plausible prebiotic conditions.

Ultralong organic phosphorescence (UOP)can be controlled by manipulating the stacking of the triplet chromophores within a crystal form. The stronger the interaction between carbazole chromophores the more favorable the generation of UOP (see 24CPhCz and 34CPhCz in the picture). Weaker interactions between the triplet chromophores, accompanied by strong interactions between benzene units resulted the disappearance of UOP and appearance of thermally activated delayed fluorescence (TADF; 35CPhCz).

Abstract

Provided here is evidence showing that the stacking between triplet chromophores plays a critical role in ultralong organic phosphorescence (UOP) generation within a crystal. By varying the structure of a functional unit, and different on‐off UOP behavior was observed for each structure. Remarkably, 24CPhCz, having the strongest intermolecular interaction between carbazole units exhibited the most impressive UOP with a long lifetime of 1.06 s and a phosphorescence quantum yield of 2.5 %. 34CPhCz showed dual‐emission UOP and thermally activated delayed fluorescence (TADF) with a moderately decreased phosphorescence lifetime of 770 ms, while 35CPhCz only displayed TADF owing to the absence of strong electronic coupling between triplet chromophores. This study provides an explanation for UOP generation in crystal and new guidelines for obtaining UOP materials.

Reagent‐free redox‐driven nanoconfinement of polyoxometalate clusters within single‐walled carbon nanotubes is demonstrated. The densely packed chains of the polyoxometalate (POM) anions within cationic single‐walled carbon nanotubes form spontaneously and irreversibly under ambient conditions. Protected from the external environment and effectively “wired” to the carbon support, the nanoconfined redox‐active POMs exhibit exceptional electrochemical stability, even in environments in which they cannot usually exist.

Abstract

The development of next‐generation molecular‐electronic, electrocatalytic, and energy‐storage systems depends on the availability of robust materials in which molecular charge‐storage sites and conductive hosts are in intimate contact. It is shown here that electron transfer from single‐walled carbon nanotubes (SWNTs) to polyoxometalate (POM) clusters results in the spontaneous formation of host–guest POM@SWNT redox‐active hybrid materials. The SWNTs can conduct charge to and from the encapsulated guest molecules, allowing electrical access to >90% of the encapsulated redox species. Furthermore, the SWNT hosts provide a physical barrier, protecting the POMs from chemical degradation during charging/discharging and facilitating efficient electron transfer throughout the composite, even in electrolytes that usually destroy POMs.

Molecular machines: Four [3]rotaxane‐based molecular shuttles with two interacting macrocycles have been synthesized. The interactions among the three components (two macrocycles and one axle) were shown to not only affect the relative positions of the macrocycles along the axles with different spacer lengths, but also cause a synchronized motion of the two macrocycles when adding stimuli.

Abstract

Noncovalent interactions between all the neighboring components in biomolecular machines are responsible for their synchronized motion and thus complex functions. This strategy has rarely been used in multicomponent molecular machines. Here, we report four [3]rotaxane‐based molecular shuttles. Noncovalent interactions among the three components (two interacting macrocycles and one axle) not only cause a “systems‐level” effect on the relative positions of the two macrocycles along the axle, but also result in a synchronized motion of the two macrocycles when adding partial amount of stimuli. Moreover, the intermediate state with one shuttled macrocycle even exist predominantly in the solution during the titration of stimuli, which is theoretically unexpected for the [3]rotaxane with two non‐interacting rings. This biomimetic strategy may provide a method for constructing highly complex molecular machines.

Nature, Published online: 19 August 2019; doi:10.1038/d41586-019-02479-7