Fabian Schwer

Organic Materials 2023; 5: 35-47
DOI: 10.1055/a-1972-5895

Herein, a novel and versatile method for the synthesis of N-heteroarylated dithieno[3,2-b:2,3′-d]pyrroles (DTPs) is reported. By microwave-assisted Cu-catalyzed coupling of parent H-DTP 1 with 5- and 6-membered heteroaromatic halides, a variety of novel N-functionalized DTPs were obtained. Supported by quantum chemical calculations and X-ray structure analysis, structural and optoelectronic properties of the π-conjugated systems were investigated and led to valuable structure–property relationships. Selected derivatives were electropolymerized to corresponding conducting DTP polymers.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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A series of highly twisted and fully armchair-edged graphene nanoribbons (AGNRs) have been synthesized by Cu-catalyzed deoxygenative coupling. These twisted AGNRs have lengths up to 2.65 nm and display strong emission with a fluorescence quantum yield up to 81 %.

Abstract

Graphene nanoribbons (GNRs) are promising in organic optoelectronic materials, and their properties largely depend on the size, edge, and conformation. Herein, the fully armchair-edged GNRs (AGNRs) with lengths up to 2.65 nm by using a Cu-catalyzed deoxygenative coupling as a key step. The resulting AGNRs (2HBT, 3HBT, and 4HBT) possess highly twisted π-scaffolds, and the torsion angles between the adjacent triphenylene moieties are larger than 32°, as proved by crystallographic analyses. Theoretical and spectroscopic studies show that the butoxy groups endow AGNRs with electron-rich features, the extension of the π-system from 2HBT to 4HBT reinforces S₀→S₁ excitation, and the distortion of the π-scaffold enhances the fluorescence quantum yield (Φ _F). In particular, 4HBT has the lowest oxidation potential (E _ox ¹=0.55 V vs. SCE) and displays red fluorescence with a Φ _F value of 81 %.

Organic Materials 2022; 4: 73-85
DOI: 10.1055/a-1906-6875

Two [60]fullerene dumbbell-like molecules with a single or double perylene-3,4,9,10-tetracarboxylic acid bisimide (PBI) linker were synthesized to study the structural and photophysical properties in addition to the complex formation with [10]cycloparaphenylene ([10]CPP). Due to their special optical properties, it is possible to describe the complexation using conventional spectroscopic methods such as NMR and fluorescence. However, isothermal titration calorimetry (ITC) was used to complete the analysis of the bis-pseudorotaxane formation by investigating the binding stoichiometries as well as the thermodynamic and kinetic parameters. It was observed that the PBI bridges do not inhibit the complexation with [10]CPP, giving rise to the formation of 1 : 1 and 1 : 2 complexes in o-dichlorobenzene with affinities of around 105 · M−1, similar to the [10]CPP⊃C60 reference system. A novel global analysis by combination of data sets from different techniques allowed us to follow the species distribution very precisely. ITC has proven to be a very powerful method for studying the complexation between fullerene derivatives and strained carbon nanohoops, which provides not only binding affinities and stoichiometries, but also all thermodynamic and kinetic parameters of the bis-pseudorotaxane formation. These results are of significant interest for the investigation of fullerene complexes in supramolecular chemistry and for their future applications in semiconductors and optoelectronics.
[...]

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Analogous to allosteric enzymes, guest binding introduces a directional pulling or pushing force that acts on the reverse side of a Zn salen complex. This tunable intramolecular force promotes various degrees of conformational and torsional strain, as predicted by both classical conformational analysis and DFT. This strain energy can be further applied to cleave chemical bonds, and the efficiency can be tuned by the identity of the allosteric guest.

Abstract

Recently, polymer mechanochemistry has attracted much scientific interest due to its potential to develop degradable polymers. When the two ends of a polymer chain experience a linear pulling stress, molecular strain builds up, at sufficiently strong force, a bond scission of the weakest covalent bond results. In contrast, bond-breaking events triggered by conformational stress are much less explored. Here, we discovered that a Zn salen complex would undergo conformational switching upon allosteric complexation with alkanediammonium guests. By controlling the guest chain length, the torsional strain experienced by Zn complex can be modulated to induce bond cleavage with chemical stimulus, and reactivity trend is predicted by conformational analysis derived by DFT calculation. Such strain-release reactivity by a Zn(salen) complex initiated by guest binding is reminiscent of conformation-induced reactivity of enzymes to enable chemical events that are otherwise inhibited.

A pentabenzopentaaza[10]circulene has been synthesized as the largest fully conjugated hetero[n]circulene via a fold-in oxidative fusion reaction of a cyclic pentapyrrole precursor. This circulene takes a saddle-distorted structure with bond lengths of the central ten-membered-ring in the range of 1.455–1.493 Å. The energy barrier for saddle-to-saddle interconversion was estimated to be quite small (≈3 kcal mol⁻¹).

Abstract

A pentabenzopentaaza[10]circulene has been synthesized as the largest fully conjugated hetero[n]circulene via a fold-in oxidative fusion reaction of an ortho-phenylene-bridged cyclic pyrrole pentamer. This circulene takes a saddle-distorted structure with bond lengths of the central ten-membered-ring in the range of 1.455–1.493 Å. Relatively broad absorption and fluorescence spectra were observed, which reflects its flexible structure, in accordance with the low-temperature NMR spectra and theoretical calculations. The energy barrier for saddle-to-saddle interconversion was estimated to be quite small (≈3 kcal mol⁻¹).

Cobalt carbonyl complexes have been used as temporary masking group, and temporary stoppers, in the synthesis of polyyne [3]rotaxanes with two macrocycles threaded on a C₂₈ thread. Comparison of the thermal stability of two [3]rotaxanes with different threaded macrocycles shows that the 2,6-pyridyl cycloparaphenylene nanohoop effectively stabilizes the polyyne chain.

Abstract

New strategies for synthesizing polyyne polyrotaxanes are being developed as an approach to stable carbyne “insulated molecular wires”. Here we report an active metal template route to polyyne [3]rotaxanes, using dicobalt carbonyl masked alkyne equivalents. We synthesized two [3]rotaxanes, both with the same C₂₈ polyyne dumbbell component, one with a phenanthroline-based macrocycle and one using a 2,6-pyridyl cycloparaphenylene nanohoop. The thermal stabilities of the two rotaxanes were compared with that of the naked polyyne dumbbell in decalin at 80 °C, and the nanohoop rotaxane was found to be 4.5 times more stable.

Two exceeds one: Diazapentabenzocorannulenium, a cationic corannulene derivative bearing an internal imidazolium core, was prepared by a bottom-up synthetic strategy. The introduction of positive charge and two nitrogen atoms into corannulene resulted in remarkable molecular properties, such as the formation of charge-segregated one-dimensional columns, high dispersibility in water, and selective introduction into the mitochondria of tumor cells.

Abstract

Polycyclic aromatic molecules are promising functional materials for a wide range of applications, especially in organic electronics. However, their largely hydrophobic nature has impeded further applications. As such, imparting high solubility/hydrophilicity to polycyclic aromatic molecules leads to a breakthrough in this research field. Herein, we report the synthesis of diazapentabenzocorannulenium, a cationic nitrogen-embedded buckybowl bearing a central imidazolium core, by a bottom-up strategy from polycyclic aromatic azomethine ylide. X-ray crystallography analyses have revealed a bowl-shaped molecular structure that is capable of forming charge-segregated one-dimensional columns by bowl-in-bowl packing. In addition to its fluorescence capabilities and high dispersibility in water, the molecule was found to selectively localize in the mitochondria of various tumor cells, showing potential as viable mitochondria-selective fluorescent probes.

Concave–convex interactions between negatively and positively curved molecular nanographene with C₆₀ allow the formation of complexes with 1:1, 1:2, and 2:1 stoichiometries. Theoretical calculations predict the photoinduced electron transfer from the curved nanographene to the electron acceptor C₆₀. Transient absorption spectroscopy confirms solvent dependent electron transfer after photo-excitation.

Abstract

The formation of supramolecular complexes between C₆₀ and a molecular nanographene endowed with both positive and negative curvatures is described. The presence of a corannulene moiety and the saddle shape of the molecular nanographene allows the formation of complexes with 1:1, 1:2, and 2:1 stoichiometries. The association constants for the three possible supramolecular complexes were determined by ¹H NMR titration. Furthermore, the stability of the three complexes was calculated by theoretical methods that also predict the photoinduced electron transfer from the curved nanographene to the electron acceptor C₆₀. Time-resolved transient absorption measurements on the ns-time scale showed that the addition of C₆₀ to NG-1 solutions and photo-exciting them at 460 nm leads to the solvent-dependent formation of new species, in particular the formation of the one-electron reduced form of C₆₀ in benzonitrile was observed.

We present a new type of MIM comprised by two “open” U-shaped metallotweezers. The dissociation into its two components is hampered by mechanical bonds, as the presence of bulky tert-butyl groups provides the mechanical coercion required for avoiding the slippage that would otherwise produce the disassembly.

Abstract

In this study we report the preparation of a new mechanically interlocked molecule formed by the self-aggregation of two metallotweezers composed by two pyrene-imidazolylidene gold(I) arms and a pyridine-centered pentacyclic bis-alkynyl linker. The mechanically interlocked nature of this molecule arises from the presence of the bulky tert-butyl groups attached to the sides of the pyrene moieties of the arms of the tweezer, which act as stoppers avoiding the dissociation of the self-aggregated metallotweezer dimer once it is formed. By combining experimental techniques, we were able to confirm the mechanically interlocked nature of this molecule in solution, in the gas phase and in the solid state. The behavior of the tert-butyl substituted tweezer differs greatly form that shown by the tweezer lacking of these bulky groups, whose dimeric structure is in equilibrium with the monomeric structure, therefore not showing any mechanical coercion that avoids the disassembly of the self-aggregated structure.

The synthesis and properties of a perylene bisimide dye bridged by one or two quinquethiophene units are described. The compounds show panchromatic light absorption in the UV/Vis spectrum, multiple reversible redox processes, and a highly efficient charge separation by photoinduced electron transfer.

Abstract

Two macrocyclic architectures comprising oligothiophene strands that connect the imide positions of a perylene bisimide (PBI) dye have been synthesized via a platinum-mediated cross-coupling strategy. The crystal structure of the double bridged PBI reveals all syn-arranged thiophene units that completely enclose the planar PBI chromophore via a 12-membered macrocycle. The target structures were characterized by steady-state UV/Vis absorption, fluorescence and transient absorption spectroscopy, as well as cyclic and differential pulse voltammetry. Both donor–acceptor dyads show ultrafast Förster Resonance Energy Transfer and photoinduced electron transfer, thereby leading to extremely low fluorescence quantum yields even in the lowest polarity cyclohexane solvent.

A zinc phthalocyanine-[7]helicene hybrid molecular structure forms a discrete homochiral dimer and exhibits chiral self-sorting behavior also in a racemic mixture. The self-assembled dimeric structure shows remarkable stability in solution and the solid state, as well as effective electronic communication. The [7]helicene units induce an intense CD effect to the characteristic absorption band in the NIR region of phthalocyanine.

Abstract

In this communication, we demonstrate a novel approach to prepare a discrete dimer of chiral phthalocyanine (Pc) by exploiting the flexible molecular geometry of helicenes, which enables structural interlocking and strong aggregation tendency of Pcs. Synthesized [7]helicene-Pc hybrid molecular structure, zinc-[7]helicenocyanine (Zn-7HPc), exclusively forms a stable dimeric pair consisting of two homochiral molecules. The dimerization constants were estimated to be as high as 8.96×10⁶ M⁻¹ and 3.42×10⁷ M⁻¹ in THF and DMSO, respectively, indicating remarkable stability of dimer. In addition, Zn-7HPc exhibited chiral self-sorting behavior, which resulted in preferential formation of a homochiral dimer also in the racemic sample. Two phthalocyanine subunits in the dimeric form strongly communicate with each other as revealed by a large comproportionation constant and observation of an IV-CT band for the thermodynamically stable mixed-valence state.

Chiral π-conjugated nanopillar molecules based on naphthodithiophene diimide feature rigid pillar shapes along with a wealth of unique optical and chiral properties, which render them ideal building blocks for constructing important two-dimensional supramolecular architectures.

Abstract

The synthesis, structures, and properties of [4]cyclonaphthodithiophene diimides ([4]C-NDTIs) are described. NDTIs as important n-type building blocks were catenated in the α-positions of thiophene rings via an unusual electrochemical-oxidation-promoted macrocyclization route. The thiophene–thiophene junction in [4]C-NDTIs results in an ideal pillar shape. This interesting topology, along with appealing electronic and optical properties inherited from the NDTI units, endows the [4]C-NDTIs with both near-infrared (NIR) light absorptions, strong excitonic coupling, and tight encapsulation of C₆₀. Stable orientations of the NDTI units in the nanopillars lead to stable inherent chirality, which enables detailed circular dichroism studies on the impact of isomeric structures on π-conjugation. Remarkably, the [4]C-NDTIs maintain the strong π–π stacking abilities of NDTI units and thus adopt two-dimensional (2D) lattice arrays at the molecular level. These nanopillar molecules have great potential to mimic natural photosynthetic systems for the development of multifunctional organic materials.

A family of sulphur-embedded hydrocarbon belts, [n]cyclothianthrenes, were successfully constructed and characterized. The reported synthetic strategy allows access to not only the smallest and most strained cyclothianthrene, but also unprecedented chiral belts including a Möbius strip. Further studies reveal these belt-like molecules are redox-active and potential materials for host-guest chemistry.

Abstract

Cyclothianthrenes, a series of sulphur-embedded hydrocarbon belts proposed a decade ago, were successfully constructed through a stepwise bottom-up synthesis. The belt [6]cyclothianthrene ([6]CT) is the smallest and most strained member of the family yet reported. Both [6]CT and [8]CT are the first examples of cyclothianthrene characterized by single crystal X-ray diffraction. An unprecedented chiral belt [7]CT and a Möbius-shaped [9]CT were also achieved via modular synthesis. Crystallographic and computational studies show that belts [6]CT-[8]CT have prism-like conformations with well-defined tubular cavities which have potential for guest molecule inclusion. Cyclic voltammograms further revealed that these belts are redox-active. The success of constructing sulphur-embedded hydrocarbon belts, that is, cyclothianthrenes, greatly enriches the chemistry of heteroatom-doped molecular belts and tubes.

Organic Materials 2021; 03: 146-154
DOI: 10.1055/s-0041-1727182

The chemo- and regioselective functionalization of fullerenes is a long-standing problem of organic synthesis. Over the past five years, this fundamental challenge has gained technological relevance, because studies on single bis-adduct isomers in new-generation solar cells have demonstrated that the widespread use of isomer mixtures leads to suboptimal power conversion efficiencies. Herein, we review recent work on supramolecular approaches for achieving chemo- and regioselective syntheses of multiply functionalized derivatives of C60.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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