The reported syntheses of dipyrromethanes and tetrapyrroles suffer from accompanying polymerization processes lowering yields and necessitating a laborious workup. Here we present the reaction of geminal dimethoxyethers (i.e., acetals or ketals) with pyrrolic nucleophiles under mild conditions solving those problems. The observed minimal polymerization enables greatly simplified purification procedures. This is possible, because under anhydrous, mildly acidic conditions, geminal dimethoxyethers are more reactive than their carbonyl counterparts. The reaction of geminal dimethoxyethers with pyrrolic nucleophiles proceeds smoothly and selectively at 0 degrees C. Computational studies suggest that geminal dimethoxyethers react readily, while unfeasibly high intermediate energies hamper the reaction of carbonyl compounds under the same conditions. We demonstrate a high functional group tolerance and high yields by the preparation of 27 dipyrromethanes, one porphyrin, and 20 calix[4]pyrroles, many of which include synthetic anchor points for facile postfunctionalization. The method was scaled up to a 500 mmol scale for a dipyrromethane and a 252 mmol scale for a two-walled calix[4]pyrrole, without loss in yield or purity.

Many commonly used dye classes suffer from strong overlap of their absorption and emission spectra, favoring reabsorption and hampering the combination of several dyes for multi-analyte sensing with single wavelength excitation. This can be overcome by increasing the energy difference between absorption and emission using donor-acceptor dyes with charge-transfer processes. A neglected concept to finetune the Stokes shift is meta-substitution, which we exploited to design a single-benzene fluorophore exhibiting the largest Stokes shift of a zwitterionic compound. The meta-substitution of permanently-charged donor and acceptor groups provides a Stokes shift of >10 000 cm-1 (1.24 eV), absorbing light in the UV-region at 375 nm and emitting yellow-orange light at 605 nm. Relative to para-substitution, the orbitals are primed for more effective intramolecular charge-transfer and more energy is dissipated by structural reorganisation upon excitation, stemming from greater excited-state antiaromaticity. The large Stokes shift is retained by π-extended derivatives, thus meta-substitution of zwitterionic groups is a general way to design organic fluorophores with small spectral overlap.

Hexacyanotrimethylenecyclopropane (CN6CP) is an exceptionally strong organic electron acceptor in its neutral form, and widely applied for molecular doping to induce charge transfer processes and enable electrochemical systems. Yet, its fundamental molecular properties have remained largely unknown. Here, we show the first comprehensive structure-analytical characterization of CN6CP, enabled by an improved, low-temperature synthesis and the first solid-state structure of the neutral compound. The resulting procedure affords isolable, crystalline CN6CP that is stable for weeks at -30°C and can be recrystallised. Across all redox states, combined IR/Raman, UV-Vis and NMR measurements, together with NICS calculations, reveal an oxidation-state-dependent redistribution of electron density. These data show that CN6CP possesses a σ-aromatic cyclopropane core with tunable π-delocalisation, which is enhanced upon reduction while the additional charge is predominantly localised on the exocyclic acceptor framework. Cyclic voltammetry experiments unveil two reversible one-electron processes and an exceptionally low LUMO energy of -5.85 eV, which is the lowest reported for small organic molecules being significantly lower than those of benchmark acceptors such as F4TCNQ or F6TCNNQ. All together, these findings establish CN6CP as a structurally unique, extremely strong electron acceptor and provide the molecular basis underlying its performance in organic electronics and redox-active materials.

The new methodology for the diastereoselective synthesis of αα "two-wall" calix[4]pyrroles with aliphatic walls ("αα sp 3 C[4]Ps") offers a unique access to these elusive building blocks. Their conventional synthesis by acid-condensation of dipyrromethanes with acetone lacks stereocontrol and the formed αα and αβ diastereomers are commonly inseparable by chromatography. In this study, a robust chromatography method for "two-wall" sp 3 C[4]Ps was developed for the analysis of C[4]P diastereomeric mixtures. To circumvent the difficult, labour and material intensive diastereoseparations entirely, we developed a modular "scaffold-assisted" synthesis that utilises a catechol-based dicarboxylic acid tether "Henkel" and different dipyrromethanes for the convergent preparation of strapped C[4]Ps on the g-scale. Cleavage of the strap produces the desired αα C[4]P building blocks diastereoselectively. This approach offers a platform for the diastereoselective synthesis of various αα C[4]Ps due to the simplicity, inexpensiveness and scalability to the multi 100 g scale of the "Henkel" synthesis. Both, αα C[4]Ps with aromatic and aliphatic "walls" are easily obtained by the method in good to excellent yields. The obtained αα C[4]Ps are versatile building blocks for C[4]P-based supramolecular architectures and smart materials. Their structures are discussed based on XRD analysis. The small αα sp 3 C[4]P offers flexible walls and a synthetic handle close to the C[4]P core, while the αα sp 2 C[4]P features electron-poor aromatic walls. To aid future investigations, diverse post-modification methods for the C[4]Ps and their precursor dipyrromethanes were developed.

Oxo-graphene (oxoG), an alternative form of graphene oxide with a low number of defects, is regarded as a versatile platform for covalent surface modification due to its abundant oxygen functional groups and a large surface area. Among the different functionalization strategies, epoxide ring opening is widely employed. However, reactions using bifunctional molecules like 3-aminopropyltriethoxysilane (APTES) often produce unpredictable outcomes, jeopardizing the characterization and hampering a clear identification of the chemical structure of the resulting conjugate. Here, we investigate the functionalization of oxoG with APTES in different solvents, providing unequivocal evidence that the amine group preferentially reacts via epoxide ring opening. The resulting oxoG-APTES was characterized using X-ray photoelectron spectroscopy and thermogravimetric analysis. Subsequent silanization with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) confirmed the presence of terminal silane groups, and further nucleophilic ring-opening with 4-(trifluoromethyl)benzylamine (FMBA) validated the stepwise covalent modification. Simplified molecular model reactions analyzed via1H NMR corroborated these findings and highlighted the critical influence of solvent and temperature on the outcomes of multistep reactions. This study provides a detailed mechanistic understanding of oxoG functionalization using silanes and demonstrates the importance of combining complementary analytical techniques to unambiguously characterize the different conjugates, enabling more predictable design of graphene-based nanomaterials for advanced applications.

We report the synthesis, structural characterization, and optoelectronic properties of a highly electron‐deficient bi(cyclopropylidene)‐framework (CN8CP2). The developed one‐pot synthesis gives access to the dianionic species via thermally induced homocoupling of an iodinated precursor. The controlled oxidation yields the radical anion, whereas the neutral molecule is accessible only as an electrochemically generated in situ species. Single‐crystal X‐ray diffraction studies of the dianion reveal molecular layers separated by counterions, thereby enabling fluorescence in the solid state. The structure of the radical anion reveals a highly ordered arrangement of π‐stacked molecules. Optical spectroscopy and quantum chemical calculations indicate that the vibronic fine structure is governed by the vibrational modes of the cyclopropane core. The analysis of the electronic structures confirms extensive spin delocalization for the radical anion and a pronounced σ‐aromatic character. The exceptionally low energy levels of the acceptor orbitals are determined as −5.66 eV for the radical anion and −6.18 eV for the neutral species. Consequently, charge transfer to the neutral molecule or the radical anion results in the formation of the closed‐shell dianion, which circumvents instabilities that are associated with open‐shell species formed for conventional electron acceptors. Thus, CN8CP2 appears as one of the strongest small‐molecule organic acceptors for advanced organic electronic materials.

The first push-pull quino [3]radialene fluorescent dye is reported. Herein, the novel bis(dicyanomethylene)-[3]radialene electron acceptor is connected to a benzimidazole donor. With protonation, a substantial redshift of fluorescence wavelength is observed, while the absorption maximum remains stable. This process is accompanied with an increased fluorescence quantum yield to about 70%. Further, the findings are explained by a combined experimental and theoretical approach, and it is found that vibronic coupling plays a crucial role. This study highlights the yet unexplored potential of [3]radialene-based motifs for the design of environment-responsive fluorophores.

In the design of nanoscale materials, hybrid van der Waals heterostructures that integrate the excitonic landscape of atomically thin transition metal dichalcogenide (TMDC) semiconductors with molecular electric dipoles offer enhanced control over light-matter interactions and charge carrier dynamics. Even minor deviations in homogeneity can profoundly affect their optoelectronic properties and, consequently, device performance, necessitating stringent quality control capable of probing structural and compositional divergences down to the nanoscale. However, the reliable characterization of such complex, multilayered systems, remains challenging due to the interplay of chemical, structural, and optical inhomogeneities across different length scales. In this study, we examine a trilayer heterostructure consisting of chemical vapor deposition (CVD) graphene (G), a self-assembled layer of Rhodamine 6G (R6G), and a transferred monolayer MoS2 (G/R6G/MoS2), incorporating regions of a tri- and multilayer MoS2 as well. Comprehensive structural and optical characterization was performed to identify possible inhomogeneities, employing photoluminescence (PL) spectroscopy, Raman spectroscopy, Kelvin probe force microscopy (KPFM), and scattering-type scanning near-field optical microscopy (s-SNOM). Analytical methods indicate that the TMDC layer has almost uniform molecular coverage and preserved crystallinity. Importantly, near-field optical imaging demonstrates the propagation of exciton-polaritons in MoS2, with a clear redshift of the polariton wavelength upon R6G integration, signifying substantial modulation of the local dielectric environment and excitonic response. These findings underscore the tunability of hybrid 2D molecular-inorganic interfaces and their promise for advanced applications in nanophotonic devices, excitonic circuitry, and quantum optoelectronics.

Connecting two-dimensional (2D) material layers via interface linkers represents a new avenue for fabricating 2D heterostructures. Utilizing light to remotely modulate this interface function allows for seamless assembly and patterning in a single run. Here, an efficient method for fabricating patterned 2D heterostructures using direct laser writing is demonstrated, drawing a conceptual parallel to laser printing. In the approach, functionalized transition metal dichalcogenide (TMD) dispersions serve as inks, graphene as the substrate, and a Raman laser as the patterning tool. Unlike laser printing's electrostatic interactions, the method achieves patterned assembly through covalent bonding between TMDs and graphene. Selective Raman laser irradiation of functionalized TMD/graphene heterostructures triggers localized reactions, forming chemically modified domains exclusively in the laser-irradiated regions, as confirmed by Raman spectroscopy, Kelvin probe force microscopy (KPFM), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Experimental and theoretical analyses of the interface composition and structure provide new insights into laser-induced chemistry. The work demonstrates the potential for high-throughput assembly of customizable 2D heterostructures, with enhanced compatibility for subsequent patterning through photolabile linkers and photoinduced coupling. Additionally, the results provide deeper insights into chemistry within confined 2D spaces, offering a novel approach to nanoscale heterostructure engineering.

We report the synthesis of a fluorescent polycyclic aromatic hydrocarbon dye with a "symmetry-broken" core, derived from the related hexa-peri-benzocoronene (HBC) core with a fluoranthene subunit. The fluorophore is composed of a pure carbon skeleton without heteroatoms and exhibits remarkable photoluminescence properties with a photoluminescence quantum yield (PLQY) of up to 67% in toluene, exceeding that of the parent HBC by a factor of 30. The single crystal X-ray structure reveals the distorted polycyclic aromatic hydrocarbon structure, which is responsible for the optoelectronic properties, as supported by density functional theory calculations. We show that the new fluorescent dye can be readily used for the fabrication of organic light-emitting diodes (OLED) without extensive optimization, whereby solubility in a variety of solvents and successful film formation are decisive.

Functionalization of graphene derivatives is a common approach to tune material properties for use in various applications. Because of the low reactivity of the unsaturated carbon lattice of graphene, not only are few chemical approaches suitable for successful functionalization, such as those involving highly reactive in situ formed radical species or nitrene and carbene compounds, but also the degree of functionalization is usually limited, modifying only a few percent of the carbon atoms. Typically, uncontrolled side reactions such as homocoupling and oligomerization of newly introduced functional groups can occur instead of direct coupling to the carbon lattice. We want to turn this unwanted side reaction into an advantage and use intentionally formed covalent dendrimeric oligophenylene structures for secondary functionalization. We show that these oligomeric structures can be grown to specific thicknesses and used for further functionalization with bromomethyl groups at high density on the surface. This functionalization opens further avenues for subsequent nucleophilic substitution, as exemplified by the introduction of versatile azide, nitrile, and phosphonate groups. The results presented here are not only applicable to large oligophenylene structures, but also demonstrate that, in principle, single aryl moieties on graphene of any size and density can be successfully functionalized.

SEM images reveal the dendritic structure of MCNDs with high surface area, excellent porosity, and uniform distribution leading to outstanding performance with Pt catalysts based on MCNDs and making MCNDs a highly effective supporting material.

Heterostructures of molecules and two-dimensional materials feature emergent properties not seen in their individual components. Here, we study excitons in bilayer transition metal dichalcogenides exposed to an intense electric field produced by charge transfer from proximal molecules. Our approach allows for reaching an electric field strength of 0.35 V nm −1 , up to a factor of two higher than previously achieved in purely solid-state gated devices. Under this field, inter- and intralayer excitons are brought into an energetic resonance, allowing us to explore a new physical regime. We detect a previously unseen interlayer exciton that only becomes visible at high electric field through hybridization with the intralayer A exciton. Moreover, the system experiences an ultra-strong Stark splitting of > 350 meV with exciton energies tunable over a large range of the optical spectrum, holding potential for optoelectronics. Our work paves the way for using strong electric fields to study new physical phenomena and control exciton hybridization in 2D semiconductors.

Tuning the optoelectronic properties of monolayer MoS2 (1L-MoS2) is highly desired for optoelectronic applications, such as molecular sensors. Stable structures that can be reproducibly fabricated are essential for this, and the mechanism leading to the optical properties can thus be well understood. Here, we demonstrate that the photoluminescence (PL) of 1L-MoS2 can be modulated by photochemically functionalized graphene (F-G), which is covalently modified by phenyl-groups. The materials and molecules, respectively, combined in a heterostructure are graphene, phenyl-groups, and 1L-MoS2. Here we show that the layer-sequence results in a significant difference in PL enhancement. MoS2 supported by F-G (F-G/MoS2) has a 5-fold PL enhancement. More importantly, MoS2 shows only a 1.8 times PL enhancement if stacked underneath F-G (MoS2/F-G). Accordingly, the results indicate that the Schottky barrier and van der Waals interaction between the graphene basal plane and MoS2 interface are dramatically weakened with the enlarged interlayer distance in F-G/MoS2. Consequently, the PL enhancement becomes reduced with the thermal de- functionalization of F-G. Due to the different PL properties induced by layer sequence, we conclude that the phenyl-groups must be considered as a separate molecular component. Thus, the F-G/MoS2 heterostructures bring us new ideas and have potential applications in optoelectronic devices.

In this proof-of-concept study, we show that polyfluorinated trityl radicals with the, to this date, highest fluorination grade can be accessed in quantitative yields in a straightforward manner starting from the perfluorinated trityl cation. The trityl skeleton is functionalized with trimethylsilyl halides to yield perhalofluoro trityl cations, which are subsequently reduced using commercial zinc powder. In this way, we prepare three perhalofluoro trityl radicals and analyze the impact of the fluorine ligands on their electro-optical properties, revealing some interesting trends. In comparison to literature-known polychlorinated trityl radicals, the new polyfluorinated derivatives exhibit substantially higher fluorescence quantum yields, longer luminescence lifetimes, and an expanded emission range that extends into the yellow spectral region. They further display enhanced photostability under light irradiation. In radical-stained polystyrene nanoparticles, an additional broad emission band in the red-NIR wavelength region is observed, which is attributed to excimer formation. Finally, the stability of the new radicals is investigated under ambient conditions, showing the slow conversion with atmospheric oxygen yielding the respective peroxides, which are characterized by single-crystal X-ray diffraction. All in all, our study extends the present scope of luminescent trityl radicals, as the functionalization of the perfluorinated cationic precursor unlocks the path toward a vast variety of polyfluorinated trityl radicals.

We report the synthesis of a fluorescent polycyclic aromatic hydrocarbon dye with a "symmetry‐broken" core, derived from the related hexa‐peri‐benzo¬coronene core with a fluoranthene subunit. The fluorophore is composed of a pure carbon skeleton without heteroatoms and exhibits remarkable photo¬luminescence properties with a photoluminescence quantum yield of up to 67% in toluene, exceeding that of the parent hexa‐peri‐benzocoronene by a factor of 30. The single crystal X‐ray structure reveals the distorted polycyclic aromatic hydrocarbon structure, which is responsible for the optoelectronic properties, as supported by density functional theory calculations. We show that the new fluorescent dye can be readily used for the fabrication of organic light‐emitting diodes without extensive optimization, whereby solubility in a variety of solvents and successful film formation are decisive.

Die Funktionalisierung von Graphenderivaten ist ein gängiger Ansatz, um die Materialeigenschaften für den Einsatz in verschiedenen Anwendungsgebieten zu optimieren. Aufgrund der geringen Reaktivität des ungesättigten Kohlenstoffgitters von Graphen sind nur wenige chemische Herangehensweisen für eine erfolgreiche Funktionalisierung geeignet, wie z.B. solche, die hochreaktive, in situ gebildete Radikalspezies oder Nitren‐ und Carbenverbindungen einbeziehen. Trotz deren Einsatz werden in der Regel nur wenige Prozent der Kohlenstoffatome funktionalisiert. Außerdem treten häufig unkontrollierte Nebenreaktionen wie Homokupplung und Oligomerisierung mit den neu eingeführten funktionellen Gruppen auf, anstelle einer direkten Kopplung an das Kohlenstoffgitter. In der vorgestellten Arbeit konnte gezeigt werden, dass die unkontrollierte Oligomerisierung in Zukunft zum Vorteil genutzt werden kann. Kovalente dendrimere Oligophenylenstrukturen wurden gezielt mit definierten Schichtdicken aufgebaut und in weiteren Schritten chemisch umgesetzt. So war es möglich, in einem ersten Schritt Bromomethylgruppen in hoher Dichte an die Oberfläche zu bringen und diese anschließend durch nukleophile Substitution mit vielseitig einsetzbaren Azid‐, Nitril‐ und Phosphonatgruppen zu versehen. Die hier vorgestellten Ergebnisse sind nicht nur auf große Oligophenylenstrukturen anwendbar, sondern zeigen auch, dass prinzipiell einzelne Aryleinheiten auf Graphen beliebiger Größe und Dichte erfolgreich funktionalisiert werden können.

Surface chemistry and interface interactions profoundly influence the properties of two-dimensional (2D) materials and heterostructures. Therefore, developing methods to precisely control surfaces and interfaces is crucial for harnessing the properties and functions of 2D materials and heterostructures. Here, we developed a facile approach to tuning the interface distance and properties of graphene/MoS2 heterostructures (G/MoS2) by varying the functional groups attached to the surface of graphene bottom layer. We systematically investigated how different functionalized graphene bottom layers affect the interlayer distance, coupling between the interlayers, and optical properties of resulting G/MoS2 heterostructures. Our findings indicate that both the size and electron-withdrawing/donating properties of functional groups are pivotal in regulating charge transport properties, with size playing a particularly decisive role. Our approach demonstrates an efficient and flexible pathway to regulate the interlayer spacing and charge transport, highlighting the potential of engineering interface chemistry in optimizing properties of van der Waals heterostructures.

Many organic dyes are fluorescent in solution. In the solid state, however, quenching processes often dominate, hampering material science applications such as light filters, light-emitting devices, or coding tags. We show that the dimethylene-cyclopropanide scaffold can be used to form two structurally different types of chromophores, which feature fluorescence quantum yields up to 0.66 in dimethyl sulfoxide and 0.53 in solids. The increased fluorescence in the solid state for compounds bearing malonate substituents instead of dicyanomethide ones is rationalized by the induced twist between the planes of the cyclopropanide core and a pyridine ligand. The dimethylene-cyclopropanide moiety is used as key scaffold for the design of fluorescent dyes which emit light in solution and in solids. In particular, malonic ester groups induce a remarkable twist angle of about 20 degrees between a pyridinium substituent and the cyclopropanide plane, resulting in enhanced light emission in solids. image

In this study, we present a synthetic method for the preparation of oxo-graphene nanoribbons (oxo-GNRs) by oxidative cleavage of C-C bonds of enriched (6,5)-single-walled carbon nanotubes (SWCNTs). We applied a mild oxidation protocol to oxidize SWCNTs involving sulfuric acid as dispersion medium and potassium permanganate as oxidant. The obtained oxo-GNRs exhibit stunning fluorescence properties with emission maxima of about 300 nm and 400 nm, respectively, depending on oxidation time. The analyses reveal that functional oxo-groups are predominantly located at the rims of oxo-GNRs. Next to lactones, 1,3-ketones are identified, which can be further reacted with hydrazine, most likely forming pyrazoline groups. Based on our data, we propose a chemical structure model for the oxo-GNRs. The model is based on an intact inner It-system, responsible for photoluminescence properties and oxo-functionalized rims of GNRs.