Andreas Hirsch’s research while affiliated with Friedrich-Alexander-University of Erlangen-Nürnberg and other places

We present a novel approach to achieve spatial variations in the degree of non‐covalent functionalization of twisted bilayer graphene (tBLG). The tBLG with twist angles varying between ~5° and 7° was non‐covalently functionalized with 1,4,5,8,9,11‐hexaazatriphenylenehexacarbonitrile (HATCN) molecules. Our results show a correlation between the degree of functionalization and the twist angle of tBLG. This correlation was determined through Raman spectroscopy, where areas with larger twist angles exhibited a lower HATCN peak intensity compared to areas with smaller twist angles. We suggest that the HATCN adsorption follows the moiré pattern of tBLG by avoiding AA‐stacked areas and attach predominantly to areas with a local AB‐stacking order of tBLG, forming an overall ABA‐stacking configuration. This is supported by density functional theory (DFT) calculations. Our work highlights the role of the moiré lattice in controlling the non‐covalent functionalization of tBLG. Our approach can be generalized for designing nanoscale patterns on two‐dimensional (2D) materials using moiré structures as a template. This could facilitate the fabrication of nanoscale devices with locally controlled varying chemical functionality.

We present a novel approach to achieve spatial variations in the degree of non‐covalent functionalization of twisted bilayer graphene (tBLG). The tBLG with twist angles varying between ~5° and 7° was non‐covalently functionalized with 1,4,5,8,9,11‐hexaazatriphenylenehexacarbonitrile (HATCN) molecules. Our results show a correlation between the degree of functionalization and the twist angle of tBLG. This correlation was determined through Raman spectroscopy, where areas with larger twist angles exhibited a lower HATCN peak intensity compared to areas with smaller twist angles. We suggest that the HATCN adsorption follows the moiré pattern of tBLG by avoiding AA‐stacked areas and attach predominantly to areas with a local AB‐stacking order of tBLG, forming an overall ABA‐stacking configuration. This is supported by density functional theory (DFT) calculations. Our work highlights the role of the moiré lattice in controlling the non‐covalent functionalization of tBLG. Our approach can be generalized for designing nanoscale patterns on two‐dimensional (2D) materials using moiré structures as a template. This could facilitate the fabrication of nanoscale devices with locally controlled varying chemical functionality.

The synthesis of unprecedented triskelion‐shaped hexa‐peri‐hexabenzocoronenes with C3, C3h or D3h symmertry is reported. We present a new, five step synthetic access to tris‐iodinated HBC derivatives carrying different solubilizing moieties (tert‐butyl and mesityl), which serve as suitable building blocks for further functionalization. These molecules can undergo Sonogashira cross coupling reactions to obtain a series of seven ethynyl tris‐substituted HBCs. The coupling partners range from carbon‐based aromatic scaffolds (tBu‐benzene, naphthalene, phenanthrene) to ligands for metal complexes (bipyridine, phenanthroline, terpyridine, acetylacetone). The optoelectronic properties were investigated by UV/vis absorption spectroscopy resulting in a significant batho‐chromic shift of the absorption maximum compared to the iodinated starting material. Semiempirical calculations were used to determine the conformation and symmetry of the compounds.

We describe the synthesis and computational investigation of N‐heterocycle‐substituted hexa‐peri‐hexabenzocoronenes (HBCs). Following our method for the preparation of thioether‐substituted HBCs, we prepared pyrrole‐, indole‐, carbazole‐, and 1H‐benz[g]indole‐substituted HBCs from the corresponding fluorinated precursors under microwave irradiation. A series of polysubstituted benzoindole‐HBCs with windmill architectures was also synthesized using the polyfluorinated HBC analogs, and the substituent effects on the electronic properties of the HBC core were investigated. Similar to the thioether substituted HBCs, the nature of the heterocycle does not influence the optoelectronic properties of the HBC core. The attachment of multiple benzoindole substituents leads to a bathochromic shift of the absorption and emission spectra, comparable to our previous studies. Due to the circular arrangement of the benzoindole moiety, the attachment of multiple substituents results in the presence of multiple conformers at room temperature. The rotation barrier can be overcome by heating the compounds to 323–333 K. Additionally, the investigation of the relaxed geometries shows two π‐stacking motifs within the conformers.

The emerging laser writing represents an efficient and promising strategy for covalent two dimensional (2D)‐patterning of graphene yet remains a challenging task due to the lack of applicable reagents. Here, we report a versatile approach for covalent laser patterning of graphene using a family of trivalent organic iodine compounds as effective reagents, allowing for the engraving of a library of functionalities onto the graphene surface. The relatively weak iodine‐centered bonds within these compounds can readily undergo laser‐induced cleavage to in situ generate radicals localized to the irradiated regions for graphene binding, thus completing the covalent 2D‐structuring of this 2D‐film. The tailor‐made attachment of distinct functional moieties with varying electrical properties as well as their thermally reversible binding manner enables programming the surface properties of graphene. With this delicate strategy the bottleneck of a limited scope of functional groups patterned onto the graphene surface upon laser writing is tackled.

The non‐covalent functionalization of black phosphorus (BP) was studied with a scope of ten tailor‐made perylene diimides (PDIs). A combination of UV/Vis‐, fluorescence‐, as well as Raman spectroscopy and atomic force microscopy was used to investigate the structural factors, which contribute to a pronounced PDI‐BP interaction and thus support the protection of BP nanosheets against oxidative degradation. We were able to show, that water‐soluble, amphiphilic PDIs with highly charged head groups can be used for the non‐covalent functionalization of BP in aqueous media. Here, based on the hydrophobic effect, an efficient adsorption of the respective PDI molecules takes place and leads to the formation of a passivating film, yielding a considerable stabilization of the BP flakes under ambient conditions exceeding 30 days.

The emerging laser writing represents an efficient and promising strategy for covalent two dimensional (2D)‐patterning of graphene yet remains a challenging task due to the lack of applicable reagents. Here, we report a versatile approach for covalent laser patterning of graphene using a family of trivalent organic iodine compounds as effective reagents, allowing for the engraving of a library of functionalities onto the graphene surface. The relatively weak iodine‐centered bonds within these compounds can readily undergo laser‐induced cleavage to in situ generate radicals localized to the irradiated regions for graphene binding, thus completing the covalent 2D‐structuring of this 2D‐film. The tailor‐made attachment of distinct functional moieties with varying electrical properties as well as their thermally reversible binding manner enables programming the surface properties of graphene. With this delicate strategy the bottleneck of a limited scope of functional groups patterned onto the graphene surface upon laser writing is tackled.

Fluorination of two-dimensional antimonene hexagons synthesized through colloidal synthesis has been reached using CF 4 plasma through a reactive ion etching process.

We report the synthesis and characterization of library of new 2,3–disubstituted norbornadiene/quadricyclane couples. For the first time, the para–tolylsulfone moiety was employed as electron–withdrawing substituent in combination with a variety of different electron donors as counterparts. Comprehensive characterization was conducted for every interconversion couple. By comparison with structurally related molecules published before we established the tosyl moiety as suitable alternative to previously investigated ester functionalities by providing similar photophysical properties. The photo–induced interconversion behavior was investigated via UV/Vis‐ and NMR–spectroscopy. The UV/Vis experiments were carried out exclusively in acetonitrile, whereas several solvents were investigated in the NMR studies. A detailed description and comparison of the isomerization behavior is provided, while examining relevant optical properties like λmax and λonset. Thereby, an enhanced red‐shift up to λmax=394 nm combined with an λonset value of 469 nm could be generated which is necessary for potential applications.