Wir berichten zum ersten Mal über die Bisfunktionalisierung von Graphen auf der Basis zweier konsekutiver Reduktions- und kovalenter Additionsschritte. Dieser Ansatz wurde sowohl für die lösungsmittelbasierte Funktionalisierung von Graphen im präparativen Maßstab als auch für die Derivatisierung individueller Kohlenstofflagen auf Oberflächen genutzt. Im ersten Fall ist der elektrophile Angriff aus beiden Halbräumen der Basalebene möglich, was zum Aufbau spannungsfreier Architekturen führt. Im zweiten Fall hingegen gewinnen Retrofunktionalisierungsreaktionen an Bedeutung, insbesondere wenn das entsprechende Anion des Erstaddenden eine gute Abgangsgruppe darstellt.

For the first time, the bisfunctionalization of graphene by employing two successive reduction and covalent bond forming steps is reported. Bulk functionalization in dispersion and functionalization of individual sheets deposited on surfaces have both been carried out. Whereas in the former case attacks from both sides of the basal plane are possible and can lead to strain-free architectures, in the latter case, retrofunctionalizations can become important when the corresponding anion of the addend is a sufficiently good leaving group.

The synthesis and characterization of a new type of very large perylene-based molecules 9 are reported. The extension of the conjugated π system was accomplished by the facile condensation of two bay-functionalized perylene moieties with 1,2,4,5-tetraaminobenzene. The resulting chromophore in 9 consists of 35 conjugated π-electron pairs and, therefore, is comparable to pentarylenes and hexarylenes containing 31 and 36 conjugated π-electron pairs, respectively. The unsubstituted imine N atoms of the benz-bisimidazole bridges in 9 can be readily and reversibly protonated to give the dications 9aH₂²⁺. The twofold protonation of 9 is accompanied by a bathochromic shift of the main absorption band and pronounced fluorescence quenching. The experimental results were corroborated by quantum mechanical calculations.

A novel polycationic [60]fullerene hexakis-adduct has been synthesized and investigated by electrospray ionization and tandem mass spectrometry. The polycationic ligand system comprises 12 pre-formed positive charges, compensated in the neutral molecule by bromide anions. Stable quasi-molecular cations were obtained through the release of the anionic counter ions covering a charge-state envelope from 3+ to 12+. Collision-induced dissociation experiments revealed three fragmentation pathways. A dominant neutral loss channel leads to daughter ions of the same charge state as the highly charged precursor ion and singly charged daughter ions can be expelled from the polycations through two distinct dissociation channels involving both the neutral and the charge-carrying part of their ligands.

The facile assembly of shell-by-shell (SbS)-coated nanoparticles [TiO₂PAC₁₆]@shell 1–7 (PAC₁₆=hexadecylphosphonic acid), which are soluble in water and can be isolated as stable solids, is reported. In these functional architectures, an umpolung of dispersibility (organic apolar versus water) was accomplished by the noncovalent binding of ligands 1–7 to titania nanoparticles [TiO₂PAC₁₆] containing a first covalent coating with PAC₁₆. Ligands 1–7 are amphiphilic and form the outer second shell of [TiO₂PAC₁₆]@shell 1–7. The tailor-designed dendritic building blocks 3–5 contain negative and positive charges in the same molecule, and ligands 6 and 7 contain a perylenetetracarboxylic acid dimide (PDI) core (6/7) as a photoactive reporter component. In the redox and photoactive system [TiO₂PAC₁₆]@shell 7, electronic communication between the inorganic core to the PDI ligands was observed.

Flexible, linked dendritic tetraphenylporphyrin (TPP)–fullerene hybrids were synthesized. They were designed to gain insight into and mimic the primary events in the natural photosynthetic reaction center. These multiporphyrin moieties are based on a light-harvesting concept. Moreover, they incorporate multiple redox components aligned along a redox gradient. Newkome-type dendrons were added to these TPP–fullerene hybrids. In principle they can mediate pH-dependent water solubility, which, however, could not be observed in this case. A protecting-group strategy using tert-butyldiphenylsilyl groups allows convergent synthesis of the dendritic compounds. The dendritic multiporphyrins were synthesized separately and can be used as individual building blocks. Atropisomerism was observed in the dendritic compounds, and single atropisomers could be assigned to the corresponding peaks of a characteristic pattern in the NMR spectra. Deprotection of the Newkome-type dendrons was shown to be feasible under mild conditions that leave the redox gradient intact.

In the current work, we present the successful functionalization and stabilization of P-25 TiO₂ nanoparticles by means of N1,N7-bis(3-(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (1). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO₂ surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO₂ agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light-scattering, and zeta potential measurements. As a complement to this, the formation of layer-by-layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO₂ nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20-(phenoxyacetic acid)-porphyrin (2) and 5,10,15,20-(4-(2-ethoxycarbonyl)-4-(2-phenoxyacetamido)heptanedioic acid)-porphyrin (3), is documented. To this end, the layer-by-layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several “on-off” cycles of illumination, we derive monochromatic incident photo-to-current conversion efficiencies of around 3 %.

A series of covalently linked axially symmetric porphyrin–fullerene dyads with a rigid pyrrolo[3,4-c]pyrrolic linker enabling a fixed and orthogonal arrangement of the chromophores has been synthesized and studied by means of transient absorption spectroscopy and cyclic voltammetry. The lifetime of the charge-separated state has been found to depend on the substituents on the porphyrin core, reaching up to 4 μs for a species with meso-(p-MeOC₆H₄) substituents. The ground and excited electronic states of model compounds have been calculated at the DFT and TD-DFT B3LYP(6-31G(d)) levels of theory and analyzed with regard to the effect of the substituent on the stabilization of the charge-separated state in the porphyrin–fullerene ensemble with a view to explaining the observed dependence.

A series of several new families of ferrocene-containing imidazolium salts were synthesized by etherification of ferrocene methanol, acylation of ferrocene, and amide coupling of ferrocene carboxylic acid. The etherification was achieved by an acid-catalyzed procedure and very good yields of between 86–93 % were obtained. Next to the nature of the linkage itself, the lengths of the alkyl chains linking the ferrocenyl moiety and the imidazolium group and the nature of the counterions were also varied. Interestingly, a γ-effect can be observed for the ether compounds but this effect was only visible in ¹³C NMR spectroscopy. These new redox-active ionic liquids were fully characterized by FTIR, ¹H, ¹⁹F, and ¹³C NMR spectroscopy, and by MS, HRMS and elemental analysis.

The chemical production of graphene as well as its controlled wet chemical modification is a challenge for synthetic chemists. Furthermore, the characterization of reaction products requires sophisticated analytical methods. In this Review we first describe the structure of graphene and graphene oxide and then outline the most important synthetic methods that are used for the production of these carbon-based nanomaterials. We summarize the state-of-the-art for their chemical functionalization by noncovalent and covalent approaches. We put special emphasis on the differentiation of the terms graphite, graphene, graphite oxide, and graphene oxide. An improved fundamental knowledge of the structure and the chemical properties of graphene and graphene oxide is an important prerequisite for the development of practical applications.

Through a combination of an electronic-type selective diazonium-based attachment of a Hamilton receptor unit onto the carbon nanotube framework and a supramolecular recognition approach of a cyanuric acid derivative, we herein introduce a highly promising strategy for the tuning of carbon nanotube solubility and, directly related to that, a solution-based easy and straightforward separation of covalently functionalized carbon nanotube derivatives with respect to their unfunctionalized counterparts. The supramolecular complexation of the cyanuric acid derivative provides the driving force for the dramatically increased dispersibility and for the long-time stability of the individualized single-walled carbon nanotube derivatives in chloroform. The selective covalent functionalization of metallic carbon nanotubes can easily be analyzed with the aid of scanning Raman microscopy techniques. The functional derivatives have furthermore been characterized by UV/Vis-NIR and fluorescence spectroscopy as well as by mass spectrometric coupled thermogravimetric analysis. The investigation of the supramolecular complexation is based on an in-depth UV/Vis-NIR analysis and atomic force microscopy investigations.

A new prototype of dendritic perylenes suitable for the chemical functionalization of inorganic nanoparticles was synthesized and characterized. The bay-functionalized perylene core of these molecular architectures was coupled to a catechol moiety, which serves as an anchor group for the functionalization of metal oxides, in particular ZnO. To increase the solubility of both the perylene and the targeted hybrid nanostructures, a Newkome-type dendron bearing nine positive charges was introduced. This charge was also employed to stabilize the nanoparticles and further protect them from Ostwald ripening through Coulombic repulsion. ZnO quantum dots with an average diameter of 5 nm were synthesized and functionalized with the perylene derivative. Successful functionalization was clearly demonstrated by dynamic light scattering, zeta-potential measurements, thermogravimetric analysis/MS, and UV/Vis and fluorescence spectroscopy. The generated particle dispersions were stable against agglomeration for more than eight weeks.

The covalent functionalization of carbon allotropes represents a main topic in the growing field of nano materials. However, the development of functional architectures is impeded by the intrinsic polydispersibility of the respective starting material, the unequivocal characterization of the introduced functional moieties, and the exact determination of the degree of functionalization. Based on a novel carbon allotrope functionalization reaction, utilizing λ³-iodanes as radical precursor systems, we were able to demonstrate the feasibility to separate and to quantify thermally detached functional groups, formerly covalently linked to carbon nanotubes and graphene through thermogravimetric GC-MS.

The synthesis and characterization of a new type of chromophore, namely PePc consisting of a central phthalocyanine core and four fused perylene–bisimide (PBI) units is described for the first time. The entire architecture represents a highly extended conjugated heterocyclic π-system with C_4h symmetry. In order to guarantee pronounced solubility in organic solvents the corresponding PBI units were bay-functionalized with tert-butylphenoxy substituents. Next to the metal-free macrocycle, PePcH₂, also metallated macrocycles PePcM (M=Zn, Ni, Pb, Ru, Fe) were synthesized. The extensive fusion of the corresponding aromatic building blocks to the very large extended π-system leads to a very narrow HOMO–LUMO gap and as a consequence to transparency in the visible but light absorption in the NIR region. Significantly, the azomethine N-atoms N1N4 of PePcM and PePcH₂ are highly basic. The corresponding tetraprotonated systems can only be deprotonated with very strong non-nucleophilic bases such as phosphazene bases. In the protonated forms PePcMH₄⁴⁺ and PePcMH₆⁴⁺ the absorption maximum is shifted back to the visible region due to the loss of conjugation. The experimental findings were corroborated with quantum mechanical calculations.

A method for the sequential fullerenylation of bis-malonates with parent C₆₀ and C_2v-symmetric pentakis-adducts is reported. This approach relies on the finding that (a) chloromalonates can be used for the nucleophilic cyclopropanation of [6,6] double bonds of C₆₀, and (b) chloromalonates, in contrast to bromomalonates, do not undergo base-catalyzed halogen exchange reactions. For the proof of concept, we synthesized a heptafullerene by using a divergent approach based on a fullerene hexakis-adduct with six bis-malonate addends in octahedral positions, each of which is suitable for an additional cyclopropanation of a fullerene building block.

A new class of C₃-symmetrical fullerene building blocks with a well-defined spatial arrangement of addends has been developed. They comprise compounds with a e,e,e-trisaddition pattern and a mixed octahedral hexakisaddition pattern. Fullerenophosphates with a e,e,e-addition pattern were used for the spatial preorganization of the addends. After deprotection seven different trisbromides (12–16, 15a, 16a) with varying chain lengths and orientation of the functional groups were obtained. Acetylenes could be coupled to these compounds by click chemistry through an intermediate trisazide. For the synthesis of mixed hexakisadducts 19–21 a template system based on a central benzyl moiety was attached to the free hemisphere of the trisadduct fullerenophosphates. It was shown that the phosphate and the benzyl template can be removed independently. Fully deprotected building block 24 bearing both terminal bromide and hydroxy moieties was prepared. In addition, rather complex hybrid architecture 29 bearing three porphyrin units in the polar addend zone was successfully synthesized.