Carlo Thilgen

Covalent Fullerene Chemistry

The covalent functionalization of C60 has developed vigorously over the past 5 years. Several methods are now available for the formation of C60 monoadducts. Regioselective formation of multiple adducts has allowed study of the changes in chemical and physical properties that occur when the conjugated fullerene chromophore is reduced during an increase in functionalization. The systematic development of covalent fullerene chemistry provides an unprecedented diversity of tailor-made three-dimensional building blocks for technologically interesting materials.

Assessment of time-dependent density-functional theory for the calculation of critical features in the absorption spectra of a series of aromatic donor–acceptor systems

Singlet and triplet vertical excitation energies of a series of acceptor parasubstituted N,N-dimethyl–anilines [NC–C6H4–N(CH3)2, NC–C6H4–NH2, OHC–C6H4–N(CH3)2, NC–C6H2(CH3)2–N(CH3)2, (H2N)OC–C6H4–N(CH3)2, (CH3)OC–C6H4–N(CH3)2, O2N–C6H4–N(CH3)2, named, respectively, 4DMAB–CN, 4AB–CN, 4DMAB–CHO, TMAB–CN, 4DMAB–CONH2, 4DMAB–COMe, and 4DMAB–NO2] have been calculated with TDDFT. Geometry optimization and excitation energy calculations have been performed, in most cases, with the B3LYP functional using a 6-31G(d) and a 6-311+G(2d,p) basis set (hereafter referred to as Sm and Bg, respectively). 4DMAB–CN and TMAB–CN have been investigated with particular care since gas-phase absorption spectra exist for those two molecules allowing thus a direct comparison with experimental results. The first and second singlet excited states of 4DMAB–CN, commonly named locally excited (LE) state and charge transfer (CT) state, are 0.1 and 0.04 eV higher than the experimental results at the B3LYP-Bg level, leading to a 0.06 eV underestimation of the gap between the two states. In the case of TMAB–CN, which is twisted in its ground state, B3LYP–(Sm/Bg) results show an error of 0.36 eV for the singlet CT state. Better agreement with experiment is obtained using the MPW1PW91 functional and Bg basis set with an underestimation of 0.17 eV for the singlet CT state and an overestimation of 0.16 eV for the second singlet state. Contrary to DFT/SCI results, the relative order and position of excitation energies of 4AB–CN and 4DMAB–CHO are well reproduced compared to solution spectra results. The singlet CT state using B3LYP and a Bg basis set is calculated 0.1 eV higher in energy than the experimental value obtained in isopentane for 4DMAB–CONH2, while the same excitation energy is predicted 0.08 and 0.28 eV too low compared to the gas-phase values for 4DMAB–COMe and 4DMAB–NO2, respectively. Finally, the CT excitation energy and its relative position to the LE state agrees with the acceptor strength concept.Singlet and triplet vertical excitation energies of a series of acceptor parasubstituted N,N-dimethyl–anilines [NC–C6H4–N(CH3)2, NC–C6H4–NH2, OHC–C6H4–N(CH3)2, NC–C6H2(CH3)2–N(CH3)2, (H2N)OC–C6H4–N(CH3)2, (CH3)OC–C6H4–N(CH3)2, O2N–C6H4–N(CH3)2, named, respectively, 4DMAB–CN, 4AB–CN, 4DMAB–CHO, TMAB–CN, 4DMAB–CONH2, 4DMAB–COMe, and 4DMAB–NO2] have been calculated with TDDFT. Geometry optimization and excitation energy calculations have been performed, in most cases, with the B3LYP functional using a 6-31G(d) and a 6-311+G(2d,p) basis set (hereafter referred to as Sm and Bg, respectively). 4DMAB–CN and TMAB–CN have been investigated with particular care since gas-phase absorption spectra exist for those two molecules allowing thus a direct comparison with experimental results. The first and second singlet excited states of 4DMAB–CN, commonly named locally excited (LE) state and charge transfer (CT) state, are 0.1 and 0.04 eV higher than the experimental results at the B3LYP-Bg level, leading to a 0.06 eV un...

Chemistry of C84: Separation of Three Constitutional Isomers and Optical Resolution of D2‐C84 by Using the “Bingel–Retro‐Bingel” Strategy

The pure enantiomers of D2 -C84 as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C84 (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C84 , separated, and unambiguously structurally characterized.

Supramolecular synthons on surfaces: controlling dimensionality and periodicity of tetraarylporphyrin assemblies by the interplay of cyano and alkoxy substituents.

The self-assembly of three porphyrin derivatives was studied in detail on a Cu(111) substrate by means of scanning tunneling microscopy (STM). All derivatives have two 4-cyanophenyl substituents in diagonally opposed meso-positions of the porphyrin core, but differ in the nature of the other two meso-alkoxyphenyl substituents. At coverages below 0.8 monolayers, two derivatives form molecular chains, which evolve into nanoporous networks at higher coverages. The third derivative self-assembles directly into a nanoporous network without showing a one-dimensional phase. The pore-to-pore distances for the three networks depend on the size and shape of the alkoxy substituents. All observed effects are explained by 1) different steric demands of the alkoxy residues, 2) apolar (mainly dispersion) interactions between the alkoxy chains, 3) polar bonding involving both cyanophenyl and alkoxyphenyl substituents, and 4) the entropy/enthalpy balance of the network formation.

The Higher Fullerenes: Covalent Chemistry and Chirality

Many higher fullerenes, including some of their isomers, can be separated by high performance liquid chromatography (HPLC) on a number of stationary phases, a remarkable fact in view of the similarity of the carbon spheroids which differ mainly in shape and electronic properties of their π-systems, in addition to slight variations in size. Except for C70, which is available in preparative amounts from fullerene soot extract without tedious HPLC purification and has been derivatized in many ways, most separations of the larger carbon spheroids are limited to the milligram scale and require a multistep chromatographic purification. Furthermore, taking into account the relatively small amounts of these carbon cages contained in fullerene soot, the availability of pure higher fullerenes has remained the bottleneck in the field of their multifaceted chemistry. Still, a number of pure adducts of C76, C78 and C84 has now been isolated and characterized, and reactivity as well as regioselectivity principles begin to emerge for the higher fullerenes.

Self‐Assembly and Two‐Dimensional Spontaneous Resolution of Cyano‐Functionalized [7]Helicenes on Cu(111)

Birds of a feather flock together: STM and DFT studies provide the first example of spontaneous chiral resolution of a helicene on a surface. Racemic 6,13-dicyano[7]helicene forms fully segregated domains of pure enantiomers (2D conglomerate) on Cu(111). The propensity of the system to optimize intermolecular CN⋅⋅⋅HC(Ar) hydrogen bonding and CN⋅⋅⋅CN dipolar interactions translates into chiral recognition with preferential assembly of homochiral molecules.

Chirality Transfer in 1D Self-Assemblies : Influence of H-Bonding vs Metal Coordination between Dicyano[7]helicene Enantiomers

Chiral recognition as well as chirality transfer in supramolecular self-assembly and on-surface coordination is studied for the enantiopure 6,13-dicyano[7]helicene building block. It is remarkable that, with this helical molecule, both H-bonded chains and metal-coordinated chains can be formed on the same substrate, thereby allowing for a direct comparison of the chain bonding motifs and their effects on the self-assembly in experiment and theory. Conformational flexure and both adsorbate/adsorbent and intermolecular interactions can be identified as factors influencing the chiral recognition at the binding site. The observed H-bonded chains are chiral, however, the overall appearance of Cu-coordinated chains is no longer chiral. The study was performed via scanning tunneling microscopy, X-ray-photoelectron spectroscopy and density functional theory calculations. We show a significant influence of the molecular flexibility and the type of bonding motif on the chirality transfer in the 1D self-assembly.

Polysiloxane-supported fullerene derivative as a new heterogeneous sensitiser for the selective photooxidation of sulfides to sulfoxides by 1O2

A heterogeneous photosensitiser for the generation of singlet oxygen was synthesized by covalent attachment of a methanofullerene derivative to polysiloxane-based Deloxan® DAP beads and its performance in the photooxidation of sulfides to sulfoxides was investigated. As opposed to C60 and many of its derivatives, the heterogeneous sensitiser can be readily used in protic solvents such as methanol which makes the photooxygenation highly selective, affording good to excellent yields of sulfoxides with aliphatic and benzylic sulfides. Moreover, the sensitiser is easily recovered at the end of the reaction by simple filtration.

Achiral and Chiral Higher Adducts of C70 by Bingel Cyclopropanation

Five optically active isomeric C70 bis-adducts with (R)-configured chiral malonate addends were prepared by Bingel cyclopropanation (Scheme 1) and their circular dichroism (CD) spectra investigated in comparison to those of the corresponding five bis-adducts with (S)-configured addends (Fig. 2). Pairs of diastereoisomers, in which the inherently chiral addition patterns on the fullerene surface have an enantiomeric relationship, display mirror-image shaped CD spectra that are nearly identical to those of the corresponding pairs of enantiomers (Fig. 3, b and c). This result demonstrates that the Cotton effects arising from the chiral malonate addends are negligible as compared to the chiroptical contribution of the chirally functionalized fullerene chromophore. A series of four stereoisomeric tetrakis-adducts (Fig. 4) was prepared by Bingel cyclopropanation starting from four stereoisomeric bis-adducts. A comparison of the CD spectra of both series of compounds showed that the magnitude of the Cotton effects does not decrease with increasing degree of functionalization (Fig. 5). Bingel cyclopropanations of C70 in Me2SO are dramatically faster than in apolar solvents such as CCl4, and the reaction of bis-adducts (±)-13 and 15 with large excesses of diethyl 2-bromomalonate and DBU generated, via the intermediacy of defined tetrakis-adducts (±)-16 and 17, respectively, a series of higher adducts including hexakis-, heptakis-, and octakis-adducts (Table 1). A high regioselectivity was observed up to the stage of the hexakis-adducts, whereas this selectivity became much reduced at higher stages of addition. The regioselectivity of the nucleophilic cyclopropanations of C70 correlates with the coefficients of the LUMO (lowest unoccupied molecular orbital) and LUMO+1 at the positions of preferential attack calculated by restricted Hartree-Fock – self-consistent field (RHF-SCF) methods (Figs. 9 – 11). Based on predictions from molecular-orbital calculations (Fig. 11) and the analysis of experimental 13C-NMR data (Fig. 7, a), the structure of a unique hexakis-adduct ((±)-22, Fig. 12), prepared from (±)-13, was assigned. The C2-symmetrical compound contains four 6−6-closed methanofullerene sub-structures in its polar regions (at the bonds C(1)−C(2), C(31)−C(32), C(54)−C(55), and C(59)−C(60)), and two 6−5-open methanofullerene sub-structures parallel to the equator (at C(22)−C(23) and C(26)−C(27)). The 6−5-open sub-structures are formed by malonate additions to near-equatorial 6−5 bonds with enhanced LUMO coefficients, followed by valence isomerization (Fig. 12).

Die Chemie von C84: Trennung von drei Konstitutionsisomeren des Fullerens C84 und der Enantiomere von D2-C84 durch die „Bingel-Retro-Bingel”-Strategie

Die reinen Enantiomere vonD2-C84 sowie ein drittes Konstitutionsisomer dieses hoheren Fullerens wurden durch Retro-Bingel-Reaktion der ersten organischen C84-Derivate erhalten (siehe Schema). Diese wurden durch Bingel-Cyclopropanierung von C84 synthetisiert und konnten getrennt und strukturell eindeutig zugeordnet werden.