[4]Cyclo-N-ethyl-2,7-carbazole: Synthesis, Structural, Electronic and Charge Transport Properties

Nanorings, which are macrocycles possessing radially directed π-orbitals have shown fantastic development in the last ten years. Unravelling their unusual electronic properties has been one of the driving forces of this research field. However, and despite promising properties, their incorporation in organic electronic devices remains very scarce. In this work, we aim to contribute to bridge the gap between organic electronics and nanorings by reporting the synthesis, the structural and electronic properties and the incorporation in an organic field-effect transistor (OFET) of a cyclic tetracarbazole, namely [4]cyclo-N-ethyl-2,7-carbazole ([4]C-Et-Cbz). The structural, photophysical and electrochemical properties have been compared to those of structurally related analogues [4]cyclo-9,9-diethyl-2,7-fluorene [4]C-diEt-F (with carbon bridges) and [8]-cycloparaphenylene [8]CPP (without any bridge) in order to shed light on the impact of the bridging in nanorings. This work shows that nanorings can be used as an active layer in an OFET and provides a first benchmark in term of OFET characteristics for this type of molecules.

Multifunctional Tricarbazolo Triazolophane Macrocycles: One-Pot Preparation, Anion Binding, and Hierarchical Self-Organization of Multilayers

Programming the synthesis and self-assembly of molecules is a compelling strategy for the bottom-up fabrication of ordered materials. To this end, shape-persistent macrocycles were designed with alternating carbazoles and triazoles to program a one-pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF6 (-) , with surprisingly high affinities (β2 =10(11)  M(-2) in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K2 /K1 )=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface-templated self-assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co-facial and edge-sharing seams that exist between shape-persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self-association observed in solution, with self-association constants of K=300 000 M(-1) (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self-assemblies.

Vernier-templated synthesis, crystal structure, and supramolecular chemistry of a 12-porphyrin nanoring

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier-templated synthesis of a 12-porphyrin nanoring. NMR and small-angle X-ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo-oligomerization reaction. UV/Vis/NIR titrations show that the three-component assembly of the 12-porphyrin nanoring figure-of-eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single-crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular C–H⋅⋅⋅N contacts involving the tert-butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12-porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition.

Two-dimensional oligo(phenylene-ethynylene-butadiynylene)s: all-covalent nanoscale spoked wheels

Round and round: Covalently bound spokes induce an efficient template-directed cyclization towards a rigid molecular wheel (see figure) and afford dramatically increased shape-persistence properties compared with non-strutted macrocycles.The synthesis and characterization of a shape-persistent two-dimensional (2D) organic compound is described in detail. In a rational modular synthesis of a dodecaacetylene precursor and its subsequent template-aided cyclization, we obtained a molecularly defined, stable, C(6)-symmetric, rigid, spoked wheel. Peripheral tert-butyl groups and alkyl chains attached to the plane of the molecule provide sufficient solubility, so that the 2D oligomer can be fully characterized by MALDI-MS, GPC, and (1)H NMR, UV/Vis absorption, and fluorescence spectroscopy. Molecular mechanics and dynamics simulations indicate that the most stable conformer of the molecule in vacuum is a shallow boat conformation with a small dihedral angle. Comparisons with the precursor as well as a ring-only structure clearly reveal the high rigidity of the title compound. Small-angle neutron scattering (SANS) experiments in [D(8)]THF and CDCl(3) affirm the rigid backbone structure in solution, that is, a radius of about 2.7 nm and a thickness of about 0.22 nm. STM investigations illustrate that the wheel molecules adsorb with their molecular plane parallel to the surface and can form hexagonal crystalline domains (unit cell parameters are a=b=6.0+/-0.2 nm and theta=60+/-2 degrees ), with the tert-butyl groups on the apexes staggered. Such staggering induces chirality in the organized domains. AFM investigations demonstrate that the wheel molecules inside overlayers organize in the same way as in the layer directly in contact with the surface. This indicates an epitaxial growth characteristic of the film.

Columnar mesophase formation of cyclohexa-m-phenylene-based macrocycles

Two novel discotic macrocycles, substituted cyclohexa-m-phenylene (CHP) and cyclo-3,6-trisphenanthrylene (CTP), and the linear oligomer 3,3':6',3''-terphenanthrene (TP) as a model substance have been synthesized by repetitive cross-coupling reactions. To correlate the molecular design with the supramolecular architecture and the established macroscopic order, 2D wide-angle X-ray scattering experiments were performed on mechanically extruded filaments. At room temperature in their crystalline phases, all three compounds revealed columnar assemblies in which the macrocycles self-organized by pi-stacking interactions. The degree of macroscopic order was found to depend upon the planarity and stiffness of the aromatic core. The flexible CHP ring showed a poor macroscopic order of the columnar structures and a low isotropization temperature, whereas the more-planar, less-flexible CTP self-assembled into well-defined superstructures. The larger pi-stacking area and the more-pronounced intermolecular interactions for CTP led to the formation of a mesophase over a very large temperature range. The surprising columnar organization of the "open" TP system was explained by back-folding of the molecule into a ringlike structure.

Dehydrogenation of Methanol by Vanadium Oxide and Hydroxide Cluster Cations in the Gas Phase

Bare vanadium oxide and hydroxide cluster cations, V(m)O(n)+ and V(m)O(n-1) (OH)+ (m = 1-4, n = 1-10), generated by electrospray ionization, were investigated with respect to their reactivity toward methanol using mass spectrometric techniques. Several reaction channels were observed, such as abstraction of a hydrogen atom, a methyl radical, or a hydroxymethyl radical, elimination of methane, and adduct formation. Moreover, dehydrogenation of methanol to generate formaldehyde was found to occur via four different pathways. Formaldehyde was released as a free molecule either upon transfer of two hydrogen atoms to the cluster or upon transfer of an oxygen atom from the cluster to the neutral alcohol concomitant with elimination of water. Further, formaldehyde was attached to V(m)O(n)+ upon loss of H2 or neutral water to produce the cation V(m)O(n)(OCH(2))+ or V(m)O(n-1) (OCH(2))+, respectively. A reactivity screening revealed that only high-valent vanadium oxide clusters are reactive with respect to H2 uptake, oxygen transfer, and elimination of H2O, whereas smaller and low-valent cluster cations are capable of dehydrogenating methanol via elimination of H2. For comparison, the reactivity of methanol with the corresponding hydroxide cluster ions, V(m)O(n-1) (OH)+, was studied also, for which dominant pathways lead to both condensation and association products, i.e., generation of the ions V(m)O(n-1) (OCH(3))+ and V(m)O(n-1) (OH)(CH(3)OH)+, respectively.