Giant Macrocycles Research Articles

Giant macrocycles composed of thiophene, acetylene, and ethylene units

Fully conjugated π-expanded macrocyclic oligothiophenes with 60π–180π electron systems have been synthesized using modified McMurry coupling reaction as a key step. X-ray analyses of 60π and 72π systems revealed unique molecular and packing structures, reflecting planar cyclic structures with large inner cavities. All giant macrocycles exhibit multi-step reversible redox behavior with fairly low first oxidation potentials, reflecting their cyclic conjugation. Doping of macrocycles with iodine forms semiconductors owing to their π-donor properties and π–π stacking ability. Interestingly, 90π and 120π systems self-aggregate in the solid state to form red nanofibers. The structures of fibrous aggregates have been established by SEM and AFM analyses. Furthermore, two-photon properties of 72π, 108π, 144π, and 180π systems show that the increasing π-conjugation leads to an increase in the two-photon absorption cross-section with magnitudes as high as 100,000 GM in the visible spectral region.

Giant Macrocycles Composed of Thiophene, Acetylene, and Ethylene Building Blocks

Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.

6 + 6] Schiff‐Base Macrocycles with 12 Imines: Giant Analogues of Cyclohexane.

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Self-Condensation of a Thiazole-Peptide Bearing a 21-Membered Loop into a Library of Giant Macrocycles with Multiple Orthogonal Loops

[reaction: see text] Tetrapeptide analogue H-[Glu-Ser-Lys(Thz)]-OH, containing a turn-inducing thiazole constraint, was used as a template to produce a 21-membered structurally characterized loop by linking Glu and Lys side chains with a Val-Ile dipeptide. This template was oligomerized in one pot to a library (cyclo-[1](n)(), n = 2-10) of giant symmetrical macrocycles (up to 120-membered rings), fused to 2-10 appended loops that were carried intact through multiple oligomerization (chain extension) and cyclization (chain terminating) reactions of the template. A three-dimensional solution structure for cyclo-[1](3) shows all three appended loops projecting from the same face of the macrocycle. This is a promising approach to separating peptide motifs over large distances.

6 + 6] Schiff-base macrocycles with 12 imines: giant analogues of cyclohexane

Hexagon-shaped [6 + 6] Schiff-base macrocycles with 12 imine bonds are reported. These giant macrocycles possess 6 N2O2 coordination environments and mass spectrometry evidence for hexametallation of one macrocycle is provided. Semi-empirical calculations reveal two stable conformations with boat and chair geometries for the macrocycles metallated with Ni(II), analogous to the conformations observed for cyclohexane.

Cover Picture: A Giant Conjugated Molecular Ring (Angew. Chem. Int. Ed. 27/2003)

As a circular path for electrons a giant macrocycle with a periphery consisting of exclusively conjugation‐active units has been designed. With a diameter of 12 nm it is probably the largest synthesized, shape‐persistent, and monodisperse cyclic structure to date. In addition, the front wheel of a bicycle is shown, the 16‐fold symmetry of which inspired the design of the molecule. For more information on this molecule see the Communication by M. Mayor and C. Didschies on page 3176 ff.

Formation and isolation of huge cyclic oligomers: posycondensation of 1,5-bis(1-hydroxy-3,6,9-trioxanonyl) naphthalene and terephthaloyl chloride

Polycondensation of 1,5-bis(1-hydroxy-3,6,9-trioxanonyl) naphthalene 3and terephthaloyl chloride 4 gives giant macrocycles, i.e. crownophanes (2n) with 30n(n= 1–5) atom perimeters, in ca. 30%m/m overall yield; owing to self-complementarity by edge–face arene–arene interactions, a packing ratio of 71. 8% is found for 2(1).