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

Fully conjugated giant macrocyclic oligothiophenes with 60π, 90π, 120π, 150π, and 180π 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 60−180π 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 π−π interactions.
Doping of 1a−3a with iodine forms semiconductor due to its π-donor properties and π−π 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.