Giant macrocycles composed of thiophene, acetylene, and ethylene units

Fully conjugated pi-expanded macrocyclic oligothiophenes with 60 pi-180 pi electron systems have been synthesized using modified McMurry coupling reaction as a key step. X-ray analyses of 60 pi and 72 pi 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 pi-donor properties and pi-pi stacking ability. Interestingly, 90 pi and 120 pi 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 72 pi, 108 pi, 1447r, and 180 pi systems show that the increasing pi-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. To cite this article: M. Iyoda, C R. Chimie 12 (2009). (c) 2008 Published by Elsevier Masson SAS on behalf of Academie des sciences.