Conjugated giant macrocyclic oligothiophenes
2Tn (n=2-4),
5Tn (n=2-6), and
6Tn (n=2-5) composed of 2,5-thienylenes, ethynylenes, and vinylenes with 24π to 180π electron systems have been synthesized using a modified McMurry coupling reaction as the key step. For the synthesis of cyclo[n](2,5-thienylene-ethynylene)s
nCTE (n=10 and 12) composed of 2,5-thienylenes and ethynylenes, a bromination-dehydrobromination then double elimination procedure was employed. X-ray analyses of
2T2 (24π),
5T2 (60π), and
6T2 (72π) revealed unique molecular and packing structures, reflecting their planar cyclic frameworks having medium to large inner cavities. Interestingly, giant macrocycles self-aggregate in the solid state to form various nanostructures reflecting their nanophase separation, and the two-photon absorption properties of
6Tn (n=2-5) show that increasing π-conjugation leads to an increase in the two-photon absorption cross section with magnitudes as high as 100,000 GM being realized. Furthermore, the giant macrocycle
6T5 behaves as a synthetic cyclic pigment comparable to the natural light-harvesting system.
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