Giant conjugated macrocycles: Synthesis and applications

Abstract

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 modifled 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, reecting their planar cyclic frameworks having medium to large inner cavities. Interestingly, giant macrocycles self- aggregate in the solid state to form various nanostructures reecting 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.