Macrocyclic Oligofurans: a Computational Study

Macrocyclic structures with a π-conjugated backbone often display unique structures, properties and functions. In many cases, the physical properties of linear oligomers are influenced by undesired chain-end effects. In this respect, fully π-conjugated macrocycles represent model systems that combine the ‘infinite’ defect-free π-conjugated chain of an idealized polymer with the advantage of a structurally well-defined oligomer, while excluding perturbing end-effects. This renders them interesting candidates for various future applications in organic and molecular electronics and for the study of host–guest interactions, aggregation, and self-assembly on surfaces.^[i] While macrocyclic oligothiophenes (nCT) were extensively explored – both computationally and experimentally – macrocyclic oligofurans (nCF) remain unknown. Following the recent introduction of linear long oligofurans,^[ii] we were interested in exploring the properties of macrocyclic oligofurans.

Here we report the computational study of macrocyclic oligofurans in syn- and anti-conformations at the B3LYP/6-311G(d) level of theory.^[iii] Strain energies, bond length alternations, HOMO−LUMO gaps, ionization potentials, and reorganization energies are among the properties studied. Our results indicate that contrast to nCF, where small macrocycles display non-planar conformations, nCF with 6-8 units are relatively planar (Figure) with a strong quinoid character and low HOMO–LUMO gaps. We therefore conclude that 6CF-8CF should be ideal candidates for applications such as organic semiconductors.

[i] (a) M. Iyoda, H. Shimizu, Chem. Soc. Rev. 2015, 44, 6411-6424; (b) P. Bauerle, Angew. Chem. Int. Ed. 2000, 39, 3481-3486

[ii] O. Gidron, M. Bendikov, Angew. Chem. Int. Ed. 2014, 53, 2546-2555

[iii] O. Dishi, O. Gidron, in preperation.