Impact of Molecular Geometry and Functionalization on Solution Complexation of Coronene-Based Buckybowls and Fullerenes

Abstract

Contorted polycyclic aromatic molecules, such as corannulenes and sumanenes, have been studied as host molecules for fullerenes due to their complementary geometries. It has been suggested that stronger associations with fullerenes can be attained by extending their π surface or by incorporating heteroatoms, as unsubstituted corannulene and sumanene do not readily complex with fullerenes in solution. Here, we design and synthesize πextended buckybowls derived from contorted hexabenzocoronene and pentabenzocoronene with either pentyl or butoxy side chains. These coronene-based buckybowls have approximately twice the π surface compared to unsubstituted corannulene and sumanene. Buckybowls with pentyl side chains complex with C 60 in a preferred 1:1 buckybowl-to-C 60 stoichiometry, with association constants on the order of 10 3 M −1 . Complexation with C 60 further strengthens with the addition of heteroatoms in buckybowls bearing butoxy side chains. We find a preferred 1:2 association stoichiometry with fullerene and association constants on the order of 10 4 M −1 . Density functional theory calculations suggest the larger dipole moment on the butoxy-substituted buckybowls relative to their pentyl-substituted counterparts is responsible. This greater dipole moment polarizes C 60 , leading to a preferred 1:2 stoichiometry and larger association constants in the complexation of buckybowls with butoxy side chains and C 60 .

Recent advances in supramolecular fullerene chemistry

“…Apart from corannulene derivatives, [359][360][361] Nabeshima and colleagues developed a series of chiral concave p-systems comprising phosphorus atoms, 343,347 which bind C 60 due to the concaveconvex interactions. In addition to buckybowls, [362][363][364][365] a bowlshaped nanobelt reported by Wu and coworkers, which could selectively capture C 70 with a large binding constant (log(K a ) E 5; in toluene) from a mixture of C 60 /C 70 due to size and shape complementarity. 366 Isobe and coworkers synthesized a nanometer-sized geodesic phenylene bowl comprising 20 phenylene units, which forms a 1 : 1 ball-in-bowl complex with C 60 .…”