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

Contortedpolycyclic aromatic molecules, such as corannulenes andsumanenes, have been studied as host molecules for fullerenes dueto their complementary geometries. It has been suggested that strongerassociations with fullerenes can be attained by extending their & pi;surface or by incorporating heteroatoms, as unsubstituted corannuleneand sumanene do not readily complex with fullerenes in solution. Here,we design and synthesize & pi;-extended buckybowls derived fromcontorted hexabenzocoronene and pentabenzocoronene with either pentylor butoxy side chains. These coronene-based buckybowls have approximatelytwice the & pi; surface compared to unsubstituted corannulene andsumanene. Buckybowls with pentyl side chains complex with C-60 in a preferred 1:1 buckybowl-to-C-60 stoichiometry, withassociation constants on the order of 10(3) M-1. Complexation with C-60 further strengthens with the additionof heteroatoms in buckybowls bearing butoxy side chains. We find apreferred 1:2 association stoichiometry with fullerene and associationconstants on the order of 10(4) M-1. Densityfunctional theory calculations suggest the larger dipole moment onthe butoxy-substituted buckybowls relative to their pentyl-substitutedcounterparts is responsible. This greater dipole moment polarizesC(60), leading to a preferred 1:2 stoichiometry and largerassociation constants in the complexation of buckybowls with butoxyside chains and C-60.