Chiral “Pinwheel” Heterojunctions Self-Assembled from C60 and Pentacene

Abstract

We demonstrate the self-assembly of C60 and pentacene (Pn) molecules into acceptor- donor heterostructures which are well-ordered and – despite the high degree of symmetry of the constituent molecules – chiral. Pn was deposited on Cu(111) to monolayer coverage, produc- ing the random-tiling (R) phase as previously described. Atop R-phase Pn, post-deposited C60 molecules cause rearrangement of the Pn molecules into domains based on chiral supramolec- ular ‘pinwheels’. These two molecules are the highest-symmetry achiral molecules so far observed to coalesce into chiral heterostructures. Also, the chiral pinwheels (composed of 1 C60 and 6 Pn each) may share Pn molecules in different ways to produce structures with differ- ent lattice parameters and degree of chirality. High-resolution scanning tunneling microscopy (STM) results and knowledge of adsorption sites allow the determination of these structures to a high degree of confidence. The measurement of chiral angles identical to those predicted is a further demonstration of the accuracy of the models. VdW-DFT calculations reveal that the Pn molecules around each C60 are torsionally flexed around their long molecular axes and that significant charge transfer from C60 to Pn is present in each pinwheel.