  We demonstrate the self-assembly of C$_{60}$ and pentacene (Pn) molecules
into acceptor-donor heterostructures which are well-ordered and -- despite the
high degree of symmetry of the constituent molecules -- {\it chiral}. Pn was
deposited on Cu(111) to monolayer coverage, producing the random-tiling ($R$)
phase as previously described. Atop $R$-phase Pn, post-deposited C$_{60}$
molecules cause rearrangement of the Pn molecules into domains based on chiral
supramolecular `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 C$_{60}$ and 6 Pn each) may share Pn
molecules in different ways to produce structures with different 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. Van der Waals density functional
theory calculations reveal that the Pn molecules around each C$_{60}$ are
torsionally flexed around their long molecular axes and that there is charge
transfer from C$_{60}$ to Pn in each pinwheel.
