Molecular design is critical in order to both study and exploit chirality in two-dimensional (2D) self-assembled molecular networks at surfaces and interfaces. Here, we investigate the supramolecular structures of two prochiral π-conjugated molecular systems on a graphite surface by scanning tunneling microscopy at the solid?liquid interface. By systematically extending the periphery of such molecular systems, we demonstrate how the expression of chirality of the resulting supramolecular networks can be rationally controlled, driving the assembly from an achiral to a chiral organization. Our approach provides fundamental insights into the role of molecular geometry in governing the physical properties of 2D self-assembled molecular networks, and it offers a rational bottom-up strategy for the fabrication of chiral surfaces from prochiral building blocks.