AbstractThe π‐conjugated supramolecular polymers (SMP) have gained vast popularity in materials chemistry and biomedicine due to their spectacular self‐assembling behaviour. A detailed account of the electronic structure and bonding through quantum theory of atoms‐in‐molecules, non‐covalent interactions, and energy decomposition analysis (EDA) in the oligomers of perylene, perylene diimide (PDI), and thionated‐PDI (t‐PDI) is presented. The oligomers of all three molecules show a slip angle of θ≈62° thus forming H‐aggregates. The stacking pattern in perylene oligomers prefers a slip‐stacked brick‐layer order, while the bulkier PDI and t‐PDI prefer a parallel step‐wise pattern in their oligomers. Successive addition of monomers leads to a consequent rise in the association energy, although to a much greater extent in PDI and t‐PDI than in perylene. While the major contribution to this association energy comes from the dispersion interactions in all three systems, the steric interactions in t‐PDI quench the cooperativity in its SMP formation. A detailed analysis of the non‐covalent interactions reveals the presence of π‐π, π‐hole⋅⋅⋅O=C, and π‐hole⋅⋅⋅S=C electrostatic interactions playing a crucial role in the self‐assembly process, which can be further implemented on developing force field‐based methods for understanding the self‐assembling mechanism in higher degree of oligomers.