Minimal requirements for one-dimensional aggregation in simple coarse-grained models of charged porphyrinoid units

We present a Monte Carlo simulation study of cooperative self-assembly of oppositely charged porphyrin-like molecules, with a focus on disentangling the roles of electrostatic attraction and π-π stacking in supramolecular nanowire formation. Electrostatic interactions were described by a screened Debye-Hückel potential, and the short-range cohesive interactions were introduced via a Lennard-Jones (LJ) potential acting on the neutral cores. Our simulations reveal that Coulombic interactions alone cannot sustain aggregation; a critical LJ strength between 1.5 and 2k_BT triggers the transition from disordered clusters to ordered one-dimensional nanowires. This disorder-to-order transition was quantitatively supported by changes in radial distribution functions, cluster size distributions, and charge alternation indices. Increased ionic strength weakens long-range electrostatic attraction, thus delaying nanowire formation, although the short-range cohesive interactions alone can still drive aggregation under these conditions. These findings reveal the delicate balance between electrostatic screening and short-range forces in directing supramolecular organization in aqueous colloidal systems. These results provide design principles for tuning the morphology of porphyrin-based nanostructures with potential applications in colloidal engineering, interfacial science, and functional nanomaterials.