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Although hydrogen bonding and \u03c0\u2013\u03c0 interactions are recognized as key forces in shaping its architecture, their individual contributions remain poorly defined. Among its molecular precursors, the canonical monomer 5,6\u2010dihydroxyindole (DHI) is notable for forming extensive hydrogen\u2010bonded networks that stabilize supramolecular assemblies. To clarify how hydrogen bonding influences supramolecular topology in eumelanin precursors, we investigate selectively methylated derivatives of DHI, examining how subtle modifications to hydrogen\u2010bonding motifs alter crystal packing, intermolecular arrangements, and optical properties. Single\u2010crystal structures reveal that O\u2010methylation (DMI) changes hydrogen\u2010bonding dimensionality yet preserves helical assemblies, whereas full O\u2010 and N\u2010methylation (DMI\u2010Me) suppresses hydrogen\u2010bonding, giving rise to zigzag arrangements dominated by van der Waals forces. Solid\u2010 and solution\u2010state NMR measurements independently confirm the differences in the hydrogen\u2010bonded assemblies. Complementary electronic spectroscopy shows that noncovalent architectures of the eumelanin derivatives exhibit pronounced excitonic coupling between neighboring chromophores. Electronic structure calculations support these observations, demonstrating that coupling originates primarily from Coulombic interactions, with minimal contributions from charge transfer. By linking molecular substitution to packing motifs and excitonic interactions, this work establishes hydrogen bonding as a design element for directing supramolecular order and emergent optoelectronic behavior in eumelanin\u2010inspired materials.<\/jats:p>","DOI":"10.1002\/chem.202503052","type":"journal-article","created":{"date-parts":[[2026,1,14]],"date-time":"2026-01-14T14:08:12Z","timestamp":1768399692000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Modulating Supramolecular Topology via Hydrogen Bonding in a Eumelanin Monomer"],"prefix":"10.1002","volume":"32","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7537-0335","authenticated-orcid":false,"given":"Kavya","family":"Vinod","sequence":"first","affiliation":[{"name":"School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram  Thiruvananthapuram Kerala 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