This work investigates the magnetic properties of a series of poly(alkylthiophene)s (PATs) with varying chain topologies and morphologies. The materials are engineered by integrating ill-coupled bithiophene defect units, revealing the effect of conjugation length on the optical band gap through UV-vis analysis. Differential scanning calorimetry (DSC) is used to differentiate between amorphous and semi-crystalline samples. Various morphologies with a constant number of topological defects are created via thermal treatment, allowing for an analysis of how topology and morphology influence the magnetic properties of PATs, which are categorized into amorphous and semi-crystalline types. Field- and temperature-dependent SQUID magnetization experiments show that the magnetic susceptibility of all samples comprises up to four contributions. A consistent diamagnetic susceptibility is identified, while many samples exhibit complex temperature-dependent susceptibility akin to the Curie-Weiss behavior of antiferromagnetic solids. The density of spins contributing to this behavior is estimated, revealing that antiferromagnetic coupling weakens as conjugation length increases, eventually vanishing in amorphous samples with high conjugation length. An ab initio π-based molecular magnetism model simulates the temperature-dependent magnetization curves, providing insights into the susceptibility from spins in triplet states. This research hi
