Donor–acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell electronic structures offer a fundamentally new paradigm for integrating the spin degree of freedom within emerging functional devices. Recent advancements have demonstrated that extended π-conjugation inherent to these polymeric materials overcomes the intrinsic instability of these electronic configurations in light element materials. This has enabled low-spin (<i>S</i> = 0) and high-spin (<i>S</i> = 1) DA CPs with distinct properties not available to their closed-shell counterparts. While strategies for control of spin alignment and exchange are emerging, dedicated studies of the magnetic behavior of these materials remain rare. Here, we utilize a combination of vibrating sample and superconducting quantum interference device magnetometry techniques to analyze the magnetic properties of open-shell CPs with low- and high-spin ground states to overcome challenges associated with inherently weak magnetic signatures. The weak magnetic moments associated within organic materials results in a measurement environment in which the background signal always contributes and can significantly affect the result. We also discuss the application of Pascal’s constants to calculate a correction factor to remove diamagnetic contributions. Through careful analysis following established models for paramagnetic materials, we precisely quantify the spin quantum number and determine the ground state spin alignment. These studies articulate approaches that enable precise characterization of the bulk magnetic features of these heterogenous and disordered materials systems, providing a path for rational property elucidation that will enable the integration of these materials within emerging technologies.

Magnetic susceptibility measurements of open-shell donor–acceptor conjugated polymers

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