The overarching goal of the proposed work was to set up a partnership between the University of Southern Mississippi (USM) and Oak Ridge National Laboratory (ORNL) to develop novel approaches to measure the backbone rigidity of conjugated polymers (CPs) and understand the critical role of sidechains on the backbone conformation and the materials macroscopic property. The backbone rigidity greatly influences the electronic properties of CPs, which ultimately determines the functionality and performance of these materials. Improvements in the electronic properties of CPs would allow for enhanced charge transport in semiconductor devices, improved photovoltaic performance, recycling of waste heat in thermoelectrics, and discovery of new phenomena that will enable the next generation of energy technologies. Although significant progress has been made to optimize the optical and electronic properties of CPs, largely through Edisonian methodologies, it remains a challenge to experimentally characterize conjugated backbone conformation (chain rigidity, torsion, planarity, and short-range order) and relate these to the fundamental optical and electronic properties (electronic coupling, charge transport, etc.). This has left fundamental gaps in our knowledge of the most basic structure/property relationships within these systems, precluded the study of fundamental physical phenomena, and constrained the design and realization of new electronic and device functionalities. Thus, the major goal of this work is to use novel deuteration methodologies via systematic synthetic approaches, and neutron scattering techniques to comprehensively characterize the structural and dynamic properties of CPs in contrast-matching solvents. Our work would, for the first time, elucidate the relationship between backbone rigidity and macroscopic properties. They will also allow a rational formulation of design principles for next-generation CPs that are resilient to disorder through precise control of the delocalized electrons along the polymer backbone. Overall, this project will advance our understanding of the structure, dynamics, and fundamental physics of these materials, which is crucial for enabling the prediction, design, control, and manipulation of current and emerging material electronic properties.

Open-shell conjugated polymers (CPs) offer new opportunities to integrate the spin degree of freedom within emerging technologies. Central to their realization are strong acceptors that stabilize unpaired spins within the x-conjugated backbones. Here, we demonstrate a high-spin CP composed of alternating benzo[1,2-b:4,5-b ']dithiophene donors and a new, strongly electron-withdrawing 6,7,8,9-tetrachloro-[1,2,5]thiadiazolo[3,4-b]phenazine acceptor. A comparative study with a 6,7dimethyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) acceptor demonstrates that annulation and chlorination of the TQ framework facilitates a transition between closed-shell aromatic and high-spin quinoidal forms. This is accompanied by a concomitant reduction of the bandgap, high electron affinity, delocalization of spin density, and n-type conduction. These insights enable access to a broader range of open-shell CPs and the manipulation of important properties such as topology, exchange interactions, and carrier polarity.

Donor-acceptor (DA) conjugated polymers (CPs) with narrowbandgaps and open-shell electronic structures offer a fundamentally newparadigm for integrating the spin degree of freedom within emerging functionaldevices. Recent advancements have demonstrated that control of long-rangeelectronic correlations enables low-spin (S= 0) and high-spin (S= 1) DA CPs, inwhich extended pi-conjugation overcomes the intrinsic instability of theseelectronic configurations in light-element materials. While design strategies thatarticulate mechanisms of spin alignment, topology control, and quantummechanical exchange are emerging, dedicated studies of the magnetic behaviorof these materials remain rare. Here, we utilize sensitive magnetometry techniquesto analyze the magnetic properties of open-shell DA CPs with low- and high-spinground states. We demonstrate improved measurement accuracy through combining vibrating sample magnetometry andsuperconducting quantum interference device magnetometry. This serves to overcome challenges associated with the inherentlyweak magnetic moments of these materials and a measurement environment in which the background signal is always significant andmust be carefully removed. Analyzing the results following established models for paramagnetic materials enables precisequantification of the spin quantum number and temperature-dependent spin alignment. These studies articulate approaches thatenable precise characterization of the bulk magnetic features of these heterogeneous and disordered materials systems, providing apath for rational property elucidation that will enable the integration of these materials within emerging technologies.

The development of open-shell organic molecules that magnetically order at room temperature,which can be practically applied, remains a grand challenge in chemistry, physics, and materials science. Despite the exploration of vast chemical space, design paradigms for organic paramagnetic centers generally result in unpaired electron spins that are unstable or isotropic. Here, a high-spin conjugated polymer is demonstrated, which is composed of alternating cyclopentadithiophene and benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole heterocycles, in which macromolecular structure and topology coalesce to promote the spin center generation and intermolecular exchange coupling. Electron paramagnetic resonance (EPR) spectroscopy is consistent with spatially localized spins, while magnetic susceptibility measurements show clear anisotropic spin ordering and exchange interactions that persist at room temperature. The application of long-range π-correlations for spin center generation promotes remarkable stability. This work offers a fundamentally new approach to the implementation of this long-sought-after physical phenomenon within organic materials and the integration of manifold properties within emerging technologies.