B02 • Engineering Stable Boron-Based Diradicals with Controlled Spin Interactions

Diradicals are even-electron compounds containing two radical centers with unpaired electrons, which, in the present context, weakly interact to give two spin states (singlet and triplet). In nature these species are usually short-lived, due to their propensity to form covalent bonds by radical recombination.
Diradicals are key intermediates in the formation of light-emitting states in optoelectronic organic materials, while the presence of unpaired electrons imparts them with high electric conductivity without the need for added dopants, making them candidates for use in applications such as organic thermoelectric materials. Despite their vast potential utility, three major challenges stand in the way of the proliferation and wider adoption of organic/main-group-based diradical species.
Firstly, their applications in optoelectronics require stable specimens, which remain rare as their syntheses are generally difficult, time-consuming and/or have unpredictable outcomes. Further, the unpaired electrons of many diradicals tend to recombine through delocalization across the spacer units, which quenches any diradical character. These difficulties have hampered the full exploration of the chemical space of diradical species and prevented systematic and broad-scope synthetic studies.
Secondly, very little is known about the optical, electrical and spin properties of these diradical species, and in particular how these properties change under certain perturbations (e.g., magnetic fields) – the application of advanced methods combining a perturbation with multidimensional measurements are sorely needed.
Lastly, highly accurate quantum-chemical evaluations of diradicals and their reactions require a balanced treatment of dynamic and nondynamic correlation contributions, which poses a significant challenge in view of the large sizes of stable candidate molecules.
This project will address diradicals based on a modular and stable boron-containing radical unit that exhibits rich photophysics and has potential for application. The synthesis of a wide range of these species has recently become feasible and this project will establish the missing links between stability, structure, spin states and light emission. To achieve these challenging goals, a highly interdisciplinary approach combining synthesis, spin-sensitive characterization, and quantum-chemical analysis will be pursued.