Modular Donor-Acceptor Diradicaloids Based on an Electron Deficient N-Heteroacene Acceptor

Conjugated organic molecules with open-shell diradical character (y) possess two weakly paired electron spins interacting across their constituent π-systems. These materials provide fundamental insight into the nature of electron pairing, enabling the utilization of the spin degree of freedom within emerging technologies. However, materials systems that synergistically offer high modularity, tunable y, high chemical stability, and interrelated (opto)electronic functionalities remain limited. Here, we report the facile synthesis of donor-acceptor-donor diradicaloids comprised of a central electron-deficient 6,7,8,9-tetrachloro-[1,2,5]thiadiazolo[3,4-b]phenazine acceptor flanked by electron-rich thiophene-based donors. Nuclear magnetic resonance and electron paramagnetic resonance spectroscopies, and theoretical investigations that account for the multiconfigurational nature of these species, connect a narrowing of the singlet-triplet splitting (∆E_ST), extension of π-conjugation, and electronic correlations with the evolution of diradical character. These data demonstrate that the differences in structural, electronic, spin, magnetic, physicochemical, and transport properties of the materials can be modulated, while the inherent multireference nature of the electronic structure can be predicted using optimally tuned long-range corrected Mixed-Reference Spin-Flip Time-Dependent Density Functional Theory. These insights enable facile access to a broader range of open-shell materials and facilitate the manipulation of important properties such as electronic structure, topology, exchange, and interrelated optoelectronic and transport functionalities.