Synthesis of a quinoidal dithieno[2,3-d;2′,3′-d]benzo[2,1-b;3,4-b′]-dithiophene based open-shell singlet biradicaloid
A fused heteroacene derivative, bis(dicyanomethylene)-end-capped-dithieno[2,3-d;2′,3′-d]benzo[2,1-b;3,4-b′]-dithiophene (4CN-DTmBDT) was synthesized. Its open-shell biradical character in the ground state is studied by a combination of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). Structural assignment was verified with single crystal X-ray diffraction analysis. A highly stable biradicaloid with a low energy gap and low LUMO level is achieved.