Benzo Extended Cyclohepta[def]fluorene Derivatives with Very Low Lying Triplet States

Open shell non alternant polycyclic hydrocarbons PHs are attracting increasing attention due to their promising applications in organic spintronics and quantum computing. Herein we report the synthesis of three cyclohepta[def]fluorene based diradicaloids 1 3 , by fusion of benzo rings on its periphery for the thermodynamic stabilization, as evidenced by multiple characterization techniques. Remarkably, all of them display a very narrow optical energy gap Egopt 0.52 0.69 amp; 8197;eV and persistent stability under ambient conditions t1 2 11.7 33.3 amp; 8197;h . More importantly, this new type of diradicaloids possess a low lying triplet state with an extremely small singlet triplet energy gap, as low as 0.002 amp; 8197;kcal amp; 8201;mol amp; 8722;1, with a clear dependence on the molecular size. This family of compounds thus offers a new route to create non alternant open shell PHs with high spin ground states, and opens up novel possibilities and insights into understanding the structure property relationship