Wu, F.; Ma, J.; Lombardi, F.; Fu, Y.; Liu, F; Huang, Z.; Liu, R.; Komber, H.; Alexandropoulos, D.I.; Dmitrieva, E.; Lohr, T.G.; Israel, N.; Popov, A.A.; Liu, J.; Bogani, L.; Feng, X.: Benzo-Extended Cyclohepta[def]fluorene Derivatives with Very Low-Lying Triplet States. Angewandte Chemie - International Edition 61 (2022), p. e202202170/1-7
10.1002/anie.202202170
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Abstract:
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 eV) and persistent stability under ambient conditions (t1/2=11.7–33.3 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 kcal mol−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 relationships.