Benzo‐Extended Cyclohepta[def]fluorene Derivatives with Very Low‐Lying Triplet States. Issue 23 (5th April 2022)

• Record Type: Journal Article
• Authors: Wu, Fupeng; Ma, Ji; Lombardi, Federico; Fu, Yubin; Liu, Fupin; Huang, Zhijie; Liu, Renxiang; Komber, Hartmut; Alexandropoulos, Dimitris I.; Dmitrieva, Evgenia; Lohr, Thorsten G.; Israel, Noel; Popov, Alexey A.; Liu, Junzhi; Bogani, Lapo; Feng, Xinliang
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 23(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-05
• Subjects: Azulenes -- Fused-Ring Systems -- Magnetic Properties -- Open-Shell Diradicaloids -- Polycyclic Hydrocarbons; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202202170
• Languages: English
• ISSNs: 1433-7851

Abstract

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 ( E g opt =0.52–0.69 eV) and persistent stability under ambient conditions ( t 1/2 =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. Abstract : Three open‐shell non‐alternant polycyclic hydrocarbons (PHs) based on the skeleton of cyclohepta[ def ]fluorene are synthesized via an efficient benzannulation stabilization strategy. The obtained persistent singlet diradicaloids have a narrow optical energy gap (0.52–0.69 eV). Moreover, variable‐temperature EPR measurements indicate that all of them have a low‐lying triplet state with an extremely small singlet–triplet energy gap.