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

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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.


Original languageEnglish
Article numbere202202170
Number of pages7
JournalAngewandte Chemie - International Edition
Issue number23
Publication statusPublished - 30 May 2022

External IDs

PubMed 35290699
WOS 000794175900001


Research priority areas of TU Dresden

DFG Classification of Subject Areas according to Review Boards

ASJC Scopus subject areas


  • Azulenes, Fused-Ring Systems, Magnetic Properties, Open-Shell Diradicaloids, Polycyclic Hydrocarbons