Benzo-extended cyclohepta[def]fluorene derivatives with very low flowing triplet states

 
An illustration of the deriviatives with benzannulation and kinetic and thermodynamic stablization

Open-shell non-alternant polycyclic hydrocarbons (PHs) are attracting increasing attention due to their promising applications in organic spintronics and quantum computing.

In the paper 'Benzo-extended cyclohepta[def]fluorene derivatives with very low-lying triplet states', the synthesis of three cyclohept[def]fluorene-based diradicaloids, by fusion of benzo rings on its periphery for the thermodynamic stabilisation are evidenced by multiple characterisation techniques.  Remarkably, all of them display a very narrow optical energy fap and persistent stability under ambient conditions.

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-alternate open-shell PHs with high-spin ground states, and opens up novel possibilities and insights into understanding the structure-property relationships.