Tuning diradical character is an important topic for organic diradicaloids. Herein, we report the precise borylation enabling structural isomerism as an effective strategy to modulate diradical character and thereby properties of organic diradicaloids. We synthesized a new B-containing polycyclic hydrocarbon that has the indeno[1,2-b]fluorene π-skeleton with the β-carbons bonding to two boron atoms. Detailed theoretical and experimental results show that this bonding pattern leads to its distinctive electronic structures and properties in comparison to that of its isomeric molecule. This molecule has the efficient conjugation between boron atoms and π-skeleton, resulting in downshifted LUMO and HOMO levels. Moreover, it exhibits smaller diradical character and thereby inhibited diradical properties, such as significantly blue-shifted light absorption, larger energy bandgap and weak para-magnetic resonance. Notably, this B-containing polycyclic hydrocarbon possesses much stronger Lewis acidity and its Lewis acid-base adducts display enhanced diradical character, demonstrating the positive effects of Lewis coordination on modulating diradical performance.
Keywords: boron; borylation; diradical character; organic diradicaloids; structural isomerism.
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