From elusive non-Kekulé species to bottle-able functional molecular bricks – NO-KEKULE-RULES

The discoveries of stable versions of elusive intermediates are historic landmarks, which have had deep impacts on modern organic chemistry, and beyond. Stable carbenes and radicals are typical examples. Although they were regarded essentially as academic curiosities when they were first disclosed, their uncommon properties have led in the long term to groundbreaking innovations in a remarkable range of scientific fields.
In this proposal, I want to consider a class of organic species that lie outside of conventional representations. Their atypical topologies preclude a description with classical Kekulé-type structures, in which all atoms of the delocalized system are involved in a double bond. As a consequence, these compounds can only be assigned to diradical or zwitterionic resonance forms. My preliminary results demonstrate that several families of so-called non-Kekulé molecules, which have been disregarded for long as non-isolable oddities, are about to shift from elusive species to bottle-able functional molecular bricks. In other words, they are now ready to meet the fate of carbenes and radicals.
Although very little is known about these compounds, it is already clear that they constitute a vast class of species, whose original properties remain yet to be disclosed and exploited. In particular, the proposed targets have been especially chosen for their potential as game-changers in singlet fission, an underdeveloped charge carrier multiplication process, which can occur at the molecular level and hold the promise for decisive advances in the quest for efficient cost-effective dye-sensitized solar cells. The present project intends to deliver flexible and general protocols for their syntheses and to showcase not only biradicaloid dyes with spectacular stability, but also more reactive variants featuring original reactivity with perspective towards catalysis.