Revisiting the Dehydroannulenes

Dehydroannulenes are cyclic, conjugated materials containing a mixture of sp2- and sp-hybridized carbon atoms within the conjugated circuit. As with the more familiar annulenes (containing only sp2-hybridized atoms), dehydroannulenes generally follow Hückel's rules for aromaticity - circuits with 4n+2 pi-electrons are aromatic, while those with 4n ð-electrons are considered anti-aromatic. Unlike the annulenes, however, the formally "antiaromatic" dehydroannulenes can be synthesized, isolated, and characterized. Research in this area was quite popular in the 1960s, leading to a wide variety of novel cyclic structures. More recently, benzannelated versions of dehydroannulenes have been studied for their structural and photonic properties - however benzannelation disrupts the inherent aromaticity / antiaromaticity of the dehydroannulene itself, masking any particular contribution of the larger macrocycle. For this project, the parent dehydroannulenes will be revisited, utilizing modern synthetic approaches and characterization techniques. The focus in particular will be on two classes of dehydro[12]annulenes, whose formal anti-­?aromatic character promise interesting and potentially useful electronic and photophysical properties. The first task will be to develop appropriate functionalization schemes to yield stable materials. Subsequently, we will tune functionalization in order to tune aggregation, both in solution and in the solid state. The nature of aggregation is key to a wide array of important phenomena, and the lack of a C-­H periphery (as in e.g. aromatic or annulene systems) will dramatically shift the nature of intermolecular electronic interaction. The strength of these interactions will then be probed both in nanoaggregates and in the solid state to see the impact of intermolecular order on processes such as singlet fission and charge transport.