π-Extended Pentalenes: Formally Antiaromatic, Redox-Active PAHs

The formal antiaromaticity of pentalene explains the ability of PAHs containing this moiety to accept two electrons, as this forms the formally aromatic dianion. Thus, such molecules are attractive as new n-type molecules for use in organic electronics. In 2009, we serendipitously discovered a versatile route to construct pentalenes from simple haloenyne building blocks, and several related methods have since been reported by other groups. We have also explored the interesting possibility of the fusion of two or more pentalenes into a single PAH framework. To determine how this would affect electronic properties, PAHs containing both two and three embedded pentalenes were synthesized. These compounds, which are surprisingly air and moisture stable, exhibited both enhanced optical properties (e.g. a five-fold increase in absorption coefficient) and strong modulation of redox properties resulting from interactions of the pentalene centers.