Exploring Crystal Structure in Ethyne-Substituted Pentacenes, and Their Elaboration into Crystalline Dehydro[18]annulenes

Approaches to control the self-assembly of aromatic structures to enhance intermolecular electronic coupling are the key to the development of new electronic and photonic materials. Acenes in particular have proven simple to functionalize to induce strong π-stacking interactions, although finer control of intermolecular π-overlap has proven more difficult to accomplish. In this report, we describe how very weak hydrogen bonding interactions can exert profound impact on solid-state order in solubilized pentacenes, inducing self-assembly in either head-to-tail motifs with strong 2-D π-stacking, or head-to-head orientations with much weaker, 1-D π-stacking arrangements. In order to achieve 3-D π-stacking useful for photovoltaic applications, we elaborated a series of diethynyl pentacenes to their trimeric dehydro[18]annulene forms. These large, strongly interacting structures did indeed behave as acceptors in polymer photovoltaic devices.