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

Abstract

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.

Cyclodimers and Cyclotrimers of 2,3 ‐Bisalkynylated Anthracenes, Phenazines and Diazatetracenes

“…The quasiplanar dimers 3 a 2 and 3 c 2 form slightly offset onedimensional staircases with π-π stacking distances of 351 and 338 pm (averaged through both chromophores and butadiinylene linkers), respectively. In the supramolecular structures, one acenylene subunit is centered above the octadehydro [12] annulene moiety of the neighboring molecule, hinting at lessthan-ideal charge transport properties. Unlike the Hay-type dimers, 3 a-c 3 deviate from planarity -the (aza)acenylene subunits are slightly twisted with respect to each other, a feature also observed in Anthony's pentacene-based dehydroannulenes, [11,12] which is most likely a crystal packing effect as gas-phase structures were calculated to be planar.…”

“…In the supramolecular structures, one acenylene subunit is centered above the octadehydro [12] annulene moiety of the neighboring molecule, hinting at lessthan-ideal charge transport properties. Unlike the Hay-type dimers, 3 a-c 3 deviate from planarity -the (aza)acenylene subunits are slightly twisted with respect to each other, a feature also observed in Anthony's pentacene-based dehydroannulenes, [11,12] which is most likely a crystal packing effect as gas-phase structures were calculated to be planar. In contrast to the pentacene-based annulene exhibiting three-dimensional π-stacking interactions, only two-dimensional ones are observed in the trimers: In 3 a 3 (co-crystallyzing with chloroform) and 3 c 3 (solvent-free packing), two of the three "arms" overlap-distances between π-system distances amount to ~3.4 Å.…”

“…Yet, only benzene rings [6] were investigated until, in 1998, Komatsu published the dimerization of diethynylnaphthalene derivatives furnishing B , [7] and Anthony prepared structure C as the cyclotrimer of a substituted 2,3‐diethynylpentacene. [8] …”

“…Note that only Anthony's trimer was employed in an organic electronic device, albeit in a photovoltaic cell. [8] TFTs were fabricated in bottom gate/top contact architectures (Figure 5 and Supporting Information) with silver as contact electrodes, using a SAM modified dielectric. [16] Thin films of 3 c 2 and 3 c 3 were obtained by drop‐casting ( 3 c 2 : toluene, 0.5 mg/mL; 3 c 3 : CH 2 Cl 2 , 0.5 mg/mL).…”