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A completely cofacial organic semiconductor

Crystals of 1,3,5-tripyrrolebenzene (TPB) contain closely packed, perfectly cofacial stacks of benzene rings with large wavefunction overlap, making it an interesting candidate organic semiconductor. We study TPB using a variety of ab-initio and band-structure techniques, and find very large $π$ overlap in the benzene stacks, broad bands (especially for electrons), and relatively small binding energies for polarons of both signs, making TPB a promising quasi-one dimensional electron-transport agent. We then explore the sources of the unusual packing in TPB, finding that calculations of intermolecular interactions using dispersion-corrected density functional theory provide valuable insights into why the crystals contain perfectly cofacial $π$-networks.