Hydrogen Bonding Versus Pi-Stacking In Charge-Transfer Co-Crystals

We report a comparative study of two structurally similar donor-acceptor complexes with (1a) and without (2a) H-bonding using X-ray crystallography, spectroscopic analysis, and density functional theory calculations. H-Bonding enhances the donor-acceptor interactions, as manifested in a narrower band gap and shorter pi-stacking distance in 1a versus 2a, despite 2 being a stronger donor than 1. Thin-film transistors of 1a showed ambipolar charge transport with "double dip" characteristics, whereas no transistor behavior was observed for 2a.