Approaching isotropic charge transport of n-type organic semiconductors with bulky substituents

n-type organic semiconductors exhibiting two-dimensional isotropic charge transport are rarely reported. Here the authors show that using bulky substituents, BQQDI demonstrates near-isotropic charge transport, resilience to dynamic disorder, as well as high electron mobility both in single- and polycrystalline thin-film transistors. Benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI) is an n-type organic semiconductor that has shown unique multi-fold intermolecular hydrogen-bonding interactions, leading to aggregated structures with excellent charge transports and electron mobility properties. However, the strong intermolecular anchoring of BQQDI presents challenges for fine-tuning the molecular assembly and improving the semiconducting properties. Herein, we report the design and synthesis of two BQQDI derivatives with phenyl- and cyclohexyl substituents (Ph-BQQDI and Cy-6-BQQDI), where the two organic semiconductors show distinct molecular assemblies and degrees of intermolecular orbital overlaps. In addition, the difference in their packing motifs leads to strikingly different band structures that give rise to contrasting charge-transport capabilities. More specifically, Cy-6-BQQDI bearing bulky substituents exhibits isotropic intermolecular orbital overlaps resulting in equal averaged transfer integrals in both pi-pi stacking directions, even when dynamic disorders are taken into account; whereas Ph-BQQDI exhibits anisotropic averaged transfer integrals in these directions. As a result, Cy-6-BQQDI shows excellent device performances in both single-crystalline and polycrystalline thin-film organic field-effect transistors up to 2.3 and 1.0 cm(2) V-1 s(-1), respectively.

Automated summary

By synthesizing BQQDI derivatives with different substituents, the researchers demonstrated distinct molecular assemblies and charge-transport capabilities for these two organic semiconductors.