2, Marmara University, Istanbul, , Turkey
3, Nagoya University, Nagoya, , Japan
Polycyclic aromatic hydrocarbons (PAHs) have been of interest in the scientific community as organic semiconductors in field-effect transistors (FETs), light-emitting diodes (LEDs), and organic photovoltaics (OPVs). In the last 100 years, interest has evolved towards curved aromatic hydrocarbons, such as corannulenes and helicenes, that are three-dimensional and can be either chiral or achiral. These materials usually pack in a columnar manner or with partial π-π stacking, which allows for close orbital contacts between molecules for high multi- dimensional charge transport. We report a computational study on the effect of side-chain substitution and unique crystal packing on the charge transport of two double helical molecules, whose synthesis and crystal structure were reported by the Itami group. These molecules, which we refer to as double helicenes (DHs) are structural hybrids of nonplanar helicene and planar tribenzo[b,n,pqr] perylene (TBP). Using a previously described method rooted in Marcus theory and kinetic Monte Carlo (kMC) simulations, we calculated charge-transport properties and hole mobilities for perfect order and disordered DH systems. We find that side-chain substitution has small effect on intrinsic electronic properties in DHs molecular structure but dramatically impacts the packing arrangement, morphologies and transport network. Using these methods, we have established a direct link between the morphology, transport connectivity and hole mobilities. The results show that both unsubstituted and substituted DHs have high hole mobilities in the crystal phase. However, with the inclusion of positional disorder, mobility of crystalline DH1 was relatively lower while the mobility of DH2 remained nearly unchanged. We relate this effect to the dimensionality of their unique transport network. Both DH1 and DH2 are promising organic semiconductors with high mobilities in crystal and crystalline phases, with predicted values that lie in the range of ~1 to 10 cm2 V-1 s-1.