Origin of the High Carrier Mobilities of Nonperipheral Octahexyl Substituted Phthalocyanine

Abstract

The carrier transport properties of nonperipheral octahexyl substituted phthalocyanine H2Pc(C6H13)8np in its crystal and columnar (Col) liquid crystal (LC) phase were investigated using density functional theory (DFT) calculations in combination with molecular dynamics (MD) and kinetic Monte Carlo (KMC) simulations. In the crystal phase, we found that the nonperipherally substituted chains of H2Pc(C6H13)8np, that interpenetrate adjacent phthalocyanines (Pcs), significantly alter the Pc-core stacking such that higher hole mobilities are observed for this system than for the nonsubstituted H2Pc. This chain interpenetration was found to be inherited by the column stacking in the Col phase and hindered the Pc-core in-plane rotations between adjacent Pcs. This rotational hindrance further caused a nonuniform distribution of the adjacent dimer Pc-core in-plane orientation configurations. The relatively high carrier mobility in the Col phase in this system can be rationalized by the nonuniform distribution of the dimer configurations that give relatively high electronic coupling between the adjacent dimers. Our results show the remarkable effects of nonperipheral substitutions on the carrier transport properties in both the crystal and Col LC phases.