Impact of Polarity on Anisotropic Diffusion of Conjugated Organic Molecules on the (101̅0) Zinc Oxide Surface

Abstract

We study the influence of polarity on the binding and diffusion of single conjugated organic molecules on the inorganic (1010) zinc oxide surface by means of all-atom molecular dynamics simulations at room temperature and above. In particular, we consider the effects of partial fluorination of the para-sexiphenyl (p-6P) molecule with chemical modifications of one head group (p-6P2F) or both (symmetric) head and tail (p-6P4F). Quantum-mechanical and classical simulations both result in consistent and highly distinct dipole moments and densities of the fluorinated molecules, which interestingly lead to a weaker adhesion to the surface than for p-6P. The diffusion for all molecules is found to be normal and Arrhenius-like for long times. Intriguingly, close to room temperature, the polar molecules diffuse 1–2 orders of magnitude slower compared to the p-6P reference in the apolar x-direction of the electrostatically heterogeneous surface, whereas in the polar y-direction, they diffuse 1–2 orders of magnitud...