Columnar Packing Motifs of Functionalized Perylene Derivatives: Local Molecular Order Despite Long-Range Disorder

Abstract

We elucidate local packing motifs and dynamical order parameters in a perylene tetracarboxydiimide derivative (C(8,7)-PDI), one of the most promising candidates for rationally designed, self-assembling, and self-healing molecular wires. Spectroscopic fingerprints obtained from solid-state NMR spectroscopy are interpreted by means of first-principles calculations and molecular dynamics simulations. The interplay of steric repulsion, H bonding, and pi-pi packing effects leads to a specific relative molecular pitch angle of approximately 35 +/- 10 degrees between successive molecules in the stack. Dynamical order parameters, determined from NMR sideband patterns as a measure of molecular motion, yield values of S approximately = 1.0 in the core of the columnar stack, corresponding to an almost frozen molecular dynamics at ambient temperature. This rigidity is compatible with characteristic intermolecular distances obtained from dipolar couplings between specific hydrogens via double-quantum NMR experiments and further supported by ab initio calculations.