Anharmonic Lattice Vibrations in Small-Molecule Organic Semiconductors

Abstract

The intermolecular lattice vibrations in small-molecule organic semiconductors have a strong impact on their functional properties. Existing models treat the lattice vibrations within the harmonic approximation. In this work, we use polarization-orientation (PO) Raman measurements to monitor the temperature-evolution of the symmetry of lattice vibrations in anthracene and pentacene single crystals. Combined with first-principles calculations, we show that at 10 K the lattice dynamics of the crystals are indeed harmonic. However, as the temperature is increased specific lattice modes gradually lose their PO dependence and become more liquid-like. This finding is indicative of a dynamic symmetry breaking of the crystal structure and shows clear evidence of the strongly anharmonic nature of these vibrations. Pentacene also shows a subtle phase transition between 80-150 K, indicated by a change in the vibrational symmetry of one of the lattice modes. Our findings lay the groundwork for accurate predictions and new design rules for high-mobility organic semiconductors at room temperature.

References in corpus (6)

• Long-range correlation energy calculated from coupled atomic response functions
• Temperature dependent effective third order interatomic force constants from first principles
• The transient localization scenario for charge transport in crystalline organic materials
• Chasing the killer phonon mode for the rational design of low disorder, high mobility molecular semiconductors
• Heat capacity of matter beyond the Dulong-Petit value
• Interplay between organic cations and inorganic framework and incommensurability in hybrid lead-halide perovskite CH3NH3PbBr3

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• Conductivity of an electron coupled to anharmonic phonons
• Accurate Machine Learning Interatomic Potentials for Polyacene Molecular Crystals: Application to Single Molecule Host-Guest Systems