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Dielectric permittivity of small-molecule matrices for organic optoelectronics: The key contribution of solid state molecular dynamics

Davide Giavazzi and Anna Painelli

Luca Grisanti*

Gabriele D'Avino†

  • Dipartimento di Scienze Chimiche, della Vita e della Sostenibilità Ambientale, Università di Parma, Parma, Italy

  • *Contact author: grisanti@iom.cnr.it
  • †Contact author: gabriele.davino@unive.it
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Phys. Rev. Materials 10, 024601 – Published 2 February, 2026

DOI: https://doi.org/10.1103/fc1j-sp6w

Abstract

The dielectric response of amorphous organic solids at the timescale of atomic motion has broad implications for their photophysics, governing spectroscopic properties and excited-state relaxation, among other phenomena. We present an original approach to the calculation of the vibrational contribution to the frequency-dependent dielectric permittivity. Our methodology, combining molecular dynamics simulations, density functional theory calculations, and linear response theory, is applied to a set of amorphous carbazole-based small-molecule matrices, widely used as host materials in organic light-emitting diodes. Our analysis reveals the crucial role of hindered molecular rotations (librations) in the solid-state matrices of dipolar compounds. These modes manifest in the very-low frequency (<100cm−1) region of the dielectric function, accounting for up to one-third of the total vibrational contribution to the static dielectric constant in a dipolar compound like 3,3'-di(carbazol-9-yl)-5-cyano-1,1'-biphenyl. This low-frequency contribution is found to be crucial for determining the variations in the static dielectric constant across various materials.

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Phys. Rev. Materials 10, 024601– Published 2 February, 2026
  • Received 24 September 2025
  • Accepted 7 January 2026
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