Structural and dielectric properties of trans-stilbene–TPD-type molecular composites

Abstract

The crystallization behaviour and dielectric response of trans‑stilbene embedded in a small‑molecule hole‑transport matrix were examined as a function of composition. In contrast to polymeric hosts, the crystallizing tritolyl‑triarylamine-based material – structurally related to TPD – enables a direct analysis of mutual crystallization effects between the two molecular solids. Composite films containing 5–80% trans-stilbene were prepared by drop casting and characterized using X-ray diffraction, optical microscopy, and dosed charging measurements. XRD and microscopy reveal concentration-dependent phase coexistence and morphological evolution, while dielectric measurements show a pronounced nonmonotonic dependence on the composition, with an enhanced effective permittivity at intermediate concentrations (20–40%). The results highlight the interplay between molecular crystallization and interfacial polarization as a key mechanism governing and enhancing the electrostatic properties of stilbene-tolylamine intermolecular composites.