Interface Induced Crystal Structures of Dioctyl-Terthiophene Thin Films

Langmuir. 2012 Jun 5;28(22):8530-6. doi: 10.1021/la301213d. Epub 2012 May 23.

Abstract

Temperature dependent structural and morphological investigations on semiconducting dioctyl-terthiophene (DOTT) thin films prepared on silica surfaces reveals the coexistence of surface induce order and distinct crystalline/liquid crystalline bulk polymorphs. X-ray diffraction and scanning force microscopy measurements indicate that at room temperature two polymorphs are present: the surface induced phase grows directly on the silica interface and the bulk phase on top. At elevated temperatures the long-range order gradually decreases, and the crystal G (340 K), smectic F (348 K), and smectic C (360 K) phases are observed. Indexation of diffraction peaks reveals that an up-right standing conformation of DOTT molecules is present within all phases. A temperature stable interfacial layer close to the silica-DOTT interface acts as template for the formation of the different phases. Rapid cooling of the DOTT sample from the smectic C phase to room temperature results in freezing into a metastable crystalline state with an intermediated unit cell between the room temperature crystalline phase and the smectic C phase. The understanding of such interfacial induced phases in thin semiconducting liquid crystal films allows tuning of crystallographic and therefore physical properties within organic thin films.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calorimetry, Differential Scanning
  • Crystallization
  • Crystallography, X-Ray
  • Liquid Crystals / chemistry*
  • Microscopy, Atomic Force
  • Molecular Conformation
  • Phase Transition
  • Semiconductors
  • Silicon Dioxide / chemistry*
  • Surface Properties
  • Temperature
  • Thermodynamics
  • Thiophenes / chemistry*

Substances

  • Thiophenes
  • Silicon Dioxide