In-Plane Anisotropic Molecular Orientation of Pentafluorene and Its Application to Linearly Polarized Electroluminescence

Takeshi Komino, Hiroyuki Kuwae, Akiko Okada, Weixin Fu, Jun Mizuno, Jean Charles Ribierre, Yuji Oki, Chihaya Adachi

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

By preparing parallelly aligned 1.9-μm-high SiO2 microfluidic channels on an indium tin oxide substrate surface, the solution flow direction during spin-coating was controlled to be parallel to the grating. Using this technique, a pentafluorene-4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) binary solution in chloroform was spin-coated to embed a 40-50 nm-thick 10 wt %-pentafluorene:CBP thin film in the channels. In-plane polarized photoluminescence measurements revealed that the pentafluorene molecules tended to orient along the grating, demonstrating that one-dimensional fluid flow can control the in-plane molecular orientation. Furthermore, the dependences of the photoluminescence anisotropy on the spin speed and substrate material suggest that the velocity of the solution flow and/or its gradient in the vertical direction greatly affects the resulting orientation. This indicates that the mechanism behind the molecular orientation is related to stress such as the shear force. The effect of the solution flow on the molecular orientation was demonstrated even in organic light-emitting diodes (OLEDs). Linearly polarized electroluminescence was obtained by applying the in-plane orientation to OLEDs, and it was found that the dichroic ratio of the electroluminescence orthogonal (x) and parallel (y) to the grating is x/y = 0.75.

Original languageEnglish
Pages (from-to)27054-27061
Number of pages8
JournalACS Applied Materials and Interfaces
Volume9
Issue number32
DOIs
Publication statusPublished - 2017 Aug 16

Keywords

  • electroluminescence
  • in-plane orientation
  • linear polarization
  • molecular orientation
  • solution processed thin films

ASJC Scopus subject areas

  • Materials Science(all)

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