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[ACS Appl. Mater. Interfaces] In-Plane Anisotropic Molecular Orientation of Pentafluorene and Its Ap


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.

Takeshi Komino†‡§, Hiroyuki Kuwae§∥, Akiko Okada∥, Weixin Fu∥, Jun Mizuno⊥, Jean-Charles Ribierre‡§, Yuji Oki§¶, and Chihaya Adachi*†‡§# † Education Center for Global Leaders in Molecular System for Devices, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan ‡ Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan § ERATO, Adachi Molecular Exciton Engineering Project, Japan Science and Technology Agency, 744 Motooka, Nishi, Fukuoka 819-0395, Japan ∥ Nano-Science and Nano-Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan ⊥ Organization for Nano and Life Innovation, Waseda University, 513 Waseda Tsurumaki-cho, Shinjuku, Tokyo 162-0041, Japan ¶ Department of Electronics, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan # International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan ACS Appl. Mater. Interfaces, Article ASAP DOI: 10.1021/acsami.7b05570 Publication Date (Web): August 3, 2017 Copyright © 2017 American Chemical Society *E-mail: adachi@cstf.kyushu-u.ac.jp.

Link: http://pubs.acs.org/doi/abs/10.1021/acsami.7b05570

#08102017 #MaterialScience

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