Two-Photon Laser-Written Photoalignment Layers for Patterning Liquid Crystalline Conjugated Polymer Orientation

Yuping Shi, Patrick S. Salter, Mo Li, Robert A. Taylor, Steve J. Elston, Stephen M. Morris, Donal Bradley

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Systematic tuning of chemical and physical structure allows fine control over desired electronic and optical properties, including those of conjugated polymer semiconductors. In the case of physical structure, orientation via liquid crystalline alignment allows access to fundamental optical anisotropies and the associated refractive index modification offers great potential for fabrication of photonic structures. In this paper, photoalignment is used to orient the liquid crystalline conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), specifically involving two-photon infrared laser writing of patterns in an azobenzene sulphonic dye (SD1). These patterns are transferred into the overlying film by thermotropic orientation in the nematic melt, then frozen in place by quenching to a room temperature nematic glass. Optimization of laser power and scan speed allows features with linewidths ≤ 1 µm. Photoluminescence (PL) peak anisotropy values reach PLII/PL⊥ = 13 for laser writing, compared with PLII/PL⊥ = 9 for polarized ultraviolet light emitting diode exposure of the same SD1 layer. These two approaches also result in different film microstructures; evidenced by characteristic changes in PL spectra. The anisotropic PL spectra provide information on emissive excited states that complements previous studies on non-oriented F8BT and related copolymers, also suggesting two emissive states.
Original languageEnglish (US)
Pages (from-to)2007493
JournalAdvanced Functional Materials
Volume31
Issue number7
DOIs
StatePublished - Nov 30 2020

Bibliographical note

KAUST Repository Item: Exported on 2021-11-21
Acknowledgements: Y.S. and D.D.C.B. gratefully acknowledge the Hong Kong Jockey Club Graduate Scholarship at the University of Oxford for financial support. P.S.S. gratefully acknowledges funding from the Engineering and Physical Sciences Research Council UK (EP/R004803/1). The authors collectively thank Dr. Ian Dobbie and the Micron Centre for Advanced Bioimaging in the Department of Biochemistry at the University of Oxford for help to obtain the polarized fluorescence images in Figure 2. Y.S. thanks Professor Paul Stavrinou for useful discussions regarding polarized UV-vis absorption spectroscopy. D.D.C.B. thanks Dr. Hiroshi Hasebe and DIC Corporation Japan for providing the SD1 photoalignment layer material used in these experiments and Professor Hoi Sing Kwok for facilitating the interaction. D.D.C.B. further thanks the Jiangsu Industrial Technology Research Institute–Oxford University Innovative Materials for Advanced and Critical Technologies (JITRI-Oxford IMPACT) Institute for partial support.

ASJC Scopus subject areas

  • General Chemical Engineering
  • Electronic, Optical and Magnetic Materials

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