UV‐induced refractive index modulation of photoreactive polymers bearing N‐acylcarbazole groups |
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Authors: | T Griesser A Wolfberger M Edler M Belzik G Jakopic G Trimmel W Kern |
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Institution: | 1. Institute of Chemistry of Polymeric Materials, University of Leoben, Franz Josef Str. 18, 8700 Leoben, Austria;2. Polymer Competence Center Leoben GmbH, Roseggerstrasse 12, 8700 Leoben, Austria;3. Institute for Nanostructured Materials and Photonics, Joanneum Research, Franz Pichler Strasse 30, 8160, Weiz, Austria;4. Institute for Chemistry and Technology of Materials and Christian Doppler Pilot Laboratory for Nanocomposite Solar Cells, Graz University of Technology, Stremayrgasse 16, 8010 Graz Austria |
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Abstract: | In this study, we report on the synthesis and characterization of photoreactive polymers bearing N‐acetylcarbazole and N‐formylcarbazole groups, respectively. These polymers were easily accessible by polymer analogous acylation of commercially available poly‐(2‐vinylcarbazole). While poly(1‐(2‐vinyl‐9H‐carbazol‐9‐yl)ethanone) (poly‐ 1 ) undergoes a partial photochemical Fries rearrangement, poly(2‐vinyl‐9H‐carbazole‐9‐carbaldehyde) (poly‐ 2 ) decarbonylates smoothly when exposed to UV irradiation. The difference in reactivity between the two acylated polymers is because of the lower stability of the formyl radical, which is formed in the first stage of this photoreaction. Ellipsometric measurements of thin films showed that the photo‐Fries rearrangement in poly‐ 1 causes a change in refractive index by Δn = +0.01 at 650 nm. UV illumination of poly‐ 2 results in a change of the refractive index by Δn = +0.03 at 650 nm, which can be explained by the high yield of the photodecarbonylation of the N‐formylcarbazole groups. Refractive index patterns can be easily realized using lithographic techniques as demonstrated by optical microscopy using a phase contrast set‐up for visualization. Patterned films of poly‐ 1 and poly‐ 2 with feature sizes of about 5 μm were obtained with a mask aligner. Photoreactive polymers bearing N‐acylcarbazole groups are of potential interest for optical applications such as waveguides, optical switches, and data storage devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 |
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Keywords: | lithography photochemistry refractive index |
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