Photo-Cross-Linkable Polymer Inks for Solution-Based OLED Fabrication

• Published in: Macromolecules Vol. 52; no. 23; pp. 9105 - 9113
• Main Authors: Kunz, Susanna V, Cole, Cameron M, Welle, Alexander, Shaw, Paul E, Sonar, Prashant, Thoebes, Nico-Patrick, Baumann, Thomas, Yambem, Soniya D, Blasco, Eva, Blinco, James P, Barner-Kowollik, Christopher
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.12.2019
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.9b02030

We introduce a catalyst-free, highly efficient, ambient temperature Diels–Alder reaction employing o-methylbenzaldehyde derivatives as photocaged dienes as an ideal approach for forming three-dimensional insoluble networks for inkjet printing of OLED emissive layer. Herein, poly­(methyl methacrylate) based polymers containing 4-(9H-carbazol-9-yl)-2-(3′-hydroxy-[1,1′-biphenyl]-3-yl)­isoindoline-1,3-dione as a blue-green (λmax = 495–500 nm) thermally activated delayed fluorescence (TADF) emitter and a photochemically active maleimide/o-methylbenzaldehyde cross-linker couple were synthesized and their photo-cross-linking behavior was studied. Time resolved fluorescence measurements confirm that the TADF properties are maintained upon integration in a polymer network and HOMO/LUMO levels of the emitter species remain unchanged by the photo-cross-linking at 365 nm of the polymer chains. The network formation of the fluorescent films is evidenced by solvent resistance tests and monitored by Fourier transform infrared (FT-IR) spectroscopy as well as time of flight secondary ion mass spectroscopy (ToF-SIMS), showing the consumption of maleimide and o-methylbenzaldehyde groups with increasing irradiation time. The surface roughness is investigated via atomic force microscopy (AFM) and found to be unchanged by a solvent wash after the cross-linking. Furthermore, confirmation that the polymer solution can be printed on an inkjet-printer and subsequently photo-cross-linked for multilayer OLED device fabrication is obtained.