Three Color Random Fluorene-Based Oligomers for Fast Micrometer-Scale Photopatterning

In this contribution we show that random fluorene cooligomers with photo reactive acrylate units can be prepared in a simple 1-step Yamamoto synthesis. The acrylate functionalities are preserved quantitatively under Yamamoto conditions. NMR and Maldi-ToF measurements point to an almost statistical incorporation of the comonomers into the oligomer chain. Maldi-ToF analyses give a further insight into the chain compositions, and we found fluorene-only oligomers to be present in low quantities. Thin films of the aromatic amine containing cooligomer show a blue fluorescence, the benzothiadiazole oligomer shows yellow photoluminescence, and the bithiophene oligomer emits orange-red light upon excitation. Compared to pure fluorene oligomers with a HOMO of 5.7 eV the HOMO levels of the TPD and bithiophene derivatives are increased to 5.25 and 5.31 eV, respectively, whereas the HOMO level of the benzothiadiazole oligomer is decrased to 5.85 eV. Photolithography experiments reveal that a careful optimization of the conditions, for example, the choice of the photoinitiator, temperature, and irradiation wavelength, leads to well-resolved micrometer sized patterns. A minimum feature size of 1 μm was obtained. Thus we showed that with a simple 1-step Yamamoto coupling oligomers with photo-cross-linkable acrylate groups are accessible. UV irradiation leads to densely cross-linked, insoluble networks. Thus these materials are ideal candidates for multilayer as well as patterned semiconducting devices.