Light-emitting properties of photo-curable polyfluorene derivatives

An alternating copolymer composed of bis-(4-octyloxyphenyl)fluorene and bis((3-hexyloxy-3′-ethyl)oxetane) fluorene [poly(PF-alt-OXTF)], and a terpolymer composed of the above two monomers with N-hexylphenotiazine [poly(PF-co-OXTF-co-PTZ)] have been synthesized by Suzuki coupling polymerization. The synthesized poly(PF-alt-OXTF) and poly(PF-co-OXTF-co-PTZ) films became insoluble after UV irradiation in the presence of a proper photo-acid generator. The UV–vis absorption and PL emission spectra of the polymers before and after photo-cross-link reaction were almost same. The EL devices were constructed with ITO/PEDOT:PSS/polymer/LiF/Al configuration. The EL devices using the photo-cross-linked polymer films also showed lower operating voltages than the devices using the corresponding polymer films without cross-link. Moreover, the EL device of the poly(PF-co-OXTF-co-PTZ) film with photo-cross-link showed better device performances than the device without cross-link, and the maximum brightness and power efficiency of the device were 4750 cd/m2 and 0.68 cd/A, respectively. Furthermore, we obtained a well-patterned thin film with poly(PF-co-OXTF-co-PTZ) after a successive lithographic process.