Synthesis and characterization of novel red-emitting copolymers containing fluorene, diketopyrrolopyrrole, and phenothiazine units

A novel three-component copolymer (PFDP), derived from 9,9-dihexylfluorene, diketopyrrolopyrrole( DPP), and 10-octylphenothiazine, was synthesized through palladium-catalyzed Suzuki polycondensation in good yields. PFDP possessed moderate molecular weight and polydispersity, well-defined structure, and excellent thermal properties with an onset decomposition temperature at 357°C. PFDP in thin film exhibited red photoluminescence from DPP chromophore exclusively, with a peak at 602 nm. Electron-rich phenothiazine units sighificantly improved the injection and transport of holes by incorporating into polymer backbone. Light-emitting device was fabricated in the ITO/PEDOT: PSS/PVK/ polymer/Ba/Al configuration using PFDP as the emitting layer. The device based on PFDP showed red emission [CIE coordinate value (0.62, 0.38)] that was close to the standard red (0.66, 0.34). The results on electroluminescent performance revealed that PFDP may be a promising candidate for the red emitter with a maximum brightness of 259 cd/m2 and a maximum external quantum efficiency of 0.25%.