Synthesis of polyfluorene-polytriarylamine block copolymers with light-emitting benzothiadiazole moieties: effect of chromophore location on electroluminescent properties

To evaluate the effect of chromophore location on electroluminescent performance, three types of block copolymers consisting of polyfluorene and polytriarylamine with benzothiadiazole (BT) moieties were synthesized and characterized. A BT unit was incorporated at the junction between blocks (BP 1) in the polytriarylamine block (BP 2) or in the polyfluorene block ( BP 3). An electroluminescent device based on BP 1 exhibited the best performance. This result is reasonably explained by considering the difference in recombination probability in the phase-separated active layers. Different chemical structures of emitting sites afford different emission wavelengths, which are dependent on the electron-donating nature of substituents on the BT rings.