Poly(3,6-silafluorene-co-2,7-fluorene)-based high-efficiency and color-pure blue light-emitting polymers with extremely narrow band-width and high spectral stability

A new series of copolymers (PSiFF) based on 3,6-silafluorene and 2,7-fluorene were synthesized via the Suzuki polycondensation. The influences of the 3,6-silafluorene content in the copolymers on the thermal, photophysical, electroluminescence and electrochemical properties were investigated. The incorporation of 3,6-silafluorene into the polyfluorene main chain not only suppressed the long-wavelength emission but significantly improved the efficiency and color purity of the copolymer-based devices. Both fluorene and 3,6-silafluorene took part in pi-conjugation of the main chain and the electroluminescence spectra were remarkably blue-shifted with increasing wide bandgap 3,6-silafluorene content. The device based on PSiFF90 with the configuration of ITO/PEDOT : PSS/PVK/polymer/Ba/Al showed a quantum efficiency of 3.34% and a luminous efficiency of 2.02 cd A(-1) at a brightness of 326 cd m(-2) with CIE 1931 chromaticity coordinates of (0.16, 0.07), which almost match the NTSC standard blue pixel coordinates of (0.14, 0.08). Moreover, the incorporation of 3,6-silafluorene into the polyfluorene main chain significantly improved the spectral stability at annealing. The results indicate poly(3,6-silafluorene-co-2,7-fluorene) could be a promising candidate for blue-emitting polymers of high efficiency and good color purity.