Abstract:

Two novel D-A type red dopants containing naphthothiadiazole(NT) or benzoselenadiazole(BS) electron withdrawing unit were synthesized. Through covalently attaching red dopants to polyfluorene(PFO) backbones and tuning the doping concentration, we obtained a series of red polymers. All these red polymers exhibit similar absorption spectra as PFO. Their photoluminescent(PL) spectra show not only blue emission from the PFO backbone but also red emission from the dopant. The relative intensity of the red emission increases successively with doping concentration. Unlike the PL spectra, the electroluminescent(EL) spectra of all the polymers predominantly exhibit red emission, which is attributed to the red dopants, with a weak blue emission from PFO backbone. It realizes completely energy transfer from PFO host to red dopants at 1% molar fraction doping level. The single-layer devices with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al(PEDOT: poly(3,4-ethylenedioxythiophene); PSS:poly(styrenesulfonate)) show saturated red emission at 632 nm with a luminous efficiency of 1.61 cd/A and CIE of (0.63, 0.35) for PFR-10NT, and pure red emission at 620 nm with a luminous efficiency of 1.10 cd/A and CIE of (0.63, 0.36) for PFR-10BS, respectively.

Key words: Electroluminescence, red polymer, “dopant/host”, polyfluorene, Naphthothiadiazole, Benzoselenadiazole