Synthesis And Properties Of White Electroluminescence From Star-shaped Single-polymer Materials

Multi-armed structure of photoelectrical materials have been successfully used in many optoelectronic devices, due to their unusual molecular topology structures and excellent opto-electronic properties, especially in solubled white organic light electroluminescent diodes(WOLEDs). Through changing the type of the central cores and the peripheral type of arms group, adjusted its molecular spectroscopy and energy level, the phenomenon of intermolecular exciton migration could be effectively controlled to facilitate the tuning of multicolor emission, effectively restrain the molecular aggregation, eliminate the intramolecular forces, to improve the luminous efficiency of the device, improve the solubility and stability of the materials have important influence. In this paper, we systematically examines the single molecule white light in optical physics, polymer material of electrochemical and optical performance.Firstly, a series of star-shaped dopant/host single-polymer systems with a P-N type star-shaped red core, three green benzothiadiazole arms and three blue polyfluorene arms were designed and synthesized. Through tuning the doping concentration of the red core and green unit, highefficiency saturated white electroluminescence has been achieved. A typical single-layer white light emitting device(ITO/PEDOT:PSS/polymer/TPBI/Li F/Al) was studied and discussed, realizing pure white emission with a luminous efficiency of 2.09 cd A-1, an external quantum efficiency of 1.08% and CIE coordinates of(0.34, 0.33) for TM-R3G4. Meanwhile, a luminous efficiency of 2.41 cd A-1, an external quantum efficiency of 1.05% and CIE coordinates of(0.34, 0.35) were observed for TN-R3G4. The high efficiency of the devices could be mainly attributed to the suppressed concentration quenching of the dopant units, partial efficient energy transfer from polyfluorene host to the red and green dopant.Then, a four-armed star-shaped single-polymer system with 4,7-bis(5-(4-(9H-carbazol-9-yl)phenyl)-4-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole(FTBT) as a red emissive core, polyfluorene(PF) as blue emissive arms and,1,3-benzo thiadiazole(BT) as green emissive arms was designed and synthesized, in which red, green, and blue(RGB) emission balance can be achieved by adjusting the doping concentration of FTBT and BT discreetly. A typical single-layer device(ITO/ PEDOT:PSS/polymer/TPBI/Li F/Al) was studied and discussed, realizing the pure and stable white emission with a luminous efficiency(LE) of 1.59 cd A-1, an external quantum efficiency of 0.70% and CIE coordinates of(0.31, 0.34). The high-color-quality white electroluminescence of the devices could be mainly attributed to the suppressed intermolecular interactions, and partial energy transfer from the polyfluorene(PF) arms to the red dopant and green dopant.Finally, A six-armed star-shaped single-polymer system consisting of simultaneous three emission species, 7,7’,7’’-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1’,2’-c] fluorine-2,7,12-triyl)tris(4-(4-(9H-carbazol-9-yl)phenyl)benzo[c][1,2,5]thiadiazole)(TRCZ) as a green emissive core, polyfluorene(PF) as blue emissive arms and 4,7-bis(4-hexylthiophen-2-yl) benzo[c][1,2,5] thiadiazole(BBT) as red emissive dopants, has been designed and synthesized. By means of choosing the appropriate doping concentration of TRCZ and BBT, the resulting polymers are found to have high-color-quality and stable white electroluminescence with a luminous efficiency(LE) of 1.45 cd A-1, an external quantum efficiency(EQE) of 1.37% and a saturated Commission Internationale d’Eclairage(CIE) coordinates of(0.33, 0.33), which matches exactly with the standard saturated white color of(0.33, 0.33). The performance of this six-armed single-polymer system is superior to that of the linear single-polymer system and polymer-blend system. The pure and stable white emission of the devices are mainly attributed to the multi-armed hyperbranched structures, which play an important role in fine controlling the incomplete energy transfer as well as preventing intermolecular interactions and phase separation in a single-polymer system.