Polyphenylbenzene as a platform to fabricated blue-emitting polymers: The effect of aggregation inhibition and application in PLED

Abstract

The modification of polyfluorene is of significance. Here according to the two factors that influence the blue emission, we design and synthesize two copolymers which contain polyphenylbenzene and fluorene, polyphenylbenzene and carbazole, respectively. Thermogravimetric analysis (TGA) results conforms that the introducing of polyphenylbenzene unit can improve thermal stability of the polymer. Through the research of photophysical data and comparing with copolymers contain benzene unit, we get that the polyphenylbenzene unit can not only largely improve the solubility, but also effectively inhibit the contaction between polymer chains. This can guarantee the original blue emission even in solid state. Theoretical calculation results show that in the optimized structures, the dihedral angle between polyphenylbenzene and fluorene unit is 61.1°, bigger than that in the polyphenylbenzene and benzene copolymer (36.9°). This further conform that the introducing of polyphenylbenzene unit can make polymers twisted and reduce conjugation. Also, the formation of excimers can be inhibited which can guarantee blue emission. Based on their good emission efficiency and stability, we fabricated polymer light emission diodes using them as light emission layers. Devices results show that polyphenylbenzene and carbazole copolymer can exhibit better deep-blue emission, the CIE can stay at (0.19, 0.13). All these results show that the polyphenylbenzene unit can be used as an effective building block to fabricate polymer with deep-blue emission.