Zigzag molecules from pyrene-modified carbazole oligomers: synthesis, characterization, and application in OLEDs

A series of monodisperse, pyrene-modified oligocarbazoles were synthesized and fully characterized. Carbazoles were linked by ethynylene through the 3- and 6-positions, forming a zigzag molecular backbone and stable, size-independent absorption, and emission were observed from these oligomers in solutions because their conjugation length was confined. Oligomers with pyrene exhibited much higher fluorescence quantum yields than those of oligomers without it. Different positions of pyrene in the oligocarbazole main chain resulted in a remarkable change in absorption and emission spectra. Moreover, devices with four different architectures (types 1-4) based on these oligomers were fabricated and investigated. Pyrene-modified carbazole oligomers exhibited bifunctional properties (light-emitting and hole-transport). Moreover, these devices showed moderate performances; for example,the device based on Cz3PyCz3 presented an external quantum efficiency of 0.69% and a maximum brightness of 1782 cd/m2 at 13.5 V, which indicated these oligomers were promising optoelectric materials.