Alternating pyrene–fluorene linear copolymers: Influence of non-conjugated and conjugated pyrene on thermal and optoelectronic properties

In order to explore the influence of non-conjugated and conjugated pyrene on the properties of polymers, four alternating pyrene–fluorene linear copolymers, PDOF-PPF, PDAOPF-PPF, PDOF-P and PDAOPF-P (Scheme 1), were designed, synthesized and characterized. They show greatly higher thermal stability than their oligomers due to curving of polymer chain. They also show high Tg due to high internal rotation barrier originated from large pyrene group. For non-conjugated pyrene substituted PDOF-PPF and PDAOPF-PPF, absorption spectra show sharp peak at about 354 nm, which should be attributed to intramolecular interaction of pyrene and main conjugation. And in contrast, conjugated pyrene substituted PDOF-P and PDAOPF-P show structureless spectra. They also show stable spectra even annealed due to the high internal rotation barrier originated from pyrene. The spectra data are consistent with electrochemical and calculated data. It proves that conjugated pyrene plays much less contribution to frontier orbitals than non-conjugated pyrene. At last, the polymers were used as emitter to fabricated PLEDs, and the devices showed low onset voltage of about 4 V, with maximum brightness of 1050 and 1520 cd/m2 for PDOF-PPF and PDAOPF-PPF as emitters.