Pyrene-functionalized oligofluorenes as non-doped deep blue emitters for solution-processed organic light-emitting diodes

Two pyrene-functionalized oligofluorenes (TPA-PyF₃ and CBP-PyF₃) are prepared using the condensation reaction by the Friedel-Crafts procedure. In the produced oligomers, the triphenylamine or N,N′-dicarbazolyl-4,4′-biphenyl core serves as a spacer bearing spiro-linked fluorene moieties to form a multi-H shaped structure. This specific structure efficiently retards the crystallization tendency of the pyrene groups, and gives the materials completely amorphous morphological structure and film forming ability. Solution-processed OLEDs with the structure of ITO/PEDOT:PSS (25 nm)/TPA-PyF₃ or CBP-PyF₃ (40 nm)/TPBI (35 nm)/Ca (10 nm)/Ag (100 nm) show low turn-on voltages of 3.6 V, and the maximum external quantum efficiencies reach 1.78% and 2.07% for TPA-PyF₃ and CBP-PyF_3, respectively. Moreover, both devices exhibit stable deep-blue light emission with Commission International de I'Eclairage (CIE) coordinates of around (0.16, 0.09) at the brightness of 100-1000 cd m^-2.