A Molecular Glass for Deep-Blue Organic Light-Emitting Diodes Comprising a 9,9′-Spirobifluorene Core and Peripheral Carbazole Groups

Abstract

Novel fluorene-based compounds, TCPC-6 and TCPC-4, with rigid central spirobifluorene cores and peripheral carbazole groups are synthesized using the Suzuki coupling reaction. The optical, electrochemical, and thermal properties of these compounds are characterized. The compounds show strong deep-blue emission both in solution and as thin films. Both TCPC-6 and TCPC-4 exhibit amorphous morphologies in the solid state with high glass transition temperatures (T_g) of 108 and 143 °C, respectively. Atomic force microscopy (AFM) measurements indicate that high-quality amorphous films of these novel compounds can be prepared by spin-coating. The oxidation potentials of TCPC-6 and TCPC-4 are significant lower than that of model compounds without peripheral carbazole groups, which suggests that these compounds have relatively high highest occupied molecular orbital (HOMO) energy levels and better hole-injection capabilities. Light-emitting devices fabricated by spin-coating films of these molecules exhibit deep-blue emission with Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of (0.16, 0.05); the devices fabricated using spin-coated TCPC-6 and TCPC-4 layers exhibit high luminance efficiencies of 1.35 and 0.90 cd A^–1 (with external quantum efficiencies of 3.72 and 2.47 %), respectively.