Synthesis and characterization of a solution processible deep blue light-emitting molecule composed of fluorene and pyrene units

Abstract

A solution processible deep blue light-emitting molecule composed of pyrene and dialkylfluorene units, 1,6-bis(9,9'-dioctylfluorene-2-yl)pyrene (BDOFP) was synthesized and characterized. The synthesized compound was soluble in common organic solvents and the solution gave a smooth thin film after spin coating. The compound was characterized by using thermogravimetric analysis (TGA), differential calorimetry (DSC), UV-visible spectroscopy, fluorescence spectroscopy and cyclic voltammetry. The maximum UV-visible absorption and PL emission of BDOFP thin film were more red-shifted than those of BDOFP solution due to strong intermolecular interaction between flat segments. To improve color purity and film stability BDOFP was doped to a well-known charge-transporting polymer, poly(N-vinylcarbazole) (PVK). BDOFP thin film showed it maximum PL at 457 nm but the thin films of BDOFP doped PVK films showed it at 443 nm. Organic light-emitting diodes were fabricated with the simple structure of ITO/PEDOT:PSS/emitter/BmPyPB/LiF/Al configuration. BDOFP or three kinds of BDOFP: PVK blends with different ratios (10: 90, 30: 70, 50: 50 by weight) were used as the emissive layers and [1,3-bis(3,5-dipyrid-3-yl-phenyl) benzene] (BmPyPB) as the electron-transporting layer. All of light-emitting devices showed their electroluminescence in blue region of spectrum, especially EL using BDOFP: PVK (1: 9) showed a deep-blue light emission with CIE coordinates of (0.14, 0.07). Maximum brightness, external quantum efficiency and current efficiency of the device were 500 cd/m(2), 0.7% and 0.44 cd/A, respectively. (C) 2011 Elsevier B.V. All rights reserved.