Spirobifluorene derivative: a pure blue emitter (CIEy ≈ 0.08) with high efficiency and thermal stability

Abstract

A spirobifluorene derivative containing phenanthrene moiety, 2,7-di(phenanthren-9-yl)-9,9′-spirobifluorene (DPSF), has been synthesized. It shows absorption peaks at 254 nm, 310 nm, and 327 nm and a fluorescence peak at 383 nm in CHCl₃ that shifts to 398 nm in the film state. The quantum yield is 0.79 calibrated with a standard of coumarin 102 (0.93). A pure blue emission at Commission Internationale de l′Éclairage (CIE) (0.15, 0.08), has been achieved using DPSF as the emitter, poly(3,4-ethylene dioxythiophene) : poly(styrene sulfonic acid) (PEDOT : PSS) as the hole injecting layer, 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino] biphenyl (NPB) as the hole transporting layer, and 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene (TPBI) mixing with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) (2 : 1) as the electron transporting material. The maximum current efficiency (CE) and power efficiency (PE) of the DPSF device are 3.24 cd A⁻¹ and 2.54 lm W⁻¹, corresponding to 5.41% of maximum external quantum efficiency (EQE). The spirobifluorene derivative show high thermal stabilities, 178 °C for the glass transition temperature (T_g) and 503 °C for the decomposition temperature (T_d). The synthesized spirobifluorene derivative shows potential application as a highly efficient pure blue emitter for organic light emitting devices (OLED).