Color-tunable organic light emitting diodes based on exciplex emission

A fluorene derivative of 2,3-bis(9,9-dihexyl-9H-fluoren-2-yl)quinoxaline (BFLYQ) with blue fluorescence peaking at 425 nm is synthesized. The blend film of BFLYQ and N,N'-di(naphthalen-2-yl)-N,N'-diphenyl-benzine (NPB) exhibited an additional bathochromic shifted and broadbanded emission at 513 nm besides blue light in photoluminescence (PL) spectrum. The bilayer device with a structure of indium-tin-oxide (ITO)/NPB (40 nm)/BFLYQ (40 nm)/Mg : Ag showed a low-energy emission peaking at green area in electroluminescent (EL) spectra, which is due to exciplex emission between NPB and BFLYQ molecules, and the blue emission from BFLYQ increased with the enhancement of bias voltage. Based on exciplex emission, using 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as red dye, the color-tunable organic light-emitting diodes (OLEDs) are fabricated by conventional thermal vacuum deposition. The devices showed emission from red to white light with increasing the distance of DCJTB and the interface of NPB/BFLYQ. Also, the luminescent mechanism of DCJTB is discussed.

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