Energy Transfer Efficiency Control from the Blue Emitting Aromatics to the Yellow Fluorescent Intramolecular Charge Transfer Type Dye for Electroluminescence

초록

An intramolecular charge transfer type yellow fluorescent material, (Z)-4-(2-[4,4- bis(dimethylamino)-1,1:4,1-terphenyl-2-yl]-2-1-cyanovinyl)benzonitrile (BDAT-CP) was synthesized for the implimentation to organic light emitting diodes (OLEDs). The molecules of the this catagory often have electro-conductivity and show high luminescence at longer wavelength in visible region. The BDAT-CP exhibited a large Stokes shift from 329nm (UV absorption maximum) to 628nm of photoluminescence(PL) in chloroform solvent. Solid powder PL showed yellow emission peaked at 582 nm. The device structures were indium tin oxide (ITO) / N,N-bis-(1-naphyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (NPB, 50nm) / 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN, 30nm): BDAT-CP (x %) / 4,7-diphenyl-1,10-phenanthroline (BPhen, 30nm) / Liq(2nm) / Al. The maximum luminance measured were 14700 cd/m(2) (x = 5%), 9825 cd/m(2) (x = 10%) and 7901 cd/m(2) (x = 15%) for each BDAT-CP concentration. The luminance efficiency and quantum efficiency observed were 7.14 (x = 5%), 4.72 (x = 10%) and 3.19 (x = 15%), and 2.77 (x = 5%), 2.09 (x = 10%) and 1.59 (x = 15%), respectively. The device emitted yellow light corresponding to Commission Internationale de I'Eclairage (CIExy) coordinates of (0.492, 0.494) (x = 5%) and (0.523, 0.470) (x = 10%) and (0.545, 0.451) (x = 15%) at 8V. This study showed that the energy transfer from MADN to BDAT-CP was dependent on the concentration of yellow dye, which affected the hole transporting properties of the OLED.

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