ABSTRACT
The device performance of red organic light-emitting diodes (OLEDs) was dramatically improved by co-doping of the red fluorescent material of (2Z,2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]-bis(2-phenylacrylonitrile) (ABCV-P) with the hole transport material of N'-bis-(1-naphyl)-N,N'-diphenyl-1,1 '-biphenyl-4,4'-diamine (NPB) and the electron transport material of bis(2-methyl-8-quninolinato)-4-phenylphenolate aluminum (BAlq). The device structures were ITO/NPB/emitting layers/BAlq/Liq/Al in which the emitting layers were MADN:ABCV-P (40%) (device A), MADN:ABCV-P (40%):NPB (10%) (device B), MADN:ABCV-P (40%):BAlq (10%) (device C) and MADN:ABCV-P (40%):NPB (10%):BAlq (10%) (device D), respectively. The device D co-doped with NPB and BAlq exhibited maximum luminance of 9784 cd/m2, maximum luminous efficiency of 2.82 cd/A and maximum quantum efficiency of 3.19%, respectively, whereas those of the device A doped with only ABCV-P were 7563 cd/m2, 1.98 cd/A and 1.99%.
ABSTRACT
A novel yellow light-emitting material, (2Z)-3-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2'-yl]-2-phenylacrylonitrile (BDAT-P), having the modified molecular structure from red fluorescent compound, (2Z, 2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis(2-phenylacry-lonitrile) (ABCV-P), was synthesized in order to study the effect of the molecular structure on the optoelectronic properties of a light-emitting material. UV-visible absorption and photoluminescence (PL) emission peaks measured in various solvent systems were summarized in Table I. In the respective solvent system, the bathochromic shift of PL emission peak relative to the peak of UV-visible absorption was much larger for ABCV-P with two electron donor-acceptor pairs than for BDAT-P with one electron donor-acceptor pair. EL emission peaks of devices using BDAT-P and ABCV-P as the host emitters measured to be 573 and 613 nm, respectively. Commission Internationale de l'Eclairage (CIExy) coordinate of device using BDAT-P was measured to be (0.4855, 0.5021) at 7 V, which was correspond to the yellow color.
ABSTRACT
Typical small red light-emitting molecules for organic light emitting diodes (OLEDs) were highly susceptible to fluorescence concentration quenching in solid state. Red fluorophores, (2Z, 2'Z)-3, 3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-29',5'-diyl]bis(2-phenylacrylonitrile) (ABCV-P), (2E, 2'E)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) and (2Z, 2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis[2-(2-naphthyl)acrylonitrile] (ABCV-Np), capable of preventing fluorescence concentration quenching were designed and synthesized. These compounds have intramolecular charge transfer (ICT) properties which were estimated by measurement of UV-Visible absorption and photoluminescence (PL) emission spectra with variation of solvent polarity (n-Hexane/Chloroform = 99/1, 1/1; Chloroform; Methylene chloride). The magnitude of ICT for ABCV-Th was measured to be the largest and that for ABCV-Np was slightly larger compared to that for ABCV-P. The magnitude of ICT resulted in a shift of peak wavelength of PL emission. Therefore, this result well supported substituent effect on the color change of PL emission. The peak wavelengths of photoluminescence for ABCV-P, ABCV-Np and ABCV-Th were observed to be 607.5, 611.5 and 617.5 nm, respectively, and those of EL spectra were measured to be 612.5, 619.5, 621.0 nm, respectively. The emission maxima of PL and EL spectra for these red fluorescent compounds were well correlated with substituent effect on ICT for them.
