Search

New deep-red light-emitting phosphorescent dendrimers with hole-transporting carbazole dendrons were synthesized by reacting tris(2-benzo[b]thiophen-2-yl-pyridyl) iridium (III) complex with carbazolyl dendrons by DCC-catalyzed esterification. The resulting first-, second-, and third-generation dendrimers were found to be highly efficient as solution-processable emitting materials and for use in host-free electrophosphorescent light-emitting diodes. We fabricated a host-free dendrimer EL device with configuration ITO/PEDOT:PSS (40 nm)/dendrimer (55 nm)/BCP (10 nm)/ Alq 3 (40 nm)/LiF (1 nm)/Al (100 nm) and characterized the device performance. The multilayered devices showed luminance of 561 cd/m 2 at 383.4 mA/cm 2 (12 V) for 15, 1302 cd/m 2 at 321.3 mA/cm 2 (14 V) for 16, and 422 cd/m 2 at 94.4 mA/cm 2 (18 V) for 17. The third-generation dendrimer, 17 (η ext = 6.12% at 7.5 V), showed the highest external quantum efficiency (EQE) with an increase in the density of the light-harvesting carbazole dendron. Three dendrimers exhibited considerably pure deep-red emission with CIE 1931 (Commission International de L'Eclairage) chromaticity coordinates of x = 0.70, y = 0.30. The CIE coordinates remained very stable with the current density. The integration of rigid hole-transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution-processable materials for dendrimer light-emitting diode (DLED) applications.

Three-armed, star-shaped molecules containing 4-(N,N-diphenyl)amino-4'-nitroazobenzene chromophores were synthesized to study the diffraction behavior after inscribing surface relief gratings. The two molecules dif- fered in terms of their mode of chromophore attachment to the core. In compound 5, they were bound to the core laterally through alkylene spacers, whereas the chromophores were tethered perpendicularly to the core in com- pound 4. Although 60 wt% of the polar azobenzene chromophores was comprised of large molecules, no aggrega- tion behavior was observed in the absorption spectra of the thin films. The surface relief gratings were elaborated on the surface of the molecular films by the two-beam interference method. The dynamics of grating formation were studied in terms of the diffraction efficiency using two different film samples made up of two star-shaped molecules. The maximum diffraction efficiency of D-(ENAZ) , compound 4, was measured to be about 30%, which was sig- nificantly high. The mode of chromophore attachment affected the dynamic properties of the diffraction gratings.

New light emitting dendrimers were synthesized by reacting 3,5-bis-(3,5-bis-benzyloxy-benzyloxy)-benzoic acid or 3,5-bis-[3,5-bis-(3,5-bis-benzyloxy-benzyloxy)-benzyloxy]-benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue-emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10, revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3, 9, and 10 showed luminances of 1021 cd m -2 at 5 V, 916 cd m -2 at 6 V, and 851 cd m -2 at 6.5 V, respectively. The largest dendrimer, 10, bearing a greater number of benzyloxy dendrons, exhibited a blue-like emission with CIE 1931 chromaticity coordinates of x= 0.16 and y = 0.13, which is due to the influence of a higher shielding effect.

Modified polycaprolactone was synthesized by melt reaction of PCL and reactive monomers such as glycidyl methacrylate (GMA) and maleic anhydride (MAH) in the presence of benzoyl peroxide in Brabender mixer. MAH showed a different grafting phenomenon compared to GMA. The reaction mechanism was discussed with different reactive monomers. Reactive blends of the PCL-g-GMA and the gelatinized starch with glycerin were prepared and their mechanical properties and biodegradabilities were investigated. Reactive blends of PCL-g-GMA and starch showed well-dispersed starch domain in the matrix and better mechanical strength than the unmodified PCL/starch blend. However, the reaction between PCL-g-GMA and starch induced a crosslinking during the reactive blending and this crosslinking in the blend lowered the biodegradation of the blend during the composting test. The biodegradability was investigated by the weight loss and surface morphology change of the blend in the composting medium.