Very bright blue organic light emitting diodes were fabricated using highly fluorescent dipyrazolopyridine derivatives, 4-(4-substituted phenyl)-1,7-diphenyl-3,5-dimethyl-1,7dihydrodipyrazolo[3,4-b,4′,3′-e]pyridine (PAP–X, X=CN, Ph, and OMe), as emitter by doping the dye in an electron-transporting host, 2,2′,2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] (TPBI). Two hole-transporting layers, 4,4′-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (NPB) and 4,4′-dicarbazolyl-1,1′-biphenyl (CBP) were used to achieve the emission from PAP–X. The devices with a general configuration of indium tin oxide/NPB/CBP/TPBI:PAP(2%)/Mg:Ag showed a bright blue emission. The PAP–CN-based device is exceptionally good, with a brightness of 11 200 cd/m2 at 14.2 V and the peak external quantum efficiency of 3.2%. The efficiency is the highest for the blue emission.

Selectively bridged model compounds related to the chromophore in photoactive yellow protein have been synthesized where the single bond adjacent to the benzene ring (bond 1) and where both bond 1 and the adjacent double bond (bond 2) are bridged. They were compared to the nonbridged reference compound regarding their photophysical properties using steady-state and time-resolved fluorescence at various temperatures. Quantum chemical calculations were additionally performed and showed that several conformers are populated in the ground state. The neutral model compounds show that the nonradiative deactivation channel is linked to both single- and double-bond twisting. The relative importance of single-bond twisting is increased for the corresponding deprotonated hydroxy compounds with an enhanced donor character. The simultaneous photochemical activity of both single and double bonds explains the ease of photochemical isomerization in the confined environment of the natural PYP protein and also of the primary step in the vision process in rhodopsin.

quinolines (PAQ) carrying various substituents at the 6-or 7-position (PAQ-X, X ) OMe, t-Bu, H, F, CN, CF 3 , NEt 2 ) were synthesized and studied as emitting materials in an organic light-emitting diode (OLED). The 4,4′-bis[N-(1naphthyl)-N-phenylamino]biphenyl (R-NPB) and 4,4′-dicarbozolyl-1,1′-biphenyl (CBP) were used as hole-transporting materials, whereas electron-transporting 2,2′,2′′-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI) was used as a host for the PAQ-X dopant. The device with a general configuration of ITO/NPB/CBP/TPBI:PAQ-X/TPBI/Mg:Ag, where the PAQ-X dye concentration was kept around 2 wt %, was fabricated, and emits a bright blue light for all PAQ dyes except diethylamino-substituted PAQ, which emits blue-green light. With the same structure details, the electroluminescence, turn-on voltage, and external quantum efficiency show a dependence on the substitution. In particular, the external quantum efficiency and power efficiency are higher for devices doped with electron-rich PAQs and lower for electron-deficient PAQs.

A series of highly luminescent dipyrazolopyridine (PAP) dyes were synthesized and assessed as light-emitting materials in electroluminescent devices. Multilayer devices were fabricated using these dyes along with a hole-transporting material, NPB (4,4′-bis[N-(1naphthyl-1-)-N-phenyl-amino]-biphenyl) and an electron-transporting material, AlQ (tris-(8-hydroxyquinoline) aluminum), or TPBI (2,2′,2′′-(1,3,5-benzenetriyl)tris[1-phenyl-1Hbenzimidazole]). Both ITO/NPB/PAP/AlQ/Mg:Ag and ITO/NPB/PAP/TPBI/Mg:Ag devices gave a bright blue or blue-green emission, depending on the substituent group in the parent PAP dye. The performance of these devices such as turn-on voltage, brightness, and efficiency as a function of the substituent is discussed.

A series of 2-(stilben-4-yl)benzoxazole derivatives (BOXSB-X) was prepared and used as a dopant in the fabrication of organic light-emitting diodes. With a device structure of ITO/ NPB/CBP/TPBI:3%BOXSB-X/TPBI/Mg:Ag, where NPB, CBP, and TPBI stand for 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl, 4,4′-dicarbazolyl-1,1′-biphenyl, and 2,2′,2′′-(1,3,5phenylene)tris-[1-phenyl-1H-benzimidazole], respectively, light emission from the dopant was observed under electric bias, presumably due to energy transfer between the host TPBI exciton and the dopant. Bright blue emission with a luminance ranging between 8 000 and 13 000 cd/m 2 was obtained depending on the substituent on the stilbene moiety. However, with a device structure of ITO/NPB/TPBI:3%BOXSB-X/TPBI/Mg:Ag, where no CBP layer was present, the recombination/emission region shifted to the NPB layer except in the device doped with dimethylamino-substituted benzoxazole derivative, in which case the carrier trap mechanism is suggested to be responsible for the emission from the dopant.

A novel class of electroluminescent pyrazole-based polymers have been synthesised and their electroluminescent properties have been demonstrated. These materials show bright electroluminescence and promising properties for electroluminescent applications.

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A multilayer organic light-emitting diode was fabricated using a fluorescent compound {6-N,N-diethylamino-1-methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoline} (PAQ–NEt2) doped into the hole-transporting layer of NPB {4,4′-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl}, with the TPBI {2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole]} as an electrontransporting material. At 16% PAQ–NEt2 doping concentration, the device gave a sharp, bright, and efficient green electroluminescence (EL) peaked at around 530 nm. The full width at half maximum of the EL is 60 nm, which is 60% of the green emission from typical NPB/AlQ [where AlQ=tris(8-hydroxyquinoline) aluminum] device. For the same concentration, a maximum luminance of 37 000 cd/m2 was obtained at 10.0 V and the maximum power, luminescence, and external quantum efficiencies were obtained 4.2 lm/W, 6.0 cd/A, and 1.6%, respectively, at 5.0 V.