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This study was concerned with the synthesis and properties of new soluble copolyimides containing naphthalene, oxadiazole and tetramethyldisiloxane units. These copolyimides were prepared by two-step polycondensation reaction in solution of aromatic diamines containing preformed oxadiazole ring with a mixture 1 : 1 of naphthalene tetracarboxylic dianhydride and tetramethyldisiloxane- [1,3-bis(4′-phthalic anhydride)]. The structure of these polymers was confirmed by Fourier transform infrared and 1H-NMR spectroscopy. The solubility, thermal stability and glass transition temperature of these copolyimides were measured and compared with those of related polyimides which do not contain siloxane groups. All these polymers emitted an intense blue color light upon irradiation with UV light. These copoly(oxadiazole-naphthylimide)s could be considered promising candidates for organo-soluble high-performance polymers for use in novel technological applications. [ABSTRACT FROM AUTHOR]

Abstract: Much attention has been paid to carbazole derivatives for their potential applications as optical materials. For the first time, the blue-light-emitting carbazole chromophore has been covalently bonded to the ordered mesoporous SBA-15 (The resultant hybrid mesoporous materials are denoted as carbazole–SBA-15) by co-condensation of tetraethoxysilane (TEOS) and prepared compound 3-[N-3-(triethoxysilyl)propyl]ureyl-9-ethyl-carbazole (denoted as carbazole–Si) in the presence of Pluronic P123 surfactant. The results of 1H NMR and Fourier transform infrared (FTIR) reveal that carbazole–Si has been successfully synthesized. Small-angle X-ray diffraction patterns (XRD) and Nitrogen (N2) adsorption/desorption measurements were employed to characterize the mesostructure of carbazole–SBA-15. Solid-state 29Si magic-angle spinning (MAS) NMR was used to confirm the preservation of the carbazole group and estimate the degree of hydrolysis-condensation. Photoluminescence (PL) measurements show that carbazole–SBA-15(0.07) [carbazole–Si:(TEOS+carbazole–Si) molar ratio is 0.07] hybrid mesoporous material exhibits a monomeric emission in the “light blue” region with a PL quantum yield ∼31%. Compared with carbazole–Si, the I car/C car (relative luminescence intensity divided by the content of carbazole) of carbazole–SBA-15(0.07) increases 24 times. The luminescence decays for 3-amino-9-ethyl-carbazole (denoted as carbazole–NH2) and carbazole–Si are single-exponential functions of time, while those for carbazole–SBA-15 mesoporous materials are fitted by double-exponential functions. The stability studies on carbazole–Si and carbazole–SBA-15(0.07) show that the carbazole chromophore in the resultant hybrid mesoporous material exhibits better thermal stability than in carbazole–Si compound. The excellent luminescent properties and thermal stability enable the hybrid mesoporous material to have potential use as blue-light-emitting material in optical field. [Copyright &y& Elsevier]

• The efficiency of the devices is increased with the additional quantum well. • The current efficiency reported is pretty high as compared with other published data. • The device with quantum well structure shows purer blue-light emission. • The color temperature stability of the device is highly improved. Currently, exciplex has drawn a great deal of attention due to its potential for efficient electroluminescence and for use as a host. In this study, we used 4,4′,4"-Tris(carbazol-9-yl) triphenylamine (TCTA) and 1,3,5-Tri(m-pyridin-3-ylphenyl) benze nee (TmPyPB) to form an exciplex host, where Bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)(FIrpic) was used as the dopant to emit blue phosphorescent light. Additional FIrpic and Bis(1phenylisoquinoline) (acetylacetonate) iridium(III) emission layers were inserted in the proposed structure to investigate how the recombination area of carriers shifts with the increase of voltage. TCTA and non-doped FIrpic layers were then inserted in both sides of the emission layer to confine the carriers, and the thickness of the emission layer was also optimized to improve the current efficiency of the proposed devices. The efficiency of the devices was increased from 56 cd/A to 63.6 cd/A with the additional quantum well structure and an emission layer thickness of 15 nm. The current efficiency reported in this paper was fairly high as compared with other published data on blue-emission exciplex-based organic light-emitting diodes. In addition, the device with the quantum well structure exhibited purer blue-light emission, and the color temperature stability was also highly improved. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescent (TADF) materials are considered as the competitive alternative to traditional fluorescent and noble-metal-based phosphorescent materials due to their high electroluminescence (EL) efficiency and low cost. Solution-processable TADF OLEDs have drawn great research attention and can be potentially applied in both flat-panel displays and lighting sources in the near future. However, the blue light emitting TADF materials with high luminance, satisfying color purity and excellent stability are still rare. Herein, two blue light emitting TADF molecules (CzAC-TRZ, DFAC-TRZ) are designed and synthesized. Due to the modified acridine units by introducing 9-phenylcarbazole and dibenzofuran as σ-groups into the molecular skeletons, CzAC-TRZ, DFAC-TRZ possess high energy states and rigid molecular configuration. Solution-processed OLEDs based on CzAC-TRZ and DFAC-TRZ achieved high EL efficiency with the external quantum efficiency (EQE) up to 11.8% and 11.5%, respectively. Moreover, compared with the analogue emitter (DMAC-TRZ) fabricated control devices, CzAC-TRZ and DFAC-TRZ OLEDs presented lower roll-offs, blue-shift and narrower EL spectra. These results have shown that introducing high energy state building blocks into the donor units via σ bonds offers a promising approach of developing stable deeper blue TADF emitters. Image 1 • σ-link strategy was employed to construct two blue TADF emitters: CzAC-TRZ and DFAC-TRZ. • In contrast to DMAC-TRZ, CzAC-TRZ and DFAC-TRZ possess blue-shift photoluminescence and improved thermal stability. • The fabricated OLEDs demonstrated blue electroluminescence with improved color purity and reduced efficiency roll-offs. [ABSTRACT FROM AUTHOR]