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The synthesis of four novel seven-member-ring-based electron-transporting materials with high thermal stability and the fabrication of high-performance OLED devices using the same are reported.

Chemoselective enantiodivergent reduction of N-benzyl-α-keto amides catalyzed by chiral oxido-vanadium(V) complexes derived from a reduced form of N-salicylidene L-tert leucinate can be achieved with good yields and good to high enantioselectivities. These chiral complexes were utilized in catalyzing the enantioselective synthesis of (R)-N-benzyl-mandelamide with pinacolborane and (S)-N-benzyl-mandelamide with catecholborane from the corresponding ketone precursors. A series of 12 different solvents and 8 different reducing agents were examined. By the use of pinacolborane (R isomer, 74–99% ee) or catecholborane (S isomer, 60–90% ee), a handy approach for complementary asymmetric reduction of α-keto amides can be attained.

A pseudo-enantiomeric pair of optically switchable helicenes containing a catalytic 4-N-methylaminopyridine (MAP) bottom unit and a C2-symmetric, (10R,11R)-dimethoxymethyl-dibenzosuberane top template was synthesized. They underwent complementary photoswitching at 290 nm (P/M′, 99) and 340 nm (P/M′, 91/9) and unidirectional thermo-rotation at 130 °C (P/M′, >99/

A new class of cis-stilbene/fluorene spiro hybrid systems with paired diphenylamino donor and cyano, N-phenylbenzimidazole, dimesitylboranyl, or β,β-diphenylethenyl acceptor units was synthesized as ambipolar materials for organic light-emitting diode applications. When coupled with hole transporting 4,4′-bis(1-naphthylphenylamino)-1,1′-biphenyl (α-NPB) and electron transporting 2,2′,2′′-(1,3,5-benzenetriyl)-tris(1-phenyl-1-H-benzimidazole) layers, they served as one of the best bluish green and pure green emitting layers with excellent external quantum efficiencies of 3.9–5.2%, electroluminescent brightness of 2202–3069 cd m−2, luminance efficiencies of 11.0–15.8 cd A−1, and power efficiencies of 5.7–6.6 lm W−1 at 20 mA cm−2, which were about 2–3 times better than those based on standard α-NPB/tris(8-hydroxyquinoline)aluminum bilayer devices.

Hybrids based on a dibenzosuberene core bearing a spiro-fluorene junction at the C-5 position and with amino donor and β-thiophenyl-α-cyanoacrylic acid acceptor groups at C-3 and C-7, respectively, serve as new organic sensitizer materials for solar cell applications. Solar cell devices based on these materials show a conversion efficiency (η) of up to 6.1% (V(oc) = 697 mV, J(sc) = 12.2 mA cm(-2), FF = 0.72) under AM 1.5 G conditions. The best IPCE values exceed 75% within the 450-550 nm absorption range.

We reveal in this communication a new finding regarding the use of a sky-blue emitter to generate purplish-blue emission from organic light emitting diodes (OLEDs) with a polarity matching and high-energy exciton generating host. The resulting device exhibits CIExy coordinates of (0.155, 0.063) and a 3.5% external quantum efficiency, with a 1.2 lm W−1 power efficiency at 100 cd m−2 as a sky-blue emitter, 1-((9,9-diethyl-9H-fluoren-2-yl)ethynyl)pyrene with CIExy of (0.190, 0.241) is doped into a host of 4,4′-bis(9-carbazolyl)-biphenyl, for example. The resulting purplish-blue emission enables a greater than 100% color saturation. The extraordinarily marked blue-shift may result from a low doping concentration to prevent bathochromic shift due to emitter segregation, a polarity matching host to further disperse the emitter, and an efficient host and guest energy level pairing that enables excitons to be generated on the host to trigger short wavelength emission. Furthermore, the host is capable of generating excitons with higher energy to facilitate the triggering of emission with a shorter wavelength. The high efficiency may be attributed to the low doping concentration preventing efficiency roll-off caused by concentration-quenching, the excitons generated on the host facilitating the occurrence of the effective host-to-guest energy transfer, and the employed host possessing an effective host-to-guest energy transfer effect. Notably, the new approach also works for other light-blue emitters in yielding a highly desirable deep-blue light, provided their molecular structure is free of steric hindrance.

We designed a stepwise approach for co-sensitization of a zinc porphyrin sensitizer (LD12) with a spirally configured organic dye (CD5) for dye-sensitized solar cells. The co-sensitized LD12 + CD5 device showed significantly enhanced VOC and JSC relative to its individual single-dye sensitized devices. Upon optimization, the device made of the LD12 + CD5 system yielded JSC/mA cm−2 = 16.7, VOC/V = 0.74, FF = 0.73 and η = 9.0%; this performance is superior to that of either individual device made from LD12 (η = 7.5%) and CD5 (η = 5.7%) under the same conditions of fabrication. To understand the effects of the potential shift and charge recombination on the cell performance, we measured charge-extraction (CE) and intensity-modulated photovoltage spectra (IMVS). Upon sensitization with each dye, the TiO2 potentials are similar, but co-sensitization causes the potential to shift down (cathodic shift). Charge recombination was significantly retarded for the co-sensitized system relative to each individual dye-sensitized system, to account for the enhanced VOC for the former relative to the latter. A test of stability indicates a systematic trend between the LD12 + CD5 and LD12 devices; the performance of the co-sensitized device degraded only ∼15% and remained stable during the period of 500–1000 h near 295 K.

Co-sensitization of two or more dyes with complementary absorption spectra on a semiconductor film is an effective approach to enhance the performance of a dye-sensitized solar cell (DSSC). Porphyrin sensitizer YD2-oC8 showed outstanding photovoltaic performance co-sensitized with an organic dye to cover the entire visible spectral region, 400–700 nm. To promote the light-harvesting capability beyond 700 nm, a porphyrin dimer (YDD6) was synthesized for a co-sensitized system. We report a systematic approach for engineering of molecular co-sensitization of TiO2 films in a cocktail solution containing YD2-oC8, an organic dye (CD4) and YDD6 in a specific molar ratio to optimize the photovoltaic performance of the device. The resulting device showed panchromatic spectral features in the IPCE action spectrum in the region 400–700 nm attaining efficiencies of 75–80%; the spectrum is extended to the near-IR region attaining 40–45% in 700–800 nm region, giving JSC/mA cm−2 = 19.28, VOC/mV = 753, FF = 0.719, and η = 10.4% under standard AM 1.5 G one-sun irradiation. This performance is superior to what is obtained from the individual single-dye devices and the two-dye co-sensitized systems. The shifts of TiO2 potential upon dye uptake and the kinetics of charge recombination were examined through measurements of the charge extraction (CE) and intensity-modulated photovoltage spectroscopy (IMVS), respectively. Five co-sensitized systems were investigated to demonstrate that suppression of dye aggregation of YDD6 in the co-sensitized film is a key factor to further improve the device performance.

This paper demonstrates the employment of a multi-emissive-layer device architecture with smooth cascading energy levels to improve markedly the efficiency, roll-off, and color-stability of a fluorescent yellow organic light-emitting diode. As a tri-emissive layer structure was used in lieu of neat film, for example, the resultant external quantum efficiency was increased from 2.2 and 1.8% to 8.2 and 8.6% between 100 and 1000 cd m−2, while current efficiency increased from 5.8 and 4.6 cd A−1 to 26.5 and 27.2 cd A−1 and efficacy from 4 and 2.4 lm W−1 to 20.6 and 18.3 lm W−1. Moreover, the color stability of the tri-emissive layer structure has become of even higher quality than the neat film counterpart has. The reason why the multi-emissive-layer device exhibits both high efficacy and high color-stability may be attributed to the stepwise energy levels that enable a significant reduction in injection barriers, a wider recombination zone, and a more effective carrier confinement. Additionally, the paired host and guest energy-levels in two of the emissive layers allow excitons to generate on the host to facilitate the occurrence of host-to-guest energy transfer and, thus, high device efficiency. The little roll-off may be due to the different paired host and guest energy-levels in the third emissive layer allowing excitons to generate predominantly on the guest at low voltage, but with increasing excitons generating on the host as the voltage increases, fully utilizing all the possible recombination sites.

A series of TiO2 particles of varying particle sizes from nano to micro scales was treated with three different oxidants (O2, TBHP, and aqueous H2O2) under irradiation conditions to form activated TiO2 particles bearing surface peroxo Ti(O2) species. The resultant, heterogeneous catalysts were tested for photo-catalytic acetylation of 2-phenylethanol by acetic anhydride in 8 different solvents. The best scenario involves the use of 32 nm grade of TiO2 nanoparticles and aqueous H2O2 for pre-activation and the use of CH2Cl2 as the reaction solvent. The 2-phenethyl acetate product can be completely formed in 10 h and isolated in essential quantitative yield. It was also found that catalysts derived from TiO2 nanoparticles are superior to those from ZrO2, Y2O3 and WO3 nanoparticles by using the oxidative, photo-activation protocol. The newly developed heterogeneous catalytic system can be smoothly applied to photocatalytic acetylation of several representative primary aliphatic and aromatic alcohols. The intermediacy of Ti–OH or TiO surface groups was proposed in the photo-catalytic acetylation conditions.

The titled hybrid (Q-H) works as a clippable optoelectronic unit. Q-spacer-Q systems function as efficient orange emitters reaching EL intensities (L) of up to 6840 cd m-2 with etaext of 0.77% and operation efficiencies of 1.60 cd A-1 and 0.8 lm W-1. Notably, Q-An acts as a (bluish) green emitter, reaching L of 12347 cd m-2 with similar operational efficiency.