Blue Light Emission from a Fluorene‐Carbazole‐Fluorene Trimer Incorporated as the Side Chain into a Polynorbornene

Summary: A well defined blue electroluminescent fluorene‐carbazol‐fluorene trimer 3,6‐bis‐(9,9‐dihexyl‐9H‐fluoren‐3‐yl)‐9‐alkyl‐9H‐carbazole was synthesized using a Suzuki type cross coupling reaction as the key step. A way to attach this chromophore to a norbornene was developed and the resulting electroactive monomer was polymerised using the “3^rd generation Grubbs catalyst” (N,N‐bis(mesityl) 4,5‐dihydroimidazol‐2‐ylidene)(3‐bromo‐pyridine)₂(Cl)₂Ru?CHPh), yielding an amorphous polymer with a narrow molecular weight distribution, which was used to build a light‐emitting diode exhibiting electroluminescence peaking at 410 nm.

Incorporation of the fluorene‐carbazol‐fluorene trimer as the emissive layer in an ITO/PEDOT:PSS/emitter/Ca/Al light emitting device.     

Novel Light Emitting Diode Using Organic Electroluminescence Microcapsules

Novel light emitting diodes (LEDs) were prepared using electroluminescence (EL) material/polymer microcapsules (ELC). N‐vinylcarbazole as a hole‐transporting component and methyl methacrylate (MMA) were copolymerized for producing the seed particles using dispersion polymerization. An oxadiazole derivative, synthesized as a electron‐transporting component, and tris(8‐hydroxyquinolinato) aluminium(III) (Alq₃) were incorporated into the polymer particles by using the solute co‐diffusion method (SCM). The LEDs for the EL characterization were fabricated in a thin sandwich configuration: Al anode/ELC/ITO cathode. The surface imaging of the LED prepared using ELC was performed by atomic force microscopy (AFM). The EL characteristics of the ELC were investigated by UV, photoelectron and luminescence spectroscopy, and the current‐voltage and the light‐voltage characteristics for the LED were determined.

Encapsulation procedure using solute co‐diffusion method (SCM).     

Blue‐Green Light Emitting Poly(phenylenevinylene) Derivatives as Candidates for Polymer LEDs: Synthesis and Characterization

Summary: Alkoxy substituted derivatives of poly‐ and oligo[(m‐phenylenevinylene)‐alt‐(p‐phenylenevinylene)] were synthesized via the Wittig ( P1 , OPV1 , OPV2 ) and the Wittig‐Horner ( P2 , OPV3 , OPV4 ) condensation routes. The polymers were characterized by ¹³C NMR, ¹H NMR, FT‐IR spectroscopy and GPC. ¹H NMR was a convenient tool to distinguish between the cis and trans double bonds in the compounds. Poly[(4‐decyloxy‐1,3‐phenylenevinylene)‐alt‐(1,4‐phenylenevinylene)] ( P1 ) contained cis and trans double bonds in significant amounts, the vinylene configuration of poly[(4‐decyloxy‐1,3‐phenylenevinylene)‐alt‐(2,5‐dipentyloxy‐1,4‐phenylenevinylene)] ( P2 ) was nearly exclusively trans. Model compounds ( OPV1–4 ) were also synthesized to support the structural and optical characterization. UV‐vis absorption, photoluminescence (PL) and cyclic voltammetry measurements have been performed to investigate the influence of the positions and the number of substituents on electronic levels. The polymers exhibited an intensive solid‐state emission in the blue‐green ( P1 ) and the green ( P2 ) region of the spectrum. Light emitting diodes have been fabricated consisting of ITO, PEDOT:PSS, P2 and Ca/Al. They exhibited high luminance of 100 cd · m^?2 at 5.9 V and low onset voltages (4.3 V) for the electroluminescence (EL).

Schematic representation of a light emitting diode fabricated by use of an alkoxy substituted derivative of poly[(m‐phenylenevinylene)‐alt‐(p‐phenylenevinylene)] ( P2 ).     

A Wide‐Bandgap Semiconducting Polymer for Ultraviolet and Blue Light Emitting Diodes

A novel wide‐bandgap conjugated polymer (PDHFSCHD) consisting of alternating dihexylfluorene and rigidly twisted biphenyl units has been synthesized. The new fluorene‐based copolymer composed of rigid twisting segments in the main‐chain exhibits an optical bandgap of as high as 3.26 eV, and a highly efficient ultraviolet emission with peaks at 368 nm and 386 nm. An electroluminescence device from PDHFSCHD neat film as an active layer shows UV emission which peaks at 395 nm with a turn on voltage below 8 V. By optimizing the device conditions, a peak EL quantum efficiency of 0.054% and brightness of 10 cd · m^?2 was obtained. Furthermore, blending a poly(dihexylfluorene) in the PDHFSCHD host gave pure blue emission peaking at 417 nm and 440 nm without long wavelength emission from aggregated species. Efficient energy transfer from PDHFSCHD to PDHF was demonstrated in these blended systems. Depressed chain‐aggregation of PDHF in the PDHFSCHD host can correspond to pure blue emission behaviors.

The structure of the copolymer PDHFSCHD.     

Synthesis of Diphenylamine‐Substituted Phenylazomethine Dendrimers and the Performance of Organic Light‐Emitting Diodes

Summary: We have designed and synthesized novel diphenylamine‐substituted phenylazomethine dendrimers (DP‐Gn, n = 1, 2) as hole‐transport materials for organic light‐emitting diodes (OLEDs). These dendrimers similar to phenylazomethine dendrimers showed a stepwise metal complexation with metal ions. They have good multi‐redox properties attributed to the terminal amine moieties and excellent thermal stabilities. Double layer EL devices utilizing the dendrimers as a hole‐transport material and Alq₃ as the emitting and electron transport materials were fabricated. The EL performances of the devices increased with higher dendrimer generations. Moreover, by using the metal ion (0.5 equiv. SnCl₂)‐complexed DP‐G2 dendrimers, the luminance and EL efficiency of the devices were drastically increased by more than double and over 30%, respectively. These metal complexable phenylazomethine dendrimers are novel and promising materials for highly efficient OLEDs.

Structure of the diphenylamine‐substituted phenylazomethine dendrimer DP‐G2.     

发光二极管红光照射对骨髓间充质干细胞增殖的影响

目的 观察发光二极管（LED）红光照射对大鼠骨髓间充质干细胞（MSCs）增殖的影响。 方法 通过体外培养SD大鼠骨髓MSCs,将LED红光光源置于MSCs上方2 cm处,红光波长620 nm,测得光功率密度为6.67 mW/cm2,能量密度分别设定为0,0.5,1和2 J/cm2 ,其中0 J/cm2组作为对照组,其它组作为实验组。0.5 J/cm2组、1 J/cm2组和2 J/cm2组分别给予75 s,150 s和300 s LED红光照射,12 h后重复照射1次,共照射3次。于照射后48 h分别采用细胞计数试剂盒-8(CCK-8)检测各组细胞增殖活性,采用EdU细胞增殖试剂盒检测各组细胞DNA复制水平,采用流式细胞仪检测各组MSCs细胞周期变化情况。 结果 经620 nm红光照射后,发现各实验组细胞增殖活性及DNA复制水平均较对照组明显增强（P<0.05）,细胞生长周期均较对照组明显缩短（P<0.05）,且上述指标变化幅度均以0.5 J/cm2组最显著。 结论 低能量LED红光照射能增强SD大鼠骨髓MSCs细胞DNA复制活性,缩短细胞生长周期,从而促进MSCs体外增殖。     

The effect of nocturnal blue light exposure from light-emitting diodes on wakefulness and energy metabolism the following morning

Objectives

The control of sleep/wakefulness is associated with the regulation of energy metabolism. The present experiment was designed to assess the effect of nocturnal blue light exposure on the control of sleep/wakefulness and energy metabolism until next noon.

Methods

In a balanced cross-over design, nine young male subjects sitting in a room-size metabolic chamber were exposed either to blue LEDs or to no light for 2 h in the evening. Wavelength of monochromatic LEDs was 465 nm and its intensity was 12.1 μW/cm².

Results

During sleep, sleep architecture and alpha and delta power of EEG were similar in the two experimental conditions. However, the following morning, when subjects were instructed to stay awake in a sitting position, duration judged as sleep at stages 1 and 2 was longer for subjects who received than for those who received no light exposure. Energy metabolism during sleep was not affected by evening blue light exposure, but the next morning energy expenditure, oxygen consumption, carbon dioxide production and the thermic effect of breakfast were significantly lower in subjects who received blue light exposure than in those who received no light exposure.

Conclusions

Exposure to low intensity blue light in the evening, which does not affect sleep architecture and energy metabolism during sleep, elicits drowsiness and suppression of energy metabolism the following morning.     

Differential effects of light wavelength in phase advancing the melatonin rhythm

Shorter wavelength light has been shown to be more effective than longer wavelengths in suppressing nocturnal melatonin and phase delaying the melatonin rhythm. In the present study, different wavelengths of light were evaluated for their capacity to phase advance the saliva melatonin rhythm. Two long wavelengths, 595 nm (amber) and 660 nm (red) and three shorter wavelengths, 470 nm (blue), 497 nm (blue/green), and 525 nm (green) were compared with a no-light control condition. Light was administered via a portable light source comprising two light-emitting diodes per eye, with the irradiance of each diode set at 65 microW/cm(2). Forty-two volunteers participated in up to six conditions resulting in 15 per condition. For the active light conditions, a 2-hr light pulse was administered from 06:00 hr on two consecutive mornings. Half-hourly saliva samples were collected on the evening prior to the first light pulse and the evening following the second light pulse. The time of melatonin onset was calculated for each night and the difference was calculated as a measure of phase advance. The shorter wavelengths of 470, 495 and 525 nm showed the greatest melatonin onset advances ranging from approximately 40-65 min while the longer wavelengths produced no significant phase advance. These results strengthen earlier findings that the human circadian system is more sensitive to the short wavelengths of light than the longer wavelengths.     

A Polymer Lost in the Shuffle: The Perspective of Poly(para)phenylenes

During 1990s, poly(para)phenylenes (PPPs) are one of the most prominent and hyped classes of conjugated polymers. Even though they have been heavily investigated for different applications, they are now eking out a rather niche existence. It is believed that this decline of interest partly has come from the early obstacle of synthesizing high-molecular weight, processable, and defect-free PPPs. Early examples of PPPs are not only rather oligomers than polymers but also contain many regiochemical and structural defects. Furthermore, early unsubstituted materials are infusible and insoluble, which have made their practical application almost impossible. Another reason for the decline of research interest in PPPs may be their underperformance in early applications, particularly in organic light-emitting diodes (OLEDs), which ultimately lead to a lack of follow-up publications. However, over the last two decades not only more precise and advanced synthesis methods have arisen but also a more profound understanding of those applications has been achieved within which new technological approaches have emerged. It is believed that PPPs would benefit from this development. Accordingly, in this perspective, the synthesis, structures, properties, and applications of PPPs reported so far as well as their potential in future technologies are discussed.