Orange-red Light Research Articles

Synthesis and Optical and Electroluminescent Properties of Novel Conjugated Copolymers Derived from Fluorene and Benzoselenadiazole

A novel series of light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3-benzoselenadiazole (BSeD) is prepared by means of palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to BSeD were 50:50, 85:15, 92:8, and 98:2, respectively. All of the copolymers are soluble in common organic solvents and highly fluorescent in solid state. Devices from such copolymers emit orange-red light with λmax = 570−600 nm. The maximal EL emissions of the devices slightly red-shifted gradually with increasing BSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 1.0%, which indicates that this new seleno-containing EL polymer based on fluorene and benzoselenadiazole is a promising candidate for fabricating PLEDs.

Navigation of Lutzomyia longipalpis (Diptera: Psychodidae) under dusk or starlight conditions.

The responses of male and female Lutzomyia longipalpis (Lutz & Neiva) to different wavelengths of light was tested by presenting the sandflies with two light sources simultaneously, a series of test wavelengths between 350-670 nm and a 400 nm control. To test whether L. longipalpis could discriminate between the test and control, three sets of experiments were carried out in which the test wavelengths were presented at higher, equivalent or lower intensity than the control. In all three experiments, ultra-violet (350 nm) and blue-green-yellow (490-546 nm) light was more attractive to L. longipalpis than the control wavelength. However, at low intensity, UV was less attractive, than equivalent or higher intensity UV light. At intensities equivalent to or higher than the control wavelength, ultra-violet light was more attractive than blue-green. Furthermore, at low intensity, green-yellow (546 nm) light was more attractive to males whereas blue-green (490 nm) was more attractive to females. Blue-violet (400 nm) and orange-red (600-670 nm) light were least attractive in all three sets of experiments. Response function experiments indicated that the responses were dependent on both intensity and wavelength and that therefore more than one photoreceptor must be involved in the response. The results indicated that L. longipalpis can discriminate between different wavelengths at different intensities and thus have true colour vision. It also suggests that L. longipalpis may be able to navigate at dusk or under moonlight or starlight conditions using light in the blue-green-yellow part of the spectrum. The difference in response of males and females to light in this region is interesting and may indicate the different ecology of the sexes at night. Overall, these results may have important implications for sandfly trap design.

Electroluminescence by a Sm 3+-diketonate-phenanthroline complex

An organic light emitting diode (OLED) emitting reddish-orange light has been constructed using a Sm 3+ complex, composed of 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1,10-phenanthroline, as emitting layer and poly(vinylcarbazole) (PVK) and 2-(4-biphenylyl)-5-(4- tert-butylphenyl)-1,3,4-oxadiazole (PBD) as hole and electron transporters, respectively. Photoluminescence (PL) spectra suggest that energy pumping is made through both Sm 3+-complexed ligands and poly(vinylcarbazole) providing an efficient electroluminescent system.

Experimental evidence for a non-clock role of the circadian system in spider mite photoperiodism

In the spider mite Tetranychus urticae photoperiodic time measurement proceeds accurately in orange-red light of 580 nm and above in light/dark cycles with a period length of 20 h but not in ‘natural’ cycles with a period length of 24 h. To explain these results it is hypothesized that the photoperiodic clock in the spider mite is sensitive to orange-red light, but the Nanda-Hamner rhythm (a circadian rhythm with a free-running period τ of 20 h involved in the photoperiodic response) is not and consequently free runs in orange-red light. To test this hypothesis a zeitgeber was sought that could entrain the Nanda-Hamner rhythm to a 24-h cycle without inducing diapause itself, in order to manipulate the rhythm independently from the orange-red sensitive photoperiodic clock. A suitable zeitgeber was found to be a thermoperiod with a 12-h warm phase and a 12-h cold phase. Combining the thermoperiod with the long-night orange-red light/dark regime, both with a cycle length of 24 h, resulted in a high diapause incidence, although neither regime was capable of inducing diapause on its own. The conclusion is that the Nanda-Hamner rhythm is necessary for the realization of the photoperiodic response, but is not part of the photoperiodic clock, because photoperiodic time measurement takes place in orange-red light whereas the rhythm is not able to ‘see’ the orange-red light. It is speculated that the Nanda-Hamner rhythm is involved in the timely synthesis of a substrate for the photoperiodic clock in the spider mite.

New Iridium Complexes as Highly Efficient Orange–Red Emitters in Organic Light‐Emitting Diodes

Two new iridium complexes with pyrazine derivatives as ligands (see Figure) were synthesized. The electroluminescent devices based on these metal complexes emit orange–red light at ∼ 610 nm with exceedingly high brightness and external quantum, current, and power efficiencies.

Spectral sensitivity in a sponge larva.

Cilia at the posterior pole of demosponge larvae are known to cause directional swimming, sometimes in response to light gradients, but so far neither the spectral sensitivity of, nor the molecular basis for, this response has been investigated. We exploited the fact that the larval cilia respond to sudden changes in light intensity, a shadow response, in order to determine the action spectrum of photosensitivity. Our results show that larvae of the haplosclerid sponge Reniera sp. respond most to blue light (440 nm), and have a smaller, secondary response peak to orange-red light (600 nm). These data suggest that the photoreceptive pigment in sponge larvae may be a flavin or carotenoid.

Light-Emitting Electrochemical Cell (LEC) Using Polythiophene Derivative

Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of polymer electrolytes and urethane-containing polythiophene (PURET) as active material. We have prepared various types of polymer electrolytes such as poly(acrylate)s and poly(ether ester)s. The devices emit orange-red light with the maximum intensity at 590 nm at room temperature. The typical voltage (V) – current density (I) – luminance characteristics of an ITO / PURET + polymer electrolyte complexed with LiClO4 / Al cell under forward and reverse bias conditions were measured. The I-V curve is symmetric at zero bias. The apparent threshold voltages for current injection and visible light emission are around 2 ∼ 3V.

Hydroxyphenyl-pyridine Beryllium Complex (Bepp2) as a Blue Electroluminescent Material

A novel blue luminescent chelate complex Bepp 2 (pp = 2-(2-hydroxyphenyl)pyridine) was synthesized as an electroluminescent material. The single-crystal X-ray diffraction study showed that there are intermolecular π...π interactions in the solid state of Bepp 2 . This structural character can facilitate charge transport ability. The photoluminescence and electroluminescence properties of Bepp 2 were characterized. Bepp 2 exhibits very strong photoluminescence at 440 nm in chloroform solution. Its PL quantum yield is 80% higher than that of Alq 3 in solution. In this paper we report that Bepp 2 can be used as an emitting material to fabricate blue light electroluminescent devices. The devices with the configuration of [ITO/Cu-Pc/TPD/Bepp 2 /LiF/Al] show electroluminescent efficiency up to 0.55 lm/W. Bepp 2 shows blue EL emission centered at 450 nm. We also demonstrated that Bepp 2 can be used as host material to prepare orange-red EL devices. For the devices of [ITO/TPD/DCM (2wt %) doped Bepp 2 /Al], orange-red color light was observed.

New orange-red light emitting diode from poly[2-(5-cyclo-hexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene

Poly[2-(5-cyclohexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene] (PMCYHPV) was synthesized through dehydrohalogenation polymerization. This polymer shows good solubility in common organic solvents. The absorption and photoluminescence (PL) emission maxima of PMCYHPV are 497 nm and 590 nm, respectively. The electroluminescence (EL) properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and PMCYHPV were studied by means of the EL spectra, current-voltage characteristics, and EL power-current characteristics. The measured relative EL quantum efficiency of PMCYHPV is about 6 times higher than that of MEH-PPV. The EL enhancement of PMCYHPV originates from the reduction of non-radiative decay of excitons caused by better separation of the polymer chains due to the rigid cyclohexyl side group. Furthermore, we found that the PL quantum efficiency of PMCYHPV is 15% higher than that of MEH-PPV.

New orange-red light emitting diode from poly[2-(5-cyclo-hexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene

Poly[2-(5-cyclohexylmethoxypentyloxy)-5-methoxy-1,4-phenylenevinylene] (PMCYHPV) was synthesized through dehydrohalogenation polymerization. This polymer shows good solubility in common organic solvents. The absorption and photoluminescence (PL) emission maxima of PMCYHPV are 497 nm and 590 nm, respectively. The electroluminescence (EL) properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and PMCYHPV were studied by means of the EL spectra, current-voltage characteristics, and EL power-current characteristics. The measured relative EL quantum efficiency of PMCYHPV is about 6 times higher than that of MEH-PPV. The EL enhancement of PMCYHPV originates from the reduction of non-radiative decay of excitons caused by better separation of the polymer chains due to the rigid cyclohexyl side group. Furthermore, we found that the PL quantum efficiency of PMCYHPV is 15% higher than that of MEH-PPV.

Change in the emission color and the quantum efficiency enhancement in urethane-substituted polythiophene/ tris(8-hydroxyquinoline) aluminum double layer light-emitting devices

We have obtained bright red color from orange–red light emitting urethane-substituted polythiophene (PURET) by placing tris(8-hydroxyquinoline) aluminum (alq 3) between the PURET layer and the cathode. Rearrangement of PURET chains or alq 3 molecules at the interface induced by the interfacial interaction between PURET and alq 3 via hydrogen bond is suggested as a mechanism for the change in the emission color. Light output intensity increased with alq 3 film thickness but is insensitive to the PURET film thickness. Combination of the charge blocking effect and the doping induced quantum efficiency enhancement has been performed by annealing the double layer device. Annealing of the double layer device increased further the light output intensity and caused the EL spectrum to shift toward blue, resulting in bright greenish-yellow light emission. In situ absorption and photoluminescence measurements during the annealing process exhibit the diffusion of alq 3 molecules into the PURET layer and the formation of a doped region at the interface. Energy transfer from doped alq 3 molecules to PURET chains and the doping-induced deformation of PURET chains are examined to occur within the doped region. In this paper, we propose the annealing of polymer/organic double layers as an effective method to improve the quantum efficiency of polymer light-emitting devices.

Solid-State Light-Emitting Devices Based on the Trischelated Ruthenium(II) Complex. 1. Thin Film Blends with Poly(ethylene oxide)

Thin-film solid-state light-emitting devices have been fabricated by using blends of a trischelated complex of ruthenium(II) with 4,7-diphenyl-1,10-phenanthroline disulfonate ligands and lithium triflate complexed poly(ethylene oxide). Charge injection occurs via an electrochemical redox mechanism and the mechanism of light production is similar to electrogenerated chemiluminescence. Orange-red light is emitted with a turn-on voltage of 2.5−3.0 V. At 6 V, devices reach luminance levels of about 100 cd/m2 with an external quantum efficiency of 0.02% photons/electron. The admixed PEO acts both as a film processing aid, giving uniform, homogeneous, and reproducible devices, and as a polymer electrolyte for ruthenium complex and counterion diffusion. Devices reach about 50% of their maximum luminance within a few seconds, and reach maximum luminance in about a minute. This behavior can be realized without the need of elaborate charging schemes involving the use of elevated temperatures or solvent treatments that enhance ionic conductivity. Devices of this type can be fabricated via conventional processing routes and conditioned to high light ouput with a few simple voltage scans.

Enhanced performance of polythiophene derivative based light emitting diodes by addition of europium and ruthenium complexes

Fabrication of polymer light emitting diodes (PLEDs) from a urethane containing processable polythiophene derivative, poly[2-(3-thienyl) ethanol n-butoxy carbonylmethyl urethane], (PURET) and its composites with luminescent Ruthenium (II) and Europium (III) complexes is discussed. Enhanced electroluminescence (EL) performance was observed, when 1% by weight of europium (III) or ruthenium (II) complexes were added to the PURET polymer. Multi-layered devices with polyaniline as a hole injecting layer and tris-8-hydroxyquinoline-aluminum as an electron injecting layer have also been fabricated. PLEDs from PURET polymer have a threshold voltage of 3.6 V and emit an orange-red light with a brightness of about 500 cd/m 2 under forward bias of 9 V, upon the addition of 1% of europium (III) thenoyl trifluoroacetonate complex to the polymer.

Abnormal Accumulation of Porphyrin Derivatives in the Kidneys of Long-Evans Cinnamon Rats, as Evidenced by Microspectrophotometry

In the study described here we have revealed an abnormal accumulation of porphyrin derivatives in the kidneys of Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. In addition, we have confirmed that the derivatives emitted red-orange light in renal sections under UV excitation. This renal red-orange emission has previously been identified as luminescence from cuprous metallothioneins [Cu(I)-MTs], which also accumulate in both the kidneys and liver of LEC rats. In this study, we measured the emission spectra of the luminescence in the kidneys using microspectrophotometry. The spectra of the renal red-orange emission resembled those of porphyrin derivatives rather than those of Cu(I)-MTs. We then extracted these derivatives from the kidneys. An abundance of porphyrin derivatives was established. A significant increase in the levels of the derivatives in the liver and urine of the LEC rats was also confirmed. These results provide evidence of a heme-metabolism abnormality in LEC rats.

Electroluminescence of Polymer Blend Composed of Conjugated and Nonconjugated Polymers. White-Light-Emitting Diode

We report on the investigations of electroluminescence (EL) for the polymer blend composed of two organic soluble polymers. The blends consist of main chain conjugated poly[(2-methoxy-5-((2-ethylhexyl)oxy)-1,4-phenylene)vinylene] (MEH−PPV) and a side chain luminescent polymer, an alkoxy(trifluoromethyl)stilbene-substituted PMA derivative (CF3−PMA). Emitting colors of the polymer blends varied with the blending ratios of two polymers. The electroluminescent peak of the MEH−PPV-rich polymer blend ranged over 580−800 nm (orange-red light), and of the CF3−PMA-rich polymer blend ranged from 380 to 800 nm, resulting in a white-light emission. Additional new EL peaks of polymer blends at around 380 and 800 nm would originate from the CF3−PMA and the exciplex formed by photoinduced electron transfer between two polymers.

Effects of sequential stimuli on Halobacterium salinarium photobehavior

We analyzed the motor photoresponses of Halobacterium salinarium to different test stimuli applied after a first photophobic response produced by a step-down of red-orange light (prestimulus). We observed that pulses given with a suitable delay after the prestimulus produced unusual responses. Pulses of blue, green, or red-orange light, each eliciting no response when applied alone, produced a secondary photophobic response when applied several seconds after the prestimulus; the same occurred with a negative blue pulse (rapid shut-off and turning on of a blue light). Conversely, no secondary photophobic response was observed when the test stimulus was a step (a step-up for red-orange light, a step-down for blue light) of the same wavelength and intensity. When the delay was varied, different results were obtained with different wavelengths; red-orange pulses were typically effective in producing a secondary photophobic response, even with a delay of 2 s, whereas the response to a blue pulse was suppressed when the test stimulus was applied within 5 s after the prestimulus. The secondary photophobic response to pulses was abolished by reducing the intensity of the prestimulus without affecting the primary photophobic response. These results, some of which were previously reported in the literature as inverse effects, must be produced by a facilitating mechanism depending on the prestimulus itself, the occurrence of reversals being per se ineffective. The fact that red-orange test stimuli are facilitated even at the shortest delay, whereas those of different wavelengths become effective only after several seconds, suggests that the putative mechanism of the facilitating effect is specific for different signaling pathways.

New fluorescent polyimides for electroluminescent devices based on 2,5-distyrylpyrazine

New fluorescent polyimides, having an electroluminescent (EL) active unit, 2,5-distyrylpyrazine (DSP), were synthesized by the poly-condensation of 2,5-bis(4-aminostyryl)pyrazine 4 with various tetracarboxylic dianhydrides 5 . Intense photoluminescence originating from the DSP chromophore units was demonstrated. Furthermore, a light emitting diode (LED) was fabricated based on the polyimide Langmuir-Blodgett film, using indium tin oxide and a Mg-Ag alloy as the anode and the cathode, respectively. Under forward bias, orange-red light emission ( λ max = 560 nm) could be observed, which was similar to the emission generated by photoexcitation. Meanwhile the EL intensity linearly depended on the applied current density, which indicated that light emission resulted from recombination of the injected charges in the polyimide layer.

Dibenzotetraphenylperiflanthene: Synthesis, Photophysical Properties, and Electrogenerated Chemiluminescence

Fissure coupling of the fluoranthene adduct (7,12-diphenyl)benzo[k]fluoranthene (3) using AlCl3/NaCl, CoF3/TFA, or Tl(OCOCF3) gave the new polyaromatic hydrocarbon dibenzo{[f,f’]-4,4’,7,7’-tetraphenyl}diindeno[1,2,3-cd:1‘,2‘,3‘-lm]perylene (4). Crystal data for 4: triclinic space group P1̄, a = 10.569(2) Å, b = 11.565(4) Å, c = 13.001(3) Å, α = 95.05(2)°, β = 111.24(1)°, γ = 100.53(1)°, Z = 1, RF = 0.075%. Compounds 3 and 4 are both highly fluorescent in solution and display relative fluorescence quantum yields of φF = 1.0 and 0.85, respectively. The electrochemistry and electrogenerated chemiluminescence (ECL) of each compound has been investigated. The cyclic voltammogram of 3 in benzene−acetonitrile (9:1) shows that the compound undergoes a reversible reduction and an irreversible oxidation, whereas the cyclic voltammogram of 4 displays the reversible formation of both singly and doubly charged cations and anions. Compounds 3 and 4 undergo ECL to yield blue and orange-red light, respectively, with an ECL efficiency of ∼2% for 4. Emission from 4 is observed in the ECL of unstirred solutions of 3. This indicates that 4 is produced at the electrode during the ECL experiment, presumably via an electrochemical oxidative coupling process during the anodic potential steps.

Enhancement of Organic Electroluminescent Intensity by Doping Hole-Property Polymers

Organic electroluminescent (EL) diodes with one-layer poly(3-octylthiophene) (P3OT) and P3OT doped with poly(N-vinylcarbazole) (PVK) (P3OT/PVK) as EL emitting layer sandwiched between indium/tin oxide (ITO) and aluminium electrodes have been fabricated by spin coating onto ITO respectively. The P3OT/PVK EL diode starts to emit red-orange light at 5 V in our experiment, the luminance and the current for the P3OT/PVK EL diode at bias voltage was compared with those for the only P3OT EL diode, indicating that the PVK dopant has power over the P3OT electroluminescence.

High quantum efficiency for a porous silicon light emitting diode under pulsed operation

A high quantum efficiency for a porous silicon light emitting diode (LED) is demonstrated under pulsed operation. The LED is fabricated from a p+nn+ structure by anodic/hydrofluoric etching followed by deposition of a transparent gold contact. The LED shows a rectifying behavior and emits orange-red light under forward bias with a spectral width significantly narrower than the corresponding photoluminescence spectrum. By calibrated measurements, we here demonstrate electroluminescence external quantum efficiencies of ∼0.2% under pulsed operation corresponding to internal quantum efficiencies of a few percent.