Three 8-hydroxyquinolato (q) boron compounds B(C 2 H 5 ) 2 q (1), BPh 2 q (2), and B(2-naph) 2 q (3) have been synthesized by the reaction of 8-hydroxyquinoline with an appropriate BR 3 compound. Compounds 1-3 have a tetrahedral geometry as demonstrated by the structure of 1 determined by a single-crystal X-ray diffraction analysis. Compounds 1-3 emit a greenblue color at λ max ) 495-500 nm when irradiated by UV light. The electroluminescent (EL) properties of 2 and 3 were examined by fabricating EL devices using 2 and 3 as the lightemitting layer, respectively. The devices of 2 produce a yellow-green light with broad emission spectra, attributed to the formation of an exciplex of 2 with the N,N′-di-1-naphthyl-N,N′diphenylbenzidine (NPB) in the hole transport layer while the intrinsic EL emission of compound 3 was observed. Both 2 and 3 were found to be good electron transport materials in EL devices.

Poly{(4-nitrophenyl)-3-[N-[2-(methacryloyloxy)ethyl]carbazolyl]]diazene} was prepared and its photoinduced birefringence, diffraction grating, and photorefractive asymmetric two-beam gain coupling were studied. The monomer was obtained by performing azo coupling in a two-phase water−dichloromethane system in the presence of a phase transfer catalyst. Photoinduced birefringence of up to 0.09 was observed and diffraction efficiencies of up to 25% were obtained, with atomic force microscopy studies revealing that the grating profile exhibited a sinusoidal shape. Asymmetric two-beam coupling is observed, indicating photorefractive properties, but the energy transfer phenomena are more complex, involving also diffraction by the photoinduced gratings. The combination of these three optical propertiesphotoinduced birefringence, surface gratings, and two-beam couplingis believed to be unique and may eventually produce an all-optical device built of a single polymer film.

Bright blue light with a maximum at 450 nm is emitted by both structural isomers of the novel, stable B (O)(7-azain) Ph (7-azain=7-azaindole anion) on irradiation with UV light. The isomer shown in the picture has approximate C symmetry (the other isomer approximate C symmetry) and electroluminesces when used as the emitting layer in an electroluminescent device.

The carrier generation process in poly(p-phenylene vinylene) (PPV) has been investigated by using fieldinduced fluorescent quenching and delayed-collection-field techniques under pulsed illumination. Relative photoresponse and fluorescent quenching have been measured at electric fields of up to 300 V/µm. The results demonstrate a linear relation between fluorescent quenching and photoresponse at high electric fields, indicating that almost all field-quenched excited states lead to carrier generation. Experimental results also indicate that the time decay of e-h pairs is highly dispersive and the majority (70%) of them decay nonexponentially to ground state in ∼1 ms after illumination. Fluorescent quenching and carrier generation efficiencies obtained at the highest applied electric field are 34% and 42%, respectively. Results also suggest that carrier generation in PPV is a two-step process. In the first step, excited singlet states dissociate into bound geminate e-h pairs, and in the second step, the geminate pairs are separated into free carriers. Both steps are influenced by the applied electric field.

Since the pioneering work of Tang et al., [1] which first demonstrated efficient electroluminescent (EL) devices based on organic materials, many efforts have been devoted to exploring new EL materials for display applications. Two distinct classes of organic materials, namely small organic molecules [1,2] and conjugated polymers, [3] have been developed for this purpose. Motivated by the success of tris(8-hydroxyquinoline) aluminum (Alq 3 ) in vacuum-deposited EL devices, organic metal±chelate compounds in particular have attracted a lot of attention. This class of compounds generally offers many attractive properties such as displaying a double role of electron transport and light emission, high thermal stability, and ease of sublimation. The major drawback of metal±chelate compounds, however, is the lack of suitable blue-emitting molecules.Only a few types of blue-emitting metal±chelate compounds, such as metal complexes based on 2-methylquinolin-8-ol, [4] azomethine, [5] and 7-azaindole, [6] have been previously reported. In this communication, we present a new class of blue-emitting compounds for EL applications based on oxadiazole ligands. Oxadiazole derivatives, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,5-oxadiazole (PBD), have shown promising electron transport and emission characteristics when used in organic EL devices. [7] Oxadiazole units have also been used to design photoluminescent polymers with improved electron transport properties. [8] The new class of oxadiazole metal±chelate compounds is expected to offer the combined properties of metal±chelates and oxadiazoles in EL application. Two beryllium chelate compounds, 2a and 2b, have been synthesized for the present study. As shown in Scheme 1, they can be readily obtained by the direct metal chelation of oxadiazole ligand, 1, with beryllium sulfate in the presence of sodium hydroxide, and purified by the train sublimation technique.[9] Compound 1 was prepared from a reaction between acetylsalicyloyl chloride and an aryltetrazole derivative. We have also synthesized the zinc metal complexes of 1, which gave poor sublimation yields and were less fluorescent compared to the beryllium compounds. All metal complexes possessed very low solubility in most organic solvents. The formula of 2a and 2b were confirmed by elemental analysis. Figure 1 illustrates the molecular structure of 2b as determined by X-ray diffraction analysis. All metal complexes were reasonably stable upon exposure to air, and exhibited high thermal stability. The melting points of 2a and 2b as measured by differential scanning calorimetry (DSC) were 433 and 404 C, respectively. Both beryllium chelate compounds can form smooth and uniform films by vacuum evaporation. As anticipated, 2a and 2b display intense photoluminescence (PL) in the solid state when irradiated with UV light. Figure 2 illustrates their PL spectra recorded from vacuum-deposited thin films. 2a and 2b provided very similar spectra with emission peaks at 452 and 458 nm, respectively. Substituting a nap...

No abstract

No abstract

Although green-light-emitting devices based on poly(p-phenylene vinylene) ppv, have been made and reported by several researchers, it is also of interest to design light emitting devices which emit light in various parts of the visible spectrum, particularly in the blue region. In this letter the effect of doping and conversion time on the photoluminescence (PL) of pvv are investigated. It is observed that treating ppv films with sulfuric acid shifts the PL peaks to the blue region, and Li doping red-shifts the spectra. Unconverted and partially converted ppv films, on the other hand, show PL peaks at about 470 to 480 nm in the dark blue range. The shift in PL peak from green to blue is expected to be due to the decrease in conjugation length which determines the size of the band gap.