Naphthyl end-capped quarterthiophene: A simple organic semiconductor with high mobility and air stability

An organic semiconductor that can be mass produced is synthesized by end-capping quaterthiophene with naphthyl units (NaT4). An organic thin-film transistor (OTFT, see figure) has been fabricated using this organic semiconductor, and exhibits stability under ambient conditions with a mobility of up to 0.40 cm(2) V-1 s(-1).

White electrolumineseence from a single-polymer system with simultaneous two-color emission: Polyfluorene as the blue host and a 2,1,3-benzothiadiazole derivative as the orange dopant on the main chain

New single-polymer electroluminescent systems containing two individual emission species - polyfluorenes as a blue host and 2,1,3-benzothiadiazole derivative units as an orange dopant on the main chain - have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue(lambda(max) = 421 nm/445 nm) and orange emission (lambda(max) = 564 nm)from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light-emitting diodes (PLEDs) based on the single-polymer systems has been investigated. The introduction of the highly efficient 4,7-bis(4-(N-phenyl-N-(4-methylphenyl)amino)phenyl)-2,1,3-benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single-layer device fabricated in air (indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure-white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m(-2), luminance efficiency of 7.30 cd A(-1), and power efficiency of 3.34 lm W-1 can be obtained.

Highly efficient pure-white-light-emitting diodes from a single polymer: Polyfluorene with naphthalimide moieties

Light-emitting diodes exhibiting efficient pure-white-light electroluminescence have been successfully developed by using a single polymer: polyfluorene derivatives with 1,8-naphthalimide chromophores chemically doped onto the polyfluorene backbones. By adjusting the emission wavelength of the 1,8-naphthalimide components and optimizing the relative content of 1,8-naphthalimide derivatives in the resulting polymers, white-light electroluminescence from a single polymer, as opposed to a polymer blend, has been obtained in a device with a configuration of indium tin oxide/poly(3,4-ethyleiledioxythiophene)(50 nm)/polymer(80 nm)/Ca(10 nm)/Al(100 nm). The device exhibits Commission Internationale de I'Eclairage coordinates of (0.32,0.36), a maximum brightness of 11900 cd m(-2), a current efficiency of 3.8 cd A(-1), a power efficiency of 2.0 lm W-1. an external quantum efficiency of 1.50 %, and quite stable color coordinates at different driving voltages, even at high luminances of over 5000 cd m(-2).

Highly efficient electroluminescence from green-light-emitting electrochemical cells based on Cu-I complexes

The complexes [Cu(dnpb)(DPEphos)](+)(X-) (dnpb and DPEphos are 2,9-di-n-butyl-1,10-phenanthroline and bis[2-(diphenyl-phosphino)phenyl]ether, respectively, and X- is BF4-, ClO4-, or PF6-) can form high quality films with photoluminescence quantum yields of up to 71 +/- 7%. Their electroluminescent properties are studied using the device-structure indium tin oxide (ITO)/complex/metal cathiode. The devices emit green light efficiently, with an emission maximum of 523 nm, and work in the mode of light-emitting electrochemical cells. The response time of the devices greatly depends on the driving voltage, the counterions, and the thickness of the complex film. After pre-biasing at 25 V for 40 s, the devices turn on instantly, with a turn-on voltage of ca. 2.9 V. A current efficiency of 56 cd A(-1) and an external quantum efficiency of 16% are realised with Al as the cathode. Using a low-work-function metal as the cathode can significantly enhance the brightness of the device almost without affecting the turn-on voltage and current efficiency. With a Ca cathode, a brightness of 150 cd m(-2) at 6 V and 4100 cd m(-2) at 25 V is demonstrated. The electroluminescent performance of these types of complexes is among the best so far for transition metal complexes with counterions.

Electrogenerated chemiluminescence sensors using Ru(bpy)(3)(2+) doped in silica nanoparticles

A novel electrogenerated chemiluminescence (ECL) sensor based on Ru(bpy)(3)(2+)-doped silica (RuDS) nanoparticles conjugated with a biopolymer chitosan membrane was developed. These uniform RuDS nanoparticles ( similar to 40 nm) were prepared by a water-in-oil microemulsion method and were characterized by electrochemical and transmission electron microscopy technology. The Ru( bpy)(3)(2+)-doped interior maintained its high ECL efficiency, while the exterior nanosilica prevented the luminophor from leaching out into the aqueous solution due to the electrostatic interaction. This is the first attempt to branch out the application of RuDS nanoparticles into the field of ECL, and since a large amout of Ru(bpy)(3)(2+) was immobilized three-dimensionally on the electrode, the Ru( bpy)(3)(2+) ECL signal could be enhanced greatly, which finally resulted in the increased sensitivity. This sensor shows a detection limit of 2.8 nM for tripropylamine, which is 3 orders of magnitude lower than that observed at a Nafion-based ECL sensor. Furthermore, the present ECL sensor displays outstanding long-term stability.

Synthesis and characterization of soluble oligo (9,10-bisalkynylanthrylene)s

Soluble oligo(9,10-bialkynylanthryiene)s up to pentamers were synthesized by means of the Suzuki coupling reaction. A solution processed thin film field-effect transistor from pentamer OA-5b shows a charge carrier mobility of 2.95 x 10(-3) cm(2)/V center dot s.

Tunable photoluminescent and cathodoluminescent properties of ZnO and ZnO : Zn phosphors

ZnO and ZnO: Zn powder phosphors were prepared by the polyol-method followed by annealing in air and reducing gas, respectively. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and photoluminescence (PL) and cathodoluminescence ( CL) spectra, respectively. The results indicate that all samples are in agreement with the hexagonal structure of the ZnO phase and the particle sizes are in the range of 1-2 mu m. The PL and CL spectra of ZnO powders annealed at 950 degrees C in air consist of a weak ultraviolet emission band ( similar to 390 nm) and a broad emission band centered at about 527 nm, exhibiting yellow emission color to the naked eyes. When the sample was reduced at the temperatures from 500 to 1050 degrees C, the yellow emission decreased gradually and disappeared completely at 800 degrees C, whereas the ultraviolet emission band became the strongest. Above this temperature, the green emission ( similar to 500 nm) appeared and increased with increasing of reducing temperatures.

Synthesis and characterization of blue-light-emitting poly(aryl ether)s containing oligofluorenes in the main chain

A series of blue light-emitting poly(aryl ether)s (PAEs) containing ter- or pentafluorenes in the main chain have been synthesized via nucleophilic substitution polycondensation reaction. The energy levels of the polymers were tuned by introducing hole-transporting triaryamine groups in the side chains and/or incorporating electron-transporting oxadiazole segments in the main chain. The optical properties of the polymers are dominantly determined by the well-defined oligofluorene segments, and therefore all polymers show high photoluminescence quantum yield. Differential scanning calorimeter (DSC) characterizations indicate that they are vitrified polymers with high glass transition temperature (up to 156 degrees C). The polymers comprising pentafluorenes exhibit electroluminescent properties equal to or better than fully conjugated fluorene homopolymers. With the device structure of ITO/PEDOT:PSS/polymer/Ca/Al, an external quantum efficiency of 1.4% along with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.09) has

Tuning the saturated red emission: synthesis, electrochemistry and photophysics of 2-arylquinoline based iridium(III) complexes and their application in OLEDs

A series of novel iridium(III) complexes with two 2-arylquinoline derivatives as cyclometalated ligands and one monoanionic ligand, such as acetylacetonate (acac), N,N'-diethyldithiocarbamate (Et(2)dtc) and O,O'-diethyldithiophosphate (Et(2)dtp), as ancillary ligands have been synthesized and structurally characterized by H-1 NMR, MS and elemental analysis (EA). The cyclic voltammetry, absorption, emission and electroluminescence properties of these complexes were systematically investigated. Through extending pi-conjugation, introducing electron-donating groups in the ligand frame, or changing the ancillary ligands, the HOMO energy levels of the iridium(III) complexes can be tuned, while their LUMO levels remain little affected; in consequence, the emission wavelengths of the iridium(III) complexes can be tuned in the range 606-653 nm. The highly efficient organic light-emitting diodes (OLEDs) with saturated red emission have been demonstrated. A maximum current efficiency of 10.79 cd A(-1), at a current density of 0.74 mA cm(-2), with an emission wavelength of 616 nm and Commisioon Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which are very close to the National Television System Comittee (NSTC) standard red emission, have been achieved when using complex (DPQ)(2)Ir(acac) as a phosphor dopant.

Sol-gel synthesis and photoluminescence properties of spherical SiO2@LaPO4 : Ce3+/Tb3+ particles with a core-shell structure

LaPO4: Ce3+ and LaPO4: Ce3+, Tb3+ phosphor layers have been deposited successfully on monodispersed and spherical SiO2 particles of different sizes ( 300, 500, 900 and 1200 nm) through a sol - gel process, resulting in the formation of core - shell structured SiO2@ LaPO4: Ce3+/ Tb3+ particles. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microcopy (SEM), transmission electron microscopy (TEM), and general and time-resolved photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting SiO2@ LaPO4: Ce3+/ Tb3+ samples. The XRD results demonstrate that the LaPO4: Ce3+, Tb3+ layers begin to crystallize on the SiO2 templates after annealing at 700 degrees C, and the crystallinity increases on raising the annealing temperature. The obtained core - shell phosphors have perfectly spherical shape with a narrow size distribution, non-agglomeration, and a smooth surface. The doped rare-earth ions show their characteristic emission in the core - shell phosphors, i.e. Ce3+ 5d - 4f and Tb3+5D4 - F-7(J) (J = 6 - 3) transitions, respectively. The PL intensity of the Tb3+ increased on increasing the annealing temperature and the SiO2 core particle size.

Seed-mediated synthesis of branched gold nanoparticles with the assistance of citrate and their surface-enhanced Raman scattering properties

We report an easy synthesis of highly branched gold particles through a seed-mediated growth approach in the presence of citrate. The addition of citrate in the growth solution is found to be crucial for the formation of these branched gold particles. Their size can be varied from 47 to 185 nm. The length of the thumb-like branch is estimated to be between about 5 and 20 nm, and changes slightly as the particle size increases. Owing to these obtuse and short branches, their surface plasmon resonance displays a marked red-shift with respect to the normal spherical particles. These branched gold particles exhibit stronger SERS activity than the non-branched ones, which is most likely related to these unique branching features.

Silica supported submicron SiO2@Y2SiO5 : Eu3+ and SiO2@Y2SiO5 : Ce3+/Tb3+ spherical particles with a core-shell structure: Sol-gel synthesis and characterization

X-1-y(2)SiO(5):Eu3+ and X-1-Y2SiO5:Ce3+ and/or Tb3+ phosphor layers have been coated on nonaggregated, monodisperse, submicron spherical SiO2 particles by a sol-gel process, followed by surface reaction at high temperature (1000 degrees C), to give core/shell structured SiO2@Y2SiO5:Eu3+ and SiO2@Y2SiO5:Ce3+/Tb3+ particles. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), TEM, photoluminescence (PL), low voltage cathodoluminescence (CL), and time-resolved PL spectra and lifetimes are used to characterize these materials. The XRD results indicate that X-1-Y2SiO5 layers have been successfully coated on the sur- face Of SiO2 particles, as further verified by the FESEM and TEM images. The PL and CL studies suggest that SiO2@Y2SiO5:Eu3+, SiO2@Y2SiO5:Tb3+ (or Ce3+/Tb3+), and SiO2@Y2SiO5:Ce3+ core/shell particles exhibit red (Eu3+, 613 rim: D-5(0)-F-7(2)), green (Tb3+, 542nm: D-5(4)-F-7(5)), or blue (Ce3+, 450nm: 5d-4f) luminescence, respectively. Pl, excitation, emission, and time-resolved spectra demonstrate that there is an energy transfer from Ce3+ to Tb3+ in the SiO2@Y2SiO5:Ce3+,Tb3+ core/shell particles.

Highly efficient iridium(III) complexes with diphenylquinoline ligands for organic light-emitting diodes: Synthesis and effect of fluorinated substitutes on electrochemistry, photophysics and electroluminescence

A series of novel cyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline ligands with fluorinated substituent were prepared and characterized by elemental analysis, NMR and mass spectroscopy. The cyclic voltammetry, absorption, emission and electroluminescent properties of these complexes were systematically investigated. Electrochemical studies showed that the oxidation of the fluorinated complexes occurred at more positive potentials (in the range 0.57-0.69 V) than the unfluorinated complex 1 (0.42 V). In view of the energy level, the lowering of the LUMO by fluorination is significantly less than that of the HOMO. The weak and low energies absorption bands in the range of 300-600 nm are well resolved, likely associated with MLCT and (3)pi-pi* transitions. These complexes show strong orange red emission both in the solution and solid state. The emission maxima of the fluorinated complexes showed blue shift by 9, 24 and 15 nm for 2, 3 and 4, respectively, with respect to the unfluorinated analogous 1. Multilayered organic light-emitting diodes (OLEDs) were fabricated by using the complexes as dopant materials. Significantly higher performance and lower turn-on voltage were achieved using the fluorinated complexes as the emitter than that using the unfluorinated counterpart 1 under the same doping level.

Investigation of charge-carrier injection characteristics in NPB/Alq3 heterojunction devices

The effect of copper phthalocyanine (CuPc) and LiF interfacial layers on the charge-carrier injection in NN'-di(naphthalene-l-yl)N,N'-diphenyl-benzidine (NPB)/tris(8-hydroxyquinoline) aluminium (Alq(3)) organic heterojunction devices have been studied through the analysis of current-voltage characteristics. The investigation clearly demonstrated that the hole injection into NPB from anode is Fowler-Nordheim (FN) tunneling and the electron injection into Alq3 from cathode is Richardson-Schottky (RS) thermionic emission. The barrier heights obtained from the FN and RS models proved that the band alignments for charge-carrier injection are greatly improved by the CuPc and LiF interfacial layers, which should fully clarify the role of the interfacial layer on the improvement of device performance.

Tuning of emission: Synthesis, structure and photophysical properties of imidazole, oxazole and thiazole-based iridium (III) complexes

Three new iridium (III) complexes with two cyclometalated (CN)-N-boolean AND ligands (imidazole, oxazole and thiazole-based, respectively) and one acetylacetone (acac) ancillary ligand have been synthesized and fully characterized. The structure of the thiazole-based complex has been determined by single crystal X-ray diffraction analysis. The Ir center was located in a distorted octahedral environment by three chelating ligands with the N-N in the trans and C-C in the cis configuration. By changing the hetero-atom of (CN)-N-boolean AND ligands the order S, O and N, a marked and systematic hypsochromic shift of the maximum emission peak of the complexes was realized. The imidazole-based complex emits at a wavelength of 500 nm, which is in the blue to green region. The tuning of emission wavelengths is consistent with the variation of the energy gap estimated front electrochemistry results. An electroluminescent device using the thiazole-based complex as a dopant in the emitting layer has been fabricated. A highly efficient yellow emission with a maximum luminous efficiency of 9.8 cd/A at a current density of 24.2 mA/cm(2) and a maximum brightness of 7985 cd/m(2) at 19.6 V has been achieved.