Band Gap Tunable, Donor-Acceptor-Donor Charge-Transfer Heteroquinoid-Based Chromophores: Near Infrared Photoluminescence and Electroluminescence

A series of D-pi-A-pi-D type of near-infrared (NIR) fluorescent compounds based on benzobis(thia diazole) and its selenium analogues were synthesized and fully characterized by H-1 and C-13 NMR, high-resolution mass spectrometry, and elemental analysis. The absorption fluorescence, and electrochemical properties were also studied. Photoluminescence of these chromophores ranges from 900 to 1600 nm and their band gaps are between 1.19 and 0.56 eV.

Enhanced amplified spontaneous emission by assistant Forster energy transfer in DCJTB-C545T-Alq(3) coguest-host system

Amplified spontaneous emission (ASE) characteristics of a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were significantly improved by assistant Forster energy transfer. The coguest-host system was composed of an electron transport organic molecule tris(8-hydroxyquinoline) aluminum (Alq(3)) as host and a green fluorescent dye (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one) (C545T) as assistant dopant codoped with the guest red dye DCJTB as emitter in a matrix of polystyrene (PS).

Mechanisms of efficiency enhancement in the doped electroluminescent devices based on a europium complex

In this study, we investigated the dependence of electroluminescence (EL) efficiency on carrier distribution in the light-emitting layer (EML) of the device based on Eu(TTA)(3)phen (TTA = thenoyltrifluoroacetone, phen = 1, 10-phenanthroline) doped 4,4'-N,N'-dicarbazole- biphenyl (CBP) system. We found that EL efficiency increases monotonously with increasing hole injection even when holes are the majority carriers. This phenomenon was attributed to the accumulation of holes in EML, which improves the balance of holes and electrons on Eu(TTA)(3)phen molecules, thus enhancing the EL efficiency.

Gold nanoparticle-based near-infrared fluorescent detection of biological thiols in human plasma

In this work, a new fluorescent method for sensitive detection of biological thiols in human plasma was developed using a near-infrared (NIR) fluorescent dye, FR 730. The sensing approach was based on the strong affinity of thiols to gold and highly efficient fluorescent quenching ability of gold nanoparticles (Au NPs). In the presence of thiols, the NIR fluorescence would enhance dramatically due to desorption of FR 730 from the surfaces of Au NPs, which allowed the analysis of thiol-containing amino acids in a very simple approach. The size of Au NPs was found to affect the fluorescent assay and the best response for cysteine detection was achieved when using Au NPs with the diameter of 24 nm, where a linear range of 2.5 x 10(-8) M to 4.0 x 10(-6) M and a detection limit of as low as 10 nM was obtained. This method also demonstrated a high selectivity to thiol-containing amino acids due to the strong affinity of thiols to gold.

Counterions in polyelectrolyte multilayers: A vehicle for introducing functionalities

Counterions present at the surface of polyelectrolyte multilayers were utilized for the introduction of charged species into the multilayer via ion exchange. A typical polyelectrolyte multilayer film with Na+ counterions in the outermost layer was immersed in an AgNO3 aqueous solution and the rapid ion-exchange process was complete within 1 min. The silver ions thus introduced were then reduced in situ and silver nanoparticles were produced at the surface of the multilayer assembly. This example demonstrates that the counterions naturally occurring in every polyelectrolyte multilayer film can be a convenient vehicle for the introduction of various functionalities to the film.

Surface enhanced Raman scattering of brilliant green on ag nanoparticles and applications in living cells as optical probes

In this article, surface enhanced Raman scattering (SERS) of different concentrations of brilliant green (13G) on Ag nanoparticles (AgNPs) has been investigated. The results indicate that only 10(-12) M BG can be detected on AgNPs while as low as 10(-11) M BG can be detected upon the activation of AgNPs by chloride ions. The additional improvement of the detection of BG mainly derives from the increase of the electromagnetic field around AgNPs and partially from the reorientation of BG on AgNPs induced by chloride ions, which was proved by the different spectra feature in the two systems. Adsorption of BG on AgNPs has also been demonstrated in applications of living cells as optical probes based on SERS, indicating that dye-AgNPs can probe the local environment in the living cells. The related cytotoxicity measurements demonstrated that BG-AgNPs produced little cytotoxicity to the cells, which shows great potential in biornedical applications of BG labeled-AgNPs for SERS nanosensors in cells as optical probes. Meanwhile, SERS spectra of BG on AgNPs in the presence chloride ions are expected to be used in living cells as more sensitive optical probes.

Sensitive, selective and label-free protein detection using a smart polymeric transducer and aptamer/ligand system

We have demonstrated a smart polymeric transducer and aptamer/intercalating dye system that allows the label-free detection of protein with high sensitivity and selectivity.

A plasma sputtering decoration route to producing thickness-tunable ZnO/TiO2 core/shell nanorod arrays

We report a radio frequency magnetron sputtering method for producing TiO2 shell coatings directly on the surface of ZnO nanorod arrays. ZnO nanorod arrays were firstly fabricated on transparent conducting oxide substrates by a hydrothermal route, and subsequently decorated with TiO2 by a plasma sputtering deposition process. The core/shell nanorods have single-crystal ZnO cores and anatase TiO2 shells. The shells are homogeneously coated onto the whole ZnO nanorods without thickness change. This approach enables us to tailor the thickness of the TiO2 shell for desired photovoltaic applications on a one-nanometer scale. The function of the TiO2 shell as a blocking layer for increasing charge separation and suppression of the surface recombination was tested in dye-sensitized solar cells. The enhanced photocurrent and open-circuit voltage gave rise to increased photovoltaic efficiency and decreased dark current, indicating successful functioning of the TiO2 shell.

Synthesis of symmetric H-shaped block copolymer by the combination of ATRP and living anionic polymerization

A novel fluorescent dye labeled H-shaped block copolymer, (PMMA-Fluor-PS)(2)-PEO-(PS-Fluor-PMMA)(2), is synthesized by the combination of atom transfer radical polymerization (ATRP) and anionic polymerization (AP). To obtain the designated structure of the copolymer, a macroinitiator, 2,2-dichloro acetyl-PEO-2,2-dichloro acetyl (DCA-PEO-DCA), was prepared from DCAC and poly(ethylene oxide). The copolymer was characterized by H-1 NMR, GPC and fluorescence spectroscopy.

Surface enhanced Raman scattering of brilliant green on ag nanoparticles and applications in living cells as optical probes

In this article, surface enhanced Raman scattering (SERS) of different concentrations of brilliant green (13G) on Ag nanoparticles (AgNPs) has been investigated. The results indicate that only 10(-12) M BG can be detected on AgNPs while as low as 10(-11) M BG can be detected upon the activation of AgNPs by chloride ions. The additional improvement of the detection of BG mainly derives from the increase of the electromagnetic field around AgNPs and partially from the reorientation of BG on AgNPs induced by chloride ions, which was proved by the different spectra feature in the two systems. Adsorption of BG on AgNPs has also been demonstrated in applications of living cells as optical probes based on SERS, indicating that dye-AgNPs can probe the local environment in the living cells. The related cytotoxicity measurements demonstrated that BG-AgNPs produced little cytotoxicity to the cells, which shows great potential in biornedical applications of BG labeled-AgNPs for SERS nanosensors in cells as optical probes. Meanwhile, SERS spectra of BG on AgNPs in the presence chloride ions are expected to be used in living cells as more sensitive optical probes.

Conversion process of the dominant electroluminescence mechanism in a molecularly doped organic light-emitting device with only electron trapping

In this work, the detailed conversion process of the dominant electroluminescence (EL) mechanism in a device with Eu(TTA)(3)phen (TTA=thenoyltrifluoroacetone, phen=1,10-phenanthroline) doped CBP (4,4(')-N,N-'-dicarbazole-biphenyl) film as the emitting layer was investigated by analyzing the evolution of carrier distribution on dye and host molecules with increasing voltage. Firstly, it was confirmed that only electrons can be trapped in Eu(TTA)(3)phen doped CBP. As a result, holes and electrons would be situated on CBP and Eu(TTA)(3)phen molecules, respectively, and thus creates an unbalanced carrier distribution on both dye and host molecules. With the help of EL and photoluminescence spectra, the distribution of holes and electrons on both Eu(TTA)(3)phen and CBP molecules was demonstrated to change gradually with increasing voltage. Therefore, the dominant EL mechanism in this device changes gradually from carrier trapping at relatively low voltage to Forster energy transfer at relatively high voltage.

Change of the dominant luminescent mechanism with increasing current density in molecularly doped organic light-emitting devices

We have fabricated and measured a series of electroluminescent devices with the structure of ITO/TPD/Eu(TTA)(3)phen (x):CBP/BCP/ ALQ/LiF/Al, where x is the weight percentage of Eu(TTA)3phen (from 0% to 6%). At very low current density, carrier trapping is the dominant luminescent mechanism and the 4% doped device shows the highest electroluminescence (EL) efficiency among all these devices. With increasing current density, Forster energy transfer participates in EL process. At the current density of 10.0 and 80.0mA/ cm(2), 2% and 3% doped devices show the highest EL efficiency, respectively. From analysis of the EL spectra and the EL efficiency-current density characteristics, we found that the EL efficiency is manipulated by Forster energy transfer efficiency at high current density. So we suggest that the dominant luminescent mechanism changes gradually from carrier trapping to Forster energy transfer with increasing current density. Moreover, the conversion of dominant EL mechanism was suspected to be partly responsible for the EL efficiency roll-off because of the lower EL quantum efficiency of Forster energy transfer compared with carrier trapping.

Improved color purity and efficiency by a coguest emitter system in doped red light-emitting devices

We demonstrate red organic light-emitting diodes (OLEDs) with improved color purity and electroluminescence (EL) efficiency by codoping a green fluorescent sensitizer 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1, 1, 7,7-tetramethyl-1H, 5H, 11H-(1)-benzopyropyrano(6,7-8-ij)quinolizin-11-one (C545T) as the second dopant and a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the lumophore into tris(8-hydroquinoline) aluminum (Alq(3)) host. It was found that the C545 T dopant did not by itself emit but assisted the carrier trapping from the host Alq(3) to the red emitting dopant. The red OLEDs realized by this approach not only kept the purity of the emission color, but also significantly improved the EL efficiency. The current efficiency and power efficiency, respectively, reached 12 cd/A at a current density of 0.3 mA/cm(2) and 10lm/W at a current density of 0.02 mA/cm(2), which are enhanced by 1.4 and 2.6 times compared with devices where the emissive layer is composed of the DCJTB doped Alq(3), and a stable red emission (chromaticity coordinates: x = 0.64, y = 0.36) was obtained in a wide range of voltage. Our results indicate that the coguest system is a promising method for obtaining high-efficiency red OLEDs.

Evaluation of different culture conditions for high-level soluble expression of human cyclin A(2) with pET vector in BL21 (DE3) and spectroscopic characterization of its inclusion body structure

In this paper, we evaluated various parameters of culture condition affecting high-level soluble expression of human cyclin A, in Escherichia coli BL21(DE3), and demonstrated that the highest protein yield was obtained using TB(no glycerol) + 0.5% glucose medium at 25 degrees C. By single immobilized metal ion affinity chromatography, we got highly purified human cyclin A(2) with a yield ranged from 20 to 30 mg/L. By amyloid-diagnostic dye ThT binding and Fourier transform infrared spectroscopy, we observed a significant decrease in alpha-helix content and an increase in beta-sheet structure in cyclin A(2) inclusion body in comparison to its native protein, and confirmed the resemblance of the internal organization of cyclin A(2) inclusion body and amyloid fibrils.

Electrostatic assembly of polyaniline and platinum-poly(amidoamine) dendrimers hybrid nanocomposite multilayer, and its electrocatalysis towards CO and O-2

The electrostatic layer-by-layer assembly method was successfully used in a multilayer buildup of polyaniline (PANT) and platinum nanocrystals encapsulated in the carboxyl-terminated poly(amidoamine) dendrimers (generation 4.5 G4.5COOH) (Pt-G4.5COOH NPs) on solid substrates. Multilayer growth was monitored by ultraviolet-visible (UV-vis) absorption spectroscopy. The AFM observation revealed a molecularly smooth (PANI/Pt-G4.5COOH NPs) multilayer film which is rougher and thicker than the multilayer of PANT and G4.5COOH (G4.5COOH/PANI)(m). The PANI/Pt-G4.5COOH NPs multilayers show a fast surface-confined electron-exchange process at the Au electrode in an acid solution, and remains stable, reversible and electroactive, even in neutral solution. Furthermore, the multilayers show a strong elect rocatalytic response towards CO oxidation and O-2 reduction, and the catalytic capability can be easily tuned by the control of multilayer thickness.