Green Synthesis Of Polycyclic Benzimidazole Derivatives And Organic Semiconductors

Polycyclic benzimidazole derivatives, an important class of compounds in organic electronics and photovoltaics, were prepared using a solvent-free green process based on heating carboxylic acid anhydrides and arylene diamines in the presence of zinc acetate in the solid state. Products were isolated and purified directly by train sublimation of the crude reaction mixtures. The reaction conditions were optimized using various carboxylic acid anhydrides. Optical and electrochemical properties of these materials are also described

True Blue: Blue-emitting Aluminum(iii) Quinolinolate Complexes

Blue-emitting heteroleptic aluminum(III) bis(2-methyl-8-quinolinolate) phenolate complexes were synthesized. A tunable, blue-to-green emission is achieved by attaching electron-withdrawing modulators to the emisssive quinaldinate ligand. The electronic nature of modulator substituents attached to the position of the highest HOMO (highest occupied molecular orbital) density is used to modulate ligand HOMO levels to achieve effective emission tuning to obtain blue-emitting materials. Optical and electrochemical properties of the resulting complexes were investigated and compared to the results of density functional theory (DFT/B3LYP/6-31G*) studies. The resulting materials may find application as organic light-emitting device materials

Encapsulated Energy-transfer Cassettes With Extremely Well Resolved Fluorescent Outputs

This paper concerns the development of water-compatible fluorescent imaging probes with tunable photonic properties that can be excited at a single wavelength. Bichromophoric cassettes 1a-1c consisting of a BODIPY donor and a cyanine acceptor were prepared using a simple synthetic route, and their photophysical properties were investigated. Upon excitation of the BODIPY moiety at 488 nm the excitation energy is transferred through an acetylene bridge to the cyanine dye acceptor, which emits light at approximately 600, 700, and 800 nm, i.e., with remarkable dispersions. This effect is facilitated by efficient energy transfer that gives a quasi-Stokes shift between 86 and 290 nm, opening a huge spectral window for imaging. The emissive properties of the cassettes depend on the energy-transfer (ET) mechanism: the faster the transfer, the more efficient it is. Measurements of rates of ET indicate that a through-bond ET takes place in the cassettes la and 1b that is 2 orders of magnitude faster than the classical through-space, Forster ET. In the case of cassette 1c, however, both mechanisms are possible, and the rate measurements do not allow us to discern between them. Thus, the cassettes 1a-1c are well suited for multiplexing experiments in biotechnological methods that involve a single laser excitation source. However, for widespread application of these probes, their solubility in aqueous media must be improved. Consequently, the probes were encapsulated in calcium phosphate/silicate nanoparticles (diameter ca. 22 nm) that are freely dispersible in water. This encapsulation process resulted in only minor changes in the photophysical properties of the cassettes. The system based on cassette la was chosen to probe how effectively these nanoparticles could be used to deliver the dyes into cells. Encapsulated cassette la permeated Clone 9 rat liver cells, where it localized in the mitochondria and fluoresced through the acceptor part, i.e., red. Overall, this paper reports readily accessible, cyanine-based through-bond ET cassettes that are lypophilic but can be encapsulated to form nanoparticles that disperse freely in water. These particles can be used to enter cells and to label organelles

Ultrafast Dynamics Of Triplet Excitons In Alq(3)-bridge-pt(ii)porphyrin Electroluminescent Materials

Excited-state dynamics are crucial for maximizing the performance of organic light-emitting diodes (OLEDs). Because electron-hole recombination yields singlet and triplet excited states in a 3:1 ratio, it is important to harvest the energy of triplets in light-emitting processes. Self-assembled multichromophore electroluminescent materials consisting of a trisquinolinolate aluminum(III) (Alq(3)) donor, fluorene-based conjugated oligomers; as a bridge, and Pt(II)tetraphenylporphyrin as an acceptor and phosphorescent emitter are described. In these materials, the energy of singlet as well as triplet states is harvested and emitted as red phosphorescence from the porphyrin acceptor. Attention was devoted to the triplet exciton dynamics, which was investigated by ultrafast transient spectroscopy, and the observations are compared with phosphorescence in thin films and with electroluminescence from OLEDs. It was found that exothermicity of the forward Alq(3)-to-fluorene bridge triplet transfer appears to be a less stringent requirement for triplet transfer electroluminescence. In contradistinction, the energy alignment between the bridge and Pt(II)porphyrin emitter is of crucial importance. It is shown that the triplet exciton dynamics has a dominant effect on the electroluminescence properties of conjugated donor-bridge-acceptor materials. The triplet-energy transfer operates on an ultrafast time scale (k (TTET) = (4-6) x 10(10) s(-1)) and requires careful energy alignment of the components ((3)Delta E (D-B) approximate to (3)Delta E (B-A) \u3e= 0.1 eV) to prevent endothermic energy transfer and severe quenching of the electroluminescence. To the best of our knowledge, this is the first time triplet dynamics was directly observed in donor-acceptor electroluminescent materials and direct connection to device efficiency was established

Bright Deep Blue TADF OLEDs: The Role of Triphenylphosphine Oxide in NPB/TPBi:PPh3O Exciplex Emission

Very bright (≈14 000 cd m−2) deep blue exciplex organic light emitting diodes (OLEDs) peaking at ≈435 nm, where the photopic response is ≈0.033, and with CIE color coordinates (0.1525, 0.0820), are described. The OLED properties are interestingly linked to PPh3O (triphenylphosphine oxide) and attributes of the emitting layer (EML) comprising NPB interfacing host:guest TPBi:PPh3O 5:1 weight ratio. A neat PPh3O layer that is central for device performance follows the EML (NPB/TPBi:PPh3O 5:1/PPh3O). The bright electroluminescence originates from NPB/TPBi:PPh3O exciplexes involving triplets via thermally activated delayed fluorescence, as evident from the strong quenching of the photoluminescence (PL) by oxygen and interestingly, the monomolecular emission process. The transient PL decay times of a NPB/TPBi:PPh3O 5:1/PPh3O film are 43 ns in air versus 136, 610, and weak ≈2000 ns in N2. For comparison, the respective PL decay times of films of NPB:TPBi are 16 ns in air versus 131 and 600 ns in N2, and of NPB:PPh3O they are 29 ns in air versus 56, 483, and weak ≈2000 ns in N2. It is suspected that slow emitting states are associated with a PPh3O aggregate interacting with NPB

Synthesis and Studies of Materials for Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) are solid state lighting devices which offer many advantages in respect to current lighting and displays technologies. OLEDs offer low power consumption and a wide viewing angle, which make them a perfect replacement for liquid crystal displays (LCD). Since OLEDs emit light due to the process of electroluminescence, they do not need extra light sources to be used in small electronic displays or as stand alone pixels for television sets. In this past decade, OLEDs have also been speculated as replacements for light-bulbs and fluorescent tubes. Many reports have been published describing how to obtain white light from OLEDs (WOLEDs). However, to obtain pure white light and efficient lighting devices, researchers in organic electronics have studied many ways to properly utilize all primary colors (red, green and blue) that organic dyes can achieve. Since white light requires the combination of several colors, we have studied how to simply manipulate the highest occupied molecular orbitals in fluorescence aluminum(III) complexes. By introducing electro withdrawing groups on position five of 2-methyl-8-hydroxy-quinoline, we show that is possible to obtain roughly 40 nm blue-shifted emission (454 nm) from our complexes in respect to the emission of the parent 2-methyl-8-hydroxy-quinolinolate aluminum(III) complex (495 nm), achieving in this way true-blue fluorescent emitters that can be used for OLEDs. Another approach to obtain more colors and higher efficiency in OLEDs from organic compounds is to utilize phosphorescent dyes doped in appropriate hosts (PhOLEDs). Most deep blue (~ 420- 450 nm) emitters have high triplet-energies, rendering difficult the reward for hosts with at least 0.2 eV higher triplet energy, which could avoid back energy transfer and in consequence obtain higher external quantum efficiency from the OLEDs. We show that is possible to design hosts with high triplet energies and high electron mobilities, by introducing diphenylphosphine oxide moieties in the structure of biphenyl, fluorene, dibenzophosphole and benzene compounds. We were able to obtain triplet energies ranging between of 2.71 eV (457 nm) and 3.39 eV (365 nm) from the different fluorene, biphenyl and benzene compounds, each containing two diphenylphosphine oxide groups in their structure. We also show that is possible to use diphenylphosphine oxide in conjunction with carbazole, in order to prepare ambivalent hosts with a triplet energy of 2.86 eV. We also demonstrate that synthesizing compounds containing heavy atoms (i.e. bromine) and diphenylphosphine groups, it is possible to observe phosphorescence emission at room temperature in solutions and in solid state films (including OLEDs) without suffering from extreme quenching due to dioxygen. Finally, we show that utilizing triphenylphosphine oxide as a host in PhOLEDs, it is possible to obtain electrophosphorescence from compounds like tris(4-carbazol-9-yl-phenyl)amine (TCTA), bathocuproine (BCP), 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI), meta-biscarbazolylphenyl (m-CP), tris-(8-hydroxyquinoline) aluminum (Alq3) and other materials used regularly in OLEDs in roles other than emitters. This ability to obtain electrophosphorescence at room temperature from all-organic compounds opens the possibility to achieve white light by combining the characteristic broad phosphorescence from these compounds in a way that could cover the entire visible region

Analysis of non-covalent interactions between the nanoparticulate fillers and the matrix polymer as applied to shape memory performance

Non-covalent interactions between filler particles and polyurethanes were investigated using fluorescence emission spectroscopy. The results were used in the analysis of shape memory (SM) performance of polyurethanes. Composites of shape memory polyurethane (SMPU) and carbon nanofiber (CNF), oxidized carbon nanofiber (ox-CNF), organoclay, silicon carbide, and carbon black were prepared from diphenylmethane diisocyanate, 1,4-butanediol, and poly(caprolactone)diol. It was revealed by fluorescence emission spectroscopy that primarily the urethane groups located in the hard segments of SMPU interacted with the polar functional groups on filler particles. A close correlation between the extent of non-covalent filler-matrix interactions, soft segment crystallinity, and SM properties of polyurethane composites was discussed. It was observed that weak non-covalent interactions of polymer chains with CNF and SiC particles caused significant reductions in soft segment crystallinity of SMPU and hence the shape memory properties of the composites. © The Royal Society of Chemistry 2010.Las interacciones no covalentes entre las partículas de relleno y los poliuretanos se investigaron mediante espectroscopia de emisión de fluorescencia. Los resultados se utilizaron en el análisis del rendimiento de la memoria de forma (SM) de los poliuretanos. Se prepararon compuestos de poliuretano con memoria de forma (SMPU) y nanofibra de carbono (CNF), nanofibra de carbono oxidada (ox-CNF), organoarcilla, carburo de silicio y negro de humo a partir de diisocianato de difenilmetano, 1,4-butanodiol y poli(caprolactona)diol . La espectroscopia de emisión de fluorescencia reveló que principalmente los grupos de uretano ubicados en los segmentos duros de SMPU interactuaban con los grupos funcionales polares en las partículas de relleno. Se discutió una estrecha correlación entre el alcance de las interacciones matriz-relleno no covalentes, la cristalinidad del segmento blando y las propiedades SM de los compuestos de poliuretano. Se observó que las interacciones débiles no covalentes de las cadenas poliméricas con partículas CNF y SiC causaron reducciones significativas en la cristalinidad del segmento blando de SMPU y, por lo tanto, en las propiedades de memoria de forma de los compuestos. © La Real Sociedad de Química 2010.Universidad Nacional, Costa RicaEscuela de Químic

Bright Deep Blue TADF OLEDs: The Role of Triphenylphosphine Oxide in NPB/TPBi:PPh3O Exciplex Emission

Very bright (≈14 000 cd m−2) deep blue exciplex organic light emitting diodes (OLEDs) peaking at ≈435 nm, where the photopic response is ≈0.033, and with CIE color coordinates (0.1525, 0.0820), are described. The OLED properties are interestingly linked to PPh3O (triphenylphosphine oxide) and attributes of the emitting layer (EML) comprising NPB interfacing host:guest TPBi:PPh3O 5:1 weight ratio. A neat PPh3O layer that is central for device performance follows the EML (NPB/TPBi:PPh3O 5:1/PPh3O). The bright electroluminescence originates from NPB/TPBi:PPh3O exciplexes involving triplets via thermally activated delayed fluorescence, as evident from the strong quenching of the photoluminescence (PL) by oxygen and interestingly, the monomolecular emission process. The transient PL decay times of a NPB/TPBi:PPh3O 5:1/PPh3O film are 43 ns in air versus 136, 610, and weak ≈2000 ns in N2. For comparison, the respective PL decay times of films of NPB:TPBi are 16 ns in air versus 131 and 600 ns in N2, and of NPB:PPh3O they are 29 ns in air versus 56, 483, and weak ≈2000 ns in N2. It is suspected that slow emitting states are associated with a PPh3O aggregate interacting with NPB.</p

Selection of reference genes for qPCR in hairy root cultures of peanut

<p>Abstract</p> <p>Background</p> <p>Hairy root cultures produced via <it>Agrobacterium rhizogenes</it>-mediated transformation have emerged as practical biological models to elucidate the biosynthesis of specialized metabolites. To effectively understand the expression patterns of the genes involved in the metabolic pathways of these compounds, reference genes need to be systematically validated under specific experimental conditions as established by the MIQE (Minimum Information for Publication of Quantitative Real-Time PCR Experiments) guidelines. In the present report we describe the first validation of reference genes for RT-qPCR in hairy root cultures of peanut which produce stilbenoids upon elicitor treatments.</p> <p>Results</p> <p>A total of 21 candidate reference genes were evaluated. Nineteen genes were selected based on previous qPCR studies in plants and two were from the T-DNAs transferred from <it>A. rhizogenes</it>. Nucleotide sequences of peanut candidate genes were obtained using their homologous sequences in <it>Arabidopsis</it>. To identify the suitable primers, calibration curves were obtained for each candidate reference gene. After data analysis, 12 candidate genes meeting standard efficiency criteria were selected. The expression stability of these genes was analyzed using geNorm and NormFinder algorithms and a ranking was established based on expression stability of the genes. Candidate reference gene expression was shown to have less variation in methyl jasmonate (MeJA) treated root cultures than those treated with sodium acetate (NaOAc).</p> <p>Conclusions</p> <p>This work constitutes the first effort to validate reference genes for RT-qPCR in hairy roots. While these genes were selected under conditions of NaOAc and MeJA treatment, we anticipate these genes to provide good targets for reference genes for hairy roots under a variety of stress conditions. The lead reference genes were a gene encoding for a TATA box binding protein (<it>TBP2</it>) and a gene encoding a ribosomal protein (<it>RPL8C</it>). A commonly used reference gene <it>GAPDH </it>showed low stability of expression suggesting that its use may lead to inaccurate gene expression profiles when used for data normalization in stress-stimulated hairy roots. Likewise the <it>A. rhizogenes </it>transgene <it>rolC </it>showed less expression stability than <it>GAPDH</it>. This study proposes that a minimum of two reference genes should be used for a normalization procedure in gene expression profiling using elicited hairy roots.</p