First Total Synthesis of 7-Isovaleryloxy-8-methoxygirinimbine

© Georg Thieme Verlag Stuttgart New York Synthesis. We describe the first total synthesis of the pyrano[3,2- a ]carbazole alkaloid 7-isovaleryloxy-8-methoxygirinimbine, using a palladium(II)-catalyzed double C-H-bond activation for construction of the carbazole framework and a phenylboronic acid catalyzed annulation of the pyran ring as key steps

Device Optimization of Tris-Aluminum (Alq3) Based Bilayer Organic Light Emitting Diode Structures

In this work we present detailed analysis of the emitted radiation spectrum from tris(8-hydroxyquinoline) aluminum (Alq3) based bilayer OLEDs as a function of: the choice of cathode, the thickness of organic layers, and the position of the hole transport layer/Alq3 interface. The calculations fully take into account dispersion in the glass substrate, the indium tin oxide anode, and in the organic layers, as well as the dispersion in the metal cathode. Influence of the incoherent transparent substrate (1 mm glass substrate) is also fully accounted for. Four cathode structures have been considered: Mg/Ag, Ca/Ag, LiF/Al, and Ag. For the hole transport layer, N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) and N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) were considered. As expected, emitted radiation is strongly dependent on the position of the emissive layer inside the cavity and its distance from the metal cathode. Although our optical model for an OLED does not explicitly include exciton quenching in vicinity of the metal cathode, designs placing the emissive layer near the cathode are excluded to avoid unrealistic results. Guidelines for designing devices with optimum emission efficiency are presented. Finally, several different devices were fabricated and characterized and experimental and calculated emission spectra were compared

Transport properties of copper phthalocyanine based organic electronic devices

Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied experimentally in field-effect transistors and metal-insulator-semiconductor diodes at various temperatures. The electronic structure and the transport properties of CuPc attached to leads are calculated using density functional theory and scattering theory at the non-equilibrium Green's function level. We discuss, in particular, the electronic structure of CuPc molecules attached to gold chains in different geometries to mimic the different experimental setups. The combined experimental and theoretical analysis explains the dependence of the mobilityand the transmission coefficient on the charge carrier type (electrons or holes) and on the contact geometry. We demonstrate the correspondence between our experimental results on thick films and our theoretical studies of single molecule contacts. Preliminary results for fluorinated CuPc are discussed.Comment: 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topic

Directed emission of CdSe nanoplatelets originating from strongly anisotropic 2D electronic structure

ntrinsically directional light emitters are potentially important for applications in photonics including lasing and energy-efficient display technology. Here, we propose a new route to overcome intrinsic efficiency limitations in light-emitting devices by studying a CdSe nanoplatelets monolayer that exhibits strongly anisotropic, directed photoluminescence. Analysis of the two-dimensional k-space distribution reveals the underlying internal transition dipole distribution. The observed directed emission is related to the anisotropy of the electronic Bloch states governing the exciton transition dipole moment and forming a bright plane. The strongly directed emission perpendicular to the platelet is further enhanced by the optical local density of states and local fields. In contrast to the emission directionality, the off-resonant absorption into the energetically higher 2D-continuum of states is isotropic. These contrasting optical properties make the oriented CdSe nanoplatelets, or superstructures of parallel-oriented platelets, an interesting and potentially useful class of semiconductor-based emitters

Cytokinins shape plant-herbivore interactions in Nicotiana attenuata

Cytokinins (CK), a group of plant hormones, are well known for their functions in growth and development as well as in environmental interactions. Except for some prominent examples like green islands and leafgalls caused by endophytic insects via CK, only little is known about the function of CK in plantinsect interaction. In my thesis I have studied the role of CK in the ecological model plant Nicotiana attenuata and two of its most abundant specialized free living herbivores, the larvae of the tobacco hawkmoth Manduca sexta as well as the mirid bug Tupiocoris notatus. I studied the effect of herbivory on CK levels and CK pathway and used transgenic plants with altered CK biosynthesis or perception to demonstrate the effect of CK on expression of herbivore induced defenses (HID). HID follow a developmentally dependent concentrationgradient predicted by the Optimal Defense Theory: High concentrations of HID in young leaves with a higher value for the plants reproductive success, and low levels in old leaves. We observed that CK follow the same gradient and that increasing CK levels in old leaves was sufficient to increase HID levels in old leaves to levels comparable to young leaves. However, this increase in HID did not improve the plants resistance against herbivory. This is possibly due to CK simultaneously inhibiting senesce processes which might be an important part of a plants defense against specialized herbivores. T. notatus seems capable to actively manipulate these senescence processes via CK and stabilize nutrient levels in attacked leaves. With 15N labeled plants we could prove that T. notatus transfers the CK N6isopentenyladenine to its hostplant via its oral secretions. A phenomenon so far not described for free living insects. Based on my results I suggest that the role of CK goes far beyond the known cases of endophytes and that CK have rather a key role in the interaction of plants and insects