Moiety, electron transport

Electron-hopping is the main charge-transport mechanism in ECHB materials. There is precedence in the photoconductivity Held for improved charge transport by incorporating a number of redox sites into the same molecule. A number of attempts to adapt this approach for ECHB materials have been documented. Many use the oxadiazole core as the electron-transport moiety and examples include radialene 40 and dendrimer 41. However, these newer systems do not offer significant improvements in electron injection over the parent PBD. 

Thiophene-S,S-Dioxides as Emissive and Electron Transport Moieties... 

Keywords Device performance Electron-transport moiety Hole-transport moiety Polyfluorenes Polymer light-emitting diode... 

The corresponding response surface plot of the fit to the luminance efficiency (Fig. 11.14(b)) also shows that the concentration of the electron-transporting moiety in the layer is the major parameter controlling the device performance. In fact, increasing the PBD concentration from 10 to 35 wt. % doubles the luminance efficiency. Also, the rather small scatter of the experimental data around the fitting function (calculated for a constant value of cIr) suggests, that the Ir(mp-py)3 concentration has only a weak influence on the device efficiency. However, there are few data points situated well above the fit, which were all measured for devices with Ir(mppy)3 concentrations less than 0.5 wt. %. Apparently,... 

Figure 19.1 Energy diagram of substituted PT 14b(PBET), 14c(PCBET)and9e(P30T). Reprinted with permission from S.-H. Ahn, M.-z. Czae, E.-R. Kim, H. Lee, S.-H. Han, J. Nob, M. Hara, Synthesis and characterization of soluble polythiophene derivatives containing electron-transporting moiety. Macromolecules, 34, 2522-2527 (2001). Copyright 2001 American Chemical Society.

Poly(arylene ethers) are obtained from -propyl isocyanate blocked highly aromatic bisphenols and difluoroarenes. In this manner polsrmers containing hole (electron) transport moieties are obtained (97). 

A hypothesis for the oxidation of purines in the presence of this enzyme has been elaborated by Bergmann and his colleagues. It postulates that the purine, often in one of its less prevalent tautomeric forms, is adsorbed on the protein, or the riboflavin coenzyme, of the enzyme then hydration occurs under the influence of the electronic field of the enz5rme, and this must involve a group that is not sterically blocked by the enzyme but which is accessible to the electron-transport pathway of the riboflavin moiety. Finally, the secondary alcohol is assumed to be dehydrogenated in this pathway to give a doubly... 

Figures 12-12 and 12-13 document that trap-free SCL-conduction can, in fact, also be observed in the case of electron transport. Data in Figure 12-12 were obtained for a single layer of polystyrene with a CF -substituted vinylquateiphenyl chain copolymer, sandwiched between an ITO anode and a calcium cathode and given that oxidation and reduction potentials of the material majority curriers can only be electrons. Data analysis in terms of Eq. (12.5) yields an electron mobility of 8xl0 ycm2 V 1 s . The rather low value is due to the dilution of the charge carrying moiety. The obvious reason why in this case no trap-limited SCL conduction is observed is that the ClVquatciphenyl. substituent is not susceptible to chemical oxidation.

As we already mentioned, electron-transporting properties of PPV polymers can be adjusted by introduction of an oxadiazole moiety in the polymer structure. A variety of PPV copolymers... 

Efficient blue emission and good electron affinity and electron-transporting properties were demonstrated for two fluorene copolymers with dicyanobenzene moiety in the main chain, 271a,b (Scheme 2.41) [363], Due to improved electron transport properties, the device... 

Due to relatively high electron affinity and very good PL efficiency, molecular materials based on oxadiazole, particularly, PBD (21) are among the most popular electron transport materials for OLEDs. The oxadiazole moieties, including PBD, were introduced as pendant... 

Introducing heteroaromatic moieties (mainly with N and, to a lesser extent, with O and S) in the backbone of the polymer or as a pendant group, can substantially modify the LUMO level of the materials, improving their electron-transport properties and facilitating electron injection in PLEDs, but the efficiencies still lag behind the other systems. 

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