Lowest unoccupied molecular orbital LUMO energy levels

The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of fluorenone are shown in Fig. 4.28. Consistent with charge trapping, the fluorenone defects function as both a hole trap and an electron trap the HOMO and LUMO of fluorenone fall within the Jt-it gap of PFO [47]. In addition, the hole (electron) can be injected from the PEDOT PSS (Ca) electrode directly into the HOMO (LUMO) of fluorenone because of the small energy barrier between PEDOT PSS and the HOMO (or between Ca and the LUMO) of fluorenone. 

The two electrode materials are in direct contact with the liquid electrolyte, an environment made up of molecular species, characterized by their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. Adding an electron to the electrolyte s LUMO results in the reduction of the latter, whereas removing an electron from its HOMO results in its oxidation. So long as the positive electrode material s Fermi level is situated above the electroljde s HOMO level, no electron transfer will occur from the electrolyte to the positive electrode, and the electrolyte remains electrochemically stable since it does not oxidize continually on contact with the electrode. This remains theoretically true for positive electrode materials whose potential does not exceed approximately 4.5 V versus Li /Li, which is the case for the usual materials, such as LiCo02. 

Although this reaction is exothermic (AH is generally between -50 and —65 kcal/ mol), it is characterized by high activation barrier (approximately 25 kcal/mol for methyl azide and propyne) that requires a high-temperature reaction to achieve satisfying reaction rates for inactivated reactants. Furthermore, because the differences between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for both azides and alkynes are of similar... 

The most extensive calculations of the electronic structure of fullerenes so far have been done for Ceo- Representative results for the energy levels of the free Ceo molecule are shown in Fig. 5(a) [60]. Because of the molecular nature of solid C o, the electronic structure for the solid phase is expected to be closely related to that of the free molecule [61]. An LDA calculation for the crystalline phase is shown in Fig. 5(b) for the energy bands derived from the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for Cgo, and the band gap between the LUMO and HOMO-derived energy bands is shown on the figure. The LDA calculations are one-electron treatments which tend to underestimate the actual bandgap. Nevertheless, such calculations are widely used in the fullerene literature to provide physical insights about many of the physical properties. 

In the course of investigation of reactivity of the mesoionic compound 44 (Scheme 2) the question arose if this bicyclic system participates in Diels-Alder reactions as an electron-rich or an electron-poor component <1999T13703>. The energy level of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals were calculated by PM3 method. Comparison of these values with those of two different dienophiles (dimethyl acetylenedicarboxylate (DMAD) and 1,1-diethylamino-l-propyne) suggested that a faster cycloaddition can be expected with the electron-rich ynamine, that is, the Diels-Alder reaction of inverse electron demand is preferred. The experimental results seemed to support this assumption. 

The fact that the electrochemical oxidation of ds-[M2(cp)2(/r-SR)2(CO)4] and of [M2(/r-SR)2(CO)8] is reversible despite the amount of structural reorganization involved suggests that these changes require low activation energy. Extended Htlckel Molecular Orbital (EHMO) calculations on the model complex ds-13 (R = H) indicated that the Lowest Unoccupied Molecular Orbital (LUMO) was the level [47]. Weakening of the... 

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