HOMO and LUMO energy levels

When parameters of the Pariser-Parr-Pople configuration interaction molecular orbital (PPP-CI MO) method were modified so as to reproduce the Aol)s values for l,3-di(5-aryl-l,3,4-oxadiazol-2-yl)benzenes 16 and 17, the calculated HOMO and LUMO energy levels corresponded with the experimental ionization potential and electron affinity values. The relationships between the electrical properties and molecular structures for the dyes were investigated. The absorption maximum wavelengths for amorphous films were found to be nearly equal to those for solution samples <1997PCA2350>. 

Y. Xiao, W. Yu, S. Chua, and W. Huang, A novel series of copolymers containing 2,5-dicyano-l,4-phenylene vinylene — synthetic tuning of the HOMO and LUMO energy levels of conjugated polymers, Chem. Eur. J., 6 1318-1321, 2000. 

Bis(2-(2-hydroxphenyl)benzothiazolate)zinc(II) (Zn(BTZ)2, 85) is an excellent white emitter. The HOMO and LUMO energy levels of Zn(BTZ)2 are —5.41 eV and —2.65 eV, respectively. Just as was found by Zuppiroli et al. for Znq2 derivatives, Zhu et al., found that the electron transport of Zn(BTZ)2 is better than Alq3, though the electron injection barrier is higher for Zn(BTZ)2 [136]. This has been explained by the strong intermolecular interaction of Zn(BTZ)2 molecules. This same group has examined the use of Zn(BTZ)2 as an ETM in PLEDs and the results are consistent with those with SMOLEDs [137]. 

Matched HOMO and LUMO energy level with host materials. 

In poly[2,5-bis(3,4-ethylene-dioxy-2-thienyl)pyridine], a copolymer of thiophene and pyridine in a 2 1 ratio, the effective HOMO and LUMO energy levels of the ir-system are controlled in such a way that both p-doped and n-doped states are accessible (Scheme 9) [43]. The thin fdms display multicolor... 

As we have already seen, delocalization of electrons by conjugation decreases the energy difference between the HOMO and LUMO energy levels, and this leads to a red shift. Alkyl substitution on a conjugated system also leads to a (smaller) red shift, due to the small interaction between the cr-bonded electrons of the alkyl group with the K-bond system. These effects are additive, and the empirical Woodward-Fieser rules were developed to predict the 2max values for dienes (and trienes). Similar sets of rules can be used to predict the A ax values for a,P-unsaturated aldehydes and ketones (enones) and the Amax values for aromatic carbonyl compounds. These rules are summarized in Table 2.4. 

Cyclic voltammetry studies showed the ionization potential and electron affinity of each component of the molecule in solution. The HOMO and LUMO energy levels were estimated from the equations Ehomo = E x + 4.4 eV and Elumo = T 14+4.4 eV, where E(r]x and E%, were oxidation and reduction potentials with respect to the standard hydrogen electrode (SHE) and the value of 4.4 is the ionization potential for hydrogen in eV [94,95], The HOMO and LUMO energy levels of the methine dye (compound 6) (Scheme 13) were determined to be -5.82 and -3.48 eV, respectively, with respect to the vacuum level from... 

To describe the transport through a molecular system having HOMO and LUMO energy levels, one of the applicable models is the Franz two-band model.75-81 This model provides a non-parabolic energy-momentum E(k) dispersion relationship by considering... 

Fig. 2 Relative placement of HOMO and LUMO energy levels in a molecular dimer. The dashed lines indicate the energies for the homo-dimer. For the heterodimer, these levels are shifted up or down by e so that the band off-set is 2e. In the discussion, we assume that AEa = AEb. Shown also is the electron/hole configuration corresponding to state 3 = — .

Fig. 32 Typical electrophosphorescent multilayer device architecture composed of a hole injection layer (HIL), a hole transport layer (HTL), a emission layer (EL), a hole blocking layer (HBL), an electron blocking layer (EBL), and finally an electron transporting layer (ETL). Shown are the HOMO and LUMO energy levels of the corresponding molecules [77]. The vacuum level is assumed to be constant...

As stated above, the notions of n and p-type do not have the same meaning as for inorganic semiconductors. At the current state of the art, an organic n-type material is one in which electrons are more easily injected than holes. This is therefore more a matter of HOMO and LUMO energy level rather than possibility of doping. In other words, an n-type organic semiconductor is characterized by high electron affinity. 

It is evident from the above discussion that the threshold voltage, current density, power efficiency, luminous efficiency and, to some extent, device lifetime of OLEDs using organic low-molar-mass compounds, oligomers and polymers depends on intrinsic molecular properties, such as HOMO and LUMO energy levels, efficiency of hole and electron injection and subsequent transport, efficiency of singlet formation and fluorescence efficiency. The... 

Electronic states of the fused-silole-thiophene derivatives have been obtained by ab initio MO calculations on model compounds at the level of RHF/6-31G. Relative HOMO and LUMO energy levels derived from the MO calculations are given in Table 18 <2004OM5622>. 

Table 18 Relative HOMO and LUMO energy levels for slide derivatives and related energy levels derived from MO calculations at the level of RHF/ 6-31G (in units of eV)...

Remark In the terminology of HMOtheory, 7,(X) and 7 (X) corres pond to HOMO and LUMO energy levels. 

Heeger and coworkers adopted bithiophene as comonomer to copolymerize with fluorene and found that the EL emission can be tuned to emit green light with a peak at 493 nm and a shoulder at 515 nm [57]. The HOMO and LUMO energy levels of copolymer 26 are 5.30 and 2.85 eV, respectively, as estimated... 

Fig. 3 A schematic diagram showing the HOMO and LUMO energy levels of various polymers of fluorene and dibenzosilole, as well as the energy levels of PEDOT PSS and LiF/AI electrode. The energy levels of polymers 44 and 45 are reported in comparison to differing HOMO and LUMO levels for PF8 at - 5.80 and - 2.87 respectively [39,42]...

Figure 7.5 (a) Schematic showing HOMO and LUMO energy levels of CuPc and Qo- Energy levels are... 

Table 3.2 HOMO and LUMO energy levels, HOMO-LUMO energy gaps (Ee-l) of SiQDs with different surface passivations in their ground and first excited singlet states (unit eV). Note that HOMO and LUMO in excited state are actually two singly occupied orbitals [26]. Reprinted with permission from (Li QS, Zhang RQ, Lee ST, Niehaus TA, Frauenheim T (2008) Optimal surface functionalization of sihcon quantum dots, J Chem Phys 128 244714). Copyright (2008), American Institute of Physics...

Cyclic voltammetry experiments were earried out on an EG G Prineeton Applied Researeh Model potentio-stat/galvanostat at 20 1 °C under argon atmosphere. Eleetroehemieal experiments were carried out in a three-compartment three-eleetrode glass eell with an aqueous saturated calomel eleetrode as the referenee electrode. Platinum sheets were used both as the working eleetrode ( 4 = 1 cm ) and as the eounter eleetrode A = 2.83 cm ). The potentials are reported versus SCE (saturated ealomel electrode). Determination of the HOMO and LUMO energy levels was done using the following equations [16] ... 

Fig. 4.28 HOMO and LUMO energy levels of fluorenone are compared to the jt- and jt -band edges of PFO.

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