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HOMO Energies (homo + energy)
Terms modified by HOMO Energies Selected AbstractsStudy of Energy Transfer and Triplet Exciton Diffusion in Hole-Transporting Host MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Chao Wu Abstract A device structure is used in which the hole-transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL-host/hole blocker/electron-transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL-host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl- p- phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements. [source] Temperature-dependent kinetic study for ozonolysis of selected tropospheric alkenesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2002Elena V. Avzianova Ozonolysis reactions of alkenes are suggested to play major roles in the chemistry of the troposphere. Rate constants for the gas-phase reactions of O3 with a series of alkenes were determined using relative rate technique based on GC/FID measurements of alkene decays. Experiments were carried out in air over the temperature range of 278,353 K at an atmospheric pressure of 760 Torr. An excess of 1,3,5-trimethylbenzene was used as a HO radical scavenger in all experiments. Arrhenius parameters were calculated for ozonolysis of 1-butene, 1-pentene, 1-hexene, 1-heptene, 2-methyl-1-butene, isobutene, trans -2-butene, trans -2-pentene, cis -2-pentene, trans -2-hexene, cis -2-hexene, 3-chloropropene, 1,1-dichloroethene, and isoprene from temperature-dependent studies of the rate constants. The rate constants obtained in this study are compared with previous literature data. A good linear correlation between the logarithms of the rate constants and calculated HOMO energies of selected alkenes is observed. However, no clear correlation could have been drawn for chlorinated substituted alkenes. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 678,684, 2002 [source] Theoretical studies on the electronic and optical properties of two new alternating fluorene/carbazole copolymersJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2005Li Yang Abstract Poly(fluorene)-type materials are widely used in polymer-based emitting devices. During operation there appears, however, an additional emission peak at around 2.3 eV, leading to both a color instability and reduced efficiency. The incorporation of the carbazole units has been proven to efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate two series of alternating fluorene/carbazole oligomers and copolymers poly[2,7-(N-(2-methyl)-carbazole)- co - alt -2,7-m(9,9-dimethylfluorene)], namely, PFmCz (m = 1,2) and gain a detailed understanding of the influence of carbazole units on the electronic and optical properties of fluorene derivatives. The electronic properties of the neutral molecules, HOMO-LUMO gaps (,H-L), in addition to the positive and negative ions, are studied using B3LYP functional. The lowest excitation energies (Egs) and the maximal absorption wavelength ,abs of PFmCz (m = 1,2) are studied, employing the time-dependent density functional theory (TD-DFT). The properties of the two copolymers, such as ,H-L, Eg, IPs, and EAs were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n = 0). The outcomes showed that the carbazole unit is a good electron-donating moiety for electronic materials, and the incorporation of carbazole into the polyfluorene (PF) backbone resulted in a broadened energy gap and a blue shift of both the absorption and photoluminescence emission peaks. Most importantly, the HOMO energies of PF1Cz and PF2Cz are both a higher average (0.4 eV) than polyfluorene (PF), which directly results in the decreasing of IPs of about 0.2 eV more than PF, indicating that the carbazole units have significantly improved the hole injection properties of the copolymers. In addition, the energy gap tends to broaden and the absorption and emission peaks are gradually blue-shifted to shorter wavelengths with an increase in the carbazole content in the copolymers. This is due to the interruption of the longer conjugation length of the backbone in the (F1Cz)n series. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 969,979, 2005 [source] Structure-stability correlations for imine formation in aqueous solutionJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2005C. Godoy-Alcántar Abstract Imine formation between 25 aldehydes and 13 amines in aqueous solution in the pH range 7,11 was studied by 1H NMR spectroscopy. A three-parameter linear equation correlating logarithms of imine formation constants with pKa and HOMO energies of amines and LUMO energies of aldehydes is proposed. In view of the widespread occurrence of imine-forming processes in both chemistry and biology, the data presented are of significance for physical organic chemistry and of particular interest for dynamic combinatorial chemistry. Copyright © 2005 John Wiley & Sons, Ltd. [source] Tunable Injection Barrier in Organic Resistive Switches Based on Phase-Separated Ferroelectric,Semiconductor Blends,ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Kamal Asadi Abstract Organic non-volatile resistive bistable diodes based on phase-separated blends of ferroelectric and semiconducting polymers are fabricated. The polarization field of the ferroelectric modulates the injection barrier at the semiconductor,electrode contact and, hence, the resistance of the comprising diodes. Comparison between the on- and off-current of the switching diodes, with the current measured for semiconductor-only diodes reveals that the switching occurs between bulk-limited, i.e., space-charge-limited, and injection-limited current transport. By deliberately varying the HOMO energy of the semiconductor and the work-function of the metal electrode, it is demonstrated that injection barriers up to 1.6,eV can be surmounted by the ferroelectric polarization yielding on/off current modulations of more than five orders of magnitude. The exponential dependence of the current modulation with a slope of 0.25,eV/decade is rationalized by the magnitude of the injection barrier. [source] Organic Photovoltaic Cells Based On Solvent-Annealed, Textured Titanyl Phthalocyanine/C60 HeterojunctionsADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Diogenes Placencia Abstract Organic photovoltaic cells (OPV) with good near-IR photoactivity are created from highly textured titanyl phthalocyanine (TiOPc)/C60 heterojunctions. Vacuum deposited TiOPc thin films are converted to the near-IR absorbing "Phase II" polymorph using post-deposition solvent annealing. The Phase I,,,Phase II transition broadens the absorbance spectrum of the Pc film producing absorptivities (,,,,105,cm,1) from 600,900,nm, along with substantial texturing of the Pc layer. Atomic force microscopy and field-emission scanning electron microscopy of the solvent annealed films show that the surface roughness of the Pc layers is increased by a factor of greater than 2× as a result of the phase transformation. Current,voltage (J,V) responses for white light illumination of ITO (100,nm)/TiOPc (20,nm)/C60 (40,nm)/BCP (10,nm)/Al (100,nm) OPVs show a near doubling of the short-circuit photocurrent (JSC), with only a small decrease in open-circuit photopotential (VOC), and a concomitant increase in power conversion efficiency. Incident photon current efficiency (IPCE) plots confirmed the enhanced near-IR OPV activity, with maximum IPCE values of ca. 30% for devices using Phase II-only TiOPc films. UV-photoelectron spectroscopy (UPS) of TiOPc/C60 heterojunctions, for both Phase I and Phase II TiOPc films, suggest that the Phase II polymorph has nearly the same HOMO energy as seen in the Phase I polymorph, and similar frontier orbital energy offsets, EHOMOPc,ELUMOC60, leading to comparable open-circuit photovoltages. These studies suggest new strategies for the formation of higher efficiency OPVs using processing conditions which lead to enhance near-IR absorptivities, and extensive texturing of crystalline donor or acceptor films. [source] Substituent effects on ion complexation of para - tert -butylcalix[4]arene esters,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2006Márcio Lazzarotto Abstract Phenoxy-carboxy-methoxy- p-tert -butylcalix[4]arene esters were synthesized in order to evaluate the role of electronic parameters on the complexation of alkaline metal cations. Extraction constants of metal picrates to organic phase were determined. Plots of log (KR/KH) against Hammett , and , gave good linear correlations. The best correlations with , were obtained for K+ and Rb+, while the best correlations with , were obtained for Li+ and Na+. All Hammett plots gave a straight descending line, which is consistent with a dependence of the electronic density on the CO. Treatment of data using the Yukawa,Tsuno equation revealed a variation in the contribution of resonance in the complexation of alkaline metal ions, which is maximum for Na+ and minimum for Rb+. Electronic parameters were calculated for a related acyclic model structure and only the HOMO energy showed a good correlation with log (KR/KH). Copyright © 2007 John Wiley & Sons, Ltd. [source] Substituent effects on the photofading of disperse azo dyes on poly(ethylene terephthalate) substrateCOLORATION TECHNOLOGY, Issue 3 2010Yasuyo Okada The relationships between the chemical structures and oxidative fading of the disperse azo dyes, p -nitrophenylazo- and benzothiazoleazo-anilines, on poly(ethylene terephthalate) substrate are discussed in terms of the parameters k0,i (rate constants of reaction towards 1O2) and fi (photosensitivity), the molecular parameters of molecular orbital theory and substituents in the diazo and coupling components, on the assumption that the initial rates of oxidative fading are proportional to the product of k0,i and fi. 2-Methoxy-5-acetylamino- N -substituted aniline couplers exhibited large fi values. 2-Chloro and 4-nitro substituents of aniline diazo components exhibited small fi values or high quantum yields of internal conversion, while 4-nitro substituent did not. A close correlation between N -substituents and light fastness, proposed by Müller and supplemented by Dawson, demonstrates the applicability of frontier orbital theory, through the highest occupied molecular orbital (HOMO) energy of the dyes, to the analysis of oxidative fading. Dyes with N -2-cyanoethyl substituents, which gave a lower HOMO energy, also exhibited superior light fastness compared with N -2-hydroxyethyl substituents. [source] | ||||||||||