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Electronic Energy Levels (electronic + energy_level)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Electronic Energy Levels in all- trans Long Linear Polyenes: The Case of the 3,20-Di(tert -butyl)-2,2,21,21-tetramethyl-all- trans -3,5,7,9,11,13,15,17,19-docosanonaen (ttbp9) Conforming to Kasha's Rule

CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2005
Javier Catalán Prof. Dr.
Abstract The absorption, fluorescence and fluorescence excitation spectra for 3,20-di(tert -butyl)-2,2,21,21-tetramethyl-all- trans -3,5,7,9,11,13,15,17,19-docosanonaen (ttbP9) in dilute solutions of 2-methylbutane were recorded at temperatures over the range 120,280 K. The high photostability of this nonaene allows us to assert that it exhibits a single fluorescence and that this can be unequivocally assigned to emission from its 11Bu excited state, it being the first excited electronic state. Available photophysical data for this polyene and the wealth of information reported for shorter all- trans polyenes allow us to conclude that if the first excited electronic state for the chromophore possessed 21Ag symmetry, then the energy of such a state might have been so close to that of the 11Bu state that: 1) the radiationless internal conversion mechanism would preclude the observation of the emission from the 11Bu state reported in this work and 2) the 21Ag state reached through internal conversion would be vibrationally coupled to 11Bu and would facilitate the detection of the emission from 21Ag, which was not observed in any of the solvents used in this work. The spectroscopic and photochemical implications of these findings for other polyenes are discussed. [source]

Low Bandgap Polymers by Copolymerization of Thiophene with Benzothiadiazole

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2009
Youjun He
Abstract Three low bandgap copolymers of thiophene and benzothiadiazole with electron-donating and electron-withdrawing substituents, P1, P2, and P3, have been synthesized by Pd-catalyzed Stille-coupling. Electronic energy levels of the polymers are estimated by cyclic voltammetry. The polymer films show a broad absorption band in the wavelength range from 300 to 750 nm. Among the polymers, the polymer that contains the 5,6-dinitrobenzothiadiazole unit, P3, possesses the smallest bandgap of 1.55 eV calculated from its absorption band-edge at ,800 nm. With the increase of the electron-withdrawing ability of the substituents on the benzothiadiazole unit, the energy bandgap of the polymers decreased in the order P1,>,P2,>,P3. The results indicate that stronger electron-withdrawing substituents on the acceptor unit can effectively decrease the bandgap of the polymers. [source]

High-Yield Synthesis and Electrochemical and Photovoltaic Properties of Indene-C70 Bisadduct

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2010
Youjun He
Abstract [6, 6]-Phenyl-C61 -butyric acid methyl ester (PC60BM) is the widely used acceptor material in polymer solar cells (PSCs). Nevertheless, the low LUMO energy level and weak absorption in visible region are its two weak points. For enhancing the solar light harvest, the soluble C70 derivative PC70BM has been used as acceptor instead of PC60BM in high efficiency PSCs in recent years. But, the LUMO level of PC70BM is the same as that of PC60BM, which is too low for the PSCs based on the polymer donors with higher HOMO level, such as poly (3-hexylthiophene) (P3HT). Here, a new soluble C70 derivative, indene-C70 bisadduct (IC70BA), is synthesized with high yield of 58% by a one-pot reaction of indene and C70 at 180 °C for 72 h. The electrochemical properties and electronic energy levels of the fullerene derivatives are measured by cyclic voltammetry. The LUMO energy level of IC70BA is 0.19 eV higher than that of PC70BM. The PSC based on P3HT with IC70BA as acceptor shows a higher Voc of 0.84 V and higher power conversion efficiency (PCE) of 5.64%, while the PSC based on P3HT/PC60BM and P3HT/PC70BM displays Voc of 0.59 V and 0.58 V, and PCE of 3.55% and 3.96%, respectively, under the illumination of AM1.5G, 100 mW cm,2. The results indicate that IC70BA is an excellent acceptor for the P3HT-based PSCs and could be a promising new acceptor instead of PC70BM for the high performance PSCs based on narrow bandgap conjugated polymer donor. [source]

Intrinsic Surface Dipoles Control the Energy Levels of Conjugated Polymers

ADVANCED FUNCTIONAL MATERIALS, Issue 24 2009
Georg Heimel
Abstract Conjugated polymers are an important class of materials for organic electronics applications. There, the relative alignment of the electronic energy levels at ubiquitous organic/(in)organic interfaces is known to crucially impact device performance. On the prototypical example of poly(3-hexylthiophene) and a fluorinated derivative, the energies of the ionization and affinity levels of , -conjugated polymers are revealed to critically depend on the orientation of the polymer backbones with respect to such interfaces. Based on extensive first-principles calculations, an intuitive electrostatic model is developed that quantitatively traces these observations back to intrinsic intramolecular surface dipoles arising from the , -electron system and intramolecular polar bonds. The results shed new light on the working principles of organic electronic devices and suggest novel strategies for materials design. [source]

Engineering the line up of electronic energy levels at inorganic,organic semiconductor interfaces by variation of surface termination and by substitution

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2008
Thomas Mayer
Abstract In the Anderson model the alignment of electronic energy levels follows from the assumption that the vacuum-levels of the contacting phases are at equal height. Engineering of the line up may be attempted by changing the ionization energy of the substrate and/or of the adsorbate. We report on the variation of the Si(111) ionization energy by induced surface dipoles of ,CH3, ,H, and ,GaSe terminations and the induced variation of the HOMO line up of PTCDA and ZnPc layers. In addition the variation of the line up by changing the organic molecule ionization energy is exemplified by F substitution in ZnPc. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]