Aromatic Units (aromatic + unit)

Distribution by Scientific Domains


Selected Abstracts


Copolymers of Cyclopentadithiophene and Electron-Deficient Aromatic Units Designed for Photovoltaic Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Johan C. Bijleveld
Abstract Alternating copolymers based on cyclopentadithiophene (CPDT) and five different electron-deficient aromatic units with reduced optical band gaps are synthesized via Suzuki coupling. All polymers show a significant photovoltaic response when mixed with a fullerene acceptor. The frontier orbital levels of the new polymers are designed to minimize energy losses by increasing the open-circuit voltage with respect to the optical band gap, while maintaining a high coverage of the absorption with the solar spectrum. The best cells are obtained for a copolymer of CPDT and benzooxadiazole (BO) with a band gap of 1.47,eV. This cell gives a short-circuit current of 5.4,mA cm,2, an open-circuit voltage of 0.78,V, and a fill factor of 0.6, resulting in a power conversion efficiency of about 2.5%. [source]


Sequence-Selective Peptide Recognition with Designed Modules

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2006
Mark Wehner
Abstract A concept for the rational design of sequence-selective peptide receptors has been extended: in addition to recognition modules for polar, aromatic and basic amino acids, the series has now been completed with new receptor units for apolar and acidic amino acids. The underlying strategy uses the intermolecular ,-sheet stabilization of a dipeptide as a prerequisite to bind its N-terminal amino acid side chain through a strategically placed recognition tip at the end of a U-turn protruding from the receptor moiety. Thus, a diaminopyrazole has been covalently attached to Kemp's triacid by way of a cyclic imide, while a meta -substituted aniline was coupled as an amide to the pendant third carboxylate arm, bringing the two aromatic units into a sub-van der Waals distance in a tight conformational lock. NMR titrations, Karplus analyses and Monte-Carlo simulations demonstrate the effective sequence-selective recognition of alanine-containing dipeptides. No example of such a rationally designed set of peptide receptors had existed previously. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Copolymers of Cyclopentadithiophene and Electron-Deficient Aromatic Units Designed for Photovoltaic Applications

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Johan C. Bijleveld
Abstract Alternating copolymers based on cyclopentadithiophene (CPDT) and five different electron-deficient aromatic units with reduced optical band gaps are synthesized via Suzuki coupling. All polymers show a significant photovoltaic response when mixed with a fullerene acceptor. The frontier orbital levels of the new polymers are designed to minimize energy losses by increasing the open-circuit voltage with respect to the optical band gap, while maintaining a high coverage of the absorption with the solar spectrum. The best cells are obtained for a copolymer of CPDT and benzooxadiazole (BO) with a band gap of 1.47,eV. This cell gives a short-circuit current of 5.4,mA cm,2, an open-circuit voltage of 0.78,V, and a fill factor of 0.6, resulting in a power conversion efficiency of about 2.5%. [source]


Self-Assembly of a Chiral Lipid Gelator Controlled by Solvent and Speed of Gelation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 38 2009
Pengchong Xue Dr.
Abstract Glutamine derivative 1 with two-photon absorbing units has been synthesized and was found to show gelation ability in some solvents. Its self-assembly in the gel phase could be controlled by the solvent and speed of gelation. For example, in DMSO the organogelator self-assembled into H-aggregates with weak exciton coupling between the aromatic moieties. On the other hand, in DMSO/diphenyl ether (1:9, v/v) the molecules formed 1D aggregates, but with strong exciton coupling due to the small distance between the chromophores. Moreover, the formation of these two kinds of aggregates could be adjusted by the ratio of DMSO to diphenyl ether. In DMSO/toluene, DMSO/butanol, DMSO/butyl acetate, and DMSO/acetic acid systems similar results were observed. Therefore, conversion of the packing model occurs irrespective of the nature of the solvent. Notably, a unique sign inversion in the CD spectra could be realized by controlling the speed of gelation in the DMSO/diphenyl ether (1:9, v/v) system. It was found that a low speed of gelation induces the gelator to adopt a packing model with strong ,,, interactions between the aromatic units. Moreover, the gels, when excited at 800,nm, emit strong green fluorescence and the quantum chemical calculations suggest that intramolecular charge transfer leads to two-photon absorption of the gelator molecule. [source]


2-Phenanthrenyl,DNA: Synthesis, Pairing, and Fluorescence Properties

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2009
Nikolay
Abstract Three 2,-phenanthrenyl- C -deoxyribonucleosides with donor (phenNH2), acceptor (phenNO2), or no (phenH) substitution on the phenanthrenyl core were synthesized and incorporated into oligodeoxyribonucleotides. Duplexes containing either one or three consecutive phenR residues, which were located opposite each other, were formed. Within these residues, the phenR residues are expected to recognize each other through interstrand stacking interactions, in much the same way as described previously for biphenyl DNA. The thermal, thermodynamic, and fluorescence properties of such duplexes were determined by UV melting analysis and fluorescence spectroscopy. Depending on the nature of the substituent, the thermal stability of single-modified duplexes can vary between ,2.7 to +11.3,°C in Tm and that of triple-modified duplexes from +7.8 to +11.1,°C. Van,t Hoff analysis suggested that the observed higher thermodynamic stability in phenH- and phenNO2 -containing duplexes is of enthalpic origin. A single phenH or phenNO2 residue in a bulge position also stabilizes a corresponding duplex. If a phenNO2 residue is placed in a bulge position next to a base mismatch this can lead, in a sequence-dependent manner, to duplex destabilization. The phenNO2 residue was found to be a highly efficient (10,100-fold) quencher of phenH and phenNH2 fluorescence if placed in the opposite position to the fluorophores. When phenH and phenNH2 residues were placed opposite each other, efficient quenching of phenH and enhancement of phenNH2 fluorescence was found, which is an indicator for electron- or energy-transfer processes between the aromatic units. [source]