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Chromophore Units (chromophore + unit)
Selected AbstractsEfficient Photosensitized Splitting of Thymine Dimer by a Covalently Linked Tryptophan in Solvents of High PolarityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005Qin-Hua Song Abstract Tryptophan-thymine dimer model compounds used to mimic the repair reaction of DNA photolyase have been synthesized. The photosensitized cleavage of the dimer by the covalently linked tryptophan is strongly solvent-dependent with the reaction rates increasing in increasingly polar solvents, for example, the quantum yield , = 0.004 in THF/hexane (5:95) and 0.093 in water. The fluorescence of the tryptophan residue is quenched by the dimer moiety by electron transfer from the excited tryptophan to the dimer. Fluorescence-quenching studies indicated that the electron transfer was efficient in polar solvents. The splitting efficiency of the dimer radical anion within the tryptophan·+,dimer·, species is also remarkably solvent-dependent and increases with the polarity of the solvents. The back-electron-transfer reaction in the charge-separated species, which competes with cleavage, was suppressed in polar solvents. These results are in contrast to those of earlier solvent-dependent studies of indole-dimer systems, but they can be rationalized in terms of the differences in the distances between the chromophore unit and the attached dimer. The pH-dependent measurements of the splitting reaction and the deuterium isotope effect showed that the tryptophan radical cation within the charge-separated species does not deprotonate prior to the cleavage of the dimer radical anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Influence of azobenzene units on imidization kinetic of novel poly(ester amic acid)s and polymers properties before and after cyclodehydrationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Ewa Schab-Balcerzak Abstract In this article, the imidization reaction kinetic of novel poly(ester amic acid)s with azobenzene units as side groups was studied by dynamic experiments by means of differential scanning calorimetry. Polymers differ in the number of chromophore moieties in their repeating unit and position in which azobenzene group is attached to the polymer chain. The kinetic parameters of poly(ester amic acid)s conversion to poly(ester imide)s was compared with data calculated for parent polymer, that is, without azobenzene groups. For the first time to our knowledge, the imidization kinetic of polymers with side azobenzene groups was studied. Kinetic parameters, such as the activation energy and frequency factor were estimated with the by Ozawa model [(E(O) and A(O)), respectively] and Kissinger model [(E(K) and A(K), respectively]. The values of activation energy determined with both models were in the range 167.1,198.3 kJ/mol. The lowest activation energy of imidization reaction exhibited polymer in which azobenzene units were placed between amide linkages. Polymers were characterized by FTIR, 1H-NMR, X-ray, and UV,vis methods. The glass transition temperature of resultant poly(ester imide)s was in the range of 217,237°C. The presence of chromophore units slightly decreased Tg and significantly improved their solubility and optical properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Crosslinkable maleimide copolymers for stable NLO propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2001. E. Serhatli Abstract Second-order, nonlinear optical polymers based on epoxy-substituted methylvinylisocyanates and N -substituted maleimides were synthesized and characterized with spectral and thermal analysis. The photocrosslinking and thermal-crosslinking reactions of copolymers with different chromophore contents were studied. Thermally induced crosslinking during the poling process, performed at the glass-transition temperature (Tg), was prevented by Tg being decreased through the addition of a plasticizer. Electrooptic coefficients (r33), measured for crosslinked and noncrosslinked systems, had similar absolute values and relaxation dynamics. This behavior was explained in terms of the similar rotational mobility of the chromophore units and the paucity of crosslinking sites. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1589,1595, 2001 [source] Organic Nanomaterials: Morphological Control for Charge Stabilization and Charge TransportCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2009P. Pramod Dr. Abstract How grows it? Organic nanostructured materials have been projected as active components in optoelectronic devices. Recent efforts in manipulating the morphology of organic nanomaterials, particularly on their size and shape, are summarized in this Focus Review. Potential application of organic nanostructured materials in charge stabilization and transporting are also discussed. Chromophoric systems with proper recognition motifs can organize into well-defined arrays forming supramolecular assemblies and further into nanoscopic materials. The optical and electrical properties of organic nanomaterials depend upon the stacking modes of organic molecules and also on the kind of interaction between different chromophore units (such as H- and J- type aggregates). These types of aggregates can dramatically alter the opto-electronic properties of organic nanostructures. Hence efforts are currently directed towards manipulating the morphology of organic nanomaterials, particularly on their size and shape by adopting different techniques and these aspects are discussed. Recent studies have shown that such nanostructures are extremely important in the development of optoelectronic systems such as photovoltaic devices. This Focus Review also discusses the potential application of organic nanomaterials in charge stabilization and transport. [source] | |||||||||||||