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Charge-transfer Reaction (charge-transfer + reaction)

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Chemistry100%

Selected Abstracts

Photoisomerization of a Maleonitrile-Type Salen Schiff Base and Its Application in Fine-Tuning Infinite Coordination Polymers

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2010
Chun-Wei Lin
Abstract Strategically designed salen ligand 2,3-bis[4-(di- p -tolylamino)-2-hydroxybenzylideneamino]maleonitrile (1), which has pronounced excited-state charge-transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z*,1E isomerization takes place by rotation about the C2C3 bond, which takes on single-bond character due to the charge-transfer reaction. The isomerization takes place nonadiabatically from the excited-state (1Z) to the ground-state (1E) potential-energy surface in the singlet manifold; 1Z and 1E are neither thermally inconvertible at ambient temperature (25,30,°C), nor does photoinduced reverse 1E*,1Z (or 1Z*) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a ZnII precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N,-dicyanoethenebis(salicylideneimine)dicarboxylic acid (2). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere- and needlelike nanostructure, respectively) of their infinite coordination polymers with ZnII. [source]

Transient Optical Studies of Interfacial Energetic Disorder at Nanostructured Dye-Sensitised Inorganic/Organic Semiconductor Heterojunctions

CHEMPHYSCHEM, Issue 1 2003
Saif A. Haque Dr.
Broadening needs energy: Hole-transfer reactions at a dye-sensitised nanocrystalline TiO2/organic hole-conductor (HTM) interface are mainly driven by the free energy difference ,G(dye-HTM). Inhomogeneous broadening of ,G(dye-HTM) controls the yield of this interfacial charge-transfer reaction (see picture, curve b) and is therefore an important limitation on the voltage output of photovoltaic devices based upon such interfaces. [source]

Primary Photophysical Processes in Photosystem II: Bridging the Gap between Crystal Structure and Optical Spectra

CHEMPHYSCHEM, Issue 6 2010
Thomas Renger Prof. Dr.
Abstract This Minireview summarizes our current knowledge of the optical properties of photosystem II (PS-II) and how these properties are related to the photosynthetic function, that is, excitation energy transfer from the antenna complexes to the reaction center (RC) and the subsequent transmembrane charge separation in the latter. Interpretation of the optical spectra of PS-II is much more difficult than for the RC of purple bacteria, due to the "spectral congestion" problem, namely, the strong spectral overlap of optical bands in PS-II. Recent developments in deciphering the optical properties of the pigments in PS-II, the identification of functional states, and the kinetic details of the primary excitation energy and charge-transfer reactions are summarized. The spectroscopic term P680 that is generally used in the literature no longer indicates the same entity in its cationic and singlet excited form but different subsets of the six innermost pigments of the RC. The accessory chlorophyll ChlD1 forms a sink for singlet excitation and triplet energy and most likely represents the primary electron donor in PS-II. In this respect, a special chlorophyll monomer in PS-II plays the role of the special pair in purple bacteria. Evidence that exciton transfer between the core antenna complexes CP43 and CP47 and the RC is the bottleneck for the overall photochemical trapping of excitation energy in PS-II is discussed. A short summary is provided of PS-II of Acaryochloris marina, which mainly contains chlorophyll d instead of the usual chlorophyll a. This system does not suffer from the spectral congestion problem and, therefore, represents an interesting model system. The final part of this Minireview provides a discussion of challenging problems to be solved in the future. [source]

Ionic Liquid for in situ Vis/NIR and Raman Spectroelectrochemistry: Doping of Carbon Nanostructures

CHEMPHYSCHEM, Issue 9 2003
Ladislav Kavan Prof. Dr.
Abstract 1-butyl-3-methylimidazolium tetrafluoroborate (an ionic liquid) is an advantageous electrolyte for the study of charge-transfer reactions at single-walled carbon nanotubes (SWCNTs) and fullerene peapods (C60@SWCNT). Compared to traditional electrolyte solutions, this medium offers a broader window of electrochemical potentials to be applied, and favorable optical properties for in situ Vis/NIR and Raman spectroelectrochemistry of nano-carbon species. The electrochemistry of both nanotubes and peapods is dominated by their capacitive double-layer charging. Vis/NIR spectroelectrochemistry confirms the charging-induced bleaching of transitions between Van Hove singularities. At high positive potentials, new optical transitions were activated in partly filled valence band. The bleaching of optical transitions is mirrored by the quenching of resonance Raman scattering in the region of tube-related modes. The Raman frequency of the tangential displacement mode of SWCNT shifts to blue upon both anodic and cathodic charging in the ionic liquid. The Raman modes of intratubular C60 exhibit a considerable intensity increase upon anodic doping of peapods. [source]