Intramolecular electron transfer defined

Now, as we have defined wire-like transport by a motion that is assisted by molecular bridges, we may proceed to the mechanistic point of view. In particular, we will contrast theoretical results with experimental data for molecular wire-like behavior in regard to the transfer of electronic charge and/or energy. Intramolecular electron-transfer (ET) rate constants characterize the charge transport in DBA conjugates and in electronic transport junction we can apply the word conductance . 

Excited state lifetime tq is another important parameter to be controlled, especially if the photoactive complex is intended for bimolecular photochemical electron transfer. MLCT excited states of most polypyridine complexes decay both radia-tively and non-radiatively, with the respective rate constants and k r. The inherent excited state lifetime is defined as tq = l/( r + nr)- The non-radiative decay pathway in most cases prevails k r K. Hence To = 1 /km- Non-radiative decay of MLCT excited states can be treated as intramolecular electron transfer in the Marcus inverted region ... 

The concept of valence tautomerism was introduced to define the properties of a molecular adduct A — D+ (A = acceptor, D = donor) whose electronic ground state is described by two or more isomers with different charge distributions. The interconversion between different valence tautomers is accomplished by an intramolecular electron transfer according to the following equation A-(D+) (A+)-D. To... 

Reaction (4) implies a weak associative interaction, erroneously defined previously as of outer-sphere type (76). Encounter complexes have heen described and characterized in the nitrosylation/denitrosylation reactions of aromatic compounds and were proposed to he inner-sphere adducts containing weakly bound NO (77). They were considered as immediate precursors of transition states for intramolecular electron transfer, as in reaction (5). The equifihrium constants for reactions (6—7) should be high. The ligand interchange within the adduct-complex, reaction (6), is rate-controlled by the cleavage of the Fe —H2O bond, coupled to a fast NO -coordination. Therefore, for the kinetic analysis, processes (6—7) could be collected into a single kinetic constant fe h20-... 

In the MO theory, the most reliable approach for the study of reaction pathways perhaps is CASSCF [12, 13], but multi-VBSCF is essentially at the same level with CASSCF [14]. Since a VB wave function can be expanded into the combination of numerous Slater determinants that are used to define configurations in the MO theory, the VB theory provides a very compact, accurate description for chemical reactions. While both MO and VB theories have their own advantages as well as disadvantages, in our opinions, there are some areas where the VB theory is particularly superior to the MO theory 1) the refinement of molecular mechanics force field 2) the development of empirical or semi-empirical VB approaches 3) the impact of intermolecular charge transfer or intramolecular electron delocalization on the structure and properties 4) the validation of classical chemical theories and concepts at the quantitative level 5) the elucidation of chemical reactions and excited states intuitively. 

Evaluation of solvent-sensitive properties requires well-defined referena i ran eis. A macroscopic parameter, dielectric constant, does not always give interpretable correlations of data. The first microscopic measure of solvent polarity, the Y-value, based on the solvolysis rate of t-butyl chloride, is particularly valuable for correlating solvolysis rates. Y-values are tedious to measure, somewhat complicated in physical basis, and characterizable for a limited number of solvents. The Z-value, based on the charge-transfer electronic transition of l-ethyl-4-carbomethoxy-pyridinium iodide , is easy to measure and had a readily understandable physical origin. However, non-polar solvent Z-values are difficult to obtain b use of low salt solubility. The Et(30)-value , is based on an intramolecular charge-transfer transition in a pyridinium phenol b ne which dissolves in almost all solvents. We have used the Er(30)-value in the studies of ANS derivatives as the measure of solvent polarity. Solvent polarity is what is measured by a particular technique and may refer to different summations of molecular properties in different cases. For this reason, only simple reference processes should be used to derive solvent parameters. 

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