Charge transfer band shapes

The effects of temperature on the shape of intervalence charge-transfer bands for the radical cations of bis(2-f-butyl-2,3-diazabicyclo[2.2.2]oct-3-yl)hydrazines that are bridged by 2,5-xylene-1,4-diyl, durene-l,4-diyl, naphthalene-1,4-diyl, biphenyl-4,4-diyl and 9,9-dimethylfluorene-2,7-diyl aromatic rings were studied by ESR. ... 

Another difficulty comes from the spectroscopic technique used to probe the degree of electronic interaction, which relies basically on the observation of a metal-to-metal charge transfer band (intervalence band) in the near-infrared (NIR). A simple analysis based on the Franck-Condon principle leads to the conclusion that its shape and energy may depend on the geometry change between the reduced and... 

The visible spectrum of the sodium salt in methanol has the same shape as that of diaquo complex in chloroform a split peak at 511 and 488.5 mu (e 13), with a shoulder at 461 m/a. The charge-transfer band is at 278 m/u.. The infrared spectrum in the range 4000-650 cm. is very similar to that of Co(acac)2, except that all the peaks are much sharper. 

The model has been applied to a series of ruthenium (III, 11) complexes, calculating parameters such as the degree of valence localization, from the observed shapes of the intervalence charge-transfer bands. 

PAPs are optimally active at weakly acidic conditions, with pH optima ranging from 5.0 to 6.3. The PAPs exhibit bell-shaped pH-rate profiles, typified by the kidney bean enzyme, which has an optimum of 5.9 and apparent p iTa values of 4.8 and 6.9. Very similar pAg values are found for the bovine spleen and recombinant human PAPs. Because the lower pffa is also found in pH variations of the EPR spectra and of the charge-transfer band (28), it is attributed to the deprotonation of an Fe +-coordinated water molecule. 

Carrier generators in molecular conductors have been associated for a long time to a partial charge transfer between the HOMO (or LUMO) electronic band and other chemical species. These systems are known as two-component molecular conductors. Tetrathiofulvalene derivatives are versatile systems for the formation of molecular organic conductors due to their electron donor capacity by transferring one u-electron from the HOMO orbital, and to their planar shape that promotes their stacking as a consequence of the n-n orbital overlap. The electronic properties of these salts are essentially determined by the packing pattern of the donor molecules which, in turn, depends on the counter-ion. 

TDDFT calculations results were consistent with the band shapes of the optical spectra of the parent complexes and are shown in Fig. 14. The calculated optical transitions are shown as bars under the experimental spectra and consist of MLLCT, ligand-to-ligand charge transfer transitions (LLCT), intraligand n - tt transitions (IL), and metal-complex delocalized-charge transfer transitions (MCDCT). Triplet state energies were also calculated based on a3 MLLCT state and correlated with experimental emission spectral results [53]. 

Independent support for interflavin o-contacts comes from recent chemical studies by Favaudon and Lhoste (13,14). The french authors describe, as already anticipated, a nearby diffusion-controlled dimer formation in aprotic polar medium as the first step in the interflavin contact between oxidized and reduced states, which would finally yield two flavin radicals. This dimer was shown to be not identical in any respect with the well known quinhydrone which can only be obtained in aqueous systems at high flavin concentrations. The long wave band in the absorption spectrum of the new dimer appears to be of charge transfer type, but with a highly reduced half width and better resolved shape than the flavoquinhydrone spectrum. 

Although the localization and shape of the CT bands depend on a degree of charge transfer from the electron donor-to-acceptor molecule, this spectral region is not suitable for evaluation of the amount of transferred electrons in organic conductors. Raman scattering and vibrational spectra are more useful for this purpose. 

This chapter concerns the energetics of charge-transfer (CT) reactions. We will not discuss subjects dealing with nuclear dynamical effects on CT kinetics. " The more specialized topic of employing the liquid-state theories to calculate the solvation component of the reorganization parameters is not considered here. We concentrate instead on the general procedure of the statistical mechanical analysis of the activation barrier to CT, as well as on its connection to optical spectroscopy. Since the very beginning of ET research, steady-state optical spectroscopy has been the major source of reliable information about the activation barrier and preexponential factor for the ET rate. The main focus in this chapter is therefore on the connection between the statistical analysis of the reaction activation barrier to the steady-state optical band shape. 

When the donor and acceptor are sufficiently close, as in an ion pair or in covalently linked complexes, electron transfer can be promoted by the absorption of light. An absorption band corresponding to the light induced electron transfer is usnally called a charge transfer (CT) absorption band . The molecnlar parameters that determine the CT absorptivity, bandwidth, and band shape are the same molecular parameters that determine the magnitude of the electron-transfer rate constant.In the weak-coupling limit, the absorptivity of the CT absorption band is small (much less than 10 cm ) in the strong-... 

Electronic Absorption Spectroscopy. Theoretical considerations of the light absorption spectra of /3-carotene (189) and related polyenes have been presented.A method has been devised for describing the shapes of the absorption spectra of polyenes such as -carotene and retinyl acetate as lognormal distribution curves.A new absorption band is seen in the spectrum of jS-carotene acting as electron donor in charge-transfer complexes.The triplet-triplet... 

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