Charge-transfer absorption band transition energy corresponding

The charge-transfer absorption band results from the promotion of an electron from the EDA ground state to the excited state. For weakly interacting donors and acceptors (in which a b), populating this excited state by irradiation of the CT band essentially promotes an electron from the donor orbital to one located on the acceptor — usually represented by the HOMO and LUMO, respectively. This transition effectively corresponds to a direct electron transfer without the intermediacy of a (local) excited state of either D or A. The energy of this transition, and thus the frequency (wavelength) of the absorption is given by... 

The Z value was defined by Kosower as the energy of electronic transition corresponding to the charge-transfer absorption band of l-ethyl-4-carbo-methoxy pyridinium iodide, a substance which has an ultraviolet spectrum remarkably sensitive to solvent polarity. Application of this method involves the determination of the spectral characteristics of the solubilizate in a number of solvents of known Z values and the establishment of a relationship between Z values and the energy of transition which is readily obtained from the wavelength of maximum absorbance. From this relationship the Z value of the micellar micro-environment may be determined from the wavelength of maximum absorbance of the solubilizate when solubilized within the micelle. Utilizing this... 

UV-vis DRS spectra of the calcined titanium mesoporous materials are shown in Figure 2. An absorption band centered at ca. 220 nm is observed in all the samples, and this band is usually assigned to a low-energy charge-transfer transition between tetrahedral oxygen ligands and central Ti4 ions [9, 10]. The shoulder at 270 nm probably corresponds to partially polymerized hexa-coordinated Ti species [10], and some polymeric species are suspected to co-exist with the isolated Ti sites in all the mesoporous samples prepared. However, anatase-like TiO, phase at 330 nm was absent in these samples. 

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