Charge transfer band origin

In its reduced state, the paramagnetic Rieske cluster shows a temperature-dependent MOD spectrum composed of numerous positive and negative C-terms that originate from the 8 = 1 ground state. The MOD spectra lack the Fe" 8 charge transfer bands that are observed as intense negative bands between 300 and 350 nm and a posi-... 

The electronic spectra of these materials recorded in chloroform solution appear to be dominated by intense bands originating from internal ligand transitions, metal-ligand and ligand-metal charge-transfer bands, whose intensities change markedly with changes in the population of the two spin states [7]. 

Electronic spectra of metalloproteins find their origins in (i) internal ligand absorption bands, such as n->n electronic transitions in porphyrins (ii) transitions associated entirely with metal orbitals (d-d transitions) (iii) charge-transfer bands between the ligand and the metal, such as the S ->Fe(II) and S ->Cu(II) charge-transfer bands seen in the optical spectra of Fe-S proteins and blue copper proteins, respectively. Figure 6.3a presents the characteristic spectrum of cytochrome c, one of the electron-transport haemoproteins of the mitochondrial... 

The theoretical description of photochemistry is historically based on the diabatic representation, where the diabatic models have been given the generic label desorption induced by electronic transitions (DIET) [91]. Such theories were originally developed by Menzel, Gomer and Redhead (MGR) [92,93] for repulsive excited states and later generalized to attractive excited states by Antoniewicz [94]. There are many mechanisms by which photons can induce photochemistry/desorption direct optical excitation of the adsorbate, direct optical excitation of the metal-adsorbate complex (i.e., via a charge-transfer band) or indirectly via substrate mediated excitation (e-h pairs). The differences in these mechanisms lie principally in how localized the relevant electron and hole created by the light are on the adsorbate. 

A similar situation is encountered in other systems. For instance, in the case of the pair pyrene (acceptor)-dimethylaniline (donor) connected by a propyl [( 112)3] chain, one of the conformers is found to exhibit a charge-transfer band at the origin [19]. Another conformer, possibly a stretched one, shows only locally excited fluorescence at the origin, and exciplex type as the vibronic energy is increased. It seems that for strong acceptors, such as pyrene, an n = 3 chain is sufficiently long to allow... 

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