Transfer CT Transitions

LMCT and MLCT transitions depend on the symmetry, on the oxidation state of the metal and on the nature of the ligand or of the other metal atoms. In particular, the energy of CT transitions increases with the optical electronegativity difference between the metal and the ligand [20-22]. 

Optical electronegativity values (%opt) are assigned to elements in a given oxidation state and Pauling electronegativity values for haUde ions are used as references. The wavenumber of the first CT absorption band is expressed as [23, 24] 

CT transitions can involve metal ions in aU electronic configurations, and then, as in the case of TMIs, are also responsible for optical bands for systems containing d or d TMIs, that, conversely, do not produce d-d absorption. 

Intra-valence, or metal to metal, CT transitions can also occur within systems containing ions of different oxidation state, as Fe — Fe in Fe304 or Fe — Ti in sapphire [4]. 

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It is well known that intermolecular interactions between two organic compounds or organic and inorganic compounds give rise to a new absorption band(s), not present in the components. The new absorption band is characteristic of a loose reversible complex between an electron donor D and electron acceptor A, and ascribed to an electronic transition from D to A. The transition is called charge-transfer (CT) transition 53). 

The assignment of the betaine bands in 9 is complicated. The long wavelength band is most probably a charge transfer (CT) transition. This has been shown to be... 

Charge-transfer (CT) transition An electronic transition in which a large fraction of an electronic charge is transferred from one region of a molecular entity, called the electron donor, to another, called the electron acceptor (intramolecular CT) or from one molecular entity to another (intermolecular CT). Typical for donor-acceptor complexes or multichromophoric molecular entities. In some cases the charge transfer absorption band may be obscured by the absorption of the partners. 

Kosower [5, 55] has taken the longest-wavelength intermolecular charge-transfer (CT) transition of l-ethyl-4-(methoxycarbonyl)pyridinium iodide as a model process. It exhibits a marked negative solvatochromism cf. the formula of this dye and its UV/Vis... 

The charge-transfer (CT) transitions can be of the metal-to-ligand or of the ligand-to-metal type (MLCT or LMCT, respectively). They have been discussed extensively in the literature (18,51). To this we would like to add the following. 

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