Internal charge transfer

A number of fluorescent dyes with internal charge transfer mechanism allow the molecule to twist (rotate) between the electron donor and electron acceptor moieties of the fluorescent dipole. In most cases, the twisted conformation is energetically preferred in the excited Si state, whereas the molecule prefers a planar or near-planar conformation in the ground state. For this reason, photoexcitation induces a twisting motion, whereas relaxation to the ground state returns the molecule to the planar conformation. Moreover, the Si — So energy gap is generally smaller in the twisted conformation, and relaxation from the twisted state causes either a... 

Bosch LI, Mahon MF, James TD (2004) The B-N bond controls the balance between locally excited (LE) and twisted internal charge transfer (TICT) states observed for aniline based fluorescent saccharide sensors. Tetrahedron Lett 45(13) 2859-2862... 

Arimori S, Bosch LI, Ward CJ, James TD (2001) Fluorescent internal charge transfer (ICT) saccharide sensor. Tetrahedron Lett 42(27) 4553-4555... 

Fromherz P, Heilemann A (1992) Twisted internal charge-transfer in (aminophenyl)pyridi-nium. J Phys Chem 96(17) 6864-6866... 

The model shown in Scheme 2 indicates that a change in the formal oxidation state of the metal is not necessarily required during the catalytic reaction. This raises a fundamental question. Does the metal ion have to possess specific redox properties in order to be an efficient catalyst A definite answer to this question cannot be given. Nevertheless, catalytic autoxidation reactions have been reported almost exclusively with metal ions which are susceptible to redox reactions under ambient conditions. This is a strong indication that intramolecular electron transfer occurs within the MS"+ and/or MS-O2 precursor complexes. Partial oxidation or reduction of the metal center obviously alters the electronic structure of the substrate and/or dioxygen. In a few cases, direct spectroscopic or other evidence was reported to prove such an internal charge transfer process. This electronic distortion is most likely necessary to activate the substrate and/or dioxygen before the actual electron transfer takes place. For a few systems where deviations from this pattern were found, the presence of trace amounts of catalytically active impurities are suspected to be the cause. In other words, the catalytic effect is due to the impurity and not to the bulk metal ion in these cases. 

The internal charge transfer A depends also on the potential. It should be emphasized that AP and 17p can be defined in principle for any arbitrary choice of/P(r) in Equation 24.44. Derivation of f. (r) does not involve any chemical potential. It is an unique property of the Hamiltonian with N electrons [28,33]. 

The generalization of the Fukui functions to nonlinear and nonlocal chemical responses is done in Refs. [26,32] by using N derivatives and the KS perturbation equations. In this section, we propose a brief survey of a complementary derivation based on the concept of the internal charge transfer A introduced above. A more detailed discussion, including computational schemes, will be presented elsewhere. 

Z. R. Grabowski, K. Rotkiewicz, W. Rubaszewska, and E. Kirkor-Kaminska, Spectroscopy and kinetic of the twisted internal charge-transfer (TICT) excited state formation in p-substituted dialkylanilines, Acta Phys. Pol. A 54, 767 (1978). 

R Plaza, N. Dai Hung, M. M. Martin, Y. H. Meyer, M. Vogel, and W. Rettig, Ultrafast internal charge transfer in a donor-modified rhodamine, Chem. Phys. 168, 365-373 (1992). 

In this last interpretation, B could promote the electron transfer through a superexchange mechanism involving the (P B H) charge-transfer state. A variant of this model involves an internal charge-transfer state of the Bchl dimer [172]. 

Optical Detection of the Lanthanoid Ion Contraction by Internal Charge-Transfer Absorption of Rare Earth Bisporphyrinate Double-deckers... 

On the contrary, a quite systematic behavior with the lanthanoid ion contraction is observed. A plot of the energy of CTI band versus the ionic radius at coordination number 8 of the Ln ions (16) indicates a linear decrease of this energy as the ionic radius increases. This is seen in Figure 3, and illustrates a bare size effect of the energy variation. The phenomenon is called "optical detection of the lanthanoid ion contraction by internal charge transfer absorption". 

TICT Twisted Internal Charge Transfer States... 

The PET systems of the aminoalkyl aromatic type discussed so far display a very simple behavior in that luminescence intensity (or quantum yield) is the only variable. Such systems are very user-friendly as a result and tolerate a wide variety of communication wavelengths. However these simple systems could be adapted to include an additional absorptiometric sensing channel which can confirm the results of ion density (pH say) obtained via luminescence. Of course, such increased user-confidence is only attained with a proportionate reduction in simplicity. Now excitation needs to be done at the isosbestic wavelength. These systems, e.g. 11 and 12, use a push-pull fluorophore with electron donor and acceptor substituents which give rise to internal charge transfer (ICT) excited states. In contrast, the simple PET systems employed aromatic hydrocarbon fluorophores with essentially pure nn excited states. The charge separation in ICT states can cause electrostatic... 

The electronic absorption, fluorescence and excitation spectra of these compounds indicate the presence of an internal charge transfer (ICT) excited state giving rise to a fluorescence band that displays strong solvatochromism. Both the emission wavelengths and the Stokes shifts increase with solvent polarity, in agreement with a large increase in dipole moment in the excited state. As the chain length increases the... 

The triarylborane-porphyrin conjugate receptor 45 [40] can bind a F ion concurrent with the change from sp2 to sp3 hybridization of the boron atom. The change in the hybridization interrupts both the electronic communication and the dipolar interaction between the triarylborane and porphyrin unit as well as the internal charge transfer in the presence of F". Bathochromic shifts... 

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