Sensitisation process

The first stage of an IgE allergy is a sensitisation process where mast cells and basophils, which are specialised cells in the blood, become... 

The sensitisation process associated with producing lanthanide luminescence consists of a number of steps, including excitation of the antenna and energy transfer to the lanthanide. The details of this process and the considerations required in designing complexes working on this principle are discussed in the following sections. 

Scheme 2 Initial steps of sensitisation process - the antenna excitation...

Fig-1 Illustration of energy transfer to the lanthanide ion in sensitisation process for Tb(III), from triplet state of the antenna and the corresponding emission spectra for Tb(III)... 

Method C and Method D are again similar to that described above. In each case the antenna is structurally modified to accommodate a receptor allowing for the inclusion of a guest. This guest inclusion results in changes in the antenna properties, such as alterations in the effectiveness of the sensitisation process, the intensity/quantum yield, as well as to the lifetime of the metal-centred luminescence. 

This final section will look at complexes where the antenna is integrated into the lanthanide complex and are purposely designed with a receptor incorporated, leading to modulation of the sensitisation process upon guest recognition. 

Both energy transfer and electron transfer from a photoexcited compound to a given substrate are distance dependent. This property allows one to delineate—at least on paper—a catalytic cycle for a sensitised process with an appropriately modified template (Scheme 14). If the passive tetrahydronaphthalene shield in 12 is replaced by a photoactive moiety, this part of the compound can, after excitation, facilitate an energy or electron transfer significantly faster at a bound than at an unbound substrate. 

Curri ML, Petrella A, Striccoli M et al. Photochemical sensitisation process at photosynthetic pig-ments/Q-sized colloidal semiconductor hetero-junctions. Synth Met 2003 139 593-596. 

The efficiency of the sensitisation processes depends critically on the distance between the ion and the sensitiser the antenna chromophore needs to be in close contact with the lanthanide to ensure efficient transfer, as has been demonstrated for the fluorescein-type of antenna chromophore [7, 18]. The intensity of the ligand... 

The mechanism of spectral sensitisation has been shown to involve the direct transfer of an electron from the excited state of the dye into the AgX conduction band (see Fig. 11.8). In confirmation of this mechanism, excellent correlation has been demonstrated between the sensitisation capability of dyes and their electrochemical reduction potential. For the most efficient dyes, the quantum yield of the electron transfer step is close to 1.0. Using picosecond laser pulse excitation to measure the fluorescence decay rates of dyes adsorbed to AgX crystals, it has been shown that the electron transfer is very fast, with rate constants in the region of 10 s having been reported [24]. Once an electron has been transferred into the AgX conduction band, the latent image formation process ensues more or less as it does following direct absorption by AgX itself. The difference in the case of the dye-sensitised process is that the positive holes are trapped at the dye molecules. 

A host of extremely ingenious and informative experiments has been conducted on multilayer L-B films, including studies of fluorescence energy transfer, dye sensitisation processes, electron tunnelling and many others(2). 

Dye-sensitisation of ZnO Electrodes Compared with Ti02, the dye-sensitisation process of ZnO is more complicated due to reduced stability towards acidic media. Carboxyl groups are commonly used as anchoring groups for chemisorption of dye molecules onto metal oxide surfaces. Protons from this anchoring group cause dissolution of Zn surface atoms and the formation of complexes in the pores of the... 

Figure 3.46 A schematic drawing of the problems associated with the dye-sensitisation process of protonated anchoring groups on ZnO surfaces. Reprinted with permission from Boschloo et al., Copyright (2006) with permission from Elsevier...

The Charge Transfer State Mediated Sensitisation Process... 

The optimisation of the two-photon cross-section has triggered the discovery of a new sensitisation process mediated by a antenna charge transfer excited state. 

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