Complexing bifluorophores

For the design of complexing bifluorophores, much attention should be paid to the Forster critical radius of the donor-acceptor pair as compared to the interchromophoric distance (Figure 2.13). This critical radius depends on the donor quantum yield and on the spectral overlap between donor emission and acceptor emission. Complex-... 

Our aim is to design fluorescent sensors that undergo photophysical changes (extinction coefficient, fluorescence intensity, shifts in absorption and emission spectra) as marked as possible upon cation binding. Special attention is of course paid to selectivity and complex stability. With this in mind, two types of systems are being investigated in our laboratory fluoroionophores and complexing bifluorophores. 

Complexing bifluorophores are composed of two different fluorescent dyes linked by a flexible spacer containing heteroatoms (oxygen, nitrogen or sulphur atoms). Cation binding is thus possible and results in a decrease of the distance... 

Complexing bifluorophores are of limited use for fie detection of metal cations for which many other methods arc available, but they are of potential use for organic cations like guanidinium ion, as shown in scheme 3. 

Complexadon of a bifluorophore would lead to a much larger increase in transfer efficiency if the interchromophoric distance were larger than the Forster critical radius in the free ligand and lower in the complex. In fact, because of the sixth power of the ratio R/Rq involved in the expression of transfer efficiency (29)... 

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