Excitation, Emission, Quenching

The simplest excitation-emission-quenching scheme (which does not allow for radiationless decay processes) is given in Equations 13.15-13.17. 

If the total excitation-emission quenching scheme is more complicated than shown in Equation 13.15-13.17 in that it also includes radiationless decay processes for D, then, instead of Equation 13.19, one obtains Equation 13.21, where ku is the sum of all the unimolecular decay processes of D. ... 

Emission quenching is also observed with mononucleotides. In that case the quenching efficiency decreases from GMP (guanosine 5 monophosphate) to AMP (adenosine 5 monophosphate) i.e. it also follows the redox potentials of the bases, as G is more easily oxidisable than A, although the oxidation potential valura reported in the literature are rather different from one author to the other [101-104], Moreover the quenching rate constant by GMP in a Kries of different TAP and HAT complexes plotted versus the reduction potential of the excited state (Fig. 12) [95] is consistent with an electron transfer process. Indeed, as will be demonstrated in Sect. 4.3.1, these quenchings (by the mono-and polynucleotides) originate from such processes. 

Next, a strong solvent dependence emerges. When varying the solvent polarity from, for example, toluene to benzonitrile, the Cemission quenching increases (Fig. 9.44). In summary, such observations imply charge-transfer interactions between the Ceo electron acceptor and exTTF electron donor. Obviously, the charge transfer pathway passes the transiently formed C,l0 singlet excited state. 

V vs. SCE), reductive quenching of the excited complexes by the appended indole ( ,0[indole+,°] < +1.06 V vs. SCE) is favoured by > 0.2-0.4 eV. From this, together with results from transient absorption spectroscopic measurements, it is concluded that the emission quenching of the indole-containing complexes is a result of electron-transfer. The interactions of these rhenium(I) indole complexes with... 

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