Distance dependence quenching

Many experiments have been carried out where the distance between the fluorophore and the metal nanoparticle surface is varied yet only quenching is observed. In these cases the nanoparticles are usually small spherical metal nanoparticles. The following examples demonstrate distance-dependent quenching in a couple of nanoparticle-fluorophore systems. 

Another model for quenching, the so-called distance-dependent quenching (DDQ) model, assumes that the quenching rate is dependent on the F-Q distance as shown in the lower half of Figure 9.26. Such an exponential dependence on electron-transfer and electron-exchange interactions. For distance-dependent inter tions, the rate of quenching at an F-Q distance r is given by... 

Shan Y, Xu JJ, Chen UY (2009) Distance-dependent quenching and enhancing of electrochemiluminescence from a CdS Mn nanocrystal film by Au nanoparticles for highly sensitive detection of DNA. Chem Commun 905-907... 

Et /ZG AG -0.2 V fluorescence quenching correlates with CT driving force no spectral overlap for energy transfer no Zs in injection site or intervening sequence k = 2 x 1011 s 1 observed up to 20 A in time-resolved and steady-state experiments shallow dependence of CT yield between 6-24 A (y = 0.2-0.3) no dependence of kci between 10-17 A strong efficiency and distance dependence of CT yield vary with Z flanking sequence and intervening mismatches... 

St /G AG-0.14 V fluorescence quenching stilbene radical anion detected in transient absorption no Gs near injection site or in intervening sequence k = 1012-108 s 1 for 0-4 intervening A-T base-pairs (-3.4-17 A) exponential distance dependence of CT rate constant (3 0.6-0.7 A"1 small variations in k depending on whether G is in the A or T arm of the hairpin... 

Since any quenching action is a bimolecular process, it is essential that the molecules M and Q should be in relatively close contact, but not necessarily in hard sphere (van der Waals) contact. Theoretical models lead to the distance dependence of the quenching rate constants as exponentials or sixth powers of r, the centre-to-centre distance of M and Q. Since these distance dependences are very steep, it is convenient to define a critical interaction distance r at which the quenching efficiency is, this being the distance at which 50% of the molecules M decay with emission of light (or undergo a chemical reaction) and 50% are quenched by some nearby molecule Q. 

Figure 8.21 gives a schematic representation of the type of photophysical experiments which can be performed in L-B films. The distance dependence of a quenching action through energy transfer or electron transfer can be... 

It is tempting to use static Ru(II) -emission quenching in bimolecular studies involving donors and acceptors intercalated into DNA to learn about the distance dependence of the ET quenching reaction. However, these studies are always open to two interpretations. One interpretation is that the donors and... 

Schneider, G., Decher, G., Nerambourg, N., Praho, R., Werts, M. H. V. and Blanchard-Desce, M. (2006). Distance-dependent fluorescence quenching on gold nanoparticles ensheathed with layer-by-layer assembled polyelectrolytes. Nano Lett. 6 530-536. 

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