Lifetime quenching

Temperature-dependent luminescence measurements in the range from 77 to 300 K show quenching of the peak luminescence by a factor of about 15. Similar behavior is observed in the lifetime quenching [665, 666], As the band gap of the PECVD a-Si H is about 1.6 eV, nonradiative deexcitation of Er may occur at elevated temperatures. The amount of quenching lies in between that of c-Si and LPCVD a-Si H, just like the bandgap. 

The opportunities for near-IR fluorescence sensors are of course not only limited to analytical chemistry. Physical parameters such as temperature can also be measured. For example, Grattan and Palmer have used the fluorescence lifetime quenching of neodymium glass fluorescence at 1054 nm, excited at 810 nm with a gallium-alumi-... 

Absorption and emission properties were similar to those of unattached [Re(phen)(CO)3 (py)]+ with high quantum efficiencies and long emission lifetimes. Quenching of the emission occurred in the presence of O2 suggesting their use for dioxygen sensors. 

C. G. Hiibner, A. Renn, I. Renge and U. P. Wild, Direct observation of the triplet lifetime quenching of single dye molecules by molecular oxygen, J. Chem. Phys. 115, 9619 (2001). 

Figure 5 Quenching of A-[Ru(phen)2dppz]2+ luminescence by viologens in the presence of poly(dA-dT)-poly(dA-dT)—comparison of steady-state and lifetime quenching. ( ) Short lifetime, ( ) long lifetime, ( ) steady-state intensity, and (o) intensity calculated from lifetimes (Sot). Upper panel MV2+ and lower panel Me2DAP2+. [Ru(phen)2dppz]2+ = 20 pM bp = 500 pM buffer is 5 mM sodium phosphate (pH 7).

A Stern-Volmer plot can be obtained also from fluorescence lifetime quenching. In fact, the fluorescence lifetime in the absence of a quencher is... 

If students have access to a fluorescence lifetime instrument, it would be useful to see how one can measure fluorescence lifetime. In this case, it will be useful if students can perform the experiments described by following fluorescence lifetime quenching with KI and compare their results with intensity quenching experiments. 

When [Rh(phi)2(phen)]3+ is titrated into a solution containing [Ru(phen)2(dppz)]2+ and B-form DNA, the photoinduced luminescence of the ruthenium(II) complex is quenched dramatically (53). In these experiments, luminescence is monitored by laser flash as quencher is added. Data are then plotted in Stern-Volmer format, where the ratio of initial intensity/intensity (I0/I) is given as a function of quencher concentration [Q. The degree of lifetime quenching can also be described by plotting the inverse of the lifetime (r0/r) versus [Q. Normally, when chromophore and quencher interact bimolecularly, Stern-Volmer graphs are linear with [Q] and the slope for r0/r is the same as that for I0/I. 

In case of electron scavenging (and no Ps lifetime quenching, as is true for both Cl" and Tl+), no other positron states are present than free e+ and Ps then, the intensities from PALS and from DB are the same. The p-Ps and o-Ps intensities are expected to decrease so that the fwhm of the DB spectra should increase with solute concentration (the narrow components are suppressed). The variations of fwhm with C can be completely calculated, knowing the intensities Ij from PALS and the Tj previously established for a given solvent. This is illustrated by the solid line in Figure 4 for Tl+ this ion, as expected from its high solvated electron scavenging rate constant, is thus shown to suppress Ps formation by electron capture. 

The observation of intensity but not lifetime quenching was attributed to a component of ultrafast (static) electron transfer. In order to distinguish between the distance dependence of static electron transfer and the results of dynamic measurements, Barton has used the term y to define the distance dependence of the fluorescence quantum yield data. Values of y = 0.33 and 0.20 were obtained for two duplexes having different bases adjacent to Z [47]. A substantial decrease in the quenching efficiency was observed when the base-paired partner for Z was changed from C to T, A, or G. These observations establish that the fluorescence intensity of ET in these duplexes is sensitive to the location of Z, the neighboring base pairs, and the presence of mismatches. 

We have previously used the Cu ion as a convenient cationic quencher for polyanion - bound chromophores. In these previous papers it was found that the apparent second order rate constant was extremely high, presumably because of the electrostatic attraction between Cu and the polyelectrolyte. The quenching was found previously to be largely static in that the total fluorescence intensity was quenched very efficiently but there was little or no lifetime quenching. 

Figure 2.20. Fluorescence intensity / lifetime quenching of fluorescein in presence of increased concentrations of KI. Curtosey from Amersham Science.

Rotational correlation time of tyrosine in small peptides can be performed with intensity or / and lifetime quenching. 

Measiuements of the emission anisotropy A as a function of added collisional quencher are made with the steady fluorescence intensity, which integrates the different weighted fluorescence lifetimes. Quenching emission anisotropy plot of 1 /A vs I (Fig. 5.14) yields for A(o) a value of 0.246 and 0.243 for [L-Met2] DREK and DREK, respectively. These values, lower than that (0.278) measured at - 45 °C for tyrosine at 280 nm (Lakowicz and Maliwal, 1983), indicate that tyrosine residue in both peptides display residual motion independent of the global rotation of the peptide. It is possible to measure the relative importance of the mean residual motions of the tyrosine residues ... 

Fig. 27 Porphyrin fluorescence lifetime quenching by coordinated Ru centers in compounds 5, 8,17-20 (py stands for pyridylporphyrin)...

Shown in Fig. 2 is the luminescence lifetime quenching of sensor 1 as a function of the cyanide concentration. Prior to cyanide addition, 1 exhibits a single exponential lifetime (x=380 ns). At low [CN ], the decay profiles could be adequately fit Ity a single exponential function. 

Pro4 sans trp Lifetime Quenching rate 2 - — Model fit... 

Figure 12 Representative photoluminescence data illustrating intensity quenching (a), lifetime quenching (b), and the associated Stem-Volmer plot demonstrating a purely dynamic process.

Figure 14 Luminescence intensity (a) and lifetime quenching (b) of [Ru(dpp)3] + by the closed form of BTF6 in degassed acetonitrile solution. AU data were obtained with 390nm excitation. The data in (b) were detected at 610 nm and represent averages of 64 transients. (Adapted with permission from Ref. 45. American Chemical Society, 2004.)...

Figure 18 Time-resolved photoluminescence decays monitored at 620 nm for [Ru(deeb)3] + in acetonitrile (a) and dichloromethane (b) as a function of increased [TBAI]. (Inset a) A Stern-Volmer plot for lifetime quenching from which Ksw = 1.0 0.1 x 10 was abstracted. (Inset b) A Stern-Volmer plot for both lifetime (black) and amplitude (red) quenching components where quenching constants, Ksy = 4.1 0.2 x 10 M and = 2.30 0.03 x 10 M , were abstracted. (Adapted with pamission from Ref. 55. Royal Society of Chemistry, 2011.)...

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