Quenching-Resolved Emission Spectra

Quenching resolved emission anisotropy experiments could be performed at emission wavelengths in the blue (< 330 nm) and red (> 330 nm) portions of the spectrum to yield a more consistent data surface. However, this could be possible if at each edge of the fluorescence spectrum the emission occurs mainly from the buried or the surface Trp residues. Unfortunately, this is not the case since for example at 315 nm, the fractional contribution to the total fluorescence of the surface Trp residue is 42%. 

Upon combination of complexes 1 and 2 in an equimolar 0.025 mM aqueous solution, the absorption spectrum displayed features of both complexes. On the contrary, the emission spectrum of such mixture showed a maximum centered at 645 nm, which resembled only one of the complex 1, while the emission of complex 2 was not detected. The time-resolved emission analysis confirmed that the decay was only related to complex 1 above the CMC. These findings strongly indicate a full and efficient energy transfer process involving the iridium-based metallosurfactant 2, being quenched by the ruthenium-based amphiphilic complex 1 in a system that can be depicted as a mixed aggregate. 

For each solution in the Cr + G series, Table 8.2 (1) measure the UV-vis spectrum to obtain the absorbance A at Aex, and (2) measure an emission spectrum and obtain the integrated emission intensity, I. Also, prepare a solution having [G] the same as the last in your series (Table 8.2), but with no chromium complex. This will serve as a control sample. Save your sample solutions for time-resolved luminescence quenching if you are conducting these experiments (see below). Save all UV-vis and luminescence spectra files that you acquire—they may be useful for data analysis. 

However, it is in xwtant to mentkm here that the presence of 5 Trp readues makes the analysis by tbe mo fied Stem-Volmer equation very approxiuate Selective quenching cannot in no way resolve the fluoiEScaice emission spectrum of each Tip residue. However, it allows quantifying the percentage of accessible fluorophores to the quencher. 

Figures 8.4 and 8.5 show the luminescence spectrum and the time-resolved emission decay of MEH-PPV/ Cgo composites compared with MEH-PPV alone. The strong photoluminescence of MEH-PPV is quenched by a factor in excess of 10, and the luminescence decay time is reduced from 7o 550 picoseconds to Trad 60 picoseconds (the instrumental resolution) indicating the existence of a rapid quenching process [53,54, 63]. An estimate of the transfer rate, l/td, is given by decay rate of the photoluminescence in the MEH-PPV/Cgo composite (charge transfer will cut off the radiative decay).

The violet emission of the radiation-induced center (COs) " is well known in steady-state luminescence spectra of calcite (Tarashchan 1978 Kasyanenko, Matveeva 1987). The problem is that Ce also has emission in the UV part of the spectrum. In time-resolved luminescence spectroscopy it is possible to differentiate between these two centers because of the longer decay time of the radiation-induced center. Its luminescence peaking at 405 nm becomes dominant after a delay time of 100-200 ns while emission of Ce is already quenched (Fig. 4.14f). 

The luminescence spectrum of the Canada apatite contains the yellow band, which is similar to Mn + emission in the Ca(II) site (Fig. 5.71). Nevertheless, this band has short decay time, which is not suitable for strictly forbidden d-d transitions in Mn +. It dominates in the time-resolved spectrum with a delay of 10 ps and gate of 100 ps when the shorter-lived centers are quenched, while the longer-Hved ones are not detected. A change in the lifetime may be indicative of the energy transfer from Mn + by a radiationless mechanism. A condition necessary for this mechanism is coincidence or a close distance between energy level pairs of the ion sensitizer and the ion activator. Here, the process of luminescence is of an additive nature and a longer duration and greater quantum yield of the activator luminescence accompany a reduced... 

Sometimes luminescence lines appear in the midst of the regular Raman lines in the 200-900 cm spectral range. For example, titanite time resolved spectra under excitation by 532 nm reveal pure Raman spectrum with zero delay and 10 ns gate (Fig. 6.25a) while after delay of 500 ns when all Raman signals are definitely quenched, bivalent REE emission clearly dominates the spectrum (Fig. 6.25b). 

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