Spectroscopy for Materials Characterization. Группа авторов
3.9b) does not modify the shape of the signal. However, the entire signal now undergoes a progressive decay (compare the amplitude of the two signals in Figure 3.9b). Notably, a detailed analysis shows that the two timescales of this decay are found identical to those of solvation.
This result is consistent with a model in which fluorescence quenching is caused by an electron transfer from the CD to the ions: the consequent loss of correlation between electron and hole hinders radiative recombination causing the deactivation of the fluorescence, which we see in real time as a progressive decay of the SE signal in Figure 3.9b. Interestingly, the result that this electron transfer occurs bi‐exponentially on the same timescales of aqueous solvation, 0.19 and 2.1 ps, suggests that the photochemical electron transfer reaction is essentially driven by solvation. In this picture, while solvent molecules rearrange around the surface of the photoexcited CD–ion complex, on picosecond and sub‐picosecond timescales, they are responsible for driving the photoexcited system from the initial state to a final one in which the surface electron has been entirely transferred to the interacting metal ion, so destroying the e–h pair and fully quenching the emission.
Figure 3.9 TA spectra of bare CDs (a) and with 100 mM of Cu2+ (b) recorded at 300 fs and 10 ps after the photoexcitation. (c) Normalized kinetics traces at the SE signal with different amounts of copper ions (0, 20 mM, 100 mM).
Source:[29]. Adapted by permission of the Royal Society of Chemistry.
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