Excited fluorophore

Oxidized fluorophore

Electron-poor quencher

Fig. 4.6.7. Differences between oxidative HT and reductive ET. In both a photoexcited fluorophore is used to initiate the CT process. In oxidative HTan electron is removed from the HOMO of the DNA (A) into the HOMO of

Reduced quencher

D. In reductive ETthe photoexcited electron is shifted from the LUMO of D into the LUMO of the DNA (A). In the former DNA is oxidized whereas in the latter case DNA is reduced.

intramolecular ET yielding the corresponding pyrimidine radical anion and the pyrenyl radical cation (Py'+-dX'_). Py-dU and Py-dC were prepared by Suzuki-Miyaura-type cross-coupling reactions [27]. We subsequently characterized the properties and dynamics of the ET in Py-dU and Py-dC by steady-state fluorescence spectroscopy and femtosecond transient absorption spectroscopy (Figure 4.6.10) [28]. Our results showed that the pyrimidine radical anions generated are of dif-

hv f

3X-x~DX~X~X~T T~X~X~X 5' 5'X-X-X-X-X-X-X-X-X-X-X 3'

0 0

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