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摘要
The excited electronic state dynamics of N-6,N-6-dimethyladenine (DMAde), a molecule known to emit dual fluorescence, has been studied in aqueous solution using femtosecond fluorescence upconversion spectroscopy. Time profiles of the fluorescence of DMAde excited at gimel = 258 nm were measured at a series of wavelengths in the range 320 nm <= gimel(fl) <= 650 nm. At wavelengths in the near UV (gimel(fl) <= 420 nm), the time profiles were dominated by a very short- lived decay component with a lifetime between 0.2 ps <= tau(1) <= 0.6 ps, depending on the detection wavelength. Two other components with lifetimes of tau(2) approximate to 3.5 ps and tau(3) E 60 ps gave minor contributions. In the emission observed at longer wavelengths (gimel(fl) >= 500 nm), which appeared slightly delayed compared to the UV fluorescence, the long-lived fluorescence component (t3) dominated, the second component (tau 2) disappeared. The results are consistent with the assumption that DMAde is primarily excited to a short- lived local excited (LE) electronic state that fluoresces mostly in the UV and decays rapidly, on a similar to 0.5 ps timescale, to an intramolecular charge transfer (ICT) state that emits only at longer wavelengths in the visible spectrum. The fluorescence-time profiles and transient fluorescence spectra reconstructed from the time profiles provided further information on secondary relaxation processes within and between the excited states and their non-radiative relaxation to the electronic ground state.
- 出版日期2006
