Work Group Prof. Dr. F. Temps

ss- and ds-DNA oligonucleotides

    (Ade)2
The adenine dincucleotide in water
adopts  the  B-DNA  configuration.

As shown by femtosecond time-resolved fluorescence and absorption measurements, the excited-state lifetimes of single- and double-stranded DNA oligonucleotides and natural DNA can be three to four orders of magnitude longer than the lifetimes of the free nucleobases in solution. These huge differences have to be attributed to strong electronic coupling mechanisms between the nearly coplanar stacked bases in a DNA strand. It is highly controversally debated, however, whether the long lifetimes are due to dipole-coupled (Frenkel) excitons, which can be delocalized over a number of bases, or whether the local ππ* photoexcited states transform to long-lived excimer- resp. exciplex-like states with (partial) charge transfer character involving a neighboring base.

Since the excited state structures of long oligonucleotides with > 4 - 5 bases are far too complex to elucidate, we have turned to the investigation of small di-, tri- and tetranucleotides as nearly ideal model systems. For the adenine dinucleotide as an example, we have recently been able to time-resolve the transition from the initially excited exciton state to the long-lived (380 ps) excimer state which takes place in the first 100 - 500 fs after excitation. A sizable energetic stabilization of the excimer is reflected by strong red- and blue-shifts by ~1 eV, respectively, in the observed fluorescence and absorption spectra. Distinctive spectral features of the exciton and excimer states were identified.

In a bottom-up approach, we are studying the related dynamics in selected other di- and oligonucleotides to elucidate the excited-staet dynamics in larger DNA molecules. 

Important papers:

  • M. C. Stuhldreier, K. Röttger, F. Temps, "Distinctive Spectral Features of Exciton and Excimer States in the Ultrafast Electronic Deactivation of the Adenine Dinucleotide", in: Ultrafast Phenomena XIX, K. Yamanouchi, S. Cundiff, R. de Vivie-Riedle, M. Kuwata-Gonokami, L. DiMauro (Eds.), Springer Proceedings in Physics, Band 162, 452 - 454 (2015).  DOI:  10.1007/978-3-319-13242-6_110
  • M. C. Stuhldreier, F. Temps, "Ultrafast Photo-Initated Molecular Quantum Dynamics in the DNA Dincleotide d(ApG) Revealed by Broadband Transient Absorption Spectroscopy", Faraday Discuss. 163, 173 - 188 (2013).  DOI: 10.1039/C3FD00003F
  • N. K. Schwalb, F. Temps, "Base Sequence and Higher-Order Structure Induce the Complex Excited-State Dynamics in DNA", Science 322, 243 - 245 (2008).  DOI: 10.1126/science.1161651