Samuel Leutwyler - Cytosines: Excited-State Lifetimes, Nonradiative Decay Mechanism and Water Clusters
CFEL Molecular Physics Seminar
- Datum: 24.11.2016
- Uhrzeit: 10:00 - 11:00
- Vortragende(r): Samuel Leutwyler
- University of Bern, Switzerland
- Ort: CFEL (Bldg. 99)
- Raum: Seminar Room I-II, EG.076-078
- Gastgeber: Melanie Schnell
However, we have recently shown that jet-cooled cytosine (Cyt) and its derivatives exhibit much longer lifetimes (e.g. τ = 930 ps for 1-ethylcytosine) when excited at or closely above the S1(ππ*) electronic origins . Only above 500 cm-1 vibrational excess energy in the S1(ππ*) state does internal conversion sets in, the lifetimes of higher-lying vibronic levels decreasing to < 20 ps. We now prove that the internal conversion mechanism involves twisting of the C5-C6 double bond in the S1(ππ*) state by chemically “clamping” this bond in 5,6-trimethylene-cytosine (5,6-TMCyt), see (c,d) in the figure. The clamped 5,6-TMCyt has a lifetime of τ = 3.2 ns at its 0-0 band, and the onset of internal conversion increases to 4300 cm-1 above the electronic origin. The availability of 5,6-TMCyt and similar derivatives with longer lifetimes allows to investigate the UV spectra and determine excited-state lifetimes of cytosine-water clusters, Cyt⋅(H2O)n.
 S. Blaser, M. Trachsel, S. Lobsiger, T. Wiedmer, H.M. Frey, S. Leutwyler. J. Phys. Chem. Lett., 7 (2016) 752.