Solvation shift of a conical intersection in clusters of excited tetrakis(dimethyl amino)ethylene with ammonia and acetonitrile molecules

Abstract

To cite this version:S. Sorgues, J. M. Mestdagh, B. Soep. Solvation shift of a conical intersection in clusters of excited tetrakis(dimethyl amino)ethylene with ammonia and acetonitrile molecules. Chemical Physics Letters, Elsevier, 2004, 399, pp.234-238 The supersonic expansion of the title molecule (TDMAE) with a mixture of helium and a solvent molecule S (S = ammonia or acetonitrile), generates a beam carrying TDAME(S) 10 clusters. The femtosecond pump (266 nm)-probe (800 nm) technique is used to investigate their excited state dynamics. It corresponds to a wavepacket movement along slopes of the S 1 potential energy surface of TDMAE where the molecule switches from the valence V(ππ * ) to the Zwitterionic C + C − configuration. As a first approximation, this occurs in the vicinity of a conical intersection. The present results where TDMAE is solvated by polar molecules, are compared with former results using argon as a solvent. Whereas argon slows down of the wavepacket movement by what was called a chistera effect, the present case is dominated by a change in the location of the conical intersection that accelerates the time scale for the V-to-Z energy transfer. The interaction of a final charge transfer state with the solvent is also discussed.

Solvent Effect on the Singlet Excited-State Lifetimes of Nucleic Acid Bases: A Computational Study of 5-Fluorouracil and Uracil in Acetonitrile and Water

“…Preliminary calculations on 5FU in acetonitrile suggest that an additional decay channel exists for this molecule in acetonitrile, involving a dark n/π* state (hereafter S n ) almost isoenergetic to the S π state in the Franck−Condon (FC) region . Besides its significance for the excited-states behavior of nucleobases, the possibility that solvent modulates the accessibility of the different decay channels is very important for the study of photoexcited molecules in solution, − and thus it would be interesting to verify this hypothesis by state of the art quantum mechanical calculations in the condensed phase. To this aim and to get a more complete picture of solvent effects on the behavior and the lifetimes of uracil excited states, it is necessary to address several basic questions.…”