Berlin 2014 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 5: Posters 1: Electronic Spectroscopy, Photochemistry, Femtosecond Spectroscopy

MO 5.22: Poster

Montag, 17. März 2014, 16:30–18:30, Spree-Palais

Temperature-Dependent Femtosecond Spectroscopy reveals Energy Barriers in Ultrafast Electronic Deactivation     — •Uta Corinna Stange and Friedrich Temps — Institute of Physical Chemistry, Christian-Albrechts-University Kiel, Germany

The dissipation of excess electronic energy is of utmost importance to biological molecules such as the DNA to avoid photochemical damage. To understand the photophysical mechanisms of electronic deactivation of DNA building blocks detailed information on the involved potential energy surfaces (PES) is needed. While quantum chemical calculations become feasible for these molecules, the experimental characterization of specific features of the PES remains a challenge even for femtosecond spectroscopy.

Here we demonstrate a straightforward method to reveal local minima and energy barriers on deactivation pathways: temperature-dependent femtosecond time-resolved fluorescence spectroscopy. Our measurements of the DNA building blocks adenine (A) and its dinucleotide (d(A₂)) clearly show temperature-dependent behavior for their ultrafast electronic deactivations. Excited-state lifetimes decrease with increasing temperature indicating thermal activation. Observed activation energies can be assigned to shallow potential energy wells along the deactivation pathways of the excited states in the monomer and to excimer states in the dimer. The results allow us to quantify the depth of potential energy wells and barriers experimentally.