Dresden 2011 – scientific programme

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ISS: Intersectional Sessions

ISS 5: Transport and Spectroscopy in Molecular Nanostructures I (CPP, MO, related to SYMN)

ISS 5.9: Talk

Wednesday, March 16, 2011, 16:15–16:30, ZEU 160

Förster Resonant Energy Transfer (FRET) in Orthogonal Chromophores — •Igor Pugliesi¹, Heinz Langhals², and Eberhard Riedle¹ — ¹LS BioMolekulare Optik, LMU München — ²Dept. Chemie, LMU München

FRET has become a process of ubiquitous importance in chemistry and biochemistry. While proximity measurements of light absorbing and fluorescent structures still rely on the basic theory of FRET, recent results from 2D electronic spectroscopy on light harvesting complexes show, that a more refined model is required for an accurate description of this photophysical process [1]. We investigate the very principles of FRET on a set of perylene bisimide dyads by pump-probe spectroscopy, chemical variation and calculations. These dyad undergo transfer with near unit quantum efficiency although the transition dipole moments of donor and acceptor are in a perfectly orthogonal arrangement to each other in the equilibrium geometry. According to the point dipole approximation used in Förster theory no energy transfer should occur. Experimentally we do, however, observe ultrafast transfer times ranging from 1 ps up to 45 ps. With the transition density cube approach, the change of the spacer both in length and chemical character and temperature variations we demonstrate that energy transfer is enabled through low frequency ground state vibrations, which break the orthogonal arrangement of the transition dipole moments. The dyads presented here therefore are a first example that shows with extreme clarity the decisive role vibrational motion plays in energy transfer processes [2].

[1] Yuan-Chung Cheng and Graham R. Fleming, Annu. Rev. Phys. Chem., 241, 60, 2009.

[2] Heinz Langhals, Andreas J. Esterbauer, Andreas Walter, Eberhard Riedle, and Igor Pugliesi, J. Am. Chem. Soc., 16777, 132, 2010.