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Ultrafast Intersystem Crossing in Aromatic Carbonyl Compounds (Femtochemistry - Femtobiology)
Photo-excited aromatic carbonyls like bezophenone and xanthone and
their derivatives are well known to undergo ultrafast
intersystemcrossing (ISC) to long-lived triplet states. That makes them
ideal candidates to investigate the detailed mechanism of the ISC
process which is of fundamental interest for many photochemical
reactions. Furthermore, xanthone derivatives recieve growing interest
as fluorescent chemosensors (Angew.
Chem. 2006, 118, 5644) and
as part of photo-labile protecting groups which are used in DNA-chip
chemistry (Angew. Chem. 2006, 118, 3042). All of these
applications depend on the photophysical properties of xanthone and its
derivatives. For future development and implication of these compounds
a thorough knowledge of the involved excited states and dynamics is
imminent.
To pursue this task we use ultrafast transient absorption and fluorescence spectroscopy. We
could prove the ultrafast nature of the ISC process in xanthone by
performing a triplet quenching experiment on the femtosecond timescale.
A subsequent study has been adressed to the unusually strong solvent
dependence of the fluorescence of xanthone. Here, we further elucidate
details excited states involved in the ISC process in xanthone and
propose a delayed fluoresence mechanism to explain our observations.
In a cooperation with the group
of Prof. Steiner at the University of Konstanz we currently
investigate thioxanthone derivatives which are used as photo-labile
protecting groups in oligonucleotid synthesis. The xanthone moiety in
these compounds serves as an antennta to collect the photon energy
which is then transferred intramolecularly.
Previous coworkers: | Stefan Berner Peter Gilch Bjoern Heinz Stefan Laimgruber
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Publications: | "On the Mechanism of Intramolecular Sensitization of Photocleavage of the 2-(2-Nitrophenyl)propoxycarbonyl (NPPOC) Protecting Group" Dominik Wöll, Stefan Laimgruber, Marina Galetskaya, Julia Smirnova, Wolfgang Pfleiderer, Björn Heinz, Peter Gilch, Ulrich E. Steiner
J. Am. Chem. Soc. 129 (2007) 12148 Details
"Slow Fluorescence and Fast Intersystem Crossing - The Xanthone Anomaly" B. Heinz, B. Schmidt, C. Root, F. Milota, B. Fierz, T. Kiefhaber, W. Zinth, P. Gilch
Ultrafast Phenomena XV, Springer Series in Chem. Physics, Eds. Andrew M. Weiner and R. J. Dwayne Miller, Springer-Verlag, Berlin (2006) Details
"On the unusual fluorescence properties of xanthone in water
" B. Heinz, B. Schmidt, C. Root, H. Satzger, F. Milota, B. Fierz, T. Kiefhaber, W. Zinth and P. Gilch
Phys. Chem. Chem. Phys. 8 (2006) 3432-3439 Details
"Ultrafast quenching of the xanthone triplet by energy transfer: New insight into the intersystem crossing kinetics" H. Satzger, B. Schmidt, C. Root, W. Zinth, B. Fierz, F. Krieger,
J. Phys. Chem. A. 108 (2004) 10072-10079 Details
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