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. Author manuscript; available in PMC: 2008 Nov 6.

Published in final edited form as: J Am Chem Soc. 2005 Dec 28;127(51):18100–18106. doi: 10.1021/ja051210k

Polarization-sensitive vis/IR spectroscopy on the trans/cis isomerization of the chromophore of PYP. When the marker modes involve local vibrational motions, the experimentally measured anisotropies (with relative angle Θ^e between the electronic ( _vis) and infrared ( _IR) transition dipole moments) can directly be correlated to geometric configurations of the (transient) states. For delocalised normal modes experimental findings have to be compared to results of quantum chemical calculations. Our results show that for the dark P state, with the chromophore in the trans configuration (a), a local mode picture only holds for the νC=O mode of Glu46 wheras the stretching motion of the chromophore carbonyl moiety strongly mixed with other chromophore modes. For the cis conformation in the I₀ state (b) on the other hand both vibrational modes can be considered as local modes.

Inline graphic — Polarization-sensitive vis/IR spectroscopy on the trans/cis isomerization of the chromophore of PYP. When the marker modes involve local vibrational motions, the experimentally measured anisotropies (with relative angle Θ^e between the electronic ( _vis) and infrared ( _IR) transition dipole moments) can directly be correlated to geometric configurations of the (transient) states. For delocalised normal modes experimental findings have to be compared to results of quantum chemical calculations. Our results show that for the dark P state, with the chromophore in the trans configuration (a), a local mode picture only holds for the νC=O mode of Glu46 wheras the stretching motion of the chromophore carbonyl moiety strongly mixed with other chromophore modes. For the cis conformation in the I₀ state (b) on the other hand both vibrational modes can be considered as local modes.