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MO: Molekülphysik
MO 12: Ultrafast Structural Changes
MO 12.4: Talk
Monday, March 13, 2006, 15:00–15:15, H12
Determination of the excited state twisting angle of the chromophore of green fluorescent protein — •Omar F. Mohammed1, Anwar Usman1, Jian Dong2, Kyryl M. Solntsev2, Erik T. J. Nibbering1, and Laren M. Tolbert2 — 1Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin, Germany — 2School of Chemistry and Biochemistry, Georgia Institute of Technology; Atlanta, GA, USA
Whereas in wild type green fluorescent protein (GFP), the photochemical dynamics of the chromophore consists of a Förster cycle with excited state proton transfer and a high quantum yield for fluorescent emission, the chromophore in solution, p-hydroxybenzylidene-imidazolidinone (HBDI) shows ultrafast internal conversion. We report [J. Am. Chem. Soc. 127, 11214 (2005)] on ultrafast polarization-sensitive infrared (IR) spectroscopy of the excited state structure of HBDI, from which we draw conclusions on the importance of twisting motions. Our focus is on the orientation of the transition moment of the IR-active carbonyl stretching vibration of HBDI relative to that of the electronic transition dipole moment, which indicates that the C=O vibration acts as a spectator mode for the relative orientation of the phenolate and imidazolidinone groups. We have determined the anisotropy of the C=O vibration of HBDI in the S0 and S1 states for three charged configurations (anionic, neutral and cationic form). We find that our estimated value for the C=O bond vector in the S1-state can only be explained by a single twist of 120 degrees or a hula twist of 150 degrees, much larger than the twisting angle of 90 degrees found in quantum chemical calculations.