Hannover 2013 – scientific programme
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MO: Fachverband Molekülphysik
MO 26: Electronic Spectroscopy II
MO 26.7: Talk
Thursday, March 21, 2013, 15:30–15:45, F 107
Dispersed fluorescence spectroscopy on 5-Cyanoindole — •Anne Gräßle, Benjamin Stuhlmann, Michael Schmitt, and Karl Kleinermanns — Heinrich Heine-Universität, Institut für Physikalische Chemie I, Düsseldorf
Indole is the chromophore of the aromatic amino acid tryptophan. The fluorescence of tryptophane is utilized in the spectroscopy of proteins.
The energetic order of the two first electronically excited singlet states of indole, La and Lb strongly depends on the polarity of its environment, e.g. the hydrophile outer region or the hydrophobe inner region of a protein: The La is stabilized by polar interactions because of its larger permanent dipole moment.
These electronic states can also be affected by the indroduction of substituents with different inductive (and mesomere) effects in different positions. The cyano-group has a negative inductive effect and in the 5-position relative to the pyrrole-nitrogren it leads to a stabilization of the La state.
We used high resolution dispersed fluorescence spectroscopy and laser induced fluorescence in order to determine the changes of the geometry upon electronic excitation using the rotational constants and the Franck-Condon factors of different La→S0 transitions of 5-cyano indole to confirm this hypothesis.