1. Spectral tuning by switching C–H...O hydrogen bonds: Rotation-induced spectral shifts of 7-hydroxyquinoline·HCOOH isomers.
- Author
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Thut, Markus, Manca, Carine, Tanner, Christian, and Leutwyler, Samuel
- Subjects
SPECTRUM analysis ,HYDROGEN bonding ,PHYSICAL & theoretical chemistry ,DIHYDROGEN bonding ,HYDROXYQUINOLINE - Abstract
Spectral tuning effects on visible chromophores by hydrogen bonds are central to the chemistry of vision and of photosynthesis. A model for large spectral tuning effects by hydrogen bond switching is provided by the 7-hydroxyquinoline·HCOOH complex, which forms two isomers, CTN1 and CTN2, both with an HCOOH...N hydrogen bond but with different (quinoline)C–H...O==C hydrogen bonds. A 180° rotation of the HCOOH moiety around the O–H...N hydrogen bond exchanges the C–H...O hydrogen bonds, rotates the dipole moment of HCOOH, and leads to an ∼850 cm
-1 shift of the electronic spectrum. Mass-selected S1 ←S0 resonant two-photon ionization, UV-UV holeburning, S1 →S0 fluorescence spectra, and photoionization efficiency curves of the two 7-hydroxyquinoline·HCOOH isomers were measured in supersonic expansions. Comparison to ab initio calculations allow us to determine the H-bond connectivity and structure of the two isomers and to assign their inter- and intramolecular vibrations. The Franck-Condon factors of the intermolecular shear vibration χ in the S1 ←S0 spectra indicate that the weak C–H...O hydrogen bond contracts markedly in the CTN1 isomer but expands in the CTN2 isomer. These changes of H-bond lengths agree with the spectral shifts. In contrast, the strong O–H...N hydrogen bond undergoes little change upon S1 ←S0 excitation. [ABSTRACT FROM AUTHOR]- Published
- 2008
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