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Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
Published on: June 27, 2014
Charge transfer in photoacids observed by stark spectroscopy
Lisa N Silverman1, D B Spry, Steven G Boxer
1Department of Chemistry, Stanford University, Stanford, California 94305, USA.
The Journal of Physical Chemistry. A
|September 19, 2008
Summary
Excited-state proton transfer in pyrene photoacids is driven by charge redistribution. The electronic state excited, not protonation state, dictates charge transfer magnitude, impacting excited-state proton-transfer dynamics.
Area of Science:
- Photochemistry
- Physical Chemistry
- Molecular Spectroscopy
Background:
- Excited-state proton transfer (ESPT) is crucial in chemical and biological systems.
- Understanding charge redistribution in photoexcited molecules is key to controlling ESPT.
- Pyrene photoacids serve as model systems for studying ESPT mechanisms.
Purpose of the Study:
- To investigate charge redistribution in pyrene photoacids upon photoexcitation.
- To correlate charge transfer with electronic transitions and protonation states.
- To elucidate the driving forces behind ESPT processes.
Main Methods:
- Stark spectroscopy was employed to measure changes in electric dipole moments.
- Comparison of charge transfer magnitudes for protonated and deprotonated states.
- Analysis of two distinct electronic transitions ((1)Lb and (1)La states).
Main Results:
- For neutral pyrene photoacids, charge transfer magnitude is primarily dictated by the excited electronic state, not the protonation state.
- Transitions to the (1)Lb state exhibit smaller dipole changes than transitions to the (1)La state.
- For cationic (ammonium) pyrene photoacids, photoexcitation leads to significantly less charge transfer in the protonated state compared to the deprotonated state.
Conclusions:
- The electronic state accessed upon photoexcitation is a critical determinant of charge redistribution in pyrene photoacids.
- This finding provides insights into controlling ESPT pathways by selecting specific electronic transitions.
- The study highlights the nuanced interplay between electronic structure and proton transfer dynamics.
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