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Hydrogen bonding in the electronic excited state
1State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China.
Accounts of Chemical Research
|November 11, 2011
Summary
This study investigates excited-state hydrogen bonding dynamics, revealing how these ultrafast interactions influence photophysical and photochemical processes. Understanding these dynamics is key to controlling light-induced reactions and molecular behavior.
Area of Science:
- Physical Chemistry
- Photochemistry
- Spectroscopy
Background:
- Hydrogen bonding is crucial in science, with ground-state properties extensively studied.
- Excited-state hydrogen bonding, vital for photophysical and photochemical reactions, remains under-investigated.
- Electronic excitation causes molecular reorganization and ultrafast hydrogen bond dynamics (femtosecond scale).
Purpose of the Study:
- To review recent advances in electronic excited-state hydrogen-bonding dynamics.
- To elucidate the significant role of excited-state hydrogen bonding in various photophysical processes.
- To explore the interplay between photons and hydrogen bonds in excited states.
Main Methods:
- Femtosecond time-resolved vibrational spectroscopy to monitor ultrafast dynamics.
- Quantum chemistry calculations for excited-state properties.
- Comparative analysis of hydrogen-bonded complexes versus separated molecules in ground and excited states.
Main Results:
- Demonstrated strengthening of intermolecular hydrogen bonds in excited states for coumarin chromophores and weakening for thiocarbonyl chromophores.
- Correlated hydrogen bond strengthening/weakening with red-shifts and blue-shifts in electronic spectra, respectively.
- Showed that excited-state hydrogen bonding significantly influences radiationless deactivations (e.g., internal conversion, electron transfer) and fluorescence.
Conclusions:
- Excited-state hydrogen bonding dynamics are coupled to electronic excitation and occur on ultrafast timescales.
- Hydrogen bond strength in excited states directly impacts electronic spectral shifts and fluorescence properties.
- This research provides a foundation for understanding excited-state hydrogen bonding in photophysics, photochemistry, and photobiology.
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