Hydrogen Bonds in Excited State Proton Transfer

Area of Science:

• Photochemistry
• Biophysics
• Spectroscopy

Background:

• Hydrogen bonding influences biological chromophore photochemistry and function.
• Excited state proton transfer (ESPT) is a key initial step in these systems, affecting stability and relaxation.
• The precise mechanism of ESPT across hydrogen bonds remains challenging to study.

Purpose of the Study:

• To investigate the impact of a single hydrogen bond on photochemical reaction outcomes.
• To elucidate the mechanism of excited state proton transfer at a hydrogen bond.
• To understand how ESPT influences chromophore stabilization and relaxation pathways.

Main Methods:

• Time-resolved photoelectron imaging measurements.
• Comparative analysis of isolated vs. hydrogen-bonded chromophores.
• Spectroscopic investigation of photochemical dynamics.

Main Results:

• Addition of a hydrogen bond dramatically altered the photochemical reaction outcome.
• Isolated chromophores underwent rapid dissociation, while hydrogen-bonded systems showed stabilization and ground state recovery.
• The mechanism of ESPT was uncovered, involving sequential hydrogen and charge transfer.

Conclusions:

• Excited state proton transfer across hydrogen bonds is crucial for stabilizing biological chromophores.
• The study reveals a sequential hydrogen and charge transfer mechanism for ESPT.
• Understanding ESPT dynamics is vital for comprehending chromophore function in biological environments.