Femtosecond X-ray Spectroscopy Directly Quantifies Transient Excited-State Mixed Valency

Area of Science:

• Photochemistry
• Physical Chemistry
• Spectroscopy

Background:

• Quantifying charge delocalization in short-lived photoexcited states of molecular complexes in solution is experimentally challenging.
• Femtosecond experimental probes are required for time-evolving electron transfer studies.

Purpose of the Study:

• To quantify the evolving valence hole charge distribution in the photoexcited charge transfer state of a mixed valence bimetallic iron-ruthenium complex in water.
• To establish a spectroscopic ruler for quantifying excited-state valency in solvated complexes.

Main Methods:

• Combining femtosecond X-ray spectroscopy measurements with time-dependent density functional theory (TD-DFT) calculations.
• Investigating the excited-state dynamics of [(CN)5FeIIcyanoRuIII(NH3)5]- in water.

Main Results:

• Estimated valence hole charge accumulated at the Fe atom to be 0.6 ± 0.2.
• Observed excited-state metal-to-metal charge transfer on an approximately 60 fs timescale.

Conclusions:

• The combined experimental and computational approach successfully quantifies excited-state valency.
• This method provides a valuable tool for studying ultrafast charge dynamics in solvated complexes.