Electron-transfer acceleration investigated by time resolved infrared spectroscopy

Area of Science:

• Photochemistry and Photophysics
• Quantum Dynamics
• Spectroscopy

Background:

• Ultrafast electron transfer (ET) is crucial in photosynthesis and molecular electronics.
• Biological ET can occur rapidly over long distances.
• Time-resolved infrared absorption (TRIR) and Raman spectroscopies offer structural insights beyond kinetics.

Purpose of the Study:

• To investigate photoinduced ET involving the Re(I)(CO)3(N,N) moiety that proceeds faster than predicted by standard theories.
• To explore mechanisms accelerating ET, including vibrational excitation and electronic interactions.
• To highlight the role of quantum nuclear dynamics in ET reactivity.

Main Methods:

• Utilized time-resolved infrared absorption (TRIR) and Raman-based spectroscopies.
• Employed laser-pulse irradiation to generate excited states for reaction studies.
• Combined experimental spectroscopy with Density Functional Theory (DFT) calculations and structural studies.

Main Results:

• Observed ultrafast picosecond ET in [Re(4-N-methylpyridinium-pyridine)(CO)3(N,N)](2+) exceeding the adiabatic limit due to vibrational/solvational excitation.
• Demonstrated accelerated excited-state Trp → *Re(II) ET in Re-tryptophan assemblies due to protein interaction and electronic delocalization.
• Showcased accelerated back-ET in a porphyrin-Re(I)(CO)3(N,N) dyad via hot product formation in the Marcus inverted region.

Conclusions:

• ET rates can be enhanced by increasing electronic interactions and inducing vibrational excitation in the system and its environment.
• Quantum nuclear dynamics significantly influence ET reactivity.
• Time-resolved vibrational spectroscopies are powerful tools for elucidating ET mechanisms at the molecular level.