Electron transfer rate modulation in a compact Re(I) donor-acceptor complex.

Area of Science:

• Photochemistry
• Spectroscopy
• Materials Science

Background:

• The formation of charge transfer states is crucial in photochemistry and energy conversion.
• Rhenium complexes like fac-[Re(I)(CO)3(DCEB)(3DMABN)] (ReEBA) exhibit charge transfer dynamics.
• Understanding modulation of these states by vibrational excitation is key to controlling photochemical reactions.

Purpose of the Study:

• To investigate the influence of vibrational excitation on the charge separation reaction in ReEBA.
• To explore how specific vibrational modes of the donor and acceptor impact the charge transfer rate.
• To analyze energy transport dynamics in both ground and excited electronic states.

Main Methods:

• Utilized 3-pulse UV-pump - IR-pump - IR-probe spectroscopy to study ReEBA.
• Employed relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy for ground state analysis.
• Analyzed vibrational modes including cyano group stretch, ring stretch, and carbonyl symmetric stretch (νSS(CO)).

Main Results:

• Vibrational excitation of the DCEB acceptor's ring mode significantly modulated charge separation.
• Excitation of the 3DMABN donor's cyano group mode showed no significant rate modulation.
• Charge separation rate increased by approximately 28% upon specific vibrational excitation.
• Observed vibronic coupling between bpy ring mode and νSS(CO) in the excited state.
• Measured energy transport times of 4 ± 0.7 ps (ground state) and 5 ± 1.5 ps (excited state).

Conclusions:

• Vibrational modes of the electron acceptor play a critical role in modulating charge separation rates.
• The study provides insights into controlling charge transfer dynamics through vibrational coherence.
• Demonstrates the utility of multi-pulse IR spectroscopy for probing ultrafast photochemical processes.