Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes

Area of Science:

• Physical Chemistry
• Spectroscopy
• Photochemistry

Background:

• The Born-Oppenheimer approximation, assuming independent nuclear and electronic motion, often fails.
• Nuclear-electronic (vibronic) coupling is crucial for ultrafast photophysics and photochemistry.
• Advanced spectroscopic tools are needed to probe vibronic coupling on ultrafast timescales.

Purpose of the Study:

• To investigate vibronic coupling using time-dependent spectroscopic methods.
• To compare vibrational dynamics in ground and excited electronic states of charge transfer complexes.
• To demonstrate control over electron transfer pathways by perturbing vibrational modes.

Main Methods:

• Utilized frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy.
• Employed a UV-visible pump, narrowband IR pump, and broadband IR probe pulse sequence.
• Investigated vibrational dynamics in Re and Ru charge transfer complexes and a Pt(II) donor-bridge-acceptor system.

Main Results:

• Intramolecular vibrational redistribution and energy transfer were significantly faster in excited states compared to ground states.
• Electron transfer rates in a Pt(II) complex were found to be highly dependent on vibrational energy localization.
• Selective IR pumping of specific vibrational modes (C≡C stretch) completely altered charge separation pathways and photoproduct yields.

Conclusions:

• Electronic structure profoundly influences vibrational coupling patterns.
• Vibronic coupling can be modulated through vibrational stimulation, offering a pathway to control charge transfer.
• Controlling vibronic coupling presents opportunities for advancements in solar energy conversion and molecular electronics.