Solvent reorganizational red-edge effect in intramolecular electron transfer

Area of Science:

• Photochemistry and Photophysics
• Solvent Effects on Electronic Spectra
• Molecular Dynamics in Polar Media

Background:

• Polar solvents exhibit a distribution of solute-solvent interaction energies, leading to inhomogeneous broadening in electronic spectra.
• Excitation at the red edge of absorption bands enables photoselection of high-energy solute-solvent configurations.
• Intramolecular electron transfer (LE to CT state) in bianthryl typically requires solvent relaxation and is hindered in vitrified polar solutions.

Purpose of the Study:

• To investigate the facilitation of intramolecular electron transfer in bianthryl using red-edge excitation in a polar solvent.
• To spectroscopically isolate and study the charge-transfer (CT) state of bianthryl.
• To correlate the observed CT state properties with the relaxational characteristics of the solvent.

Main Methods:

• Utilized red-edge excitation spectroscopy on bianthryl molecules in low-temperature propylene glycol glass.
• Analyzed solute electronic spectra to observe inhomogeneous broadening and photoselection effects.
• Developed a qualitative potential model to explain the observed photophysical phenomena.

Main Results:

• Demonstrated that red-edge excitation dramatically facilitates intramolecular electron transfer from the locally excited (LE) to the charge-transfer (CT) state in bianthryl.
• Successfully obtained spectroscopically pure CT forms of bianthryl.
• Observed a dependence of the CT state on the relaxational properties of the propylene glycol solvent.

Conclusions:

• Red-edge excitation is a powerful tool for controlling and studying electron transfer processes in polar solvents.
• The study provides insights into the interplay between solvent dynamics and intramolecular charge transfer.
• The findings contribute to understanding spectral properties and reaction pathways in complex polar environments.