Ultrafast Charge Transfer Dynamics in a Slip-Stacked Donor-Acceptor-Acceptor System

Area of Science:

• Photochemistry
• Molecular Photophysics
• Charge Transfer Dynamics

Background:

• Molecular aggregates exhibit altered charge-transfer dynamics due to excitonic coupling.
• Excitonic coupling can enable novel photophysical pathways like symmetry-breaking charge separation (SB-CS).

Purpose of the Study:

• Investigate the impact of excitonic coupling on charge-transfer dynamics in a covalent donor-acceptor-acceptor system (Per-PDI).
• Compare femtosecond transient absorption data of Per-PDI with related systems (Per-PDI and PDI dimer) to understand excitonic effects.

Main Methods:

• Selective photoexcitation of perylenediimide (PDI) chromophores.
• Femtosecond transient absorption spectroscopy.
• Comparative analysis of molecular systems with varying donor-acceptor configurations.

Main Results:

• Electron transfer from the perylene donor (Per) to the PDI dimer's lower exciton state was slower than in a single PDI acceptor system.
• Excitonic coupling between PDIs electronically stabilized the system, reducing the driving force for charge separation.
• Strong π-π interaction between Per and PDI in Per-PDI broke the PDI dimer's electronic symmetry, leading to Per oxidation instead of SB-CS.

Conclusions:

• The electronic coupling in molecular systems must be carefully balanced to promote desired photophysical pathways like SB-CS.
• Designing systems for SB-CS requires optimizing the interplay between the donor, acceptor, and their excitonic interactions.