Reversible excited state electron transfer in an acceptor-acceptor hetero dyad

Area of Science:

• Photochemistry and Photophysics
• Supramolecular Chemistry
• Organic Electronics

Background:

• Electron donor-acceptor systems are crucial for energy conversion and optoelectronic devices.
• Controlling excited-state electron transfer dynamics is key to optimizing material performance.
• Understanding solvent effects on charge transfer processes is essential for molecular design.

Purpose of the Study:

• To synthesize and characterize a novel hetero dyad comprising perylene diimide (PDI) and aza dioxa triangulenium (ADOTA).
• To investigate the unusual and reversible excited-state electron transfer (PET) process within this dyad.
• To elucidate the role of solvent polarity in modulating the PET dynamics and equilibrium.

Main Methods:

• Synthesis of the PDI-ADOTA hetero dyad.
• Femtosecond (fs) transient absorption and time-resolved fluorescence spectroscopy.
• Electrochemistry and spectroscopic analysis of chemically reduced species.

Main Results:

• The PDI-ADOTA dyad exhibits rapid energy transfer from PDI to ADOTA (∼1 ps) followed by PET.
• A reversible PET process establishes an equilibrium between the fluorescent locally excited state and a non-fluorescent charge-shifted state.
• Solvent polarity significantly influences the PET deactivation rate and the reduction pathways of the dyad, favoring different products in DCM and DMF.

Conclusions:

• The near-isoenergetic HOMO and LUMO levels of PDI and ADOTA enable the observed reversible PET.
• Solvent-induced shifts in energy levels are responsible for the sensitivity of the electron transfer process to the environment.
• This study presents a unique molecular system with tunable photophysical properties for potential applications in molecular switches and sensors.