Supramolecular control over donor-acceptor photoinduced charge separation

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Photochemistry

Background:

• Donor-bridge-acceptor (DBA) systems are crucial for artificial photosynthesis and molecular electronics.
• Controlling the distance and interaction between donor and acceptor units is key to optimizing charge separation efficiency.
• Oligomeric bridges offer tunable conformational flexibility for modulating DBA interactions.

Purpose of the Study:

• To synthesize and characterize a novel DBA system with a flexible oligomeric bridge.
• To investigate the influence of solvent polarity on the conformation of the oligomeric bridge.
• To correlate bridge conformation with photoinduced energy and charge transfer processes.

Main Methods:

• Covalent synthesis of a p-phenylene vinylene (OPV) - m-phenylene ethynylene (FOLD) - perylene diimid (PERY) system.
• Spectroscopic characterization in different solvent polarities (chloroform, heptane).
• Analysis of photoexcitation dynamics to determine energy and charge transfer pathways.

Main Results:

• The oligomeric bridge adopts a random coil in polar solvents and folds into helical stacks in apolar solvents.
• Photoexcitation leads to intramolecular energy transfer in the random coil conformation.
• A charge-separated state (OPV(+)-FOLD-PERY(-)) is favored in the folded conformation, particularly in apolar media.
• Photoinduced charge separation is significantly enhanced in apolar solvents due to bridge folding.

Conclusions:

• The conformational flexibility of the oligomeric bridge dictates the efficiency of photoinduced charge separation.
• Apolar media promote bridge folding, bringing donor and acceptor units closer and enhancing charge separation.
• This work demonstrates a novel strategy for controlling charge separation in DBA systems by tuning solvent-induced conformational changes.