Control over charge transfer through molecular wires by temperature and chemical structure modifications

Area of Science:

• Supramolecular Chemistry
• Organic Electronics
• Photophysics

Background:

• Electron donor-acceptor systems are crucial for artificial photosynthesis and organic electronics.
• π-conjugated oligofluorenes (oFL) offer tunable electronic properties for linking functional units.
• Zinc porphyrin (ZnP) and fullerene (C(60)) are well-established electron donor and acceptor moieties, respectively.

Purpose of the Study:

• To synthesize and characterize novel electron donor-acceptor arrays based on ZnP, oFL, and C(60).
• To investigate the electronic interactions and charge transfer dynamics within these arrays.
• To evaluate the role of the oligofluorene linker in mediating electron transfer and its molecular wire behavior.

Main Methods:

• Convergent synthesis for preparing ZnP-oFL(n)-C(60) arrays.
• Cyclic voltammetry, UV-visible, and fluorescence spectroscopy for electronic characterization.
• Femto/nanosecond transient absorption spectroscopy and temperature-dependent photophysical studies for charge transfer dynamics.

Main Results:

• No significant ground-state electronic interactions were observed between ZnP and C(60) through the oFL linker.
• Photoexcitation led to the formation of a long-lived radical ion pair [ZnP(•+)-oFL(n)-C(60)(•-)] with microsecond lifetimes.
• The oligofluorene linker demonstrated molecular wire behavior with an attenuation factor (β) of 0.097 Å(-1), indicating efficient charge transport.

Conclusions:

• The ZnP-oFL(n)-C(60) arrays facilitate long-range electron transfer, primarily driven by the π-conjugated pathway.
• Charge separation and recombination processes exhibit molecular wire characteristics, controllable by temperature.
• Alterations in the oligofluorene linker's π-electron system significantly impact conjugation and charge transport efficiency.