Charge and Spin Transfer Dynamics in a Weakly Coupled Porphyrin Dimer

Area of Science:

• Physical Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Investigating electron and spin transfer is crucial for developing advanced molecular devices.
• Zinc-porphyrin dimers offer a promising scaffold for controlling spin states and electron dynamics.
• Understanding localized vs. delocalized electron behavior is key for molecular electronics.

Purpose of the Study:

• To probe electron and spin transfer in a tetramethylbiphenyl-linked zinc-porphyrin dimer.
• To evaluate parameters for designing single-molecule spin valves.
• To explore the creation of a platform for photogenerating high-multiplicity spin states.

Main Methods:

• Utilized variable-temperature continuous wave Electron Paramagnetic Resonance (EPR) and pulsed proton Electron-Nuclear Double Resonance (ENDOR) spectroscopy.
• Employed transient EPR and optical spectroscopy for time-resolved measurements.
• Supported findings with Density Functional Theory (DFT) calculations and reference compound comparisons.

Main Results:

• Radical cation is localized on one porphyrin unit, not delocalized, at low temperatures.
• Rapid intramolecular electron transfer (10.0–53.9 MHz) observed at room temperature, indicating spin density hopping.
• Photogenerated triplet state spin density localizes on one porphyrin unit within nanoseconds.

Conclusions:

• The interporphyrin electronic coupling is suitable for single-molecule spin valve applications.
• The zinc-porphyrin dimer serves as a platform for localized photogenerated triplet states.
• This system can be further explored for generating high-multiplicity spin states.