Spin-dependent charge recombination along para-phenylene molecular wires

Area of Science:

• Physical Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Radical pair recombination is crucial for understanding charge transfer in molecular systems.
• Spin-dependent recombination dynamics influence reaction pathways and efficiencies.
• Molecular wires facilitate electron transport, making them key for molecular electronics.

Purpose of the Study:

• To investigate spin-dependent charge recombination in phenothiazine-phenyl-PDI molecular wires (PTZ•+-Phn-PDI•-).
• To extract singlet and triplet charge recombination rate constants using a novel quantum mechanical method.
• To elucidate the mechanisms governing spin-selective charge recombination in relation to wire length.

Main Methods:

• Development and application of an efficient quantum mechanical method for radical pair recombination.
• Analysis of spin-dependent charge recombination dynamics along PTZ•+-Phn-PDI•- molecular wires.
• Fitting magnetic field-dependence data to quantum spin dynamics simulations to extract rate constants.

Main Results:

• Singlet and triplet charge recombination rate constants were extracted for wires with n = 2-5.
• Triplet recombination rate constant shows exponential decay with wire length, indicative of superexchange.
• Singlet recombination rate constant is largely independent of wire length, suggesting incoherent hopping.

Conclusions:

• The study differentiates between superexchange and hopping mechanisms for triplet and singlet recombination, respectively.
• Marcus theory provides a qualitative explanation for the observed spin-selective recombination behaviors.
• Evidence for a magnetic field-independent background contribution to triplet yield suggests further experimental investigation.