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Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor-Acceptor Systems
Hao Minh Hoang1,2, Van Thi Bich Pham2, Günter Grampp2
1Ho Chi Minh City University of Technology and Education, Vo Van Ngan 01, Linh Chieu Ward, Thu Duc District, Ho Chi Minh City 700000, Vietnam.
ACS Omega
|September 11, 2018
Summary
Magnetic field effects on charge recombination reactions were studied in donor-acceptor systems. Longer chain lengths amplified these effects, with solvent polarity influencing the magnetic field response.
Area of Science:
- Photochemistry and Photophysics
- Chemical Physics
- Organic Electronics
Background:
- Exciplex-forming donor-acceptor systems are key models for studying magnetic field effects (MFEs) on charge recombination.
- MFEs arise from singlet-triplet interconversion in transient radical ion pairs (RIPs) in equilibrium with exciplexes.
Purpose of the Study:
- Synthesize and investigate MFEs in chain-linked N,N-dimethylaniline (DMA)/9-methylanthracene (MAnt) systems.
- Determine the influence of chain length and solvent polarity on MFEs.
- Elucidate spin dynamics and interconversion processes.
Main Methods:
- Synthesis of MAnt-(CH2)n-O-CH2-CH2-DMA systems for n = 6, 8, 10, 16.
- Measurement of magnetic field effects (MFEs) and solvent dependence.
- Field-resolved measurements (MARY spectra) and spectrally resolved MFE measurements.
Main Results:
- MFEs increase with increasing chain length, reaching 37.5% for n=16.
- MFEs exhibit a maximum at intermediate solvent polarities.
- MARY spectra indicate negligible average exchange interaction for longer chains, but significant singlet-triplet dephasing.
- A dip in fluorescence for n=6 suggests a nonzero exchange coupling (~±5 mT).
- Long-chain systems show reversible interconversion between RIP, exciplex, and locally excited fluorophore.
Conclusions:
- Chain length and solvent polarity significantly modulate MFEs in these donor-acceptor systems.
- Spin dynamics are governed by singlet recombination rates and singlet-triplet dephasing.
- Reversible interconversion pathways are revealed in long-chain systems, impacting spin dynamics.
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