Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

Richert, Sabine; Rosspeintner, Arnulf; Landgraf, Stephan; Grampp, Günter; Vauthey, Eric; Kattnig, Daniel R.

doi:10.1021/ja407052t

Cited by 55 publications

(113 citation statements)

References 70 publications

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“…9−11 We have not studied the permittivity dependence of the n = 6 compound in detail as the MFE was found to be very small (χ E = 1.0% in BN; see below). The MFEs have been determined from steady-state measurements at B 0 = 75 mT and the Earth’s magnetic field ( B 0 ≈ 0 mT) and corrected for background fluorescence as detailed in eq 8.…”

Section: Results and Discussionmentioning

confidence: 99%

Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor–Acceptor Systems

et al. 2018

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Donor–acceptor systems forming exciplexes are versatile models for the study of magnetic field effects (MFEs) on charge recombination reactions. The MFEs originate from singlet–triplet interconversion within transient radical ion pairs (RIPs), which exist in a dynamic equilibrium with the exciplexes. Here, we describe the synthesis and MFEs of the chain-linked N,N-dimethylaniline (DMA)/9-methylanthracene (MAnt) donor–acceptor system MAnt–(CH2)n–O–CH2–CH2–DMA for n = 6, 8, 10, and 16. The MFEs are found to increase with increasing chain length. Effects as large as 37.5% have been observed for the long-chain compound with n = 16. The solvent dependence of the MFEs at magnetic field intensity 75 mT is reported. For the range of solvent static dielectric constants εs = 6.0–36.0, the MFEs go through a maximum for intermediate polarities, for which the direct formation of RIPs prevails and their dissociation and reencounter are balanced. Field-resolved measurements (MARY spectra) are reported for solutions in butyronitrile. The MARY spectra reveal that for n = 8, 10, 16, the average exchange interaction is negligible during the coherent lifetime of the radical pair. However, singlet–triplet dephasing broadens the lineshape; the shorter the linker, the more pronounced this effect is. For n = 6, a dip in the fluorescence intensity reveals a nonzero average exchange coupling of the order of ±5 mT. We discuss the field-dependence in the framework of the semiclassical theory taking spin-selective recombination, singlet–triplet dephasing, and exchange coupling into account. Singlet recombination rates of the order of 0.1 ns–1 and various degrees of singlet–triplet dephasing govern the spin dynamics. In addition, because of a small free energy gap between the exciplex and the locally excited fluorophore quencher pair, a fully reversible interconversion between the RIP, exciplex, and locally excited fluorophore is revealed by spectrally resolved MFE measurements for the long-chain systems (n = 10, 16).

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Section: Results and Discussionmentioning

confidence: 99%

Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor–Acceptor Systems

et al. 2018

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“…2 The authors take this into account as a reduction in the concentration of the radical ion pairs all along the transfer of the system to the exciplex state.…”

Section: Methodsmentioning

confidence: 99%

“…PET processes in linked systems, dyads and triads, are often used as a model of enzyme-substrate interactions, as well as at the individual stages of photosynthesis. 2,3 Dyads are also utilized for the simulation of binding between medicine molecules and various transport proteins, because it is known that these processes often include donor-acceptor interactions. 4 The main attention in such studies is paid to the detection of short-lived particles with partial and full charge transfer, namely, exciplexes and radical ion pairs (RIP), and clarification of the role of these particles.…”

Section: Introductionmentioning

confidence: 99%

Low field photo-CIDNP in the intramolecular electron transfer of naproxen–pyrrolidine dyads

Magin

Polyakov

Kruppa

et al. 2016

Phys. Chem. Chem. Phys.

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Photoinduced processes with partial (exciplex) and full charge transfer in donor-acceptor systems are of interest because they are frequently used for modeling drug-protein binding. Low field photo-CIDNP (chemically induced dynamic nuclear polarization) for these processes in dyads, including the drug, (S)-and (R)-naproxen and (S)-N-methyl pyrrolidine in solutions with strong and weak permittivity have been measured. The dramatic influence of solvent permittivity on the field dependence of the N-methyl pyrrolidine 1 H CIDNP effects has been found. The field dependences of both (R,S)-and (S,S)-dyads in a polar medium are the curves with a single extremum in the area of the S-T+ terms intersection. Moreover, the CIDNP field dependences of the same protons measured in a low polar medium present curves with several extrema. The shapes of the experimental CIDNP field dependence with two extrema have been described using the Green function approach for the calculation of the CIDNP effects in the system without electron exchange interactions. The article discusses the possible causes of the differences between the CIDNP field dependence detected in a low-permittivity solvent with the strong Coulomb interactions and in a polar solvent.

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“…Although it was shown in a recent Ref. 17 that upon increasing the solvent polarity the relative importance of the distant electron transfer quenching increases nonetheless the direct exciplex formation (Scheme I) dominates. Moreover, in a medium polarity solvent, like tetrahydrofuran, ion pairs are almost exclusively generated upon dissociation of the exciplex and that their recombination also occurs with the exciplex as intermediate.…”

Section: Introductionmentioning

confidence: 91%

Diffusion affected magnetic field effect in exciplex fluorescence

Burshteǐn

Ivanov

2014

The Journal of Chemical Physics

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The fluorescence of the exciplex, (1)[D(+δ)A(-δ)], formed at contact of photoexcited acceptor (1)A(*) with an electron donor (1)D, is known to be very sensitive to an external magnetic field, reducing the spin conversion efficiency in the resulting geminate radical ion pair, (1, 3)[D(+)…A(-)]. The relative increase of the exciplex fluorescence in the highest magnetic field compared to the lowest one, known as the magnetic field effect, crucially depends on the viscosity of the solvent. This phenomenon first studied experimentally is at first reproduced here theoretically. The magnetic field effect is shown to vanish in both limits of high and low solvent diffusivity reaching a maximum in between. It is also very sensitive to the solvent dielectric constant and to the exciplex and radical-ion pair conversion rates.

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Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

Cited by 55 publications

References 70 publications

Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor–Acceptor Systems

Magnetic Field-Sensitive Radical Pair Dynamics in Polymethylene Ether-Bridged Donor–Acceptor Systems

Low field photo-CIDNP in the intramolecular electron transfer of naproxen–pyrrolidine dyads

Diffusion affected magnetic field effect in exciplex fluorescence

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