Pham VTB, Hoang HM, Grampp G, Kattnig DR. Effects of Preferential Solvation Revealed by Time-Resolved Magnetic Field Effects.
J Phys Chem B 2017;
121:2677-2683. [PMID:
28263599 PMCID:
PMC5377269 DOI:
10.1021/acs.jpcb.7b00510]
[Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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External
magnetic fields can impact recombination yields of photoinduced electron
transfer reactions by affecting the spin dynamics in transient, spin-correlated
radical pair intermediates. For exciplex-forming donor–acceptor
systems, this magnetic field effect (MFE) can be investigated sensitively
by studying the delayed recombination fluorescence. Here, we investigate
the effect of preferential solvation in microheterogeneous solvent
mixtures on the radical pair dynamics of the system 9,10-dimethylanthracene
(fluorophore)/N,N-dimethylaniline
(quencher) by means of time-resolved magnetic field effect (TR-MFE)
measurements, wherein the exciplex emission is recorded in the absence
and the presence of an external magnetic field using time-correlated
single photon counting (TCSPC). In microheterogeneous environments,
the MFE of the exciplex emission occurs on a faster time scale than
in iso-dielectric homogeneous solvents. In addition, the local polarity
reported by the exciplex is enhanced compared to homogeneous solvent
mixtures of the same macroscopic permittivity. Detailed analyses of
the TR-MFE reveal that the quenching reaction directly yielding the
radical ion pair is favored in microheterogeneous environments. This
is in stark contrast to homogeneous media, for which the MFE predominantly
involves direct formation of the exciplex, its subsequent dissociation
to the magneto-sensitive radical pair, and re-encounters. These observations
provide evidence for polar microdomains and enhanced caging, which
are shown to have a significant impact on the reaction dynamics in
microheterogeneous binary solvents.
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