Spin Radical
Enhanced Magnetocapacitance Effect in
Intermolecular Excited States
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Abstract
This article reports the magnetocapacitance
effect (MFC) based
on both pristine polymer MEH-PPV and its composite system doped with
spin radicals (6R-BDTSCSB). We observed that a photoexcitation leads
to a significant positive MFC in the pristine MEH-PPV. Moreover, we
found that a low doping of spin radicals in polymer MEH-PPV causes
a significant change on the MFC signal: an amplitude increase and
a line-shape narrowing under light illumination at room temperature.
However, no MFC signal was observed under dark conditions in either
the pristine MEH-PPV or the radical-doped MEH-PPV. Furthermore, the
magnitude increase and line-shape narrowing caused by the doped spin
radicals are very similar to the phenomena induced by increasing the
photoexcitation intensity. Our studies suggest that the MFC is essentially
originated from the intermolecular excited states, namely, intermolecular
electron–hole pairs, generated by a photoexcitation in the
MEH-PPV. More importantly, by comparing the effects of spin radicals
and electrically polar molecules on the MFC magnitude and line shape,
we concluded that the doped spin radicals can have the spin interaction
with intermolecular excited states and consequently affect the internal
spin-exchange interaction within intermolecular excited states in
the development of MFC. Clearly, our experimental results indicate
that dispersing spin radicals forms a convenient method to enhance
the magnetocapacitance effect in organic semiconducting materials