th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
WF28<br />
DYNAMIC NUCLEAR POLARIZATION IN ORGANIC CONDUCTORS<br />
t<br />
Robert A. Wind, Herman Lock and Gary E. Maciel<br />
Department of Chemistry<br />
Colorado State University<br />
Fort Collins, CO 80523<br />
In solids containing unpaired electrons, nuclear spin magnetization<br />
can be enhanced via Dynamic Nuclear Polarization (DNP). This can be used<br />
for, among o<strong>th</strong>er <strong>th</strong>ings, increasing <strong>th</strong>e signal-to-noise ratio of an NMR<br />
signal, obtaining information about <strong>th</strong>e vicinity of <strong>th</strong>e unpaired elec-<br />
trons and determination of electron mobilities. We have applied DNP in<br />
combination wi<strong>th</strong> IH and 13C NMR to two organic compounds <strong>th</strong>at become<br />
metallic by doping <strong>th</strong>em wi<strong>th</strong> a suitable agent, namely trans-polyacetylene<br />
and (fluoroan<strong>th</strong>enyl)2PF 6. The main results are:<br />
(i) Trans-polyacetylene. Even undoped trans-polyacetylene contains<br />
mobile electrons, <strong>th</strong>e so-called "solitons". We found <strong>th</strong>at electron<br />
mobility is restricted: part of <strong>th</strong>e time <strong>th</strong>e unpaired electrons can be<br />
considered as fixed in space, whereas <strong>th</strong>e rest of <strong>th</strong>e time <strong>th</strong>ey are<br />
moving over <strong>th</strong>e polymer chains wi<strong>th</strong> about <strong>th</strong>e velocity of sound. Fur-<br />
<strong>th</strong>ermore, <strong>th</strong>e influence of air oxidation has been investigated, <strong>th</strong>e<br />
effects bo<strong>th</strong> on <strong>th</strong>e amount and types of defects created by <strong>th</strong>is oxidation<br />
and on <strong>th</strong>e amount and mobility of <strong>th</strong>e unpaired electrons.<br />
(ii) (Fluoran<strong>th</strong>enyl)2PF6. This work has been done in collaboration<br />
wi<strong>th</strong> Michael Mehring. The 13 C spectrum consists of seven distinguishable<br />
lines. It has been found <strong>th</strong>at <strong>th</strong>e locations of at least four of <strong>th</strong>ese<br />
lines shift by irradiating wi<strong>th</strong> increasing microwave power at <strong>th</strong>e ESR<br />
frequency. This proves <strong>th</strong>at <strong>th</strong>ese locations are at least partially<br />
determined by a Knight shift due to <strong>th</strong>e mobile electrons.
Change language