th  - 1987 - 51st ENC Conference

MF39
HIGH RESOLUTION DNP-NMR AND KNIGHT SHIFt SUPPRESSION IN A
ONE DIMENSIONAL CHARGE TRANSFER CONDUCTOR
R. D. Kendrick, H. Seidel? a, D. A. Singel, TM
W. StOcklein, lc* and C. S. Yannoni
IBM Almaden Research Center, San Jose, CA
Over the last few years, a wide variety of magnetic resonance experiments have been
performed on a new class of charge transfer complexes which exhibit high one-dimensional
conductivity (~100 (~2 cm)'l). 2 Since the linewidth of the ESR due to the conducting spins
is extremely narrow (~10 milligauss at 9 GHz), proton Overhauser enhancements as high
as 525 have been achieved in this material. 2a
We report here a 13C NMR study of the fluoranthenyl (FA) radical cation salt (FA):PF 6.
Using a 60 MHz DNP spectrometer based on a Fabry-.Perot cavity? we have been able to
observe signals from as few as 1016 carbon-13 nuclei in a single scan at room temperature.
The Knight shift of the 13C spins 2c depends on the difference in population between
electron Zeeman levels: thus, by saturating the ESR line, we have been able to suppress the
Knight shift. A study of the power dependence of this suppression permits correlation of
the Knight and chemical shifts.
The ramifications of a variety of other interactions such as the shift of the ESR line due
to saturation with microwaves (Overhauser shift 2a) or to the proton and fluorine
decoupling fields (Bloch-Siegert shift) will be discussed.
_ --'4-
m -- 2
(FA) 2PF 6
PF 6"
1. Current address: (a) Physics Department, Stuttgart University; b) Chemistry
Department, Harvard University; (c) Physics Department, Bayreuth University.
2. (a) W. St0cklein and G. Derminger, Mol. Cryst. Liq. Cryst. 136, 335 (1986) and
references therein; (b) H. Brunner, K. H. Hausser, H. J. Keller and D. Schweitzer,
Solid State Comm. 51,107 (1984); (c) M. Mehring, M. Helmle, D. KOngeter, G. G.
Maresch and S. Demuth, Proc. of the Intl. Conf. on Synthetic Metals, ICSM86, Kyoto,
Japan, 1986 (to be published in Synthetic Metals).
3. R.D. Kendrick, H. Seidel, D. A. Singel and C. S. Yannoni (to be published).