NMR polarization echoes in a nematic liquid crystal

P.R. LEVSTEIN; A.K. CHATTAH; H.M. PASTAWSKI; J. RAYA; J. HIRSCHINGER

American Institute of Physics

Año: 2004 vol. 121 p. 7313 - 7313

have modified the polarization echo ~PE! sequence through the incorporation of Lee-Goldburg cross polarization steps to quench the 1H-1H dipolar dynamics. In this way, the 13C becomes an ideal local probe to inject and detect polarization in the proton system. This improvement made possible the observation of the local polarization P00(t) and polarization echoes in the interphenyl proton of the liquid crystal N-4-methoxybenzylidene!-4-butylaniline. The decay of P00(t) was well fitted to an exponential law with a characteristic time t C'310 ms. The hierarchy of the intramolecular dipolar couplings determines a dynamical bottleneck that justifies the use of the Fermi Golden Rule to obtain a spectral density consistent with the structural parameters. The time evolution of P00(t) was reversed by the PE sequence generating echoes at the time expected by the scaling of the dipolar Hamiltonian. This indicates that the reversible 1H-1H dipolar interaction is the main contribution to the l