L. Pasimeni et al., Preferential orientation of fulleropyrrolidine bisadducts in E7 liquid crystal: A time-resolved electron paramagnetic resonance study, J PHYS CH B, 103(51), 1999, pp. 11275-11281
The effect of the orientating potential in the E7 liquid crystal on a serie
s of fulleropyrrolidine bisadducts has been examined. Photoexcited triplet
states, populated by spin-orbit promoted intersystem crossing, have been us
ed as spin probes to determine the preferential orientations of the guest m
olecules in the anisotropic medium. Time-resolved electron paramagnetic res
onance (TREPR) spectroscopy has been applied and spectra with the external
magnetic field set parallel or perpendicular to the director n of the mesop
hase have been measured. Spectrum analysis has enabled us to determine the
preferred orientation of n with respect to the principal axis frame of the
dipolar interaction and to calculate the order parameters by using the orie
ntational distribution function obtained by spectral simulation. It has bee
n found that the macroscopic order degree induced by the mesophase on the g
uest molecules varies from one bisadduct to another. Bisadducts with D-2h s
ymmetry have exhibited tripler spectra due to dimers besides those of monom
ers, The measured zero field splitting parameters and magnetic level popula
tions of the monomer and dimer triplet states have been analyzed, and a str
ucture of the dimer has been postulated.