F. Barbosa et al., Radical ions of crownophanes derived from tetraphenylethene. Solution structures and ion-pairing phenomena, J ORG CHEM, 63(24), 1998, pp. 8806-8814
Radical anions and radical cations of parent tetraphenylethene (1) and its
cyclophane derivatives 2-8 were generated by chemical methods. These parama
gnetic species were characterized by their ESR and simultaneously recorded
optical spectra. The hyperfine coupling constants were substantiated by END
OR and their signs by general TRIPLE spectroscopy. The structures of the ra
dical ions were established with the help of quantum chemical calculations.
The electron distribution in the phane radical ions is closely related to
that found for 1(.-)/1(.+). In the radical anions no specific complexation
of alkali-metal counterions, K+ and Li+, by the crown-ether moieties could
be observed. When the radical cations were generated by oxidation with Tl-I
II trifluoroacetate in 1,1,1,3,3,3-hexafluoropropanol, distinctly different
ESR spectra were recorded as with the use of other oxidants. This observat
ion is rationalized by the characteristic solvation properties of 1,1,1,3,3
,3-hexafluoropropanol.