Radical ions of crownophanes derived from tetraphenylethene.: Solution structures and ion-pairing phenomena

Radical anions and radical cations of parent tetraphenylethene (1) and its cyclophane derivatives 2-8 were generated by chemical methods. These paramagnetic species were characterized by their ESR and simultaneously recorded optical spectra. The hyperfine coupling constants were substantiated by ENDOR and their signs by general TRIPLE spectroscopy. The structures of the radical 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-III trifluoroacetate in 1,1,1,3,3,3-hexafluoropropanol, distinctly different ESR spectra were recorded as with the use of other oxidants. This observation is rationalized by the characteristic solvation properties of 1,1,1,3,3,3-hexafluoropropanol.