202579-24-6Relevant articles and documents
Intramolecular electron transfer between 2,5-dimethoxy-1,4-phenylene units in [n.n]paracyclophane radical cations
Wartini, Alexander R.,Valenzuela, Jorge,Staab, Heinz A.,Neugebauer, Franz A.
, p. 139 - 148 (2007/10/03)
A range of [n.n]paracyclophane radical cations (4?+-12?+), in which two 2,5-dimethoxy-1,4-phenylene units are connected by alkano bridges of varying length, have been studied by ESR and ENDOR spectroscopy. In the [2.2]- and [3.3]paracyclophane radical cations 4?+-6?+, 10?+ and 11?+ the delocalization of the unpaired electron over both π-moieties and the distinct difference between the first and second oxidation potentials, ΔE= E20 - E10, are evidence for a strong intramolecular electronic interaction between the two electrophores. The [5.5] and [7.7] species (8?+ and 9?+) are localized radical cations at low temperature (ca. 220 K). At room temperature, the higher molecular flexibility leads to a significant increase in the number of internal collisions between the electrophores, resulting in a fast (ESR time scale) intramolecular electron transfer. The intermediate [4.4]paracyclophane radical cations 7?+ and 12?+ are apparently also localized radical cations. The close interplanar distance between the two it-moieties, however, facilitates their mutual contacts. In 7?+, the intramolecular electron transfer becomes fast on the ESR time scale at room temperature; in 12?+ the transfer is fast over the temperature range 200-300 K.
