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Abstract:
Three types of tetrone radical anions in which two 1,4-benzoquinone units are connected by ethano (1·−, 2·−), [2.2]paracyclophane (3·−, 4·−), and anthracene bridges (5·−, 6·−) have been studied by ESR and ENDOR spectroscopy. The displacement of the unpaired electron over the two π moieties in the [2.2]cyclophane radical anions 1·−−4·− and the marked difference between the first and second reduction potentials, ΔE = |E20 − E10| ≥ 0.20 V, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Similar ΔE data for the syn- (3) and anti-naphthalenophanes (4) indicate that most of the intramolecular electronic interaction takes place through the [2.2]paracyclophane bridge. When ion pairing is inhibited by complexation of the cation, the unpaired electron in 5·− and 6·− is also delocalized over the whole pentacenetetrone system at temperatures as low as 160 K.
