Electronic structure of tetraaza[1.1.1.1]o,p,o,p-cyclophane and its oxidized states

Abstract

From a structural point of view, the smallest macrocyclic oligoarylamine bearing the alternant ortho–para-linkage, tetraaza[1₄]o,p,o,p-cyclophane, can be considered as an intriguing compound: two para-phenylenediamine (para-PD) redox-active units are rigidly fixed in close proximity, being reminiscent of [2.2]para-cyclophane. The electrochemical, spectroelectrochemical and ESR spectroscopic studies revealed that the present overcrowded redox-active macrocycle increased its rigidity with increasing degree of oxidation with the assistance of complementary quantum chemical studies. In the radical cation of the macrocycle, very fast dynamic spin (or charge) transfer between the neutral and oxidized para-PD units via the ortho-phenylene π-bridges was observed in the measured temperature range, while the static spin-delocalization took place within a single para-PD unit.