Abstract
Cyclazines, of which unique tricyclic structures and perfectly conjugated perimeters of sp2 hybridized carbon atoms, have attracted much attentions from theoretical chemists in analyzing the essential nature of aromaticity/anti aromaticity. Among a series of peripheral conjugated compounds, cycl[3.2.2]azine has been taken as an ideal [10]pai perimeter model bearing an isoelectronic system with [10]-anulene, aimed to assess its aromaticity from a topological viewpoint. Its physicochemical properties as well as chemical reactivity, however, have not yet satisfactory elucidated. In particular, the UV/Vis absorption bands have not fully analyzed in a theoretical way. Here we report the novel synthesis of cycl[3.2.2]azine derivatives and their electronic spectra, followed by a series of molecular orbital calculations (TD-DFT and MS-CASPT2) aimed to characterize the intense absorption peaks. Our results have shown that the absorption peak position associated with the lowest pai-pai excitation has been correctly predicted with both TD-DFT and MS-CASPT2. The corresponding oscillator strength, however, has been considerably underevaluated using TD-DFT. This abnormality has been corrected using highly accurate MS-CASPT2.
