Nonplanar aromatic compounds. 8. Synthesis, crystal structures, and aromaticity investigations of the 1,n-dioxa[n](2,7)pyrenophanes. How does bending affect the cyclic pi-electron delocalization of the pyrene system?

ABSTRACT

A series of 1,n-dioxa[n](2,7)pyrenophanes (n = 7-12) with increasingly nonplanar pyrene moieties was synthesized by a 9-10 step sequence starting from 5-hydroxyisophthalic acid. The crystal structure of each member of this series was determined crystallographically. Several spectroscopic properties were found to vary with the extent of the nonplanarity of the pyrene unit. The way in which the distortion from planarity of the pyrene system influences its pi-electron delocalization was investigated by using two quantitative descriptors of aromaticity based on geometry (HOMA) and magnetism (magnetic susceptibility and NICS). Both methods suggest that the aromaticity of the pyrene moiety is diminished only slightly upon increasing the bend angle theta from 0 degrees to 109.2 degrees.