Highly Strained 1,8-Naphthalene-Bridged Cyclic Oligophenylenes and Their Open-Shell Diradical Dications.

The synthesis and characterization of two 1,8-naphthalene-bridged cyclic oligo-para-phenylenes with four or eight phenylene units are reported. Both molecules exhibit a highly strained structure with two nearly face-to-face arranged p,p'-biphenylylene/p,p'-quaterphenylylene chains. Their dications were obtained by chemical oxidation with NO·SbF6, and both showed open-shell singlet diradical character with a small singlet-triplet energy gap.