Synthesis, Structures and Properties of [n]Dendralenes Substituted with Electron-Donating Groups

Dendralenes, acyclic cross-conjugated polyenes having a nonplanar structure, containing 1,3-dithiole (DT) rings are of considerable interest as novel multi-stage redox systems for potential application to electrical conducting, magnetic, electrochromic, and nonlinear optical materials. In the present review, we focus on the electronic structures of DT[n]dendralenes and their pi-extended compounds in which phenylene, thienylene, furylene, or tetrathiapenthalene (TTP) moieties are inserted. DT[n] dendralenes (n = 3 and 4) employ a non-planar structure due to the steric effect, and cyclic voltammetry (CV) suggested multi-redox behavior of extended vinylogues. Their electronic structure and conjugation pathway in cationic states are strongly affected by the aromaticity of the inserted aryl groups. As for dication of DT[4] dendralenes with two thiophene spacers, the electronic structures depend on their substituents. In the cationic states of DT[5] dendralenes with two thiophene spacers, the positive charges are mainly located on the outer TTF moieties. On the other hand, cationic species of DT[3] dendralene having two TTP moieties, the positive charges are distributed mainly in the outer branching vinylogues.