One-Dimensional Polycyclic Aromatic Hydrocarbons Incorporating Multiple Dithiafulvene Units-Novel Multi-Redox and Electrochromic Systems.

The combination of polycyclic aromatic hydrocarbons (PAHs) and dithiafulvene (DTF) units provides large π-conjugated scaffolds with multi-redox behavior. Here, we present the synthesis and properties of PAHs containing seven or nine alternating and fused six- and five-membered rings and three or four DTF units located along the PAHs, tri-DTF and tetra-DTF PAH scaffolds. The synthesis relied on the generation of PAH cores with carbonyl groups at the five-membered rings to allow for Horner-Wadsworth-Emmons reactions to introduce the DTF units. These planar molecules exhibited very strong associations in neutral and oxidized states, and the various redox states had distinct UV-vis-NIR absorptions. Proceeding from an odd number to an even number of DTF units had a remarkable consequence for the redox properties. Thus, cyclic voltammetry revealed the tri-DTF PAH to undergo stepwise one-electron oxidations to form the trication with a broadened first oxidation wave owing to associations. Instead, the radical cation of the tetra-DTF PAH underwent a single three-electron oxidation, signaling an exceptional driving force for generating the tetracation. By electrocrystallization both mixed-valence neutral-radical cation and radical cation salts were generated. These multi-DTF PAHs are particularly interesting as potential components for electrochromic and conducting materials or as redox-controllable tectons for molecular self-/disassembly.