Expanded Indacene-Tetrathiafulvalene Scaffolds: Structural Implications for Redox Properties and Association Behavior.

Redox-controlled dimerization of tetrathiafulvalene (TTF) derivatives is an important tool for achieving reversible assemblies. Herein, the synthesis and characterization of indacene-TTF hybrids, in which the central core is fused to naphtho or benzothieno units, are reported. The orientation of these units has a strong influence on the redox properties, with regard to the number of electrons involved in the first oxidation event and the ability of the oxidized forms to associate. The formation of mixed-valence and π-dimer complexes is turned off for those systems in which geometrical constraints provide nonplanar π-systems. Introduction of bulky substituents presents another way of preventing association, as revealed by studies of indenofluorene and diindenoanthracene scaffolds with (triisopropylsilyl)ethynyl groups. Horner-Wadsworth-Emmons reactions present a general synthetic protocol to access superextended TTFs, by using diones of polycyclic conjugated hydrocarbons as substrates.