Redox states of well-defined π-conjugated oligothiophenes functionalized with poly(benzyl ether) dendrons

The redox states of a series of well-defined hybrid dendrimers based on oligothiophene cores and poly(benzyl ether) dendrons have been studied using cyclic voltammetry and variable-temperature UV/visible/ near-IR spectroscopy. The oxidation potentials and the electronic transitions of the neutral, singly oxidized, and doubly oxidized states of these novel hybrid materials have been determined as a function of oligothiophene conjugation length varying between 4 and 17 repeat units. The attachment of poly(benzyl ether) dendritic wedges at the termini of these lengthy oligothiophenes considerably enhances their solubility, thus enabling the first detailed investigation of the electronic structure of oligothiophenes having 11 and 17 repeat units with minimal β-substitution. In the case of the undecamer and heptadecamer, we find that the dicationic state consists of two individual polarons, rather than a single bipolaron. The effect of the dendritic poly(benzyl ether) solubilizers on the properties of the redox states varies with the oligothiophene length and dendron size. More specifically, we observe a kinetic limit to the electrochemical oxidation of the oligothiophene core when the dendron is large compared to the electrophore. Finally, we have observed the first example of self-complexation of cation radicals via π-dimerization leading to the formation of dendritic supramolecular assemblies.