Effect of substituents on electrochemical and optical properties of thienyl-derivatized polypyrenes

A series of pyrene-based monomers that incorporate thiophene or 3,4-ethylenedioxythiophene (EDOT) units at the 1- and 1,6-positions were synthesized and electropolymerized. Through manipulating the heterocycle groups attached to pyrene unit, the electronic properties and energy levels of the polymers were effectively tuned. Substitution with alkoxy functionalized thiophene, i.e., EDOT, results in a decrease in the monomer and polymer oxidation potentials, narrowing of the electronic bandgap relative to the corresponding thiophene substituted pyrenes. With the increase of the number of substituent groups on pyrene units, the polymers show much bigger conjugated length. Moreover, the introduction of two substituent units lowers much more band gap than that of one substituent unit. These results suggested a simple and effective approach for tuning the bandgap in a conjugated polymer through modification of the pendant substituent groups.