The electronic characterization of conjugated aryl-substituted 2,5-bis(2-thien-2-ylethenyl) thiophene-based oligomers

A series of 2,5-bis(2-thien-2-ylethenyl) thiophene-based oligomers with a para-R-arylethenyl substituent have been subjected to electrochemical (cyclic voltammetry and electronic absorption spectroscopy) and density functional theory characterization. The primary aim of this investigation is to characterize the behavior of these oligomers in the oxidized state. Oligomers without methyl ‘end-caps’ undergo facile σ-dimerization; however there is no evidence for the formation of higher oligomers. The oxidized σ-dimers exist in both cationic and dicationic form. Oligomers with methyl ‘end-caps’ do not show any evidence of σ-dimerization. The inductive capacity of the para-R substituent has a significant bearing on the electronic properties of the oligomer, in particular, oligomers with more electron-withdrawing substituents have charge transfer character associated with the dominant electronic excitations.