Voltammetric and Spectroscopic Investigation of Electrogenerated Oligo-Thiophenes: Effect of Substituents on the Energy-Gap Value

Abstract

Oligothiophenes are especially appealing due to their promising applications in different fields, including photosensitive devices. In this context, anchoring a selected substituent on the main structure of the starting material can induce changes in redox and spectroscopic features, according to the nature of the substituent and its position on central or terminal rings. Here, an electrochemical and spectroscopic comparison between 2,2′:5′,2″-terthiophene (2), 5-Br-terthiophene (3) and 5-ethynyl-terthiophene (5-ET) is reported, aimed at elucidating the effect of the nature of the substituent on the energy gap value of the terthiophene skeleton. Furthermore, in order to understand the influence of a selected substituent in varying its position on the terthiophene backbone, 5-ET is compared to the previously described 3′-ethynyl-terthiophene (3′-ET). Experimental results are confirmed by DFT calculations, showing a higher extension of the electron density in 5-ET compared to 2 and 3, as well as to 3′-ET. In addition, as a consequence of the presence of the unsaturated fragment on the C-5-position, the energy gap value of poly-5-ET (the electrogenerated film from 5-ET) appears significantly lower than poly-2 and poly-3. Finally, the higher conjugation effect of a terminal acetylene fragment compared to a central one is confirmed by the energy gap values of poly-5-ET and poly-3′-ET.

Europium Sulfide Driven at Bipolar-Polymerized Polypyrrole: A Highly Active Photoelectrocatalyst for Hydrogen Evolution Reaction

“…On the other hand, the energy states of valence and conduction bands of EuS were identified by CV at Na 2 SO 4 solution (Figure S7). From eqs S3–S5, the energy of the valence band and conduction band (HOMO and LUMO) is estimated . The energy gap ( E Bg ) value is the difference between E LUMO and E HOMO and calculated to be 1.65, which is confirmed by E Bg evaluated from the DRS spectrum.…”

“…From eqs S3−S5, the energy of the valence band and conduction band (HOMO and LUMO) is estimated. 60 The energy gap (E Bg ) value is the difference between E LUMO and E HOMO and calculated to be In view of the calculated energy levels of EuS/Ppy/Au, the suggested photocatalytic occurrence is shown in Scheme 2c. The hybridized S 2− 3p with Eu 2+ 4f 7 orbitals are situated as the valence band, and Eu 4d orbitals are the conduction bond.…”