Thiophene‐based conjugated oligomers and polymers with high electron affinity

Abstract

The control of the bandgap of thiophene‐based polymers and oligomers has become an important topic in recent years. One strategy is the introduction of electron‐withdrawing groups in particular positions in the conjugated chain. An extension of this strategy is reported here: the synthesis and electrochemical investigation (e.g., analysis of the electropolymerization behavior) of a new series of π‐conjugated oligomers containing 3, 4, and 5 heterocycles and two CN groups at various positions of the ethylene linkage.

From Easily Oxidized to Easily Reduced Thiophene-Based Materials

“…One of the possible ways to achieve this objective is functionalization with strongly electron-withdrawing groups, which can be designed to increase the electron affinity of the material. [11] We report here a new strategy towards functionalization of oligothiophenes that consists of the chemical transformation of thienyl sulfurs into the corresponding S,S-dioxides. We show that this kind of functionalizationÐwhich implies the dearomatization of the thiophene ringsÐleads to very stable oligomers with increased electron delocalization and has also a dramatic effect on their electron affinity as deduced from their electrochemical reduction potential.…”

Synthesis and Optical and Electronic Properties of Thiophene Derivatives

“…However, upon subsequent CV scans, we observed two oxidation peaks in the CV between 0 V and 1 V that we attributed to a highly coloured, oligomeric species observed with related bis-(thienylvinyl)thiophenes formed during the reductive cycle. [59,65] On the first anodic scan of a clean electrode, the oxidation peaks between 0 and 1 V were absent, and after several cycles, we did not observe any visible film on the electrode surface owing to the solubility of the oligomeric species in THF.…”

“…The conversion to the bis(2-thienylacrylonitrile)-thiophene was nearly quantitative with yields ranging from 91-97 % in a 30 min reaction. Both Roncali et al [64] and Hanack et al [65] have synthesized the 3,4-proton version of 4a, which showed a λ max value at 480 nm in CH 2 Cl 2 and reversible oxidation and reduction waves. In addition, electrochemical anodic polymerization of the protonated derivative produced a polymer film with a band-gap of 0.65 eV.…”

“…The two quasireversible reduction waves we tentatively assigned to the radical anion and dianion delocalized over the entire molecule, [58,59] as suggested by the LUMO of 1c. Spectroelectrochemical experiments are ongoing to determine the identity of the reduced species.…”

Macromolecular systems with the p-type conductivity

“…For instance, introduction of a dicyano or keto group at position 3 of the thiophene ring or to the vinylene fragment of poly (thienylethylene) leads to a decrease in E g to 1.5 eV as compared to E g = 2 eV for poly(thiophene). 26 Addition of electron releasing groups, such as alkyl, alkoxy, or alkyl sulfanyl groups, also leads to a decrease in the band gap, though with lower efficiency than on introduction of elec tron withdrawing groups; 4) an increase in the percentage of the quinoid form due to the fussion of the thiophene ring with the aromatic systems of higher resonance energy. Among such systems are poly(benzo[c]thiophene) (E g = 1.10 eV) (12), 27 poly (dihexylthieno [3,4 b]pyrazine) (E g = 0.95 eV) (13), 28 poly(thieno [3,4 b]thiophene) (E g = 0.80-0.90 eV) (14); 29 5) alternation of electron releasing and withdrawing groups, leading to the widening the valence and conduc tion bands and finally to the narrowing the band gap; 30 6) synergetic combination of structural effects, allow ing one to decrease E g to 0.36 eV (the value was obtained for the alternated copolymer of 3,4 ethylenedioxythio phene and thienopyrazine) (15).…”