Hydrogen Bonding as a Tool to Control Chain Structure of PEDOT: Electrochemical Synthesis in the Presence of Different Electrolytes

Abstract

The current knowledge about the presence of cation radicals in organic semiconductors is connected with oxidized constitutional units and their interaction with counterions. In this work, we have shown that the formation of cation radicals in poly­(3,4-ethylene­dioxythiophene) is induced by intermolecular electrostatic interactions, particularly by hydrogen-bond formation between formic acid and polymer. Raman, XPS, UV–vis, and EPR spectroscopies were used to prove that by using the simplest carboxylic acid, which can form hydrogen bonding, it is possible to form localized cation radicals. Moreover, it was shown that by replacing formic acid with o-phosphoric acid, it is possible to obtain delocalized cation radicals. The gained new understanding how to tune the formation and nature of cation radicals in organic semiconductors can be used in the design of organic electronics.

Effect of Hydrogen Bonding on a Value of an Open Circuit Potential of Poly‐(3,4‐ethylenedioxythiophene) as a Beneficial Mode for Energy Storage Devices

“…That fact was confirmed by high‐resolution X‐ray photoelectron spectroscopy (XPS) by the detailed investigation of the valent electron shell of sulfur in thiophene ring, where two peaks were observed, which correspond to the presence of sulfur in two oxidations states. [ 12 ]…”

“…Previously it has been proved by us the chemical structure of PEDOT studied by the Raman spectroscopy and XPS and it was shown that PEDOT polymerized in the presence of formic acid is in a reduce state, and there is no oxidized sequence. [ 12 ] On the other hand, it was shown that hydrogen bonds between formic molecules and polymer chains induced the formation of cation radicals and therefore partially oxidized sulfur in thiophene (from XPS spectra it was estimated to be 27%). [ 12 ] Also, it was shown that orthophosphoric acid could interact with PEDOT chains with the formation of delocalized cation radicals.…”

“…Recently, the ability of the protic acid, namely formic acid, to form hydrogen‐bonds with lone pair of electrons of sulfur atoms of PEDOT (and thus to induce the formation of localized cation‐radicals in the conjugated system of PEDOT) was studied. [ 12 ] Moreover, by replacing of formic acid with another protic acid, such as ortho‐phosphoric acid, the delocalization of cation radicals was observed.…”

Method of Preparation of Soluble PEDOT: Self‐Polymerization of EDOT without Oxidant at Room Temperature

“…[ 7 ] Detection of the cation radicals in the final powder could be explained by the presence of acid (formic acid), which is able to induce electrostatic interactions (hydrogen bonding formation), as recently shown by us. [ 31 ]…”

“…We know that formic acid can interact with PEDOT by hydrogen bonding. [ 31 ] Such interactions can induce electron‐charge transfer from thiophene sulfur to hydrogen in formic acid, accompanied by the formation of cation radicals. This interaction observed in the EPR signal of the final PEDOT powder (Figure 3c).…”