Electrochemical, Magnetic, and Electrical Properties of α,ω-Capped Sexithiophene Films. Part 3. Conduction in Poly(bis-terthienyl-B)s (B = Ethane, Disulfide, Diacetylene, Acetylene, Ethylene)

Abstract

Electrochemical oxidation of bis-terthienyl-B (B = ethane, disulfide, diacetylene, acetylene, ethylene) has been investigated. Monomers without and with 3,3′′-dialkylsubstitution are regularly coupled to polymers alternating sexithiophene and B moieties. The corresponding terthienyl homopolymers have also been produced for comparison. The polymers obtained are characterized by cyclic voltammetry, EQCM, UV−vis, and FTIR spectroscopy, in situ ESR and in situ conductivity. The conductivities of p-doped polymers with ethane or disulfide bridges fall in a narrow range (1−5 × 10−2 S cm−1) and are practically the same as those of α,ω-dimethylsexithiophene (1 × 10−2 S cm−1), suggesting that conduction proceeds without the help of the links via a direct redox hopping between sexithiophene blocks of adjacent polymer chains. In the cases of diacetylene and acetylene, conduction changes from redox to bipolaron-type but only in the case of ethylene the conductivity jumps to high values (1−5 S cm−1) corresponding to those of the polymers without the bridging moiety B, i.e., with shortened thiophene rings. DFT calculations of the bridge energy levels account for this result.

Analysis of Conjugated Polymers Conductivity by in situ Electrochemical‐Conductance Method

“…Nowadays, the two bands electrode has been replaced by more sophisticated electrodes arrangements. The main limitation of this type of parallel microelectrodes, is that conductivity values smaller than 0.1 Ω −1 cm −1 cannot be obtained . This first system was improved by Harima et al ., who used as working electrode a four‐band platinum electrode for in‐situ conductivity measurement of PANI (Figure b) .…”

“…The main limitation of this type of parallel microelectrodes, is that conductivity values smaller than 0.1 Ω À 1 cm À 1 cannot be obtained. [45][46][47] This first system was improved by Harima et al, who used as working electrode a four-band platinum electrode for in-situ conductivity measurement of PANI ( Figure 3b). [48] An additional power supply (3) ( Figure 3b) is needed to apply the V d between the inner electrodes.…”

Poly(disulfide)s

“…Poly(disulfide) 67 was prepared as part of a series of polymers with alternating sexithiophene sequences and bridge moieties of varied conjugation. 44 The disulfide was of interest because of a possible participation of the electron-rich S-S moiety to the conjugated path. However, the conductivities of p-doped 67 suggested that conduction proceeds via a direct hopping between stacked sexithiophene moieties of cofacial polymer chains.…”

Properties of Thiol End‐Capped and Iodine‐Doped Sexithiophene Disulfide Semiconducting Polymers Bridging Nanogap Gold Electrodes

“…[ 18 ] Formation of the disulfi de bond is an effective way to extend the length of oligothiophenes. [19][20][21] Compared to oligothiophene polymers, disulfi de oligothiophene polymers have worse π -conjugated systems and lower conductance. Nevertheless, the conductivity of polymers can be signifi cantly increased when a dopant is used.…”