Syntheses of New Alternating CT-Type Copolymers of Thiophene and Pyrido[3,4-b]pyrazine Units:  Their Optical and Electrochemical Properties in Comparison with Similar CT Copolymers of Thiophene with Pyridine and Quinoxaline

Abstract

Four kinds of new π-conjugated copolymers of electron-donating thiophene with highly electron-withdrawing pyrido[3,4-b]pyrazine derivatives have been prepared by using the Stille reaction and electrochemical oxidative polymerization in high yields, and their optical and electrochemical properties have been compared with those of previously reported CT-type π-conjugated polymers. Chemically prepared polymers show an [η] value of about 0.3 dL g-1. The π−π* absorption bands (λmax = ca. 633 nm) of the copolymers are observed at a longer wavelength by about 30 nm than those of similar CT-type copolymers of thiophene with pyridine and quinoxaline. These UV−vis data are considered to reflect a stronger CT interaction between thiophene and pyrido[3,4-b]pyrazine, which has a higher electron-withdrawing ability than pyridine and quinoxaline. The copolymers are electrochemically active in both oxidation and reduction regions. In the reduction (n-doping) region, the copolymers show normal three couples of n-doping and n-undoping between −1.55 and −2.25 V vs Ag/Ag+. On the other hand, they receive oxidation (p-doping) at E pa of 0.9 V vs Ag/Ag+. The electrochemical p- and n-doping of the film of the copolymers is accompanied by changes in its UV−vis spectra (electrochromism), and new absorption bands emerge in the range 900−1500 nm by the p- and n-doping. The X-ray diffraction pattern of the copolymer having a long alkyl side chain suggests self-assembling of the polymer assisted by side chain crystallization.

High Electron Mobility and Ambipolar Charge Transport in Binary Blends of Donor and Acceptor Conjugated Polymers

“…The d-spacing calculated corresponding to the diffraction spots was 4.5 Å, which is in agreement with previous powder X-ray diffraction on PTHQx, which also showed a diffraction peak at 4.5 Å. [18] The other diffraction peaks at 3.7 Å (p-p stacking) and 13.6 Å (interchain spacing) observed in the powder X-ray diffraction studies [18] were not observed in the electron diffraction of the single-crystalline phase of the blends.…”

Intramolecular Hydrogen‐Bond‐Assisted Planarization of Asymmetrically Functionalized Alternating Phenylene–Pyridinylene Copolymers

“…In the oxidation region, a peak was observed at % + 1.3-1.5 V with reference to (Ag + / Ag) and was assigned to the oxidation of the phenylene group (main polymer chain). Such oxidation potentials have been observed for other pyridine-containing copolymers, [16,42,46] and these values may be useful towards establishing the electron-transport properties. Additional oxidation peaks were observed at À0.1 and À0.4 V for P 1 and P 2, respectively.…”

“…[12][13][14] Among them, conjugated pyridine-incorporated polymers have attracted much attention owing to the possibility of finetuning the optical properties by means of 1) the electron-accepting ability, 2) N-protonation, 3) N-oxidation, 4) N-alkylation, and 5) metal complexation. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] p-Conjugated polymers that incorporate aryl heterocyclic units, such as pyridine, pyrrole, and thiophene rings, have been synthesized and employed in industrial applications. [30][31][32][33][34] The laddertype polymers incorporated with pyrazines, [35] benzothiadazoles, [36] pyrroloimides, [37] pyridobisimidazoles, [38] and benzothiazole [39] that contain intramolecular hydrogen bonds along the polymer backbone are also known in the literature.…”

3,4‐Ethylenedioxythiophene–Pyridine‐Based Polymers: Redox or n‐Type Electronic Conductivity?

“…reduction to ±1.1 V. The increased acceptor strength allows for the insertion of a second electron per polymer repeat unit [16] 2 exhibits a second reduction process at ±1.6 V, the same potential as the reduction for 1. It is interesting to note that the reduction potential of 2 is about 100±200 mV more positive than those of the thiophene-based pyrido [3,4-b]pyrazine polymers [16] and pyrido [3,4-b]pyrazinevinylene polymers, [17] demonstrating the effect the donor has on the conduction band in relative energy space. In-situ conductance measurements of thin films on interdigitated microelectrodes show onsets of the doping processes consistent with that from cyclic voltammetry (Fig.…”