Synthesis and Electrochemical Properties of New Main Chain Type Polyquinones Constituted of Thiophene-Fused Benzoquinone and Transformation of the Polymers to a Dicyanoquinonediimine Type Polymer

Abstract

ABSTRACT:New main chain type polyquinones, poly (3,7-dialkylbenzo[1,2-b:4,5-b ]dithiophene-4,8-dione-2,6-diyl), P(2,6-Th 2 Bq(diR)) (R = hexyl(Hex); octyl(Oct); dodecyl(Dod)), and poly(benzo[1,2-c:4,5-c ]dithiophene-4,8-dione-1,3-diyl), P(1,3-Th 2 Bq), were prepared by organometallic polycondensation. P(2,6-Th 2 Bq(diR)) was soluble in organic solvents such as chloroform and dichloromethane. P(1,3-Th 2 Bq) is soluble in CF 3 COOH, NMP, and DMI (1,3-dimethyl-2-imidazolidione). P(2,6-Th 2 Bq(diHex)) received electrochemical two step reduction with peak reduction potentials (E pc ) of −1.18 V and −1.84 V vs. Ag + /Ag, respectively. This electrochemical reduction corresponds to Wurster type reduction characteristic of quinones. P(1,3-Th 2 Bq) was also electrochemically active and its reduction took place at E pc = -1.50 V and -1.74 V vs. Ag + /Ag. The film of P(1,3-Th 2 Bq) changed its color from brown to blue (electrochromism) on the electrochemical reduction. Powder XRD patterns of P(2,6-Th 2 Bq(diR))s indicated that they assumed an ordered structure; they showed an XRD peak in a low angle region (2θ (Cu-Kα)< 7• ). The d-value of the peak increased linearly with increase in the number of the carbon of the R groups, suggesting that the d-value corresponded to a distance between the polymer main chains separated by the R groups and P(2,6-Th 2 Bq(diR)) took a stacked structure in the solid. The quinone unit of P(2,6-Th 2 Bq(diR))s was transformed to a strong electron withdrawing dicyanoquinonediimine (DC-QNI) unit by reaction with bis(trimethylsilylcarbodiimide) (TMS-N = C = N-TMS); a high degree of transformation was observed by elemental analysis. A cast film of the obtained polymer underwent the electrochemical reduction with the first E pc 1 at a very high potential of -0.56 V vs. Ag + /Ag, reflecting the high electron-withdrawing properties of the DCNQI unit. KEY WORDS π-Conjugated Polymer / Organometallic Polycondensation / Thiophene-Fused Benzoquinone / Electrochemical Response / Thiophene-Fused Dicyanoquinonediimine (DCNQI) / There has been current interest in the synthesis of novel π-conjugated polymers as interesting and useful optical and electronic materials. 1 Among the π-conjugated polymers, those constituted of redox active recurring units have attracted attention due to their interesting electrochemical behavior. Quinones are known as typical redox active compounds and a number of papers have been published about redox behaviors of quinone and its derivatives. 2 In spite of their attractive properties, examples of polymers consisting of the quinone units are still limited. 3, 4 Peover and co-workers reported the preparation of meta-bonded poly(hydroquinone) and its electrochemical responses. 3a Arai and co-workers reported electrochemical synthesis of poly(mercapto-p-benzoquinone) and poly(mercapto-p-hydroquinone). 3b However, in these cases, the bonding modes of the monomeric units in the polymer chains are not controlled and their chemical properties have not been revealed well.Previously, we rep...

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