Chiem Van Pham

A Convenient Synthesis of 3-Alkylthiophenes

Abstract The known procedures for the synthesis of 3-alkylthiophenes are rather lengthy or involved. By using the NiDPPP++ catalyzed cross-coupling method between 3-bromothiophene and Grignard reagents derived from alkyl halides a number of 3-alkylthiophenes have been prepared in a one-step reaction in good to excellent yields.

A Convenient Synthesis of 2,5-Thienylene Oligomers; Some of Their Spectroscopic and Electrochemical Properties

Abstract A convenient synthesis of a number of oligomeric thiophcnes and oligomeric methyl-, and ethyl-substituted thiophenes as building blocks for novel conducting polymers is reported. The synthesis is based on a NiCl2(dppp) (dppp = Ph2PCH2CH2CH2;PPh2) catalyzed coupling reaction between appropriately substituted bromothiophenes and Grignard compounds derived of them. The λmax of the UV spectra of the unsubstituted oligomeric thiophenes increases, as expected, with the number of thiophene units in the oligomers. Also, as expected, the oxidation potential Emax of these compounds decreases with increasing the number of thiophene units. In the series of the methyl- or ethyl-substituted oligomeric thiophenes such a clear cut relationship is not observed. This behavior is discussed on the basis of diminishing coplanarity due to steric hindrances by the alkyl groups in the 3,3′-positions, which results in a blue shift of the λmax of the UV spectra and a decreased stability of the radical cation formed upon e...

The Electrochemical Behavior in Aqueous Media of Conducting Polymers II . The Insoluble Fractions Obtained on the Cu(II) Catalyzed Polymerization of (2,5‐Dibromo‐3‐Group IV Substituted) Thiophenes

Abstract : The chemical polymerization of (2,5-dibromo-3-substituted) thiophenes utilizing Cu(II)Cl2 as a copromoter yields an amorphous insoluble polymer fraction which exhibits a very high electronic conductivity. These materials have been used as electrode materials. The redox chemistry of the Cu(II) containing polymer in contact with supporting electrolyte only shows a distinct internal (Cu(II)/Cu(I) cyclic voltammetric wave. No redox behavior for the thiophene ring system is observed. This material is very stable in aqueous media and appears to be conducting at positive and negative electrode potentials (contrary to the redox response of electrodeposited polythienylene films). The lack of 3-substituent steric effects is discussed. The similarities and, more important, the dissimilarities of the properties of these polymers and Cu(II)-dithiolate complexes are also discussed.

The Electrochemical Behavior in Aqueous Media of Conducting Polymers: I: The Methanol Soluble Fraction Obtained on the Cu(II) Catalyzed Polymerization of 2,5-Dibromo-3-Methylthiphene

Abstract The methanol soluble amorphous fraction obtained on the CuCl2 induced polymerization of 2,5-dibromo-3-methylthiophene exhibits redox waves on cyclic voltammetric potential polarization for a copper redox couple (for the metal ion incorporated in the polymer matrix) and a redox couple associated with the polymer matrix itself. Furthermore, when used as an electrode for the ferri/ferrocyanide couple in the electrolyte phase it acts as a well behaved electrode surface. Electrodes made from this material show a remarkable stability in aqueous media.

The Electrochemical Behavior of Conducting Polymers Derived from the Oxidation of Thiophene and 3-Methylthiophene Oligomers: Electrodeposition of the Oligomers by Potential Cycling

Abstract The electrochemical polymerization of thiophene, 3-methylthiophene and several unsubstituted and 3-methyl substituted thiophene oligomers using an applied cyclic potential wave form is examined. In all cases the polymer films formed by potential cycling are electrochemically unstable compared to those formed by constant potential oxidation. Also, except for the two tetrathiophene unit oligomers, the nature of the polymer film cyclic voltammograms are distinctly different for the two preparative methods. Differences in polymer chain lengths and morphology are suggested.

The Electrochemical Behavior in Aqueous Media of Conducting Polymers. III: The Redox Reactions of Strongly Oxidizing Metal Cations on the Cu(II) Catalyzed Polymers of 3-Substituted-2,5-Dibromothiophene

Abstract The vigorous evolution of oxygen from the surface of Cu(II) catalyzed 3-substituted-2,5-poly(thienylene) on exposure to solutions of strongly oxidizing metal cations, M+n, and the degradation of the polymer matrix has been observed and investigated. In all cases, a simultaneous degradation of the electronic conductivity and its physical stability were observed. The general mechanism of this redox reaction of M+n with the polymer material and the redox potentials involved have been elucidated.

Synthesis of oligomeric 2,5-thienylenes; their u.v. spectra and oxidation potentials

Oligomeric 2,5-thienylenes and 3-methyl-2,5-thienylenes have been synthesized by NiCl2(dppp)(dppp = Ph2PCH2CH2CH2PPh2) coupling of Grignard compounds with the appropriate bromothiophene; u.v. spectra and oxidation potentials of the oligomers are dicussed in terms of coplanarity of the oligomeric species.

The effect of ‘water and transition metal ion doping’ on the conductivity of poly(3-substituted thiophene-2,5-diyls)

Poly(3-substituted Thiophene-2,5-diyls) incorporating co-ordinated transition metals have been shown to exhibit a dramatic increase in conductivity on ‘doping’ with water from 10–8 to greater than 10–1 S cm–1; however, only the polymer containing CuII exhibits electronic conduction and internal electrochemical redox waves.