2,2 -Bithiophene spectroscopy

Since the ionization potential of thiophene is relatively high, the electric fields required for its anodic polymerization are rather steep (= 20V vs SCE). In addition, the simplest supporting electrolyte for this operation is Li BE- and deposition of Li at the cathode (usually Pt) is also energetically unfavorable. Recently, Druy (13) reported that substitution of 2,2 -bithiophene for thiophene gave better quality films, probably due to the lower ionization potential of the dimer relative to thiophene. An additional improvement consisted in replacing the Pt counter electrode by A1 (9). Spectroscopy revealed that dedoped PT films produced with the above improvements were indistinguishable in quality from the chemically coupled PT. 

Ultraviolet photoelectron spectroscopy (UPS) has been used to study the evolution of the valence electronic states as a function of conjugation length for thiophene, bithiophene, terthiophene, and sexithiophene films deposited in vacuum on gold substrates at 130 K. 

Tanguy J et al 1991 Poly(3-alkylthiophenes) and poly(4,4 -dialkyl-2,2 -bithiophenes) a comparative study by impedance spectroscopy and cyclic voltammetry Synth. Met. 45 81-105... 

The spirit is to show some of the results, but also to guide users of the approach by pointing to the problems and limitations of the method. The review covers some of the newer applications in the spectroscopy of organic molecules acetone, methylenecyclopropene, biphenyl, bithiophene, the protein chromophores indole and imidazole, and a series of radical cations of conjugated polyenes and polyaromatic hydrocarbons. The applications in transition metal chemistry include carbonyl, nitrosyl, and cyanide complexes, some dihalogens, and the chromium dimer. 

J e and coworkers have analyzed the sensing properties of boron-modified PTs 116-118 toward pyridine or 2-picoline [234]. Polymerization was achieved under mild conditions by treatment of distannylated bithiophene with the corresponding bifunctional arylboron bromides at ambient temperature leading to polymers soluble in common organic solvents. Binding of pyridine was investigated by NMR, UV-vis, and fluorescence spectroscopy. 

In 1995, Swager et al. synthesized the first calixarene-coupled diiodinated bithiophene, which afforded copolymer 2.166 (Chart 1.36) by Stille-type cross-coupling with distannylated 3,3 -bis(methoxyethoxy) bithiophene [263]. Selective recognition of Na+ ions was studied by UV-Vis spectroscopy and cyclic voltammetry. After addition of 0.5 mMNa+, cyclic voltammetric measurements showed a positive shift of the oxidation potential of about -1-100 mV with a simultaneous dramatic decrease in conductivity. This finding was attributed to an electrostatic effect of the Na+ ions and reduced electron-donating ability of the sodium bound oxygen atoms of the calixarene. 

As stated earlier, polymer deposition occurs by precipitation of the oligomers when their chain length attains a value of critical solubility [38]. The growth of PT and poly(bithiophene) has been studied by time-resolved ultraviolet visible (UV-vis) spectroscopy. Comparison of the spectra of the reaction solution with those of authentic neutral thiophene oligomers has led to the conclusion that oligomers formed by 7-12 monomer units are formed in solution during electropolymeriza-... 

Strictly, this is an alternating copolymer of bithiophene and pyrrole, rather than a random copolymer of thiophene and pyrrole. The copolymer, deposited on either transparent electrodes or platinum, was characterized by in-situ visible/near IR spectroscopy as a function of oxidation level and by FTIR, four-point probe conductivity, and CV... 

In addition to the routine characterization of these copolymers with UV-visible, near IR and FTIR spectroscopy, XPS, elemental analysis and four-point probe conductivity measurements, Mossbauer [17] and photoluminescence (PL) [18,19] spectroscopy of the copolymer were used. When the thiophene content in the copolymer is higher than 50 mole%, there are three peaks at 2.0, 1.8 and 1.7 eV in the PL spectra of the copolymer. Below 50 mole%, the copolymer does not exhibit photoluminescence. Details of the fabrication of a type II conducting polymer heterolayer superlattice by the electrochemical copolymerization of pyrrole and bithiophene by the potential-programmed electropolymerization (PPEP) method are given in a recent review [19]. 

Neither copper perchlorate nor ferric perchlorate reacts with thiophene to yield a conducting polymer. However, electrically conductive polymers are synthesized by the reaction of 3-methylthiophene or bithiophene with ferric perchlorate. With copper perchlorate, only bithiophene undergoes a simultaneous polymerization and oxidation reaction. X-ray photoelectron spectroscopy of the PT derivatives with perchlorate as counter ion indicates that a significant amount of the chlorine may be covalently bonded to the polymer [288, 574], The electrical conductivity of polymerized bithiophene reaches values as high as 4.5 S cm [574]. 3-Dodecyl-2,2 -bithiophene, 3-(3-phenylpropyl)thiopheneand 3,4-dibutoxythiophene can be polymerized oxidatively using either copper perchlorate, copper tetrafluoroborate, or ferric perchlorate [575]. 

The deposition of copolymers of ruthenium complexes with 3-methylthiophene or bithiophene is inhibited by residual water in the polymerization solution [656]. The surface chemistry of PBT studied by parallel time-of-flight secondary ion mass spectrometry/X-ray photoelectron spectroscopy (ToF-SIMS/XPS) is strictly correlated to the amount of water in the cycling solution [237,674,675]. PT films prepared by electrochemical polymerization in aqueous HCIO4 have about 8-10 mol% of CIOT at the surface, but not in the bulk. Carbonyl groups are formed due to the participation of water in the polymerization of thiophene [676]. 

To increase the scattered light intensity in Raman spectroscopy, which was thought to insufficiently low, Bazzaoui et al. [960, 961] prepared polymers of bithiophene in the presence of silver ions in a rather complex electrolyte solution. The silver thus incorporated in the polymer film caused enhancement effects usually observed in SERS. The reported spectroscopic results did not differ markedly from those reported before. 

With in situ UV-vis spectroscopy, Zagdrska and Krische [1024] found evidence to indicate a more regular structure of polymers prepared from 4,4 -dibutyl-2,2 -bithiophene and 4,4 -dioctyl-2,2 -bithiophene and modified electrochemically as compared to polymers prepared from 3-alkylthiophenes. Nevertheless, a shorter conjugation length was found. 

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