Dario Iarossi

Gas sensing measurements and analysis of the optical properties of poly[3-(butylthio)thiophene] Langmuir–Blodgett films

Abstract Films of poly[(3-butylthio)thiophene] were prepared via Langmuir–Blodgett (LB) deposition and casting techniques for applications in gas sensor devices. A description of the preparation of the sensing layer is given for both methods: the LB deposition of the polymer in mixture with arachidic acid and the solvent casting by using directly a solution of the polymer in chloroform. In both cases, alumina substrates equipped with gold interdigitated electrodes have been used. In particular, the samples so prepared show variation in the electrical conductivity when exposed to NO2-oxidising or NH3-reducing agents at a working temperature of about 100°C. The refractive index n and the extinction coefficient k at normal incidence have been determined in the 400–800 nm spectral range and an energy gap (highest occupied-molecular-orbital or conduction band (HOMO)–lowest unoccupied molecular-orbital or valence band (LUMO) separation) of about 1.9 eV has been estimated.

Synthesis and characterization of poly[3-(butylthio)thiophene]: a regioregular head-to-tail polymer

Poly[3-(butylthio)thiophene] was obtained from 2,5-dibromo-3-(butylthio)thiophene according to the method of Kobayashi. The polymer was characterized as having regioregular head-to-tail (HT) connections with significant extended conjugation length and optical properties, such as solvatochromism and photoluminescence. The polymer is soluble in common organic solvents and can easily form films.

Spectroscopic comparison between poly[3-(6-methoxyhexyl)thiophene]s with different steric hindrance

Abstract An alternating methoxyhexylthiophene–thiophene copolymer was synthesized from 3-(6-methoxyhexyl)-2,2′-bithiophene and studied chiefly by means of optical absorption and nuclear magnetic resonance spectroscopy. The results were compared with those of the previously obtained poly[3-(6-methoxyhexyl)-2,5-thienylene]. The differences in the UV-Vis spectra of the two polymers in pure solvents, solvent/non-solvent mixtures and in films are discussed on the basis of the microstructure and the steric hindrance along the backbone. NMR spectroscopy revealed copolymer configuration to be regiorandom with a slight prevalence of head-to-head and tail-to-tail junctions.

Langmuir–Blodgett films of poly[3-(butylthio)thiophene]: optical properties and electrical measurements in controlled atmosphere

Abstract Experimental results on the gas-sensing properties of polymer thin films are presented. Langmuir–Blodgett films were formed from a 2:1 M mixture of poly[3-(butylthio)thiophene] (PBTT) and arachidic acid. A stable monolayer was prepared at 20°C on the water surface and it was reiteratively transferred onto various substrates by vertical dipping. The visible spectra of the films indicate a HOMO-LUMO separation of around 1.8 eV with an absorption maximum at about 520 nm. Electrical conductivity measurements performed in controlled atmosphere showed large gas sensitivity to electron-acceptor gases such as nitrogen dioxide at a working temperature of the active layer of about 50°C.

Regiochemistry characterization of poly(3-hexanoyloxyethyl-2,5-thienylene) through proton and carbon nuclear magnetic resonance spectroscopy

Abstract The poly(3-hexanoyloxyethyl-2,5-thienylene) was studied by means of mono- and bidimensional nuclear magnetic resonance spectroscopy. The regiochemistry of the polymer is assigned on the basis of the 13 C chemical shifts, which are easily obtained through inverse detection experiments, utilizing a triad-based model.

Conformational properties of 3,3′-,3,4′- and 4,4′-dimethyl- and -bis(methylsulfanyl)-2,2′-bithiophenes

The conformational properties of the title compounds, which are the basic head-to-head, head-to-tail and tail-to-tail repeat units of regioregular poly(3-methylthiophenes) and poly[3-(methylsulfanyl)thiophenes], are discussed. The paper reports the X-ray structures of the two 4,4′-derivatives, 1H NMR NOE data on the 3,4′ and 4,4′-derivatives and force field MM2 calculations of the conformation of the three bis(methylsulfanyl) derivatives.

Synthesis and characterization of isomeric α,α′-bithienyls with β-methylsulfanyl substituents

The three isomeric bithienyls, 1, 2 and 3, formally related to the dimerization of 3-(methylsulfanyl)-thiophene, have been synthesized by the metal-catalysed coupling between a metallated and a halogenated derivative of thiophene of suitable structure. The 1H and 13C NMR data are discussed.

Preferred orientations of the SO bond in methylsulphinyl derivatives of furan and thiophene: an experimental study based on 1H, 13C, and 17O NMR spectroscopy

Abstract The preferred conformations of the methylsulphinyl group bonded to the heterocycles furan and thiophene have been studied with NMR techniques in solution. The presence of one halogen atom ortho to the methylsulphinyl group determines the orientation of the SO bond in the opposite direction with respect to the halogen, and the degree of coplanarity of this bond with the ring depends on the substitution pattern. The higher degree of coplanarity is found when the methylsulphinyl group and the halogen substituent are in position 3 and 4. Two ortho substituents determine structures with large twists of the methylsulphinyl group. The chemical shifts of 1 H, 13 C and 17 O nuclei of the methylsulphinyl group and referred to spectra in solution do not evidence trends of general validity for all the compounds examined as a function of the orientation of the methylsulphinyl group with respect to the ring. Such trends were present in the case of the cor- responding phenyl derivatives. Nevertheless, by examining the behaviour of long-range n J (C,H) coupling constants, involving the carbon nucleus of the methyl group, together with chemical shifts, conclusions regarding the conformational behaviour of these molecules in solution can be derived. Possible perturbations of the equilibrium caused by the polarity of the medium are evidenced as well. The results indicate that in the 2-methylsulphinyl derivatives of furan the S0 bond is preferentially oriented in the O,O-cis direction and significantly twisted from the ring plane, yet the S,O-cis conformer, with a smaller twist, is preferred for the corresponding thiophene derivative. For the 3-methylsulphinyl derivatives, similar behaviour is found for the two hetero- cycles. The molecules consist of an equilibrium mixture of the X,O-cis and X,O-trans conformers, with the latter more abundant and increasing in more polar solvents. For compounds with an iodine atom in position 4, the X,O-cis conformation is the one most preferred in solution.

1H and 13C NMR characterization of poly[3‐(6‐methoxyhexyl)‐2,2′‐bithiophene]

A full 1H and 1C NMR study through the use of one‐ and two‐dimensional techniques (HMQC, HMBC, TOCSY and NOE‐difference spectroscopy) was carried out on poly[3‐(6‐methoxyhexyl)‐2,2′‐bithiophene]. Inter‐ring correlations detected in the HMBC spectra proved to be a valuable tool in the assignment of regiochemistry. NMR data can be interpreted on the basis of a four‐triad model. Copyright

Synthesis of 3,4′-Dibromo-2,2′-bithiophene: A Useful Intermediate for 3,4′-Disubstituted 2,2′-Bithiophenes. X-Ray Molecular Structure of 3,4′ -Dibromo-2,2′-bithiophene.

The first synthesis of 3,4′-dibromo-2,2′-bithiophene via metal-catalysed cross-coupling between a metallated and a halogenated thiophene derivative is described. An X-ray crystal structure of 3,4′-dibromo-2,2′-bithiophene is reported. 3,4′-Dibromo-2,2′-bithiophene was converted into corresponding bis(alkylsulfanyl) derivatives through bromine–lithium exchange, followed by reaction with two dialkyl disulfides (Me2S2 or Bu2S2). The 1H and 13C NMR data are discussed.