Thiophene Protons Research Articles

A Competitive n‐Type OECT Material via Copolymerization of Electron Deficient Building Blocks

AbstractThe classical acceptor motifs diketopyrrolopyrrole (DPP) and thienopyrrolodione (TPD) are copolymerized to yield the acceptor–acceptor polymer “Poly(DPP‐TPD).” The fundamental design idea is to maximize the electron affinity (EA), thus increasing the ambient stability of the reduced state against oxygen and water while ensuring high ion compatibility through the incorporation of hydrophilic oligoethylene glycol N‐substituents. Additionally, a highly planarized polymer structure is anticipated, due to the extended noncovalent interactions (conformational locking) between the carbonyl oxygen and the thiophene protons. Cyclic voltammetry, spectroelectrochemistry, ultraviolet photoelectron spectroscopy, ultraviolet‐visible absorption spectroscopy, and organic field effect transistor (OFET) characterization demonstrate the suitability for n‐type organic electrochemical transistor (OECT) devices. High EA, ionization potential, and good electron mobility (µe(OFET)) are shown, in addition to the electrochemical reduction of polymer films in aqueous electrolyte. In n‐type OECTs, poly(DPP‐TPD) demonstrates a moderate threshold voltage of Vth = 0.58 V and an outstanding µC* value of 7.62 F cm−1 V−1 s−1. Cycling studies consisting of pulsed on‐ and off‐switching of the device at gate voltages between Vg = 0.6–0.8 V in the saturation regime reveal high stability for more than 2700 cycles with rapid switching kinetics.

Regular square planer bis-(4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione)/copper(II) complex: Trans/cis-DFT isomerization, crystal structure, thermal, solvatochromism, hirshfeld surface and DNA-binding analysis

Trans-[Cu(O∩O)2] complex, O∩O = 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione was reported with high potential toward CT-DNA binder. The solved XRD-structure of complex indicated a perfect regular square-planer geometry around the Cu(II) center. The trans/cis-DFT-isomerization calculation supported the XRD seen in reflecting the trans-isomer as the kinetic-favor isomer. The desired complex structure was also characterized by conductivity measurement, CHN-elemental analyses, MS, EDX, SEM, UV–Vis., FT-IR, HAS and TG/DTG. The Solvatochromism behavior of the complex was evaluated using four different polar solvents. MPE and Hirshfeld surface analysis (HSA) come to an agreement that fluoride and thiophene protons atoms are with suitable electro-potential environment to form non-classical H-bonds of type CThH⋯F. The DNA-binding properties were investigated by viscosity tests and spectrometric titrations, the results revealed the complex as strong calf-thymus DNA binder. High intrinsic-binding constants value ∼1.8 × 105 was collected.

A Generalized Packing Model for Bulk Crystalline Regioregular Poly(3‐alkylthiophenes) with Extended Side Chains

AbstractPoly(3‐alkylthiophenes) are one of the most frequently used conjugated polymer classes in organic photovoltaics. Here, a generalized packing model for the polythiophene main chains in the crystalline form I of high molecular weight regioregular poly(3‐alkylthiophenes) with extended side chains (pentyl through octyl) is reported. The model is based on structural constraints from solid‐state NMR: short internuclear distances of less than 4.0 Å of neighboring thiophene protons parallel to the stacking direction and the isotropic chemical shift for the thiophene protons is high‐field shifted by 0.9 ± 0.1 ppm. Nucleus‐independent chemical shift calculations show that only the most recent structure for P3HT (space group P21/c) is compatible with these structural constraints. On this basis, a generalized packing model is developed, showing that slipping parallel to the stacked polymer chains of up to 1.5 Å is allowed, while out‐of‐plane tilts perpendicular to the stacked chains are only tolerated up to 20°.

N‐Methyl‐21‐thiaporphyrins

AbstractWe synthesized five N‐methyl‐meso‐tetraaryl‐21‐thiaporphyrins in 55–60 % yield by treating the appropriate meso‐tetraaryl‐21‐thiaporphyrin with CH3I. The N‐methyl‐21‐thiaporphyrins were characterized by HRMS, 1D and 2D NMR spectroscopy, absorption spectroscopy, fluorescence spectroscopy, and electrochemical techniques, and the structure of one of the compounds was obtained by X‐ray crystallography. 1D and 2D NMR spectroscopy were used to identify all of the resonances observed in the 1H NMR spectra of the N‐methyl‐21‐thiaporphyrins. NMR studies indicated that the methylation occurred at the pyrrole ring that is opposite to the thiophene ring. In the 1H NMR spectra, the methylation resulted in significant upfield shifts of the pyrrole and thiophene protons; the maximum shifts were noted for the protons of the N‐methylated pyrrole ring of the N‐methyl‐21‐thiaporphyrins. The X‐ray structure of one of the N‐methyl‐21‐thiaporphyrins revealed significant deviation of the N‐methylated pyrrole ring from the reference plane defined by the four meso carbon atoms, and the porphyrin ring is strongly distorted compared to the 21‐thiaporphyrin ring. The absorption studies revealed that the N‐methyl‐21‐thiaporphyrins showed four Q bands and one strong Soret band, which were bathochromically shifted compared to those of the 21‐thiaporphyrins. The electrochemical studies on the N‐methyl‐21‐thiaporphyrins indicated that the oxidation potentials became less positive and there were negligible shifts in the reduction potentials; the HOMO–LUMO energy gap decreased compared with that of the 21‐thiaporphyrins. The N‐methyl‐21‐thiaporphyrins are weakly fluorescent with low quantum yields and singlet‐state lifetimes. The spectral and electrochemical studies indicated that N‐methylation of the pyrrole ring of 21‐thiaporphyrins significantly alters the electronic properties of the 21‐thiaporphyrin macrocycle.

Effect of cyclohexene on thiophene adsorption over NaY and LaNaY zeolites

NaY and LaNaY were used as adsorbents to remove thiophene from model gasoline (MG) with and without cyclohexene (CHE) by static adsorption experiments at room temperature (RT). The adsorbents were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 physisorption and pyridine infrared spectrum (IR). The adsorption experiments show that the desulfurization performance of NaY decreases with the rise of CHE concentration in MG, whereas that of LaNaY first increases then declines. FT-IR spectra of thiophene adsorption indicate that thiophene is mainly adsorbed on NaY via π electron interaction, but adsorbed on LaNaY via π electron interaction, La–S direct interaction and protonation of thiophene. The Brönsted acid sites of LaNaY are found to play a crucial role and be responsible for the protonation of either thiophene or CHE molecules, which results in the alkylation reactions between thiophene and CHE in MG. The gas chromatograph–sulfur chemiluminescence detector (GC–SCD) and ultraviolet–visible (Uv–vis) spectra results also confirm the formation of alkylated thiophenes. The improved desulfurization over LaNaY may be attributed to the formation of alkylated thiophenes, owing to the larger molecular sizes and the higher electron densities on sulfur atoms of the alkylated thiophenes.

Effects of toluene on thiophene adsorption over NaY and Ce(IV)Y zeolites

Zeolites NaY and Ce(IV)Y were employed as adsorbents to remove organic sulfur compounds from model gasoline (MG) solutions with and without toluene in static adsorption experiments at room temperature (RT) and atmospheric pressure. The adsorbents were characterized by XRD, XRF and pyridine infrared spectrum (IR). The adsorption experiments show that the desulfurization performance of Ce(IV)Y is much better than that of NaY. The sulfur removal over both NaY and Ce(IV)Y decreases with the increase of toluene concentration in MG, however, the decline tendency on Ce(IV)Y is smooth, and it is steep on NaY. FT-IR spectra of thiophene adsorption indicate that thiophene molecules are mainly adsorbed on NaY via π electron interaction, but on Ce(IV)Y, in addition to the π electron interaction, both Ce4+-S direct interaction and protonation of thiophene also play important roles. Toluene molecules are adsorbed on NaY also via π electron interaction. Although the amount of Brönsted acid sites is increased due to the introduction of Ce4+ ions into NaY zeolite, it is not found to influence the adsorption mode of toluene over Ce(IV)Y. Compared with NaY zeolite, the improved desulfurization performance over Ce(IV)Y for removing organic sulfur compounds from MG solution, especially those containing large amount of aromatics, may be ascribed to the direct Ce(IV)-S interaction, which is much resistant to the influence resulted from toluene adsorption.

A theoretical investigation into the thiophene-cracking mechanism over pure Brønsted acidic zeolites

The mechanism of thiophene cracking catalyzed by Brønsted acidic zeolites was computed at the level of B3LYP density functional theory. It was found that this catalytic reaction involves two major steps: (1) protonation of thiophene associated with an electrophilic aromatic substitution to another thiophene in a concerted way to form 2-(2,5-dihydrothiophen-2-yl) thiophene, and (2) C S bond dissociation in 2,5-dihydrothiophene promoted by further protonation. The intermediate, 4-mercapto-1-(thiophen-2-yl)but-2-en-1-ylium, was found to have a CH 2 group close to a C C bond and a SH group, in agreement with the experimental findings. A strong stabilization effect of the zeolite framework on the transition states was found by embedding the 5T cluster into the larger 34T and 56T clusters. The rate-determining step is the electrophilic aromatic substitution.

Mechanism of the aromatic hydroxylation of thiophene by acid-catalyzed peracid oxidation.

The oxidation of thiophene (1) with peracids in a strongly acidic environment yielded thiophen-2-one (4) as the product of an apparent direct hydroxylation of the thiophene aromatic ring together with the anticipated thiophene-S-oxide dimers, 2a,b, as the main products. Formation of the latter dimers can be rationalized in a straightforward manner by initial oxidation at the sulfur atom of thiophene (1) to yield thiophene-S-oxide followed by subsequent dimerization in a Diels-Alder type reaction. Trapping experiments in the presence of a competing dienophile indicated that thiophen-2-one (4) did not originate from the monomeric thiophene-S-oxide but was the product of an independent reaction pathway. The extent of thiophen-2-one (4) formation correlated with the acidity of the reaction medium and was suppressed in the presence of water, the latter presumably acting as a competing base. As evidenced by the use of 2,5-dideuterated thiophene (1-D), its mechanism of formation involved a 1,2-hydride shift, a feature commonly described in the peracid-mediated epoxidation of aromatic hydrocarbons and indicative for the occurrence of cationic intermediates. In agreement with all these observations we propose a mechanism involving initial protonation of thiophene followed by nucleophilic attack of the peracid in position 2 of the thiophene ring. Intramolecular epoxidation may lead to the formation of thiophene 2,3-epoxide as a highly reactive intermediate that then undergoes heterolytic ring opening and a 1,2-hydride shift to yield thiophen-2-one (4) after a final, acid-catalyzed, isomerization of the double bond.

Spectroscopic studies on monomers and dimers of thiaporphyrins

Synthesis and spectroscopic properties of porphyrin macrocycles with sulphur as the heteroatom in the porphyrin core have been studied. Electronic absorption spectra of these macrocycles show porphyrin-like behaviour with a strong Soret band and weakQ-bands. Substitution of the -NH groups of tetraphenylporphyrin (TPPH2) by sulphur causes a red shift of all the absorption bands and the magnitude of the red shift depends on the number of sulphur atoms substituted. Both the mono and dications of dithiaporphyrins (S2TPP) show larger bathochromic shifts ofQ-bands relative to TPPH2 indicating a stronger resonance interaction with the phenyl groups. A positive shift for both oxidation and reduction potentials is observed upon substitution of sulphur atoms.1H NMR spectra of symmetrically substituted dithiaporphyrins show two sharp singlets for pyrrole protons and thiophene protons confirming the presence of a two-fold axis of symmetry. Only monothia derivatives (STPPH) form metal complexes [Ni(II), Cu(II)] and these metal complexes are five-coordinate with an apical chloride ligand.

NMR Study of Protonated Halothiophenes. II. An ab Initio Self-consistent Field Calculation of the Protonation of Chlorothiophenes

Abstract The STO-3G method was applied to the protonation of thiophene and chlorothiophenes. The optimized structures and charge densities thus obtained are consistent with the experimental results obtained from the 1H NMR spectral data. In the neutral molecule, the β-chloro substituent lowers the total energy more than the α-one; however, the latter stabilizes the protonated state more than the former.

On the nitration of 2‐benzylthiophene and the spectroscopic behaviour of nitro‐2‐benzylthiophenes

AbstractNitration of 2‐benzylthiophene with nitric acid (molar ratio 1:1) in acetic anhydride gave only nitro‐2‐benzylthiophenes, indicating the benzene ring is unreactive to this electrophilic substitution. The main reaction product was 2‐benzyl‐5‐nitrothiophene (about 87%) the amounts of the 3‐nitro and 4‐nitro isomers were about 10% and 3%, respectively. These percentages, determined by glc and nmr techniques, were found to be constant using various nitration conditions. The syntheses of the nitro‐2‐benzylthiophenes are described, together with some spectroscopic properties.The uv spectra confirm that the conjugation of the nitro group in the α position is greater than in the β position. The isomer structures have been assigned by nmr chemical shifts and coupling constant of the thiophene protons. Also infrared spectra are briefly considered.