Thiophene Oligomers Research Articles

Charge-induced spin polarization in thiophene oligomers

Charge-induced spin polarization in small organic molecules is a key factor for spin transport and magnetic effects in related organic devices. In this work, we study spin polarization in charged thiophene oligomer molecules by calculating the magnetic moment with density functional theory. It is found that the emergence and variation of the net magnetic moment is related to both the amount of charge injected and the polymerization of the oligomer. In combination with model analysis, we conclude that the strong electron–electron interaction and electron–lattice interaction in organic materials are responsible for charge-induced spin polarization.

Large negative differential resistance and rectifying behaviors in isolated thiophene nanowire devices

We design isolated molecular nanowires composed of thiophene oligomers sandwiched between two one-dimensional gold electrodes. Electronic transport through the molecular junctions with two interface geometries is studied by performing the first principles calculations based on density functional theory and nonequilibrium Green's function. The current-voltage (I-V) curves of the molecular wires display an unexpected negative differential resistance and rectifying behaviors along with the oscillation effects, different from other theoretical and experimental studies about the analogous thiophene devices. The significant difference is attributed to the design of the one-dimensional gold electrodes with large enough vacuum layer in transverse direction in order to suppress the interaction between wires. Such transport behaviors indicate that the thiophene molecular device would be an important candidate in future molecular electronics.

Phenylene–Thiophene Oligomer Derivatives for Thin-Film Transistors: Structure and Semiconductor Performances

Two phenylene–thiophene oligomer derivatives, 2,8-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene (28HPTDBT) and 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene (37HPTDBT), were used as active materials in thin-film organic field-effect transistors (OFETs). Although the two molecules have similar structures, they exhibited obvious differences in photophysical, crystal, π-stacking, and electrical properties. 28HPTDBT is an amorphous material and hence showed no semiconductor characteristics in its thin-film OFETs, while 37HPTDBT exhibited high crystallinity and strong π-stacking in the solid state, thus resulting in high charge carrier mobilities. The effects of gate insulators and annealing treatment on transistor performances were also investigated. Thin-film OFETs based on 37HPTDBT with an octadecanyltrichlorosilane (OTS)-treated SiO2 gate insulator exhibited excellent field-effect performances with a maximum mobility of 0.3 cm2 V-1 s-1 and a high Ion/Ioff current ratio of 1.5×105. Although annealing treatment improved the crystallinity of the thin films, the appearance of voids (cracks) resulted in a decrease in the charge carrier mobilities in the OFETs.

Synthesis, crystal structure, and polymerization of butterfly-shaped thieno[3,2-b]thiophene oligomers

A series of new butterfly-shaped thieno[3,2-b]thiophene oligomers with phenyl and thiophene units were synthesized through Suzuki coupling and Stille coupling reactions. The optical and thermal properties of these materials can be tuned by varying both substituents and the conjugation length. The crystal structures have been determined and showed a syn- or anticlinal conformation in the crystal of molecule 4. The electronic properties of the monomers and their electropolymerization ability are discussed and rationalized as a function of their molecular structure. Moreover, stable cross-linked conjugated polymers were formed by electropolymerization.

Flexible Organic Solar Cells Based on Spin-Coated Blend Films of a Phenylene-Thiophene Oligomer Derivative and PCBM

Flexible organic solar cells were fabricated on a polyethylene terephthalate (PET) substrate using a phenylene–thiophene oligomer, 3,7-bis[5-(4-n-hexylphenyl)-2-thienyl]dibenzothiophene-5,5-dioxide (37HPTDBTSO), as a photoactive donor. In bulk-heterojunction (BHJ) solar cells, many factors such as blend weight ratio, and solution and substrate temperatures have great effects on the photovoltaic performances. The flexible solar cell fabricated from the blend solution with a weight ratio of 1:2 of 37HPTDBTSO to phenyl-C61-butyric acid methyl ester (PCBM) and a temperature of 50°C, exhibited a high open-circuit voltage of 0.74 V and the highest power conversion efficiency of 0.26%.

Donor–acceptor–donor thienyl/bithienyl-benzothiadiazole/quinoxaline model oligomers: experimental and theoretical studies

A comprehensive spectral and photophysical investigation of four donor-acceptor-donor (DAD) oligomers consisting of electron-deficient 2,1,3-benzothiadiazole or quinoxaline moieties linked to electron-rich thienyl or bithienyl units has been undertaken. Additionally, a bis(dithienyl) substituted naphthalene was also investigated. The D-A-D nature of these oligomers resulted in the presence of an intramolecular charge transfer (ICT) state, which was further substantiated by solvatochromism studies (analysis with the Lippert-Mataga formalism). Hereby, significant differences have been obtained for the fluorescence quantum yields of the oligomers in the non-polar solvent methylcyclohexane vs. the polar ethanol. The study was further complemented with the determination of the optimized ground-state molecular geometries for the oligomers together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The electronic transitions show a clear HOMO to LUMO charge-transfer character. In contrast to the thiophene oligomers (the oligothiophenes with n = 1-7), where the intersystem crossing (ISC) yield decreases with n, the studied DAD oligomers were found to show an increase in the ISC efficiency with the number of (donor) thienyl units.

Antiaromatic Supramolecules: F⋅⋅⋅S, F⋅⋅⋅Se, and F⋅⋅⋅π Intermolecular Interactions in 32 π Expanded Isophlorins

jugated systems with structural features akin to annulenes, and have contrasting ring current effects. 4np macrocycles can react quickly to lose their antiaromatic character. The isophlorin/porphyrin redox couple further illustrates the unstable nature of isophlorin relative to porphyrin under ambient conditions. Similar to the isophlorin p framework, the inherently antiaromatic tetraepoxy annulenes are susceptible to oxidation/reduction to form the corresponding aromatic macrocyclic ions. Their large ring size induces structural flexibility leading to inseparable conformational isomers. Interestingly, steric hindrance favor macrocycles to undergo structure-induced loss of p delocalization. Giant porphyrinoids are well studied examples for macrocycles which adopt figure-eight conformations. Such nonplanar cyclic conjugated systems lack ring current effects and are considered to be nonaromatic in nature. Relative to aromatic systems, the experimental evidence reported for antiaromaticity is found to be far less than satisfactory. There are very limited reports to bridge theoretical predictions with experimental data, particularly for large antiaromatic systems. In this context, the synthesis of stable quintessential planar 4n p molecules is crucial not only to understand the electronic effects of p conjugation but also imperative to the development of novel materials for applications in molecular electronics. Expanding the p framework of either 1 or the modified isophlorin 2 is an attractive strategy for generating a variety of expanded isophlorins (3 and 4, respectively). Its effective conjugation and rigid structural skeleton affords a unique opportunity to explore the chemistry of antiaromatic molecules. But the synthesis of stable antiaromatic isophlorinoids is hindered by the inherent unstable nature of 4np systems. Amongst a few isophlorins known so far, the synthetic strategy employed for 2 is probably the simplest to obtain stable antiaromatic macrocycles from easy-to-make precursors. Adopting a similar synthetic strategy, with modified precursors, we describe the syntheses and structural features of novel and stable 32p vinylogous expanded isophlorins which display unprecedented short F···X (X=p/S/Se) and p–p intermolecular contacts for antiaromatic systems. Replacing two methine carbon bridges in 3 by an equal number of ethylene bridges can convert a (4n+ 2)p system into a 4np system. McMurry coupling is widely used to couple dialdehydes of thiophene oligomers into macrocycles with ethylene bridges. We adopted a modified Rothemund-type synthesis, (Scheme 1), wherein diols of five-membered heterocycles were condensed with bis(thiophene)s under

Interfacial States in Donor-Acceptor Organic Heterojunctions: Computational Insights into Thiophene-Oligomer/Fullerene Junctions.

Donor-acceptor heterojunctions composed of thiophene oligomers and C60 fullerene were investigated with computational methods. Benchmark calculations were performed with time-dependent density functional theory. The effects of varying the density functional, the number of oligomers, the intermolecular distance, the medium polarization, and the chemical functionalization of the monomers were analyzed. The results are presented in terms of diagrams where the electronic states are classified as locally excited states, charge-transfer states, and delocalized states. The effects of each option for computational simulations of realistic heterojunctions employed in photovoltaic devices are evaluated and discussed.

Long-Chain 3,4-Ethylenedioxythiophene/Thiophene Oligomers and Semiconducting Thin Films Prepared by Their Electropolymerization

A series of soluble H-terminated conjugated oligomers incorporating 3,4-ethylenedioxythiophene (EDOT) combined with a small number of thiophene units and ranging in length from four to eight EDOT/thiophene groups was prepared with the ultimate goal to investigate if facile formation of a reactive trication radical species would enable electrochemical polymerization of such long-chain oligomers. Spectroscopic and electrochemical studies of the oligomers revealed some general dependencies of their electronic properties on the total number and position of EDOT groups. It was the number of consecutive EDOT units rather than total number of these units which was found to have the most profound effect on electronic energy gap and conjugation length. This influence originates from the especially strong planarization induced in the conjugated backbone by the incorporation of EDOT units. In contrast, incorporation of thiophene units was found to result in loss of the conformational stabilization. This phenomenon was analyzed using the natural bond orbital computational approach, which revealed the predominantly hyperconjugative nature of the EDOT-induced conformational stabilization. Whereas shorter oligomers, in agreement with the general consensus, were found to be inert toward electrochemical polymerization due to low reactivity of electrochemically generated cation radical and dication species, the longest oligomer showed an unprecedentedly efficient electropolymerization to yield a stable thin film of an electroactive polymer. The efficient electropolymerization of the long-chain oligomer was found to be in agreement with the formation of a reactive trication radical species. The electronic and spectral properties of the resulting semiconducting polymer film were studied by various electrochemical and spectroelectrochemical methods, as well as conductive probe AFM technique, and revealed a number of unusual features (such as electrical rectifying switching behavior) consistent with the possibility of increased molecular order in this material.

Theoretical study of phenylene–thiophene oligomers: Structure–properties relationship

Theoretical results including geometrical characteristics, electronic structures, photophysical parameters (lowest excitation energies, electron affinities (EAs), ionization potentials (IPs), maximum of absorption and emission) and vibrational modes of some new oligomers, based on phenylene–thiophene motives, are investigated using Density Functional Theory DFT/B3LYP/6-31G(d) approach.The electronic and optical properties of phenylene-based derivatives can be tuned through the insertion of thiophene in the main oligomers backbone as well as the addition of alkoxy-substituent groups on 2 and 5 positions on phenylene groups. It can be noticed, that different conformational behaviors and steric effects take place. Then, an increase in conjugation length induces a decrease in the gaps energy and a bathochromic shift of absorption/emission spectra. Based on these computed results, which are consistent with the available experimental data, the correlation structure–properties is better understood, where these nanostructures show a great potential for opto-electronic devices.

Single‐Piece Solid‐Contact Pb2+‐Selective Electrodes Based on Thiophene Oligomer

AbstractA single‐piece solid‐contact Pb2+‐selective electrode was prepared by adding a thiophene oligomer into the ion‐selective cocktail directly. The one‐step fabrication yielded an electrode with Nernstian response spanning a wide concentration range of 10−3–10−8 mol L−1, and detection limit as low as 5.6×10−9 mol L−1. The electrode had a quick response time of approximately 10–15 s and showed excellent selectivity over the most common univalent and divalent cations. The practical application of the proposed electrode has been tested by determining Pb2+ in real water samples.

Theoretical studies on the electronic structures and optical properties of the thiophene oligomer containing 2-(trifluoromethyl) thieno [3, 4-b] thiophene moiety and the CF3 end-caps

Structural, electronic, and optical properties of a series of π-conjugated thiophene oligomers P1-P3 and CF3P1-CF3P3 have been theoretically investigated. P1-P3 contain the 2- (trifluoromethyl) thieno [3, 4-b] thiophene moiety as the centre and 1–3 repeating thiophene units adjacent to its two sides respectively, while their corresponding derivatives CF3P1-CF3P3 with the CF3 as end-caps. The geometric structures of the oligomers in the ground and excited state were optimized by PBE1PBE and CIS methods with 6–31G (d) basis sets, respectively. All the oligomers exhibit zigzag arrangements. The absorptions and emissions were calculated by the time-dependent density functional theory method (TD-PBE1PBE). The lowest-lying absorptions of all the oligomers can be characterized as π-π* electron transition. For each series of oligomers, there is a progressive lowering in HOMO-LUMO gap with the increase of the repeating unit, being consistent with the red-shifted trend in the lowest-lying absorption and fluorescence from P1 to P3 and CF3P1 to CF3P3. To compare the P- and corresponding CF3P-oligomers, the end-cap CF3 group causes the slight blue shifts in absorption and emission spectra. The ionization potentials (IPS), electron affinities (EAs), and reorganization energies (λ) as well as the hole/electron extraction energies (HEP/EEP) of the oligomers were explored and those of the corresponding polymer were obtained by extrapolation method. The IP and HEP of P-polymer are lower than those of CF3P-polymer, indicating that the P-polymer is more suitable for hole transport than CF3P-polymer, while the higher EA and EEP for CF3P-polymer suggest the better electron transfer property. For CF3 end-caps, the CF3P-polymer exhibits the equal reorganization energy between electron and hole, which is a precondition for the charge transfer balance.

Calculation of the diffusion coefficient of thiophene oligomers using molecular dynamics

Electropolymerisation is a very useful methodology for conducting polymers synthesis. A total comprehension of this process will help on the designing of new materials with improved optical and electrical properties. In this sense, computational simulations can deliver important information at atomic scale. Within a kinetic Monte Carlo scheme, diffusion rates are crucial to obtain accurate predictions; however, experimental values of this dynamic property for different oligomers are very scarce among literature. In this study, the diffusion coefficient (D) of thiophene oligomers (1Th–6Th) has been calculated using molecular dynamics simulations coupled with the Einstein expression. Results are in the order of experimental values, demonstrating that this methodology is a fast and reliable alternative to calculate diffusion coefficients with low computational costs.

Oligothiophene Nanoparticles: Photophysical and Electrogenerated Chemiluminescence Studies

Thiophene oligomer nanoparticles (NPs) were studied by fluorescence spectroscopy and electrogenerated chemiluminescence (ECL). Distinct spectroscopic differences between aggregates or NPs of thiophene hexamers having differing substitution patterns of solubilizing alkyl groups were observed. The α,ω-unsubstituted thiophene hexamer, Hexamer-2, exhibited fluorescence properties that were similar in solution and as colloidal NPs; there was only a small red shift compared with what was observed for the discrete system dissolved in tetrahydrofuran (THF). In contrast, the oligomer substituted in the α,ω-positions with branched alkyl substituents (Hexamer-1) displayed a gradual bathochromic shift of the fluorescence maximum in proportion to the amount of a poor solvent (water) added to the THF solution. Moreover, the fluorescence characteristics for the oligomer(s) dissolved in a mixture of THF and water were similar to those seen by annihilation ECL in a mixture of benzene/acetonitrile. On this basis, we conclude that annihilation ECL may be a useful technique for monitoring the formation of organic nanoparticles.

Vibrations of polythiophenes

Structural and vibrational properties of thiophene oligomers up to the dodecamer have been investigated by first principles calculations. The main goal is to provide more detailed interpretations of the infrared and Raman spectra, extending the insights to odd-sized polythiophenes, which have not been treated so far. The calculated electronic, geometric, and vibrational features show better consistency and agreement with experimental data than previously published theoretical results.

P4‐064: Neuroprotective effects of thiophene oligomer derivatives on beta‐amyloid‐induced toxicity

P4‐064: Neuroprotective effects of thiophene oligomer derivatives on beta‐amyloid‐induced toxicity

Organic field-effect transistors based on two phenylene–thiophene oligomer derivatives with a biphenyl or fluorene core

The synthesis and full characterization are described of two phenylene–thiophene oligomer derivatives, 2,7-bis[5-(4-n-hexylphenyl)-2-thienyl]fluorene (HPTFTPH) and 4,4′-bis[5-(4-n-hexylphenyl)-2-thienyl]biphenyl (HPTPPTPH), which are based on a structural combination of a fluorene or biphenyl core, thienyl units, and end-cap hexylphenyl groups. Remarkable shifts in the UV–vis and photoluminescence spectra of thin films relative to their solutions indicate the existence of strong intermolecular π–π interactions in the solid state of the two oligomers. In addition, relatively large energy gaps and low highest occupied molecular orbital energy levels imply that the two oligomers are promising and durable semiconducting materials. Thin-film organic field-effect transistor devices based on the two oligomers show good p-type performances with high hole mobilities. The highest mobility (0.20cm2/Vs) was obtained for the HPTPPTPH oligomer with biphenyl core.

The Role of Weak Bonding in Determining the Structure of Thiophene Oligomers inside Carbon Nanotubes

The orientation preference of methyl-terminated thiophene oligomers inside an armchair nanotube was evaluated using density functional theory calculations with dispersion corrections (B97-D functional). According to the B97-D calculations, internal thiophene oligomers prefer to be located near the walls of the armchair nanotubes rather than at their center. The attractive π···π and CH···π interactions operating between the thiophene guest and nanotube host are sufficient within the nanotube to overcome the energy cost of deforming the thiophene oligomer from the more stable gas-phase conformation. As a result, thiophene oligomers inside the nanotube tend to form nearly planar structures, even though adjacent thiophene rings rotate around the connecting bond in the gas phase. These weak attractive interactions enhance the planarity of thiophene oligomers confined within larger-diameter nanotubes.

Novel Phenylene–Thiophene Oligomer Derivatives with Dibenzothiophene 5,5-Dioxide Core: Synthesis, Characterization, and Applications in Organic Solar Cells

Abstract Donor–acceptor–donor oligomers with dibenzothiophene 5,5-dioxide core and end-cap phenylene–thiophene substitutes were newly synthesized. New oligomers were characterized by UV–vis absorption and photoluminescence spectroscopy, cyclic voltammetry, and applied as electron donor in bulk-heterojunction solar cells. The results indicate that phenylene–thiophene oligomer derivatives containing dibenzothiophene 5,5-dioxide moiety are appraised to be valuable electron donors.

The role of relativity and dispersion controlled inter-chain interaction on the band gap of thiophene, selenophene, and tellurophene oligomers

Ab initio relativistic density functional theoretical calculations have been carried out on π-conjugated oligomers of increasing length with S, Se, and Te as heteroatoms. The band gap of the corresponding polymers has been obtained by plotting lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO)gap against the reciprocal of the number of monomer units (1/N) and extrapolating the curve to 1/N = 0. With B3LYP functional, we predict that role of relativistic correction terms is not very significant in the determination of final band gap of thiophene, selenophene, and tellurophene polymer. The origin of this observation is provided through the density of states (DOS) analysis which manifests that DOS contribution across the Fermi level of these polymers is mostly governed by C atoms and as a consequence relativistic correction terms due to heavy heteroatom remain insignificant to the band gap modification. We also inspected the role of inter-chain interaction in determining the net LUMO-HOMO gap of π-stacked double chain oligomers of increasing length. We have found that due to the exciton splitting in the stacked configurations, the LUMO-HOMO gap decreases steadily. Furthermore, we have noticed that dispersion force has important role in the reduction of the LUMO-HOMO gap of the oligomers studied.