Regioregular Polythiophene Derivatives Research Articles

Regioregularity and deposition effect on the physical/chemical properties of polythiophene derivatives films

Polythiophene thin films are widely studied for applications in organic electronics. However, some comparisons are still missing, regarding distinct deposition techniques and regioregularity. Here regioregular and regiorandom alkyl-substituted polythiophene derivatives (P3ATs) were deposited on solid substrates using both Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) techniques. The main goal was to verify the possible influence of the regioregularity as well the deposition technique on their optical, electrical and electrochemical properties. LB and LS films of regioregular and regiorandom poly(3-butylthiophene) (P3BT) and poly(3-octylthiophene) (P3OT) were deposited onto glass/Indium–Tin-Oxide) substrates and characterized by UV–visible optical spectroscopy, atomic force microscopy, cyclic voltammetry, and conductivity measurements. The results demonstrated the influence of the deposition technique on the electrical outcome, moreover, the regioregularity affected all the performed characterizations. In addition, this paper may be useful to understand how the amphiphilic molecule addition affected the film properties of regioregular and regiorandom P3ATs, particularly the energy diagram provided by the electrochemical and absorption features.

Langmuir-Schaefer films of regioregular polythiophene derivatives as VOCs sensors

Conjugated polymers have been extensively studied in recent years, with high technological potential for application as an active layer of organic devices. In this context, polythiophene derivatives have attracted attention due to properties as stability and easy processability. In this work, poly(3-hexylthiophene) and poly(3-octylthiophene) were studied in the form of nanostructured films fabricated by the Langmuir-Schaefer deposition technique. The films were characterized by optical (UV–Vis absorption spectroscopy and Raman scattering) and electrical measurements allowing the evaluation of the material concerning the technological potential to the manufacture of VOCs electric sensors.

Preparation of uncurled and planar multilayered graphene using polythiophene derivatives via liquid-phase exfoliation of graphite

We have investigated the effects of the preparation conditions of polythiophene/graphene complexes on their dispersion in organic solvents, and on the in-solution morphology of the multilayered graphene. Among four different regioregular polythiophene derivatives synthesized, poly(3-hexylthiophene) (P3HT) with a low molecular weight (Mn 6000) was the most effective derivative for exfoliating graphite and for dispersing the multilayered graphene in toluene. Spectroscopic analysis revealed that P3HT interacted strongly with graphene to form a P3HT/graphene complex. We investigated the in situ morphology of multilayered graphene in organic solvents, using a flow particle image analyzer (FPIA) and revealed that the presence of polythiophenes produced larger P3HT/graphene complexes than that prepared in N-methylpyrrolidone (NMP). Microscopy analysis demonstrated that graphite flakes and multilayered graphene shrunk in the absence of P3HT when drying in organic solvents. The presence of P3HT immobilized the extended morphology of the multilayered graphene by forming the complex. This prevented shrinkage of the multilayered graphene when drying in toluene. Transmission electron, atomic force and field-emission scanning electron microscopy observations revealed that the P3HT/graphene complex consisted of relatively flat and ultrathin multilayered graphene of approximately <10 nm in thickness. The polythiophene/graphene complexes had high electrical conductivity, which depended on the kinds of polythiophenes. These findings further our understanding of the morphology of multilayered graphene, and will promote the development of uncurled multilayered graphene.

Influence of the Supramolecular Arrangement in the Electrical Conductivity of Poly(thiophene) Thin Films.

Thin films of regioregular polythiophene derivatives have had their optical, structural and morphological properties characterized, but there is still a lack of comparative studies to determine the effect from deposition techniques, especially on the electrical properties. In this study, we produced Langmuir-Schaefer and spin-coated films of regioregular alkyl-substituted polythiophene derivatives (P3AT) to investigate how distinct supramolecular arrangements can affect their properties. The Langmuir-Schaefer films deposited on indium-tin oxide substrates were observed to grow linearly with the number of layers, according to UV-visible absorption spectroscopy. Atomic force microscopy and Brewster angle microscopy were carried out for morphological characterization. From electrical transport measurements, the DC electrical conductivity of Langmuir-Schaefer films of P3AT was higher than the corresponding spin-coated films, which can be related to the dissimilar roughness and molecular-level organization provided by the Langmuir-Schaefer technique.

Side chain engineering of poly-thiophene and its impact on crystalline silicon based hybrid solar cells

The influence of ether groups in the side chain of spin coated regioregular polythiophene derivatives on the polymer layer formation and the hybrid solar cell properties was investigated using electrical, optical, and X-ray diffraction experiments. The polymer layers are of high crystallinity but the polymer with 3 ether groups in the side chain (P3TOT) did not show any vibrational fine structure in the UV-Vis spectrum. The presence of ether groups in the side chains leads to better adhesion resulting in thinner and more homogeneous polymer layers. This, in turn, enhances the electronic properties of the planar c-Si/poly-thiophene hybrid solar cell. We find that the power conversion efficiency increases with the number of ether groups in the side chains, and a maximum power conversion efficiency of η = 9.6% is achieved even in simple planar structures.

Polythiophene-Based Optical Sensors for Small Molecules

Water-soluble, regioregular polythiophene (PT) derivatives are conformational sensitive to external stimuli, and their spectral responses are determined by conformation changes, π-π interactions and scattering of visible lights originated from PT aggregates. In this paper, we review the synthesis of water-soluble PTs and their photophysical properties, and then highlight our efforts toward the development of PT-based optical sensors for small molecules. Mechanism studies indicate that the interplay between side-chain steric/electrostatic repulsive and interchain attractive interactions is responsible for the assembly and disassembly of water-soluble PTs in aqueous media. Consequently, the planarization/deplanarization of PT backbones provides the possibility for colorimetric and fluorescent dual detection of small bioanalytes and chemical species.

Quadrimolecular recombination kinetics of photogenerated charge carriers in the composites of regioregular polythiophene derivatives and soluble fullerene

Light-induced electron spin resonance (LESR) measurements have been performed on the composites of regioregular polythiophene derivatives and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in order to study the recombination kinetics of photogenerated charge carriers. We adopt two regioregular polymers with different side chains; head-to-tail poly(3-hexylthiophene) (RR-P3HT) and head-to-head poly(3-dodecynylthiophene-2,5-diyl) [HH-P3(C≡CDec)Th]. In both systems, two LESR signals due to positive polarons on the polymer (g∼2.002) and fullerene radical anions (g∼2.000) have been observed. Quadrimolecular recombination (QR) kinetics, previously reported for RR-P3HT/C60 composites, where two positive polarons and two radical anions recombine simultaneously, has been confirmed in both systems by the observation of Iex0.25 dependence of the LESR intensity on the excitation light intensity (Iex) and the decay curve of the LESR intensity. This process implies the formation of doubly-charged states such as bipolarons or polaron pairs on the polymer to attract two radical anions. Temperature dependence of the QR rate constant, γ, in both systems has exhibited a crossover of the transport mechanism from low temperature tunneling to high temperature hopping process, as in the case of RR-P3HT/C60 composites. In the RR-P3HT/PCBM composites, γ has exhibited marked dependencies on the PCBM concentration or annealing, which may be related to the change of the crystallinity of the phase-separated polymer and fullerene domains as well as their interface structures, affecting the carrier mobilities or the trap states at the interface. Associated change of the molecular orientation of RR-P3HT crystalline domains with the lamellar structure has been further confirmed from the anisotropic LESR signals of the cast films on the substrates, exhibiting a qualitative agreement with the reported x-ray or optical analyses. In the HH-P3(C≡CDec)Th/PCBM composite, γ has been smaller than those in the RR-P3HT/PCBM composites, reflecting the difference of local structures due to the different molecular structure. Furthermore, the hyperfine-determined LESR linewidth of the positive polaron has exhibited a smaller value than those in the RR-P3HT composite, implying the larger extension of the polaron wave function on the polymer chain, which is consistent with the highly coplanar structure of this polymer.

Design and Synthesis of Alternating Regioregular Oligothiophenes/Benzothiadiazole Copolymers for Organic Solar Cells

Low-bandgap regioregular polythiophene derivatives, PTh6BTD, PTh8BTD, and PTh4TTBTD, were synthesized through Stille coupling reaction. These are alternating copolymers of an electron-deficient ben...

Faraday Rotation Measurements on Thin Films of Regioregular Alkyl-Substituted Polythiophene Derivatives

The authors describe a magneto-optic measurement system for the determination of Faraday rotation from ultrathin films relative to a substrate reference. The setup is intrinsically immune to reciprocal effects such as circular birefringence and thermal fluctuations. Faraday rotation measurements on thin films of 3-hexyl and 3-dodecyl derivatives of regioregular polythiophene are reported. The authors show that the Faraday rotation from these films is largely dependent on the supramolecular organization within the thin films of these polymers.

Solution-Processed Organic Field-Effect Transistors Based on Polythiophene Derivatives with Conjugated Bridges as Linking Chains

Novel regioregular polythiophene derivatives with conjugated bridges as linking chains, PT-VTVTV2 and PT-VTVTV4, can be used as the semiconductors in organic field-effect transistors (OFETs) and show excellent FET characteristics with a field-effect mobility of 3.8 × 10-3 cm2 V-1 s-1 and a current on/off ratio of 104.

Highly Ordered Polymer Films of Amphiphilic, Regioregular Polythiophene Derivatives

The fabrication and characterization of highly ordered thin films made from amphiphilic, regioregular polythiophene derivatives are described. Films of poly(3-(11-(2-tetrahydropyranyloxy)undecyl)thiophene (PTHPUDT) were prepared by the Langmuir-Blodgett technique. The amphiphilic nature of the polymer affords layer-by-layer deposition and the formation of multilayer films of head-to-head and tail-to-tail Y-type structure. X-ray diffraction studies indicate bilayer separations of approximately 30 A. Anisotropic optical absorption in the plane of the film indicates that the thiophene backbones are preferentially oriented along the dipping direction. Further, polarized light microscopy studies indicate that these films are highly birefringent and that the optical retardation is uniform over the entire film. Ellipsometry studies confirm the sizable magnitude of the birefringence. Optical second-harmonic generation studies of multilayer films provide information regarding both the thiophene orientation within the film and the anisotropic distribution of chromophores in the surface plane. Taken together, these data offer strong evidence of highly ordered films in which the hydrophobic polythiophene chains lie parallel to the substrate surface with their alkyl chains oriented normal to the surface, as dictated by the hydrophilic nature of the alkyl chain's terminal tetrahydropyran functional group. As such, these films offer the potential for elucidating the connection between polymer morphology and physical property in materials that are otherwise subject to a sufficiently complex distribution of morphologies that such a correspondence is precluded.

Synthesis and Physical Properties of Regioregular Poly(3-alkoxy-4-methylthiophene)s

We synthesized poly(3-alkoxy-4-methylthiophene)s (PMThO) by conventional oxidative polymerization using iron trichloride to investigate the effect of length of the alkoxy chain introduced into the 3-position of the thiophene ring on the physical properties. Regioregular PMThO derivatives were obtained and the regioregularity of PMThO derivatives was confirmed by 1 H NMR and 13 C NMR measurements. In the UV-vis spectra of PMThO derivatives, vibronic peaks characteristic of the regioregular polythiophene derivatives were observed around 540 nm, and new peaks of 275 nm and 400 nm assigned to the PMThO derivatives with non-planar conformation for the polymer backbone appeared with increasing temperature. The band gap energy of PMThO derivatives was about 1.9 eV that was lower than that of conventional polythiophenes. The electrical conductivity of doped PMThO derivatives hearing longer alkoxy chains was about 10 0 S cm -1 .

Thermal and Optical Properties of Regioregular Polythiophene Derivatives Containing Mesogenic Group in the Side Chain

We synthesized regioregular liquid crystalline polythiophene (PTh) derivatives by chemical oxidative polymerization using iron trichloride to investigate the effect of the regioregularity on their physical properties. The regioregularity was about 90% for the PTh derivatives. A smectic phase was observed for two PTh derivatives. Plural peaks based on vibronic coupling characteristic of the regioregular PTh derivatives were observed in the π–π* transition absorption band of the UV-vis spectra. The vibronic coupling disappeared with increasing temperature and a new peak assigned to the PTh derivatives with non-planar conformation for the polymer backbone was observed in shorter wavelength range. The electrical conductivity was about 10-3–10-4 S cm-1 for the PTh derivatives doped with I2 vapor in the film state.

Soluble Regioregular Polythiophene Derivatives as Semiconducting Materials for Field-Effect Transistors

Soluble regioregular polythiophene derivatives with chiral alkyl side chains, bulky side chains, and carboxylic side chains have been synthesized. Their thin-film field-effect transistor performance and structural characteristics have been investigated. The above properties were found to be strongly affected by the nature of the side chains. Poor molecular ordering and low crystallinity were found for regioregular polythiophenes with bulky or carboxylic-substituted side chains, and their resulting transistor devices showed poor field-effect mobilities (less than 10-5−10-4 cm2/(V s)). A chiral alkyl-substituted regioregular polythiophene showed high crystallinity. However, its π−π overlap distance between the polythiophene backbones increase substantially (i.e., to ∼4.3 vs 3.8 A for regioregular poly(3-hexylthiophene) (PHT)) through the introduction of methyl branches in the side chains. The field-effect mobility of this polymer is reasonably high for solution-processable conjugated polymers (i.e., of the ...

Self-Assembly and Disassembly of Regioregular, Water Soluble Polythiophenes: Chemoselective Ionchromatic Sensing in Water

The development of polythiophene (PT) derivatives with essentially 100% head-to-tail (HT) couplings1,2 has led to the discovery of materials that self-assemble both in solution and in the solid state. Light-scattering studies on regioregular, HTpoly(3-dodecylthiophene) (HT-PDDT) show that a supramolecular organization occurs via intermolecular aggregation.3 This solution aggregation is precursive to a microcrystalline, self-assembled structure which has been characterized by X-ray studies.1,2,4 Polythiophenes possessing this metastable organization evidence high electrical conductivities1,2,5-8 and very small bandgaps. Previous work in our lab has shown that both conformational order and solid state organization in regioregular PT derivatives are remarkably sensitive to the placement and nature of the substituent chains.1,6,7,9 This sensitivity provides the opportunity to design new conducting polymers in which self-assembly is controlled by environmental factors. One remarkable example is HT-2,5-poly(thiophene-3-propionic acid) (3, PTPA). This polymer was designed such that upon deprotonation, water soluble polythiophene salts are formed.10 Both 3 and its partially deprotonated derivative 5 undergo protein-like hydrophobic assembly, with subsequent H-bond stabilization, to generate a self-assembled conducting polymer aggregate. Varying the size of the counterion in the carboxylate polymer changes the effective steric bulk of the substituent. Small cations favor a self-assembled (purple) state and large cations can completely disrupt the aggregated phase. In fact, a remarkable chemoselective counterion size-dependent chromaticity (Figure 1) is observed for polymer 5. The UV-vis λmax can be varied over a 130 nm range (from purple to yellow) simply by changing the countercation. Initially, we prepared the carboxylate precursor polymer 2 using the Ni(dppp)Cl2 cross-coupling method for the synthesis of HT polythiophenes.5,6,9 This method leads to low molecular weights (Mn ) 1.5-3.0 K), low yields (<5%), and polymers that show variable ionic chromaticity. However, the regioregular oxazoline polythiophene (2) (Mn ) 8 K, PDI ) 1.2) is prepared (Scheme 1) from monomer11 1 in high yields (84%)

Chromic phenomena in neutral polythiophene derivatives

AbstractThermochromic phenomena in various regioregular and non‐regioregular polythiophene derivatives have been investigated both in the solid state and in solution. These studies have revealed the existence of two different types of thermochromic phenomena which are correlated to the substitution pattern of the polymers. Formation of delocalized conformational defects (twistons) has been observed in regioregular polythiophene derivatives but did not occur in non‐regioregular polythiophenes. For the latter polymers, only localized conformational defects can be created along the polymer backbone leading to a monotonic blue shift of the absorption maximum upon heating. It is suggested that all these optical features are driven by order‐disorder transitions of the side‐chains, side‐chain disordering increasing their steric hindrance and/or disrupting short‐range ordered assemblies, which then force the thiophene backbone to adopt a nonplanar conformation. It has been also found that non‐covalent interactions between alkali metal ions and regioregular ether‐substituted polythiophenes can modify the side‐chain organization and can lead to interesting ionochromic effects. It is believed that chromic phenomena can be induced via a large range of external stimuli which should lead to the development of novel affinitychromic and photochromic materials.

Chromic Phenomena in Regioregular and Nonregioregular Polythiophene Derivatives

Chromic Phenomena in Regioregular and Nonregioregular Polythiophene Derivatives