Calculations of Band Gaps in Polyaniline from Theoretical Studies of Oligomers

Theoretical Study of Vinyl-Sulfonate Monomers and Their Effect as the Dopants of Polyaniline Dimers

Establishing the structure–property relationships of monomers and polymers via theoretical chemistry is vital for designing new polymer structures with a specific application. Developing bifunctional monomers with selective polymerizable sites is one of the strategies employed to obtain complex polymeric systems. In this work, a theoretical study on anilinium 2-acrylamide-2-methyl-1-propanesulfonate (ani-AMPS) and anilinium 4-styrenesulfonate (ani-SS) monomers and their respective doped polyaniline dimer (PAni-d AMPS or PAni-d SS) was performed. The study focused on understanding the susceptibility of the vinyl group to a radical attack and the conformation changes resulting from the coordinated covalent bond between sulfonate and aniliniun. Applying Density Functional Theory with the B3LYP functional and a basis set of 6 − 31 + G(d,p), the structures of the ani-AMPS, ani-SS, PAni-d AMPS, and PAni-d SS were optimized, and the different chemical descriptors were determined. The simulation showed that the reactivity of the vinyl group in the ani-AMPS is slightly higher. The sulfonate group undergoes a conformational change when bonding with PAni-d AMPS or PAni-d SS compared to its respective bifunctional monomer. Additionally, the electronegativity of PAni-d depends on the dopant’s structure. Thus, the bonded spacer between the vinyl and sulfonate groups (dopant) plays a notable role in the final characteristics of ani-AMPS, ani-SS, PAni-d AMPS, and PAni-d SS.

A Comparative Study of Biomimetic Synthesis of EDOT-Pyrrole and EDOT-Aniline Copolymers by Peroxidase-like Catalysts: Towards Tunable Semiconductive Organic Materials

It has been two decades since biomimetic synthesis of conducting polymers were first reported, however, the systematic investigation of how catalysts influence the properties of the conducting polymers has not been reported yet. In this paper, we report a comparative study between peroxidase-like catalyst, dopants, and their effect on the properties of poly (3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). We also investigate the EDOT-Pyrrole and EDOT-Aniline copolymerization by enzymomimetic synthesis using two catalysts (Ferrocene and Hematin). It was found that, chemically, there are no detectable effects, only having small contributions in molar ratios greater than 0.7-0.3. Spectroscopic data provide solid evidence concerning the effect in the variation of the molar fractions, finding that, as the molar fraction of EDOT decreases, changes associated with loss of the conjugation of the structure and the oxidation state of the chains were observed. The electrical conductivity was considerably modified depending on the type of catalyst. Hematin produces conductive homopolymers and copolymers when doped with p-toluene sulfonic acid (TSA), while ferrocene produces low conductive copolymers under the same conditions. The mole fraction affects conductivity significantly, showing that as the EDOT fraction decreases, the conductivity drops drastically for both EDOT-PY and EDOT-ANI copolymers. The type of dopant also notably affects conductivity; the best values were obtained by doping with TSA, while the lowest were obtained when doping with polystyrene sulfonate (PSS). We also draw a biomimetic route to tailor the fundamental properties of conducting homopolymers and copolymers for their design and scaled-up production, as they have recently been found to have use in a broad range of applications.

DFT modeling of polyaniline: a computational investigation into the structure and band gap of polyaniline

The band gaps of three forms of polyaniline (PANI) are calculated using the DFT method with the B3LYP functional and SV(P) basis set. This marks the first time that the band gap for this polymer has been calculated using this DFT method. The calculations include an investigation of the effect of varying the benzoid–quinoid structural units, the effect of increasing oligomer length, and the inclusion of Michael’s addition structures, which could be residual in the polymer depending on the chosen synthetic method. All results were compared with the experimentally determined band gap of 1.5 eV as typically reported in the literature. A commonly used structural motif of alternating benzoid–quinoid units and a ratio of 0.5:0.5 benzoid–quinoid resulted in a computed band gap of 1.9 eV. Inclusion of one extra quinoid unit gave rise to a band gap of 1.3 eV. Incorporation of a Michael’s addition structure was found to dominate the band gap calculation, yielding a localized LUMO and a band gap of 1.3 eV that was insensitive to the polymer chain length and composition.

Theoretical Studies of Conducting Polymers: A Mini Review

The present short review discusses the computational studies carried out on polyacetylene (PAc), polyaniline (PANI), polypyrrole (PPy), and other conducting polymers for predicting their electronic, optoelectronic and structural properties. Studies...

Charge transport in polythiophene molecular device: DFT analysis

We report the charge transport phenomenon in polythiophene molecular device and the ways of controlling the nature of charge transport through the device. By using density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalisms, two ways of controlling the nature of charge transport have successfully been demonstrated by introducing conformational changes in the channel and applying external gate potential. Functional groups with negative mesomeric effect such as nitrous and carboxyl and positive mesomeric effect such as amino have been used as substituents as part of introducing conformational changes in the channel. The results indicate that the nature of charge transport in polythiophene molecular device can be changed from hole dominant to electron dominant and vice versa just by introducing minor conformational changes in the channel and by changing the polarity of external gate potential. Moreover, the negative differential resistance (NDR) behavior has been observed in amino-substituted thiophene device. These findings will be very useful in understanding the design of both p and n-type transistors out of same molecule for the next-generation molecular electronics.

Conjugated polymer nanostructures displaying highly photoactivated antimicrobial and antibiofilm functionalities

This work reports the use of conjugated polymer nanostructures (CPNs) as photoactivated antimicrobial compounds against Gram-positive and Gram-negative microorganisms. Two representative CPNs of polythiophene (PEDOT) and polyaniline (PANI) were prepared as nanofibres with an average diameter of 40 nm and length in the micrometer range. Both CPNs exhibited strong antimicrobial activity under UVA irradiation with the same fluence rate as the UVA component of the solar spectrum. The effect was tested using the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. The reduction of colony forming units (CFUs) reached >6 log for PEDOT concentrations as low as 33 ng mL-1. For PEDOT nanofibers, a complete inhibition of S. aureus and E. coli growth was reached at 883 ng mL-1 and 333 ng mL-1 respectively. The photoactivation effect of PANI nanofibres on S. aureus and E. coli was also high, with a CFU reduction of about 7 log and 4 log respectively for an exposure concentration of 33 ng mL-1. The antimicrobial activity was only high under light irradiation and was almost negligible for bulk PEDOT and PANI. The effect of polymeric nanofibers could be attributed to the photoinduced generation of reactive oxygen species, which may induce cell membrane damage, eventually leading to bacterial impairment and inhibition of their biofilm forming capacity. CPN PEDOT and PANI coatings were able to keep surfaces free of bacterial attachment and growth even after 20 h of previous contact with exponentially growing cultures in the dark. PEDOT and PANI CPNs demonstrated good cytocompatibility with human fibroblasts and the absence of hemolytic activity. The materials demonstrated advantages in terms of broad antibacterial spectrum, biofilm inhibition, and the absence of acute toxicity for biomedical applications.

Spatially resolved electrochemical reversibility of a conducting polymer thin film imaged by oblique-incidence reflectivity difference

The spatially resolved electrochemical reversibility of a polyaniline (PANI) thin film is successfully imaged by an oblique-incidence reflectivity difference (OIRD) technique.

Structures, Photoresponse Properties, and Biological Activity of Dicyano-Substituted 4-Aryl-2-pyridone Derivatives

Described in this work is the synthesis of a novel dicyano-substituted N-2-aminoethyl-4-(3-pyridinyl)-2-pyridone organic compound (1) that is characterized by several spectroscopic methods. Compound (1) was utilized for the preparation of its perchlorate (2), chloride (3), and bromide (4) salts. Single-crystal X-ray structures of these three salts were determined, and noncovalent weak interactions involving the aromatic rings, anions, and water molecules in (2-4) were investigated in detail. Solid-state UV-vis spectrum of the reported compounds (1-4) was utilized to calculate their optical band gaps, which clearly indicated that they belong to the semiconductor family. Under illumination condition, the magnitudes of electrical properties of (1) and its salts (2-4) improve remarkably although the improvement differs from salt to salt and the result was analyzed theoretically. Salt (2) was tested for its DNA binding ability.

Structures, photoresponse properties and DNA binding abilities of 4-(4-pyridinyl)-2-pyridone salts

Three salts [perchlorate (2), chloride (3) and tetrafluoroborate (4)] were synthesized from a 1-(2-aminoethyl)-6-hydroxy-2-oxo-1,2-dihydro-[4,4'-bipyridine]-3,5-dicarbonitrile compound (1) and characterized by spectroscopic and single crystal X-ray diffraction methods. Various noncovalent interactions (e.g., anion⋯π+, π⋯π, lp⋯π) are explored in the solid state crystal structure of the salts. Optical band gaps of all the four compounds were determined from their solid-state UV-vis spectrum. Electrical properties like electrical conductivity, photosensitivity, etc. were calculated and the results revealed that they have potential to act as optoelectronic devices. The values of the electrical parameters increase several times when they are exposed to visible light rather than in dark conditions. The light sensing properties of the salts (2-4) are enhanced compared to that of the mother organic compound 1 but the magnitude of this enhancement is not same for the three salts. This observation has been rationalized by theoretical considerations. Moreover, the DNA binding ability of one of the representative salts (compound 2) was examined to check the biological importance of the synthesized salts.

Redox-Responsive Polymer Template as an Advanced Multifunctional Catalyst Support for Silver Nanoparticles

Hybridization of metal nanoparticles (NPs) with redox-switchable polymer supports not only mitigates their aggregation, but also introduces interfacial electron pathways desirable for catalysis and numerous other applications. The large surface area and surface accessible atoms for noble metal nanoparticles (e.g., Ag, Au, Pt) offer promising opportunities to address challenges in catalysis and environmental remediation. Herein, AgNPs were supported onto redox-switchable polyaniline that acts as an advanced multifunctional conducting template for enhanced catalytic activity. At the initial stage of reduction of Ag⁺, leucoemeraldine is oxidized in situ to pernigraniline (PG), which acts as interfacial pathway between NPs for electron transport. With the contribution of BH₄^-, PG acts as an electron-acceptor site, which creates interfacial electron-hole pairs, serving as additional active catalytic reduction sites. The use of a redox-responsive composite system as a template enhances catalyst performance through adjustable charge injection across interfacial sites, along with catalyst reusability for the reduction of 4-nitrophenol (4-NPh). Strikingly, from X-ray photoelectron spectroscopy results it was observed that in situ reduction of Ag⁺ onto the conductive polymer alters the electronic character of the catalyst. The unique multielectronic effects of such Ag-supported NPs enrich the scope of such catalytic systems via a tunable interface, diversified catalytic activity, fast kinetics, minimization of AgNPs aggregation, and maintenance of high stability under multiple reaction cycles.

Metal-polymer interface influences apparent electrical properties of nano-structured polyaniline films

The interface between the conductive polymer, polyaniline (PAn-Cl), and gold, platinum, or an interceding layer of electrodeposited platinum on gold or platinum, markedly influences the apparent electrical properties and the electronic to ionic transition in physiological buffers. Polyester-supported, sputter-deposited gold and platinum thin films were laser patterned to yield co-planar Thin Film Electrodes (TFEs) suitable for platinization and deposition of PAn-Cl nanofibers. Electrodeposition of platinum from chloroplatinic acid (50 mC cm^-2) onto gold produced larger feature sizes and larger surface roughness (23.5 nm) when compared to platinization of platinum (15.2 nm) and both similarly reduced interfacial impedance in water and physiologically relevant buffers, PBS and HEPES. UV-Vis characterization produced absorption edges (DI water 2.36 eV, PBS 2.64 eV, and HEPES 2.66 eV) reflective of the ionic strength of the medium. Thin films (23 ± 2 μm) of PAn-Cl nanofibers were deposited onto Au, Pt, Au|Pt, Pt|Pt TFEs and each characterized by Electrical Impedance Spectroscopy (EIS) over the range 10⁶-10^-1 Hz at RT in air, DI water, PBS, and HEPES buffers and by multiple scan rate cyclic voltammetry (MSRCV) in PBS. Platinized gold and platinized platinum decorated with PAn-Cl behaved quite differently in these test environments confirming a role for the contacting surface roughness/nano-topography in influencing apparent electrical properties. Equivalent circuit modeling of EIS data revealed a modified Randles circuit (R(QR)) of low chi-square values (<0.05) that rationalized the capacitance and membrane resistance and confirmed that platinization of gold served to increase the PAn-Cl apparent resistance while platinization of platinum served to decrease the PAn-Cl apparent resistance.

Stress Induced Mechano-electrical Writing-Reading of Polymer Film Powered by Contact Electrification Mechanism

Mechano-electrical writing and reading in polyaniline (PANI) thin film are demonstrated via metal-polymer contact electrification mechanism (CEM). An innovative conception for a non-destructive self-powered writable-readable data sheet is presented which can pave the way towards new type of stress induced current harvesting devices. A localized forced deformation of the interface has been enacted by pressing the atomic force microscopic probe against the polymer surface, allowing charge transfer between materials interfaces. The process yields a well-defined charge pattern by transmuting mechanical stress in to readable information. The average of output current increment has been influenced from 0.5 nA to 15 nA for the applied force of 2 nN to 14 nN instead of electrical bias. These results underscore the importance of stress-induced current harvesting mechanism and could be scaled up for charge patterning of polymer surface to writable-readable data sheet. Time evolutional current distribution (TECD) study of the stress-induced patterned PANI surface shows the response of readability of the recorded data with time.

Enhanced room temperature sulfur dioxide sensing behaviour of in situ polymerized polyaniline–tungsten oxide nanocomposite possessing honeycomb morphology

A polyaniline–tungsten oxide hybrid nanocomposite with honeycomb type morphology was synthesized by in situ one pot chemical oxidative method and used for sulfur dioxide (SO₂) monitoring application for the first time.

Temperature Dependent Electrical Properties of Green Synthesized Silver Nanoparticles-Polyaniline Composite

Polyaniline (PANI) Nanocomposites are potential materials for actuators, EMI shielding, Fuel cells and components in non volatile memory. Silver nanoparticles have wide range of applications such as catalysis, microelectronics, biotechnology and silver-oxide batteries. This work reports the effect of thermal alteration [lowhigh temperatur on the electrical conductivity of green synthesized silver (Ag) nanoparticles-polyaniline composite. A simple low cost green synthesis using Azadirachta indica [Neem] extract is employed for synthesis of silver nanoparticles; Polyaniline is prepared by redox polymerization of aniline using ammonium per sulphate. The silver nanoparticles are incorporated into Polyaniline during polymerization. PANI and PANI-Ag composites are characterized by FTIR, UV-Vis, TGA, XRD, TEM and DC conductivity. The DC conductivity and UV-Vis spectral response were recorded for the samples at low temperatures [263K, 273K, and 283 and high temperatures [353K, 433K, and 533. The effect of thermal alteration showed a significant change in both conductivity and UV-Vis spectral response. UV-visible spectra show the transition occurring in PANI Emeraldine salt phase to Pernigraniline with increase in temperature. TGA analysis confirms the improved thermal stability for PANI-Ag composite. The mechanism of electrical conductivity with temperature in the system is investigated and reported. Thus, this work deals with an approach to analyze the electrical behavior of green synthesized silver nanoparticles composited with a conducting polymer. The results show that these composites can be suitable for temperature dependent semiconductors, bio sensors and catalytic reactions.

THEORETICAL INVESTIGATION ON ENERGY GAP OF FLUORENE-THIOPHENE COPOLYMER

In this work, HOMO-LUMO energy gap and the lowest excitation energy of poly [2,7-(9,9-dihexylfluorene)-co-alt-2,5-(decylthiophene) were performed by different methods. The obtained results indicate that TDDFT(B3LYP/6-31G*)//B3LYP/6-31G* calculations can be useful to provide reliable energetic and structural results of this polymer. The HOMO-LUMO predictions were not accurately obtained as compared to the experimental results. The inverse chain length approximation by using TDDFT(B3LYP/6-31G*)//B3LYP/6-31G* calculations provides energy gap of 2.50 eV, which is in an excellent agreement with the experimental data. However, it was found that the HOMO-LUMO energy gaps obtained from B3LYP calculations were still far from the experimental data.

Directed self-assembly in laponite/CdSe/polyaniline nanocomposites

Laponite films provide versatile inorganic scaffolds with materials architectures that direct the self-assembly of CdSe quantum dots (QDs or EviTags) and catalytic surfaces that promote the in situ polymerization of polyaniline (PANI) to yield novel nanocomposites for light emitting diodes (LEDs) and solar cell applications. Water-soluble CdSe EviTags with varying, overlapping emission wavelengths in the visible spectrum were incorporated using soft chemistry routes within Na-Laponite host film platforms to achieve broadband emission in the visible spectrum. QD concentrations, composition and synthesis approach were varied to optimize photophysical properties of the films and to mediate self-assembly, optical cascading and energy transfer. In addition, aniline tetramers coupled to CdSe (QD-AT) surfaces using a dithioate linker were embedded within Cu-Laponite nanoscaffolds and electronically coupled to PANI via vapor phase exposure. Nanotethering and specific host-guest and guest-guest interactions that mediate nanocomposite photophysical behavior were probed using electronic absorption and fluorescence spectroscopies, optical microscopy, AFM, SEM, powder XRD, NMR and ATR-FTIR. Morphology studies indicated that Lap/QD-AT films synthesized using mixed solvent, layer by layer (LbL) methods exhibited anisotropic supramolecular structures with unique mesoscopic ordering that affords bifunctional networks to optimize charge transport.

Aromaticity of Giant Polycyclic Aromatic Hydrocarbons with Hollow Sites: Super Ring Currents in Super-Rings

We present a systematic theoretical study based on semi-empirical, Hartree-Fock (HF), and density functional theory (DFT) models of a series of polycyclic aromatic hydrocarbons (PAHs) that exhibit hollow sites. In this study we focus particularly on the magnetic criteria of aromaticity, namely (1)H NMR and nucleus-independent chemical shifts (NICS), and on their relationships with other electronic properties. The computed shifts and NICS indices indicate that an external magnetic field induces exceptionally strong ring currents in even-layered PAH doughnuts, in particular in the layer directly adjacent to the central hole of double-layered compounds. These exceptionally strong ring currents also correlate with particularly small HOMO-LUMO gaps and electronic excitation energies and to abnormally high polarizabilities, indicating in turn that these compounds have a more pronounced metallic character. Comparison is made with further depictions of aromaticity in these systems and in [18]-[66]annulene rings by employing topological, structural, and energetic criteria.

Synthesis and characterization of monolayers and Langmuir-Blodgett films of an amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline conjugate

A novel amphiphilic oligo(ethylene glycol)-C60-hexadecaaniline (A16) tricomponent conjugate, C60>(A16-EG43), possessing a well-defined number of repeating aniline donor units and a hydrophilic ethylene glycol oligomer chain was synthesized. The compound is composed of a covalently bound donor-acceptor chromophore structure. Molecular self-assembly of C60>(A16-EG43) at the air-water interface formed a densely packed Langmuir monolayer with all highly hydrophobic fullerene cages located above the liquid interface. The monolayer can then be transferred onto a glass substrate via Langmuir-Blodgett (LB) deposition. LB multilayered thin films formed by multiple deposition of the monolayer yielded broadened optical absorption peaks extending beyond 600 nm into the 950 nm region, suggesting strong intermolecular interactions among the C60 cages and the A16 moieties. An X-ray reflectometry study clearly reveals that the Langmuir film at the air-water interface consists of a C60 top layer and a bottom layer containing hexcadecaaniline and oligo(ethylene glycol) with gradually decreasing electron density over a distance of approximately 130 A above bulk water. The pressure isotherm shows that the packing density of the C60>(A16-EG43) monolayer, corresponding to a molecular area of approximately 95 A2/molecule, is similar to that of the surface area of the C60 monolayer. This result suggests that C60 packing plays a dominant role in guiding the formation of the monolayer structure. Further photoexcitation of hexadecaaniline moieties of aligned (C60>)-A16 layers by a flash light source induces cross linking between adjacent A16 segments forming an interlinked A16 array. Our results have demonstrated a unique fabrication method for preparing the aligned donor-acceptor array using strong intermolecular interactions between fullerenes as the molecular orientation guiding force in the Langmuir-Blodgett technique.

Lithium Intercalation of Phenyl-Capped Aniline Dimers: A Study by Photoelectron Spectroscopy and Quantum Chemical Calculations

Structural and electronic properties of pristine and lithium-intercalated, phenyl-capped aniline dimers as a model for the lithium-polyaniline system have been studied by photoelectron spectroscopy and quantum chemical calculations. It was found that the electronic structure of reduced and oxidized forms of oligoanilines is only weakly affected by isomerism. Upon intercalation, charge transfer from the Li-atoms is remarkable and highly localized at N-atomic sites, where configurations are energetically favored in which both N atoms of the dimers are bound to Li atoms. Conversion of nitrogen sites is different for the two forms of aniline dimers and incomplete up to high intercalation levels, indicating a pronounced role of solid-state effects in the formation of such compounds.

The Fate of Dicationic States in Molecular Clusters of Benzene and Related Compounds

Calculations employing density functional theory indicate that, rather than undergoing fragmentation, dicationic clusters of benzene, hexafluorobenzene, and naphthalene produced by sequential one-electron or sudden double-ionization experiments on the neutrals can relax via the formation of inter-ring covalent C-C bonds, along with a series of proton transfers that enable a substantial reduction of inter- and intramolecular Coulomb repulsions. The theoretically predicted chemically bound structures correspond to deep local energy minima on the potential energy surface pertaining to the lowest electronic state of the dications and can therefore be regarded as metastable (kinetically long-lived) species. This discovery invalidates on theoretical grounds the liquid-droplet model of multiply charged clusters and sheds very unexpected light on possible consequences in chemistry of the intermolecular Coulombic decay (ICD) mechanism [Cederbaum, L. S.; et al. Phys. Rev. Lett. 1997, 79, 4778; Jahnke, T.; et al. Phys. Rev. Lett. 2004, 93, 163401] for deep inner-valence ionized states. Propagation of charge rearrangement reactions and proton transfers to several monomers may eventually lead to the formation of rather extended dicationic assemblies.

Doping of Polyaniline by Acid−Base Chemistry: Density Functional Calculations with Periodic Boundary Conditions

Calculations with Gaussian orbitals and periodic boundary conditions using several density functionals are carried out to study the proton-doping of polyaniline. We explore previously proposed mechanisms to explain the spectacular increase of the electrical conductivity of polyaniline upon protonation. The structural and spectroscopic theoretical predictions for both polaron and bipolaron lattices agree quite well with the experimental data, and we find that the bipolaron structure is lower in energy.