Pyrrole Oligomers Research Articles

Conjugation-modulated optoelectronic and anti-corrosion properties of pyrrole oligomer: Insights from DFT/TD-DFT analysis

To investigate the influence of π-conjugation on optical properties, models of Pyrrole oligomers with varying π-bridge lengths, ranging from 1 to 5, were constructed. The π-bridge plays a crucial role in tuning and modulating the optoelectronic characteristics of these molecules. By employing FMO (Frontier Molecular Orbital) analysis, the band gap values were determined. Notably, the pyrrole oligomer with a 1π-bridge exhibited a higher band gap (2.68 eV) compared to the 5π-bridge variant (1.53 eV). Moreover, the calculated hyperpolarizability (β°) values exhibited a substantial increase from 37 esu to 1876 esu as the extent of π-conjugation was augmented. This suggests that enhanced π-conjugation promotes greater nonlinear optical properties. Further analysis revealed that the pyrrole oligomer with 5π-bridges displayed maximal absorption at a longer wavelength, specifically 1024 nm. This information provides valuable insights into the absorption characteristics of these molecules. Additionally, the NBO (Natural Bond Orbital) analysis successfully captured the stable donor-acceptor interactions responsible for the ground state stabilization observed in pyrrole oligomers. On the other hand, the QTAIM (Quantum Theory of Atoms in Molecules) analysis provided detailed information regarding weak interactions, such as hydrogen bonding, which contribute to the stabilization of the modeled monomers. In summary, the creation of Pyrrole oligomer models with varying π-bridge lengths facilitated the evaluation of the impact of π-conjugation on the optical properties. The findings indicate that increasing the π-conjugation leads to a decrease in the band gap, an increase in hyperpolarizability, and absorption at longer wavelengths. Additionally, the stability of the ground state and the nature of weak interactions were elucidated through NBO and QTAIM analyses, respectively.

Density functional theory studies of polypyrrole and polypyrrole derivatives; substituent effect on the optical and electronic properties

Electronic and vibrational structures of pyrrole oligomer and its derivatives were established on the basis of Density Functional Theory (DFT) and Time-dependent DFT (TD-DFT) computations. The influence of substituent groups on optical and electronic properties was investigated for polypyrrole and polypyrrole derivatives. Molecular structure and frontier molecular orbitals of neutral and ionized oligomers were analyzed. The energy gap, ionization potential, electron affinity, electronegativity, and hardness were calculated and discussed.

Controlled Bioactive Delivery Using Degradable Electroactive Polymers.

Biomaterials capable of precisely controlling the delivery of agrochemicals/biologics/drugs/fragrances have significant markets in the agriscience/healthcare industries. Here, we report the development of degradable electroactive polymers and their application for the controlled delivery of a clinically relevant drug (the anti-inflammatory dexamethasone phosphate, DMP). Electroactive copolymers composed of blocks of polycaprolactone (PCL) and naturally occurring electroactive pyrrole oligomers (e.g., bilirubin, biliverdin, and hemin) were prepared and solution-processed to produce films (optionally doped with DMP). A combination of in silico/in vitro/in vivo studies demonstrated the cytocompatibility of the polymers. The release of DMP in response to the application of an electrical stimulus was observed to be enhanced by ca. 10–30% relative to the passive release from nonstimulated samples in vitro. Such stimuli-responsive biomaterials have the potential for integration devices capable of delivering a variety of molecules for technical/medical applications.

Kinetics and characterization of preparing conductive nanofibrous membrane by In-situ polymerization of Polypyrrole on electrospun nanofibers

Polypyrrole (PPy) is a conductive polymer that can be fabricated into various structures via in-situ polymerization for different applications. However, a kinetics study of its in-situ polymerization is needed for a better understanding of the mechanisms of pyrrole polymerization. This paper develops two different kinetics models based on existing PPy polymerization mechanisms. The most suitable mechanism is first identified by comparing the model results with experimental data. Then, in-situ polymerizations of PPy on electrospun fibrous polyacrylonitrile (PAN) templates were produced at temperatures ranging from 273 to 285 K. The results show that the overall reaction rate of the in-situ polymerization process in the presence of electrospun fibrous template is faster than that without the template. Further investigation confirms that the increase in the overall reaction rate is attributed to the enhanced reactions between oxidized pyrrole oligomers and neutral pyrrole monomers, as the corresponding reaction rate constant and activation entropy increased by 158.2–209.6% and 37.7%, respectively. The reason is that the considerable number of available reaction sites between oxidized oligomers and neutral monomers are created by the fibrous template. In addition, the composite membrane obtained from the in-situ polymerization exhibited well-developed fibrous nanostructure, good electrical conductivity (0.29 ± 0.04 S∙m−1), sufficient mechanical strength (UTS of 8.7 MPa) and relatively stable thermal properties (up to 250 °C).

Tuning pyrrole oligomers for optoelectronic and anti-corrosion applications: a DFT/TDDFT study

The determination of optoelectronic properties for 15 pyrrole oligomers tagged with different donor and acceptor groups and their potential anti-corrosion properties were considered. Density functional theory and time-dependent density functional theory (DFT/TDDFT) calculations have been utilized to explore the structure, molecular properties and anti-corrosion abilities of pyrrole oligomers. Frontier molecular orbital analysis gives qualitative information about the band gap and details of orientation of HOMOs and LUMOs on π-bridge, donor and acceptor moiety. The hyperpolarizability (β°) values are in good agreement with the calculated band gap. TDDFT calculation reveals the absorption maxima of pyrrole oligomers are in the UV–Visible region. The fraction of electron (∆N) an essential factor for corrosion inhibition is calculated as per Lukovit study. On the whole, modelled pyrrole oligomers illustrate better inhibition property than the experimentally reported inhibitor and exhibit optoelectronic property.

Single-molecule tunnel magnetoresistance of p-type doped polypyrrole

Single-molecule electric current of pyrrole oligomers, as a model of p-type doped polypyrrole, was studied theoretically using the first-principles calculation method. Elementary excitations in doped polypyrrole, such as polaron and bipolaron, were modeled in this study as cation and singlet-dication, respectively. The oligomer was sandwiched between the ferromagnetic nickel electrodes, of which magnetic alignment was varied from parallel to antiparallel to confirm tunnel magnetoresistance (TMR) by a difference of electric currents under each magnetic configuration. Although the values of the electric current of the doping state increased compared to that of the neutral state, the TMR performance of the polaron state deteriorated compared to that of the neutral state, and the TMR performance of the bipolaron exceeded that of the neutral state. Therefore, it was found that the completed p-type doping state of the bipolaron improved the TMR effect performance.

Water-Chloroform Interface Assisted Microstructure Tuning of Polypyrrole-Silver Sheets.

The liquid-liquid interface of two immiscible solvents remarkably controls the morphology of polymeric nanostructures as compared to the polymerization in single solvent systems. The polymerization of pyrrole in the water-chloroform medium using silver nitrate (AgNO3) as oxidant yields polypyrrole/silver (PPy/Ag) sheets. The water-chloroform interface acts as a template for the growth of PPy/Ag hybrids into sheets by preventing the secondary growth of silver associated pyrrole oligomers in a three-dimensional (3-D) manner. On the contrary, the 3-D growth of pyrrole oligomers into spherical shapes at the water-chloroform interface is observed when ammonium persulfate (APS) is used as the oxidant. Transmission electron microscopic and scanning electron microscopic images reveal the sheetlike morphology of PPy/Ag with a relatively uniform distribution of Ag NPs (∼100 nm) on PPy sheets. The ratio of aqueous-organic bisolvent and the concentration/type of oxidant have a distinct effect on morphology, crystallinity, and electrical properties of PPy/Ag sheets. The dispersed PPy/Ag sheets are stable in moderately polar solvents up to 2 weeks. The electrochemical behavior of PPy/Ag sheets is confirmed by H2O2 sensing capability through cyclic voltammetry experiments. The antibacterial activity toward E. coli and S. aureus is quantitatively assessed using the minimum bactericidal concentration (MBC) determination.

Polypyrrole Nanoparticles Doped with Fullerene Uniformly Distributed in the Polymeric Phase: Synthesis, Morphology, and Electrochemical Properties

Composites of polypyrrole and fullerene C60 were prepared by the introduction of fullerene during polymerization of pyrrole initiated by the oxidation of pyrrole oligomers with C60. Composites were precipitated in the form of spherical particles, and their sizes ranged from 20 to 400 nm depending on the time of polymerization. Fullerene C60 nanocrystals with approximate size of 1 nm were uniformly distributed within the polymeric material. The amount of fullerene incorporated into polypyrrole depended on the C60 concentration in the solution used for the composite formation. An investigation of the composite using infrared spectroscopy indicated partial charge transfer between polypyrrole chains and fullerene nanocrystals. Such process was also confirmed by the theoretical investigation of electronic properties of composite. The composites were electrochemically active over a large potential window. At negative potentials, fullerene nanocrystals were reduced. In the positive potential range, polypyrrole c...

Sensor applications of polypyrrole for oxynitrogen analytes: a DFT study

Density functional theory calculations are performed to evaluate the sensing ability of polypyrrole for oxynitrogen analytes. Interaction energies of PPy-X (X = NO2-, NO2, and NO) are calculated at B3LYP-CP/6-31G(d) and B3LYP/6-31G(d) levels of theory and compared with the high level calibrated method (M05-2X/aug-cc-pVDZ). B3LYP-CP/6-31G(d) gives the best correlation with the high level calibrated method compared to B3LYP/6-31G(d). Interaction of oligopyrrole with analytes shows a significant effect on the geometric and electronic properties; the conjugation is increased in the pyrrole oligomers and movement of charge is increased over the polymeric backbone. The charge is transferred from analytes to pyrrole oligomers (except nPy-NO2), and a more pronounced effect of charge transfer is observed in the case of nitrite ion (NO2-) compared to NO. In nPy-NO2, the charge is transferred from polymer to analyte. This transfer of charge indicates the n-type doping effect of analytes. The HOMO-LUMO gap decreases after interaction with analytes, which results in a drop of resistance (conductivity increases). These theoretical outcomes are consistent with the experimental results; polypyrrole has more sensing ability toward the nitrite anion (NO2-). Graphical abstract High sensitivity of polypyrrole towards NO over NO2 and NO2.

Strategies towards the control of one‐dimensional polypyrrole nanomorphology and conductivity

AbstractConducting polypyrrole nanotubes rank among the most conducting polymer materials and find applications in organic electronics and energy conversion devices. They are produced by the chemical oxidation of pyrrole in globular form, which converts to nanotubes or nanofibres in the presence of suitable templates and is often accompanied by a pronounced conductivity increase. This is illustrated by the anionic dye, methyl orange, where the template formation is based on azo–hydrazone tautomerism associated with hydrogen atom transfer caused by the acidity change. In other words, the soluble salt of the dye converts to an insoluble acid, and its one‐dimensional aggregates serve as a locus for the adsorption of pyrrole oligomers. This is followed by the growth of polypyrrole chains constituting the nanotube wall. Safranin, a cationic dye, produces a template by a completely different mechanism, the oxidative generation of insoluble safranin oligomers that perform with similar results. Other mechanisms of template formation are also proposed and discussed but mainly organic dyes have a significant potential to support the one‐dimensional growth of polypyrrole. The role of surfactants that affect the morphology of templates, and subsequently also of polypyrrole, is demonstrated. © 2018 Society of Chemical Industry

The predictive power of aromaticity: quantitative correlation between aromaticity and ionization potentials and HOMO-LUMO gaps in oligomers of benzene, pyrrole, furan, and thiophene.

Aromaticity is a central and ubiquitous concept in organic chemistry, and is used extensively to explain various phenomena. Yet, aromaticity cannot be observed or measured as a property in its own right and, to date, only qualitative and semi-quantitative relationships have been described between aromaticity and an observable property. We now demonstrate for the first time a robust quantitative relationship between the HOMO-LUMO gap and adiabatic ionization potential of a polycyclic aromatic hydrocarbon oligomer - both measurable physical quantities - and its aromaticity, as quantified by the Nucleus Independent Chemical Shift (NICS) index. The agreement found for a range of structurally and electronically diverse oligomeric systems of varying lengths is so well-behaved as to enable accurate prediction of the properties of longer members of the respective oligomer family. The established correlation allows for preliminary screening of compounds geared towards functional use.

Room-Temperature-and-Pressure Vapor Deposition of Trace Amount of Pyrrole for Improving the Ageing Resistance and Electrochemical Performance of LiFePO4/C

There are many reports on addressing the issues concerning low electronic and ionic conductivity of LiFePO4, but it is ignored by researchers that how to improve the ageing resistance and retain the electrochemical properties of LiFePO4 and carbon-coated LiFePO4 (LiFePO4/C) after long-term exposure to ambient atmosphere. In this report, an ambient-temperature-and-pressure vapor deposition approach is designed to improve the ageing resistance and electrochemical performance of LiFePO4/C upon exposure to ambient atmosphere. The mechanism of this approach is based on (1) a spontaneous process for evaporation of pyrrole; (2) a fine tuning of the pores in the carbon layer; and (3) restrained contact of LiFePO4 with H2O and electrolyte by in-situ formed oligomers of pyrrole with atomic-layer thickness. As a result, the surface-modified LiFePO4/C samples after exposure to ambient atmosphere for 4 months exhibit high ageing resistance and enhanced electrochemical performance as compared to the initial LiFePO4/C.

Green synthesis of degradable conductive thermosensitive oligopyrrole/chitosan hydrogel intended for cartilage tissue engineering

Electroactive scaffolds containing conductive polymers can promote tissue repair and regeneration. However, these polymers are non-degradable and cannot be removed from body. To overcome this limitation of conductive polymers, we developed a novel injectable electroactive hydrogel containing pyrrole oligomers which possessed the unique properties of being both electrically conductive and biodegradable. First, pyrrole oligomers were synthesized via chemical polymerization and were found to be amorphous with a non-globular morphology. Then, three different compositions of injectable chitosan/beta glycerophosphate hydrogels containing different concentrations of pyrrole oligomers were synthesized and characterized for chemical structure, morphology, conductivity, swelling ratio, In vitro biodegradation and gelation time. An increase in oligopyrrole content resulted in decreased pore size, and increased gelation time, swelling ratio, conductivity and degradation time. Among all the hydrogel compositions, the sample with pyrrole oligomer:chitosan ratio of 0.1 (w/w) showed the most prominent biodegradability, biocompatibility, electro-activity, swelling ratio and pore size values and was chosen as the optimal electroactive hydrogel composition in this work.

Electronic and optical properties of pyrrole and thiophene oligomers: A density functional theory study

AbstractThe conductive mechanism of pyrrole (Py) and thiophene (Th) oligomers is investigated in the framework of density functional theory. Geometric constructions and electronic structures of neutral n‐Py/n‐Th and oxidized n‐Pym+/n‐Thm+ oligomers (6 ≤ n ≤ 48, 2 ≤ m ≤ 18) are reported as a function of oligomer length. The charges in the oxidized oligomers have a localized distribution along the oxidized n‐Pym+/n‐Thm+ oligomers, and each set of two positive charges is localized in one area. Therefore, the charge carriers in oxidized n‐Pym+/n‐Thm+ oligomers are bipolarons. Furthermore, the nonlinear optical properties of the n‐Py/n‐Th oligomers are investigated, for which the static polarizability α, the first polarizability β, and the second polarizability γ are calculated. When the ratio of m/n is 1/3, the static polarizability <α> and the polarizability anisotropy Δα are maximized. In addition, neutral n‐Py/n‐Th oligomers have maximum <γ> values. The values of β were determined mainly by the dipole of the molecule, while the values of γ were closely related to the aromaticity of the oligomer. The stronger the aromaticity, the bigger the γ value. All calculations indicate that the polarizability and absorption spectrum can be tuned by controlling the oxidation level, making these oligomers applicable as good nonlinear optical materials.

Preparation of nitrogen and sulfur co-doped ordered mesoporous carbon for enhanced microwave absorption performance

Ordered mesoporous carbon nanomaterials (OMCs) co-doped with homogeneous nitrogen and sulfur heteroatoms were prepared by nanocasting with the pyrrole oligomer catalyzed by sulfuric acid as a precursor and ordered mesoporous silica SBA-15 as a hard-template. By multi-technique approach utilization, it was demonstrated that the N and S co-doped OMCs possessed high ordered mesoporous structures, large surface areas and homogeneous distribution of heteroatoms. As a microwave absorber, the as-prepared materials exhibited a minimum reflection loss (RL) of −32.5 dB at the thickness of 2.5 mm and an absorption bandwidth of 3.2 GHz (RL < −10 dB) in X-band (8.2–12.4 GHz). The good microwave absorption performance was mainly originated from the high electrical conductivity induced by the high surface activity and special structures. And microwave energy can be effectively attenuated through multiple reflections and absorptions in complex conductive network. The design strategy in this work would contribute to the production of a lightweight absorber, presenting a strong absorbency and a wide bandwidth in microwave frequency.

Polypyrrole/TiO2 composites for the application of photocatalysis

Density functional theory (DFT) study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. The simulated results of band structure (band gap, and band edge positions), molecular orbitals, and UV–vis spectra of the optimized nPy-Ti16O32 systems strongly support the existence of strong interactions between Py and TiO2 in the composite. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites.

Inter-molecular interaction in Polypyrrole/TiO2: A DFT study

Density functional theory study of Polypyrrole/TiO2 have been carried out at molecular level, to find its internal nature for the tuning of photocatalytic efficiency. Molecular isolated TiO2 interacts with various pyrrole oligomers for the investigation of inter-molecular interaction. A narrowing in band gap and better visible light absorption are achieved compared to their individual constituents, based on electronic properties simulations. Electrostatic potential, the density of states, IP, EA, UV–vis spectra and band gap are also supportive to the composite formation. Inter-molecular interaction energy (−28 to −45 kcal mol−1), counterpoised corrected (BSSE), and ΔEgCP-D3 methods are employed which confirm the existence of a strong covalent type of bonding between Py and TiO2 in nPy-TiO2 composites. Finally, Mulliken and natural bonding orbital analysis have pointed out that Py oligomers are p-type and donated electron cloud density to TiO2 in all of the nPy-TiO2 composites.

π-Delocalization and the vibrational spectroscopy of conjugated materials: computational insights on Raman frequency dispersion in thiophene, furan, and pyrrole oligomers.

The symmetric C═C stretching frequency (ν(Я)) of conjugated polymers and oligomers is a sensitive spectroscopic reporter of molecular structure and material morphologies; however, thorough understanding of how structure affects this frequency is lacking because computational investigations of this relationship have been undertaken with limited approaches. We present a comprehensive computational investigation of the structure-dependent Raman spectroscopy of oligothiophenes, oligofurans, and oligopyrroles in their ground electronic states using density functional theory. We assessed how various functionals (BLYP, B3LYP, BHLYP, and CAM-B3LYP) impact predictions of length-dependent trends in ν(Я). The amount of Hartree-Fock exchange in a functional is critical for accurately treating π-delocalization and polarizability and hence the structure-dependent Raman behavior. BLYP and B3LYP fail to accurately predict trends in ν(Я) with oligomer length because they over-represent delocalization; in contrast, the range-corrected CAM-B3LYP functional produces the same trends observed experimentally for oligomers in solution and in the solid phase. Through comparisons with a simple mechanical model, we demonstrate that the length- and conformation-dependent spectroscopy of oligothiophenes results from a delicate balance between delocalization-induced softening of ν(Я) and the coupling of oscillators that increase ν(Я). These findings are used to address how variations in inter- and intramolecular order impact the Raman spectroscopy of polythiophenes.

Computational investigation of interaction of polypyrrole on the surface of single-walled carbon nanotube.

A density functional theory investigation of adsorption of monomer, dimer and trimer forms of pyrrole on the outer surface of zigzag (7,0) single-walled carbon nanotube (SWCNT) has been reported. Geometries of the complexes were optimized using the M06-2X functional and the 6-31G(d,p) basis set. Moreover, 6-311G(d,p), cc-pVDZ and cc-pVTZ basis sets were used for the adsorption energy calculation and such energies were corrected for the basis set superposition error. Vertical ionization potential and electron affinity of the investigated system were also computed. The interaction of polypyrrole on the SWCNT surface is characterized by the stacking interaction. Adsorption (binding) energy of pyrrole on the SWCNT surface is weak, but such energy increases with the number of monomer units in the pyrrole oligomer. In the SWCNT-pyrrole complexes, the oxidation and reduction processes will take place only at the SWCNT. The influence of larger unit on the electronic properties of the complex has been detailed.

Linear and non-linear optical properties of hetero-cyclic aromatic polymers

We investigated linear and non-linear optical properties of non-fused and fully fused hetero-cyclic thiophene, selenophene and pyrrole oligomers. We found that these oligomers show relatively better environmental stability in their fused form than non-fused geometry. Linear extrapolation of calculated energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in the polymer limit exhibits extremely good agreement with experimentally reported band gap for thiophene, selenophene and pyrrole oligomers in their non-fused form. The lowest singlet dipole allowed excited state was calculated using time-dependent density functional theory and extrapolated optical gap estimated were in good agreement with experimental observation. Static linear and first hyperpolarisabilities were also studied as a function of chain length for donor–acceptor substituted polymers. The (hyper)polarisabilities are increasing as a function of chain length in both forms although the non-fused pyrrole oligomers show slow variation. Our study on hyperpolarisability also shows that donor–acceptor substituted non-fused selenophene oligomers are most promising candidates to contribute significantly in non-linear photonics and all fully fused hetero-cyclic oligomers show strong NLO responses.