Π-conjugated Polymer Chain Research Articles

Electrolyte-triggered in-situ polymerization of multi-site organic cathodes for superior-longevity cation-anion co-storage secondary batteries

Organic electrodes are promising as next-generation energy storage materials owing to their diverse structures, low mass, and environmental friendliness. Nevertheless, the dissolution and degradation of organic active species in electrolytes are remaining obstacles to their authentic commercialization. Herein, we report an instantaneous in-situ upgrading strategy to convert multi-site organic cathode materials, e.g., 1-aminoanthraquinone (1-AAQ) and 1,5-diaminoanthraquinone (1,5-DAAQ), into poly(1-aminoanthraquinone) (PAAQ) and poly(1,5-diaminoanthraquinone) (PDAAQ) simply by dropping the electrolyte during battery assembly without extra operations. The remarkable chemistry is essentially a chemical polymerization process of redox-active organic monomers triggered by the electrolyte containing magnesium bis(hexamethyldisilazide) (Mg(HMDS)2) as an initiator. Notably, due to the π-conjugated polymer chain with inhibited dissolution, high conductivity, and improved stability, the as-obtained PDAAQ cathode delivered a high specific capacity (254 mAh/g at 100 mA/g), superior rate performance (83 mAh/g at 2000 mA/g), and excellent cycling stability for over 8000 cycles accompanied by an average capacity decay of only 0.0026 % per cycle. Detailed characterizations further explore the kinetic behaviors and verify a reversible hybrid cation–anion co-redox mechanism of PDDAQ cathode, which involves reversible Mg2+ cation insertion/extraction on AQ units and anion doping/de-doping reactions on the PANI backbones. Density functional theory (DFT) computations demonstrate the optimized structure of the discharged products and indicate that Mg2+ preferably interact with two carbonyls oxygen atoms and nitrogen atom for both PAAQ and PDAAQ. This study demonstrates an intriguing in-situ chemical-polymerization synthetic approach for preparing multi-site organic electrode materials that compromise structure optimization and synthetic efforts, offering great promise for high-performance and sustainable secondary batteries.

Electrolyte initiated instaneous in-situ chemical polymerization of organic cathodes for ultralong-cycling magnesium ion batteries

Redox-active organic compounds are promising electrode materials for rechargeable batteries owing to their diverse structures, light weight, resource recyclability and low cost, but the solubility and side reactions in electrolytes impede their practical applications. Herein, we report that pyrrole-based redox-active organic monomers can be instantly converted into π-conjugated polymer derivatives via a convenient and efficient in-situ chemical polymerization method during battery assembly without tedious fabrication procedures, which, in essence, is to use the electrolyte originally containing bis(hexamethyldisilazido)magnesium (Mg(HMDS)2) to induce the instantaneous in-situ polymerization of 2-pyrrolanthraquinone (2-PyAQ). Benefited from the intrinsic high ionic mobility and minimal electrolyte solubility of the redox-active π-conjugated polymer chains, the as-obtained poly(N-anthraquinoyl pyrrole) (PAQPy) cathode material exhibit high specific capacity, good rate performance and ultralong cycling stability over 4,000 cycles (with a capacity decay rate of only 0.00098% per cycle). Electrochemical kinetics analyses revealed a high Mg-ion diffusivity in the order of 10−11 cm2 s−1 and a high total capacity originated from both capacitive and diffusion-controlled contributions. A series of in-situ and ex-situ spectroscopic studies verified an extraordinary dual-ion storage mechanism based on both the insertion/extraction processes of Mg2+ and MgCl+ cations on anthraquinone side groups and the doping/de-doping processes of HMDS- anions on polypyrrole chains. This work demonstrates an effective and universal stabilization strategy of redox-active organic electrode materials via electrolyte initiated in-situ chemical polymerization to propel the exploration of high-performance secondary batteries.

Sustainable Carbon Dioxide Reduction of the P3HT Polymer-Sensitized TiO2/Re(I) Photocatalyst.

In this study, a p-type π-conjugated polymer chain, poly(3-hexylthiophene-2,5-diyl) (P3HT), was physically adsorbed onto n-type TiO2 nanoparticles functionalized with a molecular CO2 reduction catalyst, (4,4-Y2-bpy)ReI(CO)3Cl (ReP, Y = CH2PO(OH)2), to generate a new type of P3HT-heterogenized hybrid system (P3HT/TiO2/ReP), and its photosensitizing properties were assessed in a heteroternary system for photochemical CO2 reduction. We found that P3HT immobilization on TiO2 facilitated photoinduced electron transfer (PET) from photoactivated P3HT* to the n-type TiO2 semiconductor via rapid interfacial electron injection (∼65 ps) at the P3HT and TiO2 surface interface (P3HT* → TiO2). With such effective charge separation, the heterogenization of P3HT onto TiO2 resulted in a steady electron supply toward the co-adsorbed Re(I) catalyst, attaining durable catalytic activity with a turnover number (TON) of ∼5300 over an extended time period of 655 h over five consecutive photoreactions, without deformation of the adsorbed P3HT polymer. The long-period structural stability of TiO2-adsorbed P3HT was verified based on a comparative analysis of its photophysical properties before and after 655 h of photolysis. To our knowledge, this conversion activity is the highest reported so far for polymer-sensitized photochemical CO2 reduction systems. This investigation provides insights and design guidelines for photocatalytic systems that utilize organic photoactive polymers as photosensitizing units.

RGO / MnO2 / Polyterthiophene ternary composite: pore size control, electrochemical supercapacitor behavior and equivalent circuit model analysis

In this work, a new electrode active materials including reduced graphene oxide (rGO), Manganese dioxide (MnO2) / polyterthiophene (PTTh) has been synthesized as a nanocomposite using in-situ polymerization method, microwave-assisted method for obtaining reduced graphene oxide and chemical synthesis of metal-oxide for supercapacitor devices. A ternary nanocomposites of rGO/MnO2/PTTh were characterized by the analysis of Fourier transform infrared-attenuated transmission reflectance (FTIR-ATR), Raman spectroscopy, scanning electron microscopy-energy dispersion X-ray analysis (SEM-EDX), transmission electron microscopy (TEM), thermal-gravimetric analysis (TGA-DTA), Brunauer-Emmett Teller (BET) pore analysis, Ultraviolet-visible (UV-vis) spectrophotometer, X-ray diffraction (XRD) analysis, electrochemical impedance spectroscopy (EIS), galvanostatic charge/discharge (GCD), and cyclic voltammetry (CV). The highest specific capacitance (Csp) was obtained as Csp = 908.86 F/g for rGO/MnO2/PTTh nanocomposite at 1 mV/s for [MnO2]o/[TTh]o = 1/3. Moreover, equivalent electrical circuit model of LR(QR) was chosen to interpret EIS analysis of supercapacitor device. rGO/MnO2/PTTh nanocomposite has both electrochemical double-layer capacitance and pseudocapacitance due to the fast and reversible redox processes related to the π-conjugated polymer chains.

Charge mobility induced by Brownian fluctuations in π-conjugated polymers in solution.

We study the motion of a doped charge in a π-conjugated polymer chain in solution subject to Brownian fluctuations. Specifically, we take poly(para-phenylene) to be our model system where the Brownian fluctuations cause rotational motion of the phenylene rings. The instantaneous torsional fluctuations cause Anderson localization of the charge wavefunction, with the lower-energy spectrum being composed of local ground states and the higher-energy spectrum being composed of quasi-extended states. At low temperatures, additional charge localization occurs via torsional relaxation. The dynamical torsional fluctuations lead to two distinct modes of motion of the charge: adiabatic and non-adiabatic. Adiabatic motion is a 'crawling' motion of the charge along the polymer chain while the charge remains in its local ground state. Non-adiabatic motion is a rapid 'hopping' motion as the charge is excited into higher energy quasi-extended states and travels ballistically along the chain before relaxing into a local ground state. The adiabatic motion dominates at low temperatures, and exhibits a linear temperature dependence and thus a constant zero-field charge mobility. Non-adiabatic motion begins to dominate as the temperature is increased, as the charge is thermally excited into higher energy states. At high temperatures the diffusion constant becomes almost temperature independent, indicating a decrease in the charge mobility with increasing temperature, which we attribute to the charge localization length being a decreasing function of temperature at high temperatures.

Synthesis of ordered conjugated polycyclic aromatic hydrocarbon polymers through polymerization reaction on Au(111)

One-dimensional π-conjugated polymer chains with variable lengths have been synthesized successfully via thermal polymerization reaction on the Au(111) surface. Such polymer chains form parallel arrays along specific directions according to the initial assembly orientations of the close-packed Br-BTTN precursors.

Ultrafast intersystem-crossing in platinum containing π-conjugated polymers with tunable spin-orbit coupling

The development of efficient organic light-emitting diodes (OLED) and organic photovoltaic cells requires control over the dynamics of spin sensitive excitations. Embedding heavy metal atoms in π-conjugated polymer chains enhances the spin-orbit coupling (SOC), and thus facilitates intersystem crossing (ISC) from the singlet to triplet manifolds. Here we use various nonlinear optical spectroscopies such as two-photon absorption and electroabsorption in conjunction with electronic structure calculations, for studying the energies, emission bands and ultrafast dynamics of spin photoexcitations in two newly synthesized π-conjugated polymers that contain intrachain platinum (Pt) atoms separated by one (Pt-1) or three (Pt-3) organic spacer units. The controllable SOC in these polymers leads to a record ISC time of <~1 ps in Pt-1 and ~6 ps in Pt-3. The tunable ultrafast ISC rate modulates the intensity ratio of the phosphorescence and fluorescence emission bands, with potential applications for white OLEDs.

Macroscopic self ordering of solution processible poly(3,3″′-dialkylquaterthiophene) by floating film transfer method

Ordering and alignment of π-conjugated polymer chains are highly desirable for high performance and long life organic electronic devices. We report here self assembly of ordered and aligned solution processible Poly(3,3″′-dialkylquaterthiophene) (PQT-12) polymer at macroscopic level using Floating Film Transfer Method (FTM). PQT-12 polymer film is formed over solution of ethylene glycol and glycerol at different temperatures viz. 22, 26, 33, and 38 °C. PQT-12 films formed by FTM technique are further characterized for optical and morphological properties. UV-vis absorption (for polarize and unpolarize light) and surface topography/phase imaging are carried out by using UV-vis spectrometer and atomic force microscope (AFM), respectively. UV-vis spectra show the polymer chains alignment perpendicular to the film propagation direction and it is well supported by AFM images. The effect of temperature on ordering and alignment of PQT-12 shows 33 °C as an optimum temperature for alignment of polymer chains (a little compromise in ordering). The heating of polymer films at 110 °C for 2 h in ambient causes significant changes in UV-vis absorbance spectra, optical anisotropy, and AFM topography/phase imaging. Our studies provide better understanding of ordering and alignment of PQT-12 chains and also disordering on heating. This work further provides a facile and user-friendly technique for the long range ordered self assembly of PQT-12, which shows enormous potential for various electronic applications.

Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals

The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene–ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene–ethynylene units, the intramolecular charge mobility increased to 8.5 cm2 V−1 s−1. Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

Dynamics of Photogenerated Polaron-Excitons in Organic Semiconductors

In this work we performed numerical simulations of one π-conjugated polymer chain subjected to photogeneration. Within the SSH model modified to include the Brazoviskii-Kirova symmetry breaking term, we investigate the dynamics of photoexcitations to address the generation mechanism of polaron-excitons using the unrestricted Hartree-Fock approximation. It was obtained that after the photoexcitation the system relaxes spontaneously into a polaron-exciton in a transient state in a range of 200 fs. Our results also show that charged polarons are generated directly after this transient state.

Rotational Effect on the One-Dimensional π-Conjugated Polymer

We have investigated the modulation of the physical and electronic properties including their band structure of poly(1,4-phenylene diethynylene-co-9,10-anthracenylene) by the co-axial rotation of π-conjugated polymer chain in the periodic boundary condition framework. The estimated rotational barrier was calculated to 2.38 kcal/mol per cell, suggesting that the aromatic rings of phenylene and anthracenylene were freely rotating each other at the room temperature. On the other hand, bandgap dramatically changes 2.0–3.0 eV by the rotation of aromatic rings. This result suggests that the electronic properties of this polymer should be influenced by rotational effect at the ambient condition.

Insulated Molecular Wire with Highly Conductive π-Conjugated Polymer Core

We have recently developed a new method for synthesizing polyrotaxanes with a high covering ratio, rigidity, photoluminescence efficiency, and solubility in a variety of organic solvents through the polymerization of structurally defined rotaxane monomers. The rigid rodlike structure of the pi-conjugated core polymers in these polyrotaxanes is thought to facilitate the effective transport of charge carriers. Here we applied this method to the synthesis of a polyrotaxane having a poly(phenylene ethynylene) backbone by the Sonogashira copolymerization of a structurally defined rotaxane with a linker molecule. According to time-resolved microwave conductivity and transient absorption spectroscopy measurements, the hole mobility along the pi-conjugated polymer chain of the polyrotaxane thus formed was extremely high and comparable to that in amorphous silicon.

Ground state of π-conjugated polymer chains forming an intermolecular charge-transfer complex as probed by Raman spectroscopy

The intermolecular charge-transfer complex (CTC) between the conjugated polymer MEH-PPV and the low-molecular organic acceptor trinitrofluorenone (TNF) has been studied by Raman and optical absorption spectroscopy. On mixing MEH-PPV with TNF, an absorption band due to the CTC appeared in the optical gap of the polymer, whereas, in the Raman spectra, characteristic bands of the polymer are shifted and their widths and intensities change. The low-frequency shift of the strongest band at 1580 cm−1 in the Raman spectrum of the polymer, assigned to the symmetric stretching vibration of the phenyl group, is shown to be due to electron density transfer from the π-conjugated system of the polymer to the acceptor and is as large as 5 cm−1, which corresponds to a charge transfer on the order of 0.1e−1. Even at a low acceptor concentration (one TNF molecule per 10 monomer units of the polymer), most Raman-active conjugated chains are involved in the CTC. It is suggested that conjugated segments of the polymer can form a CTC of variable composition MEH-PPV: TNF = 1: X, where 0.1 ≤ X ≤ 0.5 (for each monomer unit of the polymer), and one TNF molecule can thereby interact with two conjugated segments of MEH-PPV. The conjugated polymer chains involved in the CTC can become more planar, and their interaction with the local environment can noticeably change; however, their conjugation length, most likely, remains unaltered.

Weak intermolecular charge transfer in the ground state of a π-conjugated polymer chain

We show that a π-conjugated polymer chain can demonstrate weak intermolecular charge transfer in the electronic ground state. Poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene]/2,4,7-trinitrofluorenone (MEH-PPV/TNF) donor-acceptor films have been studied by optical absorption, Raman, infrared spectroscopy, and differential scanning calorimetry. The factors influencing weak intermolecular charge transfer in π-conjugated chains are discussed.

Mobilities of charge carriers hopping between π-conjugated polymer chains

Mobilities of charge carriers in a copolymer film where a possible charge transport is restricted to an interchain path are measured by electrochemical means with doping level as a parameter. The mobility in the low doping regime, corresponding to that of polarons, is 10−6 cm2 V−1 s−1, comparable with polaron mobilities in polythiophene films where hopping transports via interchain and intrachain routes are both feasible. The coincidence suggests strongly a potential role of the interchain hopping transport in the conduction mechanism of common conducting polymers. As the doping level increases, the mobility falls down to 0.4 × 10−6 cm2 V−1 s−1 and then rises up to 6 × 10−6 cm2 V−1 s−1. Based on spectroelectrochemical measurements of the copolymer film, the decrease of the mobility is interpreted in terms of the generation of cation radical π-dimers that are inactive in charge transport. The mobility increase in a high doping region is ascribed to some structural change of a polymer network, leading to enhancement of the interchain hopping probability.

Ultrafast Energy-Transfer Dynamics between Block Copolymer and π-Conjugated Polymer Chains in Blended Polymeric Systems

The blending of polymers has been conventionally employed to increase the quantum efficiencies of polymeric electroluminescence (EL) devices via the energy transfer process, which was interpreted in terms of the Forster-type energy transfer based on dipole−dipole interactions. The detailed analysis of various time-resolved spectroscopic data in the blended polymer between MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) and DSiPV (poly[1,3-propanedioxy-1,4-phenylene-1,2-ethylene(2,5-bis(trimethylsilyl)-1,4-phenylene)-1,2-ethylene-1,4-phenylene]) provides some evidence that the ultrafast energy-transfer channel via the shortest interchain distance between the adjacent constituent polymer chains should be considered to account for the dynamics of stimulated emission (SE) and photoinduced absorption (PA) in the blended polymeric systems. These interchain interactions are also responsible for the diminishment of SE of the blended polymer in the transient absorption spectra, because PA is en...

Physical Characterization of Electrochemically and Chemically Synthesized Polypyrroles

The results of temperature-dependent dc conductivity, EPR magnetic susceptibility, and X-ray photoelectron spectroscopy (XPS) experiments are compared for electrochemically and chemically synthesized polypyrrole (PPy) samples. For chemically synthesized PPy samples soluble in organic solvent with large size dopants such as dodecylbenzenesulfonic acid (DBSA) or naphthalenesulfonic acid (NSA), dc conductivity (σdc) is ≤0.1 S/cm at room temperature, and its temperature dependence [σdc(T)] shows strong localization behavior, while σdc(T) of the electrochemically synthesized PPy samples doped with hexafluorophosphate (PF6) is in the critical or the metallic regime. The density of states of chemically prepared PPy−DBSA samples is less than one-fourth that of electrochemically synthesized PPy−PF6 samples. The g values and temperature dependence of the line width obtained from EPR experiments show that the paramagnetic signals in both electrochemically and chemically synthesized PPy samples are mainly due to the polarons in π-conjugated polymer chains. We observe the existence of one dopant per three pyrrole rings in PPy−DBSA and PPy−PF6 samples. From the XPS experiments, one-fifth of the pyrrole rings of chemically prepared PPy−DBSA are incorporated into interchain links or side chains, while for electrochemically prepared PPy−PF6, one-third of the pyrrole units are in side chains or cross-links. We analyze that the side chains or cross-links of chemically synthesized PPy samples are relatively reduced, and subsequently the interchain interaction weakens. For chemically synthesized PPy samples, the synthesis method using large size dopants is one of the important roles for the reduction of side chains or cross-links and for the increase of solubility. The weakness of the interchain interaction and the reduction of side chains or interchain links for PPy systems play an important role for charge transport.

Time-resolved emission spectra of poly(3-octylthiophene): energy migration in the π-conjugated polymer chain

The excited-state dynamics of poly(3-octylthiophene) in a dilute solution was studied by picosecond time-resolved emission spectroscopy. The emission decay behavior was nonexponential and exhibited significant wavelength dependence. The decay of the longer wavelength emission is slower than that of the shorter wavelength emission and showed a rising component within 125 ps. Time-resolved emission anisotropy studies demonstrated aepolarization within 40 ps caused by the efficient energy migration along the π-conjugated chain.

MÖSsbauer Spectroscopic Study of Fecl3Complexes of Poly(N-Methyl-2,5-Pyrrolylene), Poly(2,5-Thienylene), and Poly(3-Methyl-2,5-Thienylene) Prepared by Ni-Catalyzed Polycondensation

Abstract Reaction of FeCl3 with poly(N-methyl-2,5-pyrrolylene) (PNMPy), poly(2,5-thienylene) (PTh), and poly(3-methyl-2,5-thienylene) (P3MeTh) caused reduction of FeCl3 to afford Fe2+ species. Variable temperature Mössbauer spectra of the reaction systems indicated formation of FeCl2 and FeCl− 4. The latter is regarded as a counter-anion for the cation delocalized along the π-conjugated polymer chain.