P-doping Processes Research Articles

Maroon-green-indigo color switching of thienoisoindigo-based electrochromic copolymers with high optical contrast

BackgroundDonor-acceptor (D-A) type polymers as electrochromic materials possess advantages in color regulation and performance optimization. However, the relationship between D-A type molecule structure and electrochromic properties is not very clear. MethodsThree D-A type copolymers, namely as DC-TIIG-X (X = 1, 2, 3), based on thienoisoindigo (TIIG) as acceptor unit, cyclopenta[2,1-b:3,4-b']dithiophene (DT) and carbazole (CZ) derivatives as donor units, were synthesized via Suzuki coupling reaction. The optical absorption properties of the copolymers could be regulated by changing the molar ratio of donor to acceptor. Significant findingsAll the three solution-processed copolymers show low optical band gaps of 1.50–1.53 eV, ambipolar property, and good electrochromic characteristics. During p-doping and n-doping processes, neutral DC-TIIG-X (X = 1, 2, 3) could turn from green to indigo and maroon, respectively. Especially, DC-TIIG-2 exhibits large optical contrasts of 40%, 11% and 82% and high coloration efficiencies of 284.0 cm2 C−1, 78.9 cm2 C−1 and 433.4 cm2 C−1 at the wavelengths of 440 nm, 730 nm and 1600 nm, respectively. The optical contrast of 40% in visible region is one of the highest values in neutral green electrochromic polymers. Optimizing donor/acceptor molar ratio offers an effective strategy to design high-performance D-A type polymers as electrochromic materials.

Accelerating the Oxygen Reduction Reaction and Oxygen Evolution Reaction Activities of N and P Co-Doped Porous Activated Carbon for Li-O2 Batteries

Rechargeable lithium–oxygen (Li-O2) batteries represent state-of-the-art electrochemical energy storage devices that provide high energy densities. However, their commercialization is challenging owing to their low charging/discharging efficiencies, short battery lives, high overpotentials, and high cathode manufacturing costs. In this study, we prepared a metal-free, N,P co-doped, porous activated carbon (N,P-PAC) electrode via KOH activation and P doping for application as a Li-O2 battery cathode. When used in a rechargeable Li-O2 battery, the N,P-PAC cathode showed a high specific discharge capacity (3724 mA h g−1 at 100 mA g−1), an excellent cycling stability (25 cycles with a limit capacity of 1000 mA h g−1), and a low charge/discharge voltage gap (1.22 V at 1000 mA h g−1). The N,P-PAC electrode showed a low overpotential (EOER-ORR) of 1.54 V. The excellent electrochemical performance of the N,P-PAC electrode can mainly be attributed to its large active area and oxygen-containing functional groups generated via KOH activation and P-doping processes. Therefore, the N,P-PAC prepared in this study was found to be a promising eco-friendly and sustainable metal-free cathode material for Li-O2 batteries.

Twisted ladder-like donor-acceptor polymers as electrode materials for flexible electrochromic supercapacitors

Three ladder-like donor-acceptor (D-A) polymers PI-IDT, PI-BT, PI-DPP containing twisted spirobifluorene unit were synthesized and applied as electrochromic supercapacitor electrodes. By using density functional theory (DFT), we found that the polymer exhibited a distinct HOMO/LUMO wave function distribution when the linker moiety was electron-donors and electron-acceptors, respectively. Due to the introduction of the twisted unit, PI-IDT based on electron donor indacenodithiophene (IDT) unit as the linker moiety expressed a completely separated HOMO/LUMO wave function，and possessed independent p/n-dopable redox properties. With the separation of p-doped site and n-doped site, PI-IDT exhibited excellent performances in p-doping, n-doping and full cyclic scan including p-doping and n-doping processes. The area specific capacitance could reach 6.2 mF cm−2 during p-doping process, and 2.4 mF cm−2 during n-doping process. While the other two polymers PI-BT, PI-DPP based on the benzodithiazole (BT) and diketopyrrolopyrrole (DPP) as the linking unit, respectively, were characterized as that the p-doped sites and n-doped sites were located on one moiety, showing limited capacitance and poor stability. Besides, the selection of different linking units also directly affected the electrode-electrolyte interface contact, film-forming properties, electrochromic and electrochemical properties of the polymer. In addition, PI-IDT had a rich color change (orange, green, blue) and excellent coloring efficiency (155 cm2 C−1). The asymmetric supercapacitor PI-IDT//W0.71Mo0.21O3-x with PI-IDT as anode material showed discoloration from orange to blue, and delivered an energy density of 3.89 W h kg −1.

Tuning the field emission and electronic properties of silicon nanocones by Al and P doping: DFT studies

The effect of replacing an Si atom of a silicon nanocone (SiNC) by Al or P atom on its electronic and field emission properties was investigated using density functional theory calculations. Molecular electrostatic potential surface indicates that the electrons do not spread out on the surface of SiNC evenly, and they tend to accumulate more at the apex, facilitating the electron emission from this site. Replacing an Si atom of the apex of nanocone by Al and P atoms is energetically more favorable than that of the wall by about 12.0 and 8.8 kcal/mol, respectively. Both Al- and P-doping processes increase the SiNC electrical conductivity, but the electron emission from the surface of SiNC increases after the P-doping and decreases by Al- doping. The electron emission in the P-doped SiNC is predicted to be about 600 times greater than that of the pristine SiNC at room temperature. The Al- or P-doping makes the SiNC a p-type or n-type semiconductor.

Decyloxyphenyl-substituted quinoxaline-embedded conjugated electrochromic polymers with high switching stability and fast response speed

Two novel decyloxyphenylquinoxaline-based donor-acceptor (D-A) electroactive monomers bearing dialkoxythiophene as the donor unit are synthesized using Stille coupling reaction. The corresponding polymers, poly[2,3-bis(4-decyloxyphenyl)-5,8-bis(3,4-dimethoxylthiophen-2-yl)quinoxaline] (P1) and poly[2,3-bis(4-decyloxyphenyl)-5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)quinoxaline] (P2), are directly deposited onto the working electrode surface by electropolymerization. All materials were characterized by nuclear magnetic resonance (NMR), mass spectrometry (MS), scanning electron microscopy (SEM), cyclic voltammetry (CV), ultraviolet-visible absorption spectrometry (UV-Vis) and spectro-electrochemical measurements. Electrochemical studies demonstrate that both polymers are capable of showing both reasonable n- and p-doping processes, and advanced long-term switching stabilities. 3,4-Ethylenedioxythiophene substituted for 3,4-dimethoxythiophene as a donor unit, which enhances the conjugated double-bond character of the conducting polymer, thus leading to a lower electronic band-gap. Likewise, the neutral state color of the synthesized polymer tuned from blue to blue-green corresponding to the red shift of the maximum absorption wavelengths in the visible region. In addition, kinetics study of P1 revealed 42% (595 nm), 30% (839 nm) and 69% (1500 nm) transmittance changes (ΔT%), while P2 exhibited 32% (740 nm), 71% (2000 nm) at the dominant wavelengths. It was also observed that both films could switch quickly between the neutral state and oxidation state, with the response time less than 1 s both in visible and near infrared regions.

Toward Purple-to-Green-to-Transmissive-to-Black Color Switching in Polymeric Electrochrome

A novel 3,4-ethylenedioxythiophene (EDOT)-based donor–acceptor electroactive monomer (HCQE) bearing carbazole subunit is synthesized, and then the corresponding polymer, poly(HCQE), is directly deposited onto ITO/glass surface via electrochemical process. Spectroelectrochemical studies demonstrate that poly(HCQE) is capable of showing both n- and p-doping processes. Hence, this low band polymer serves the multielectrochromic feature at three separate states (−0.4 to −2.0 V, −0.4 to 1.2 V, and 1.2 to 2.0 V) with a highly unique near colorless and colored states, fast switching times, redox switching stability, and exceptional transmittance change. To the best of our knowledge, this is the first report of a neutral state green multielectrochromic polymer exhibiting successive switching of colored-to-bleached-to-colored in three distinct regimes.

Synthesis and Electropolymerization of 3,5-Bis-(3,4-ethylenedioxythien-2-yl)-4,4-dimethyl Isopyrazole: A Donor-Acceptor-Donor Monomer

A novel donor-acceptor-donor monomer combining ethylenedioxythiophene donor units with a dimethylisopyrazole acceptor unit was prepared. Trimethylsilyl protecting groups were necessary for the synthesis, but the protected monomer would not undergo electrochemical polymerization without removal of the protecting groups. The deprotected monomer can be electrochemically polymerized to yield an electroactive polymer with accessible p-doping and n-doping processes. Cycling to n-doping potentials during polymerization resulted in irreversible reduction processes and poor polymer growth rather than the anticipated enhanced n-doping response, but oxidative polymerization and re-neutralization without cycling to n-doping potentials produced a robust, electroactive polymer with easily accessible p-doping and n-doping processes. A polymer bandgap of 1.5 eV was estimated from the polymer electrochemistry, but an optical bandgap could not be determined.

Electrochemical Kinetics in Dense, Reactive and Wet Gels. Biomimicking Reactions and Devices

Both p-doping and n-doping processes kinetics were studied by potential steps using different polymers from initial states having different conformational compaction degree. At the chronoamperometric maxima exist, in both cases, a chemical kinetic control. The kinetic coefficient, k, and the reaction order related to the active sites in the polymer chains, β, decrease for increasing packed conformations of the initial state. Rising packed conformations are obtained at rising cathodic potentials for p-doping polymers, or inside the band-gap for both p- and n-doping polymers. These materials can be used as sensors: their electrochemical responses change with the electrolyte concentration or temperature.

Redox-active and electrochromic aromatic poly(amide-imide)s with 2,4-dimethoxytriphenylamine chromophores

A dicarboxylic acid monomer with two built-in imide rings, namely 4,4′-bis(4-carboxyphthalimido)-2″,4″-dimethoxytriphenylamine, was synthesized and then directly polymerized with aromatic diamines leading to new series of aromatic poly(amide-imide)s (PAIs) containing the redox-active 2,4-dimethoxy-substituted triphenylamine (TPA) unit. These PAIs were highly soluble in many organic solvents and could be solution-cast into flexible and strong films. The polymers showed excellent thermal stability, up to 400 °C, and displayed glass transition in the range of 266–294 °C. It is noted that the PAIs have an ambipolar character (n- and p-doping processes) and are capable of repeated, stable electrochemical cycling between a neutral form and an oxidized state. For the PAIs containing the TPA unit on both the imide and amide sides, they showed two pairs of reversible oxidation couples and displayed multi-colored electrochromic behavior: pale yellow in the neutral state, yellowish-green in the semioxidized state, and cyan in the fully oxidized state.

A new low-voltage-driven polymeric electrochromic

Design, synthesis, and properties of a novel donor-acceptor-donor type low-voltage-driven green polymeric electrochrome, P1, which is based on 8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-11-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)acenaphtho[1,2-b]quinoxaline (1) are highlighted. It is noted that P1 has an ambipolar (n- and p-doping processes) character in 0.1M tetrabutylammonium hexafluorophosphate/dichloromethane solution and switches to a transmissive blue state upon oxidation. Furthermore, this new polymeric electrochromic candidate exhibits high redox stability, high coloration efficiency and/or contrast ratio, high percent transmittance (%T) and low response time (1.0s) with a band gap of 1.10eV–1.25eV.

An ambipolar neutral state green polymeric electrochromic

The synthesis and properties of highly stable neutral state green polymeric electrochromic, P1, which is based on 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,3-di(1H-pyrrol-2-yl)quinoxaline were highlighted. P1 exhibits three well-defined absorption bands with a narrow band gap (1.17 eV). The n- and p-doping (ambipolar) processes suggest that P1 is one of the most promising neutral state green polymers and it can be used in supercapacitors as either cathode or anode electrode material. Apart from the stability and the robustness of the polymer film, P1 shows multi-electrochromic behavior; gray-purple in the reduced form and highly transmissive blue color in the oxidized state.

An ambipolar low band gap material based on BODIPY and EDOT

A novel donor–acceptor type conducting polymer based on BODIPY dye as acceptor and EDOT units as donor parts is synthesized electrochemically. The unique combination of BODIPY and EDOT units provides an ambipolar (n- and p-doping processes) low band gap material ( 4). This is the first example of p–n junction in an organic π-conjugated material where BODIPY unit is incorporated directly in the main chain. Furthermore, the polymer film exhibits electrochromic behavior upon p-doping: a color change from light violet (neutral) to indigo (oxidized).

Theoretical Treatment of 3-Phenylsubstituted Thiophenes and Their Intrinsically Conducting Polymers

A series of 3-(p-X-phenyl) thiophene monomers (X= -H, -CH3, - OCH3, -COOC2H5, -COCH3,-NO2) was electrochemically polym-erized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects of the substituents on the phenyl ring as well as the semiempirically calculated heats of formation of the monomer radical cations. Moreover, the oxidation potentials of the monomers were correlated with the ionization potentials of the monomers calculated using density functional theory. The reactivity for coupling reactions and the major regioselective products of the polymerization reaction of mono- and oligo-3- phenylthiophenes are inferred from the calculated lone electron spin densities of the respective radical cations. The ionization potentials, which correspond to the energies for generating radical cations during oxidative processes were estimated.

Electrochemical materials science: calculation vs. experiment as predictive tools in tailoring intrinsically conducting polythiophenes

A series of 3-(p-X-phenyl)thiophene monomers (X = −H, –CH3, –OCH3, –COCH3, –COOC2H5, –NO2) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects of the substituents on the phenyl ring as well as the ionization potentials of the monomers calculated via density function theory, which correspond to the energies for generating radical cations during oxidative processes.

Relaxation phenomena and structural modifications of substituted polythiophenes during the p-doping processes. An electrochemical and morphological study

Electrodes modified by polythiophenes bearing different substituents have been prepared and the behaviour of the conducting polymers has been studied with respect to the structural phenomena occurring in the correspondence to the doping and the relevant undoping processes. The effects of experimental parameters, such as undoping potential and time, have been investigated. The steric hindrance of the substituents on the polymer chain is demonstrated to play a fundamental role in determining the extent of compactness of the film, as induced by polarisation of the electrode at potentials at which the previously charged polymer is neutralised. Such a conclusion is in accordance with prediction of the electrochemical stimulated conformational relaxation model. Electrochemical AFM measurements have been performed in order to acquire a direct view of the morphological modifications of the polymer coatings during the reduction.

Electrochemical materials science: tailoring intrinsically conducting polymers. The example: substituted thiophenes

A series of 3-(p-X-phenyl) thiophene monomers (X= –H, –CH3, –OCH3, –COCH3, –COOC2H5, –NO2) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects of the substituents on the phenyl ring as well as the semiempirically calculated heat of formation of the monomer radical cations.

Mixed ion transfer in redox processes of poly(3,4-ethylenedioxythiophene)

A model considering the transfer of counter ions and solvent molecules has been presented to explain the complicated ion transfer in polymer films during electrochemical redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. The results indicate that both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions is also studied. The developed model shows that solvent molecules are also transferred in conjunction with the ion transfer.

Synthesis and Properties of Random and Alternating Fluorene/Carbazole Copolymers for Use in Blue Light-Emitting Devices

Random and alternating fluorene/carbazole (F/Cz) copolymers with various carbazole contents (20−50 mol %) have been designed and synthesized for use as the hole-transporting as well as light-emitting layer in blue light-emitting diodes (LEDs). DSC analysis has indicated the complete suppression of the crystallizability of these polymers by the introduction of 3,6-carbazole linkages into the polymer backbone, which also results in changes in their optical properties. The absorption maximum has been blue-shifted with an increase in the carbazole content due to the interruption in the main chain conjugation. Meanwhile, the photoluminescent properties have been influenced by the sequence distribution of the fluorene segments as well as the carbazole content. The emission maxima and vibronic features of the alternating copolymers have changed with carbazole content, reflecting the differences in the electronic structures of the repeat units. However, in the case of the random copolymers, the emission spectra remain almost unchanged and are similar to poly(9,9-dioctylfluorene) (PF), despite the fact that the carbazole content increases up to 33 mol %. This feature has been attributed to the existence of longer fluorene segments in the random copolymers, which would be expected to have lower energy gaps, and thus effectively collect excitons from other parts of the polymer backbone. Consequently, the light emitted from these energy traps is similar to that from PF. Electrochemical studies indicate that the introduction of carbazole units effectively raises the HOMO energy levels, thereby facilitating hole injection. Controlling the carbazole content between 20 and 33 mol % results in copolymers with stable and reversible p-doping and n-doping processes. A test for a LED device from P(F3-alt-Cz) indicates that the F/Cz copolymers could be a good candidate for blue light-emitting and hole-transporting materials.

Influence of the nature of the supporting electrolyte on the formation of poly[4,4 ′-bis(butylsulphanyl)-2,2 ′-bithiophene] films. A role for both counter-ion and co-ion in the polymer growth and p-doping processes

Electrode deposits of a polythiophene with particularly interesting characteristics, i.e., poly[4,4 ′-bis(butylsulphanyl)-2,2 ′-bithiophene], have been generated in the presence of different supporting electrolytes. The formation of the coatings has been studied by coupling conventional electrochemical techniques with quartz crystal microbalance measurements. The results of simultaneous voltammetric or chronoamperometric and microgravimetric experiments allow us to show the influence exerted by the nature of the supporting electrolyte on the polymerisation and concomitant charging–discharging processes of the conducting polymer.

Electrochemical and fluorescent properties of alternating copolymers of 9,9-dioctylfluorene and oxadiazole as blue electroluminescent and electron transport materials

The properties of alternating copolymers of 9,9-dioctylfluorene and oxadiazole (F/Ox copolymers) have been studied by cyclic voltammetry (CV), photoluminescence (PL) and electroluminescence (EL). The copolymers contained oxadiazole units symmetrically dispersed in the main chain between one, P(F1-alt-Ox), three, P(F3-alt-Ox), or four, P(F4-alt-Ox), fluorene units, as well as asymmetrically distributed in the chain, P(F2-as-Ox). CV studies revealed that all the copolymers, except P(F1-alt-Ox), had high electrochemical stabilities, and exhibited both reversible n-and p-doping processes. Meanwhile P(F1-alt-Ox) only showed a stable and reversible n-doping process. The CV data also showed that the LUMO levels for the copolymers are close to the work functions of cathode materials such as Ca and Mg, indicating a favourable electron transport property of the copolymers. The PL spectra of the copolymers show a stable blue light-emitting behaviour in the solid state upon annealing under inert gas at temperatures from 40 to 150 °C. However, a broad peak appeared at 510 nm when the samples were annealed at 120 °C in the presence of oxygen. EL studies of a bi-layer light-emitting diode (LED) device produced from P(F3-alt-Ox) demonstrated stable spectra with features similar to those of the PL spectra. The results of this study suggest that F/Ox copolymers are good candidates for use as electron transport layers and blue light-emitting materials in bi-layer LED devices.