Triaryl Amine Research Articles

Magnetic field effects in rigidly linked D-A dyads: Extreme on-resonance quantum coherence effect on charge recombination

Charge recombination in the photoinduced charge separated (CS) state of a rigidly linked donor/bridge/acceptor triad with a triarylamine (TAA) donor, a 1,3-diethynyl-2,5-dimethoxy benzene bridge (OMe), and a perylenediimide (PDI) unit as an acceptor, represents a spin chemical paradigm case of a rigid radical ion pair formed with singlet spin and recombining almost exclusively to the locally excited PDI triplet state (3PDI). The magnetic field dependence of the CS state decay and 3PDI formation kinetics are investigated from 0 to 1800 mT by nanosecond laser flash spectroscopy. The time-resolved magnetic field affected reaction yields spectra of the CS state population and 3PDI population exhibit a sharp and deep resonance at 18.9 mT, indicating level crossing of the S and T+ levels separated by an exchange interaction of J = 18.9/2 mT at zero field. The kinetics are biexponential around the resonance field and monoexponential outside that range. The monoexponential behavior can be simulated by a classical kinetic model assuming a single field dependent double Lorentzian function for the energy gap dependence of all spin conversion processes. The full field dependence of the kinetics has been simulated quantum theoretically. It has been shown that incoherent and coherent hyperfine coupling contribute to S/T+ spin conversion at all fields and that the biexponentiality of the kinetics at resonance is due to a partitioning of the overall kinetics into 2/3 of the singlet hyperfine states exhibiting strong isotropic coupling to T+ and 1/3 of the singlet hyperfine states that do not or only weakly couple isotropically to T+.

Electrochromic and electrofluorochromic bifunctional materials for dual-mode devices based on ladder-like polysilsesquioxanes containing triarylamine

The display devices of the future will tend to be multifunctional, and the dual-mode device for emission and coloration satisfies the requirements of practical applications. We synthesized materials with electrochromic (EC) and electrofluorochromic (EFC) properties through the combination of triarylamine (TAA) and ladder-like polysilsesquioxanes (LPSQs). The ladder-like structure was confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and 29Si-NMR techniques. These polymers exhibit up to 37.3% fluorescence (PL) quantum efficiency (ФPL) and show strong solid-state fluorescence because TAA groups are effectively isolated in ladder-like backbone in LPSQs. The TAA-LPSQs films exhibit reversible change from colorless of bleached state to blue or green of oxidized state. Among them, the optical contrast of the MPA-LPSQ film synthesized from 1-(4-(bis(4-methoxyphenyl)amino)phenyl)-3-(3-(triethoxysilyl)propyl)urea is as high as 83.0% at 787 nm, which shows excellent cycle stability over 1000 s. Unique structure and good electrochemical activity of TAA-LPSQs make them promising materials for dual-mode device. The EC/EFC device (ECD/EFCD) was assembled using MPA-LPSQ as an active layer which showed good performance. In addition, TAA-LPSQs exhibit excellent sensitivity to 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) detection, so these materials can also be applied as highly sensitive chemosensor for explosives.

Microfabrication of 3D-hydrogels via two-photon polymerization of poly(2-ethyl-2-oxazoline) diacrylates

Bis(acrylate) functionalized poly(2-ethyl-2-oxazoline)s (PEtOx-DA) served as macromonomers as well as crosslinkers for the structured two-photon polymerization (2PP) using a novel water soluble photoinitiator (PI). The telechelics were obtained via end capping of the trans-1,4-dibromo-but-2-ene (DBB) initiated cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline. Analysis of the PEtOx-DA by means of mass spectrometry, nuclear magnetic resonance spectroscopy and size exclusion chromatography revealed that the CROP in refluxing acetonitrile was successfully scaled-up from 10 g to 200 g for degrees of polymerization of 10 and 18, respectively. The PI based on a cyclopentanone dibenzylidene based donor-acceptor-donor π system coupled to an acrylate functionalized triaryl amine proved suitable to produce structured hydrogels. Fabricated voxel arrays with different shot times and laser intensities revealed voxel widths below 20 µm showing a similar structuring capability with high resolution of PEtOx-DA as well as for poly(ethylene glycol) diacrylate (PEG-DA) via 2PP. The properties of obtained structures were characterized by a series of line arrays as well as designed Spider-Web-patterns. PEtOx-DA revealed enhanced suitability in comparison to the used PEG-DA.

From aerospace to screen: Multifunctional poly(benzoxazine)s based on different triarylamines for electrochromic, explosive detection and resistance memory devices.

Four kinds of main-chain benzoxazine polymers (PBZ) containing triarylamine (TAA) units were synthesized by Mannich reaction and characterized by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) techniques, etc. Thermal, optical, photophysical and electrochemical properties were studied. The 50% of char residue is left in N2 at 800 °C. The polymers are soluble in common organic solvents and easily spin-coated onto indium‑tin oxide (ITO) coated glass substrates. All the polymers have voltage window ranging from 0 to 1.8 V, and the colors change from yellowish to dark red when voltage is applied. Meanwhile, device assembled from polymer exhibit significant color changes. Furthermore, the polymers also have promising potential application in explosive detection and resistance memory devices.

High-Efficiency Perovskite Solar Cell Based on Sequential Doping of PTAA

Perovskite solar cells have been extensively studied and have recently demonstrated a power conversion efficiency above 23%. In our present approach, we select poly(triaryl amine) (PTAA) as the hole-transport material and use an inverted solar cell planar structure. We propose a sequential method to dope the PTAA thin film in order to reduce the solar cell's series resistance. A modified inter-diffusion method is adopted to improve the perovskite film. We optimize the solvent-assisted annealing condition to maximize the perovskite grain size and reduce the pin-hole density. The impact of PTAA's doping concentration on the solar cell's PV performance is investigated. Compared to conventional PEDOT:PSS-based perovskite solar cell, we observe an improvement in both the open-circuit voltage and the short-circuit current, resulting in a power conversion efficiency enhancement from 12.7% to 15.3%.

Efficient and Stable Perovskite Solar Cell Achieved with Bifunctional Interfacial Layers.

The elaborate control of the surface morphologies and trap states of solution-processed perovskite films significantly governs the photovoltaic performance and moisture resistance of perovskite solar cells (PSCs). Herein, a thin layer of poly(triaryl amine) (PTAA) was unprecedentedly devised on top of perovskite quasi-film by spin-coating PTAA/chlorobenzene solution before annealing the perovskite film. This treatment induced a smooth and compact perovskite layer with passivated surface defects and grain boundaries, which result in a significantly reduced charge recombination. Besides, the time-resolved photoluminescence spectra of the PTAA-treated perovskite films confirmed a faster charge transfer and a much longer lifetime compared to the control cells without the PTAA treatment. Moreover, such a hydrophobic polymer atop the perovskite layer could effectively protect the perovskite against humidity and retain 83% of its initial efficiency in contrast to 56% of control cells stored for 1 month in ambient conditions (25 °C, 35 RH%). As a result, the PTAA-treated PSCs displayed an average efficiency of 17.77% (with a peak efficiency of 18.75%), in contrast to 16.15% of the control cells, and enhanced stability. These results demonstrate that PTAA and the method thereof constitute a promising passivation strategy for constructing stable and efficient PSCs.

Optimization of device design for low cost and high efficiency planar monolithic perovskite/silicon tandem solar cells

Perovskite/silicon hybrid tandem solar cells are very close to commercialization owing to their low cost and relatively high efficiency compared to tandem cells based on III-V compound semiconductors. However, most hybrid tandem cell research is based on n-type heterojunction Si cells, which occupy only a small fraction of the total solar market. Here, we propose a new method for optimizing the design of low-cost and high-efficiency monolithic tandem cells based on p-type homojunction Si cells by realizing lossless current matching by simultaneously controlling the band gap energy and thickness of the perovskite film. In addition, systematic studies have been conducted to determine the optimal hole transport layer applicable to the tandem cell from the viewpoint of band alignment and process compatibility, in order to reduce the open-circuit voltage loss. Optimized tandem cells, which were fabricated with a 310 nm thick perovskite layer of (FAPbI3)0.8(MAPbBr3)0.2 and a hole transport layer of poly(triaryl amine), had a significantly increased efficiency of 21.19% compared to semi-transparent stand-alone perovskite (13.4%) and Si cells (12.8%). Our tandem cell represented the highest efficiency increment among all monolithic perovskite/Si tandem cells as well as the highest efficiency among monolithic perovskite/Si tandem cells based on p-type homojunction Si cells with Al back-surface fields. The design rules suggested in this study could also be applicable to different types of perovskite/Si tandem cells.

Chlorobenzene: A Processing Solvent Enabling the Fabrication of Perovskite Solar Cells with Consecutive Double‐Perovskite and Perovskite/Organic Semiconductor Bulk Heterojunction Layers

Chlorobenzene (CB), which has been used as an anti‐solvent, is demonstrated here as a processing solvent for the fabrication of perovskite films and solar cells. This approach results from the unexpected finding that butylamine‐bound organolead iodides can be dissolved in CB to form precursor solutions. Together with previously established perovskite composition transformation methods, not only conventionally structured perovskite solar cells (PSCs) with a (CH3NH3)PbI3active layer but also nonconventionally structured devices with a consecutive (CH3NH3)PbI3/(C4H9NH3)2PbI4double layer or a mixed poly(triaryl amine) (PTAA) and (CH3NH3)PbI3bulk heterojunction layer are successfully prepared and demonstrated with an optimal efficiency of 16.44%. This is the first time that nonpolar solvents are used for perovskite material processing, which can remove the solvent limitation and open a new avenue for designing and preparing perovskite devices with desired structures.

Excited state C-N bond dissociation and cyclization of tri-aryl amine-based OLED materials: a theoretical investigation.

Tri-aryl amines (TAA) such as triphenylamine (TPA) are widely used for designing chromophores for dye-sensitized solar cells (DSSC) and organic light-emitting diodes (OLED). These materials degrade over time and hence result in reduced performance. Therefore, exploring the associated mechanistic pathways and factors controlling the degradation is necessary for future development of durable TAA-based devices. Hence, in this study, the complete active space self-consistent-field (CASSCF) method coupled with second order N-electron valence perturbation theory (NEVPT2) calculations was carried out to understand the excited state phenomena occurring in TAA using TPA and N,N-diphenyl-2-naphthylamine (DPNA) as model systems. The results indicated the presence of a conical intersection between ground and first excited singlet states with C-N bond dissociation, which acts as a channel for the excited molecules to dissociate and form radical fragments (phenyl/naphthyl). This occurrence is unusual for non-saturated bonds with delocalization. The resulting radical fragments formed intra-molecular products and subsequently yielded five- and six-membered cyclized products depending on the type of aryl groups. The significant findings from this study throw light on the photostability of TAA-based OLED devices as well as on the possible route to synthesize cyclic amines such as carbazoles.

Synthesis of blue-red emissive amido-substituted di(het)aryl and tri(het)aryl amine derivatives via chemoselective N-mono and N,N-diarylation of (het) aryl amino amides using benzyne/arynes

Chemoselective synthesis of amide-substituted triaryl and diaryl amines by N-mono and N,N-diarylation of (het)aryl amino amides using arynes has been reported. Selected triarylamines showed blue-red emission.

Novel π-extended porphyrin-based hole-transporting materials with triarylamine donor units for high performance perovskite solar cells

Efficient hole transporting materials (HTMs) for perovskite solar cells (PrSCs) is highly desired in emerging solar cell technologies. Three HTMs comprising a coplanar porphyrin core with different substituted electron donating triarylamine (TAA) groups (coded as SGT-061, SGT-062, and SGT-063) were successfully developed and used as HTMs for PrSCs. The porphyrin-based HTMs with more bulky donor groups (SGT-062 and SGT-063) possess the larger dihedral angle between alkoxy-substituted phenyl ring and the donor TAA core, leading to the greater interference for the dense molecular arrangement and reducing the π-π stacking of HTM molecules. But SGT-061 with a less bulky donor enables a tight molecular arrangement to increase the π-π stacking between molecules. This renders SGT-061 to have a higher hole mobility than that of SGT-062 and SGT-063 HTMs with bigger donor groups. Moreover, the dynamic charge transfer process of perovskite/various HTM films was studied by time-resolved photoluminescence decay. And SGT-061 exhibited more efficient hole extraction ability than that of SGT-062 and SGT-063. This could be ascribed to better hole mobility and better co-facial π-π stacking between molecules. These results indicate that a less bulky electron donor unit is a preferred peripheral group for developing porphyrin based HTMs for efficient perovskite solar cells.

Synthesis and optoelectronic properties of novel alternate copolymers based on diketopyrrolopyrrole and triarylamine units spaced by flexible chain

A series of alternate copolymers D‑co‑Ts named P(DPP‑TA) P(DPP‑Cz) and P(DPP‑DB) consisting of both diketopyrrolopyrrole (DPP) and different triarylamine (TAA) units, were synthesized by Stille cross-coupling reaction in which DPP acts as an acceptor and TAA acts as a donor. These D‑co‑Ts show good thermal stability in nitrogen (N2) atmosphere. The solutions of D‑co‑Ts have strong UV–vis absorption bands in the range of 313 nm to 344 nm and have fluorescence (PL) peaks at from 415 nm to 496 nm with high quantum efficiency. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and Eg were combined with via cyclic voltammograms (CV) as −5.19 eV to −5.41 eV, −3.77 eV to −3.80 eV, and 1.42 eV to 1.62 eV, respectively. The P(DPP‑TA) film shows the evident color changes from original yellow to brownish to blue. New absorption peaks of P(DPP‑TA) appear at 412 nm and 938 nm with increasing voltage in the UV–vis spectrophotometer, indicating D‑co‑Ts can be promising electrochromic materials. The highest coloration efficiency reaches up to be 270 cm2 C−1 for the P(DPP‑Cz). The memory performances of the ITO/polymer/Al sandwich devices were also studied, in which D‑co‑Ts exhibit the typical nonvolatile rewritable flash memory characteristics. The device of P(DPP‑DB) shows an ON/OFF current ratio of 5.80 × 104 under a threshold voltage of −1.80 V. Furthermore, in the explosive detection tests, the copolymer shows new emission band at 570 nm with addition of TNT, and the PL quenching efficiency goes up to be 82%.

Multifunctional conjugated oligomers containing novel triarylamine and fluorene units with electrochromic, electrofluorochromic, photoelectron conversion, explosive detection and memory properties

A multifunctional integrated platform based on conjugated oligomers containing novel triarylamine (TAA) and fluorene units with responding to voltage, light and explosives stimuli and performing for sensors, detectors, memory media and high contrast displays was designed, and the stimuli-responsive mechanisms were studied. These oligomers show excellent thermal stability with no significant weight loss below 350 °C in nitrogen atmosphere. During the electrochemical reoxidation process, the oligomer films exhibit two pairs of obvious redox peaks with the strong color changes from yellowish of neutral state to green and blue of oxidized state, and remain good continuous cyclic stability over 500s with a cycle time of 10s. The electrofluorescent properties of the oligomers also can be tuned by electrochemistry redox, exhibiting high contrast. Meanwhile, non-volatile rewritable flash memory devices were produced with the sandwich structure ITO/oligomer/Al, which could gain the ON/OFF current ratio as high as about 104 at low threshold voltage of 1.2 V.

Nickel Dual Photoredox Catalysis for the Synthesis of Aryl Amines

In this work, a new dual photoredox nickel catalysis system has been utilized for the synthesize of aryl amines. Previously, our group has shown that a nickel catalyst in conjunction with a photosensitizer and a sacrificial electron donor can cross-couple C–C bonds via photoredox-assisted reductive coupling. Here we have built upon that system to develop a redox-neutral cross-coupling system for the formation of C–N bonds. The catalytic system is composed of just a nickel cross-coupling catalyst, a Ru photocatalyst, and base and is capable of coupling amines with aryl halides in good to excellent yields. Furthermore, it was found that these reactions are functional under ambient conditions with catalyst loadings of 1 mol %. Spectroscopic studies provide support that this amination mechanism proceeds via a nitrogen-based radical intermediate. This N-radical mechanism offers direct synthetic access to di- and triaryl amines from nickel photocatalysis.

Oxoammonium cation of 2,2,6,6-tetramethylpiperidin-1-oxyl: a very efficient dopant for hole-transporting triaryl amines in a perovskite solar cell

Abstract

Multifunctional polyamides containing pyrrole unit with different triarylamine units owning electrochromic, electrofluorochromic and photoelectron conversion properties

Four kinds of novel polyamides (PAs) containing pyrrole core with different triarylamine (TAA) groups were designed and synthesized. These PAs exhibit good solubility in various organic solvents and excellent thermal stability. The two PAs prepared from cyclohexane-1,4-dicarboxylic acid exhibit fluorescence maximum at 475–476 nm with quantum yields up to 39.0% and 57.3% in N,N-dimethylacetamide (DMAc) solution. Furthermore, the polymer films show reversible electrochemical redoxidation with color changing from yellowish to khaki to dark blue. Especially, the films have high coloration efficiency (up to 143 cm2 C−1 at 750 nm) and after over 1000 s the films still exhibit continuous cyclic stability of electrochromism. What's more, these PAs could be used as the photoelectric conversion material owing to their excellent optoelectronic properties.

A solvent- and temperature-dependent intramolecular equilibrium of diamagnetic and paramagnetic states in Co complexes bearing triaryl amines.

Complexes [Co(L)2](ClO4)2 (L = o-substituted 2-(pyridine-2-yl)-1,10-phenanthrolines 1a-c) containing three redox active centres (a Co2+ ion and two triaryl amine (Tara) units) have been synthesised. The order of oxidation steps in [Co(L)2](ClO4)2 (L = 1a-c) was determined using cyclic voltammetry and EPR/UV-vis-NIR spectroelectrochemistry. In acetonitrile solutions, at room temperature, the first oxidation is Co-centred followed by the Tara oxidation at more anodic potentials. The order of oxidation is inverted in solutions of the less polar solvent dichloromethane. The Co3+/2+-centred redox event leads to a spin transition between the paramagnetic high-spin (HS) Co2+ and the diamagnetic low-spin (LS) Co3+ state, which was proven using 1H NMR and EPR spectroscopy. After one-electron oxidation of [Co(L)2](ClO4)2, an equilibrium between the diamagnetic [Co3+(L)]3+ and paramagnetic [Co2+(L)(L+)]3+ state in [Co(L)2]3+ (L = 1a-c) was found. Cyclic voltammetry showed enhanced intermolecular electron transfer between the [Co2+(L)2]2+ and [Co3+(L)2]3+ redox states mediated by [Co2+(L)(L+)]3+. Variable temperature vis-NIR spectroscopy of in situ generated [Co(L)2]3+ revealed a temperature-dependent redox equilibrium between the [Co3+(L)2]3+ and the [Co2+(L+)(L)]3+ states (L = 1a-c). Magnetic coupling between the HS-Co2+ ion and the Tara+ radical in [HS-Co2+(L+)(L)]3+ (L = 1a,c) was deduced from broad and undetectable lines observed in the corresponding EPR spectra. Complete oxidation to [LS-Co3+(L+)2]5+ (L = 1a,c) leads to characteristic EPR spectra of Tara biradicals with non-interacting spins.

An Effective Synthesis of N,N-Diphenyl Carbazolium Salts

Tetraaryl ammonium salts are a synthetic challenge, since there is no general method for the arylation of triaryl amines. Contrary to other quaternary ammonium salts, tetraaryl ammonium salts should be very chemically stable. The ipso carbons are not very electrophilic, since the positive charge is distributed throughout the pi systems and they have no acidic β hydrogens. Here we demonstrate a simple approach to N,N-diphenyl carbazolium salts using only three synthetic steps, allowing for an easy production of these salts in large amounts and in a relatively short time. In addition, we study the Cu(I) catalyzed multi-arylation of 2,2’-diaminobiphenyl, focusing on the regioselectivity of each step. Finally, we characterize, for the first time, the solid state structure of a tetraaryl ammonium salt.

Organic-inorganic hybrid electrochromic materials, polysilsesquioxanes containing triarylamine, changing color from colorless to blue

Four kinds of soluble monomers, containing triarylamine (TAA) group with reactive siloxane group, were synthesized under mild conditions via the reaction between 3-(triethoxysilyl)propyl isocyanate (TEOSPIC) and four TAA derivatives, respectively. Then the corresponding colorless organic-inorganic hybrid materials (PSSOs) were derived from the hydrolytic condensation of the monomers. PSSOs revealed good solubility in polar solvents on account of the effect of propeller-like TAA unit as well as the auxo-action effect of the flexible chain within the monomers. The structural characteristics of these PSSOs were identified by 1H NMR, 29Si NMR, FT-IR spectroscopies and X-ray diffraction (XRD). The morphology, dynamic changes of the transmittance and current before and after electro-oxidizing reaction were studied, and didn’t show significant change suggesting good stability of the PSSOs. Meanwhile, these PSSOs performed high contrast of optical transmittance change up to 84% with the highest coloration efficiency to 241 cm2·C−1. Furthermore, electrofluorescent properties of PSSOs were investigated with high-contrast.

The Effect of Substituent‐Dependent Photoinduced Intramolecular Charge Transfer on the Photochromism of Hemithioindigos

AbstractA series of N,N′‐diarylamine‐modified hemithioindigos (HTIs) were synthesized and characterized. Photochemical Z/E isomerization around the C=C double bond occurred for all novel HTIs in various solvents. Due to a strong donor–acceptor π‐conjugated structure, the novel HTIs exhibited a strong red shift and clear solvatochromism in steady‐state absorption and fluorescence spectroscopic measurements, respectively. An intramolecular charge transfer (ICT) from the diarylamine‐substituted stilbene component (donor) to the thioindigo part (acceptor) strongly affects the isomerization behavior. HTI is the dominating photochromic unit in this system but the substitution pattern on the triarylamine (TAA) moiety causes unusually strong changes in the photostationary states (PSS) and thermal stabilities. Electron‐withdrawing substituents (such as cyano groups) strongly improve thermal stabilities and enrich the E‐isomer content in the photostationary state, however electron‐donating substituents play a converse effect, for example, in the solvents hexane and tetrachloroethene. The low E ratio in the PSS in more polar solvents, such as acetonitrile, can be explained by a very fast thermal back reaction and formation of a new decay state in OMe‐substituted compounds.