Triphenylamine Groups Research Articles

Morphology Determines an Efficient Coherent Electron Transport for Push-Pull Organic Semiconductors Based on Triphenylamine and Dicyanovinyl Groups.

The morphology of the active layer in organic solar cells is fundamental for achieving high power conversion efficiency. However, the morphological characteristics for optimal performance are still being investigated. An atomistic computational approach is required to determine the relationship between active layer morphology and performance. Since the organic solar cell has multiple phases and interfaces, the computational modeling of charge generation and transport is challenging. We then used a set of push-pull semiconductors to illustrate how the electronic transmission spectrum, derived from the Landauer-Büttiker formalism, can be used to investigate the efficiency of coherent charge transport across anisotropic organic solids. The electronic transmission spectrum was calculated from the electronic band structure obtained using the density-functional-based tight-binding method. We found that coherent charge transport was more efficient along the direction parallel with the interface between the electron-acceptor and electron-donor moieties for a herringbone morphology.

A Fluorescent and Colorimetric Chemosensor Detecting Pd2+ Based on Chalcone Structure with Triphenylamine.

A fluorometric and colorimetric chemosensor DiPP ((E)-3-(4-(diphenylamino)phenyl)-1-(pyridin-2-yl)prop-2-en-1-one) based on chalcone structure with a triphenylamine group was synthesized. Sensor DiPP detected Pd2+ with fluorescence turn-off and via colorimetry variation of yellow to purple. The binding ratio of DiPP to Pd2+ turned out to be 1 : 1. Detection limits for Pd2+ by DiPP were analyzed to be 0.67 µM and 0.80 µM through the fluorescent and colorimetric methods. Additionally, the fluorescent and colorimetric test strips were applied for probing Pd2+ and displayed that DiPP could obviously discriminate Pd2+ from other metals. The binding feature of DiPP to Pd2+ was presented by ESI-mass, Job plot, NMR titration, ESI-mass, and DFT calculations.

New electropolymerized triphenylamine polymer films and excellent multifunctional electrochromic energy storage system materials with real-time monitoring of energy storage status

Multifunctional intelligent electrochromic energy storage with real-time monitoring of energy storage level by color change has become the extremely attractive researches for the development of electrochemical energy storage systems. Herein, three novel triphenylamine-based organic monomers with star-shaped donor–acceptor structure are designed and synthesized to successfully obtain the corresponding three polymer films with different and rich color switching by electrochemical polymerization via the coupling between peripheral triphenylamine groups. Based on these three polymer films as the electrodes, a fast switching electrochromic property with a large optical contrast of 80.5 % in the visible region and a high coloration efficiency of 277.21 cm2·C−1, which are one of the best results among TPA-based electrochromic materials, is achieved for the polymer pPh-4TPA with the pyrazino[2,3-g]quinoxaline acceptor core. Meanwhile, pPh-4TPA also shows high specific capacitance of up to 423F·g−1 (475F·cm−3), high capacity of 115.3 mAh·g−1 and unparalleled rate performance. The assembled asymmetric electrochromic energy storage devices based on pPh-4TPA polymer films exhibited maximum energy density of 105.12 Wh·kg−1 (107 mWh·cm−3) and power density of 45 kW·kg−1 (45.9 W·cm−3), which are both the highest energy and power densities among the pure organic electrochromic pseudocapacitors ever reported, simultaneously accompanied by reversible color changes in appearance during charging and discharging process.

Dopant‐Free Two‐Dimensional Hole Transport Small Molecules Enable Efficient Perovskite Solar Cells

AbstractDeveloping dopant‐free hole transport materials (HTMs) to replace Spiro‐OMeTAD is a challenging but urgent issue for commercialization of state‐of‐the‐art n‐i‐p structured perovskite solar cells (PSCs). Here, this work proposes an effective two‐dimensional conjugate engineering strategy to tune molecular stacking orientation and improve the hole mobility of dopant‐free small molecule HTMs. For the first time, triphenylamine (TPA) groups are incorporated as side chains of benzo [1,2‐b:4,5‐b′]dithiophene (BDT) unit to extend the longitudinal conjugate, achieving two donor‐acceptor‐acceptor type 2D small molecules, namely XF2 and XF3, which show a dominant face‐on orientation and better hole transport mobility than the linear small molecule XF1. The incorporation of alkoxy Lewis base groups makes XF3 a more effective defect passivator for perovskite surfaces. As a result, the PSCs using pristine XF3 HTM show a dramatically improved efficiency of 20.59% along with improved long‐term stability compared to that of XF1 HTM (power conversion efficiency (PCE) = 18.84%). A champion efficiency of 21.44% is achieved through device engineering for dopant‐free XF3‐based PSCs. The results show that the building block with longitudinal conjugate extension in small molecules plays an essential role in the face‐on orientation morphology and elucidates a key design rule for the dopant‐free small molecule HTMs for high‐performance PSCs.

Design and Synthesis of Benzoheterodiazole-based Fluorescent Compounds for Emitting Applications.

Benzoheterodiazole-based fluorophores with aggregation-induced emission (AIE) properties are synthesized and their photophysical properties in different states (solution, film, and powder) are investigated. These compounds present excellent thermal stability, and the decomposition temperature is above 300 °C. Among these compounds, the fluorophores with triphenylamine (TPA) group present better fluorescent emissions in solutions as well as in aggregated states, and the highest solution fluorescent efficiency is up to 75.2% in solution. Meanwhile, the fluorescent compounds terminated with triphenylethene (TPE) exhibit the classical AIE properties. Furthermore, these compounds might be used as emissive layers for the fabrication of red, orange and green organic light emitting diodes.

Acene enlargement for absorption red-shifting and photosensitization enhancement of photosensitizers with aggregation-induced emission.

Photosensitizers with aggregation-induced emission (AIE PSs) were widely explored in photodynamic therapy. Numerous acceptors but few donors were reported to design AIE PSs. In this study, we developed a new kind of donor that can improve the comprehensive performance of AIE PSs by expanding the π extension of aromatic rings at the end of the triphenylamine group through acene enlargement. The absorption and fluorescence peaks of anthryl-substituted AIE PS are red-shifted by 29 nm and 42 nm; the photosensitization efficiency is enhanced by 1.16 times; the AIE factor is 86.1 and the fluorescence quantum yield is 9.3%. We also demonstrated that the anthryl-based AIE PS can image and ablate cancer cells well both in vitro and in vivo. The anthryl-triphenylamine donor provides an excellent option to design donor-acceptor AIE PSs with high comprehensive performance.

Exploring the potential of anthracene derivatives as fluorescence emitters for biomedical applications.

Two novel anthracene derivatives were synthesized, and detailed photo-physical and biological investigations were carried out using a variety of spectroscopy techniques. The effect of cyano (-CN) substitution was found to be effective to alter the charge population and frontier orbital energy levels via Density Functional Theory (DFT) calculations. Particularly, the introduction of styryl and triphenylamine groups attached to the anthracene core helped to increase the conjugation relative to the anthracene moiety. The results revealed that the molecules have intramolecular charge transfer (ICT) properties, occurring from the electron donating triphenylamine to the electron accepting anthracene moiety in solutions. In addition, the photo-physical properties are strongly cyano-dependent, where the cyano-substituted (E/Z)-(2-anthracen-9-yl)-3-(4'-(diphenylamino)biphenyl-4yl)acrylonitrile molecule showed stronger electron affinity due to the enhanced internal steric hindrance compared to the (E)-4'-(2-(anthracen-9-yl)vinyl)-N,N-diphenylbiphenyl-4-amine molecule, which resulted in a lower photoluminescence quantum yield (PLQY) value and a shorter lifetime in the molecule. Besides, the Molecular Docking approach was used to investigate possible cellular staining targets to confirm cellular imaging potential of the compounds. Moreover, cell viability analyses put forth that synthesized molecules do not exhibit significant cytotoxicity under 125 μg mL-1 concentration on the human dermal fibroblast cell line (HDFa). Moreover, both of the compounds showed great potential in cellular imaging of HDFa cells. Compared to Hoechst 33258, a common fluorescent dye used for nuclear staining, the compounds showed higher magnification of cellular structure imaging capacity by staining the whole cellular compartment. On the other hand, bacterial staining showed that ethidium bromide has higher resolution in monitoring Staphylococcus aureus (S. aureus) cell culture.

Imine-linked covalent organic frameworks with stable and microporous structure for effective carbon dioxide and iodine uptake

In recent years, many environmental problems including global warming and climate change have emerged due to the excessive emission of carbon dioxide. Covalent organic frameworks (COFs) exhibit good porosity and excellent stability. They can be constructed into uniform channel and tunable skeleton which are ideal for gas uptake. Here, we designed two new imine-linked COFs (ESM-COF-1 and ESM-COF-2) by condensation of two C3 symmetrical monomers. Interestingly, ESM-COF-1 and ESM-COF-2 displayed microporous features because of short length building units employed, the pore size, which is much smaller than most two-dimensional (2D) imine COFs. This virtue is good for gas adsorption via pore surroundings. Furthermore, rich methoxy units as electron-donate units on the walls delocalized electronic clouds from building units to the imine bond through π-conjugation interaction, indicating outstanding stability in harsh conditions. High-density active units from walls (triphenylamine and methoxy groups) to the imine linkage also improved the gas adsorption via the weak interaction. Interestingly, ESM-COFs exhibited stability, microporous features, and active units from walls to linkage to give a high carbon dioxide uptake at 4.64 mmol g−1, which is the excellent one among the reported 2D COFs.

Constructing molecular bridge for high-efficiency and stable perovskite solar cells based on P3HT

Poly (3-hexylthiophene) (P3HT) is one of the most attractive hole transport materials (HTMs) for the pursuit of stable, low-cost, and high-efficiency perovskite solar cells (PSCs). However, the poor contact and the severe recombination at P3HT/perovskite interface lead to a low power conversion efficiency (PCE). Thus, we construct a molecular bridge, 2-((7-(4-(bis(4-methoxyphenyl)amino)phenyl)−10-(2-(2-ethoxyethoxy)ethyl)−10H-phenoxazin-3-yl)methylene)malononitrile (MDN), whose malononitrile group can anchor the perovskite surface while the triphenylamine group can form π−π stacking with P3HT, to form a charge transport channel. In addition, MDN is also found effectively passivate the defects and reduce the recombination to a large extent. Finally, a PCE of 22.87% has been achieved with MDN-doped P3HT (M-P3HT) as HTM, much higher than the efficiency of PSCs with pristine P3HT. Furthermore, MDN gives the un-encapsulated device enhanced long-term stability that 92% of its initial efficiency maintain even after two months of aging at 75% relative humidity (RH) follow by one month of aging at 85% RH in the atmosphere, and the PCE does not change after operating at the maximum power point (MPP) under 1 sun illumination (~45 oC in N2) over 500 hours.

Ruthenium polypyridine complexes with triphenylamine groups as antibacterial agents against Staphylococcus aureus with membrane-disruptive mechanism.

Due to the emergence and wide spread of methicillin-resistant Staphylococcus aureus, the treatment of this kind of infection becomes more and more difficult. To solve the problem of drug resistance, it is urgent to develop new antibiotics to avoid the most serious situation of no drug available. Three new Ru complexes [Ru (dmob)2PMA] (PF6)2 (Ru-1) [Ru (bpy)2PMA] (PF6)2 (Ru-2) and [Ru (dmb)2PMA] (PF6)2 (Ru-3) (dmob = 4,4′-dimethoxy-2,2′-bipyridine, bpy = 2,2′-bipyridine, dmb = 4,4′-dimethyl-2,2′-bipyridine and PMA = N-(4-(1H-imidazo [4,5-f] [1,10] phenanthrolin-2-yl) -4-methyl-N-(p-tolyl) aniline) were synthesized and characterized by 1H NMR, 13C NMR and HRMS. The detailed molecular structure of Ru-3 was determined by single crystal X-ray diffraction. Their antibacterial activities against Staphylococcus aureus (Staphylococcus aureus) were obvious and Ru-3 showed the best antibacterial effect with the minimum inhibitory concentration value of 4 μg ml−1. Therefore, further study on its biological activity showed that Ru-3 can effectively inhibit the formation of biofilm and destroy cell membrane. In vitro hemolysis test showed that Ru-3 has almost negligible cytotoxicity to mammalian red blood cells. In the toxicity test of wax moth insect model, Ru-3 exhibited low toxicity in vivo. These results, combined with histopathological studies, strongly suggest that Ru-3 was almost non-toxic. In addition, the synergistic effect of Ru-3 with common antibiotics such as ampicillin, chloramphenicol, tetracycline, kanamycin and gentamicin on Staphylococcus aureus was detected by chessboard method. Finally, in vivo results revealed that Ru-3 could obviously promote the wound healing of Staphylococcus aureus infected mice.

New metal free organic dyes incorporating heterocyclic Benzofuran core as conjugated spacer: Synthesis, Opto‐electrochemical, DFT and DSSC studies

AbstractSynthesis of a series of new organic photosensitizers, designated as BZ1‐BZ4, was achieved by incorporating benzofuran core as π‐spacer, triphenylamine (TPA) and 4‐methoxy triphenylamine (4‐MeO‐TPA) as donors and cyanoacrylic acid (CAA) and rhodanine‐3‐acetic acid (RAA) as acceptor/anchoring groups. Structurally, dyes BZ1 and BZ2 carry TPA and 4‐MeO‐TPA as donors, respectively, whereas CAA constitutes as a common acceptor. On the other hand, BZ3 and BZ4 incorporate TPA and 4‐MeO‐TPA as donors, respectively, and RAA serves as a common acceptor. Key steps to access BZ1‐BZ4 involved Wittig olefination, reduction of cyano groups to aldehyde, and finally Knoevenagel condensation. In UV–visible spectra, dyes BZ1‐BZ4 exhibited intramolecular charge transfer (ICT) maxima in the range of 503 nm to 534 nm and their extinction coefficients varied from 22,600 to 40,400 M−1 cm−1. Using cyclic voltammetry and UV–visible data, we calculated the optical band gaps, (E0−0) of BZ1‐BZ4 to be 2.09, 2.00, 2.01, and 1.93 eV, respectively. DFT studies revealed that HOMOs of dyes were localized essentially on the donors triphenylamine groups, whereas the LUMOs are largely confined over electron acceptors CAA and RAA as well as partly diffused into the benzofuran spacer. DSSCs, configured using BZ1‐BZ4 as photosensitizers, showed fill factors (ff) in the range of 0.57 to 0.76, comparable to standard N3 dye (0.67). In addition, BZ1 and BZ2 dyes with CAA as an acceptor also exhibited decent open circuit voltage (Voc) in the range of 0.61 to 0.63 relative to the 0.66 observed for N3 dye. Dyes BZ1‐BZ2 carrying CAA as an acceptor exhibited an efficiency (η) of 2.03% and 1.49%, respectively, against the benchmark N3 dye, showing η of 5.02%. Due to poor Voc and short circuit current density (Isc), dyes BZ3‐BZ4 carrying RAA as acceptor/anchoring group performed significantly poor, showing η of 0.08%, and 0.32%, respectively.

Structural, Photophysical, and Water Sensing Properties of Pyrazolo[1,5‐a]pyrimidine‐Triphenylamine Hybrid Systems

AbstractThermal, structural, and photophysical properties of five pyrazolo[1,5‐a]pyrimidine‐triphenylamine hybrid systems substituted at position 3 of the fused ring were studied (probe/R: D1/H, D2/I, D3/CCSiMe3, D4/CHO, D5/CN). The solvatofluorochromism of D4 and D5 showed that the solvent dipolarity (SdP) is mainly responsible for their spectral changes, which arose from an internal charge transfer (ICT) from the triphenylamine (TPA) group to the acceptor substituent at position 3. As a result, D5 was applied for the detection of water in organic solvents (i. e., AcOEt and THF); this probe also exhibited an intense light emission in the solid‐state at 530 nm (ϕ=0.60). The five compound structures were solved and analyzed by X‐ray crystallography (XRC), with a link found between their structural characteristics and their physicochemical properties. For example, although all the probes exhibited good thermostabilities, this property decreased in D3 and was explained by frontier molecular orbital calculations based on the XRC results. Crystallographic studies were also used to interpret the differences in solid‐phase emission intensities in D1–D4 versus D5.

Electroinduced crosslinking of triphenylamine-based polybenzoxazines

Polybenzoxazines attract much attention as good phenolic resins due to their interesting and useful properties. Recently, benzoxazine monomers have been employed as crosslinking agents to enhance the properties of different types of polymers by being used as additives to a secondary cure process. In this paper, we propose a new electroinduced approach to increase the crosslinking density of electroactive polybenzoxazines through the design of new monomers that contain triphenylamine groups as electrodimerization points. The use of electrochemical techniques means the crosslinking process can be monitored and also the electrochemical reaction process upon polybenzoxazine oxidation either in solution or ionogel matrixes can be disclosed. These studies lay the foundations for the design of smart polybenzoxazines that could undergo dual-cure mechanisms at low electrochemical potential values.

Syntheses and Photovoltaic Properties of New Pyrazine-Based Organic Photosensitizers for Dye-Sensitized Solar Cells

Three novel pyrazine-based organic photosensitizers denoted as TPP, TPPS, and TPPF were synthesized for dye-sensitized solar cell (DSSC) studies. Chemical structures of the pyrazine-based photosensitizers were designed with pyrazine derivatives as acceptors, triphenylamine groups as donors, and the thiophene–cyanoacryl group as an auxiliary heterocyclic linkers-acceptor. Using UV-vis spectrophotometry, cyclic voltammetry, and density functional theory calculations, optical and electrochemical characteristics of these pyrazine-based photosensitizers were examined and explored in relation to photovoltaic parameters. The effects of the molecular structures of these photosensitizers on the performances of DSSCs were also investigated. The overall conversion efficiencies of DSSCs based on pyrazine-based photosensitizers were 1.31~2.64% under AM 1.5 irradiation of 100 mW/cm2. To confirm the effect of interfacial charge transfer on photovoltaic performances of DSSC based on pyrazine-based photosensitizers, interfacial charge transfer resistances were investigated by electrical impedance spectroscopy (EIS) measurements.

Tuning long-term mitochondrial imaging and photodynamic therapy capabilities through rational design of aggregation-induced emission luminogens

Many aggregation-induced emission luminogens (AIEgens) not only act as photosensitizers to generate cytotoxic reactive oxygen species under the irradiation of appropriate light, but also emit bright fluorescence for positioning and tracking, realizing image-guided photodynamic therapy. However, few AIEgens can achieve long-term near-infrared bioimaging, and the design of AIEgens rarely involves multi-faceted functional optimization and the combined use of different AIE groups. In this study, a series of low-toxic salicylaldehyde-based Schiff base AIEgens (NPy-AIE, NNPy-AIE, TPy-AIE and TTPy-AIE) are rational designed from multiple aspects to study structure-function relationships, which all exhibit excellent long-term bioimaging capability. Starting from NPy-AIE, its water solubility is enhanced by increasing the number of cations and constructing hydrophilic groups to obtain NNPy-AIE. Dimethylaniline groups of NPy-AIE are replaced with triphenylamine groups to acquire TPy-AIE with enhanced AIE activity. Thiophene groups are introduced in TPy-AIE to obtain TTPy-AIE with larger conjugation structure and electron donor-acceptor strength. The first two red-emitting AIEgens have better long-term mitochondrial targeting capability. NNPy-AIE has better water solubility and mitochondrial membrane potential detection capabilities. In particular, the latter two near-infrared emitting AIEgens can not only achieve long-term in vivo and in vitro near-infrared imaging, but also generate singlet oxygen under white light irradiation, which increases the level of intracellular reactive oxygen species and the proportion of apoptotic cells, showing potential as photosensitizers for image-guided photodynamic therapy. In vivo photodynamic therapy experiment of TTPy-AIE in 4T1 tumor-bearing mice has confirmed its excellent biocompatibility and photodynamic therapy ability.

Synthesis and Characterization of Diketopyrrolopyrrole-Based Aggregation-Induced Emission Nanoparticles for Bioimaging.

Conventional fluorescent dyes have the property of decreasing fluorescence due to aggregation-caused quenching effects at high concentrations, whereas aggregation-induced emission dyes have the property of increasing fluorescence as they aggregate with each other. In this study, diketopyrrolopyrrole-based long-wavelength aggregation-induced emission dyes were used to prepare biocompatible nanoparticles suitable for bioimaging. Aggregation-induced emission nanoparticles with the best morphology and photoluminescence intensity were obtained through a fast, simple preparation method using an ultrasonicator. The optimally prepared nanoparticles from 3,6-bis(4-((E)-4-(bis(40-(1,2,2-triphenylvinyl)-[1,10-biphenyl]-4-yl)amino)styryl)phenyl)-2,5-dihexyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DP-R2) with two functional groups having aggregation-induced emission properties and additional donating groups at the end of the triphenylamine groups were considered to have the greatest potential as a fluorescent probe for bioimaging. Furthermore, it was found that the tendency for aggregation-induced emission, which was apparent for the dye itself, became much more marked after the dyes were incorporated within nanoparticles. While the photoluminescence intensities of the dyes were observed to decrease rapidly over time, the prepared nanoparticles encapsulated within the biocompatible polymers maintained their initial optical properties very well. Lastly, when the cell viability test was conducted, excellent biocompatibility was demonstrated for each of the prepared nanoparticles.

Zn(II) Complexes Based on a Schiff Base: Mechanochromism- and Solvent Molecule-Dependent Acidochromism

A new Schiff base molecule (HL) with a triphenylamine group and its three zinc(II) complexes (1, 1-THF, and 1-DMF) were synthesized and characterized. As expected, three kinds of loosely packed structures that are susceptible to mechanical stimulation were adjusted through twisted conformations and weak intermolecular interactions (C–H···π, π···π, and hydrogen bonds). They all exhibit remarkable mechanochromic luminescence (MCL) behavior with high contrast upon mechanical grinding due to the phase transition between a crystalline and an amorphous state, as confirmed by powder X-ray diffraction (PXRD) studies. Especially, grinding of 1-THF was accompanied by the departure of lattice tetrahydrofuran (THF) molecules. Further investigation revealed that 1-THF and 1-DMF showed outstanding acidochromic behavior. The PXRD and thermogravimetric analysis (TGA) results proved that fumigation with HCl could destroy the interaction between the solvent and ligand molecules, resulting in the phase transition from the crystalline state to the amorphous state, which is essential for their acidochromic properties. The acidochromic mechanism is different from the reported protonation and deprotonation process. Both HL and complex 1 exhibit no acidochromism. This work will shed light on the mechanism of acidochromic properties of Schiff base zinc(II) complexes and expand the potential solid-state stimuli-responsive luminescence materials.

Two Zirconium Metal–Organic Cages with S4 and D2d Symmetry: Construction and Detection of Antibiotics

The construction of robust zirconium metal–organic cages (Zr-MOCs) with specific geometric structures and properties is of great significance but is challenging. Herein, two Zr-MOCs (Zr-MOC-1 and Zr-MOC-2), which respectively comprise triphenylamine and carbazole functional groups, are synthesized and structurally characterized. Compared with the perfect tetrahedral geometry with S4 symmetry in Zr-MOC-1, the presence of carbazole structural units leads the tetrahedral structure of Zr-MOC-2 to be distorted, and then assumes it a trigonal pyramid geometry with D2d symmetry. Furthermore, these two Zr-MOCs could be used as soluble chemical sensors for probing nitrofuran antibiotics, and the detection sensitivity of Zr-MOC-2 is higher than that of Zr-MOC-1. These results demonstrate that the introduction of appropriate structural units into Zr-MOCs may significantly impact their architectures and properties.

Two different implementation strategies for highly efficient non-doped fluorescent organic light-emitting diodes based on benzothiadiazole derivatives

Organic light-emitting diodes (OLEDs) have been widely used in flat-panel displays and solid-state lightings because of their unique advantages. The non-doped red OLEDs with satisfactory external quantum efficiency (EQE) still remains challenging. In this work, a series of red emissive materials are successfully designed and synthesized by adjusting the spatial structure and the property of excited state. PyBZTPA is constructed by the combination of electron-withdrawing benzothiadiazole (BZ), bipolar pyrene[4,5-d]imidazole (PyI) and electron-donating triphenylamine (TPA) groups, which exhibits a red emission peaking at 609 nm. On the basis of molecular structure of PyBZTPA, PyBZmTPA is obtained by introducing two methyl substituents on TPA unit, which leads to an increased charge transfer (CT) component in the molecule with a weaker exciton binding energy, facilitating the enhancement of upper-level reverse intersystem crossing (RISC). Further attaching TPA with big steric hinderance at the N1 position of PyI affords compound TPyBZTPA, which aims to increase the molecular distortion degree and reduce the non-radiative transition to improve the photoluminescence quantum yield (PLQY). The results show that both strategies can effectively improve the performance of non-doped devices. As compared with the maximum EQE of 5.3% for PyBZTPA-based non-doped OLED, the maximum EQEs of non-doped devices based on PyBZmTPA and TPyBZTPA go up to 6.8% and 7.3%, respectively. Especially, the maximum current efficiency (CE), power efficiency (PE) and brightness of TPyBZTPA device are corresponding to 12.6 cd A−1, 10.4 lm W−1 and 22682 cd m−2. To the best of our knowledge, the non-doped device performance of TPyBZTPA is fairly good among emitters containing BZ unit with CIEy ≈ 0.4.

An Ab Initio Molecular Dynamics Study of the Mechanism and Rate of Dye Regeneration by Iodide Ions in Dye-Sensitized Solar Cells

In the ambition to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs), it will be essential to understand the mechanisms and rates of dye regeneration. Although the mechanism of dye regeneration has been studied by static density functional theory (DFT) and classical molecular dynamics (CMD) simulations, ab initio molecular dynamics simulation (aiMD) has the potential to combine the insights from both methods for a deeper understanding. In this work, a series of aiMD simulations has been performed to study the interaction between an oxidized organic model dye, LEG4, and an electrolyte containing iodide ions as reducing agents. Dynamic Mulliken and natural spin population analyses show that two iodide ions, I–···I–, are required for dye regeneration. It was found that a distance between I–···I– of less than 6.5 Å at site 1 benefits from the electrostatic environment of the triphenylamine group of the LEG4 dye, and a corresponding distance of 4.8 Å at site 2 is essential for the dye regeneration process to take place. The rate constants of the LEG4 regeneration by two iodine ions range from 105 to 1012 s–1, spanning a window in which results from both experimental and static theoretical calculations fall. It is also verified that the probability of electron transfer from a radical I2– to the oxidized LEG4 dye is extremely low due to the rapid electron back-transfer. However, it has been found that the addition of an additional iodide ion at a distance of 5 Å with respect to the radical I2– opens the pathway for the reduction of the oxidized LEG4 dye with an associated formation of I3–. The current results highlight the necessity for a dynamical approach for a full understanding of the regeneration process.