Triphenylamine Core Research Articles

Dual Sulfone-Bridged Triphenylamine Heteroaromatics for High-Performance Blue Organic Electroluminescence.

Polycyclic heteroaromatics (PHAs) are a highly versatile class of functional materials, especially applicable as efficient luminophores in organic light-emitting diodes (OLEDs). Those constructed by tethered phenyl surrounding the main group center attract extensive attention due to their excellent OLED device performance. However, the development of such a class of emitters is often limited to boron, nitrogen-doped π-conjugated heterocycles. Herein, we proposed a novel kind of blue emitter by constructing a donor-acceptor molecular configuration, utilizing a dual sulfone-bridged triphenylamine (BTPO) core and mono/di-diphenylamine (DPA) substituents. The twisted D-A molecular structures and appropriate donor strength facilitate the effective separation of natural transition orbitals, endowing the emitters with charge-transfer dominant hybridized local and charge-transfer characteristics for the excited states. Both BTPO-DPA and BTPO-2DPA own small S1-T1 splitting energy, thus demonstrating blue thermally activated delayed fluorescence. The more symmetrical structure and enhanced CT features brought by additional DPA moiety confer BTPO-2DPA with a shorter delayed fluorescence lifetime, a higher fluorescence quantum yield and narrower emission. Therefore, BTPO-2DPA based OLED devices exhibit superior blue electroluminescence performance, with external quantum efficiencies reaching 12.31 %.

Methyl- and fluoro-substituted triphenylamine core toward fast-switching visible and near-infrared electrochromic polymers

Herein, two monomers MTPA and FTPA, and their corresponding polymers (PMTPA and PFTPA) based on a methyl-and fluoro-substituted triphenylamine were synthesized by Stille reaction and electropolymerization. MTPA exhibited the red-shift absorption and fluorescence emission spectra, and lower Eonset (0.53 V) compared with FTPA (0.57 V), which is beneficial to achieve high-quality polymers. The polymer films exhibited reversible color transition from yellow green to deep blue for PMPTA and from dark brown to light blue for PFTPA, respectively. In addition, both PMTPA and PFTPA films exhibited good optical contrasts of 36 % and 40 % at 1100 nm, respectively. The coloration efficiency and response times at 1100 nm are 196.4 C−1 cm2 with 0.6 s for PMTPA, and 160.9 C−1 cm2 with 1.4 s for PFTPA, respectively. These polymer films demonstrated excellent electrochemical property and electrochromic performance. These results will also provide a new strategy to rationally design the excellent electrochromic polymers based on the triphenylamine core.

Interfacial layer with a dibenzofulvene-bridged triphenylamine core for efficient and stable inverted perovskite solar cells

Considering the energy level cascade, introducing a hole transport layer (HTL) between the NiOx and perovskite layers has become a common and effective strategy to enhance the performance of inverted perovskite solar cells (PSCs). Herein, we designed and synthesized three hole-transporting interfacial layers (TPAD, TPAO, and TPAS) based on a dibenzofulvene-bridged triphenylamine (TPA) core to fabricate efficient and stable inverted NiOx-based PSCs. Dibenzofulvene, known for its sp²-hybridized structure, offers superior planarity and molecular stacking, and it easily bonds with triphenylamine derivatives, resulting in unique light-harvesting and charge mobility properties for optoelectronic applications. Specifically, diphenylamine, dimethoxy diphenylamine, and dimethylthio diphenylamine were used as end-capping units for TPAD, TPAO, and TPAS, respectively. The NiOx-based inverted PSC devices fabricated with TPAS as an interfacial layer effectively modified NiOx to improve energy level alignment, enhance film quality and crystallinity, and improve carrier transport, leading to a high-quality perovskite layer and superior interface contact behavior. Consequently, this device yielded a highly efficient cell performance of 20.30 %, surpassing those using TPAD (19.29 %) and TPAO (18.78 %) as interfacial layers, and significantly outperforming devices using only NiOx (17.69 %). Additionally, the champion cell exhibited negligible hysteresis and long-term stability. These findings demonstrate a facile approach to preparing multifunctional TPA-based hole transport materials and showcase the efficient performance of inverted cells based on a triphenylamine dibenzofulvene-based interfacial layer, contributing to the development of high-efficiency inverted PSCs.

Superhydrophilic Densely‐Packed Gecko‐Like Structures by Soft‐Template Electropolymerization

AbstractBio‐inspired by natural species and previous research works, nanotubes are prepared by soft‐template electropolymerization in micellar solution. Various thiophene‐based and carbazole‐based monomers are designed from a triphenylamine core. With one of the carbazole‐based monomers, which is fully conjugated and with a star‐like structure, gecko‐like surface structures are obtained even if the structure is not perfectly planar. Extremely long and densely packed‐microtubes are reached especially at constant potential. However, the surfaces are not both highly hydrophobic and with strong water adhesion, but are superhydrophilic. These wetting properties can be explained by a high surface energy (γSV)=41.9 mN m−1 compared to gecko foot even if the natural gecko feet are also chemically inhomogeneous, or by differences in the arrangement of the surface structures.

Novel Star-Shaped Viologens Containing Phenyl and Triphenylamine Moieties for Electrochromic Applications.

The two star-shaped viologens containing 1,3,5-substituted phenyl (1) and triphenylamine (2) central cores and n-hexyl chains were synthesized and characterized. Both compounds exhibited promising optoelectronic properties and underwent multiple oxidation/reduction processes resulting in various colors. Four possible redox states of tripyridium salt containing a phenyl or triphenylamine core can occur depending on the applied potentials. The wide color range, from colorless through blue, azure to green-gray, was observed during the electrochemical reduction of compound 1. In the case of compound 2, the color change observed during spectroelectrochemical measurements was from yellow to colorless during the cathodic process and from yellow to green during the anodic process. The observed color change for both viologens was reversible. The triphenylamine-cored viologen (2) also exhibited emission in visible range and solvatochromism. It also exhibited luminescence in the solid state when excited with a UV lamp. These studies provide insights into the design of advanced materials for applications in displays.

Time-resolved excited-state dynamics of star-shaped carbazole-based room temperature phosphorescent molecule by ultrafast absorption spectroscopy

Star-shaped room-temperature phosphorescent (RTP) molecules have attracted much attention due to high luminescence efficiency by inhibiting nonradiative transition of triplet excitons. In this work, the photophysical processes of 1,3,5-tri(9h-carbazol-9-phenyl)benzene (TCzP) and tri(4-carbazol-9-phenyl)amine (TCzTa), with benzene and triphenylamine (TPA) as central cores respectively and carbazole (Cz) as peripheral groups, are investigated. The excited state absorption (ESA) signal (625 nm) of TCzP reaches maximum intensity within 8.8 ps in the femtosecond (fs) transient absorption (TA) spectroscopy and then decays significantly with the enhancing of triplet-triplet absorption (TTA) signal (425 nm). These evolution processes of spectral signal and the appearance of isosbestic point at 450 nm together confirm the intersystem crossing (ISC) process within 5.1 ns. The TTA signal gradually disappears in the nanosecond (ns) TA spectroscopy with a phosphorescence lifetime (τph) of 2 μs. Compared to TCzP, TCzTa exhibits similar spectral evolution behavior with faster ISC of 2.1 ns and lower τph of 0.95 μs. The theoretical simulation shows that the nitrogen atoms in the TPA core of TCzTa leads to a significantly increased spin-orbit coupling constant of S1→Tn (0.86 cm−1) and T1→S0 (0.08 cm−1) than that of TCzP (0.25 cm−1 and 0.05 cm−1), resulting in the shorter experimental ISC rate constants (2.1 ns) and τph (0.95 μs). This work provides reasonable insights for understanding the real-time spectral signal evolution of star-shaped carbazole-based RTP molecules.

One‐Photon and Two‐Photon Absorption Properties of Multi‐Branched Squaraine Dyes Comprised of Triphenylamine Cores and Ethynylene Linkers

AbstractWe developed multi‐branched π‐conjugated systems using squaraine dyes with triphenylamine cores connected by ethynylene linkers. We investigated the influence of interbranch coupling between squaraine branches on their one‐photon (OPA) and two‐photon absorption (TPA) properties. These dyes with triphenylamine components showed a red‐shifted one‐photon absorption (OPA) compared to the precursor squaraine dyes. Among branched dyes, the lack of apparent splitting or shift in the absorption maxima, even as the absorption intensity increased with the number of chromophores, implies the presence of limited exciton coupling between the squaraine branches. The present squaraine dyes with triphenylamine cores exhibited a moderate TPA compared to the precursor squaraine without the triphenylamine core, due to the extended π‐conjugation. Notably, both the 3‐branched and 2‐branched dyes demonstrated additional enhancement in the TPA response, surpassing that of the monochromophoric counterpart. This resulted in achieving a substantial TPA cross section of up to 3905 GM at 830 nm.

Reversible Electrochromic/Electrofluorochromic Dual Switching in Zn(II)-Based Metallo-Supramolecular Polymer Films.

The introduction of novel materials with multifunctional chromogenic properties, such as electrochromic/electrofluorochromic (EC/EFC) properties, has recently attracted prospective interest in the development of various optoelectronic devices and smart windows. In this study, a novel Zn(II)-based metallo-supramolecular polymer (polyZn) has been developed as an ON/OFF switchable EFC application with prominent EC behavior. In this regard, the polymeric chain of polyZn was first synthesized by 1:1 complexation in a zigzag manner with Zn(II) ions at the metal center and 4,4'-[bis(2,2':6',2″-terpyridinyl)benzene]triphenylamine (LTPY-TPA) as the redox-active ditopic ligand. The polyZn exhibits excellent solubility in organic solvents and can form a very good uniform thin film on an indium tin oxide/glass substrate by spin-coating. In a neutral state, transparent polyZn exhibits a bright yellow color to the naked eye (absorption at ∼325 nm). The electroactive triphenylamine (TPA) core of LTPA-TPY, however, undergoes reversible single-electron oxidation when a positive bias of +1.6 V vs Ag/Ag+ is applied, generating radical cations (TPA ↔ TPA•+) with a significant drop in transparency (77%). A noticeable chromic shift in the hue of the film from brilliant yellow to green was observed with the appearance of a near-infrared absorption band at ∼897 nm with a tail of 1300-1600 nm. Interestingly, in addition to this EC phenomenon, the fabricated solid-state polyZn film exhibits intense, high-contrast reddish-orange photoluminescence with λem = 650 nm, which is significantly desired as a molecular probe for bioimaging. Both the TPA core and the redox-inactive Zn(II)-terpyridine core emit orange-red photoluminescence in polyZn, which is significantly quenched upon the oxidation of the film and is re-emitted at 0.0 V vs Ag/Ag+. This ON/OFF EFC transition was sustained for several cycles. This study should motivate to design and create distinctive new unique materials with combined EC/EFC behavior for the fabrication of optoelectronic devices by combining a metal-fluorescent core with a redox-active spacer.

Directional formation of microtubes by soft-template electropolymerization from fully conjugated triphenylamine-based monomers

Microtubular structures have been prepared by soft-template electropolymerization of conjugated organic monomers with the aim to mimic the strong water-adhesive forces of gecko foot or rose petals. Water-saturated solvent of low water solubility (dichloromethane) was used to form a micellar solution stabilized by tetrabutylammonium perchlorate as the electrolyte and the surfactant, in which case the formation of nanotubes was particularly efficient. The studied monomers were built from a triphenylamine core conjugated with three arms differing by their structure and positions: (i) 2- or 3-positions in the thiophene arms or (ii) carbazole arms attached to para, meta or ortho-positions of the benzene ring of the core. The formation of microtubes is due to preferential growth of polymer films and an aggregation of formed polymers/oligolymers in one direction (1D) facilitated by π–stacking interactions. The key factors influencing on the surface morphologies (monomer structures and reactivity, electrodeposition conditions, etc) are discussed. Impressive results have been obtained in studies of carbazole-containing monomers and the effect of regioisomerism in the monomers (the position of the carbazole attachment to the core). Extremely long microtubes (tens to >100 μm length, diameter ≈ 1.0–1.5 μm) were formed on the electrode surface from the monomer N-Ph-p-Cb with the carbazole attachment in the para-position. Wettability analysis showed highly hydrophobic surfaces with apparent contact angles up to 154.0° and extremely strong water adhesion comparable to rose petals or gecko feet. Such coatings can find applications in water-harvesting systems, sensing platforms or electrochemical analyses.

Synthesis, photophysical characterization, and integration of two-photon-responsive fluorophores in mesoporous organosilica nanoparticles for biological imaging use

We report the synthesis of new graftable three-branched octupolar fluorophores (F and F2), based on a triphenylamine core connected to electron-withdrawing sulfone-based peripheral groups through one or two π-conjugated phenylene-vinylene linkers. Their two-photon absorption (TPA), solvatochromism and photoluminescence properties were investigated to derive structure-property relationships. Notably, the chromophores presented TPA bands in the biological window (700–900 nm) and high TPA cross-sections at peak of 810 GM for F and F2. Then, after silylation, fluorophore F was further covalently integrated within the sol-gel synthesis of different periodic mesoporous organosilica nanoparticles (PMO NPs). Transmission electronic microscopy imaging revealed the formation of spherical NPs with good monodispersity in size, as confirmed by dynamic light scattering measurements. The obtained fluorophore-based nanoplatforms were shown to be biocompatible in vitro and demonstrated a good potential for two-photon imaging in cancer cells using two-photon excited fluorescence microscopy.

Fenton-like Cerium Metal–Organic Frameworks (Ce-MOFs) for Catalytic Oxidation of Olefins, Alcohol, and Dyes Degradation

AbstractA metal–organic framework (MOF) of cerium (Ce) ions and 4,4′,4′′-nitrilotribenzoic acid linker was synthesized via a hydrothermal method. Ce-MOF consists of a Lewis acid moiety, i.e. Ce3+ and triphenylamine cores. It showed Fenton-like properties with excellent catalytic oxidation activity for olefins, primary/secondary alcohols, and water pollutants e.g., organic dyes. It displayed high oxidation conversion of cinnamyl alcohol and styrene of 100% and 53%, respectively. It offered good selectivity towards styrene oxide and benzaldehyde (i.e. 75% and 100%, respectively). It was applied for the oxidative degradation of dyes e.g. rhodamine B (RhB), methyl blue (MeB), Congo red (CR), and direct blue (DB) using hydrogen peroxide (H2O2) as an oxidant. It exhibited high efficiency in the oxidative degradation of these water pollutants. The mechanistic study of oxidation involves the formation of radical hydroxyl (•OH) species. This study revealed the possibility of enhancing the oxidative catalytic performance, including oxidative degradation of organic pollutants, by employing advanced oxidation processes (AOPs) using Ce-MOF. The catalyst is recyclable five times without significantly decreasing of the material’s catalytic performance.

Regulating excited state of sulfone-locked triphenylamine heteroaromatics for high-efficiency ultralong room-temperature phosphorescence

• Organic RTP of ultralong lifetime and high quantum efficiency was presented. • Phosphorescence mechanism based on the excited states regualtion was proposed. • Multilevel information encryption based on liftetimes and colors was shown. Organic room-temperature phosphorescence (RTP) with ultralong lifetime and high quantum efficiency is of interest but challenging. Few phosphor systems in the monomer state demonstrate lifetimes over 0.1 s with quantum efficiencies exceeding 10% due to the lack of molecular design principle and qualified molecular system. Here we present a novel class of phosphors based on heteroaromatic sulfone-locked triphenylamine core BTPO with rational subunit modification that displays ultralong RTP in a doped polymer matrix with lifetimes up to 818 ms and quantum efficiencies over 20% simultaneously. The co-win situation is attributed to an efficient and multichannel intersystem crossing (ISC) process arising from narrower singlet-triplet exchange energy and strong spin-orbital coupling interaction between the lowest singlet state (S 1 ) and high-lying triplet states that facilitate numerous triplet excitons generation, as well as a relatively pure (π, π*) configuration for the lowest triplet state (T 1 ), ensuring the small radiative rate of phosphorescence ( k p ) and consequently ultralong lifetime. Taking advantage of RTP features with the multicolor and diverse lifetime of this phosphor family, the primary application in information encryption is well demonstrated versatilely.

Vinylpyrimidine‐Functionalized Triphenylamines: Bimodal Molecular Switches and Multilevel Systems

AbstractDue to their numerous potential applications, the interest for the elaboration of new molecular switch has never stop to grow. Among them, multi‐modal systems, where the switching between two different metastable states can be induced by using indifferently several kinds of stimulation, have a special place. In this study, we present our efforts to develop a class of multi‐modal systems based on the association of a triphenylamine core with vinylpyrimidine units that exhibits nice acido and electrochromic properties. The most performant ones can present up to three different forms allowing to modulate their absorption and luminescence properties over three discrete levels. In order to provide limitations and outlooks for such systems, their switching behaviors have been rationalized by the help of DFT and TD‐DFT calculations.

Tris(4'-Nitrobiphenyl)amine─An Octupolar Chromophore with High Two-Photon Absorption Cross-Section and Its Application for Uncaging of Calcium Ions in the Near-Infrared Region.

Compounds with high two-photon absorption (2PA) performance in the near-infrared region have attracted great attention because of their application in the material and biological science. In this study, we have developed a simple and novel octupolar chromophore, tris(4'-nitrobiphenyl)amine 1, with three nitro peripheral groups attached to a triphenylamine core via biphenyl linkers. A mono-branched analogue 2 has also been prepared to investigate the effects of octupolar and dipolar systems on photophysical and 2PA behaviors. Compound 1, despite having a much simpler structure than the previous three-branched scaffolds, exhibits comparable σ2 values, reaching 1330 GM at 730 nm and 900 GM at 820 nm in toluene. Combined with an outstanding σ2/MW ratio (2.2 GM g-1 mol) and a high fluorescence quantum yield (0.51), 1 displays potential as a promising two-photon (2P) probe for bioimaging. Subsequently, the ethylene glycol tetraacetic acid-substituted derivatives featuring octupolar (3 and 5) or dipolar (4 and 6) character have been synthesized and their one-photon (1P) and 2P photochemical reactions have been examined. Finally, 1P- and 2P-triggered uncaging of Ca2+ from these calcium chelators has been confirmed.

Spectroscopic and Physicochemical Investigations of Azomethines with Triphenylamine Core towards Optoelectronics.

Three new azomethines based on triphenylamine with two or three substituents were obtained. Chemical structure and purity were confirmed by 1H NMR, FTIR elemental analysis and mass spectroscopy. The investigations were focused on the relationship between chemical structure and properties important for optoelectronic materials. Thus, the studies of thermal, optical and electrochemical properties were carried out based on differential scanning calorimetry, thermogravimetric analysis, electronic absorption, photoluminescence and cyclic voltammetry measurements. The ongoing consideration of experimental results was complemented by theoretical calculations using the density functional theory method. The donor activity of obtained compounds was tested in bulk-heterojuntion photovoltaic cells with structure ITO/PEDOT:PSS/imine:PCBM/Al and ITO/PEDOT:PSS/imine:P3HT:PCBM/Al). The effect of the presence of the amino-thiophene-3,4-dicarboxylic acid diethyl ester groups and various number of hexyloxyphenyl units on imines properties was demonstrated.

Molecular Engineering of Enamine‐Based Hole‐Transporting Materials for High‐Performing Perovskite Solar Cells: Influence of the Central Heteroatom

Stabilizing the high‐performing perovskite solar cells (PSCs) with low‐cost and simply affordable hole‐transporting materials (HTMs) has been identified as an ongoing ambitious challenge. Herein, a series of enamine‐based HTMs having different central heteroatoms (C, N, O, and S) and a number of enamine branches is designed and synthesized. The impact of varied central heteroatom cores is investigated in‐depth including thermal, photophysical, and photovoltaic properties. Importantly, molecularly engineered HTMs are obtained by a single condensation reaction without the need for expensive catalysts, inert reaction conditions, or tedious product purification. PSCs with a power conversion efficiency (PCE) of over 20% can be realized with the triphenylamine core HTM (V1435), a result comparable with spiro‐OMeTAD. HTMs based on tetraphenylmethane (V1431) and diphenyl sulfide (V1434) cores give a slightly lower performance under similar device fabrication conditions. This work demonstrates how rational molecular engineering of a simple condensation approach can produce HTMs for high‐performing PSCs without sacrificing the PCE.

Three-branched coumarin derivatives for two-photon uncaging. How does branching influence the efficacy?

In the design of non-linear optical chromophores, the conjugation pathways in multi-branched dyes are known to influence heavily their optical properties. Herein, we investigate this strategy for the design of two-photon (2P) responsive photolabile protecting groups (PPG) by assembling via a triphenylamine core extended coumarinylmethyl derivatives. The experimental study reveals an enhancement of the 2P absorption in the tri-branched compound, but a strikingly different photophysics behaviour resulting in a decrease in bond cleavage efficiency, and aggregation in aqueous acetonitrile. These combined effects results in much poorer 2P uncaging efficiency of the three-branched derivatives. In contrast, the corresponding mono-branched coumarin exhibit very high 2P photochemical efficiency (450 GM).

Flexible Organic Photovoltaics with Star‐Shaped Nonfullerene Acceptors End Capped with Indene Malononitrile and Barbiturate Derivatives

The design and synthesis of three star-shaped nonfullerene (NFA) acceptors, TPA-2T-INCN, TPA-2T-BAB, and TPA-T-INCN, based on a triphenylamine (TPA) core and linked through π-conjugated thiophene (T) spacers to different terminal units (3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile, INCN, and 1,3-dimethylbarbituric acid, BAB), are reported. These materials are blended with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor polymer and tested in flexible organic photovoltaics (OPVs). The NFAs capped with the strong electron-withdrawing INCN unit perform best in OPVs. Both P3HT:TPA-T-INCN and P3HT:TPA-2T-INCN blends also show the highest photoluminescence quenching efficiency (95.8% and 92.6%, respectively). Surprisingly, when reducing the number of T spacers from 2 to 1, the solubility of the NFAs in o-dichlorobenzene increases, leading to easier processing during the OPV fabrication and better surface morphology. This explains the best performance of TPA-T-INCN-based blends in OPVs, with a champion power conversion efficiency of 1.13%.

Triphenylamine-based fluorophores bearing peripheral diazine regioisomers. Synthesis, characterization, photophysics and two-photon absorption

A series of six tripodal push-pull fluorophores with D-(π-A3) arrangement has been designed and synthesized. The structure of these fluorophores consists of a central electron-donating triphenylamine core and peripheral electron-withdrawing diazine units (pyridazine, pyrimidine, and pyrazine moieties), which are linked by an ethynylene π-spacer. The preparation of the fluorophores involves threefold Sonogashira cross-coupling reaction starting from the key tris(4-ethynylphenyl)amine intermediate. The structure and spatial arrangement of two fluorophores were completely confirmed by X-ray analysis. Thermal and electrochemical behavior of prepared fluorophores were investigated by differential scanning calorimetry and cyclic voltammetry. Their linear optical properties were examined by UV–Vis absorption, steady-state and time resolved fluorescent spectroscopy while 2 PA analysis was used for a study of the nonlinear optical response. Experimental data were supported by DFT calculations. Based on the experimental as well as theoretical data, structure-property relationships have been thoroughly revealed.

Star-shaped Pd(II) and Pt(II) complexes containing C3-symmetric conjugated thiophenes: Synthesis, characterization, and chemical reactions with organic unsaturated molecules

Triple oxidative addition reactions of [M0(styrene)(PMe3)2] (M = Pd/Pt) with C3-symmetric star-shaped molecules containing 1-, 3-, and 5-thiophene-substituted benzene, in 1:0.3 ratio, afforded new Pd(II) and Pt(II) trinuclear complexes in suitable yields. Analogous trinuclear complexes were formed by similar reactions of thiophenyl halide derivatives containing triazine or triphenylamine cores. Alternatively, a trinuclear Pd(II) complex was obtained by oxidative addition of a Pd(0) complex (synthesized from allyl(cyclopentadienyl) palladium(II), [(η5-C5H5)Pd(η3-C3H5)] with PEt3. Sonogashira-type coupling between trinuclear Pt(II) halides (containing C3-symmetric conjugated thiophenes) and alkynes, in the presence of cuprous halide and diethylamine, afforded alkynyl-containing trinuclear Pt(II) complexes with extended π-conjugation. Insertion reactions of organic isocyanides (CN-R) with trinuclear Pd(II) complexes yielded trinuclear Pd(II) imidoyl complexes by insertion of CN-R into Pd-carbon (thiophene) bonds. Reactions of trinuclear Pt(II) halides with Ag(OCOCF3) and NaN3 formed pseudohalogen-containing Pt(II) complexes.