Pendant Amine Research Articles

Dinitrogen Reduction by a Chromium(0) Complex Supported by a 16-Membered Phosphorus Macrocycle

We report a rare example of a Cr-N2 complex supported by a 16-membered phosphorus macrocycle containing pendant amine bases. Reactivity with acid afforded hydrazinium and ammonium, representing the first example of N2 reduction by a Cr-N2 complex. Computational analysis examined the thermodynamically favored protonation steps of N2 reduction with Cr leading to the formation of hydrazine.

Does the environment around the H-cluster allow coordination of the pendant amine to the catalytic iron center in [FeFe] hydrogenases? Answers from theory

[FeFe]hydrogenases are H2-evolving enzymes that feature a diiron cluster in their active site (the [2Fe]H cluster). One of the iron atoms has a vacant coordination site that directly interacts with H2, thus favoring its splitting in cooperation with the secondary amine group of a neighboring, flexible azadithiolate ligand. The vacant site is also the primary target of the inhibitor O2. The [2Fe]H cluster can span various redox states. The active-ready form (Hox) attains the Fe(II)Fe(I) state. States more oxidized than Hox were shown to be inactive and/or resistant to O2. In this work, we used density functional theory to evaluate whether azadithiolate-to-iron coordination is involved in oxidative inhibition and protection against O2, a hypothesis supported by recent results on biomimetic compounds. Our study shows that Fe-N(azadithiolate) bond formation is favored for an Fe(II)Fe(II) active-site model which disregards explicit treatment of the surrounding protein matrix, in line with the case of the corresponding Fe(II)Fe(II) synthetic system. However, the study of density functional theory models with explicit inclusion of the amino acid environment around the [2Fe]H cluster indicates that the protein matrix prevents the formation of such a bond. Our results suggest that mechanisms other than the binding of the azadithiolate nitrogen protect the active site from oxygen in the so-called H ox (inact) state.

Two Pathways for Electrocatalytic Oxidation of Hydrogen by a Nickel Bis(diphosphine) Complex with Pendant Amines in the Second Coordination Sphere

A nickel bis(diphosphine) complex containing pendant amines in the second coordination sphere, [Ni(P(Cy)2N(t-Bu)2)2](BF4)2 (P(Cy)2N(t-Bu)2 = 1,5-di(tert-butyl)-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane), is an electrocatalyst for hydrogen oxidation. The addition of hydrogen to the Ni(II) complex gives three isomers of the doubly protonated Ni(0) complex [Ni(P(Cy)2N(t-Bu)2H)2](BF4)2. Using the pKa values and Ni(II/I) and Ni(I/0) redox potentials in a thermochemical cycle, the free energy of hydrogen addition to [Ni(P(Cy)2N(t-Bu)2)2](2+) was determined to be -7.9 kcal mol(-1). The catalytic rate observed in dry acetonitrile for the oxidation of H2 depends on base size, with larger bases (NEt3, t-BuNH2) resulting in much slower catalysis than n-BuNH2. The addition of water accelerates the rate of catalysis by facilitating deprotonation of the hydrogen addition product before oxidation, especially for the larger bases NEt3 and t-BuNH2. This catalytic pathway, where deprotonation occurs prior to oxidation, leads to an overpotential that is 0.38 V lower compared to the pathway where oxidation precedes proton movement. Under the optimal conditions of 1.0 atm H2 using n-BuNH2 as a base and with added water, a turnover frequency of 58 s(-1) is observed at 23 °C.

Toward the Synthesis of Indenyl Molybdenum Compound [(η3-Ind)(η5-Cp)Mo(CO)2]: Modified Compounds and Structure of a Previously Unrecognized Intermediate

The mechanism of synthesis of [(η3-Ind′)(η5-Cp)Mo(CO)2] was studied on methyl-substituted derivatives (Ind′ = 2-MeC9H6; 4,7-Me2C9H5). It was observed that the initial step involving reaction with HCl gives dimeric chloride species [{(η5-Ind′)Mo(CO)2(μ-Cl)}2]. This outcome differs from the structure suggested in the literature. Furthermore, it was demonstrated by various examples that compounds of the formula [{(η5-Ind′)Mo(CO)2(μ-Cl)}2] are convenient starting materials giving [(η3-Ind′)(η5-Cp′)Mo(CO)2] through the reaction with appropriate cyclopentadienides. The variability of this method was demonstrated on several examples including weakly donating Cp ligands bearing strong electron-withdrawing functional groups [C5H4COOMe, (1,2-MeOCO)2C5H3, and 1,2-(tBuNHCO)2C5H3] as well as Cp ligands bearing a pendant amine arm (C5H4CH2CH2NMe2). Similar η3-indenyl complexes are formed when using other univalent six-electron ligands such as carbaborane (9-Me2S-7,8-nido-C2B9H10) or scorpionate (Tp, Tp*). The attempts to synthesize [(η3-Ind)(η5-Cp)Mo(CO)2] from [(η3-C3H5)(η5-Cp)Mo(CO)2] have failed because the initial reaction with HCl does not give the expected [{(η5-Cp)Mo(CO)2(μ-Cl)}2] but trivial [(η5-Cp)Mo(CO)3Cl].

The Use of Bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfide in Preparation of Microspheres with Pendant Amine Groups as a Heavy Metal Sorbent

Bis[4(2-hydroxy-3-methacryloyloxypropoxy)phenyl]sulfide-based copolymer microspheres with pendant amine groups are shown to be very efficient in removing Cu(II), Zn(II), Cd(II), and Pb(II) ions from aqueous solutions. Bis(4(2-hydroxy-3-methacryloyloxypropoxy)phenyl)sulfide (1 mol) and glycidyl methacrylate (1 mol) copolymer microspheres have been prepared by suspension-emulsion polymerisation in the presence of pore forming diluents. Amine functions have been introduced into the surface copolymers by modification of the epoxy groups with etylenediamine, diethylenetriamine, or triethylenetetramine. The swelling properties of parent and modified copolymers as well as thermal properties were investigated using a differential scanning calorimeter (DSC) and thermogravimetric analysis (TG). The Langmuir, Freundlich, and Temkin isotherm models are used to describe the adsorption characteristics of the sorbents. Additionally, the adsorption results in the quaternary systems containing Cu(II), Zn(II), Cd(II), and Pb(II) with different ratios of their initial concentrations are presented.

Chromium-based ethylene tetramerization with diphosphinoamines bearing pendent amine donors

Cr-catalyzed selective oligomerization of ethylene was carried out with diphosphinoamine ligands bearing pendent amine donors. Catalytic behavior of the Cr catalysts changed considerably, depending on the structural variation of ligands. The direct amine substitution on the nitrogen atom of backbone induced a conventional ethylene oligomerization with Schultz–Flory distribution. However, ethylene tetramerization was observed with other ligands having an ethylene or propylene linker between the two amines. Interestingly, the Cr catalysts having an ethylene linker and diisopropyl amine or having a propylene linker and diethyl amine groups showed a concurrent improvement of the selectivity for 1-hexene and 1-octene as well as the enhanced catalytic activity when the temperature increased from 30̊C to 60̊C. However, the Cr catalyst with diphosphinoamine ligand without a pendent amine donor showed that the trimerization of ethylene was increased at the expense of 1-octene selectivity with a significant loss of catalytic activity. Such a tendency was more evident at higher temperature and with chromium acetylacetonate as a precursor of the catalysts.

A New Family of Thermo-Responsive Polymers Based on Poly[N-(4-vinylbenzyl)-N,N-dialkylamine

A new family of the thermo-responsive polymers based on poly[N-(4-vinylbenzyl)-N,N-dialkylamine] with the pendent amine group as well as the doubly thermo-responsive triblock copolymer were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. These polymers showed the lower critical solution temperature (LCST) and/or the upper critical solution temperature (UCST) in alcohol and in the alcohol/water mixture. The polymer molecular weight, the polymer concentration, the cosolvent/nonsolvent and the deuterated solvent affecting the LCST and/or UCST were investigated, and their great influence on the LCST/UCST was demonstrated. The origin of the phase transition of poly[N-(4-vinylbenzyl)-N,N-dialkylamine] at LCST upon heating was investigated and the possible reason was proposed. The doubly thermo-responsive triblock copolymer of PVMA53-b-PVEA108-b-PVMA53 underwent phase transition at two LCST temperatures. The PVEA108 block underwent the initial phase transition at the first ...

Protonation of Ferrous Dinitrogen Complexes Containing a Diphosphine Ligand with a Pendent Amine

The addition of acids to ferrous dinitrogen complexes [FeX(N2)(P(Et)N(Me)P(Et))(dmpm)](+) (X = H, Cl, or Br; P(Et)N(Me)P(Et) = Et2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the νN2 band of the complex by 25 cm(-1) and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slightly smaller shift of the Fe(II/I) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)(P(Et)N(Me)P(Et))(dmpm)](+). [FeH(P(Et)N(Me)P(Et))(dmpm)](+) was found to bind N2 about three times more strongly than NH3. Computational analysis showed that coordination of N2 to Fe(II) centers increases the basicity of N2 (vs free N2) by 13 and 20 pKa units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pKa units compared to the N2 ligand. The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N2 ligand enough to promote proton transfer from the pendent amine to the N2 ligand. Instead of isolating a reduced Fe(0)-N2 complex, the reduction resulted in isolation and characterization of HFe(Et2PC(H)N(Me)CH2PEt2)(P(Et)N(Me)P(Et)), the product of oxidative addition of the methylene C-H bond of the P(Et)N(Me)P(Et) ligand to Fe.

PH-Dependent Reduction Potentials and Proton-Coupled Electron Transfer Mechanisms in Hydrogen-Producing Nickel Molecular Electrocatalysts

The nickel-based P2(Ph)N2(Bn) electrocatalysts comprised of a nickel atom and two 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane ligands catalyze H2 production in acetonitrile. Recent electrochemical experiments revealed a linear dependence of the Ni(II/I) reduction potential on pH with a slope of 57 mV/pH unit, implicating a proton-coupled electron transfer (PCET) process with the same number of electrons and protons transferred. The combined theoretical and experimental studies herein provide an explanation for this pH dependence in the context of the overall proposed catalytic mechanism. In the proposed mechanisms, the catalytic cycle begins with a series of intermolecular proton transfers from an acid to the pendant amine ligand and electrochemical electron transfers to the nickel center to produce the doubly protonated Ni(0) species, a precursor to H2 evolution. The calculated Ni(II/I) reduction potentials of the doubly protonated species are in excellent agreement with the experimentally observed reduction potential in the presence of strong acid, suggesting that the catalytically active species leading to the peak observed in these cyclic voltammetry (CV) experiments is doubly protonated. The Ni(I/0) reduction potential was found to be slightly more positive than the Ni(II/I) reduction potential, indicating that the Ni(I/0) reduction occurs spontaneously after the Ni(II/I) reduction, as implied by the experimental observation of a single CV peak. These results suggest that the PCET process observed in the CV experiments is a two-electron/two-proton process corresponding to an initial double protonation followed by two reductions. On the basis of the experimental and theoretical data, the complete thermodynamic scheme and the Pourbaix diagram were generated for this catalyst. The Pourbaix diagram, which identifies the most thermodynamically stable species at each reduction potential and pH value, illustrates that this catalyst undergoes different types of PCET processes for various pH ranges. These thermodynamic insights will aid in the design of more effective molecular catalysts for H2 production.

High Catalytic Rates for Hydrogen Production Using Nickel Electrocatalysts with Seven-Membered Cyclic Diphosphine Ligands Containing One Pendant Amine

A series of Ni-based electrocatalysts, [Ni(7P(Ph)2N(C6H4X))2](BF4)2, featuring seven-membered cyclic diphosphine ligands incorporating a single amine base, 1-para-X-phenyl-3,6-triphenyl-1-aza-3,6-diphosphacycloheptane (7P(Ph)2N(C6H4X), where X = OMe, Me, Br, Cl, or CF3), have been synthesized and characterized. X-ray diffraction studies have established that the [Ni(7P(Ph)2N(C6H4X))2](2+) complexes have a square planar geometry, with bonds to four phosphorus atoms of the two bidentate diphosphine ligands. Each of the complexes is an efficient electrocatalyst for hydrogen production at the potential of the Ni(II/I) couple, with turnover frequencies ranging from 2400 to 27,000 s(-1) with [(DMF)H](+) in acetonitrile. Addition of water (up to 1.0 M) accelerates the catalysis, giving turnover frequencies ranging from 4100 to 96,000 s(-1). Computational studies carried out on the [Ni(7P(Ph)2N(C6H4X))2](2+) family indicate the catalytic rates reach a maximum when the electron-donating character of X results in the pKa of the Ni(I) protonated pendant amine matching that of the acid used for proton delivery. Additionally, the fast catalytic rates for hydrogen production by the [Ni(7P(Ph)2N(C6H4X))2](2+) family relative to the analogous [Ni(P(Ph)2N(C6H4X)2)2](2+) family are attributed to preferred formation of endo protonated isomers with respect to the metal center in the former, which is essential to attain suitable proximity to the reduced metal center to generate H2. The results of this work highlight the importance of precise pKa matching with the acid for proton delivery to obtain optimal rates of catalysis.

Poly(2 deoxy 2 methacrylamido glucopyranose) b Poly(methacrylate amine)s: Optimization of Diblock Glycopol ycations for Nucleic Acid Delivery.

A series of nine poly(2-deoxy-2-methacrylamido glucopyranose)-b-poly(methacrylate amine) diblock copolycations The cationic block was varied in length and in the degree of methyl group substitution (secondary, tertiary, quaternary) on the pendant amine in an effort to optimize the structure and activity for plasmid DNA delivery. Upon a thorough kinetic study of polymerization for each polymer, the glycopolymers were prepared with well-controlled Mn and Ð. The binding and colloidal stability of the polymer-pDNA nanocomplexes at different N/P ratios and in biological media has been investigated using gel electrophoresis and light scattering techniques. The toxicity and transfection efficiency of the polyplexes has been evaluated with Hep G2 (human liver hepatocellular carcinoma) cells; several polymers displayed excellent delivery and toxicity profiles justifying their further development for in vivo gene therapy.

An iron complex with pendent amines as a molecular electrocatalyst for oxidation of hydrogen

The increasing energy needs of society have led to a search for technologies that can tap carbon-neutral and sustainable energy sources, such as solar and wind. Using properly designed catalysts, such sources can also be used to create fuels such as hydrogen; however, a significant barrier to the use of hydrogen as an energy carrier is the need for an inexpensive and efficient catalyst for its oxidation. The oxidation of hydrogen is the process by which electricity is produced in low-temperature fuel cells, and the best catalyst for this is platinum-a precious metal of low abundance. Here we report a molecular complex of iron (an abundant and inexpensive metal) as a rationally designed electrocatalyst for the oxidation of H(2) at room temperature, with turnover frequencies of 0.66-2.0s(-1) and low overpotentials of 160-220mV. This iron complex, Cp(C(6)F(5))Fe(P((t)Bu)(2)N(Bn)(2))(H), has pendent amines in the diphosphine ligand that function as proton relays.

Theoretical Design of Molecular Electrocatalysts with Flexible Pendant Amines for Hydrogen Production and Oxidation

The design of hydrogen oxidation and production electrocatalysts is important for the development of alternative renewable energy sources. The overall objective is to maximize the turnover frequency and minimize the overpotential. We use computational methods to examine a variety of nickel-based molecular electrocatalysts with pendant amines. Our studies focus on the proton-coupled electron transfer (PCET) process involving electron transfer between the complex and the electrode and intramolecular proton transfer between the nickel center and the nitrogen of the pendant amine. The concerted PCET mechanism, which tends to require a lower overpotential, is favored by a smaller equilibrium Ni-N distance and a more flexible pendant amine ligand, thereby decreasing the energetic penalty for the nitrogen to approach the nickel center for proton transfer. Our calculations provide predictions about designing catalysts that incorporate these properties. These design principles will be useful for developing the next generation of hydrogen catalysts.

Mechanistic studies on proton transfer in a [FeFe] hydrogenase mimic complex

Four different pathways for deprotonation of [(μ-pdt){Fe(CO)3}{Fe(CO)(κ(2)-Me2PCH2N(Me)CH2PMe2)}] (pdt = propane-1,3-dithiolate) [1Hμ](1+) were examined, including (1) the "Direct" deprotonation; (2) the "Indirect" deprotonation via the pendant amine N; (3) the "Indirect" deprotonation via the distal metal Fe; and (4) the "Indirect" deprotonation via the dithiolate S. Only deprotonation of the "Indirect" pathway via the pendant amine N is feasible at room temperature. The most favorable migration destination for the bridging hydride in [1Hμ](1+) is the pendant amine N (activation energy barrier 16.1 kcal mol(-1)). Migrations to the other two possible sites including the distal metal Fe (34.6 kcal mol(-1)) and the S in the dithiolate group (41.5 kcal mol(-1)) were hindered by high proton shuttling barriers. Once the migration barriers of those three "Indirect" pathways are overcome, the following deprotonations from all three positions including the distal atom Fe, the dithiolate S and the pendant amine N, are all feasible. The results also demonstrate a large difference for deprotonation of the hydride from the terminal and bridging sites. The low energy of the virtual orbital associated with the antibonding M-H interaction of [1HFe](1+) implies the high activity for the interaction with aniline.

Triggered degradation of poly(ester amide)s via cyclization of pendant functional groups of amino acid monomers

Poly(ester amide)s (PEAs) are of interest for a diverse range of applications as their structures and properties can be readily tuned through the incorporation of a wide variety of monomers. In this work, the incorporation of the amino acids L-2,4-diaminobutyric acid (DAB) and homocysteine (HCY) was investigated with the aim of imparting stimuli-responsive degradation properties to PEAs. First, small molecule model compounds were prepared and studied to demonstrate that upon revealing the pendant γ-amine or γ-thiol of DAB and HCY esters, intramolecular cyclizations to 5-membered lactams and thiolactones respectively were much more rapid than background ester hydrolysis. Subsequently, monomers containing these DAB and HCY self-immolative spacers were prepared and incorporated into PEAs such that cleavage of protecting groups on the pendant moieties by stimuli including acid and the reducing agent DTT induced cyclization reactions that directly cleaved esters in the PEA backbone. The degradation of these polymers both in solution and in films was studied, demonstrating stimuli-triggered degradation was more rapid than background polymer degradation. In addition, to demonstrate that the approach could be readily extended to various stimuli, a photochemically responsive PEA was prepared by simply changing the protecting group on the pendant amine. This intramolecular cyclization strategy involving pendant functional groups should therefore be useful for the development of a wide range of PEAs and other polymers for which it is desirable to initiate degradation under specified conditions.

Spatially controlled surface immobilization of nucleophiles via trapping of photo-generated thioaldehydes

A novel and very simple photochemical strategy that utilizes light as a facile means to provide spatio-temporal control for the direct covalent immobilization of nucleophiles is presented. The concept is based upon the efficient trapping of photogenerated thioaldehydes by amines, hydroxylamines, and thiols. Surface patterns of polymers and small molecules bearing pendant amine-, hydroxylamine- or thiol moieties were successfully generated and imaged in a time-of-flight secondary-ion mass spectrometry (ToF-SIMS) investigation.

Lanthanide(iii) complexes of aminoethyl-DO3A as PARACEST contrast agents based on decoordination of the weakly bound amino group

2-Aminoethyl DOTA analogues with unsubstituted (H3L1), monomethylated (H3L2) and dimethylated (H3L3) amino groups were prepared by improved synthetic procedures. Their solid-state structures exhibit an extensive system of intramolecular hydrogen bonds, which is probably present in solution and leads to the rather high value of the last dissociation constant. The protonation sequence of H3L1 in solution corresponds to that found in the solid state. The stability constants of the H3L1 complexes with La(3+) and Gd(3+) (20.02 and 22.23, respectively) are similar to those of DO3A and the reduction of the pK(A) value of the pendant amino group from 10.51 in the free ligand to 6.06 and 5.83 in the La(3+) and Gd(3+) complexes, respectively, points to coordination of the amino group. It was confirmed in the solid state structure of the [Yb(L1)] complex, where disorder between the SA' and TSA' isomers was found. A similar situation is expected in solution, where a fast equilibration among the isomers hampers the unambiguous determination of the isomer ratio in solution. The PARACEST effect was observed in Eu(III)-H3L1/H3L2 and Yb(III)-H3L1/H3L2 complexes, being dependent on pH in the region of 4.5-7.5 and pH-independent in more alkaline solutions. The decrease of the PARACEST effect parallels with the increasing abundance of the complex protonated species, where the pendant amino group is not coordinating. Surprisingly, a small PARACEST effect was also observed in solutions of Eu(III)/Yb(III)-H3L3 complexes, where the pendant amino group is dimethylated. The effect is detectable in a narrow pH region, where both protonated and deprotonated complex species are present in equilibrium. The data points to the new mechanism of the PARACEST effect, where the slow coordination-decoordination of the pendant amine is coupled with the fast proton exchange between the free amino group and bulk water mediates the magnetization transfer. The pH-dependence of the effect was proved to be measurable by MRI and, thus, the complexes extend the family of pH-sensitive probes.

Polymer cross-linking: a nanogel approach to enhancing the relaxivity of MRI contrast agents.

Polymer cross-linking was explored as an approach for increasing the relaxivity of macromolecular contrast agents for magnetic resonance imaging. Poly(ethylene glycol) methyl ether methacrylate, N-(2-aminoethyl)methacrylamide hydrochloride, and the cross-linker ethylene glycol dimethacrylate were copolymerized under free radical conditions. By tuning the cross-linker content and reaction concentration, it was possible to obtain 10 nm nanogels in a single synthetic step. The pendant amine moieties were functionalized with an isothiocyanate derivative of diethylenetriaminepentaacetic acid (DTPA) and Gd(iii) was chelated. In comparison with a linear control polymer prepared under the same conditions in the absence of the cross-linking agent, the nanogel contrast agent did exhibit enhanced relaxivity with an r1 of 20.8 ± 0.2 at 20 MHz and 17.5 ± 0.4 at 60 MHz (corresponding to the clinical field strength of 1.5 T). The nuclear magnetic resonance dispersion profile was modeled to demonstrate that the enhanced relaxivity was a result of the nanogel agent's increased rotational correlation time, that is proposed to result from the constraint on motion imparted by the cross-linking. T1 weighted imaging in mice showed enhanced contrast and vascular circulation for the nanogel relative to Gd(iii)-DTPA (Magnevist) demonstrating the future promise of these new agents.

Attachment of poly(acrylic acid) to 3-aminopropyltriethoxysilane surface-modified hydroxyapatite.

Nano-sized hydroxyapatite (HAP) is of interest in biomaterials science due to its similarity to bone mineral. In this study, HAP modification using 3-aminopropyltriethoxysilane (APTES) was carried out in toluene and the effect of reaction time and curing temperature on the surface layers formed was investigated through X-ray photoelectron spectroscopy, Fourier transform infrared (FT-IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy. It is shown that the chemical composition is strongly influenced by the curing temperature; with low temperatures of 50 and 100 °C resulting in a fully condensed APTES layer, an intermediate temperature of 150 °C causing partial oxidation of the surface layer with the conversion of some amine functionality to amides while curing at a temperature of 200 °C additionally leads to thermal decomposition of the silane layer and a loss of the pendent amine groups. However, the stability of these particles in aqueous solution indicated a loss of the silane layer for samples cured at 150 °C or less and it is concluded that there is a trade-off between the availability of functionality for further chemical grafting and the stability for these APTES-modified HAP materials. Subsequent attachment of the polyelectrolyte poly(acrylic acid) (PAA) via both ionic interaction and covalent bonding using carbodiimide chemistry resulted in particles with more negative zeta potentials (-27 to -18 mV) compared to pure HAP, which were stable to dispersion in aqueous solution, both with respect to their chemical composition at the particle surface and to aggregation.

Conjugated polymers containing trifluoren-2-ylamine, trifluoren-2-ylbenzene and trifluoren-2-yltriazine for electroluminescence

A series of light-emitting conjugated polymers (LEPs) based on building blocks of electron-donating trifluoren-2-ylamine (TFA), electrically neutral 1,3,5-trifluoren-2-ylbenzene (TFB), and electron-withdrawing 2,4,6-trifluoren-2-yltriazine (TFT) were successfully synthesized via palladium-catalyzed Suzuki cross-coupling polycondensation. Their structure–property relationships were thoroughly studied. For P1 containing electron-withdrawing backbone and electron-donating pendants, their photophysical properties in solution are strongly dependent on the solvent polarity due to the intense intramolecular charge-transfer (ICT) interaction. In addition, their emission colors and energy levels could be effectively tuned by changing the structure of the main chain as well as the substituent at the pendent fluorene of TFT, TFB, and TFA. To evaluate their electroluminescence properties, double-layer devices with a configuration of ITO/PEDOT:PSS (40 nm)/emitting layer (EML) (70–80 nm)/TPBI (30 nm)/CsF (1.5 nm)/Al were fabricated, where the developed polymers were used as an EML and TPBI (2,2′,2″-(1,3,5-benzenetriyl)-tris-(1-phenyl-1H-benzimidazole)) was used as an electron-transport and hole-block layer. Deep-blue light emission was achieved for the device based on P1d, a polymer based on TFT and the second generation (G2) of carbazole dendrimer pendant, that shows a maximum current efficiency (CE) of 1.26 cd A−1, corresponding to external quantum efficiency (EQE) of 1.27%, with Commission Internationale de L'Eclairage (CIE) coordinates of (0.16, 0.14). In comparison, due to the intense ICT interaction between the main chain and the side chain, light-green emission was achieved for the device based on P1c, a polymer based on TFT and bis(9,9-dioctyl-9H-fluoren-2-yl)amine pendant, giving the highest maximum CE of 4.10 cd A−1, corresponding to EQE of 2.45%, with CIE coordinates of (0.24,0.51), although either of the main chain and the side chain emits blue light.