Bulky Moiety Research Articles

Molecular glasses of azobenzene for holographic data storage applications

A series of D-N=N-A type molecular glasses where the electron acceptor part (A) contains several electron withdrawing substituents, but the electron donating part (D) of the glassy azochromophores contains amorphous phase promoting non-conjugated bulky triphenyl or hydroxyl groups have been synthesized and investigated. Results showed that the azodye physical properties depend not only on the incorporated electron withdrawing substituents but are also influenced by the bonding type of covalently attached bulky moieties. Synthesized glassy azocompounds showed glass transition temperatures up to 106 °C and thermal stability up to 312 °C.The ability to form holographic gratings in spin-cast thin films of the glassy azodyes was investigated using 532 nm and 633 nm lasers obtaining diffraction efficiency up to 57%, self-diffraction efficiency up to 15% and photosensitivity as high as 3.7 J/(cm2%). Surface relief grating (SRG) depths reached 1.1 μm and in some cases even exceeded the thickness of the films.

Novel carbazolyl-substituted spiro[acridine-9,9′-fluorene] derivatives as deep-blue emitting materials for OLED applications

Blue organic light-emitting diodes (OLEDs) are of great significance in the fields of flat-panel display and solid-state lighting. Herein, three carbazolyl-substituted blue emitters, namely SAF-CzB, SAF-2CzB, and F-2CzB, were designed and synthesized. Two compounds SAF-CzB and SAF-2CzB possess a rigid spiro[acridine-9,9′-fluorene] (SAF) central core. The counterpart F-2CzB, which contains 9,9-dimethylfluorene as core was, also researched for comparative purpose. The introduction of SAF into fluorene-based materials could simultaneously improve their thermal stability, hole injection and transport ability, as well as prevent the fluorenone defect. The compound SAF-2CzB shows a higher decomposition temperature (Td) of 534 °C compared to that of F-2CzB (488 °C). The hole-transporting property of SAF-2CzB is also better than that of F-2CzB demonstrated by single-carrier devices. The presence of a bulky spiro-annulated triphenylamine moiety at the C9 position of the fluorene might suppress the fluorenone defect. Non-doped OLED based on SAF-2CzB as the emitting layer shows the best performance with maximum current efficiency (CE) of 4.07 cd A−1 and power efficiency (PE) of 1.83 l m W−1, compared with 3.03 cd A−1 and 1.08 l m W−1 for SAF-CzB, 3.14 cd A−1 and 1.23 l m W−1 for F-2CzB. In particular, both SAF-2CzB- and F-2CzB-based device exhibit good color stability with CIE coordinate of (0.16, 0.11) at the voltage of 7–12 V.

Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the...

Novel Thermoplastic Cellulose Esters Containing Bulky Moieties and Soft Segments

It is still challenging to convert cellulose into melt-processable materials because natural cellulose, which has a strong hydrogen bonding network, degrades before melting. Herein, a series of novel cellulose-based thermoplastics were successfully designed and fabricated by a simple and efficient homogeneous esterification of cellulose in an ionic liquid. Introducing ester substituents containing both bulky moieties and soft segments can improve the mobility of the cellulose chain, and the glass transition temperatures (Tgs) appeared in the resultant cellulose esters. In particular, when the ester substituents consisted of bulky terminal moiety and soft middle segment, Tgs of the corresponding cellulose esters were relatively low (80–160 °C), indicating these cellulose materials were suitable for melt processing. Accordingly, these thermoplastic cellulose esters can be processed into transparent disks, dumbbells, fibers and flexible films by traditional injection molding, melt extrusion, and hot pressing...

Large-scale synthesis of novel sterically hindered acenaphthene-based α-diimine ligands and their application in coordination chemistry

An efficient method to synthesize novel highly sterically hindered acenaphthene-based α-diimine ligands bearing bulky diarylmethyl moiety was achieved by two-step reactions. These reactions could be carried out on a scale of 100 g with no chromatography involved. On the basis of this method, a series of novel highly sterically hindered acenaphthene-based α-diimine Pd(II) and Ni(II) complexes, imidazolium precursors and the corresponding NHCs-metal complexes were also successfully synthesized. These novel complexes can offer great potential for metal-catalyzed polymerizations and organic reactions.

Towards Sustainable H2 Production: Rational Design of Hydrophobic Triphenylamine‐based Dyes for Sensitized Ethanol Photoreforming

Donor-acceptor dyes are a well-established class of photosensitizers, used to enhance visible-light harvesting in solar cells and in direct photocatalytic reactions, such as H2 production by photoreforming of sacrificial electron donors (SEDs). Amines-typically triethanolamine (TEOA)-are commonly employed as SEDs in such reactions. Dye-sensitized photoreforming of more sustainable, biomass-derived alcohols, on the other hand, was only recently reported by using methanol as the electron donor. In this work, several rationally designed donor-acceptor dyes were used as sensitizers in H2 photocatalytic production, comparing the efficiency of TEOA and EtOH as SEDs. In particular, the effect of hydrophobic chains in the spacer and/or the donor unit of the dyes was systematically studied. The H2 production rates were higher when TEOA was used as SED, whereas the activity trends depended on the SED used. The best performance was obtained with TEOA by using a sensitizer with just one bulky hydrophobic moiety, propylenedioxythiophene, placed on the spacer unit. In the case of EtOH, the best-performing sensitizers were the ones featuring a thiazolo[5,4-d]thiazole internal unit, needed for enhancing light harvesting, and carrying alkyl chains on both the donor part and the spacer unit. The results are discussed in terms of reaction mechanism, interaction with the SED, and structural/electrochemical properties of the sensitizers.

Computational Study of B(C6F5)3-Catalyzed Selective Deoxygenation of 1,2-Diols: Cyclic and Noncyclic Pathways

The selective deoxygenation of polyols has emerged as an attractive approach to transform biomass-derived polyols into valuable building blocks. Herein, we present a theoretical study on the boron-catalyzed selective deoxygenation of terminal 1,2-diols. The computational results explain the different product distributions obtained with different silanes and unveil the critical role of the cyclic siloxane intermediate. Compared to noncyclic pathways, the cyclic pathway facilitates the initial deoxygenation process because the cyclic structure minimizes the steric repulsions between the reagents. It avoids overreduction because the generated bulky disiloxane moiety hinders the second deoxygenation.

Tetrasubstituted Imidazolium Salts as Potent Antiparasitic Agents against African and American Trypanosomiases.

Imidazolium salts are privileged compounds in organic chemistry, and have valuable biological properties. Recent studies show that symmetric imidazolium salts with bulky moieties can display antiparasitic activity against T. cruzi. After developing a facile methodology for the synthesis of tetrasubstituted imidazolium salts from propargylamines and isocyanides, we screened a small library of these adducts against the causative agents of African and American trypanosomiases. These compounds display nanomolar activity against T. brucei and low (or sub) micromolar activity against T. cruzi, with excellent selectivity indexes and favorable molecular properties, thereby emerging as promising hits for the treatment of Chagas disease and sleeping sickness.

Voltammetric Study of Antitumor Efficient Ethylenediamine-Type of Ligands

The electrochemical behavior of four dialkyl esters (methyl, ethyl, n-propyl and n-butyl) of (S,S)-α,α′-(1,2-ethanediyldiimino)-bis[cyclohexanepropanoic acid] with moderate antitumor activity has been studied by cyclic voltammetry. I-E curves recorded at boron-doped diamond electrode in −2.00 < Ep < 0.00 V range show a single oxidative peak located in the −0.95 < Ep,a < −0.52 V region in a form of one-electron wave. The electrochemical processes appear to be irreversible for all compounds except for the compound with methyl substituent which demonstrates well-defined reversible electron transfer. Derivatives with bulkier moieties are easier to oxidize. For all investigated compounds an amine-centered redox process is dominant. Further investigation indicates that electrochemical reaction is diffusion controlled, chemically irreversible process. The results are discussed in terms of linking their electrochemical activity to antitumor effect.

Self-Assembled Conjugated Polymer Microsphere Resonators and Lasers

We present self-assembled conjugated polymer microspheres that act as whispering gallery mode (WGM) resonators. For the preparation of conjugated polymer microspheres, vapor diffusion and miniemulsion methods are adopted. For the vapor diffusion method to obtain microspheres, amorphous aggregation of the polymers are crucial by introducing sterically bulky moieties that largely twists the polymer main chain. Focused laser irradiation to the perimeter of the microspheres excites WGM, where sharp and periodic lines appear in the PL spectrum. With a benefit of the high light confinement properties, we demonstrate long distance, directional, and efficient light energy transfer and wavelength conversion through bispheres. Furthermore, WGM lasing is achieved from conjugated polymer microspheres upon femtosecond pumping. Conjugated polymer microsphere resonators have advantages of high photoabsorptivity, high refractive index, and inherent conducting properties, as well as the simple fabrication process, which are valuable for applications to optical circuits, electrically-driven lightings, and chemical and biological sensors

Liquid‐Crystalline Phthalocyanine Derivatives Bearing Oligosiloxane Moieties: Soft Columnar Mesophases Stabilized by Nanosegregation

AbstractNovel liquid‐crystalline (LC) nickel phthalocyanine (Ni−Pc) complexes bearing eight oligosiloxane moieties such as disiloxane and trisiloxane were synthesized and their liquid‐crystalline properties, as well as their carrier transport characteristics in the liquid‐crystalline phase, were studied. These LC Ni−Pc complexes with eight oligosiloxane moieties exhibited a columnar mesophase over a wide range of temperatures, including room temperature. The bulky oligosiloxane moieties inhibited the aggregation of the Ni−Pc cores and stabilized the columnar structure by nanosegregation. Moreover, these LC Pc−Ni complexes showed homeotropic alignment in sandwich‐type cells consisting of substrates coated with indium tin oxide. Time‐of‐flight measurements revealed ambipolar carrier transport properties in the columnar mesophases, in which electron transport was predominant.

Free volume enhanced proton exchange membranes from sulfonated triptycene poly(ether ketone)

A triptycene based poly(ether ketone) (tripPEEK) was synthesized and sulfonated to form proton exchange membranes. The increase in intrinsic free volume resulting from the incorporation of sterically bulky triptycene moiety, imparts high affinity to water at all levels of relative humidity (RH) from 10% RH to 90% RH. S-tripPEEK membranes showed proton conductivities of 334mS/cm at 85°C at 90% RH and 0.37mS/cm at 85°C at 20% RH. Membranes of similar ion exchange capacity (IEC) are compared to deconvolute the effect of free volume from IEC in enhancing proton conductivity. Increasing the free volume of the membranes increases the proton conductivity and decreases the activation energy for proton conduction between 10% RH to 90% RH.

Design and synthesis of small molecule agonists of EphA2 receptor

Ligand-independent activation of EphA2 receptor kinase promotes cancer metastasis and invasion. Activating EphA2 receptor tyrosine kinase with small molecule agonist is a novel strategy to treat EphA2 overexpressing cancer. In this study, we performed a lead optimization of a small molecule Doxazosin that was identified as an EphA2 receptor agonist. 33 new analogs were developed and evaluated; a structure−activity relationship was summarized based on the EphA2 activation of these derivatives. Two new derivative compounds 24 and 27 showed much improved activity compared to Doxazosin. Compound 24 possesses a bulky amide moiety, and compound 27 has a dimeric structure that is very different to the parental compound. Compound 27 with a twelve-carbon linker of the dimer activated the kinase and induced receptor internalization and cell death with the best potency. Another dimer with a six-carbon linker has significantly reduced potency compared to the dimer with a longer linker, suggesting that the length of the linker is critical for the activity of the dimeric agonist. To explore the receptor binding characteristics of the new molecules, we applied a docking study to examine how the small molecule binds to the EphA2 receptor. The results reveal that compounds 24 and 27 form more hydrogen bonds to EphA2 than Doxazosin, suggesting that they may have higher binding affinity to the receptor.

Modification of polyamide membranes by hydrophobic molecular plugs for improved boron rejection

Commercial polyamide RO membranes, though effective in terms of flux and salt removal, have a few drawbacks, in particular, poor rejection of boron (B), thus they are often unable to remove B to the required level in a one-pass sea desalination process. This complicates the process and available solutions increase the cost of desalinated water significantly. Here we explore in-situ modification procedure that can significantly increase their boron rejection by incorporating suitable modifying molecules in the selective polyamide layer. We propose that aliphatic amines be used as such “plug” molecules that combine a bulky hydrophobic moiety with a reactive group that can chemically or physically bind to polyamide layer, tighten its structure and increase selectivity. Based on previous results, we hypothesize that hydrophobicity of the selective layer increased by the immobilized amine “plug”, along with reduced pore size, may help disrupt water-boric acid association and decouple water and boron permeation. The results show that the proposed treatment with sufficiently long (up to 10–12 carbons) aliphatic amines, using either covalent bonding or simple sorption, may indeed reduce the boron passage by a factor of 2–4, without impairing the salt rejection of the membrane. The improved selectivity comes at the expense of some flux reduction, but the flux-selectivity tradeoff improves compared with commercial polyamide membranes.

Extending donor size in D-A-π-A organic dye for dye sensitized solar cells: Anti-aggregation and improving electron injection

We have theoretically designed two D-A-π-A dyes 3 and 4 based on the efficient references 1 and 2 by introducing an extra electron donor unit (D2). Via calculating the electronic structures of isolated dyes, we obtain that dyes 3 and 4 possess stronger light-harvesting efficiency imparted by the fluorescence energy transfer of D2 part, maintain comparable lifetime of excited states, and shorten the electron injection time significantly with regard to 1 and 2. Meanwhile, dye 3 positively shifts the edge of virtual states of TiO2 in a larger extent compared to its counterparts. Then after considering the alignment morphology of multiple dyes adsorbed on TiO2 surface, we find that dyes 3 and 4 manifest the capability of anti-aggregation obviously, which is evidenced by the smaller quantity of intermolecular electronic coupling compared to that of dyes 1 and 2, definitively illustrating the prominent performance of novel dyes with the bulky D2 moiety. Finally, dye 3 is screened out as the potential candidate for future application.

Conformational Flexibility of the Benzyl-Guanine Adduct in a Bypass Polymerase Active Site Permits Replication: Insights from Molecular Dynamics Simulations.

Although translesion synthesis (TLS) polymerases play key roles in replicating DNA that contains nucleobase addition products (adducts), there are many unknowns about their function. The present work gains indispensable structural insights from molecular dynamics simulations on the replication of O6-benzyl-guanine (Bz-dG) prior to bond formation during dCTP insertion opposite the adduct by Dpo4. When combined with previous X-ray crystal structures of the Bz-dG extension complex, molecular details are now available for each stage during a single TLS replication cycle for this carcinogenic lesion. Our calculations illustrate that Bz-dG preferentially adopts an intercalated bulky moiety orientation in the Dpo4 preinsertion complex, which stabilizes the complex through Bz-dG interactions with the previously replicated 3'-base pair and positions the carcinogenic group in the dNTP binding site. Nevertheless, the maintained inherent flexibility of Bz-dG due to a stark lack of interactions with the polymerase or template DNA allows the bulky moiety to adopt a major groove position opposite an incoming dCTP in an orientation that is conducive for the experimentally observed nonmutagenic bypass. Comparison of Bz-dG and canonical dG replication clarifies that the experimentally observed decrease in dCTP binding affinity and replication efficiency upon adduct formation is likely caused by a combination of factors, including the required template nucleotide conformational change and destabilized template-dCTP hydrogen bonding. Although additional aspects of the replication process, such as the impact of the adduct on the nucleotidyl-transfer reaction, may also be important for fully rationalizing experimental replication data and must be considered in future work, the present contribution emphasizes the importance of considering the effect of DNA damage on the early stages of the TLS process.

Structural Basis of Analog Specificity in PKG I and II.

Cyclic GMP analogs, 8-Br, 8-pCPT, and PET-cGMP, have been widely used for characterizing cellular functions of cGMP-dependent protein kinase (PKG) I and II isotypes. However, interpreting results obtained using these analogs has been difficult due to their low isotype specificity. Additionally, each isotype has two binding sites with different cGMP affinities and analog selectivities, making understanding the molecular basis for isotype specificity of these compounds even more challenging. To determine isotype specificity of cGMP analogs and their structural basis, we generated the full-length regulatory domains of PKG I and II isotypes with each binding site disabled, determined their affinities for these analogs, and obtained cocrystal structures of both isotypes bound with cGMP analogs. Our affinity and activation measurements show that PET-cGMP is most selective for PKG I, whereas 8-pCPT-cGMP is most selective for PKG II. Our structures of cyclic nucleotide binding (CNB) domains reveal that the B site of PKG I is more open and forms a unique π/π interaction through Arg285 at β4 with the PET moiety, whereas the A site of PKG II has a larger β5/β6 pocket that can better accommodate the bulky 8-pCPT moiety. Our structural and functional results explain the selectivity of these analogs for each PKG isotype and provide a starting point for the rational design of isotype selective activators.

Derivatization of Phosphine Ligands with Bulky Deltahedral Zintl Clusters-Synthesis of Charge Neutral Zwitterionic Tetrel Cluster Compounds [(Ge9{Si(TMS)3}2)tBu2P]M(NHCDipp) (M: Cu, Ag, Au).

Reactions of silylated clusters [Ge9{Si(TMS)3}3]- or [Ge9{Si(TMS)3}2]2- with dialkylhalophosphines R2PCl (Cy, iPr, tBu) at ambient temperature yield the first tetrel Zintl cluster compounds bearing phosphine moieties. Varying reactivity of the dialkylhalophosphines toward the silylated clusters is observed depending on the bulkiness of the phosphine's alkyl substituents and on the number of hypersilyl groups at the tetrel cluster. Reactions between phosphines with small cyclohexyl- (Cy) or isopropyl- (iPr) groups and the tris-silylated cluster [Ge9{Si(TMS)3}3]- yield the novel neutral cluster compounds [Ge9{Si(TMS)3}3PR2] (R: Cy (1), iPr (2)) with discrete Ge-P exo bonds. By contrast, the bulkier phosphine tBu2PCl does not react with [Ge9{Si(TMS)3}3]- due to steric crowding. However, the reaction with the bis-silylated cluster [Ge9{Si(TMS)3}2]2- yields the novel cluster compound [Ge9{Si(TMS)3}2PtBu2]- (3). Subsequent reactions of compound 3 with NHCDippMCl (M: Cu, Ag, Au) yield the charge neutral zwitterionic compounds [(Ge9{Si(TMS)3}2)tBu2P]M(NHCDipp) (M: Cu, Ag, Au) (4-6), in which compound 3 acts as a phosphine ligand bearing a bulky tetrel Zintl cluster moiety. Compounds 4-6 also represent the first uncharged examples for 3-fold substituted tetrel Zintl clusters.

Synthesis of Mechanically Planar Chiral rac-[2]Rotaxanes by Partitioning of an Achiral [2]Rotaxane: Stereoinversion Induced by Shuttling.

Mechanically planar chiral [2]rotaxanes were synthesized by the introduction of bulky pyrrole moieties into the axle component of an achiral [2]rotaxane. The enantiomers were separated by chiral HPLC. The shuttling of the ring component between the two compartments at high temperature induced the stereoinversion of the mechanically planar chiral [2]rotaxane. The rate of the stereoinversion was studied quantitatively, and the kinetic parameters were determined.

Novel phosphorescent neutral iridium(III) complex with the steric hindrance for highly efficient red organic light-emitting diodes

A novel and highly efficient thiophenquinolone-based red iridium(III) complex bearing a bulky fluorophenyl moiety is designed and synthesized. The complex shows intensive red phosphorescence (596nm with shoulder at 642nm), high photoluminescence efficiency (0.62) and broad full width at half maximum (81nm). The bulky fluorophenyl moiety introduced into the complex could improve the efficiency of electroluminescence with the maximum current efficiency, power efficiency and the external quantum efficiency up to 29.0cd/A, 30.4lm/W and 17.6% due to the effective steric hindrance in solid states.