Variety Of Substituents Research Articles

Pyromellitic diimide-based luminophors: Tunable aggregation-induced emission (AIE) and reversible mechanofluorochromism characteristics

Four newly synthesized pyromellitic diimide-based fluorescent dyes with different aryl groups were first reported. All pyromellitic diimide (PMDI) derivatives were firstly displayed prominent aggregation-induced emission (AIE) properties. Additionally, the tunable fluorescence of PMDI derivatives were achieved by the varied substituent groups linked on the PMDI skeleton. With the enlarged sizes of isolation groups, aggregation-induced emission migration in the direction of red waves, as the result of the efficient inhibition of π-π stacking by the larger substituent groups. Furthermore, the mechanofluorochromic (MFC) performance of these PMDI derivatives could be tuned by different sized of the substituent groups. Interestingly, PMDI-ESCz, PMDI-PSCz and PMDI-DSCz exhibited reversible mechanofluorochromic performances, but no mechanochromism phenomenon was found for PMDI-In. These results exhibited that substituent groups had significant influence on their AIE and MFC properties.

Topology Effects in Molecular Organic Electronic Materials: Pyrene and Azupyrene*.

Pyrene derivatives play a prominent role in organic electronic devices, including field effect transistors, light emitting diodes, and solar cells. The flexibility in the desired properties has previously been achieved by variation of substituents at the periphery of the pyrene backbone. In contrast, the influence of the topology of the central π‐electron system on the relevant properties such as the band gap or the fluorescence behavior has not yet been addressed. In this work, pyrene is compared with its structural isomer azupyrene, which has a π‐electron system with non‐alternant topology. Using photoelectron spectroscopy, near edge X‐ray absorption fine structure spectroscopy, and other methods, it is shown that the electronic band gap of azupyrene is by 0.72 eV smaller than that of pyrene. The difference of the optical band gaps is even larger with 1.09 eV, as determined by ultraviolet–visible absorption spectroscopy. The non‐alternant nature of azupyrene is also associated with a more localized charge distribution. Further insight is provided by density functional theory (DFT) calculations of the molecular properties and ab initio coupled cluster calculations of the optical transitions. The concept of aromaticity is used to interpret the major topology‐related differences.

Trifluorinated Tetralins via I(I)/I(III)-Catalysed Ring Expansion: Programming Conformation by [CH2 CH2 ] → [CF2 CHF] Isosterism.

Saturated, fluorinated carbocycles are emerging as important modules for contemporary drug discovery. To expand the current portfolio, the synthesis of novel trifluorinated tetralins has been achieved. Fluorinated methyleneindanes serve as convenient precursors and undergo efficient difluorinative ring expansion with in situ generated p‐TolIF2 (>20 examples, up to >95 %). A range of diverse substituents are tolerated under standard catalysis conditions and this is interrogated by Hammett analysis. X‐ray analysis indicates a preference for the CH−F bond to occupy a pseudo‐axial orientation, consistent with stabilising σC−H→σC−F* interactions. The replacement of the symmetric [CH2−CH2] motif by [CF2−CHF] removes the conformational degeneracy intrinsic to the parent tetralin scaffold leading to a predictable half‐chair. The conformational behavior of this novel structural balance has been investigated by computational analysis and is consistent with stereoelectronic theory.

Short and Modular Synthesis of Substituted 2-Aminopyrroles.

We herein describe a simple and metal-free domino methodology to synthesize 2-aminopyrroles from alkynyl vinyl hydrazides. The domino reaction involves a novel propargylic 3,4-diaza-Cope rearrangement and a tandem isomerization/5-exo-dig N-cyclization reaction. By using this approach, a number of 2-aminopyrroles with diverse substituents have been prepared.

Synthesis of Highly Substituted Cyclobutanones by a One‐Pot Keteniminium‐Enamine Process

AbstractHerein, we describe an effective one‐pot sequence for the regio‐ and stereoselective synthesis of highly substituted cyclobutanones. This process relies on first a [2+2] cycloaddition involving a keteniminium salt intermediate with an alkene followed by isomerization of the resulting cyclobutaniminium salt into its cyclic enamine form and then reaction of the latter with an electrophile. The adduct can be either hydrolyzed or reduced to give the corresponding cyclobutanone or cyclobutanamine, respectively, with excellent diastereocontrol. A variety of electrophiles was tolerated allowing the incorporation of diverse substituents and functionalities onto the cyclobutyl ring. Additionally, the coplanarity of diverse cyclic enamines was investigated through a DFT study.

Electronic structures, bonding and energetics of non-heme mono and dinuclear iron-TPA complexes: a computational exploration

Due to their rich structural chemistry and enormous catalytic applications, TPA (tris(2-pyridylmethyl)amine) coordinated iron (Fe-TPA) complexes are widely studied as potent functional model in biomimetic area. We have done a thorough computational study on six diverse mononuclear and dinuclear FeII/FeIII-TPA complexes using density functional method. All the possible spin states for the six species were computed, and the ground state S value of these species was determined. The molecular structures, energetic profiles of spin states, electrostatic potentials, spin densities, and orbital energies of all the six complexes are reported. A comparative study among these six species was also done to gain insights about any sort of correlation in properties of these species. The observed variations as well as correlations in properties of the species are imputed to the diverse ligand substituents in Fe-TPA skeleton. Theoretical reactivity behavior was evaluated by doing frontier molecular orbital analysis for all the species by mapping HOMO-LUMO diagrams. Electrostatic potential surfaces were mapped to study charge energy distribution in the species. Our computed results are in well agreement with the experimental data.

Synthesis of Carbazoles by a Diverted Bischler–Napieralski Cascade Reaction

An unforeseen twist in a seemingly trivial Bischler–Napieralski reaction led to the selective formation of an unexpected carbazole product. The reaction proved to be general, providing access to a range of diversely substituted carbazoles from readily available substrates. Judicious variation of substituents revealed a complex cascade mechanism comprising no less than 10 elementary steps, that could be diverted in multiple ways toward various other carbazole derivatives.

Gold(I)-Catalyzed [8+2]-Cycloaddition of 8-Aryl-8-azaheptafulvenes with Allenamides and Ynamides: Regioselective Synthesis of Dihydrocycloheptapyrrole Derivatives.

Gold(I)-catalyzed higher-order [8+2] cycloadditions of 8-aryl-8-azaheptafulvenes 1 with allenamides 2 and ynamides 3 were studied. 1,8-Dihydrocycloheptapyrroles 4 were achieved by a regioselective [8+2] cycloaddition of azaheptafulvenes 1 and allenamides 2 in the presence of (2,4-ditBuC6 H3 O)3 PAuNTf2 as catalyst. Besides, ynamides 3 and 8-aryl-8-azaheptafulvenes 1, undergo a regioselective [8+2] cycloaddition, to give 2-amido-1,4-dihydrocycloheptapyrroles 7 in the presence of JohnPhosAuNTf2 as catalyst. Both reactions take place with good yields and with a variety of substituents. A plausible mechanism hypothesis suggests a nucleophilic attack of the 8-azaheptafulvene to the gold activated electron rich allene or alkyne moieties of the allenamide and ynamide, respectively.

Synthesis and anti-trypanosomal activity of 3′-fluororibonucleosides derived from 7-deazapurine nucleosides

Trypanosoma brucei parasites cause Human African Trypanosomiasis and the current drugs for its treatment are often inefficient and toxic. This urges the need to development of new antitrypanosomal agents. We report the synthesis and biological profiling of 3′-deoxy-3′-fluororibonucleosides derived from 7-deazaadenine nucleosides bearing diverse substituents at position 7. They were synthesized through glycosylation of 6-chloro-7-bromo- or -7-iodo-7-deazapurine with protected 3′-fluororibose followed by cross-coupling reactions at position 7 and/or deprotection. Most of the title nucleosides displayed micromolar or submicromolar activity against Trypanosoma brucei brucei. The most active were the 7-bromo- and 7-iododerivatives which exerted double-digit nanomolar activity against T. b. brucei and T. b. gambiense and no cytotoxicity and thus represent promising candidates for further development.

Regulation of aggregation-induced emission color of α-cyanostilbene luminogens through donor engineering of amino derivatives

In this contribution, α-cyanostilbene-based D-π-A-π-D type compounds consisting of different substituents on the amino donor group (e.g., fused, aryl/alkyl, and dialkyl) were designed, synthesized and their aggregation-induced emission was investigated thoroughly. The incorporation of these substituents furnished AIE features with tunable emission colors ranging from green-to-yellow-to-red. The compounds all showed a weak emission in THF; however, they showed an enhanced emission upon addition of water by forming emissive aggregates, which may arise from the restriction of twisted intramolecular charge transfer and E/Z isomerization. The DFT calculations revealed that the luminogens adopted distinctive conformations including a highly twisted one and a relatively coplanar one with the variation in the amino substituents.

Revisited the reaction mechanism of cobalt catalyzed [3+2] cycloaddition reactions between the derivatives of cyclopropanols and allenes: A DFT study

A theoretical study on the cobalt catalysed [3+2] cycloaddition reaction between cyclopropanol and allene has been performed using DFT method. It reveals that a stepwise pathway is favourable which involves the sequence of cleavage of cyclopropanol derivatives and carban-carbon bond formation and finally generation of cyclopentane derivatives with exocyclic double bonds. Substituted reactants raise the possibility of diastereoselectivity in the cycloaddition reactions. The steric interaction by the variation of substituents decides the reaction to progress selectively in a specific direction leading to a specific diastereomeric product in high yield. The study explains the experimentally observed selectivity of products for the metal catalysed cycloaddition in generating cyclopentane structure.

Pyrrolopyrimidine Bumped Kinase Inhibitors for the Treatment of Cryptosporidiosis.

Bumped kinase inhibitors (BKIs) that target Cryptosporidium parvum calcium-dependent protein kinase 1 have been well established as potential drug candidates against cryptosporidiosis. Recently, BKI-1649, with a 7H-pyrrolo[2,3-d]pyrimidin-4-amine, or "pyrrolopyrimidine", central scaffold, has shown improved efficacy in mouse models of Cryptosporidium at substantially reduced doses compared to previously explored analogs of the pyrazolopyrimidine scaffold. Here, two pyrrolopyrimidines with varied substituent groups, BKI-1812 and BKI-1814, were explored in several in vitro and in vivo models and show improvements in potency over the previously utilized pyrazolopyrimidine bumped kinase inhibitors while maintaining equivalent results in other key properties, such as toxicity and efficacy, with their pyrazolopyrimidine isosteric counterparts.

Modular and Divergent Syntheses of Protoberberine and Protonitidine Alkaloids

A modularly convergent and divergent strategy was established for the family synthesis of both protoberberine and protonitidine alkaloids. The robust, scalable, and flexible synthetic route featured a collective preparation of protoberberine and protonitidine alkaloids from a common isoquinoline assembled from pyridyne as the key synthon, which was based on the selective N-C or C-C cyclization via distinct processes. Through the strategy, 20 protoberberine alkaloids, 5 protonitidine alkaloids, and 11 analogues with diverse substituents were comprehensively aquired.

Synthesis of Acridinium Photocatalysts via Site-Selective C–H Alkylation

Acridinium dyes have been broadly used as photocatalysts, but it remains synthetically challenging to fine-tune their catalytic performance by functionalization of their structural cores. Acridiniu...

Substituted 2-(2-hydroxyphenyl)–3H-quinazolin-4-ones and their difluoroboron complexes: Synthesis and photophysical properties

2-(2-Hydroxyphenyl)–3H-quinazolin-4-ones with diverse substituents at phenol ring and their six-membered difluoroboron complexes have been synthesized via few-stage approach. The photophysical properties of target compounds have been investigated in two solvents as well as in the solid state. The nature of substituents and substitution point in the phenol moiety of ligands and resulting BF2-complexes on the photophysical properties of dyes have been explored. The complex bearing two t-Bu groups proved to be the most emissive in solid state, whereas its 5-methoxy and 4-diethylamino counterparts possess strong emission in toluene solution. The dyes exhibited large Stokes shifts which was attributed to excited state intramolecular proton transfer (ESIPT). Additionally, fluorescence of quinazolinones in the mixture of THF/water was studied. All ligands demonstrated emission enhancement with increase of water fraction which was due to aggregation induced emission.

Magnetic Anisotropy: Structural Correlation of a Series of Chromium(II)-Amidinate Complexes.

Systematic substituent variations on amidinate ligands bring delicate changes of CrN4 coordination in a family of chromium(II) complexes with the common formula of Cr(RNC(CH3)NR)2, where R = iPr (1), Cy (2), Dipp (Dipp = 2, 6-diisopropylphenyl) (3), and tBu (4). With the largest substituent group, 4 shows the largest distortion of the N4 coordination geometry from square-planar to seesaw shape, which leads to its field-induced single-molecule magnet (SMM) behavior. This is an indication that 4 has the strongest axial magnetic anisotropy and/or optimized magnetic relaxation process. Combined with high-frequency/field electron paramagnetic resonance (HF-EPR) experiments and ab initio calculations, we deduce that the smallest energy gap between ground 4Ψ0 and the first excited 4Ψ1 orbitals in 4 contributes the most to its strongest magnetic anisotropy. Moreover, the lower E value of 4 ensures its being a field-induced SMM. Specifically, the D and E values were found to be correlated to the dihedral angle between the ΔN1CrN2 and ΔN3CrN4 triangles, indicating that distortion from ideal square-planar geometry to the seesaw help increase axial magnetic anisotropy and suppress the transversal part. Thus, the study on this system not only expands the family of Cr(II)-based SMMs but also contributes to a deeper understanding of magneto-structural correlation in four-coordinate Cr(II) SMMs.

Modulating the water oxidation catalytic activity of iridium complexes by functionalizing the Cp*-ancillary ligand: hints on the nature of the active species

A comparative study on the behavior of a series of iridium dimeric WOCs with modified Cp* ligands reveals the key role played by the variable substituent.

ESIPT-inspired fluorescent turn-on sensitivity towards aluminium(III) detection by derivatives of O- and S-bridged bis-(phenol-imine) molecules

The need to explore possible benefits of molecular substituent derivatization on fluorescent chemosensor properties motivated the syntheses of six potentially pentadentate bis-(phenol-imine) fluorophores, which consist of five S-bridged O^N^S^N^O scaffolds 1–5 and an O-bridged O^N^O^N^O scaffold 6. The deliberate incorporation of multiple intramolecular N…HO donor–acceptor functions into the molecules helped to achieve Excited State Intramolecular Proton-electron Transfer (ESIPT) capability as well as the possession of low quantum yields in their ligand-only solutions. Interestingly, while the low quantum yield molecules 1, 2, 3 and 6 lacked the expected large Stokes shifted ESIPT fluorescence in their ligand-only solutions, they utilize the same ESIPT-oriented process to achieve varying extents of substituent-dependent fluorescent turn-on that produced sensitive and selective Al3+ detection. In particular, while molecules 1 and 3 gave dual-band fluorescence turn-on from both primary and secondary photoexcited states, the O-bridged ligand 6 is strongly turned on only at the large Stokes shifted ESIPT emission wavelength. Thus, with a 528-fold F/Fo turn-on ratio and a detection limit of 5.48 × 10−9 M, the efficiency of molecule 6 as chemosensor towards Al3+ detection can be considered to be outstanding. Based on results of Job plot experiment, fluorescent intensities during Al3+ titration, single crystal structural data and 1H NMR spectral analyses, we conclude that a 1:1 sensor-to-analyte stoichiometry is at play in the Al3+ sensing mechanism and that the sensor molecules form an unusual bidentate O^O coordination with the analyte as neutral iminium zwitterion. It could be concluded that synthetic designs leading to systematic substituent variation is a beneficial tool for tuning and isolating applicable molecular chemosensor species.

Rotation‐restricted strategy to synthesize high molecular weight polyethylene using iminopyridyl nickel and palladium catalyst

Most of the iminopyridyl Ni (II) and Pd (II) catalysts are reported to oligomerize ethylene or yield very low molecular weight polyethylene. Moreover, the molecular weight of product is not sensitive to ligand sterics. In this contribution, we demonstrate that the bulky rotation‐restricted substituents incorporated into iminopyridyl Ni (II) and Pd (II) catalysts that provide the right orientation are highly effective in retarding the chain transfer. Thus, (2,6‐bis(10,11‐dihydro‐5H‐dibenzo[a,d][7]annulen‐5‐yl)‐4‐methylphenyl)‐1‐(pyridin‐2‐yl)methanimine nickel (II) bromide (Ni3) and (2,6‐bis(10,11‐dihydro‐5H‐dibenzo[a,d][7]annulen‐5‐yl)‐4‐methylphenyl)‐1‐(pyridin‐2‐yl)methanimine palladium (II) methyl chloride (Pd3) with the phenyl substituents fixed in the diarylmethyl moiety produce polyethylene or functionalized polyethylene (ethylene‐MA copolymer) with high Mn values up to 2.5 × 104 g mol−1, while allowing the high MA incorporation (3.2%–13.8%). In addition, the effects on the (co)polymerization behavior as a function of rotation‐restricted substituent variations (free rotation, restricted rotation and fixation) were systemically studied. As a result, various molecular weight polyethylene and ethylene‐MA copolymer with high MA incorporation ratio were also obtained in this system.

Selective Modification for Red-Shifted Excitability: A Small Change in Structure, a Huge Change in Photochemistry.

We developed three bathochromic, green‐light activatable, photolabile protecting groups based on a nitrodibenzofuran (NDBF) core with D‐π‐A push–pull structures. Variation of donor substituents (D) at the favored ring position enabled us to observe their impact on the photolysis quantum yields. Comparing our new azetidinyl‐NDBF (Az‐NDBF) photolabile protecting group with our earlier published DMA‐NDBF, we obtained insight into its excitation‐specific photochemistry. While the “two‐photon‐only” cage DMA‐NDBF was inert against one‐photon excitation (1PE) in the visible spectral range, we were able to efficiently release glutamic acid from azetidinyl‐NDBF with irradiation at 420 and 530 nm. Thus, a minimal change (a cyclization adding only one carbon atom) resulted in a drastically changed photochemical behavior, which enables photolysis in the green part of the spectrum.