Picric acid sensing and CO2 capture by a sterically encumbered azo-linked fluorescent triphenylbenzene based covalent organic polymer

A sterically encumbered isopropyl group substituted fluorescent triphenylbenzene based azo-linked covalent organic polymer, iPrTAPB-Azo-COP, has been synthesized by Cu(I) catalysed homo coupling (amine-amine) reaction of 1,3,5-tris(4'-amino-3',5'-isopropylphenyl) benzene ((i)PrTAPB) under aerobic conditions. The Brunauer-Emmett-Teller (BET) and Langmuir surface areas of (i)PrTAPB-Azo-COP have been estimated to be 395 and 697 m(2) g(-1) with a pore diameter of 11.6 angstrom. Due to the presence of fluorescent triphenylbenzene platform (i)PrTAPB-Azo-COP exhibits broad emission band centred at 428 nm, when excited at 300 nm, as a result of extended conjugation. The inherent fluorescent nature of (i)PrTAPB-Azo-COP has been utilized for sensing electron-deficient polynitroaromatic compounds (PNACs) such as a picric acid (PA), dinitrotoluene (DNT), p-dinitrobenzene (p-DNB) and m-dinitrobenzene (m-DNB). Further, (i)PrTAPB-Azo-COP has also been utilized for capture of carbon dioxide as the azo-COP is enriched with CO2-philic nitrogen atoms apart from its microporosity. Since the azo (-N=N-) linkages are masked by the bulky isopropyl groups, (i)PrTAPB-Azo-COP exhibits a CO2 uptake of 6.5 and 19.4 wt% at 1 bar and 30 bar, respectively, at 273 K

1,3,5-Triphenylbenzene: a versatile photoluminescent chemo-sensor platform and supramolecular building block

Fluorescence chemo-sensors for species of environmental and biological significance have emerged as a major research area in recent years. In this account, we describe fluorescence quenching as well as enhancement-based chemo-sensors obtained by employing C3-symmetric 1,3,5-triphenylbenzene (1,3,5-TPB) as the fluorescence signalling unit. 1,3,5-TPB is a thermally and photochemically stable fluorescent platform with pi-electron-rich characteristics. Starting from this platform, supramolecular, discrete, triphenylbenzene-carbazole, covalent-organic framework, covalent-organic polymer and conjugated polymer based sensors have been developed for the selective detection of polynitroaromatic compounds, trinitrotoluene (TNT), dinitrotoluene (DNT) and picric acid (PA). Tris-salicylaldimine Schiff bases have been synthesized for the selective sensing of fluoride ions through a fluorescence turn-on mechanism. It is likely that it should be possible to develop other highly selective and sensitive chemosensors by incorporating 1,3,5-TPB as the fluorophore unit

2,2 ',6,6 '-Tetraisopropylbenzidine-Based Sterically Encumbered Ditopic C-2-Symmetric Ligand Systems and Supramolecular Building Blocks

Starting from 2,2',6,6'-tetra-isopropylbenzidine (TBZ), a family of sterically encumbered pseudo-C-2-symmetric based ligand systems and supramolecular building blocks have been synthesized. Schiff base scaffolds (iPr)(4)(C6H2)(2)(NAr')(2) (1-9) (Ar' = -CH(C6H4)(OH) (1); -CH(C6H2)(Me)(2)(OH) (2); -CH(C6H2)(tBu)(2)(OH) (3); -CH(C6H2)(tBu)(Br)(OH) (4); -CH(C6H3)(OMe)(OH) (5); -CH(C6H4)(4-OH) (6); -CH(2-Py) (7); -CH(3-Py) (8); -CH(4-Py) (9)), (iPr)(4)(C6H2)(2)(NH(C)(CH)(CO)Me-2)(2) (10), (NH2(iPr)(4)(C6H2)(2))(2) (N(C)(CH)(C)N)Me-2 (11), (NH2(iPr)(4)(C6H2)(2)N(CO)(C6H4)(CH2) (12) and (iPr)(4)(C6H2)(2)(N(CO)(C6H4)(CH2))(2) (13) have been assembled through condensation of TBZ with the corresponding formyl compounds. TBZ was also further employed to synthesize two carboxylic acid derivatives, ((iPr)(4)(C6H2)(2)(N(CH2COOH)(2))(2)) (14) and ((iPr)(4)(C6H2)(2)(COOH)(2)) (16), both potential connector ligands for MOFs. To explore main group chemistry aspects of TBZ, bis- and tetra-trimethylsilyl derivatives (iPr)(4)(C6H2)(2)(R)(2) (R= (-NH(SiMe3))(2) (17) and (-N(SiMe3)(2))(2) (18)) have been synthesized. The bis-dichlorophosphine derivative ((iPr)(4)(C6H2)(2)(N(PCl2)(2))(2)) (19), a compound with promising chemistry for P-based covalent organic frameworks, has been synthesized by a solvent-free reaction of TBZ with excess PCl3

[3+3] Imine and beta-ketoenamine tethered fluorescent covalent-organic frameworks for CO2 uptake and nitroaromatic sensing

Imine and beta-ketoenamine based covalent-organic frameworks (COFs) are nitrogen rich organic porous materials which offer enhanced affinity for carbon dioxide. In this article, synthesis, gaseous uptake and chemo-sensing properties of four new 2-D COFs with [3+3] structural motifs have been reported. The COFs have been synthesized from readily available C-3-symmetric aldehyde and amine building units via Schiff base condensation. Prior to the synthesis, reactivity and structural integrity of the building blocks were appropriated by a fully characterized model Schiff base (TAPB-Benz) obtained from the condensation of 1,3,5-tris(4'-aminophenyl)benzene (TAPB) and benzaldehyde. Reaction of 1,3,5-tris(4'-aminophenyl) benzene (TAPB) and 1,3,5-tris(4'-amino-3',5'-isopropylphenyl)benzene (iPrTAPB) with 1,3,5-tris(4'-formylphenyl)benzene (TFPB) and 1,3,5-triformylphluroglucinol (TFP) in dry dioxane and acetic acid (cat.) resulted in the formation of crystalline 2-D frameworks, TAPB-TFPB, iPrTAPB-TFPB, TAPB-TFP and iPrTAPB-TFP. The COFs feature permanent porosity with high surface area and carbon dioxide uptake. Among these, iPrTAPB-TFP revealed the highest surface area of 756 m(2) g(-1) (Brunauer-Emmett-Teller) and 1515 m(2) g(-1) (Langmuir) and carbon dioxide uptake of 105 mg g(-1) (273 K, 1 atm). Notably with 180 mg g(-1) (273 K, 1 atm), TAPB-TFP shows the highest CO2 uptake capacity among all the COFs which is also comparable to previously reported high CO2 uptake capacity COFs. Furthermore, due to the inherent fluorescent capability of triphenylbenzene, the COFs are endowed with fluorescence and fluorescence chemo-sensing ability for polynitroaromatic analytes

Zinc Dialkylhydroxybenzoates with Unusual Structures: First Example of a Discrete Three-Blade Paddle-Wheel and a Solvent Engulfed Coordination Polymer

Sterically encumbered 4-hydroxy-3,5-diisopropylbenzoic acid (H(2)diphba), bearing a carboxylic acid, a phenol and two isopropyl substituents, has been investigated for the first time as a ligand and supramolecular synthon to isolate eight Zn(II) complexes, [Zn-2(Hdiphba)(3)(OAc)(L)] (L = DMF(1) or pyz (2)), [Zn (Hdiphba)(2)(2,2'-bpy)] (3), [Zn(Hdiphba)(2)(1,10-phen)] (4), [Zn (Hdiphba)(2)(pz)(2)] (5) and [Zn-2(Hdiphba)(2)(mu(2)-dmpz)(2)(Hdmpz)(2)] (6), [Zn(Hdiphba)(2)(4,4'-bpy)](n).4nCH(3)OH (7.4nCH(3)OH), [Zn-2(Hdiphba)(4) (4,4'-azobpy)(H2O)(2)] (8.H(2)diphba), which have been structurally characterized. Compounds 1 and 2 are rare examples of symmetrically bridged triple-blade molecular tricarboxylate paddle-wheels which self-assemble into hexameric units. Compounds 3, 4 and 5 are mononuclear complexes, bearing two exposed phenolic -OH groups self-assembled into 2-D arrays via both hydrogen bonding and p-p stacking interactions. Compound 6 is a rare example of bis-pyrazolate bridged dinuclear Zn(II) complex with two pyrazole N-H and two phenolic -OH groups on the molecular periphery to form hydrogen bonds. The use of 4,4'-bpy leading to a zig-zag 1-D polymer 7 composed of [Zn(Hdiphba) 2(4,4'-bpy)] n chains, positioned 10.77 angstrom apart. The 1-D channels of 7 are occupied by hydrogen bonded methanol with a rare (CH3OH)(4) cluster as the repeating unit. Compound 8 is a discrete bimetallic complex, isolated with a free H(2)diphba ligand. The photoluminescence spectra of 1-8 exhibit ligand centered emission at around 325 nm

Dependence of the SBU length on the size of metal ions in alkaline earth MOFs derived from a flexible C-3-symmetric tricarboxylic acid

Four new alkaline-earth metal-based metal-organic frameworks, [Mg-4(TCMTB)(2)(OAc)(2)(DMA)(2)(H2O)(3)](n) (Mg-TCMTB), {[Ca-4(TCMTB)(2)(OH)(DMF)(2)(H2O)(5)] center dot Cl}(n) (Ca-TCMTB), [Sr-4(TCMTB)(2)(OH)(OAc)(DMA)(6)(H2O)](n) (Sr-TCMTB) and [Ba-9(TCMTB)(4)(NO3)(6)(DMA)(14)](n) (Ba-TCMTB) (H3TCMTB = 2,4,6-tris[(4'-carboxyphenoxy)-methyl]- 1,3,5-trimethylbenzene), have been synthesized and structurally characterized. Structural analysis of the MOFs reveals the presence of diverse structures and topologies in these systems due to the conformational flexibility and multiple coordination sites in H3TCMTB. Coordination polymers Mg-TCMTB, Ca-TCMTB and Ba-TCMTB MOFs are three-dimensional frameworks exhibiting 2-fold interpenetration and one-dimensional hexagonal channels, while Sr-TCMTB is a 2-fold interpenetrated layered MOF. The 2D layers in Sr-TCMTB are interconnected through H-O center dot center dot center dot H hydrogen bonds. Increasing ionic radii and coordination number on moving down the group results in the formation of bi-, tetra-and nona-nuclear M-O-M connected inorganic building units. Owing to its smaller size and lower coordination number, framework Mg-TCMTB gives rise to a moderate surface area of 33.0 m(2) g(-1) (SA(BET)) and 93.8 m(2) g(-1) (SA(Lang)) which is the highest observed among all the four MOFs. Emission studies of the new MOFs reveal the presence of strong photoluminescence at 380 nm

Catalysis and CO2 Capture by Palladium-Incorporated Covalent Organic Frameworks

Triazine-based imine and beta-ketoenamine linked covalent organic frameworks (COFs), TAT-DHBD(1) and TAT-TFP(2), have been synthesized from 1,3,5-tris-(4'-aminophenyl)triazine (TAT) and 2,5-dihydroxybenzene-1,4-dicarboxaldehyde (DHBD) or 1,3,5-triformylphloroglucinol (TFP) under solvothermal conditions in dioxane/mesitylene mixture. These COFs exhibit significant surface areas owing to their meso- and micropores. The presence of basic nitrogen sites offers excellent affinity towards Pd nanoparticles and carbon dioxide. Post treatment of COFs 1 and 2 with palladium acetate gives Pd-II/TAT-DHBD(3) and Pd-II/TAT-TFP(4), which on reduction by NaBH4 yields Pd-0/TAT-DHBD(5) and Pd-0/TAT-TFP(6), respectively. The new COFs have been characterized by FTIR, solid-state (CNMR)-C-13 spectroscopy, X-ray photoelectron spectroscopy (XPS), SEM, TEM, and Brunauer-Emmett-Teller (BET) surface area measurements. TEM studies corroborated the uniform distribution of Pd-II and Pd-0 sites in the COFs. Compounds 3-6 are active towards the Suzuki-Miyaura cross-coupling of arenes with meager catalyst leaching even after five cycles. In addition, 4 exhibits CO2 uptake of 11wt% and 7.5wt% at 273 and 298K, respectively, at 1 bar

Synthesis, structure, redox behavior, catalytic activity and DFT study of a new family of ruthenium(III)1-(arylazo)naphtholate complexes

Treatment of [RuCl2(DMSO)(4)] with 1-(arylazo)naphthol ligands in benzene under reflux afford the air stable new ruthenium(III) complexes with general composition [Ru(L-R)(3)] (L = bidentate O, N donor; R = H, CH3, OCH3, Br, NO2) in good yield. The 1-(arylazo)naphthol ligands behave as tris-bidentate 0, N donors via naphtholic proton and azo nitrogen. The molecular and electronic structure of the complexes have been established by elemental analysis and spectral (FT-IR, UV-vis & EPR) methods. DFT calculations were also carried out on the complexes 1 and 3 along with X-ray crystallized geometry of complex 5. These complexes in dichloromethane solution show intense ligand-to-metal charge transfer (LMCT) transitions in the visible region. The absorption and g-tensor value of these complexes (1, 3 & 5) were also computed and compared along with the available experimental results. The redox behavior of the complexes has been investigated by cyclic voltammetry and the potentials are observed with respect to the electronic nature of substituents (R) in the 1-(arylazo)naphthol ligands. These complexes have shown great promise as catalysts for the conversion of aldehydes to primary amides in good yield. (C) 2016 Elsevier B.V. All rights reserved

Alkyl-Chain-Separated Triphenybenzene - Carbazole Conjugates and their Derived Polymers: Candidates for Sensory, Electrical and Optical Materials

Four new triphenylbenzene based carbazoles (THPBCz4, THPBCz6, THPBCz8 and THPBCz10) and polycarbazoles (polyTHPBCz4, polyTHPBCz6, polyTHPBCz8 and polyTHPBCz10), have been synthesized. Photoluminescence spectra of the monomers in dichloromethane exhibit two intense bands at 353 and 369 nm. Two additional bands (410 and 435 nm) are also observed due to intermolecular interactions. These bands are more intense in the case of thin films, indicating stronger pp stacking interactions in the solid state. Due to the extended p-conjugation, the polycarbazoles display two main emission bands (495 and 520 nm) which are red shifted as compared to the monocarbazoles. Due to the presence of emissive platforms such as triarylbenzene and carbazole, both monomers and polymers, function as efficient sensors for the detection of polynitroaromatic analytes (PA, DNT, rho-DNB and m-DNB). The electrochemically polymerized carbazole derivatives showed maximum capacitance of 41 F/g for polyTHPBCz6. The SCLC measurement reveals a maximum mobility of 6 x 10(-6) cm(2)/Vs for polyTHPBCz4 that showed better packing due to flexible alkyl chains that connect the conjugated moieties