Binder driven self-assembly of metal-organic cubes towards functional hydrogels.

The process of assembling astutely designed, well-defined metal-organic cube (MOC) into hydrogel by using a suitable molecular binder is a promising method for preparing processable functional soft materials. Here, we demonstrate charge-assisted H-bonding driven hydrogel formation from Ga3+-based anionic MOC ((Ga8(ImDC)12)12-) and molecular binders, like, ammonium ion (NH4+), N-(2-aminoethyl)-1,3-propanediamine, guanidine hydrochloride and ß-alanine. The morphology of the resulting hydrogel depends upon the size, shape and geometry of the molecular binder. Hydrogel with NH4+ shows nanotubular morphology with negative surface charge and is used for gel-chromatographic separation of cationic species from anionic counterparts. Furthermore, a photo-responsive luminescent hydrogel is prepared using a cationic tetraphenylethene-based molecular binder (DATPE), which is employed as a light harvesting antenna for tuning emission colour including pure white light. This photo-responsive hydrogel is utilized for writing and preparing flexible light-emitting display.

Solvent-Modulated Emission Properties in a Superhydrophobic Oligo( p-phenyleneethynylene)-Based 3D Porous Supramolecular Framework.

A chromophoric oligo( p-phenyleneethynylene) (OPE) bola-amphiphile with dioxyoctyl side chains (H2OPE-C8) has been self-assembled with CdII to form a 1D coordination polymer, {Cd(OPE-C8)(DMF)2(H2O)} (1), which is further interdigitated to form a 2D network. Such 2D networks are further interwoven to form a 3D supramolecular framework with surface-projected alkyl chains. The desolvated framework showed permanent porosity, as realized from the CO2 adsorption profile. 1 showed high water contact angles, portraying its superhydrophobic nature. 1 also showed a linker-based cyan luminescence. Solvent removal led to a bathochromic shift in emission into the green region. Resolvation with N, N-dimethylformamide brought back the original cyan emission, whereas for tetrahydrofuran, ethanol, and methanol, it persisted at an intermediate state. Density functional theory calculations unraveled that, twisting of the OPE phenyl rings generated the red shift in emission.

Self-cleaning MOF: realization of extreme water repellence in coordination driven self-assembled nanostructures.

Bio-inspired self-cleaning surfaces have found industrial applications in oil-water separation, stain resistant textiles, anti-biofouling paints in ships etc. Interestingly, self-cleaning metal-organic framework (MOF) materials having high water contact angles and corrosion resistance have not been realized so far. To address this issue, we have used the fundamentals of self-assembly to expose hydrophobic alkyl chains on a MOF surface. This decreases the surface free energy and hence increases hydrophobicity. Coordination directed self-assembly of dialkoxyoctadecyl-oligo-(p-phenyleneethynylene)dicarboxylate (OPE-C18 ) with ZnII in a DMF/H2O mixture leads to a three dimensional supramolecular porous framework {Zn(OPE-C18)·2H2O} (NMOF-1) with nanobelt morphology. Inherently superhydrophobic and self-cleaning NMOF-1 has high thermal and chemical stability. The periodic arrangement of 1D Zn-OPE-C18 chains with octadecyl alkyl chains projecting outward reduces the surface free energy leading to superhydrophobicity in NMOF-1 (contact angle: 160-162°). The hierarchical surface structure thus generated, enables NMOF-1 to mimic the lotus leaf in its self-cleaning property with an unprecedented tilt angle of 2°. Additionally, superhydrophobicity remains intact over a wide pH range (1-9) and under high ionic concentrations. We believe that such a development in this field will herald a new class of materials capable of water repellent applications.

High aspect ratio, processable coordination polymer gel nanotubes based on an AIE-active LMWG with tunable emission.

A new TPE based low molecular weight gelator (LMWG) which displays both AIE and MCIE phenomena in gel state has been synthesized. LMWG self-assembles to form 1D nanofibers which undergo morphology transformation to coordination polymer gel (CPG) nanotubes upon metal ion coordination. CPG shows enhanced mechanical stability along with tunable emission properties.

Highly Luminescent Microporous Organic Polymer with Lewis Acidic Boron Sites on the Pore Surface: Ratiometric Sensing and Capture of F(-) Ions.

Reversible and selective capture/detection of F(-) ions in water is of the utmost importance, as excess intake leads to adverse effects on human health. Highly robust Lewis acidic luminescent porous organic materials have potential for efficient sequestration and detection of F(-) ions. Herein, the rational design and synthesis of a boron-based, Lewis acidic microporous organic polymer (BMOP) derived from tris(4-bromo-2,3,5,6-tetramethylphenyl)boron nodes and diethynylbiphenyl linkers with a pore size of 1.08 nm for selective turn-on sensing and capture of F(-) ion are reported. The presence of a vacant pπ orbital on the boron center of BMOP results in intramolecular charge transfer (ICT) from the linker to boron. BMOP shows selective turn-on blue emission for F(-) ions in aqueous mixtures with a detection limit of 2.6 µM. Strong B-F interactions facilitate rapid sequestration of F(-) by BMOP. The ICT emission of BMOP can be reversibly regenerated by addition of an excess of water, and the polymer can be reused several times.

Tunable emission in lanthanide coordination polymer gels based on a rationally designed blue emissive gelator.

Rational design and synthesis of a new low molecular weight gelator (LMWG) having 9,10-diphenylanthracene core and terminal terpyridine is reported. Tb(III) and Eu(III) ion coordination to a LMWG results in green and pink emissive coordination polymer gels, respectively, with coiled nanofiber morphology. Further, control over stoichiometry of LMWG:Tb(III):Eu(III) leads to yellow and white light emitting bimetallic gels.

Stabilization of Cu2O nanoparticles on a 2D metal-organic framework for catalytic Huisgen 1,3-dipolar cycloaddition reaction.

We report a simple methodology for the stabilization of Cu2O nanoparticles of size 2-4 nm on the polar pore surface of a 2D metal-organic framework, {[Zn(Himdc)(bipy)0.5]·DMF} (1). For the first time, a Cu2O@1a (1a: desolvated 1) composite has been utilized as a recyclable catalyst for the Huisgen 1,3-dipolar cycloaddition reaction of terminal alkynes and aliphatic/aromatic azides for the synthesis of 1,2,3-triazoles.

Amide functionalized microporous organic polymer (Am-MOP) for selective CO2 sorption and catalysis.

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (-CONH-) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N2, Ar, and O2. The CO2 molecule interacts with amide functional groups via Lewis acid-base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.

Flexible and rigid amine-functionalized microporous frameworks based on different secondary building units: supramolecular isomerism, selective CO(2) capture, and catalysis.

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH2 bdc)(bphz)0.5 ]⋅DMF⋅H2 O}n (NH2 bdc=2-aminobenzenedicarboxylic acid, bphz=1,2-bis(4-pyridylmethylene)hydrazine) composed of a mixed-ligand system. The first isomer, with a paddle-wheel-type Cd2 (COO)4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a µ-oxo-bridged Cd2 (µ-OCO)2 SBU. Both frameworks are two-fold interpenetrated and the pore surface is decorated with pendant -NH2 and NN functional groups. Both the frameworks are nonporous to N2 , revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double-step hysteretic CO2 adsorption profile, whereas the second isomer shows a typical type I CO2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO2 among other gases (N2 , O2 , H2 , and Ar), which has been correlated to the specific interaction of CO2 with the -NH2 and NN functionalized pore surface. DFT calculations for the oxo-bridged isomer unveiled that the -NH2 group is the primary binding site for CO2 . The high heat of CO2 adsorption (ΔHads =37.7 kJ mol(-1) ) in the oxo-bridged isomer is realized by NH2 ⋅⋅⋅CO2 /aromatic π⋅⋅⋅CO2 and cooperative CO2 ⋅⋅⋅CO2 interactions. Further, postsynthetic modification of the -NH2 group into -NHCOCH3 in the second isomer leads to a reduced CO2 uptake with lower binding energy, which establishes the critical role of the -NH2 group for CO2 capture. The presence of basic -NH2 sites in the oxo-bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.

Porous graphene frameworks pillared by organic linkers with tunable surface area and gas storage properties.

We report the design and synthesis of two porous graphene frameworks (PGFs) prepared via covalent functionalization of reduced graphene oxide (RGO) with iodobenzene followed by a C-C coupling reaction. In contrast to RGO, these 3D frameworks show high surface area (BET, 825 m(2) g(-1)) and pore volumes due to the effect of pillaring. Interestingly, both the frameworks show high CO2 uptake (112 wt% for PGF-1 and 60 wt% for PGF-2 at 195 K up to 1 atm). PGFs show nearly 1.2 wt% H2 storage capacity at 77 K and 1 atm, increasing to ∼1.9 wt% at high pressure. These all carbon-based porous solids based on pillared graphene frameworks suggest the possibility of designing related several such novel materials with attractive properties.