Sasanka Dalapati

An Azine-Linked Covalent Organic Framework

Condensation of hydrazine with 1,3,6,8-tetrakis(4-formylphenyl)pyrene under solvothermal conditions yields highly crystalline two-dimensional covalent organic frameworks. The pyrene units occupy the vertices and the diazabutadiene (-C═N-N═C-) linkers locate the edges of rohmbic-shaped polygon sheets, which further stack in an AA-stacking mode to constitute periodically ordered pyrene columns and one-dimensional microporous channels. The azine-linked frameworks feature permanent porosity with high surface area and exhibit outstanding chemical stability. By virtue of the pyrene columnar ordering, the azine-linked frameworks are highly luminescent, whereas the azine units serve as open docking sites for hydrogen-bonding interactions. These synergestic functions of the vertices and edge units endow the azine-linked pyrene frameworks with extremely high sensitivity and selectivity in chemosensing, for example, the selective detection of 2,4,6-trinitrophenol explosive. We anticipate that the extension of the present azine-linked strategy would not only increase the structural diversity but also expand the scope of functions based on this highly stable class of covalent organic frameworks.

Highly Emissive Covalent Organic Frameworks

Highly luminescent covalent organic frameworks (COFs) are rarely achieved because of the aggregation-caused quenching (ACQ) of π-π stacked layers. Here, we report a general strategy to design highly emissive COFs by introducing an aggregation-induced emission (AIE) mechanism. The integration of AIE-active units into the polygon vertices yields crystalline porous COFs with periodic π-stacked columnar AIE arrays. These columnar AIE π-arrays dominate the luminescence of the COFs, achieve exceptional quantum yield via a synergistic structural locking effect of intralayer covalent bonding and interlayer noncovalent π-π interactions and serve as a highly sensitive sensor to report ammonia down to sub ppm level. Our strategy breaks through the ACQ-based mechanistic limitations of COFs and opens a way to explore highly emissive COF materials.

Rational design of crystalline supermicroporous covalent organic frameworks with triangular topologies

Covalent organic frameworks (COFs) are an emerging class of highly ordered porous polymers with many potential applications. They are currently designed and synthesized through hexagonal and tetragonal topologies, limiting the access to and exploration of new structures and properties. Here, we report that a triangular topology can be developed for the rational design and synthesis of a new class of COFs. The triangular topology features small pore sizes down to 12 Å, which is among the smallest pores for COFs reported to date, and high π-column densities of up to 0.25 nm−2, which exceeds those of supramolecular columnar π-arrays and other COF materials. These crystalline COFs facilitate π-cloud delocalization and are highly conductive, with a hole mobility that is among the highest reported for COFs and polygraphitic ensembles.

Two‐Dimensional Tetrathiafulvalene Covalent Organic Frameworks: Towards Latticed Conductive Organic Salts

The construction of a new class of covalent TTF lattice by integrating TTF units into two-dimensional covalent organic frameworks (2D COFs) is reported. We explored a general strategy based on the C2 +C2 topological diagram and applied to the synthesis of microporous and mesoporous TTF COFs. Structural resolutions revealed that both COFs consist of layered lattices with periodic TTF columns and tetragonal open nanochannels. The TTF columns offer predesigned pathways for high-rate hole transport, predominate the HOMO and LUMO levels of the COFs, and are redox active to form organic salts that exhibit enhanced electric conductivity by several orders of magnitude. On the other hand, the linkers between the TTF units play a vital role in determining the carrier mobility and conductivity through the perturbation of 2D sheet conformation and interlayer distance. These results open a way towards designing a new type of TTF materials with stable and predesignable lattice structures for functional exploration.

Two-dimensional sp2 carbon–conjugated covalent organic frameworks

Conjugated covalent networks Although graphene and related materials are two-dimensional (2D) fully conjugated networks, similar covalent organic frameworks (COFs) could offer tailored electronic and magnetic properties. Jin et al. synthesized a fully π-conjugated COF through condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The reactions were reversible, which provides the self-healing needed to form a crystalline material of stacked, π-bonded 2D sheets. Chemical oxidation of this semiconductor with iodine greatly enhanced its conductivity, and the radicals formed on the pyrene centers imparted a high spin density and paramagnetism. Science, this issue p. 673 A fully π-conjugated molecular network attains high electronic spin density and unidirectional spin alignment. We synthesized a two-dimensional (2D) crystalline covalent organic framework (sp2c-COF) that was designed to be fully π-conjugated and constructed from all sp2 carbons by C=C condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The C=C linkages topologically connect pyrene knots at regular intervals into a 2D lattice with π conjugations extended along both x and y directions and develop an eclipsed layer framework rather than the more conventionally obtained disordered structures. The sp2c-COF is a semiconductor with a discrete band gap of 1.9 electron volts and can be chemically oxidized to enhance conductivity by 12 orders of magnitude. The generated radicals are confined on the pyrene knots, enabling the formation of a paramagnetic carbon structure with high spin density. The sp2 carbon framework induces ferromagnetic phase transition to develop spin-spin coherence and align spins unidirectionally across the material.

Anion recognition by simple chromogenic and chromo-fluorogenic salicylidene Schiff base or reduced-Schiff base receptors

This review contains extensive application of anion sensing ability of salicylidene type Schiff bases and their reduced forms having various substituents with respect to phenolic OH group. Some of these molecular systems behave as receptor for recognition or sensing of various anions in organic or aqueous-organic binary solvent mixture as well as in the solid supported test kits. Development of Schiff base or reduced Schiff base receptors for anion recognition event is commonly based on the theory of hydrogen bonding interaction or deprotonation of phenolic -OH group. The process of charge transfer (CT) or inhibition of excited proton transfer (ESIPT) or followed by photo-induced electron transfer (PET) lead to naked-eye color change, UV-vis spectral change, chemical shift in the NMR spectra and fluorescence spectral modifications. In this review we have tried to discuss about the anion sensing properties of Schiff base or reduced Schiff base receptors.

Luminescent Porous Polymers Based on Aggregation-Induced Mechanism: Design, Synthesis and Functions

Enormous research efforts are focusing on the design and synthesis of advanced luminescent systems, owing to their diverse capability in scientific studies and technological developments. In particular, fluorescence systems based on aggregation-induced emission (AIE) have emerged to show great potential for sensing, bio-imaging, and optoelectronic applications. Among them, integrating AIE mechanisms to design porous polymers is unique because it enables the combination of porosity and luminescence activity in one molecular skeleton for functional design. In recent years rapid progress in exploring AIE-based porous polymers has developed a new class of luminescent materials that exhibit broad structural diversity, outstanding properties and functions and promising applications. By classifying the structural nature of the skeleton, herein the design principle, synthetic development and structural features of different porous luminescent materials are elucidated, including crystalline covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and amorphous porous organic polymers (POPs). The functional exploration of these luminescent porous polymers are highlighted by emphasizing electronic interplay within the confined nanospace, fundamental issues to be addressed are disclosed, and future directions from chemistry, physics and materials science perspectives are proposed.

Study of microheterogeneous environment of protein Human Serum Albumin by an extrinsic fluorescent reporter: A spectroscopic study in combination with Molecular Docking and Molecular Dynamics Simulation

We report extrinsic fluorescent probe 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid (DMAPPDA) as a molecular reporter for studying microheterogeneous environment of protein Human Serum Albumin (HSA) via spectral modification of the probe under physiological condition. Steady state emission, fluorescence anisotropy, Red Edge Excitation Shift (REES), far-UV Circular Dichroism (CD), Atomic Force Microscopy (AFM) imaging, time resolved spectral measurements, Molecular Docking and Molecular Dynamics (MD) Simulation techniques have been used to fulfill this achievement. Interaction of the probe with HSA is signaled by the blue shift of the fluorophore emission maxima with enhancement of fluorescence intensity. The increase in steady state anisotropy, REES and fluorescence lifetime values with increasing protein concentrations indicates interaction and movement of the probe from free aqueous media to the more restricted less polar hydrophobic interior of protein. Experimental results obtained from Benesi-Hildebrand plot support the formation of 1:1 HSA-DMAPPDA complex with high binding constant and negative free energy change. Thermal denaturation of the probe bound protein has also been tracked using the spectral response of DMAPPDA. Molecular Docking studies revealed binding of the probe with in the hydrophobic cavity of subdomain IIA of HSA. MD Simulation supports greater stability of HSA-DMAPPDA complex compared to free protein.

A Multifunctional Porous Organic Schottky Barrier Diode

Mesoporous materials: A multifunctional porous organic material (ANPPIT; see picture) has been synthesized and characterized. Multifunctionality of the compound has been determined from nitrogen adsorption, guest-dependent luminescence, and electrical conductivity measurements.

Solvent modulated photophysics of 9-methyl anthroate: exploring the effect of polarity and hydrogen bonding on the emissive state.

Photophysical properties of an anthracene derivative 9-methyl anthroate (9-MA) have been investigated using absorption and emission spectroscopy, in combination with quantum chemical calculations. Solvatochromic effects on the Stokes shifted emission band clearly demonstrate the highly polar character of the excited state, which is also supported by the enhancement of dipole moment of the molecule upon photoexcitation. The emission band has been found to be dependent on polarity and hydrogen-bonding ability of the solvents. Multiple linear regression analysis method has been utilized to rationalize the effect of hydrogen bonding interaction on the emissive state, which was further confirmed by the analysis of the non-radiative decay constants and urea induced H-bonding disruption study. The experimental results correlate well with theoretical predictions obtained via density functional theory (DFT).