Covalent organic frameworks are a family of crystalline porous materials with promising applications. Although active research on the design and synthesis of covalent organic frameworks has been ongoing for almost a decade, the mechanisms of formation of covalent organic frameworks crystallites remain poorly understood. Here we report the synthesis of a hollow spherical covalent organic framework with mesoporous walls in a single-step template-free method. A detailed time-dependent study of hollow sphere formation reveals that an inside-out Ostwald ripening process is responsible for the hollow sphere formation. The synthesized covalent organic framework hollow spheres are highly porous (surface area B1,500 m 2 g À 1 ), crystalline and chemically stable, due to the presence of strong intramolecular hydrogen bonding. These mesoporous hollow sphere covalent organic frameworks are used for a trypsin immobilization study, which shows an uptake of 15.5 mmol g À 1 of trypsin.

Covalent organic nanosheets (CONs) have emerged as functional two-dimensional materials for versatile applications. Although π-π stacking between layers, hydrolytic instability, possible restacking prevents their exfoliation on to few thin layered CONs from crystalline porous polymers. We anticipated rational designing of a structure by intrinsic ionic linker could be the solution to produce self-exfoliated CONs without external stimuli. In an attempt to address this issue, we have synthesized three self-exfoliated guanidinium halide based ionic covalent organic nanosheets (iCONs) with antimicrobial property. Self-exfoliation phenomenon has been supported by molecular dynamics (MD) simulation as well. Intrinsic ionic guanidinium unit plays the pivotal role for both self-exfoliation and antibacterial property against both Gram-positive and Gram-negative bacteria. Using such iCONs, we have devised a mixed matrix membrane which could be useful for antimicrobial coatings with plausible medical benefits.

Covalent organic nanosheets (CONs) were synthesised from imide functionalised COFs. TfpBDH-CONs exhibit a "turn-on" detection capability for 2,4,6-trinitrophenol in the solid state, but show a "turn-off" detection in the dispersion state.

Synthetic oligonucleotide analogs have greatly aided our understanding of several biochemical processes. Efficient solid-phase and enzyme-assisted synthetic methods and the availability of modified base analogs have added to the utility of such oligonucleotides. In this review, we discuss the applications of synthetic oligonucleotides that contain backbone, base, and sugar modifications to investigate the mechanism and stereochemical aspects of biochemical reactions. We also discuss interference mapping of nucleic acid-protein interactions; spectroscopic analysis of biochemical reactions and nucleic acid structures; and nucleic acid cross-linking studies.The automation of oligonucleotide synthesis, the development of versatile phosphoramidite reagents, and efficient scale-up have expanded the application of modified oligonucleotides to diverse areas of fundamental and applied biological research. Numerous reports have covered oligonucleotides for which modifications have been made of the phosphodiester backbone, of the purine and pyrimidine heterocyclic bases, and of the sugar moiety; these modifications serve as structural and mechanistic probes. In this chapter, we review the range, scope, and practical utility of such chemically modified oligonucleotides. Because of space limitations, we discuss only those oligonucleotides that contain phosphate and phosphate analogs as internucleotidic linkages. CONTENTS

Canonical purine-pyrimidine base pairs, the key to the complementary hydrogen bonding in nucleic acids, are fundamental molecular recognition motifs crucial for the formation and stability of double-helical DNA. Consequently, focused study and modeling of nucleobase hydrogen-bonding schemes have spawned a vast array of chemical and biophysical investigations. The Watson-Crick, reverse Watson-Crick, Hoogsteen, and reverse Hoogsteen hydrogen-bonding schemes stabilize various nucleic acid structures. As a result, numerous modified bases have been designed to maximize such interactions, addressing specific problems related to base pairing and giving rise to supramolecular ensembles in solution or in the solid state. It is also important to realize that suitably predisposed imino nitrogens and other functional groups present in heterocyclic nucleobases present a versatile molecular framework for the construction of coordination architectures, which may be harnessed to mimic base polyads and higher order nucleic acid structures. Adenine, a purine nucleobase, is an important naturally occurring nitrogen heterocycle present in nucleic acids. It is notable that the adenine unit is also frequently encountered as an inextricable part of enzyme cofactors and second messenger systems, such as NAD(+), FADH(2), and cAMP, which are essential for certain catalytic reactions and biochemical processes. In addition, a crucial catalytic role of the adenine moiety is also observed in group II intron catalysis and at the ribosomal peptidyltransferase center. Such versatile functional roles of the adenine framework serve as an inspiration for addressing research problems, ranging from classical coordination chemistry to the development of new materials. In this Account, we begin by describing the emerging use of adenine nucleobase for the design of metal-nucleobase frameworks. The coordination of metal ions affords a variety of oligomeric and polymeric species; we focus on silver- and copper-based structures and also discuss ferrocenylated adenine tetrads. We then consider the use of supramolecular adenine coordination complexes for transferring molecular properties onto surfaces. This technique is particularly useful for transferring noncovalent interactions, such as van der Waals forces, electrostatic interactions, and hydrogen bonding, to designed architectures in nanoscale applications. Finally, we explore the issue of adenine-based catalytic entities. Here, adenine moieties are first fixed in a polymeric matrix, followed by metalation of the matrix. These metalated adenine-containing polymers are then assayed for catalytic assistance in various chemical and biochemical reactions. Taken together, the versatile coordination abilities and hydrogen-bonding capacity of adenine offer a novel entry point for a natural ligand into materials synthesis.

We are reporting ultrafast charge carrier and charge transfer dynamics of the CdTe quantum dot (QD) and type II CdTe/CdS core-shell QD materials with different shell (CdS) thicknesses. Herein, we have synthesized CdTe and CdTe/CdS core-shell quantum dots by using 3-mercaptopropionic acid as a capping agent. Steady state absorption and emission studies confirmed successful synthesis of CdTe QD and CdTe/CdS core-shell QD materials. Time-resolved emission studies indicate a longer emission lifetime of the CdTe/CdS core-shell as compared to CdTe QD materials, where in both cases only CdTe gets excited. We have carried out femtosecond transient absorption studies of these QD and core-shell materials by exciting them with 400 nm laser light and monitoring the transients in the visible to near-IR region to study charge carrier and charge transfer dynamics in the ultrafast time scale. On laser excitation, electron-hole pairs are generated which are confirmed by induced absorption signal for the charge carriers in the visible and near-IR region and an immediate bleach at excitonic position for both QD and QD core-shell. The carrier relaxation was found to be slower and the carrier lifetime was found to be longer in the QD core-shell as compared to the QD indicating charge transfer from core to shell. Carrier quenching studies have been carried out for both CdTe and CdTe/CdS by using benzoquinone (BQ, electron quencher) and Pyridine (Py, hole quencher) to assign the different relaxation processes. Details about the relaxation of hot carriers and the quenching effect on the relaxation dynamic of the charge carriers have been discussed for both QD and core-shell nanostructures.

The Crystalline Porous Polymeric materials (CPPs) also well known as Covalent Organic Frameworks (COFs) have concerned substantial research interest because of their extensive applications in molecular storage and separation, catalysis, sensing, opto-electronics etc. [1]. The overall properties and real time employments of such materials not only rely on the compositions but also their nano-scale morphology which plays an incredible role [2]. Therefore, an explicit understanding of the morphology-modulation with respect to their constituents is really demanding. This study accounted a detailed molecular level investigation on morphological evaluation in COFs emanates entirely from its primary building units. Here two new highly crystalline, permanently porous imine linked based COFs named 2,3-DhaTta (Surface area 1700 m2/g) and 2,3-DhaTab (Surface area 413 m2/g) was solvothermally synthesised by faintly varying linker core while retaining all other external factors unchanged. These COFs are found to self template into diverge morphologies including ribbons (2,3-DhaTta) and hollow spheres (2,3-DhaTab). Their mechanisms of formation have been thoroughly and systematically investigated where hollow sphere formation in this case was guided by inside out Ostwald Ripening phenomenon. Moreover, based on DFT (Density Functional Theory) study a significant correlation between stacking energy of two adjacent COF layers with their backbone planarity was established which was believed to be the predominant guiding factor for governing their crystallinity, porosity and morphological diversity evaluation [3].

A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggregate/TiO2 hybrid materials. It represents the potential of porphyrin aggregates in biomimetic artificial antenna activity.