K. Venkata Rao

Supramolecular Hydrogels and High‐Aspect‐Ratio Nanofibers through Charge‐Transfer‐Induced Alternate Coassembly

Weak charge-transfer interactions between electron-rich and electron-deficient aromatic molecules have been extensively used for the design of various supramolecular assemblies in solution, such as rotaxanes, catenanes, and foldamers. The conformation of various donor–acceptor (D–A) polymers in solution has been tuned by chargetransfer interactions in synergy with either solvophobic or ion-binding interactions. In addition, extended solid-phase assemblies of alternate donor and acceptor molecules for device applications were attained by cocrystallization and liquid-crystalline mesophase coassembly. Columnar mesophases of alternate donor and acceptor molecules have enhanced columnar organization and higher charge-carrier mobilities compared to their individual components. 1D self-assembled nanowires based on organic p-conjugated systems have attracted a great deal of attention in recent years in the field of organic and supramolecular electronics. 10] Several approaches, which make use of hydrogenbonding and p-stacking interactions, have been used to design self-assembled fibers of donor–acceptor arrays, and create supramolecular p–n heterojunctions for photovoltaics. However, use of charge-transfer interactions for the design of two-component, alternate 1D supramolecular fibers of donor and acceptor molecules in solution is difficult to achieve, as the orthogonal self-assembly (phase separation) of individual components may prevent their efficient coassembly, and hence a careful design of monomers is required. 1D charge-transfer nanofibers are expected to exhibit better conductivity caused by the directional movement of their high-density charge carriers and a well-ordered, stronger p-stacked architecture as a result of better p overlapping of face-to-face-packed aromatic molecules. 13] These observations prompted us to investigate whether nanofibers of alternate donor and acceptor molecules coassembled through charge-transfer interactions can be constructed using supramolecular chemistry design principles. Herein, we show that high-aspect-ratio cylindrical micelles and hydrogels of a donor–acceptor charge-transfer complex can be constructed by self-assembly in water. Although a variety of peptide and rod–coil amphiphiles, as well as sugar derivatives, have been reported to form hydrogels, this is the first report of hydrogel formation that exploits charge-transfer interactions between chromophores. We synthesized a donor–acceptor pair, a coronene tetracarboxylate tetrapotassium salt (CS), and a dodecylfunctionalized methyl viologen derivative (DMV) for the design of coassembled nanostructures (Scheme 1). After

Noncovalent functionalization, exfoliation, and solubilization of graphene in water by employing a fluorescent coronene carboxylate.

Single-layer graphene stabilization: An efficient methodology to make stable aqueous solutions of single-layer graphene has been demonstrated by exploiting charge-transfer interactions with a coronene tetracarboxylate acceptor molecule (see figure). Microscopic studies reveal exfoliation of few-layer graphene and selective stabilization of single-layer graphene in large quantities.

Light-Harvesting Hybrid Assemblies

Light-harvesting hybrids have gained much importance as they are considered as potential mimics for photosynthetic systems. In this Concept article we introduce the design concepts involved in the building up of light-harvesting hybrids; these resemble the well-studied organic-based assemblies for energy transfer. We have structured this article into three parts based on the strategies adopted in the synthesis of hybrid assemblies, as covalent, semicovalent, and noncovalent procedures. Furthermore, the properties and structural features of the hybrids and analogous organic assemblies are compared. We also emphasize the challenges involved in the processability of these hybrid materials for device applications and present our views and results to address this issue through the design of soft-hybrids by a solution-state, noncovalent, self-assembly process.

Highly pure solid-state white-light emission from solution-processable soft-hybrids.

Highly pure and solution processable white-light-emitting hybrids are presented. These soft-hybrids are designed by an organic-inorganic supramolecular co-assembly in water. White-light emission is achieved by partial energy transfer (ET) between donor and acceptor molecules anchored on the inorganic component. The unique and remarkable processability feature of these hybrids is demonstrated by painting/writing onto large glass and flexible plastic substrates.

Guest‐Responsive Reversible Swelling and Enhanced Fluorescence in a Super‐Absorbent, Dynamic Microporous Polymer

A swell idea! The guest-responsive reversible swelling and fluorescence enhancement of a dynamic, microporous polymer network is presented. Guest-induced breathing of hydrophobic pores imparts multi-functional properties, such as super-absorbency, phase-selective swelling of oil from water and encapsulation of C(60) (see figure), to this soft micro-porous organic polymer.

A Simple Method of Separating Metallic and Semiconducting Single-Walled Carbon Nanotubes Based on Molecular Charge Transfer

Interaction of as-prepared single-walled carbon nanotubes (SWNTs), containing a mixture of metallic and semiconducting species with the potassium salt of coronene tetracarboxylic acid, I, in an aqueous medium provides a simple method of separating semiconducting and metallic species. The metallic nanotubes precipitate out on interaction with I while the semiconducting nanotubes remain in solution. The method avoids centrifugation and is amenable for large-scale separation and can be used as a routine laboratory procedure. Interestingly, interaction with strong electron acceptor molecules brings about metal-semiconductor transitions in SWNTs.

Supramolecular Alternate Co-Assembly through a Non-Covalent Amphiphilic Design: Conducting Nanotubes with a Mixed D–A Structure

Mixing it up! The supramolecular alternate co-assembly of extended π-conjugated donor (D) and acceptor (A) molecules (i.e., oligo(phenylenevinylene) and perylenebisimide, respectively), to 1-D nanotubes with an unprecedented mixed stack D-A molecular structure is presented, through a non-covalent amphiphilic design strategy, which results in the formation of hydrogels with remarkable mechanical properties (see scheme).

Synthesis and Controllable Self-Assembly of a Novel Coronene Bisimide Amphiphile

The synthesis of an amphiphilic coronene bisimide (Amph-CBI) and its self-assembly in THF/water through pi-pi stacking and solvophobic interactions are reported. Spectroscopic and microscopic studies revealed a bilayer like self-assembly of the coronene amphiphile to different kinds of one-dimensional nanostructures, such as nanotubes and nanotapes, which can be controlled by solvent composition.

High‐Mobility Field Effect Transistors Based on Supramolecular Charge Transfer Nanofibres

Self-assembled charge transfer supramolecular nanofibres of coronene tetracarboxylate (CS) and dodecyl substituted unsymmetric viologen derivative (DMV) behave as active channel in field effect transistors exhibiting high mobility. These devices work in ambient conditions and can regenerate in the presence of a single drop of water.

Extended phenylene based microporous organic polymers with selective carbon dioxide adsorption

Two microporous conjugated polymers with extended phenylene backbones have been synthesized through Suzuki cross-coupling reactions. The structure and the pores of the polymers have been controlled by the use of para- and meta-structure directing 1,3,5-triphenyl tribromide monomers. Gas sorption studies revealed an unprecedented CO2 selectivity over N2 for these conjugated polymer networks. The networks have furthermore been tested as hydrogen storage materials and showed significant hydrogen uptake at high pressures.