Avishek Saha

Increased solubility, liquid-crystalline phase, and selective functionalization of single-walled carbon nanotube polyelectrolyte dispersions.

The solubility of single-walled carbon nanotube (SWCNT) polyelectrolytes [K(THF)]nSWCNT in dimethyl sulfoxide (DMSO) was determined by a combination of centrifugation, UV-vis spectral properties, and solution extraction. The SWCNT formed a liquid crystal at a concentration above 3.8 mg/mL. Also, crown ether 18-crown-6 was found to increase the solubility of the SWCNT polyelectrolytes in DMSO. Raman spectroscopy and near-infrared (NIR) fluorescence analyses were applied to study the functionalization of SWCNTs. Small-diameter SWCNTs were found to be preferentially functionalized when the SWCNT polyelectrolytes were dispersed in DMSO.

Optical bifunctionality of europium-complexed luminescent graphene nanosheets.

Graphene is an intriguing two-dimensional material, which could be modified for achieving tunable properties with many applications. Photoluminescence of graphene due to plasmonic emission is well-known, however, attempts to develop strong luminescent graphene have been difficult. Synthesis of a graphene-based material with a dual optical functionality, namely quenching the fluorescence of organic dyes while maintaining its own self-luminescence, is an interesting and challenging proposition. Here, we demonstrate this optical bifunctionality in a lattice-modified luminescent graphene, where europium(III) cations are complexed with graphene through oxygen functionalities. After excitation at 314 nm, a hypersensitive red emission is observed at 614 and 618 nm showing the complexation of europium(III) with graphene. We demonstrate dual functionality of this graphene by the quenching of luminescence of Rhodamine-B while displaying its own hypersensitive red emission. The decay lifetime observed through the time-resolved spectroscopy confirms its potential for applications in biosensing as well as optoelectronics.

Macroscopic Nanotube Fibers Spun from Single-Walled Carbon Nanotube Polyelectrolytes

In this work, single-walled carbon nanotube (SWCNT) fibers were produced from SWCNT polyelectrolyte dispersions stabilized by crown ether in dimethyl sulfoxide and coagulated into aqueous solutions. The SWCNT polyelectrolyte dispersions had concentrations up to 52 mg/mL and showed liquid crystalline behavior under polarized optical microscopy. The produced SWCNT fibers are neat (i.e., not forming composites with polymers) and showed a tensile strength up to 124 MPa and a Youngs modulus of 14 GPa. This tensile strength is comparable to those of SWCNT fibers spun from strong acids. Conductivities on the order of 10(4) S/m were obtained by doping the fibers with iodine.

Highly luminescent-paramagnetic nanophosphor probes for in vitro high-contrast imaging of human breast cancer cells.

Highly luminescent-paramagnetic nanophosphors have a seminal role in biotechnology and biomedical research due to their potential applications in biolabeling, bioimaging, and drug delivery. Herein, the synthesis of high-quality, ultrafine, europium-doped yttrium oxide nanophosphors (Y(1.9)O(3):Eu(0.1)(3+)) using a modified sol-gel technique is reported and in vitro fluorescence imaging studies are demonstrated in human breast cancer cells. These highly luminescent nanophosphors with an average particle size of ≈6 nm provide high-contrast optical imaging and decreased light scattering. In vitro cellular uptake is shown by fluorescence microscopy, which visualizes the characteristic intense hypersensitive red emission of Eu(3+) peaking at 610 nm ((5)D(0)-(7)F(2)) upon 246 nm UV light excitation. No apparent cytotoxicity is observed. Subsequently, time-resolved emission spectroscopy and SQUID magnetometry measurements demonstrate a photoluminescence decay time in milliseconds and paramagnetic behavior, which assure applications of the nanophosphors in biomedical studies.

Probing a Bifunctional Luminomagnetic Nanophosphor for Biological Applications: a Photoluminescence and Time‐Resolved Spectroscopic Study

and core–shell nanocomposites. [ 4 ] All of these materials are either composites or hybrid structures combining luminescent and magnetic materials individually. In these materials, organic dyes or metal complexes were immobilized on a silica layer, which leads to critical problems of leaching and photobleaching. [ 4a ] Alternatively, semiconductor quantum dots such as CdS, CdSe, and CdTe, have been demonstrated to be highly effective for cellular and animal imaging. [ 5 ] However, the use of such colloids for bioimaging applications suffers from additional issues such as toxicity, harmful solvents, and additives, [ 6 ] low light penetration depth, surface-ligand

Films of Bare Single-Walled Carbon Nanotubes from Superacids with Tailored Electronic and Photoluminescence Properties

The use of single-walled carbon nanotubes (SWCNTs) in fabricating macroscopic devices requires addressing the challenges of nanotube individualization and organization in the desired functional architectures. Previous success in depositing bare SWCNTs from chlorosulfonic acid onto silicon oxide microporous and mesoporous nanoparticles has motivated this study of their deposition onto fused silica substrates. A facile dip-coating method is reported that produces thin homogeneous films in which the carbon nanotubes are not covered by surfactants or shortened by sonication. Photophysical, electrical, chemical, and morphological properties of these SWCNT films have been characterized. When prepared at low densities, the films exhibit near-IR photoluminescence from individualized SWCNTs, whereas when prepared at high densities the films behave as transparent conductors. Sheet resistance of 471 ohm/sq has been achieved with film transmittance of ∼ 86%.

Photodoping and Enhanced Visible Light Absorption in Single‐Walled Carbon Nanotubes Functionalized with a Wide Band Gap Oligomer

Carbon nanotubes feature excellent electronic properties but narrow absorption bands limit their utility in certain optoelectronic devices, including photovoltaic cells. Here, the addition of a wide-bandgap gap oligomer enhances light absorption in the visible spectrum. Furthermore, the oligomer interacts with the carbon nanotube through a peculiar charge transfer, which provides insight into Type II heterojunctions.

Three-dimensional solvent-vapor map generated by supramolecular metal-complex entrapment.

Supramolecular assemblies have become increasingly popular over the past few years, especially in areas such as catalysis, gas sequestration, and separation. Similarly, interesting approaches for the detection of toxic gases and vapors of volatile organic compounds (VOCs) have been studied to develop an artificial nose that is capable of identifying these species in an unambiguous and simple way. The use of supramolecular and crystalline arrays of metal complexes with electronic transitions that are sensitive to the presence of a variety of volatile molecules, has received considerable attention. However, although metal complexes of platinum, gold, palladium, and copper have been widely employed for vapor detection, rhenium has been rarely used. Herein, we propose to use a zeolite framework for the supramolecular assembly of rhenium complexes with applications to vapor sensing. Zeolites are aluminosilicates with a repeating microporous structure composed of {AlO4} and {SiO4} building blocks. The internal framework is a network of cavities (supercages) that are interconnected by channels (Figure 1a). This architecture allows zeolites to act as molecular sieves, with applications ranging from catalysis to light-harvesting systems. Because of their porous structure, ion-exchange properties, and molecular and size recognition, many ions and molecules have been immobilized within zeolites. Particularly relevant for this research, the photoluminescent tris(2,2’-bipyridine)ruthenium(II) complex ([Ru(bpy)3] ) has been encapsulated in NaY and thoroughly studied. As the pore diameter of the NaY framework is smaller than the diameter of [Ru(bpy)3] , this molecule is synthesized in situ by a ship-in-the-bottle method. This method involves the loading of NaY with a ruthenium salt, followed by the addition of 2,2’-bipyridine as a ligand. The [Ru(bpy)3] 2+ complex is formed inside the supercage, and therefore it becomes entrapped within the zeolite. The material is fundamentally composed of a zeolite framework, with the supercages occupied by individual [Ru(bpy)3] 2+ ions, thus forming a true solid solution. Inspired by the aforementioned reports, we used the shipin-the-bottle method to synthesize [Re(phen)(CO)3Cl] (phen= 1,10-phenanthroline) in the cavities of the NaY zeolite. The ligands and the metal react in the NaY supercages to form the [Re(phen)(CO)3Cl] complex. The supercages of the NaY zeolite have a diameter of approximately 13 (large enough to accommodate the complex with a diameter of ca. 9 ) and pore entrances of approximately 7.4 . Therefore, the rhenium complex can fit into the supercage, but once it has been entrapped inside, it is too large to diffuse out of the cage through the pore entrance. To the best of our knowledge, Figure 1. Effect of solvent vapors on the photophysical properties of [Re(phen)(CO)3Cl]@NaY. a) Representation of the NaY zeolite showing one of the supercavities where [Re(phen)(CO)3Cl] can be entrapped. b) Photoluminescence spectra of [Re(phen)(CO)3Cl]@NaY upon treatment with different solvent vapors showing the change in emission intensity (no vapor: material before exposure to vapor, with a photoluminescence adjusted to unity). c) The normalized photoluminescence, which was obtained from the spectra in (b), emphasizes the change in photoluminescence maxima with different vapors. d) Timeresolved photoluminescence decays of [Re(phen)(CO)3Cl]@NaY under different solvent vapors. e) Digital photographs of vapor-treated [Re(phen)(CO)3Cl]@NaYmaterial under UV light. DMF=N,N-dimethylformamide, DMSO=dimethyl sulfoxide.

Single-walled carbon nanotubes shell decorating porous silicate materials: A general platform for studying the interaction of carbon nanotubes with photoactive molecules

Single-walled carbon nanotubes (SWCNTs) have been deposited onto the external surface of porous silicate materials by deposition from a solution of individualized, protonated SWCNTs in chlorosulfonic acid. It is demonstrated that the deposited SWCNTs can be deprotonated on the silicate surface, yielding a microporous or mesoporous material with individual or small bundles of SWCNTs. These carbon nanotubes present all the spectral characteristics of pristine SWCNTs, including van Hove transitions, Raman and NIR photoluminescence. Furthermore, it is shown that these materials can be used as scaffolds to study the interaction of SWCNTs with photoactive molecules loaded in the cavities of the porous silicate materials. As a proof-of-concept, we showed that the photoluminescence of tris(2,2′-bipyridine)ruthenium(II) can be quenched by protonated SWCNTs in the nearby surface decreasing its lifetime by nearly two orders of magnitude. This represents a novel application for these materials, especially considering the large amount of different molecules that can be immobilized in the internal cavities of these porous silicates.

Understanding Charge-Transfer Characteristics in Crystalline Nanosheets of Fullerene/(Metallo)porphyrin Cocrystals

Cocrystals in the form of crystalline nanosheets comprised of C70 and (metallo)porphyrins were prepared by using the liquid-liquid interfacial precipitation (LLIP) method where full control over the morphologies in the C70/(metallo)porphyrins nanosheets has been accomplished by changing the solvent and the relative molar ratio of fullerene to (metallo)porphyrin. Importantly, the synergy of integrating C70 and (metallo)porphyrins as electron acceptors and donors, respectively, into nanosheets is substantiated in the form of a near-infrared charge-transfer absorption. The presence of the latter, as reflection of ground-state electron donor-acceptor interactions in the nanosheets, in which a sizable redistribution of charge density from the electron-donating (metallo)porphyrins to the electron-accepting C70 occurs, leads to a quantitative quenching of the localized (metallo)porphyrin fluorescence. Going beyond the ground-state characterization, excited-state electron donor-acceptor interactions are the preclusion to a full charge transfer featuring formation of a radical ion pair state, that is, the one-electron reduced fullerene and the one-electron oxidized (metallo)porphyrin.