Prabhpreet Singh

Organic functionalisation and characterisation of single-walled carbon nanotubes

Since carbon nanotubes (CNTs) display unique structures and remarkable physical properties, a variety of applications have emerged in both materials and life sciences. In terms of applications, the functionalisation of nanotubes is extremely important, as it increases their solubility and processability, and combines the unique properties of single-walled carbon nanotubes (SWCNTs) with those of other classes of materials. A number of methods have been developed, which can be divided into two major approaches: (1) non-covalent supramolecular modifications, and (2) covalent functionalisation. In this tutorial review, we survey the covalent modification of SWCNTs with organic moieties, and illustrate the major analytical techniques routinely used to characterise the functionalised materials.

Synthesis and characterization of nucleobase-carbon nanotube hybrids.

We report the synthesis and characterization of adenine-single-walled carbon nanotube (SWCNT) hybrid materials, where for the first time nucleobases are covalently attached to the exosurface of SWCNTs. The structural properties of all hybrids have been characterized using usual spectroscopic and microscopic techniques. The degree of functional groups for functionalized SWCNTs (f-SWCNTs) 2a and 2b is one adenine group for each 26 and 37 carbon atoms, respectively. Solid-state magic angle spinning (13)C NMR spectroscopy (MAS NMR) and electrochemistry have been also applied for the characterization of these f-SWCNTs. AFM images of f-SWCNT 2b showed an interesting feature of horizontally aligned nanotubes along the surface when deposited on highly oriented pyrolytic graphite surface. Furthermore, we evaluated the coordinating ability of these hybrid materials toward silver ions, and interestingly, we found a pattern of silver nanoparticles localized over the surface of the carbon nanotube network. The presence of aligned and randomly oriented CNTs and their ability to coordinate with metal ions make this class of materials very interesting for applications in the development of novel electronic devices and as new supports for different catalytic transformations.

Formation of Efficient Catalytic Silver Nanoparticles on Carbon Nanotubes by Adenine Functionalization

Stuck together: adenine/carbon nanotube hybrids trigger the formation of controlled-size catalytic silver nanoparticles on the nanotube surface. The catalytic efficiency of the resulting species was assessed in the oxidation of 2-methylhydroquinone to its corresponding benzoquinone, with complete recovery and without loss of activity of the catalyst.

Aggregation Induced Emission Enhancement in Ionic Self-Assembled Aggregates of Benzimidazolium Based Cyclophane and Sodium Dodecylbenzenesulfonate

Cyclophane BIMCP-1 undergoes ionic self-assembly with surfactant sodium dodecylbenzenesulfonate (SDBS) at a concentration far below its CMC value to form aggregates with spherical morphology. The rotational restriction of rings in these aggregates facilitates 32-fold enhancement in emission intensity (AIEE) to allow fluorescence based determination of SDBS with 4 μM (1.4 ppm) as the lowest detection limit. Sodium salts of fatty acids and inorganic anions halides, CN(-), HSO4(-), SO4(2-), H2PO4(-), SCN(-), and NO3(-) do not interfere in the estimation of SDBS.

Ultratrace Detection of Nitroaromatics: Picric Acid Responsive Aggregation/Disaggregation of Self-Assembled p-Terphenylbenzimidazolium-Based Molecular Baskets

1-(p-Terphenyl)-benzimidazolium (TRIPOD-TP) molecules undergo self-assembly to form rodlike structures in aqueous medium, as shown by field-emission scanning electron microscopy, transmission electron microscopy, and dynamic light scattering studies. Upon gradual addition of picric acid (PA), these aggregates undergo an aggregation/disaggregation process to complex morphological structures (10(-12)-10(-10) M PA) and spherical aggregates (10(-9)-10(-8) M PA). These spherical aggregates undergo further dissolution to well-dispersed spheres between 10(-7)-10(-6) M PA. During fluorescence studies, these aggregates demonstrate superamplified fluorescence quenching (>97%) in the presence of 10(-5) to 0.2 equiv of the probe concentration, an unprecedented process with PA. The lowest detection limits by solution of TRIPOD-TP are 5 × 10(-13) PA, 50 × 10(-12) M 2,4-dinitrophenol, 200 × 10(-12) M 2,4,6-trinitrotoluene, and 1 nM 1-chloro-2,4-dinitrobenzene. Paper strips dipped in the solution of TRIPOD-TP demonstrate quantitative fluorescence quenching between 10(-17) and 10(-6) M PA using front-surface steady state studies and can measure as low as 2.29 × 10(-20) g/cm(2) PA.

Carbon Nanotube–Nucleobase Hybrids: Nanorings from Uracil‐Modified Single‐Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have been covalently functionalized with uracil nucleobase. The hybrids have been characterized by using complementary spectroscopic and microscopic techniques including solid-state NMR spectroscopy. The uracil-functionalized SWCNTs are able to self-assemble into regular nanorings with a diameter of 50-70 nm, as observed by AFM and TEM. AFM shows that the rings do not have a consistent height and thickness, which indicates that they may be formed by separate bundles of CNTs. The simplest model for the nanoring formation likely involves two bundles of CNTs interacting with each other via uracil-uracil base-pairing at both CNT ends. These nanorings can be envisaged for the development of advanced electronic circuits.

Perylene Diimide Appended with 8-Hydroxyquinoline for Ratiometric Detection of Cu2+ Ions and Metal Displacement Driven “Turn on” Cyanide Sensing

AbstractPerylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu2+ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show “turn-off” behavior in fluorescence with lowest limit of detection 5 × 10−7 M. The PDI 3 could be further utilized for ratiometric CN− detection colorimetrically and as “turn-on” sensor for CN− detection fluorometrically with lowest limit of detection 8 × 10−6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu2+ recognition event into ratiometric signal. FigurePDI 3 shows ratiometric behavior colorimetrically and “turn-off” behavior in fluorescence towards Cu2+ (lowest limit 5 × 10−7 M). The PDI 3-Cu2+ shows ratiometric CN− detection colorimetrically and “turn-on” sensor for CN− detection fluorometrically (lowest limit 8 × 10−6 M).

Triple-signaling mechanisms-based three-in-one multi-channel chemosensor for discriminating Cu2+, acetate and ion pair mimicking AND, NOR, INH and IMP logic functions

Chemosensor 1 shows three different responses towards Cu2+, acetate and Cu(OAc)2 ion pair at different wavelengths independently in its absorption and fluorescence behaviour following a triple-signaling mechanism, namely, internal charge transfer (ICT), CN rotation and excited state intramolecular proton transfer (ESIPT). Chemosensor 1 shows a blue shift of the absorption band from 337 nm to 308 nm in the presence of Cu2+ ions (ICT). It exhibits a fluorescence ‘turn-off’ response at λem 458 nm in the presence of 1 equivalent of Cu2+ ions. The further addition of Cu2+ (6 equivalents) results in ∼24 times enhancement in the emission intensity at λem 427 nm, mimicking an ‘ON–OFF–ON’ molecular switch (ESIPT and CN rotation). The addition of acetate ions to a solution of 1 results in a red shift of the absorption band from 337 to 360 nm (ICT) and ∼4 times enhancement of the emission intensity at λem 458 nm (ESIPT). On the addition of a Cu(OAc)2 ion pair, 1 shows the apparent effect of Cu2+ (blue shift, 337 to 308 nm) and acetate (red shift, 337 to 380 nm), which indicates the synergistic effect of both Cu2+ and AcO− on each others binding. The potential application of chemosensor 1 for the construction of INHIBIT (INH), IMPLICATION (IMP), AND, NOR, YES and NOT logic gates using Cu2+ and acetate as the inputs and absorbance/emission as the outputs is elaborated.

Novel EDTA-ligands containing an integral perylene bisimide (PBI) core as an optical reporter unit

The synthesis, characterization and metal complexation of a new class of perylene bisimides (PBIs) as an integral part of ethylenediaminetetraacetic acid (EDTA) are reported. The simplest representative, namely derivative 1a, was synthesized both by a convergent as well as a direct approach while the elongated derivatives, 1b and 1c, were obtained only via a convergent synthetic pathway. All these new prototypes of water-soluble perylenes are bolaamphiphiles and were fully characterized by (1)H- and (13)C-NMR spectroscopy, matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and IR spectroscopy. In order to acquaint ourselves with the behaviour in solution of our PBIs bearing dendritic wedges, the simplest derivative, 1a, was chosen and tested by means of UV/Vis and fluorescence spectroscopy as well as by zeta-potential measurements. A photoexcitation induced intramolecular photo-electron transfer (PET) can be observed in these molecules. Therefore their potential applications as sensors can be imagined. Model compound 1a efficiently coordinates trivalent metal cations both in water and dimethyl sulfoxide (DMSO). Significantly, the effects of the complexation strongly depend on the aggregation state of the PBI molecules in solution. As a matter of fact, in water, the presence of M(3+) ions triggers the formation of light emitting supramolecular aggregates (excimers). On the other hand, in DMSO-rich solutions metal complexation leads to the suppression of the PET and leads to a strong fluorescence enhancement.

Self-assembled vesicle and rod-like aggregates of functionalized perylene diimide: reaction-based near-IR intracellular fluorescent probe for selective detection of palladium

Herein, we report design, synthesis, and self-assembly of perylene diimide (PDI) based near-IR intracellular probe (PS-PDI). PS-PDI molecules undergo aggregation to form self-assembled nanospheres and nanorods morphology in THF : H2O (1 : 1) and DMSO : H2O (1 : 9), respectively. The nanospheres have an open hole on surface reminiscent of vesicle structure (with a diameter of internal void in the range of 20-25 nm) whereas lengths of the nanorods extended up to few μm range. The Pd0 based depropargylation leads to de-aggregation of these PS-PDI aggregates into smaller spherical aggregates as evidenced by DLS, SEM, and TEM studies. Interestingly, these aggregates of PS-PDI in solution show highly sensitive behavior in the presence of Pd0 showing absorbance changes in NIR region (λmax = 710 nm) and quenching of emission at λem 630 nm (DMSO : H2O, 1 : 9) with a limit of detection = 6.6 × 10-9 M or at λem 564 nm (THF : H2O, 1 : 1) with limit of detection = 2.1 × 10-8 M. Time and concentration dependent kinetics profiles of PS-PDI aggregates revealed an impressive rate constant value of 0.4 s-1 and 0.21 s-1 (DMSO : H2O, 1 : 9), respectively in fluorescence and UV-Vis spectroscopy using 2 × 10-5 M concentration of Pd0. PS-PDI undergoes rapid internalization into HeLa cells with low cytotoxicity and was successfully used as an intracellular imaging reagent for Pd0 in live HeLa cells. For practical applications, we exploited these nano-aggregates of PS-PDI for estimation of Pd2+ in the presence of a NaBH4-PPh3 mixture, Pd0 in drug and environmental samples, and Pd2+ in urine samples with excellent selectivity and sensitivity.