Anshu Kumar

Single step reductive polymerization of functional 3,4-propylenedioxythiophenes via direct C–H arylation catalyzed by palladium acetate

In this Communication we report a single step reductive polymerization of ProDOT derivatives which is compatible with functional side chains and is amenable for scale-up.

Sunlight Induced Preparation of Functionalized Gold Nanoparticles as Recyclable Colorimetric Dual Sensor for Aluminum and Fluoride in Water

A sunlight induced simple green route has been developed for the synthesis of polyacrylate functionalized gold nanoparticles (PAA-AuNPs), in which poly(acrylic acid) functions as a reducing as well as stabilizing agent. This material has been characterized on the basis of spectroscopic and microscopic studies; it exhibited selective colorimetric detection of Al3+ in aqueous media, and the Al3+ induced aggregated PAA-AuNPs exhibited detection of F- with sharp color change and high selectivity and sensitivity out of a large number of metal ions and anions tested. The mechanistic study revealed that, for Al3+, the color change is due to a shift of the SPR band because of the Al3+ induced aggregation of PAA-AuNPs, whereas for F-, the reverse color change (blue to red) with return of the SPR band to its original position is due to dispersion of aggregated PAA-AuNPs, as F- removes Al3+ from the aggregated species by complex formation. Only concentration-dependent fluoride ion can prevent Al3+ from aggregating PAA-AuNPs. The method is successfully used for the detection of F- in water collected from various sources by the spiking method, in toothpastes of different brands by the direct method. The solid Al3+-PAA-AuNPs were isolated, adsorbed on ZIF@8 (zeolitic imidazolate framework) and on a cotton strip, and applied as solid sensing material for detection of F- in aqueous media.

Correlation between Photovoltaic Performance and Interchain Ordering Induced Delocalization of Electronics States in Conjugated Polymer Blends

In this paper we correlate the solar cell performance with bimolecular packing of donor:acceptor bulk heterojunction (BHJ) organic solar cells (OSCs), where interchain ordering of the donor molecule and its influence on morphology, optical properties, and charge carrier dynamics of BHJ solar cells are studied in detail. Solar cells that are fabricated using more ordered defect free 100% regioregular poly(3-hexylthiophene) (DF-P3HT) as the donor polymer show ca. 10% increase in the average power conversion efficiency (PCE) when compared to that of the solar cell fabricated using 92% regioregularity P3HT, referred to as rr-P3HT. EQE and UV-vis absorption spectrum show a clear increase in the 607 nm vibronic shoulder of the DF-P3HT blend suggesting better interchain ordering which was also reflected in the less Urbach energy (Eu) value for this system. The increase in ordering inside the blend has enhanced the hole-mobility which is calculated from the single carrier device J-V characteristics. Electroluminance (EL) studies on the DF-P3HT system showed a red-shifted peak when compared to rr-P3HT-based devices suggesting low CT energy states in DF-P3HT. The morphologies of the blend films are studied using AFM and grazing-incidence wide-angle X-ray scattering (GIWAXS) suggesting increase in the roughness and phase segregation which could enhance the internal scattering of the light inside the device and improvement in the crystallinity along alkyl and π-stacking direction. Hence, higher PCE, lower Eu, red-shifted EL emission, high hole-mobility, and better crystallinity suggest improved interchain ordering has facilitated a more delocalized HOMO state in DF-P3HT-based BHJ solar cells.

Continuous-Flow Synthesis of Regioregular Poly(3-Hexylthiophene): Ultrafast Polymerization with High Throughput and Low Polydispersity Index

Regioregular poly(3-hexylthiophene), rr-P3HT, has been commonly synthesized using Grignard metathesis (GRIM) polymerization and is used as an active material for large area printing of various optoelectronic devices. Batch to batch reproducibility which is very crucial for the development of a large area printing technology for any material still remains one of the major challenges for bulk synthesis. This is due to the insolubility of the GRIM catalyst (1,3-bis (diphenylphosphino)propane nickel(II) chloride) in polymerization solvents. In this article, we have successfully developed a continuous-flow process for the ultrafast syntheses of rr-P3HT with high throughput and low polydisper-sity index (PDI). The key to success was the use of 3,4-ethylenedioxythiophene, EDOT, as an inert solvent for dissolving the GRIM catalyst. We could successfully carry out the flow syntheses of rr-P3HT at high concentration (500 mM monomer solution) with low PDI (~1.2) along with good batch to batch reproducibility and high throughput of 32.8 g per channel per hour for rr-P3HT. The combination of higher monomer concentration with ultrafast polymerization resulted in an efficient process for the large-scale syntheses of rr-P3HT with reduced chemical waste. Furthermore, the optical studies along with electrical characterization indicated better packing and higher charge carrier mobility as compared to the commercial samples with high polydispersity index.

Gate dielectric surface treatments for performance improvement of poly(3-hexylthiophene-2,5-diyl) based organic field-effect transistors

We report on enhanced performance in poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic field effect transistors (OFETs) achieved by improvement in hole transport along the channel near the insulator/semiconductor (I/S) interface. The improvement in hole transport is demonstrated to occur very close to the I/S interface, after treatment of the insulator layer with sodium dodecyl sulfate (SDS). SDS is an anionic surfactant, with negatively charged heads, known for formation of micelles above critical micelle concentration (CMC), which contribute to the passivation of positively charged traps. Investigation of field-effect mobility (μFET) as a function of channel bottleneck thickness in OFETs reveals the favorable gate voltage regime where mobility is the highest. In addition, it shows that the gate dielectric surface treatment not only leads to an increase in mobility in that regime, but also displaces charge transport closer to the interface, hence pointing toward passivation of the charge traps at I/S interface. OFETs with SDS treatment were compared with untreated and vitamin C or hexadecyltrimethylammonium bromide (CTAB) treated OFETs. All the treatments resulted in significant improvements in specific dielectric capacitance, μFET, on/off current ratio and transconductance.

New Route for Synthesis of Fluorescent SnO2 Nanoparticles for Selective Sensing of Fe(III) in Aqueous Media

A simple new route for synthesis of fluorescent SnO2 and its application as an efficient sensing material for Fe3+ in aqueous media is reported. The fluorescent SnO2 nanoparticles were obtained by oxidation of SnCl2, which when used as reducing agent for the reduction of organic nitro compounds to corresponding amino compounds in ethanol. The SnO2 nanoparticles have been characterized on the basis of powder-XRD, IR, UV-Vis, TEM, FESEM and EDX analysis and found that this material is highly fluorescent in aqueous media. Detail study revealed that this material functions as a selective probe for Fe3+ out of a large number of metal ions used. The oxygen vacancies (defects) generated on the surface of the SnO2 during synthesis, are the source of emission due to recombination of electrons with the photo-excited hole in the valance bond. The quenching of emission intensity in presence of Fe3+ is due to the nonradiative recombination of electrons and holes at the surface. This material is used for estimation of Fe3+ in real samples such as drinking water, tap water and soil.

Surfactant-monomer interactions: Towards oxidative surface polymerization of transparent conducting polymers

Surface pressure-molecular area (π-A) isotherms of mixed Langmuir monolayers of stearic acid (StA) and monomers based on 3,4-alkylenedioxythiophene (ADOTs), have been studied. Preliminary results show less (more) increase in A than expected, with increase in molar concentration for monomer M1 viz. 3,4-ethylenedioxythiophene (EDOT) (its long chain counterpart, M2). Presence of ferric chloride in subphase causes A to increase considerably for M1, but has no effect on M2. Moreover, unlike in M1, systematic decrease in slope m of ‘liquid’ L2, L2′ phases and ‘solid’ S phase with increase in concentration of M2 indicate decreased complexity of system compared to StA. Again, in presence of ferric chloride, m was found to decrease in M1, but remain unchanged in M2. Results indicate strong interplay of hydrophobic and hydrophilic interactions at air-water interface, mediated through probable interaction with subphase ions and hydrocarbon chains. Findings are a first step towards understanding structural changes oc...

Green route for synthesis of multifunctional fluorescent carbon dots from Tulsi leaves and its application as Cr(VI) sensors, bio-imaging and patterning agents

We report a one pot green strategy for the synthesis of carbon dots using tulsi leaves and their potential application in sensing of Cr(VI) selectively. The detection mechanism is based on the phenomenon called inner filter effect (IFE) and a good linear static quenching was observed in the range of 1.6 μM to 50 μM with a detection limit of 4.5 ppb. The reversible switching in fluorescence has been tested and a good recovery in fluorescence was observed up to three consecutive cycles upon addition of ascorbic acid as reducing agent. Also the low toxicity, high fluorescence and photostabilty of the CDs make them excellent imaging and patterning agent. The acid and alkali resistant property of these CDs makes it suitable for real sample analysis. The fluorescent CDs were applied for successful detection of Cr(VI) in water with spike-recoveries ranging from 93 to 99%.