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Shiv Nadar University

(SoNS) School of Natural Sciences

In this work, we report a novel donor-acceptor based solution processable low band gap polymer semiconductor, PDPP-TNT, synthesized via Suzuki coupling using condensed diketopyrrolopyrrole (DPP) as an acceptor moiety with a fused naphthalene donor building block in the polymer backbone. This polymer exhibits p-channel charge transport characteristics when used as the active semiconductor in organic thin-film transistor (OTFT) devices. The hole mobilities of 0.65 cm2 V-1 s-1 and 0.98 cm2 V -1 s-1 are achieved respectively in bottom gate and dual gate OTFT devices with on/off ratios in the range of 105 to 10 7. Additionally, due to its appropriate HOMO (5.29 eV) energy level and optimum optical band gap (1.50 eV), PDPP-TNT is a promising candidate for organic photovoltaic (OPV) applications. When this polymer semiconductor is used as a donor and PC71BM as an acceptor in OPV devices, high power conversion efficiencies (PCE) of 4.7% are obtained. Such high mobility values in OTFTs and high PCE in OPV make PDPP-TNT a very promising polymer semiconductor for a wide range of applications in organic electronics. © 2011 The Royal Society of Chemistry.

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Physics

Fulltext

Energy and Environmental Science

High mobility organic thin film transistor and efficient photovoltaic devices using versatile donor-acceptor polymer semiconductor by molecular design

Zinc oxide-organic semiconductor lateral heterostructure based field-effect bipolar transistors (FEBTs) having heterointerfaces approximately midway between the source and drain electrodes are fabricated and characterized. These hybrid FEBTs comprise zinc oxide (ZnO) and p -channel organic semiconductors [Pentacene and α -sexithiophene (6T)] supporting electron transport and hole transport on either side of the heterojunction, respectively. Current flow in the transistor channel is established as a result of carrier injection across the heterointerface followed by recombination. In steady state, such devices possess significant populations of holes and electrons in the transistor channel and operate in bipolar mode. © 2011 American Institute of Physics.

Applied Physics Letters

Electrical characteristics of zinc oxide-organic semiconductor lateral heterostructure based hybrid field-effect bipolar transistors

Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, leading to the formation of Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, can lead to an improvement of the luminescent properties. However, the intensity of electroluminescence was found to decrease drastically after exceeding an optimum concentration of the Er doping. Slow positron implantation spectroscopy (SPIS), both in single (DB) and coincidence (CDB) Doppler broadening mode, was applied to probe processes at a microscopic level which might have an impact on the optical response. It shows that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and also with the improved reverse energy transfer process between Er and Ge.

Materials Science Forum

Structural characterisation of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy

Two anomalous bias dependent resistive peaks induced by the SrTiO 3 structural phase transitions at 55 and 110 K were observed in a LaAlO3/SrTiO3 and Nb:SrTiO3 rectifying junction when the LaAlO3/SrTiO3 was depleted under reverse bias. At these transition temperatures, the barrier between LaAlO3/ SrTiO3 and Nb:SrTiO3 showed abrupt changes in the tunneling energy under forward bias. The peak at 110 K was an insulator-metal phase transition while the peak at 55 K was a metal-insulator one. We propose that the phase transitions of the SrTiO3 substrate influence the charge transfer to the LaAlO3/SrTiO3 layer, giving rise to these anomalous resistive peaks. © 2011 American Institute of Physics.

Metal-insulator transition at a depleted LaAlO3/SrTiO 3 interface: Evidence for charge transfer induced by SrTiO 3 phase transitions

Discontinuous changes in molecular structure (resulting from continuous transformations of molecular coordinates) lead to changes in chemical properties and biological activities that chemists attempt to describe through structure-activity or structure-property relationships (QSAR/QSPR). Such relationships are commonly envisioned in a continuous high-dimensional space of numerical descriptors, referred to as chemistry space. The choice of descriptors defining coordinates within chemistry space and the choice of similarity metrics thus influence the partitioning of this space into regions corresponding to local structural similarity. These are the regions (known as domains of applicability) most likely to be successfully modeled by a structure-activity relationship. In this work the network topology and scaling relationships of chemistry spaces are first investigated independent of a specific biological activity. Chemistry spaces studied include the ZINC data set, a qHTS PubChem bioassay, as well as the space of protein binding sites from the PDB. The characteristics of these networks are compared and contrasted with those of the bioassay SALI subnetwork, which maps discontinuities or cliffs in the structure-activity landscape. Mapping the locations of activity cliffs and comparing the global characteristics of SALI subnetworks with those of the underlying chemistry space networks generated using different representations, can guide the choice of a better representation. A higher local density of SALI edges with a particular representation indicates a more challenging structure-activity relationship using that fingerprint in that region of chemistry space. © 2011 American Chemical Society.

Chemistry

Journal of Physical Chemistry A

Exploration of the topology of chemical spaces with network measures

Experimental charge density distribution in 2, 5-dichloro-1, 4-benzoquinone has been carried out using high resolution X-ray diffraction data at 90 K to quantitatively evaluate the nature of C-Cl · · · O=C halogen bond in molecular crystals. Additionally, the halogen bond is studied from geometrical point of view and the same has been visualized using Hirshfeld surface analysis. The obtained results from experimental charge density analysis are compared with periodic quantum calculations using B3LYP 6-31G(d,p) level of theory. The topological values at bond critical point, three-dimensional static deformation density features and electrostatic potential isosurfaces unequivocally establish the attractive nature of C-Cl · · · O = C halogen bond in crystalline lattice. © 2011 American Chemical Society.

Crystal Growth and Design

Halogen bonding in 2,5-dichloro-1,4-benzoquinone: Insights from experimental and theoretical charge density analysis

Of good report: Synthesis and screening of an 80-member tricarbocyanine library identified CyNAMLA-381 as a near-IR surface-enhanced Raman spectroscopy (SERS) reporter with good signal stability and higher sensitivity than the standard. Encapsulation of CyNAMLA-381 on gold nanoparticles and conjugation to an antibody afforded SERS nanotags with excellent sensitivity, stability, and tumor specificity in xenograft models (see picture). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Angewandte Chemie - International Edition

Ultrasensitive near-infrared Raman reporters for SERS-based in vivo cancer detection

SERS nanotags have been prepared to accomplish the multiplex detection of cancer cells. Herein we evaluated the adequacy of lipoic acid-containing cyanine derivatives (Cy3LA and Cy5LA) to function as multiplex partners with a triphenylmethine Raman reporter (B2LA) under a single excitation wavelength. SERS experiments enabled the multiplex recognition of two different cancer cells with antibody-conjugated nanotags that were derivatized with optimized cyanine and triphenylmethine reporters. © 2011 The Royal Society of Chemistry.

Chemical Communications

Multiplex cancer cell detection by SERS nanotags with cyanine and triphenylmethine Raman reporters

In this paper, we explore the effects of the chain length of simple monohydroxy alcohol (CnOH, 2 ≥ n ≥ 8) and benzyl alcohol (C6H5CH2OH) upon the fluorescence dynamics of a dipolar solute probe, coumarin 153 (C153), in vesicles formed in aqueous solutions of two oppositely charged (cationic and anionic) surfactants in the presence of 0.05 mol kg-1 alcohol. The catanionic vesicles are composed of 70 mol % sodium dodecyl sulfate (SDS) and 30 mol % cetyltrimethylammonium bromide (CTAB). The presence of alcohols of different chain length improves the stability of the catanionic vesicles. Dynamic light scattering (DLS) experiments suggest a gentle increase in the hydrodynamic diameter of the catanionic vesicle with alcohol chain length up to n = 4 and then an abrupt increase for the rest of the alcohols considered. The polarity and dynamics of the catanionic vesicles, probed by the steady-state and time-resolved fluorescence spectroscopy, indicate a signature of confined water. Quantities measured from fluorescence experiments of these vesicles also show a mild variation for alcohols of chain length n ≥ 4, followed by a sudden variation for alcohols with n &gt; 4. Interestingly, pentanol and benzyl alcohol in catanionic vesicles showed roughly similar effects due to their equivalent chain length. All of these data are remarkably correlated with the recently observed depression of the solubility temperature of catanionics with alcohol chain length (Langmuir2009, 25, 12516-12521). © 2011 American Chemical Society.

Journal of Physical Chemistry B

Influence of chain length of alcohols on stokes' shift dynamics in catanionic vesicles

Quantum entanglement plays a crucial role in quantum information, quantum teleportation and quantum computation. The information about the entanglement content between subsystems of the composite system is encoded in the Schmidt eigenvalues. We derive here closed expressions for the spectral density of Schmidt eigenvalues for all three invariant classes of random matrix ensembles. We also obtain exact results for average von Neumann entropy. We find that maximum average entanglement is achieved if the system belongs to the symplectic invariant class. © 2011 IOP Publishing Ltd.