Department of Chemistry

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The phenomenon of intramolecular vibrational energy redistribution (IVR) is at the heart of chemical reaction dynamics. Statistical rate theories, assuming instantaneous IVR, predict exponential decay of the population with the properties of the transition state essentially determining the mechanism. However, there is growing evidence that IVR competes with the reaction timescales, resulting in deviations from the exponential rate law. Dynamics cannot be ignored in such cases for understanding the reaction mechanisms. Significant insights in this context have come from the state space model of IVR, which predicts power law behavior for the rates with the power law exponent, an effective state space dimensionality, being a measure of the nature and extent of the IVR dynamics. However, whether the effective IVR dimensionality can vary with time and whether the mechanism for the variation is of purely quantum or classical origins are issues that remain unresolved. Such multiple power law scalings can lead to surprising mode specificity in the system, even above the threshold for facile IVR. In this work, choosing the well-studied thiophosgene molecule as an example, we establish the anisotropic and anomalous nature of the quantum IVR dynamics and show that multiple power law scalings do manifest in the system. More importantly, we show that the mechanism of the observed multiple power law scaling has classical origins due to a combination of trapping near resonance junctions in the network of classical nonlinear resonances at short to intermediate times and the influence of weak higher-order resonances at relatively longer times.

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Proceedings of the National Academy of Sciences of the United States of America

Dynamical traps lead to the slowing down of intramolecular vibrational energy flow

Graphene was synthesized and used as a counter electrode in place of platinum in dye sensitized solar cells. This study reveals that the graphene synthesized by reduction of graphene oxide still contains functional groups even after reduction. The synthesized graphene counter electrodes were prepared by screen printing fabrication techniques. The influence of temperature variation on the films morphology, crystallinity, and its interfacial adhesiveness to the fluorine doped tin oxide coated glass were studied. Screen printing technique has shown uniform surface, decreased agglomeration of nanoparticles and high film adhesiveness. The screen printed film annealed at 400 degrees C reveals best surface morphology

Investigation of Chemically Synthesized Graphene as Counter Electrode for Dye Sensitized Solar Cells

European Journal of Inorganic Chemistry

Bi38 Oxocarboxylate Cages are Keplerates – Synthesis and Structural Characterization of Two Bi38 Oxocarboxylate Cages

Grayscale (halftone) laser printing is developed as a low-cost and solution processable fabrication method for ITO-free, semi-transparent and conducting Ag electrodes extendable over large area on a flexible substrate. The transmittance and sheet resistance is easily tunable by varying the grayscale value of the color fill between 10% to 20%. The operation of electrodes is demonstrated by fabricating a transparent push button, an electrochromic window and a solar cell. © 2014 The Royal Society of Chemistry.

Journal of Materials Chemistry C

Digital grayscale printing for patterned transparent conducting Ag electrodes and their applications in flexible electronics

A simple method for producing patterned Ag electrodes on transparent and flexible substrates is reported. The process makes use of a laser printed toner as a sacrificial template for an organic precursor, which upon thermolysis and toner lift off produced highly conducting Ag electrodes. Thus, the process takes only a few minutes without any expensive instrumentation. The electrodes exhibited excellent adhesion and mechanical properties, important for flexible device applications. Using Ag patterned electrodes, heaters operating at low voltages, pixelated electrochromic displays as well as organic solar cells have been demonstrated. The method is extendable to produce defect-free patterns over large areas as demonstrated by roll coating. This journal is © the Partner Organisations 2014.

Journal of Materials Chemistry A

Solution processed large area fabrication of Ag patterns as electrodes for flexible heaters, electrochromics and organic solar cells

Accurate characterization and reporting of organic photovoltaic (OPV) device performance remains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using "suitcase sample" approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner. © 2014 Published by Elsevier B.V.

Solar Energy Materials and Solar Cells

Worldwide outdoor round robin study of organic photovoltaic devices and modules

A metal (Au) wire network, nearly invisible to the naked eye, has been realized on common substrates such as glass, to serve as a transparent conducting electrode (TCE). The process involves coating a TiO2 nanoparticle dispersion to a film thickness of 10 m, which following solvent evaporation, spontaneously forms a crackle network; the film is then used as a sacrificial template for metal deposition. The TCE thus formed exhibited visible transmittance of 82% and sheet resistance of 3-6 /square for a metal fill factor of 7.5%. With polyethylene terephthalate substrate, flexible and robust TCE could be produced and with quartz, the spectral range could be widened to cover UV and IR regions. © 2014 IOP Publishing Ltd.

Materials Research Express

Metal wire network based transparent conducting electrodes fabricated using interconnected crackled layer as template

Transparent conducting electrodes (TCEs) have been made on flat, flexible, and curved surfaces, following a crack template method in which a desired surface was uniformly spray-coated with a crackle precursor (CP) and metal (Ag) was deposited by vacuum evaporation. An acrylic resin (CP1) and a SiO 2 nanoparticle-based dispersion (CP2) derived from commercial products served as CPs to produce U-shaped cracks in highly interconnected networks. The crack width and the density could be controlled by varying the spray conditions, resulting in varying template thicknesses. By depositing Ag in the crack regions of the templates, we have successfully produced Ag wire network TCEs on flat-flexible PET sheets, cylindrical glass tube, flask and lens surface with transmittance up to 86%, sheet resistance below 11 ω/□ for electrothermal application. When used as a transparent heater by joule heating of the Ag network, AgCP1 and AgCP2 on PET showed high thermal resistance values of 515 and 409 °C cm2/W, respectively, with fast response (&lt;20 s), requiring only low voltages (&lt;5 V) to achieve uniform temperatures of ∼100 °C across large areas. Similar was the performance of the transparent heater on curved glass surfaces. Spray coating in the context of crack template is a powerful method for producing transparent heaters, which is shown for the first time in this work. AgCP1 with an invisible wire network is suited for use in proximity while AgCP2 wire network is ideal for use in large area displays viewed from a distance. Both exhibited excellent defrosting performance, even at cryogenic temperatures. © 2014 American Chemical Society.

ACS Applied Materials and Interfaces

Spray coating of crack templates for the fabrication of transparent conductors and heaters on flat and curved surfaces

Codimerization of ethylene and various functionalized vinylarenes, 1,3-dienes, or strained alkenes can be carried out in the presence of nickel, ruthenium, or cobalt complexes in very high yields and exceptional regio- and stereoselectivities. Nickel appears to provide the most active catalyst, even though more recent work indicates that the other metals may have unique advantages of their own. Many of these reactions proceed under exceedingly mild conditions (-50. °C to 25. °C, 1. atm of ethylene) to produce valuable intermediates including 3-arylbutenes and skipped 1,4-dienes with a chiral carbon at the benzylic or bis-allylic center. The 3-arylbutenes can be transformed into nonsteroidal antiinflammatory drugs such as ibuprofen, naproxen, and fenoprofen in two steps. Cyclic and acyclic 1,3-dienes also undergo efficient addition of ethylene and terminal alkenes catalyzed by either Ni(II), Ru(II), or Co(II) complexes. The regio- and stereoselectivities of many of these reactions can be controlled by judicious choice of metals and ligands. In addition, the hydrovinylation reaction can be used to generate molecules with an all-carbon quaternary center. These discoveries open expeditious routes to several biologically relevant classes of compounds including bisabolanes, herbindoles, trikentrins, steroid-. D-ring 20(. S) or 20(. R)-derivatives, pyrrolidinoindolines, pseudopterosins, and various members of the serrulatane and amphilectane classes of compounds. © 2014 Elsevier Ltd. All rights reserved.

Comprehensive Organic Synthesis: Second Edition

Hydrovinylation Reactions in Organic Synthesis

A new type of counter electrode for dye sensitized solar cells has been fabricated using a stainless steel sheet as substrate and graphite, graphene and multiwall carbon nanotubes as the catalytic material which applied by screen printing technique. The sheet resistances of the substrates and there influence on the dye sensitized solar cells has been studied. The fabricated counter electrodes i.e. SS-graphite, SS-graphene SS-MWCNT and SS-platinum were tested for their photovoltaic response in the form of dye sensitized solar cells.