AIE Property and Application of Thienyl-Containing 1,3-Butadiene Derivatives
Beijing Institute of Technology (BIT), China
Due to consisting of large planar aromatic rings, the conventional fluorescent molecules easily undergo intermolecular π–π interactions in the aggregate state. The close vicinity of these chromophores often induces non-radiative energy transfer resulting in drastic reduction of the luminescence signals [Aggregation-Caused Quenching (ACQ)]. The emergence of luminogens with Aggregation-Induced Emission (AIE) or Aggregation-Enhanced Emission (AEE) characteristics discovered by Prof. Tang in 2001 can circumvent the ACQ problem. Many research efforts have been made and oriented to the exploration of their applications, including as excellent emitters for the fabrication of efficient organic light-emitting diodes, sensitive environmental and biological probes.
Herein thienyl-containing 1,3-butadiene derivative, 1,4-di(4-methoxycarbonyl)phenyl-1,4-di(3-thienyl)-1,3-butadiene (DMPB), was designed and synthesized. The fluorescence quantum efficiencies of DMPB are 26.42% in the solid and 1.16% in THF solution. That is, DMPB is AIE active. After the two carboxylate groups in DMPB was converted into the carboxylic acid, DMPB-COOH shows different fluorescent characteristics with the change of poor solvents in the aggregation state. The experimental results indicated that DMPB-COOH is AIE active in DMSO/water but AEE active in THF/hexane. Furthermore, DMPB-COOH was found to be a turn-on response to aspartic acid in DMSO/H2O and, however, a turn-off response to proline and glutamine. The mechanism of response might be different interaction with DMPB-COOH and amino acid to influence the aggregation morphology of DMPB-COOH. The specific mechanism is about to search deeply.
Cellulose Based Chemicals for Heavy Metal Removal Studied by X-Ray-Fluorescence Spectroscopy (XRF)
1Humboldt University of Berlin, Germany; 2National University of Singapore, Singapore
This poster presents first project steps, scientific investigation methods and results of the project “Cellulose – A renewable resource for environmental technologies and food substitutes”. The project is part of a research cooperation between Associate Prof. Dr. Suresh Valiyaveettil (National University of Singapore, Department of Chemistry, Singapore) and Prof. Dr. Klaus Rademann (Humboldt-Universität zu Berlin, Institut für Chemie, Germany). The joint project is focused on cellulose as a renewable and environmentally friendly resource, which can be functionalized and applied in various ways. Investigations are primarily focussed on the removal of toxic heavy metals from water with the help of functionalized cellulose. X-ray-fluorescence spectroscopy (XRF) is a powerful tool to make chemical compositions routinely visible.
Cellulose offers outstanding options for systematic research on finding the appropriate materials for water purification. We will use this opportunity to investigate specific properties of functionalized cellulose in two steps. Firstly, we will present a method for producing functionalized cellulosic materials, which selectively remove toxic chemicals in drinking water (toxic heavy metals such as thallium, cadmium, lead, mercury, copper). Secondly, we will analyse and characterise the effectivity of the developed materials.
Cyclopenta Fused Bisanthene and its Redox Species
National University of Singapore, Singapore
Cyclopenta fused bisanthene, a molecule that incorporates two five-membered rings at the bay positions of bisanthene, has been easily synthesized as a rather stable compound. Its redox species are also successfully obtained and characterized. The neutral compound displays a well-resolved intense p-band within 700 nm together with a long and weak band extending to 1100 nm. Such phenomenon is a result of its singlet diradical character as well as the paramagnetic ring current in the rim, which is because of its antiaromatic 4n pi (20) electrons in the out layer. The radical cation and dication are then attained by oxidizing the neutral with 1 and 2 equiv. of NOSbF6. They exhibit totally different electronic absorption spectra from the neutral one. The radical cation shows a weak long-wavelength absorption with onset at 1400 nm, except the moderate absorption covering the whole range from 390 nm to 810 nm. The dication then displays even more red-shifted and stronger absorption from 400 nm to 810 nm and a shoulder peak with maximum at 1033 nm, indicating that it has biradical character. The dication shows dark color. For the radical anion and dianion, they can be formed by reacting the neutral with one and two folds of sodium anthracenide. Different from the dication, the dianion is closed-shell in the ground state, thus it reveals a well resolved p band, with maximum at 650 nm and 713 nm. Same as radical cation, the radical anion also has long-wavelength absorption with onset at 1400 nm. The dianion is relatively more stable than the dication, which attributes to the formation of 5-carbon-six-electron system. In a word, the neutral, dication and dianion of hydrocarbon polycyclic compound are easily synthesized at the same time and they possess quite different physical properties from each other.
Diimine Rylene Ribbons with Unusual Diradical Character
National University of Singapore, Singapore
Polyaniline (PANI) has been known for at least 150 years, and is an important conducting and semiconducting polymer with numerous interesting properties and applications. Molecules and polymers containing the quinone diimine residue can provide materials with applications being as wide ascorrosion prevention and light emitting diodes, but never reported as magnesium properties materials with open-shell singlet diradical character. Recent resurgence of interest in rylene, which has found that from hexarylene onward they show very unusual open-shell singlet diradical character with a small singlet-triplet gap, In this work, based on a newly developed cyclopenta (CP) ring-fused perylene building block, a series of soluble and stable long rylene molecules with quinone diimine residue are successfully synthesized. It was found that perylene and qutoeylene quinone diimine show closed-shell ground state but hexarylene and octarylene quinone diimine show open-shell ground state. Their energy gaps (Eg) show clear chain-length dependence. This appearance was verified by different experimental methods, including nuclear magnetic resonance(NMR), electron spin resonance (ESR), superconducting quantum interference device (SQUID), steady-state and transientabsorption spectroscopy (TA), and X-ray crystallographic analysis, assisted by unrestricted symmetry-broken density functionaltheory (DFT) calculations.
Faraday Cage Shielding for Electronic Sensitive Device Using High Permittivity Patterned Oxide Thin Film
Singapore Institute of Technology, Singapore
Electromagnetic Interference (EMI) has been a cause of signal interference that has the potential to result in fatal consequences. Although sensitive electronics systems are required to meet shielding standards, these may not be sufficient to protect them from modern high powered device. In this work, multi stacked patterned oxide structures of BaTiO3 and Fe3O4-TiO2 have been deposited on fluorine tin oxide (FTO) glass to serve as the Faraday cage for EMI shield. CST simulation has been carried out to optimize the thickness and pattern of the layer needed to achieve given reduction in microwave signals. The oxide coated glass has high transmittance in the visible spectrum but effectively shield the microwave signals in the GHz regime. An enclosure for mobile phones have been fabricated with patterned oxide using 3D laser cutting and its shielding properties determined with the TEMARS 3 Axis meter.
Green Synthesis and Characterization of ZnO Nanoparticles using Aloe Vera Extract
Research & Post-Graduate Department of Physics, Bishop Moore College, India
Nanotechnology is the most discussed topic among the researchers. Nanoparticles were grown by several methods like physical, chemical and biological. Biosynthesis method is the most reliable synthesize method which is simple, safe, eco-friendly and cost effective. In this method we can use any of the natural elements like bacteria, fungus, yeast, plant parts etc as reducing agents. Metal nanoparticles show different properties by differing the shape and size. In present work we synthesized ZnO nanoparticle by Aloe Vera leaf extract as a reducing agent and its antimicrobial activities were studied.
Zinc acetate was taken as a salt precursor and aloe Vera as reducing agent for bio-sysnthesis route. Aloe Vera leaf was weighed accurately, washed and boiled by demineralized water. The solution was filtered by whatsmann filter paper. Then we prepared the zinc acetate solution of 1mM using demineralized water. In order to adjust the pH above 10 we used NaOH in the precursor solution. The formed white precipitate was washed repeatedly and filtered from the solution and taken for various characterizations. The experiments were repeated for different volume of Aloe Vera extract to find out the size variation of the nanoparticles. Structural and optical characterization of ZnO nanoparticles were done by X-ray analysis, UV visible spectroscopy, SEM analysis and Raman scattering studies etc. UV-Vis-NIR visible spectra had 320 nm peaks, which confirmed the growth of ZnO nanoparticles. Crystalline nature of ZnO nanoparticles were confirmed by XRD. FESEM analysis has shown uniformly placed nanostructures. FTIR and Raman scattering confirmed the vibrational characteristics of ZnO nanoparticles. ZnO nanoparticles with aloe vera solution showed antibacterial activity.
Spectroscopic Studies of Cu Substituted Ni-Mg Ferrite Nanoparticles Synthesized by Solution Combustion Route
Department of Physics, Karnatak University, India
The polycrystalline ferrite nanoparticles with the general formula Ni0.4Mg0.5Cu0.1Fe2O4 were synthesized by solution combustion route. The structural formation of the ferrite nanoparticles were confirmed by FTIR spectroscopic study. FTIR spectra for the present series show the presence of frequency bands due to the vibrations of ions in the crystal lattice. In ferrites, the metal ions are situated in two different sub lattices tetrahedral (A-site) and octahedral (B-site), according to the geometrical configuration of oxygen nearest neighbours. The two main broad metal-oxygen bands, high frequency band (ν1= 588cm-1) and low frequency band (ν2=424cm-1) were observed in the IR spectra of the spinel ferrites. UV absorption study of the ferrite nanoparticles was carried-out using UV-Vis spectrophotometry; the maximum absorption is observed at 406nm. The energy band gap of ferrite nanoparticles has been estimated using UV-Vis absorption spectra; the energy band gap obtained at 2.77eV. The surface morphology and microstructure of the ferrites were studied using atomic force microscopy (AFM) technique.
Microplastics: Investigation of Intake and Toxicity in Marine Animals
1National University of Singapore, Singapore; 2St. John's Island National Marine Laboratory, c/o Tropical Marine Science Institute, National University of Singapore, Singapore
It is reported that close to 300 Mtonnes of plastics were produced in 2013 alone, and common synthetic polymers such as polystyrene, polyethylene and poly(methylmethacrylate) are used in many commercial products. The size of such polymers can range from sub-micron range (microplastics) to a macroscale. Due to the growing market and wide spread usage, many of these articles end up in the environment, which then cause significant adverse impact on living systems. Recently, ecological and toxicological impacts of micron sized plastics in marine organism are explored in detail. In many cases, bioaccumulation of plastics inside the living organism is observed. Barnacles being filter feeders are excellent organisms to study effects of microplastics dispersed in solution. Our study is focused on understanding the impact of sub-micron sized polymer particles and their impact on marine animals such as barnacles. In our study, we employ the use of fluorescent tagged PMMA nanoparticles to track the intake and fate of particles through various growth and developmental stages of a barnacle lifetime. If not investigated in detail, the microplastics get incorporated into tissue and can potentially move up the food chain.
Novel Stamp F\for Direct Micro- and Nano- Imprint Lithography on Macroscopic Curved Surfaces
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2Engineering Product Development, Singapore University of Technology and Design, Singapore
As imprinting lithography is inherently a 2D mechanical printing process, patterning on non-planar surfaces is fundamentally challenging, despite sought after by many optics applications. Most of the effort towards non-planar imprinting has been achieved through the use of compliance elastomeric stamp such as polydimethylsiloxae (PDMS). Generally, low modulus PDMS provides high contact conformity between the soft stamp and the non-planar substrate. However, there is a trade-off between resolution of imprinting using PDMS and mechanical compliance requirement of soft stamp. Here, we demonstrate a transparent and reusable soft stamp that allows facile micro- and nano-patterning on macroscopically curved surfaces. A bilayer stamp design was used with a soft backing and a hard pattern carrying layer to overcome challenges that arise from the opposing need for stamp compliance (enable conformal contact with non-planar substrates) and also the need for stamp with high modulus (maintain the structural fidelity of imprinted features). With this bilayer design, high yield curved surface patterning (>98 %) over large area (2 X 1 cm) can be successful achieved. This work represents a systematic study to investigate the effect of mechanical properties and thickness of the bilayer stamp on the resolution and conformity of curved surface patterning. Patterns with resolution as small as 80 nm and 98.2 % conformation over macroscopic curvature radius of 4.5 mm were achieved. This can be employed for direct non-planar patterning on lens and displays.
This work was supported by the IMRE-funded core Project No. IMRE/12-1C0332.
 Rogers, John A., and Hong H. Lee, eds. Unconventional nanopatterning techniques and applications. John Wiley & Sons, 2008.
 Lim, Su Hui, Hong Yee Low, and Wui Siew Tan. "Novel soft stamp development for direct micro-and nano-patterning of macroscopic curved surfaces." Journal of Vacuum Science & Technology B 34.1 (2016): 011602.
Optical Activity In Ge2Sb2Te5 (GST)
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2Department of Materials, University of Oxford, United Kingdom; 3Electron Physical Sciences Imaging Centre (ePSIC), Diamond Light Source Ltd, United Kingdom; 4Clarendon Laboratory, Department of Physics, University of Oxford, United Kingdom; 5Optoelectronics Research Centre, University of Southampton, United Kingdom; 6Diamond Light Source, Harwell Science and Innovation Campus, United Kingdom
Ge2Sb2Te5 (GST) is an established phase-change material that undergoes fast reversible transitions between amorphous and crystalline states with a high electro-optical contrast, enabling applications in non-volatile optical and electronic memories and optically-switchable structured metamaterials. We have recently demonstrated that optical activity can be induced in pure and doped GST thin films using polarised light, opening up the possibility of controlled induction of anisotropic phase transition in these and related materials for optoelectronic and photonic applications. While the phase transition has generally been understood to proceed via a thermal mechanism, our work strongly suggests that there is an electronic component of crystallization induced by the handedness of circularly polarised nanosecond laser pulses. Significant optical activity in the inorganic thin films, measured by circular dichroism spectroscopy at a synchrotron beamline, implies the existence of chiral structures or motifs. Optically active and inactive regions in the film have been studied using electron diffraction and spectroscopic techniques in order to obtain a structural picture that can be correlated to the optical changes observed. We also propose several mechanisms for the observed effects, which may be extended to other material systems and harnessed in photonic or chiroptical applications.
Physical Exfoliation to Prepare Sb2Se3 Nanowires for High-Performance Photodetectors
Peking University, China
Sb2Se3 nanowires are drawing more and more attention because of the remarkable optoelectronic properties, on the basis of which such kind of semiconducting materials can be used to promote the development of high-performance photodetectors as well as other novel optoelectronic devices.
Currently, many strategies have been proposed to prepare this promising material, most of which are based on solvothermal synthesis, a complex and time-consuming approach. In brief, solvothermal synthesis involves massive operations and numerous regents to ensure unique features required by semiconducting electronics, and the time consumed in the preparing process is often rather long. Both shortcomings would impede its progress into wider applications.
In recent years, the trend of miniaturizing electronic devices has been extensively and deeply established due to great potential of enhancing the corresponding performance, which, in a large degree, results in the exploration of nano-materials either by top-down method or by bottom-up method. However, nanoscale Sb2Se3 materials were rarely investigated, which had been predicted to possess fantastic optoelectronic properties. Particularly, because of great difficulties in the sample preparation, one-dimension Sb2Se3 nanowires with the diameter scale as low as several nanometers have not been reported yet.
Herein, we present a simple method to prepare Sb2Se3 nanowires based on physical exfoliation of bulk materials, and several nanometers-wide nanowires can be obtained. Sb2Se3 nanowires devices are also fabricated and the optoelectronic properties are investigated, promising the potential of further applications in high-performance photodetectors.
Polyionenes: Efficient Antimicrobial Agents
Department of Chemistry, National University of Singapore, Singapore
Nowadays, one of the most encountered problems is the contamination by microorganisms in crucial fields such as food and health industry, which undoubtedly causes bacterial infections. For this reason, a large number of antimicrobial agents have been improved; however, uncontrolled use of such compounds also enhanced resistance in bacteria. Polyionenes are prepared through Menschutkin condensation reaction between ditertiary amine and dihalogenated compounds. Actual mechanism of action of such polyionenes on bacteria is not well understood. Here we have synthesized a series of polyionenes to see how they induce toxicity to the gram negative bacteria, E. Coli, P. Aeruginosa and gram-positive bacteria, M. Smegmatis and S. Aureus. Aliphatic ionenes were found to be much more efficient than aromatic ionenes. The hydrophilic-oleophilic balance of the ionene should be similar to that of the bacteria cell-wall in order to establish an interaction between them.
Stability and Quick Reversibility: Ammonia Responsive Organic-Inorganic Hybrid Perovskite
1National University of Singapore, Singapore; 2Indian Institute of Technology Kanpur, India
Organic- inorganic halide perovskite is considered as a fascinating material for next generation photovoltaic devices.Despite achieving very high photovoltaic efficiency, this class of materials are extremely fragile towards various conditions such as changes in temperature, humidity, as well as polar gases.In spite of this, the perovskite is used as a NH3 sensor material. Recently, we have developed a series of hybrid materials which is stable even after long time exposure of NH3 with retention of quick reversibility (< 1 sec). Rapid change (<1sec) in fluorescence in presence of NH3 and reversal of the original state in the absence of NH3 established these class of materials as a good NH3 responsive materials. We believe that rapid reversibility coupled with high stability widens the applicability and commercialization of organic-inorganic perovskite beyond solar cell.
Stable and Soluble High Order Acenes with Tunable Molecular Order
National University of Singapore, Singapore
Only a handful of high order acenes are reported so far, due to their enhanced reactivity towards photo-oxidation and/or dimerization, at times. Severe complications in the synthesis was the main hindrance for obtaining and fabricating devices based on these materials, though high order acenes are thought to have intriguing physical, and electrochemical properties in the class. We present a novel approach to synthesize highly stable acenes by the Scholl-type intramolecular aryl cyclization with a series of acene homologs. Protocols that we developed will result in acene molecules of rigid planar moiety with five membered rings fused on either side of the peri-position. Extended conjugation plane helps in the efficient pi-pi molecular stacking owing to a highly ordered co-facial arrangement which is very crucial in terms of charge transport in organic electronic materials. Insertion of the alkyl/alkoxy groups on the aryl groups would optimize the solubility desired for the device fabrication. The method would offer a new possibility in efficiently synthesizing highly unstable linear polybenzenoids.
Synthesis, Structural, Vibrational Spectral, Nonlinear Optical, Electron Transfer Studies of Aniline Derivatives for Optical Limiting Applications
Bishop Moore College Mavelikara, India
The open-aperture Z-scan measurement analysis of two aniline derivatives, 2-Iodo Analine (2-IA) and 2,4,5-Trichloroaniline (2,4,5-TCA) samples were performed. The samples were irradiated with 5 ns laser pulses attained from a Q-switched Nd: YAG laser source at 532 nm excitation wavelength. At the excitation wavelength, the linear transmittance of the samples was 51% in 2-IA and 78% for 2,4,5-TCA. The normalized transmittances, as well as the transmitted energy from the samples, were measured with respect to the sample position z. This normalized transmittance is obtained by the equation,
where, T is the net transmission of the sample, L and R are the length and surface reflectivity of the sample, respectively and is the linear absorption coefficient. Also, in equation (1) is a parameter given by, where is the two-photon absorption (2PA) coefficient, is the on-axis peak laser intensity and is given by .
The open-aperture Z-scan data is found to be the best fit to a two-photon absorption process and the open aperture Z-scan curve was plotted for the samples. The minimum transmittance fits in the lower value for 2-IA is 36% and 51% for 2,4,5-TCA. This reveals that the nonlinearity in both the samples was achieved through the two-photon absorption (2PA) process. The numerically calculated value of 2PA coefficient (β) is, β=2×10-7 m/W for 2-IA and β=2.8×10-11 m/W for 2,4,5-TCA and the dominant 2PA effect in the laser fluence is focused on its positive values. Thus 2-IA shows greater optical limiting property. The high nonlinear absorption coefficient of 2-IA over 2,4,5-TCA disclose the strong π conjugation obtained from outcomes of the NBO analysis. The optical limiting property of the sample deduce that the iodine attached (2-IA) crystal have more optical limiting property than chlorine attached (2,4,5-TCA) crystal.