Conference Programme

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Overview
Session
C-05: Poster Session
Time:
Tuesday, 20/Jun/2017:
4:00pm - 6:15pm

Location: Foyer

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Presentations
Poster

A Fully Characterized Pyrene Bridged Large N-heteroacene: 15 Annulated Rings Fused in a Line

Wang ZILONG1, Liu GUANGFENG1, Gu PEIYANG1, Zhang QICHUN1,2

1School of Materials Science and Engineering, Nanyang Technological University, Singapore; 2Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore

The large acenes, which can be regard as one dimensional graphene, are highly desirable, because of their special optical and electronic properties and good prospect in organic electronic applications. Although, it is tedious and challenging, scientist has made a lot of effort to synthesize the large acenes. Since the solubility and stability dramatically decrease with the conjugation increase, it is even more challenging to well characterize the large acenes, especially for the X-ray diffraction analysis. However X-ray diffraction analysis is the most powerful way to study the acenes properties, and can gives much data for theoretical calculation. By now, the longest acene confirmed by X-ray diffraction analysis is reported by Bunz group with 13 annulated rings fused in a line by embedding a coronene core.

Here, we report the synthesis of a large acene with 15 annulated rings fused in a line by embedding two pyrene units in the backbone. The cross conjugated pyrene units make the 15rings compound highly stable. The ten (Triisopropylsilyl) acetylene groups attached along the backbone make the 15rings compound highly soluble. The good stability and solubility ensured us successfully fully characterized this 15ring compound including optical and electronic properties. We also obtained the crystal of the 15rings compound and it was studied by X-ray diffraction analysis. As far as we know, this is the longest acene confirmed by X-ray diffraction


Poster

A New Fluorescence Probe for Detection of As3+ Ions Based on Glutathione-capped CdSeTe/ZnS Quantum Dots

Rui BAN, Yumei LI, Yingchun LUO

Guizhou Minzu University, China

Water-soluble CdSeTe/ZnS quantum dots (QDs) were synthesized with glutathione (GSH) as stabilizer. Their optical features and structure have been characterized by UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in detail. The as-prepared CdSeTe/ZnS QDs were directly used as a recognition probe for the detection of As3+ because of the strong interactions between the As3+ and the GSH molecule of CdSeTe/ZnS QDs. Under optimal conditions, the quenched fluorescence intensity (F0/F) increased linearly with the concentration of As3+ ranging from 5.0 to 100 μg L-1 The limit of detection (3σ) for As3+ was found to be 1 μg L-1. The practical application had been carried out for determination of As3+ in real water samples.


Poster

Cationic N-Heteroacenes

Gang LIU, Chunyan CHI

National University of Singapore, Singapore

Acenes with cyanine moieties have attracted more and more attention due to their interesting optical, photophysical, and chemical properties.The first example was reported as early as 1896. But until 1998, the zwitterionicbiscyanine structure of tetraphenylhexaazaanthracene was then prepared and confirmed by Wudl's group[1]. And they also found it was a stable ground-state singlet molecule. Since then, interest has increased in many applications, especially the potential use as organic field effect transistors (OFETs), because the replacement of C with N in acene system can build an electron-deficient core.

In this work, we successfully synthesized a series of stable N-substituted heteroacenecations which have never been reported before(para-Mes-N2+,Hex-para-Mes-N2+ and Mes-N+). The stable dicationic molecules,para-Mes-N2+ and Hex-para-Mes-N2+, can be regarded as an isoelectronic structure of the neutral acenes, pentacene and hexacene, respectively. So far, the structures of Mes-N+ and Hex-para-Mes-N2+have been confirmed by 1HNMR spectrum and ESI mass spectrum, and the structures ofpara-Mes-N2+was also confirmed by crystallography analysis.

Reference:

[1] Hutchison, K. A.; Srdanov, G.; Hicks, R.; Yu, H.; Wudl, F.;Strassner, T.; Nendel, M.; Houk, K. N. J. Am. Chem. Soc. 1998, 120,2989.


Poster

Charge Transport Studies in Doped Poly(3,4-ethylenedioxythiophene) [PEDOT] Devices

Amit ROY1, P. ANJANEYULU2, Vaibhav VARADE3, Reghu MENON1

1Indian Institute of Science Bangalore, India; 2REVA University Bangalore, India; 3Weizmann Institute of Science, Israel

Temperature dependent current voltage (I-V) and impedance measurements were carried out in electrochemically prepared doped poly(3,4-ethylenedioxythiophene) [PEDOT] devices in metal/polymer/metal geometry. Current-Voltage (I-V) were carried out over these devices by varying the doping concentration. I-V characteristics shows that the behavior of conduction mechanism changes from Ohmic (at low bias) to trap-filling space charge limited conduction (SCLC) (at moderate voltage) then trap-free SCLC (at higher voltage). Trap densities, trap energies are estimated, the effective mobility is calculated using Poole-Frenkel model. Further we studied the metal-semiconductor interface using impedance spectroscopy at room temperature by varying carrier density, substrate and synthesis temperature. With growth condition the relaxation mechanism of carries in these devices can be varied. It is observed that with decrease in carrier density in stainless steel (SS)/PEDOT/Silver (Ag) devices, the interface related mechanism dominates over bulk transport, but as the synthesis temperature is lowered the bulk transport takes over interface related mechanism. The substrate dependent studies have shown that the growth of polymer chains can alter with the electrode potential which affects the relaxation mechanism of the carriers.


Poster

Water and Moisture Resistant Lead Perovskite: A Generic Co-crystallization Approach

Sayantan SASMAL1,2, Raj G.S. PALA2, Sri SIVAKUMAR2, Suresh VALIYAVEETTIL1

1National University of Singapore, Singapore; 2Indian Institute of Technology Kanpur, India

Organic-inorganic hybrid perovskite provides a new perspective in the field of photovoltaic and has emerged as one of the most promising light harvesting material in just a few years. Although achievement of very high photovoltaic efficiency, water induced rapid degradation has imposed hindrance towards wide usage and commercialization of such fascinating materials. In this attempts to develop humidity and water stable analogues of CH3NH3PbI3, we report the exceptionally stable mixture of CH3NH3PbI3 with 4-[(N-3-butyne)carboxyamido]anilinium lead iodide (NBCAnPbI3) and investigated the properties of the material. Hydrophobic NBCAnPbI3 forms a conformal layer over CH3NH3PbI3, which significantly reduced the interaction of approaching water molecules (even under submerged conditions) with CH3NH3PbI3 and enhanced the water stability. Most importantly, such a high water stability opens a new avenue towards widening the applicability of organic-inorganic perovskites beyond solar cell such as photoelectrochemical water splitting reactions which is shown as a proof of concept.


Poster

Direct Arylation Polymerization for Synthesis of Thienothiadiazole Based Narrow Bandgap Conjugated Porous Polymers

Hassan BOHRA, Jinjun SHAO, Cangjie YANG, Amsalu EFREM, Mingfeng WANG

Nanyang Technological University, Singapore

Narrow bandgap conjugated porous polymers exhibit enhanced light-harvesting capabilities in the near-infrared region, but such materials are limited by availability of appropriate building blocks and synthetic protocols. Herein, we report a series of conjugated porous polymers synthesized under a facile direct arylation polymerization scheme. Thiophene-flanked thienothiadiazole, a narrow band-gap acceptor molecule with active C-H bonds, was reacted with multibrominated monomers with different geometries to yield narrow band-gap polymers that show strong light absorption in the near infrared region, corresponding to optical bandgaps below 1.3 eV. We observed that the porosities and morphologies of the polymers are determined by the chemical structure of the aryl bromide used. Structure-property relationships demonstrated in this study suggest that direct arylation polymerization is an attractive synthetic tool for the rational design of porous organic materials with tunable photo-physical properties for applications in photocatalysis, energy storage and conversion.


Poster

Donor-accepter Modification Effects on the Optoelectronic Properties of Bicarbazole/Cyanobenzene Hybrids: Host and Dopant Applied in Phosphorescent and TADF OLEDs

Xudong CAO, Xianping ZHANG, Youtian TAO, Wei HUANG

Nanjing Tech University, China

Intensive interests have been drawn to the TADF OLED for utilization of pure organic materials in emitting layer. And it is necessary to design proper host and dopant materials to improve the device performance. 9H,9'H-3,3'-bicarbazole (BCz) shows the donor-enhanced property and maintains the high triplet energy level (ET ~2.8 eV) from carbazole. We have designed and synthesized six bicarbazole/cyanobenzene hybris by tuning the attachment on the meta-position of cynabenzene from donor to accepter moieties, such as phenylcarbazole (PCz), phenol (OP), hydrogen (H), methyl (Me), trifluomethyl (CF3) and cynao (CN). The OP, H and Me based materials show the high T1 above 2.7 eV but broad △EST around 0.1 eV while Me and CF3 based materials possess extremely narrow △EST of 0.01 eV emitting blue and green light, respectively.


Poster

Electrically Sense Magnetoreception Based on Graphene Field Effect Transistor

Zihao LIU, Xuefeng GUO

Peking University, China

Biological magnetic sense, the ability of animals to calibrate motion navigation according to the Earth’s magnetic field, has been widely accepted as a fact, but rather controversial for the underlying mechanism. Previously the mechanism was proposed to be based on magnetite or chemical magnetoreception. Recently, a protein, MagR, mainly comprising iron-sulfur sections and Cry sections was demonstrated to possess the capability of patterning itself orderly in the magnetic field due to the inner “biocompass”, which has been attracting more and more attentions in two aspects. One is that such kind of magnetic proteins was expected to promote the depth understanding of magnetic sense. The other one, furthermore, is that magnetic features of the protein might accommodate useful tools to magnetically manipulate bio-molecules and magnetogenetics.

Although meaningful, the verification of several critical issues related to the biocompass-protein progresses slowly due to the limitation of traditional methods in the biological investigation, which be exemplified by the exploration of the mechanism of light-magnet coupling, transferring of magnetic signals within neuro, essence of Magnetoreception and so on.

Carbon materials-based biosensors have been developed dramatically, owing to the characteristics of label-free, real-time detection, high sensitivity and good selectivity. Because of the ability of detecting tiny potential changes in the environment and being modified easily, Graphene Field-Effect Transistors (G-FETs) are attractive in the identification of biological interactions, such as protein-protein, aptamer–protein, DNA-DNA, biotin-streptavidin, etc. For example, the single-molecule lysozyme dynamics has been monitored by a Single Wall Nano-Tube electronic circuit when immobilized on the surface of carbon nanotubes.

Here, We take the advantage of G-FETs through fabricating MagR-immobilized G-FET device and detect MagR protein motion behaviors by monitoring the current change under magnetic field variation. Preliminary work shows time-dependent and memory effects. Light-magnet coupling behavior will be further investigated.


Poster

Enhancement of Photovoltaic Performance of p-i-n Type Organic Solar Cells with Fullerene-Linked Benzoporphyrin

Yuto TAMURA, Mitsuharu SUZUKI, Hiroko YAMADA

Nara Institute of Science and Technology, Japan

Tetrabenzoporphyrin (BP) is one of the significant donor materials for organic photovoltaic cells and can be quantitatively obtained from its soluble precursor (CP) by heating. Because this thermal conversion from CP to BP involves solubility decrease due to the structural change, multi-layered structure can be prepared by repeating spin coating of CP and in-situ conversion from CP to BP film.

By taking advantage of this unique reaction from CP to BP, three layered p-i-n type OPV was successfully fabricated by solution process, where p-layer is polycrystalline BP film, i-layer consists of both BP and [6,6]-phenyl-C61-butyricacid methyl ester (PCBM), and n-layer is PCBM film. To construct a large donor—acceptor interface in p-i-n device, we have designed covalently linked tetrabenzoporphyrin—fullerene (BP—C­­60) as i-layer material and compared with a 1:1 mixed layer of BP and PCBM. The p-i-n device using BP—C60 showed better photovoltaic performances than the 1:1 mixture of BP and PCBM because of a better fill factor value (FF = 0.60) in former device than the latter (FF = 0.46). AFM image of BP—C60 i-layer surface on p-layer (BP) shows homogeneous structure which has no irregular grains compared with the film structure of BP:PCBM and thus the great improvement of FF values in p-i-n device is achieved with BP—C60. From these results, we believe that covalent BP—C60 system can make a good interface which is suitable for the i-layer on the highly crystalline BP p-layer.

We have also evaluated the property of BP—C60 as a morphological control agent for a mixed BP:PCBM layer to obtain enhanced device performances. The addition of the BP—C60 to the mixed layer BP:PCBM improved the photovoltaic performance of intrinsic BP:PCBM layer. The effect of the BP—C60 as an additive will be also discussed.


Poster

Extended O-Heterocyclic-quinodimethanes

Shaoqiang DONG, Chunyan CHI

National University of Singapore, Singapore

Heteroacenes are attractive organic materials for their unique physical properties and potential applications in optoelectronics.

Recently, by fusing two benzothia- groups with a p-quinodimethane (p-QDM) unit together, we synthesized a quinoidalbis(benzothia)-quinodimethane structure, this quinoidal di-S-heteropentacene exhibited much better chemical stability compared with pentacene. Based on this work, we synthesized extended quinoidal bis(benzothia)-quinodimethanes with increased diradical characters, and furthermore, the neutral compunds could be oxidized into their dications which could be regarded as genuine isoelectronic structures of all-carbon acenes.

In this work, electron negative O atom was introduced instead of S atom to construct extended O-heterocyclic-quinodimethanes. While the central position was extended by ultilizing 2,6-anthraquinodimethane to replace p-QDM, like S-heteroacenes, this O-heteroheptacene also showed diradical characters. Furthermore, benzene located at the lateral position could also be replaced by aromatic rings to extend the conjugation, anthracene is a low ordered acene with relative good chemical stability, more importantly, anthrcene is easy to be functionalized. Limited by the synthetic route, the key-step intramolecular Friedel-Crafts alkylation takes place more easily at the α-position of anthracene, which would lead to the formation of curved structure instead of linear one. In order to synthesize linear acene-like hetero-structures, to avoid the α-position reaction, two strategies were adopted, (1) the α-position of anthracene was protected by introducing two bulky mesityl groups at 9, 10-position; (2) two α-positions chemical protected rubicene was used. Herein, 2,3-anthra- or 2,3-rubi- group was introduced to the lateral positons, we synthesize two longer heterononacenes, meanwhile, this two heteroacenes could be oxidized into their dications, both of which could be regarded as isoelectronic structures of all-carbon nonacene.

Anthracene-based and rubicene-based extended O-heterononacenes provides us new ways to design and synthesize stable longer acene analogues.


Poster

Facile Preparation and Properties of Amine Functional and Modifiable Perylene Diiimide

Samarth BHARGAVA, Suresh VALIYAVEETTIL

National University of Singapore, Singapore

Perylene dyes have several interesting properties such as aggregation caused quenching, formation of H or J aggregates and excellent quantum yield in solution and solid state. These properties make perylene dyes as excellent candidates for applications in sensing, LED, or organic photovoltaic applications. Incorporation of amino-functionality at the imide position enables further functionalization to prepare multi-dye systems that are capable of FRET interactions. Here we present the synthesis of bay functionalized perylene diimide derivatives, which are soluble in common organic solvents. The derivatives have free amine moeities in the imide position that makes them modifiable. The derivatives were fully characterized by photophysical and theoretical DFT calculations.


Poster

Field-Effect Properties of (E)-2-(2-(Thiophen-2-yl)vinyl)thiophen-based Donor−Acceptor Copolymers

Liping WANG, Xiaodong XIE

University of Science and Technology Beijing, China

Donor−acceptor copolymers, PTVTBT and PTVTBO, using the highly π-extended (E)-2-(2-(thiophen-2-yl)vinyl)thiophen (TVT) as an electron-rich unit and benzodiathiazole (BT) or benzoxadiazole (BO) as an electron-deficient one, were designed and synthesized via a Pd-catalyzed Stille-coupling method. The copolymers possess high thermal stability, broad absorption, low band gap, and good film-forming ability. Meanwhile the two polymers exhibit excellent hole transport properties when used as the active layer in polymer field-effect transistor devices. The highest hole mobility can reach to 0.25 and 0.50 cm2 V1 s1 for the PTVTBT and PTVTBO thin films, respectively. This work demonstrates that PTVTBT and PTVTBO would be promising semiconductors for developing cost-effective and large-scale production of flexible organic electronics.


Poster

Friedlander Condensation for the Synthesis of Diazapentacenes as Semiconductor Material

Animesh GHOSH, Chan W. YING, Andrey V. LUNCHEV, Andrew C. GRIMSDALE

Nanyang Technological University, Singapore

Extended p-conjugated planner organic molecules with fused rings such as acenes are of great research interest because of their potential application in organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic photovoltaic devices (OPVs) [1]. Although some pentacenes have demonstrated better performance than Si semiconductors, their practical usefulness in organo-electronic devices is restricted due to low air stability and low solubility. Thus a great deal of research has been dedicated in recent years to designing acenes having high air stability, fair solubility and high charge mobility.

The introduction of symmetrically placed nitrogen atoms into the aromatic core in azacenes stabilizes their frontier molecular orbitals and increases their electron affinity while keeping HOMO-LUMO band gap similar to those of acenes. Electron rich azacenes have been reported to be more resistant to degradation than acenes and promising materials for electronic and optoelectronic devices resulting a strong demand for new heteroacene structures [2]. Various synthetic methodologies have been exploited to build substituted azacenes of different structural framework.

From organic chemistry point of view a good strategy should provide an easy access to desired material with improved properties. We report here the simple and straightforward synthesis of novel diazapentacenes derivatives having crescent type structure. The key step in the synthesis is the Friedlander condensation between 2-keto aniline and cyclic 1,2/1,3 or 1,4-diketones providing pentacyclic framework that was later dehydrogenated to give desired diazapentacene compounds.

Currently the spectroscopic and electronic properties of the molecules synthesized are under investigation.

References:

[1] Katz H. E.; Bao Z.; Gilat S. L. Acc. Chem. Res. 2001, 34, 359-369.

[2] (a) Anthony J. E. Chem. Rev. 2006, 106, 5028-5048. (b) Roman A. Irgashev. Org. Lett. 2016, 18, 804-807. (c) Uwe H. F. Bunz. Acc. Chem. Res. 2015, 48, 1676-1686.


Poster

From One-Dimensional to Two-Dimensional Organic Structures: Conjugated Polymers as Superior Anodes for Rechargeable Lithium-Ion Batteries

Jian XIE, Zongqiong LIN, Qichun ZHANG

Nanyang Technological University, Singapore

The increasing concern with respect to the use of traditional inorganic electrode materials on resource and environmental issues has strongly inspired us to search for green energy electrodes for rechargeable lithium-ion batteries (LIBs). Organic compounds are potentially renewable materials as many of them can be obtained from natural products and biomass. Additionally, the properties of organic compounds can be tuned through the modification of structures as well as the introduction of functional groups. Among all organic electrodes, conjugated ladder-structured polymers have been successfully demonstrated to show great potential due to their extended π-conjugation, good electronic conductivity, and high chemical stability. The double-stranded structure endows ladder polymers with rigid backbone property and poor solubility that can offset the serious dissolution issue encountered by most organic electrode materials. Moreover, redox-active conjugated polymers with multielectron reactions can deliver excellent specific capacities. Taking over the merits of heteroatoms doping and utilizing ladder polymers’ rigid backbone structure, herein, we demonstrate that conjugated ladder polymers in terms of their one-dimensional (1D) and two-dimensional (2D) structures with a rich number of heteroatoms could be promising anode materials for LIBs. In detail, novel 1D poly(1,4-dihydro-11H-pyrazino[2′,3′:3,4]cyclopenta[1,2-b]quinoxalin-11-one) (PPCQ) and 2D nitrogen-rich covalent organic framework (COF) in terms of their nanostructures have been developed to deliver remarkable high initial capacity values (1678 and 1021 mAh g-1, respectively at 100 mA g-1), good rate performances (up to 10 and 2.5 A g-1, respectively) and ultra-long cycling stabilities (1000 and 600 cycles, respectively) with excellent Coulombic efficiencies (99.8% and 99.6% respectively). Such superior results bring the battery performance of organic materials to a new level. These investigations provide us more confidence to continue developing novel conjugated polymers with high lithium storage for organic-based rechargeable batteries.


Poster

Full Zigzag Edge Structure Polycyclic Hydrocarbons: Synthesis, Crystal Structure and Photoelectronic Properties

Yanwei GU, Jishan WU

National University of Singapore, Singapore

Graphene is the most attractive material due to its intrinsic electronic and magnetic properties. For the graphene segment, there are two types of edge structure, zigzag and armchair. Nowadays, some groups successfully synthesized all armchair edge structures polycyclic hydrocarbons or armchair and zigzag edge structures polycyclic hydrocarbons, which possess excellent photoelectronic properties. Hence, my project is to synthesize full zigzag edge structures polycyclic hydrocarbons with various conjugation system and study photoelectronic properties.


Poster

Furan Is Superior to Thiophene: A Furan-cored AIEgen with Remarkable Chromism and OLED Performance

Zheng ZHAO, HAN NIE, Jacky W. Y. LAM, An Jun QIN, Ben Zhong TANG

Hong Kong University of Science and Technology, Hong Kong S.A.R. (China)

Luminogens with aggregation-induced emission (AIEgens) characteristics have found promising applications in organic photoelectronics.[1] Furan-cored AIEgen namely TPE-F was developed by diyne cyclization and its fluorescent and chemical properties were investigated and compared with its thiophene (TPE-T, Scheme 1) analogue. Results showed that furan was superior to thiophene in terms of fluorescence, chromism and charge transportation (Figure 1 and Table 1). The mechanism of chromism of TPE-F was investigated and its efficient solid-state photoluminescence and good charge-transporting property enabled it to serve as light-emitting material for the construction of electroluminescence devices with excellent performance. This work not only demonstrates an efficient strategy for constructing furan-cored AIEgens but also indicates that they are promising as advanced optoelectronic materials.


Poster

Kinetically Blocked Stable 5,6:12,13-Dibenzozethrene: A Laterally π-Extended Zethrene with Enhanced Diradical Character

Priya YADAV, Jishan WU

National University of Singapore, Singapore

Although the ground state and physical properties of zethrene and lately invented 1,2:8,9-dibenzozethrene have been well-studied, the other dibenzozethrene isomer, i.e., 5,6:12,13-dibenzozethrene remained unexplored. The first unsuccessful synthetic attempt was reported more than five decades back and thereafter it was overlooked by the scientific community. In 2014, our theoretical calculation predicted an open-shell singlet ground state for the parent 5,6:12,13-dibenzozethrene with a moderate diradical character (y0 = 0.292), which may explain the observed high reactivity of the parent compound. We present a short synthetic route to a kinetically blocked stable 5,6:12,13-dibenzozethrene derivative 5. The ground state was found to be open-shell singlet experimentally, and the theoretical y0 got enhanced to 0.414 which corroborates nicely with the experimental and theoretical singlet-triplet energy gap. In solid state, close contacts between the edge carbon atoms with distance of 3.267 Å was observed for 5 which may hint at moderate intermolecular spin-spin interaction.


Poster

Large-area Micro-patterned Single Crystals for Organic Complementary Circuits via Controlled Nucleating Sites

Jiake WU1,2, Hanying LI2, Benjamin C.K. TEE1,3

1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2Department of Polymer Science and Engineering, State Key Laboratory of Silicon Materials, Zhejiang University, China; 3Department of Materials Science and Engineering, National University of Singapore, Singapore

Organic single crystals are ideal candidates for high-performance flexible circuits. However, the construction of those devices is quite challenging, as the combination of patterned electrodes and single crystals is needed over large areas. Currently, majority of the methods to fabricate single crystals via a solution process lack “area-programmability”, making manufacture of complex electronic circuits difficult. Among the solution process methods, a facile method named droplet-pinned crystallization (DPC) has been developed to prepare, well-aligned and high-carrier mobility organic single crystals. Here, in order to selectively grow oriented organic single crystals in designated locations directly for large-area devices, we explore photo-defined pinners, assisted by the inkjet printer for controlled 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) solution droplet size for organic complementary circuits.


Poster

Linear and V-Shaped S-Heterocyclic Quinodimethanes

Yang CHEN, Chunyan CHI

National University of Singapore, Singapore

Quinodimethane-based materials attract much attention in recent researches due to their unique properties, which are very useful in semiconductors and chromophores.1 S-heterocyclic quinodimethane 2,3 such as 7,14-disubstituted-5,12-dithiapentacenes were synthesized by our group, and they can be considered as quinoidal heteroacenes by replacing two carbon atoms with sulfur atoms. These dithiapentacenes are much more stable than typical pentacene even though it has higher lying HOMO energy level. Their high stability can be explained by interrupting the diene conjugation in normal acenes, therefore disrupting the decomposition pass way.

In this work, we successfully synthesized more extended linear and V-shaped mesityl- substituted S-heterocyclic quinodimethanes. Their geometric and electronic structures, optical and electrochemical properties and chemical reactivity were carefully studied experimentally and theoretically. These molecules are more stable than typical acenes. The good solubility is achieved by introducing the tert-butyl group at the terminal position. The substitution of mesityl group can both block the reactive site of the backbone and avoid molecular aggregation due to π-π stacking as well. The structures of all compoundswere confirmed by mass spectrum, NMR and crystallography analysis. The linear and V-shaped molecules showed very different physical properties and ground state because of their different conjugation. In addition, their redox species were also obtained, and the tetracation of 9L is the isoelectronic structure of nonacene.

References:

[1] See recent review articles: (a) Z. Zeng, X, Shi, C. Chi, J. T. Lopez Navarrete, J. Casado, J. Wu, Chem. Soc. Rev. 2015, 44, 6578.

[2] Q. Ye, J.J. Chang, X.L. Shi, G.L. Dai, W.H. Zhang, K. W. Huang, and C. Chi, Org. Lett. 2014, 16, 3966

[3] X.L. Shi, W.X. Kueh, B. Zheng, K.W. Huang, and C. Chi, Angew. Chem. Int. Ed. 2015, 54, 14412.


Poster

Morphology Control in Small-molecule Organic Photovoltaic Layers Based on Hydrophilicity/Hydrophobicity Contrast

Takuya OKABE, Mitsuharu SUZUKI, Hiroko YAMADA

Nara Institute of Science and Technology, Japan

The performance of organic photovoltaic cells (OPVs) is largely affected by the phase-separation characteristics between donor and acceptor materials in active layers. The morphology in organic photovoltaic layers is usually modulated by either addition of a high-boiling-point additive or post-deposition annealing relying on relatively small differences in intermolecular interactions. However, successful morphological optimization often requires extensive screening of deposition/annealing conditions. In addition, low stability of active-layer morphology is a common problem among OPVs.

In this study, we examine the morphology of a ternary blend comprising a donor with hydrophilic substituents (O4-DPP), a highly hydrophobic acceptor (PCBM), and a morphological modulator having both hydrophobic and hydrophilic substituents (M-DPP). Miscibility between O4-DPP and PCBM is extremely low because of their high contrast in hydrophilicity/hydrophobicity, leading to the formation of large domains in their binary blend. On the other hand, their phase separation behavior can be systematically modulated by addition of M-DPP. The difference in phase separation is clearly manifested in a preliminary examination of photovoltaic performance, in which O4-DPP:PCBM (50:50 in wt.) and O4-DPP:PCBM:M-DPP (35:35:30 in wt.) system afforded PCEs of 1.31% and 1.73%, respectively. This result suggests that our approach of morphology control by adding modulator is effective in improving the photovoltaic performance. The presentation will report the details of structural and photovoltaic evaluation of ternary blend films, and the effect of the modulator on morphological stability.


Poster

Novel Approach to Synthesis of 6,8-diazapentacene Precursors via Friedlander Condensation

Vincent CHANDRA, Aparna JAGGI, Andrey LUNCHEV, Andrew Clive GRIMSDALE

School of Materials Science and Engineering, Nanyang Technological University, Singapore

Currently azaacenes and their derivatives have been actively studied in the fields of organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and hole transporting materials in organic photovoltaics. This significant interest to azaacenes has led to the development of synthetic pathways for these molecules. Currently, there is a variety of azaacenes that are readily available for structural studies and device fabrication due to well-developed synthetic procedures, as for various tetraazaacenes [1].

However, some nitrogen doped acenes, which should be important for understanding of various structure-property relations in the field of OFRETs, like 6,8-diazapentacene (quinolino[3,2-b]acridine) and its derivatives, have never been synthesized, and, thus, studied.

Here we report our progress towards synthesis of 6,8-diazapentacene derivatives using Friedlander condensation as a key step for building pentacyclic framework. It involves novel approach to synthesis of aromatic diamino diketones, which can be easily obtained via Sonogashira coupling followed by the one-pot reduction of nitro groups and the hydrolysis of triple bonds using SnCl2 in ethanol.

The synthetic route allows to incorporate various functional groups to the framework of 6,8-diazapentacene. The variety of 6,8-diazapentacene precursors bearing alkyl chains was synthesized in order to improve the solubility. The precursors with additional benzene rings were synthesized as well in order to improve stability of the final acene aromatic system as per “Clar’s rule”. All the precursors demonstrate strong fluorescence, which make them interesting materials for studies in the field of OLEDs. The optoelectronic properties of these materials are being studied to investigate their suitability for use in devices such as OFETs or OLEDs.

Reference:

[1] Bunz, U.H.F., Accounts of Chemical Research, 2015. 48(6): p. 1676-1686.


Poster

Rylene Ribbons with Unusual Diradical Characters

Wangdong ZENG, Jishan WU

National University of Singapore, Singapore

Armchair graphene nanoribbons (AGNRs) with a width of N = 3p + 2 are theoretically predicted to be metallic or half-metallic with a very small bandgap. However, so far, all experimental studies on this type of AGNRs have been only limited to 5-AGNR synthesized on Au(111) surface, and wet-chemistry synthesis would allow us to investigate their intrinsic electronic properties. In this work, based on a newly developed cyclopenta-fused perylene building block, a series of soluble and stable 5-AGNR model molecules, namely rylenes, up to dodecarylene are successfully synthesized. It is found that from hexarylene onward, these long rylene molecules show an open-shell singlet ground state with a small singlet-triplet energy gap. Their energy gaps (Eg) show clear chain-length dependence, and a linear exploration of the Eg ~ 1/n plot predicts that the infinite 5-AGNR fused by CP rings has a small bandgap of 0.21 eV.


Poster

Stable Fluorenyl Radical Based Macrocyclic Poly-radicaloids: Synthesis and the Influence of Geometry on Physical Properties

Xuefeng LU, Jishan WU

Department of Chemistry, National University of Singapore, Singapore

Stable π-conjugated macrocycles containing four (FR-MC4) and six (FR-MC6) fluorenyl radicals were synthesized by Suzuki coupling reaction followed by simple reduction. FR-MC4 and FR-MC6 both possess open-shell singlet ground state and exhibit moderate tetraradical and hexaradical character, respectively. Compared to the linear, flexible fluorenyl radical tetramer FR-4, the rigidified FR-MC4 shows anti-aromatic character due to cyclic π-conjugation with 36 π electrons, and consequently, it displays larger diradical character and smaller energy gap. On the other hand, FR-MC6 has figure-eight geometry with larger torsion angles and there is no obvious ring current along the macrocyclic periphery. As a result, it exhibits a larger energy gap and a smaller singlet-triplet gap compared to its linear analogue FR-6.


Poster

Synthesis and Exploration of Ladder-Structured Large Aromatic Dianhydrides as Organic Cathodes for Lithium-Ion Batteries

Wangqiao CHEN, Jian XIE, Qichun ZHANG

Nanyang Technological University, Singapore

Carbonyl-containing compounds are considered as a promising type of active cathode materials for rechargeable batteries. The redox stability of carbonyl groups offers organic cathodes a good reversibility during the charge-discharge process. In this study, we demonstrate two non-polymeric dianhydrides with large aromatic structures: NDA-4N (naphthalenetetracarboxylic dianhydride with four nitrogen atoms) and PDA-4N (perylenetetracarboxylic dianhydride with four nitrogen atoms). Their electrochemical properties were investigated between 2.0 and 3.9 V (vs. Li+/Li). Benefiting from multi-electron reactions, NDA-4N and PDA-4N could reversibly achieve 76.1% and 95.3% of their theoretical capacity, respectively. Further cycling reveals that organic compound with a relatively larger aromatic building block could be able to achieve a better stability, as an obvious 31% improvement of the capacity retention was obtained when switching the backbone from naphthalene to perylene. This study proposes an opportunity to achieve promising small-molecule based cathode materials through tailoring of organic structures.


Poster

Synthesis and Feature of Hexacycloquinohexanes: Disordered Structure Obtained from Poly-radicals Intermediate State

Jiaqi FENG, Jishan WU

National University of Singapore, Singapore

P-conjugated polyquinocumulenes have been investigated for a long time, from linear quinocumulenes to triquinocyclopropanes[1][2]. In this research, we further extend the conjugated system, aimed to synthesize the hexaphenoxy-radicals. However, Hexacycloquinohexanes was directly synthesized by oxidation of the hexaphenolic precursor. During this procedure, the hexaphenoxy-radicals form was firstly obtained as a meta-stable compound, which was then slowly decayed to the final quinoidal structure.

References:

[1] Cramer, Friedrich, Wolfram Saenger, and H-Ch Spatz., Journal of the American Chemical Society, 89 (1967), pp. 14-20.

[2] West, Robert, et al., The Journal of Organic Chemistry, 40 (1975), pp. 2295-2299.


Poster

Synthesis and Study of Fluorenyl Substituted Porphyrin-Tunable Electronic State

Hejian ZHANG, Jishan WU

National University of Singapore, Singapore

In this work, porphyrin with two fluorenyl units at opposite meso positons was synthesized. The target molecule was characterized by various experiments (NMR, UV-Vis spectrum, CV, superconducting quantum interference device(SQUID), X-ray crystallograpic). At room temperature, target molecule showed a close-shell ground state, which was confirmed by its crystal structure. After increasing the temperature, target molecule displayed interesting magnetic phenomena. For example, there was a hysteresis loop in SQUID during heating-and-cooling process. Structure change during heating was thought to be the reason. Meanwhile, if metal ion (Ni2+) was inserted into the porphyrin (named PF-Ni), the ground state would change to singlet biradical, which was confirmed by VT NMR of PF-Ni.


Poster

Synthesis, Characterisation and Nonlinear Optical Studies of Graphene Oxide Functionalised with Rubyrine

Ramakrishnan SHANMUGAM, Kavita GARG, Praveen C RAMAMURTHY

Department of Materials Engineering, Indian Institute of Science, Bangalore, India

The optical limiters are of tremendous interest due to their potential applications in optical data storage, photodynamic therapy, three-dimensional micro-fabrication, and optical limiting. Graphene is an emerging star in world of materials due to its high charge carrier mobility, thermal conductivity, and intrinsic breaking strength. Porphyrin-based functional photonic materials are important due to their thermal stability structural, electrochemical, and optical properties. Porphyrins have potential applications such as optoelectronics,and nonlinear optics. Functionalisation of porphyrins to carbon material can improve the optical properties of the systems. Porphyrins and graphene, containing significant conjugated π-electron, are best to fulfil the requirement of a perfect nonlinear material. It is well documented that large complex delocalized p-electron systems show good non-linearities. Present work demonstrates the synthesis, characterisation and optical studies of Rubyrine–graphene oxide covalent adduct (GO–Rub) synthesisized by ester linkage of graphene oxide (GO) with 5-(4-hydroxyphenyl), 10,19,24-tritolyl-29,30,32,33-tetrathiarubyrin (Rub). The functionalisation of GO and Rubyrine by ester linkage was confirmed by FT-IR and XPS techniques. The Red shifted (525 nm) in the soret band (509 nm) for RubyrineinUV spectrum, indicates strong π-π interactions between the graphene oxide and Rubyrin. The fluorescence quenching in GO-Rub dictates excellent electron and/or energy transfer from rupyrine to GO. The Non Linear Optical studies are carried out by using Z scan technique using 532 nm pulsed laser for 5 ns. The GO-Rub showed improved nonlinear limiting (NLO) properties with nonlinear optical absorption coefficients for the GO-Rub (β = 1.46×10−10 m/W) compared to both graphene oxide ((β= 0.24 × 10−10 m/W) and porphyrin ((β = 0.03 × 10−10 m/W).


Poster

The Charge Transport Investigation of Organic Field Effect Transistors based on N-Heteroacene Derivatives

Zongrui WANG1, Zilong WANG1, Qichun ZHANG1,2

1School of Materials Science and Engineering, Nanyang Technological University, Singapore; 2Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore

We have synthesized and investigated the charge transport properties of the two N-heteroacene derivatives with different molecular length azahexacene CO and azaheptacene CO. These two compounds own different crystal structures with azahexacene CO is bricklayer π-π stacking while azaheptacene CO is herringbone stacking. The OFET based on azahexacene CO exhibits much better performance than that of azaheptacene CO, which may derive from the different molecular packing for the charge transport.


Poster

The Design of Intramolecular Charge-Transfer Compounds based on Structural Design Strategy

Liang XU

Department of Chemistry, College of Science, Shantou University, China

Recently, the design and synthesis of novel structures of intramolecular charge-transfer (ICT) compounds have attracted much attention due to their diverse applications in nonlinear optical (NLO) materials, organic photovoltaics, organic light-emitting diodes (OLEDs), anion sensors, memory devices and filed effect transistors. The photoelectric properties of ICT compounds could be regulated by changing structural factors (e.g. chemical components of D and A, the conjugation length of the π-bridge, the position of the substitute, co-planarity and flexibility of the molecular frame-works). A series of ICT compounds have been designed and synthesized based on structural design strategy, and the exploration of structure-function relationship provide a rich guideline for the construction of photoelectric active materials.

References:

[1] Xu L and Zhang Q. Recent progress on intramolecular charge-transfer compounds as photoelectric active materials. SCIENCE CHINA Materials,doi: 10.1007/s40843-016-5170-2.

[2] Xu L, Zhu H, Long G, Zhao J, Li D, Ganguly R, Li Y, Xu Q and Zhang Q. 4-Diphenylamino-phenyl substituted pyrazine: nonlinear optical switching by protonation. J Mater Chem C, 2015, 3: 9191-9196.

[3] Xu L, Zhao Y, Long G, Wang Y, Zhao J, Li D, Li J, Ganguly R, Li Y, Sun H, Sun X, and Zhang Q. Synthesis, structure, physical properties and OLED application of pyrazine-triphenylamine fused conjugated compounds. RSC Adv, 2015, 5: 63080-63086.

[4] Cao L, Zhang D, Xu L, Fang Z, Jiang X, and Lu F. Pyrene Diimide (PDI)- benzanthrone Dyad: novel organic chromophores with enhanced third-order nonlinear optical activities, submitted.


Poster

Thiophene Based Open-shell Macrocycles with Infrared Absorption.

Yadagiri Gopalakrishna TULLIMILLI, Jishan WU

National University of Singapore, Singapore

π-Conjugated macrocyclic oligothiophenes have fascinating optical and electronic properties. Recent investigations explored open shell (polaron-pair) behavior and size dependency of dicationic macrocyclic oligothiophenes[1]. Molecules with open shell ground state have drawn immense attention in recent times owing to their unique optical, electronic and magnetic properties, suitable for the next generation functional materials[2]. Poly-radical character of π-conjugated polycyclic heteroarenes opens the new era in open-shell macrocyclic systems [3]. Inspired by the interesting properties of polyradicaloids, we designed and synthesised the thiophene macrocycles with open-shell ground state. Here we discuss the one pot synthesis and characterization of MC1- MC4 macrocycles. MC1 and MC3 have doublet ground state with odd number of elctrons (51π and 85π) in conjugation pathway, where as MC2 and MC4 macrocycles with singlet groundstate. The open-shell radicaloid nature of these thiophene macrocycles have been confirmed by various experimental and theoritical techniques. Interstingly the electronic bands in the Ultraviolet-visible-infrared absorption spectra reach into Infrared region of electromagetic spectrum.

References:

[1] M. Iyoda, K. Tanaka, H. Shimizu, M. Hasegawa, T. Nishinaga, T. Nishiuchi, Y. Kunugi, T. Ishida, H. Otani, H. Sato, K. Inukai, K. Tahara and Y. Tobe, J. Am. Chem. Soc., 2014, 136, 2389-2396.

[2] Z. Zeng, X. Shi, C. Chi, J. T. Lopez Navarrete, J. Casado and J. Wu, Chem. Soc. Rev., 2015, 44, 6578-6596.

[3] S. Das, T. S. Herng, J. L. Zafra, P. M. Burrezo, M. Kitano, M. Ishida, T. Y. Gopalakrishna, P. Hu, A. Osuka, J. Casado, J. Ding, D. Casanova and J. Wu, J. Am. Chem. Soc., 2016, 138, 7782-7790.


Poster

Tuning Solid-state Fluorescence of an Azaacene Derivative Through Crystal Engineering

Peiyang GU, Qichun ZHANG

Nanyang Technological University, Singapore

Although the property of azaacene derivatives can be controlled through attaching different substituted groups onto their backbones or changing different processing conditions during film/devices’ fabrication, the property tuning based single azaacene system through crystal engineering is unprecedented. Herein, we report an azaacene derivative TBIDQ which exhibits distinctly different fluorescence emission in its three crystal Forms. The fluorescence quantum yields (φ) of three crystal Forms (named as, Form I, Form II, and Form III) are 30.2%, 26.0% and 14.6%, respectively. On the basis of single-crystal structural analysis and experimental results, mean distance of interlayers and the radiative decay rate decreases and the π-π stacking interactions and the nonradiative decay rate increases. Our results suggest that planar molecules can also display the loose stacking manner and show weak π-π stacking interactions through carefully choosing the solvents to grow single crystal.


Poster

Z-Shaped Pentaleno- Acene Dimers with High Stability and Low Band Gap

Gaole DAI, Chunyan CHI

National University of Singapore, Singapore

Acene-based materials have promising applications for organic electronics but the major constrain comes from their poor stability. Herein we introduce a new strategy to stabilize reactive acenes by fusion of an anti-aromatic pentalene unit onto the zig-zag edges of two acene units to form a Z-shaped acene dimer, which turned out to be extremely stable and show a small energy gap due to intramolecular donor-acceptor interaction. X-ray crystallographic analysis revealed their unique geometry and 1D slip-stack columnar structure. Besides optical and electrochemical characterizations, solution processed field effect transistors were also fabricated.


Poster

π-Extended Acenedithiophene-Based Small Molecules for Solution-Processed Organic Solar Cells

Hideaki KOMIYAMA1, Takahiro TO1, Seiichi FURUKAWA1,2, Satoshi UWAGAWA1, Takuma YASUDA1,2

1Inamori Frontier Research Center, Kyushu University, Japan; 2Department Applied Chemistry, Graduate School Engineering, Kyushu University, Japan

Organic solar cells (OSCs) have drawn much attention as promising next-generation renewable energy sources because abundant sun-light energy can be directly converted into electricity. Recently, the power conversion efficiencies of OSCs based on small molecules with bulk heterojunction (BHJ) architectures have rapidly increased to approximately 10%, approaching those of state-of-the-art polymer-based OSCs. For application in BHJ OSCs, π-extended small molecules consisting of a central electron-donor (D) unit and terminal electron-acceptor (A) units are the most promising semiconductor materials. Such A−D−A electronic structure can provide a small bandgap energy, intense and broad light absorption, and efficient charge transport. Currently, π-extended acenedithiophenes are regarded as important D units for the material design because of their high degree of backbone coplanarity, deep-lying highest occupied molecular orbital (HOMO) energy levels, and strong intermolecular interactions. In this study, we designed and synthesized a new series of acenedithiophene-based small molecules to understand structure−property relationships. The central acenedithiophene unit and terminal A units were covalently linked with oligothiophenes as π-bridge. Effect of acenedithiophene units and length of oligothiophene π-bridge on photophysical properties, charge-carrier transport properties, and crystalline behavior as well as photovoltaic properties were investigated.



 
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