Development Of Organic Materials Research Articles

The enhancement of nonlinear optical properties of azulene-based nanographene by N atoms: a finishing touch

Functionalization of graphene-based nanomaterials by proper N-doping provides a new strategy for electronic structure modulation to enhance the second- or third-order nonlinear optical properties of materials.

Chaperone Mimetic Strategy for Achieving Organic Room-Temperature Phosphorescence based on Confined Supramolecular Assembly.

The development of organic materials that deliver room-temperature phosphorescence (RTP) is highly interesting for potential applications such as anticounterfeiting, optoelectronic devices, and bioimaging. Herein, a molecular chaperone strategy for controlling isolated chromophores to achieve high-performance RTP is demonstrated. Systematic experiments coupled with theoretical evidence reveal that the host plays a similar role as a molecular chaperone that anchors the chromophores for limited nonradiative decay and directs the proper conformation of guests for enhanced intersystem crossing through noncovalent interactions. For deduction of structure-property relationships, various structure-related descriptors that correlate with the RTP performance are identified, thus offering the possibility to quantitatively design and predict the phosphorescent behaviors of these systems. Furthermore, application in thermal printing is well realized for these RTP materials. The present work discloses an effective strategy for efficient construction of organic RTP materials, delivering a modular model which is expected to help expand the diversity of desirable RTP systems.

Boosting thermoelectric performance of conjugated polymers via interchain molecular docking: Significance of highly crystalline and percolated morphology

The development of organic materials with high thermoelectric performance requires the exploration of organic molecules having various structures and a deep understanding of the relationship between their structure and thermoelectric properties. In this study, a series of donor–acceptor-type conjugated copolymers with an isoindigo (IID) unit as a building block are synthesized and compared to investigate the effect of the molecular structure of the IID-based conjugated polymers on the microstructure and thermoelectric properties of polymer films. The crystallinity and molecular packing of the polymers change significantly depending on the symmetry of the donor unit copolymerized with the IID unit, resulting in considerable differences in the doping and charge transport characteristics of the polymers. Importantly, the polymer with high crystallinity and fibril-like crystalline network shows excellent thermoelectric performance, exhibiting a high power factor of 212 µW m−1 K−2 upon doping; this is attributed to the high electrical conductivity and high Seebeck coefficient, which result from its highly ordered structure. This study not only demonstrates the potential of the IID unit as a promising building block for high-performance conjugated polymers for thermoelectric applications but also provides important guidelines for the design of IID-based polymers having high thermoelectric performance.

Chiral Porphyrin Assemblies Investigated by a Modified Reflectance Anisotropy Spectroscopy Spectrometer.

Reflectance anisotropy spectroscopy (RAS) has been largely used to investigate organic compounds: Langmuir-Blodgett and Langmuir-Schaeffer layers, the organic molecular beam epitaxy growth in situ and in real time, thin and ultrathin organic films exposed to volatiles, in ultra-high vacuum (UHV), in controlled atmosphere and even in liquid. In all these cases, porphyrins and porphyrin-related compounds have often been used, taking advantage of the peculiar characteristics of RAS with respect to other techniques. The technical modification of a RAS spectrometer (CD-RAS: circular dichroism RAS) allows us to investigate the circular dichroism of samples instead of the normally studied linear dichroism: CD-RAS measures (in transmission mode) the anisotropy of the optical properties of a sample under right and left circularly polarized light. Although commercial spectrometers exist to measure the circular dichroism of substances, the "open structure" of this new spectrometer and its higher flexibility in design makes it possible to couple it with UHV systems or other experimental configurations. The importance of chirality in the development of organic materials (from solutions to the solid state, as thin layers deposited-in liquid or in vacuum-on transparent substrates) could open interesting possibilities to a development in the investigation of the chirality of organic and biological layers. In this manuscript, after the detailed explanation of the CD-RAS technique, some calibration tests with chiral porphyrin assemblies in solution or deposited in solid film are reported to demonstrate the quality of the results, comparing curves obtained with CD-RAS and a commercial spectrometer.

Approaching 800 nm near-infrared thermally activated delay fluorescence materials via simple malononitrile condensation strategy

The development of organic materials with near-infrared (NIR) thermally activated delayed fluorescence (TADF) has drawn growing attention in recent years, but most of the reported NIR TADF emitters have emission peaks less than 780 nm with considerable visible emission remnants. To achieve pure NIR emission, we developed a strong electron acceptor fluoren-9-ylidene malononitrile ( FM ) by malononitrile condensation with fluorenone. Exploiting FM as acceptor, two novel molecules 3TPAFM and 36DTPAFM with pure NIR TADF were facilely synthesized and displayed high thermal stability. Compared with the orange emissive non-TADF fluorenone precursors, 3TPAFM and 36DTPAFM demonstrated significantly red-shifted emission of up to 217 nm and largely reduced energy gaps between the lowest singlet and triplet states, leading to pure NIR TADF with emission peak at 802 nm in neat films. The photophysical study revealed that their nonradiative decay rates are comparable with fluorenone counterparts even with such significantly reduced optical energy gap, manifesting largely attenuated limitation from the energy gap law. The non-doped OLEDs based on 3TPAFM and 36DTPAFM achieved pure NIR emission with λ EL at 792 and 788 nm, and external quantum efficiencies of 0.21% and 0.32% at 1 mA cm −2 , respectively. This work provides a simple and powerful strategy to achieve NIR TADF by malononitrile condensation with ketone group and presents FM group as a desirable acceptor candidate to construct pure and efficient NIR emitting materials. • Two novel NIR TADF emitters were constructed through simple malononitrile condensation strategy. • They achieved significant redshifts of 217 nm while maintaining similar nonradiative decay rates with fluorenone precursors. • Their non-doped OLED devices realized pure and efficient NIR emission with peaks around 790 nm.

Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials.

Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate. Crystal structures reveal the high degree of porosity achievable with the new building block. Excellent electrochemical properties and reversible reduction to the tetraanions are shown for the imides; NMR and EPR measurements confirm the global aromaticity of the dianions and evidence the global Baird aromaticity of the tetraanions. Considering the short synthesis and unique properties, we expect widespread use of the new building block in the development of organic materials.

Advances in perception-functionalized organic field-effect transistors

<p indent="0mm">With the evolution of optoelectronics to intelligent systems, the development of organic materials and devices with sensing perception functionality has become a cutting-edge area. By modulating the conductive capability of conjugated semiconductors with electric field, organic field-effect transistors can not only serve as electronic switch to build flexible logic circuits, but can also combine the multifunctional molecular design and interface engineering to create different sensors, neural computing and adaptive devices. Over the past decade, sensory perception-functionalized organic field-effect transistors (OFETs) have attracted increasing attention and made great achievements. This review introduces the related research progress from the molecular design, interface modification to device design. Moreover, we summarize key strategy towards state-of-the-art sensory perception-functionalized OFETs, and finally propose the challenges and opportunities of this emerging frontier.

Remarkable mechanochromism and force-induced thermally activated delayed fluorescence enhancement from white-light-emitting organic luminogens with aggregation-induced emission

The development of organic materials with white-light emission and thermally activated delayed fluorescence (TADF) properties in the solid state remain a challenge. Herein, a series of white-light-emitting organic luminogens have been developed and are found to show aggregation-induced delayed fluorescence (AIDF) characteristics. The AIDF emitters present dual-emission consisted of prompt fluorescence and TADF in the crystalline state. Their white-light emissions can be easily tuned by altering the chemical structure and connecting position of the heterocyclic aromatic substituent. Under the stimuli of mechanical force and solvent vapor, the compounds exhibit remarkable and reversible mechanochromism, in which their emission colors are switchable between white and yellow. Upon grinding, they also display linearly tunable luminescence colors, as well as force-induced TADF enhancement, which may be associated with the more compact molecular packing and the restriction of intramolecular motions. The results from time-resolved emission scanning and theoretical calculation suggest that the dual-emission of the AIDF luminogens likely results from the twisted intramolecular charge transfer transitions of the molecules, and the reversible mechanochromism properties probably stem from the interconversion of the quasi-axial and the quasi-equatorial conformations.

AIE-Active Difluoroboron Complexes with N,O-Bidentate Ligands: Rapid Construction by Copper-Catalyzed C-H Activation.

The development of organic materials with high solid‐state luminescence efficiency is highly desirable because of their fundamental importance and applicability in optoelectronics. Herein, a rapid construction of novel BF2 complexes with N,O‐bidentate ligands by using Cu(BF4)2•6H2O as a catalyst and BF2 source is disclosed, which avoids the need for pre‐composing the N,O‐bidentate ligands and features a broad substrate scope and a high tolerance level for sensitive functional groups. Moreover, molecular oxygen is employed as the terminal oxidant in this transformation. A library of 36 compounds as a new class of BF2 complexes with remarkable photophysical properties is delivered in good to excellent yields, showing a substituent‐dependency on the photophysical properties, derived from the π–π* character of the photoexcited state. In addition, aggregation‐induced emission (AIE) is observed and quantified for the brightest exemplars. The excited state properties are fully investigated in solids and in THF/H2O mixtures. Hence, a new series of photofunctional materials with variable photophysical properties is reported, with potential applications for sensing, bioimaging, and optoelectronics.

Fused Aromatic Network with Exceptionally High Carrier Mobility.

Recently, studies of 2D organic layered materials with unique electronic properties have generated considerable interest in the research community. However, the development of organic materials with functional electrical transport properties is still needed. Here, a 2D fused aromatic network (FAN) structure with a C5 N basal plane stoichiometry is designed and synthesized, and thin films are cast from C5 N solution onto silicon dioxide substrates. Then field-effect transistors are fabricated using C5 N thin flakes as the active layer in a bottom-gate top-contact configuration to characterize their electrical properties. The C5 N thin flakes, isolated by polydimethylsiloxane stamping, exhibit ambipolar charge transport and extraordinarily high electron (996 cm2 V-1 s-1 ) and hole (501 cm2 V-1 s-1 ) mobilities, surpassing the performance of most pristine organic materials without doping. These results demonstrate their vast potential for applications in thin-film optoelectronic devices.

Far-Red to Near Infrared Emissive Aqueous Nanoparticles Based on a New Organic Material with Three BODIPY Dyes at the Periphery of the Core: A Combined Experimental and Theoretical Study

A new organic material with three 4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene dyes (BODIPYs) at the periphery of the central core is successfully synthesized (3BDP3T) and its corresponding aqueous nanoparticles are prepared via the encapsulation approach and characterized in detail both experimentally and theoretically with the aid of the Density Functional Theory (DFT). The linear and non-linear optical properties of the synthesized material are also studied. Until now, the development of organic materials with three BODIPYs as substituents is limited and their properties are not fully resolved. The obtained 3BDP3T-based nanoparticles exhibit far-red and near infrared (NIR) emission with photoluminescence quantum yields of 0.021, which is promising as a new fluorescent contrast agent in the far-red and NIR spectral regions.

(Invited) Materials Development for Organic Redox Flow Batteries

Because of the excellent scalability and design flexibility, redox flow batteries are especially advantageous for grid-scale energy storage. Traditional inorganic-based flow batteries are generally limited by the low energy density and high chemical costs, which greatly restricted their widespread market penetration. In this regard, organic redox-active materials have been reported as possible materials alternatives to exhibit encouraging properties and performance.1 ,2 The development of organic materials have suggested a promising avenue for enabling next-generation redox flow batteries, although further improvements are still urgently needed to demonstrate their commercialization potential. In this presentation, we will introduce our recent progress in developing aqueous organic flow battery materials and systems. Among a variety of organic candidates being investigated, a few have demonstrated high effective electron solubilities >3 M, favorable redox potentials to enable high cell voltages, and highly scalable synthesis leading to cost-effectiveness. More importantly, we have achieved basic structure-property understandings of the key factors that govern the solubility and chemical stability of organic redox-active materials. These have provided guidance for rational materials design and development strategies to harvest significantly improved energy density and cyclability of flow batteries. References X. Wei, W. Pan, W. Duan, A. Hollas, Z. Yang, B. Li, Z. Nie, J. Liu,D. Reed, W. Wang, V. Sprenkle, Materials and Systems for Organic Redox Flow Batteries: Status and Challenges. ACS Energy Lett. 2017, 2, 2187.A. Hollas, X. Wei, M. Vijayakumar, Z. Nie, B. Li, D. Reed, J. Liu, V. Sprenkle, W. Wang, A Nature-Inspired, Energy-Dense Phenazine-based Anolyte for Aqueous Organic Redox Flow Batteries. Nat. Energy, accepted. Figure 1. Cycling efficiency and capacity for an aqueous organic flow battery. Figure 1

PubChemQC Project: A Large-Scale First-Principles Electronic Structure Database for Data-Driven Chemistry.

Large-scale molecular databases play an essential role in the investigation of various subjects such as the development of organic materials, in silico drug design, and data-driven studies with machine learning. We have developed a large-scale quantum chemistry database based on first-principles methods. Our database currently contains the ground-state electronic structures of 3 million molecules based on density functional theory (DFT) at the B3LYP/6-31G* level, and we successively calculated 10 low-lying excited states of over 2 million molecules via time-dependent DFT with the B3LYP functional and the 6-31+G* basis set. To select the molecules calculated in our project, we referred to the PubChem Project, which was used as the source of the molecular structures in short strings using the InChI and SMILES representations. Accordingly, we have named our quantum chemistry database project "PubChemQC" ( http://pubchemqc.riken.jp/ ) and placed it in the public domain. In this paper, we show the fundamental features of the PubChemQC database and discuss the techniques used to construct the data set for large-scale quantum chemistry calculations. We also present a machine learning approach to predict the electronic structure of molecules as an example to demonstrate the suitability of the large-scale quantum chemistry database.

Bulk‐Heterojunction Organic Solar Cells: Five Core Technologies for Their Commercialization

The past two decades of vigorous interdisciplinary approaches has seen tremendous breakthroughs in both scientific and technological developments of bulk-heterojunction organic solar cells (OSCs) based on nanocomposites of π-conjugated organic semiconductors. Because of their unique functionalities, the OSC field is expected to enable innovative photovoltaic applications that can be difficult to achieve using traditional inorganic solar cells: OSCs are printable, portable, wearable, disposable, biocompatible, and attachable to curved surfaces. The ultimate objective of this field is to develop cost-effective, stable, and high-performance photovoltaic modules fabricated on large-area flexible plastic substrates via high-volume/throughput roll-to-roll printing processing and thus achieve the practical implementation of OSCs. Recently, intensive research efforts into the development of organic materials, processing techniques, interface engineering, and device architectures have led to a remarkable improvement in power conversion efficiencies, exceeding 11%, which has finally brought OSCs close to commercialization. Current research interests are expanding from academic to industrial viewpoints to improve device stability and compatibility with large-scale printing processes, which must be addressed to realize viable applications. Here, both academic and industrial issues are reviewed by highlighting historically monumental research results and recent state-of-the-art progress in OSCs. Moreover, perspectives on five core technologies that affect the realization of the practical use of OSCs are presented, including device efficiency, device stability, flexible and transparent electrodes, module designs, and printing techniques.

Amplified Spontaneous Emission Optimization in Regioregular Poly(3-hexylthiophene) (rrP3HT):poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) Thin Films through Control of the Morphology

The maximization of the optical gain of organic active materials is a crucial step in the development of organic lasers. In this paper we demonstrate that the amplified spontaneous emission (ASE) of regio regular-poly(3-hexylthiophene) (rrP3HT):poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) thin films is strongly affected by the film morphology, controlled by changing the solvent used for the spin-coating deposition. The solvent variation results in ASE threshold changes of up to 8-fold due to the variation in the uniformity of the two polymers mixing, determining the optical gain, and the morphology uniformity, affecting the losses. Our results demonstrate that the morphology optimization is a very important step in the development of organic materials with high optical gain.

Recent advances in purely organic phosphorescent materials.

Luminescent organic materials have attracted significant attention in recent times owing to their opportunities in various functional applications. Interestingly, unlike fluorescence, opportunities hidden within the phosphorescence properties of organic compounds have received considerably less attention even until last few years. It is only in the second decade of the 21st century, within a time span of less than last 5 years, that the concepts and prospects of organic compounds as phosphorescent materials have evolved rapidly. The previously perceived limitations of organic compounds as phosphorescent materials have been overcome and several molecules have been designed using old and new concepts, such as heavy atom effects, matrix assisted isolation, hydrogen bonding and halogen bonding, thereby gaining access to a significant number of materials with efficient phosphorescent features. In addition, significant improvements have been made in the development of RTP (room temperature phosphorescent) materials, which can be used under ambient conditions. In this review, we bring together the vastly different approaches developed by various researchers to understand and appreciate this recent revolution in organic luminescent materials.

Ceramic Tiles with Photovoltaic Properties

The development of organic materials with photovoltaic properties should enable the production of polymeric solar cells with high conversion efficiency. Due to low production cost and conversion efficiency above 10%, organic solar cells have great potential to compete with inorganic photovoltaic cells. This work proposes the development and integration of ETA (extremely thin absorber) photovoltaic cells, based on titanium oxide films and nanostructured conductive polymer in ceramic tiles, with the purpose of increasing the available area for sunlight capture, normally limited to roofs, expanding it onto the lateral sides of buildings. The nanostructured TiO2 was obtained by sol-gel process from titanium isopropoxide, followed by supercritical CO2 extraction in order to obtain a nanostructured aerogel. The conductive polymer used was the poly-3.4 (ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) synthesized with iron III p-toluene sulfonate as an oxidizing agent. The materials were deposited layer by layer on a Cu electrode mounted on a ceramic tile piece, covered with glass containing a thin conductive layer of indium doped tin oxide (ITO). Transmission electron microscopy (TEM) revealed that the nanostructured titania aerogels exhibit particle sizes in the range of 2-5 nm. Preliminary studies have shown that the developed solar cell show a behavior typical of diodes (characteristic I×V curve) when subjected to different wavelength lamps (fluorescent and UV). Ceramic wall and roof tiles with photovoltaic properties, independently of the conversion efficiency, could serve as auxiliary energy sources to reduce expenses with conventional electricity.

Organic Materials for Deep Blue Phosphorescent Organic Light‐Emitting Diodes

Recently, great progress has been made in the device performance of deep blue phosphorescent organic light-emitting diodes (PHOLEDs) by developing high triplet energy charge-transport materials, high triplet energy host and deep blue emitting phosphorescent dopant materials. A high quantum efficiency of over 25% and a high power efficiency of over 15 lm/W have already been achieved at 1000 cd m(-2) in the deep blue PHOLEDs with a y color coordinate less than 0.20. In this work, recent developments in organic materials for high efficiency deep blue PHOLEDs are reviewed and a future strategy for the development of high efficiency deep blue PHOLEDs is proposed.

Ferromagnetism in Two-Dimensional Carbon Chains Linked by 1,3,5-Benzenetriyl Units

Development of organic materials with novel magnetic properties has been an important and challenging topic in organic chemistry. A useful paradigm in this direction is to have spin-containing (SC) components linked by ferromagnetic coupling (FC) units. Compared with the traditional SC components such as poly(1,3-phenylenecarbene)s and poly(1,3-phenylenephenylmethine)s, we show that the atomic carbon chains, due to their inherent magnetism and structural simplicity, can be promising magnetic building blocks of 2-D magnetic carbon structures. Using calculations based on density functional theory, we show that the structures constructed by the carbon chains with an odd number of C atoms linked by 1,3,5-benzenetriyl units are ferromagnetic. Independent of the chain length, each structural unit cell has a magnetic moment of 6.0μB and couples ferromagnetically in the 2-D lattice, although the energy difference between the ferromagnetic and antiferromagnetic coupling decreases with increasing chain length. The dynamic stability of the structures is confirmed by frequency calculations. The middle and high vibrational frequencies corresponding to the A1g and E2g modes of the structures with odd number carbon chains lie in the range of 950–1470 cm–1, which are lower than those (980 and 1555 cm–1) with even-numbered carbon chain structures. This suggests that Raman spectra can be used to identify the parity of carbon chains.

Organic Light-Emitting Devices for Solid-State Lighting

AbstractOrganic light-emitting devices (OLEDs) have been widely developed for flat-panel displays, but only recently the efficiency of white OLEDs has risen to the point where they can be considered for solid-state lighting (SSL) applications. In this review, we discuss the requirements of solid-state lighting as they relate to OLEDs. We focus on how the color, efficiency, and cost requirements of general illumination differ from those of displays and how these differences might have an impact on the design of organic SSL. We then present some recent developments in large-area fabrication techniques that might be appropriate for solid-state lighting applications. Finally, we review recent results in the development of organic materials, device architectures, light extraction schemes, and fabrication techniques that can lead to cost-effective OLED lighting.