Electronic structure engineering in organic thermoelectric materials

Electronic structures, which play a key role in determining electrical and optical properties of π-conjugated organic materials, have attracted tremendous interest. Efficient thermoelectric (TE) conversion of organic materials has rigorous requirements on electronic structures. Recently, the rational design and precise modulation of electronic structures have exhibited great potential in exploring state-of-the-art organic TE materials. This review focuses on the regulation of electronic structures of organic materials toward efficient TE conversion. First, we present the basic knowledge regarding electronic structures and the requirements for efficient TE conversion of organic materials, followed by a brief introduction of commonly used methods for electronic structure characterization. Next, we highlight the key strategies of electronic structure engineering for high-performance organic TE materials. Finally, an overview of the electronic structure engineering of organic TE materials, along with current challenges and future research directions, are provided.

Unexpected Photocatalytic Degeneration of NAD^(+) for Inducing Apoptosis of Hypoxia Cancer Cells

Developing customized chemical reactions that could regulate a specific biological process on demand is regarded as an advanced and promising strategy for treating diseases.However,conventional chemical reactions become challenging in complex physiological environments,which demand mild reaction conditions,high efficiency,good biocompatibility,and strong controllability.Moreover,the effects of the achieved reactions on the real biological system are usually further lessened.Herein,we describe an advanced photocatalytic reaction that irreversibly converted nicotinamide adenine dinucleotide(NAD+)to nicotinamide and adenosine diphosphate(ADP)-ribose by the cationic conjugated poly(fluorene-co-phenylene)(PFP).This reaction was introduced to tumor cells and triggered cell apoptosis.Under white-light illumination,the photocatalytic reaction decreased the NAD+ratio in tumor cells,disrupted the mitochondrial membrane potential,inhibited the synthesis of adenosine triphosphate(ATP),and effectively induced apoptosis.We propose a mechanism of the reaction where PFP is photoexcited to PFP*,and the obtained photoelectrons are transferred from PFP*to NAD+to produce nicotinamide and another unstable intermediate,ADP-ribosyl radical.ADP-ribosyl radical quickly reacts with triethanolamine to form ADP-ribose.This intracellular utilization of a specific photocatalytic reaction could offer a new approach to affect biological function for efficient cancer treatment.

Monolayer organic field-effect transistors

Monolayer organic field-effect transistors(OFETs) are attracting worldwide interest in device physics and novel applications due to their ultrathin active layer for two-dimensional charge transport. The monolayer films are generally prepared by thermal evaporation, the Langmuir technique or self-assembly process, etc., but their electrical performance is relatively lower than corresponding thick films. From 2011, the performance of monolayer OFETs has been boosted by using the monolayer molecular crystals(MMCs) as active channels, which opened up a new era for monolayer OFETs. In this review, recent progress of monolayer OFETs, including the preparation of monolayer films, their OFET performance and applications are summarized.Finally, perspectives of monolayer OFETs in the near future are also discussed.

Advances in organic thermoelectric materials and devices for smart applications

Organic thermoelectric(OTE)materials have been considered to be promising candidates for large area and low‐cost wearable devices owing to their tailorable molecular structure,intrinsic flexibility,and prominent solution processability.More importantly,OTE materials offer direct energy conversion from the human body,solid‐state cooling at low electric consumption,and diversified functions.Herein,we summarize recent developments of OTE materials and devices for smart applications.We first review the fundamentals of OTE materials from the viewpoint of thermoelectric performance,mechanical properties and bionic functions.Second,we describe OTE devices in flexible generators,photothermoelectric detectors,self‐powered sensors,and ultra‐thin cooling elements.Finally,we present the challenges and perspectives on OTE materials as well as devices in wearable electronics and fascinating applications in the Internet of Things.

A high mobility air-stable n-type organic small molecule semiconductor with high UV-visible-to-NIR photoresponse

An organic semiconductor with high carrier mobility and efficient light absorption over a wide spectral range is of the most important yet challenging material for constructing a broadband responsive organic photodetector.However,the development of such organic semiconductors,especially for air-stable n-type organic small molecule semiconductors,is still at an early stage.Here we report the fabrication of high-performance n-type semiconducting crystalline nanosheets and the development of air-stable field-effect transistors,phototransistors,with high response over a broad spectrum.The n-type small molecule semiconductor is assembled into a crystalline nanosheet based on the solvent-phase interfacial self-assembly method.N-type field-effect transistors with high electron mobility are fabricated and their electrical performances exhibit excellent air stability.Impressively,the demonstrated phototransistors exhibit an ultrahigh responsivity over a wide spectral range from 365 to 940 nm,with a maximum photoresponsivity of 9.2×10^(5) AW-1 and specific detectivity of 5.26×10^(13) Jones,which is the best performance among the reported n-type organic small molecule-based phototransistors.

Organic modification of carbon nanotubes

The organic modification of carbon nanotubes is a novel research field being developed recently. In this article, the history and newest progress of organic modification of carbon nanotubes are reviewed from two aspects: organic covalent modification and organic noncovalent modification of carbon nanotubes. The preparation and properties of organic modified carbon nanotubes are discussed in detail. In addition, the prospective development of organic modification of carbon nanotubes is suggested.

Optimization of the thermoelectric properties of poly(nickel-ethylenetetrathiolate) synthesized via potentiostatic deposition

The coordination polymer poly（nickel-ethylenetetrathiolate） （poly（Ni-ett））, formed by nickel（Ⅱ） and 1,1,2,2-ethenetetrathiolate （ett）, is the most promising N-type organic thermoelectric material ever reported; it is synthesized via potentiostatic deposition, and the effect of different applied potentials on the optimal performance of the polymers is investigated. The optimal thermoelectric property ofpoly（Ni-ett） synthesized at 0.6 V is remarkably greater than that of the polymers synthesized at 1 and 1.6 V, exhibiting a maximum power factor of up to 131.6μW/mK2 at 360 K. Furthermore, the structure-property correlation ofpoly（Ni-ett） is also extensively investigated. X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） analyses revealed that the larger size of crystalline domains and the higher oxidation state of poly（Ni-ett） synthesized at 0.6 V possibly results in the higher bulk mobility and carrier concentration in the polymer chains, respectively, accounting for the enhanced power factor.

Synthesis and antioxidative properties of polyphenol-fullerenes

Fullerene derivatives have exhibited fascinating properties in biological systems. Several antioxidative hindered phenol units were connected to Ceo called radical sponge, resulting in its excellent solubility in polar solvents. The stable radical scavenging experiments were performed with electron spin resonance spectroscopy. The results indicate that both samples show desirable efficiency in eliminating free radicals.

Organic transistor for bioelectronic applications

Organic field-effect transistors(OFETs) are recently considered to be attractive candidate for bioelectronic applications owing to their prominent biocompatibility,intrinsical flexibility,and potentially low cost associated with their solution processibility.Over the last few years,bioelectronic-application-motivated OFETs have attracted increasing attention towards next generation of biosensors,healthcare elements and artificial neural interfaces.This mini review highlights the basic principles and recent progress in OFET based bioelectronics devices.The key strategies and the forecast perspectives of this research field are also briefly summarized.

Electron structures and non-linear optical properties of tert butyl-nitro-phthalocyanines

The electron structures and the non-linear optical properties of phthalocyanines and asymmetrically substituted phthalocyanines are studied with the AM1 method. The results show that the fertbutyl-nitro-phthalocyanines have much higher second order non-linear optical coefficients .

Synthesis and magnetic property of a nitroxide based on C60

The compounds containing stable nitroxide radicals possess magnetic properties for the free radical have net magnetic moment. Oxidization of the [60]fulleropyrolidine obtained from the reaction of C60 with diketone and 2-aminoisobutyric acid by m-chloroperoxybenzoic acid gives a new nitroxide integrated with C60. The stable nitroxide based on C60 is confirmed to be antiferro-magnetism with quantum design superconducting quantum interference device (SQUID).

The highly conducting carbon electrodes derived from spin-coated polyacrylonitrile films

Carbon films prepared from pyrolyzation of spin-casted polyacrylonitrile （PAN） thin films display high electrical conductivity （〉600 S/cm, at 1000 ℃ carbonization）, low sheet resistance （about 100 Y2/square at the PAN film thickness of 70 nm） and partial transmittance. These pyrolyzed PAN （PPAN） films were patterned as bottom electrodes by photolithography, and utilized as drain and source electrodes to fabricate organic field-effect transistor （OFET） devices with a p-type semiconductor （P3HT） and an n-type semiconductor （DPP-containing quinoidal small molecule） through a spin-coating procedure. The results showed that the devices with the PAN electrodes exhibited almost the same excellent performance without any further modification compared to those devices with traditional Au electrodes. Since these PPAN films had the advantages of low-cost, high performance, easier for large-area fabrication, thermal and chemical stability, it should be a promising electrode material for organic electrodes.

A near-infrared porphyrin-based electron acceptor for non-fullerene organic solar cells

In this work, a new star-shaped electron acceptor based on porphyrin as core, rhodanine and benzothiadiazole as end groups, was developed for non-fullerene solar cells. The molecule shows three distinct absorption regions due to the Sorer and Q-bands of the porphyrin and the intramolecular charge transfer in the molecule. This molecule as electron acceptor was applied into non-fullerene solar cells by using a diketopyrrolopyrrole-based conjugated polymer as electron donor, An initial PCE of 1.9% was achieved with a broad photo-response from 300-850 nm. The results demonstrate that porphyrin can be used to design near-infrared electron acceptors for organic solar cells.

Recent Advances in Molecular Design of Organic Thermoelectric Materials

Organic thermoelectric(OTE)materials have gained widespread attention because of their potential for wearable power generators and solid cooling elements.Nevertheless,the development of state-ofthe-art OTE materials still suffers from limited molecular categories because of the rarity ofmolecular design strategies,which limits further development of this emerging field.Recently,many efforts have been devoted to developing molecular design concepts for high performance OTE materials.

Special Topic on Molecular Functional Materials and Applications

Molecular functional materials have received increasing attentions in recent years because of their promising applications in various areas.Chinese scientists have made important contributions to the development of this area.In order to further promote research activities of this area in China and strengthen academic exchanges and collaborations,the Committee of Organic Solids of Chinese Chemical Society(CCS)organized the 10th National Symposium on Electronic Process in Organic Solids during August7–10,2015 at Peking University.

Thermoelectric properties of metal-(Z)-1,2-dihydroselenoethene-1,2-dithiol coordination polymers

Thermoelectric(TE)materials can realize mutual energy conversion between heat and electricity and are applied broadly in energy harvesting,local cooling or heating,and thermal sensing[1].TE devices are crucial to solve the global energy crisis with renewable energy resources.Currently,most of the research works are focused on inorganic TE materials because of their superior performance.Very recently,due to the growing demands

Influence of organic acids on UV-Vis spectra of pyrrolidino-[60]fullerene derivatives

A pyrrolidino[60]fullerene 1 with pyrrolidine group was synthesized and characterized. The UV-Vis spectra showed that the blue shift of absorption peaks was first observed when strong organic acids such as p-toluene sulfo-nic or trifluoroacetic acid were added to the solution of pyr-rolidino[60]fullerene 1 in dichloromethane. The results indicated that the pyrrolidino[60]fullerene derivatives without pyrrolidine group also possess the same phenomenon. Experiments and computation with the MOPAC 7.0 semi-empirical PM3 method demonstrated the reason that some energy gaps on [60]fullerene skeleton were increased because electronic charges on [60]fullerene framework transferred to pyrrolidine ring when strong organic acids were added into pyrrolidino[60]fullerene derivatives’ solution; as the result, the complexes could be formed and some absorption wavelengths blue shifted in the UV-Vis spectrum.

Production of Graphene Nanospheres by Annealing of Graphene Oxide in Solution

We report a simple method to produce graphene nanospheres （GNSs） by annealing graphene oxide （GO） solution at high-temperature with the assistance of sparks induced by the microwave absorption of graphite flakes dispersed in the solution. The GNSs were formed by rolling up of the annealed GO, and the diameters were mostly in the range 300-700 nm. The GNS exhibited a hollow sphere structure surrounded by graphene walls with a basal spacing of 0.34 nm. Raman spectroscopy and X-ray photoelectron spectroscopy of the GNSs confirmed that the GO was efficiently reduced during the fabrication process. The resulting GNSs may open up new opportunities both for fundamental research and applications, and this method may be extended to the synthesis of other nanomaterials and the fabrication of related nanostructures.

Tuning Reaction Processes for the Synthesis of Micron and Nanometer Sized, Single Crystalline Lamellae of Copper 7,7,8,8-tetracyano-p-quinodimethane (Phase II) with Large Area

Two simple methods have been demonstrated to obtain large area,single crystalline lamellae of copper-7,7,8,8-tetracyanoquinodimethane(CuTCNQ).The formation of the lamellae was a result of fine tuning of the processes during the synthesis processes of CuTCNQ phase II.This facile synthesis of large area single crystalline lamellae suggests bright prospects for the study and understanding of the electrical switching of CuTCNQ by using single crystals of its phase II,and future applications of the material in memory and switching devices.