以苝酰亚胺为构筑单元的氢键型超分子聚合物的组装与应用

以苝酰亚胺为构筑单元的氢键型超分子聚合物具有动态可逆的特征和独特的聚集体结构,呈现出许多新颖的光电功能特性,在有机太阳能电池,场效应晶体管和光收集材料等高新技术领域有着广阔的应用前景。本文在介绍苝酰亚胺衍生物的化学结构及其氢键组装特点的基础上,主要综述了近年来以苝酰亚胺为构筑单元,采用三重氢键,多重氢键以及其他形式氢键引导构筑的超分子聚合物的研究动态,这类超分子聚合物展示了丰富的组装体形貌结构,独特的性质功能以及在光电功能器件上的广阔的应用前景。最后,对其发展前景作了展望。     

Linear pi-conjugated systems derivatized with C60-fullerene as molecular heterojunctions for organic photovoltaics

This tutorial review covers recent contributions in the area of linear pi-conjugated systems bound to fullerenes in view of their application as active materials in photovoltaic devices. The first part discusses the concepts of double-cable polymer and molecular hetero-junction and presents several examples of chemically or electrochemically synthesized C60-derivatized conjugated polymers. The second and main part of the article concerns the various classes of C60-derivatized pi-conjugated oligomers designed in view of their utilization in single-component photovoltaic devices. Thus, C60-containing pi-conjugated systems such as oligoarylenevinylenes, oligoaryleneethynylenes and oligothiophenes are discussed on the basis of the relationships between molecular structure, photophysical properties and performances of the derived photovoltaic devices. A brief last section presents some recent examples of surface-attached molecular hetero-junctions based on self-assembled monolayers and discusses possible routes for future research.     

Designing of the white-light emission from a single-polymer system: Quantum theoretical study

Quantum-chemical calculations are applied to study the white-light emission from a single-polymer system with simultaneous blue (polyfluorene as a blue host) and orange (2,1,3-benzothiadiazole-based derivative as an orange dopant) emissions. Particular attention is paid to the variation in electronic and optical properties upon the structure tuning in pristine 2,1,3-benzothiadiazole-based derivative. Importantly, by the introduction of electron-donating groups on terminal N,N-disubstituted amino groups, the electronic and optical properties of designed 2,1,3-benzothiadiazole-based derivative have been tuned, making them to be potential candidates as orange dopants in white organic light-emitting devices based on polymers with polyfluorene as a blue-light-emitting host. Furthermore, designed 2,1,3-benzothiadiazole-based derivatives have a possibility to be good hole or ambipolar transport materials in organic light-emitting diodes from the charge hopping model. Finally, we find that the designed 2,1,3-benzothiadiazole-based derivative exhibit improved stability.     

Solution-processed bilayer photovoltaic devices with nematic liquid crystals

The cross-linking of polymerisable liquid crystalline semiconductors is a promising approach to solution-processable, multilayer, organic photovoltaics. Here we demonstrate an organic bilayer photovoltaic with an insoluble electron-donating layer formed by cross-linking a nematic reactive mesogen. We investigate a range of perylene diimide (PDI) materials, some of which are liquid crystalline, as the overlying electron acceptor layer. We find that carrier mobility of the acceptor materials is enhanced by liquid crystallinity and that mobility limits the performance of photovoltaic devices.     

Understanding and controlling organic-inorganic interfaces in mesostructured hybrid photovoltaic materials

The chemical compositions and structures of organic-inorganic interfaces in mesostructurally ordered conjugated polymer-titania nanocomposites are shown to have a predominant influence on their photovoltaic properties. Such interfaces can be controlled by using surfactant structure-directing agents (SDAs) with different architectures and molecular weights to promote contact between the highly hydrophobic electron-donating conjugated polymer species and hydrophilic electron-accepting titania frameworks. A combination of small-angle X-ray scattering (SAXS), scanning and transmission electron microscopy (SEM, TEM), and solid-state NMR spectroscopy yields insights on the compositions, structures, and distributions of inorganic and organic species within the materials over multiple length scales. Two-dimensional NMR analyses establish the molecular-level interactions between the different SDA blocks, the conjugated polymer, and the titania framework, which are correlated with steady-state and time-resolved photoluminescence measurements of the photoexcitation dynamics of the conjugated polymer and macroscopic photocurrent generation in photovoltaic devices. Molecular understanding of the compositions and chemical interactions at organic-inorganic interfaces are shown to enable the design, synthesis, and control of the photovoltaic properties of hybrid functional materials.     

Highly Efficient Au(I) Alkynyl Emitters: Thermally Activated Delayed Fluorescence and Solution-Processed OLEDs

Two-coordinate donor-metal-acceptor type coinage metal complexes displaying efficient thermally activated delayed fluorescence (TADF) have been unveiled to be highly appealing candidates as emitters for organic light-emitting diodes (OLEDs). Herein a series of green to yellow TADF gold(I) complexes with alkynyl ligands has been developed for the first time. The complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 0.76 in doped films (5 wt % in PMMA) at room temperature. The modifications of alkynyl ligands with electron-donating amino groups together with the use of electron-deficient carbene ligands induce ligand-to-ligand charge transfer excited states that give rise to TADF emission. Spectroscopic and density functional theory (DFT) calculations reveal the roles of electron-donating capability of the alkynyl ligand in tuning the excited-state properties. Solution-processed organic light-emitting diodes (OLEDs) using the present complexes as emitters achieve maximum external quantum efficiency (EQE) of up to 20 %.     

Theoretical investigation of optical and electronic property modulations of pi-conjugated polymers based on the electron-rich 3,6-dimethoxy-fluorene unit

Poly(fluorene)-type materials are widely used in polymer-based emitting devices. One of the drawbacks of light-emitting diodes based on polyfluorene derivatives is the injection of holes from the anode due to the high ionization potential (IP) of most derivatives. Substitution by electron-donating alkoxy substituents or by adding charge carriers on the conjugated polymer's backbone produces a remarkable influence on its electrical and optical properties. In this contribution, we apply quantum-chemical techniques to investigate a family of pi-conjugated polymers with substituted dimethoxy groups at the 3,6 positions of the fluorene ring, namely, poly(2,7-(3,6-dimethoxy-fluorene)(PDMOF), poly(2,7-(3,6-dimethoxy-fluorene)-co-alt-fluorene (PDMOFF), and poly(2,7-(3,6-dimeth-oxy-fluorene)-co-alt-2,5-thiophene (PDMOFT). The electronic properties of the neutral molecules, HOMO-LUMO gaps (Delta(H)(-)(L)), in addition to the positive and negative ions, are studied using the B3LYP functional. The lowest excitation energies (E(g)) and the maximal absorption wavelength lambda(abs) of PDMOF, PDMOFF, and PDMOFT are studied by employing time-dependent density functional theory (TD-DFT) and the ZINDO semiempirical method. The IP, EA, and E(g) values of each polymer were obtained by extrapolating those of the oligomers to the inverse chain length equal to zero ((1)/(n)() = 0). The influence of the presence of methoxy groups on the fluorene moiety on the ionization potential is especially emphasized. The outcomes show that the HOMO energies of these systems under study increase by about 0.4 eV and the IP values decrease by about 0.3 eV compared to those of the corresponding polyfluorene. Both effects result in a reduction of the energy barrier for the injection of holes in related polymeric light-emitting devices and should contribute to the enhancement of their performances. Because of the cooperation with thiophene in PDMOFT, which results in a good planar conformation, both the hole-creating and electron-accepting abilities are improved.     

Selective tuning of the band gap of pi-conjugated dithieno[3,2-b:2',3'-d]phospholes toward different emission colors

The systematic extension of the pi-conjugated system of strongly blue-luminescent dithieno[3,2-b:2',3'-d]phospholes has been investigated with the goal of obtaining different emission colors. Functionalization of the 2- and 6-position of the dithienophosphole scaffold with halogen substituents provided functional building blocks for subsequent cross-coupling experiments with various homo- and heteroaryls to selectively decrease the band gap of the materials. By this strategy materials with different emission colors ranging from green via yellow to orange could be obtained. This feature supports their suitability for organic light-emitting diodes with respect to an application in full-color flat-panel displays. The experimental results were nicely supported by theoretical DFT calculations providing a deeper understanding of the electronic structure in the extended materials, and also allowing for the design of future materials based on a dithienophosphole core. Furthermore, the phosphorus center in the extended molecular materials can efficiently be fine-tuned in subsequent simple chemical functionalizations. This allows for a tailoring of the optoelectronic properties of the extended dithienophospholes to suit the requirements of potential applications.     

环戊二噻吩中的硫原子被CH2、SiH2取代对化合物光电性质影响的理论研究

有机电致发光材料是国际上的研究热点之一。本文采用量子化学方法,研究了环戊二噻吩CH2和SiH2取代对其与2,1,3-苯并噻二唑和三苯胺的化合物光电性质的影响。研究结果表明,CH2取代对母体分子的电子和光谱性质的影响比SiH2取代明显。SiH2取代使吸收和发射光谱的振子强度增大的程度大于CH2取代,更有利于发光强度的提高。CH2和SiH2取代衍生物的空穴和电子重组能的差值极小,可以作为有机电致发光二极管中双极性电荷传输材料。静电势能结果表明,SiH2取代衍生物的稳定性高于母体分子的稳定性。通过探索分子结构与性质间关系,为实验设计合成新的有机电致发光材料提供了理论支持。     

Highly Emissive 9-Borafluorene Derivatives: Synthesis,Photophysical Properties and Device Fabrication

A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m⁻². These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability.     

Influence of molecular order on the local work function of nanographene architectures: a Kelvin-probe force microscopy study.

We report a Kelvin-probe force microscopy (KPFM) investigation on the structural and electronic properties of different submicron-scale supramolecular architectures of a synthetic nanographene, including extended layers, percolated networks and broken patterns grown from solutions at surfaces. This study made it possible to determine the local work function (WF) of the different pi-conjugated nanostructures adsorbed on mica with a resolution below 10 nm and 0.05 eV. It revealed that the WF strongly depends on the local molecular order at the surface, in particular on the delocalization of electrons in the pi-states, on the molecular orientation at surfaces, on the molecular packing density, on the presence of defects in the film and on the different conformations of the aliphatic peripheral chains that might cover the conjugated core. These results were confirmed by comparing the KPFM-estimated local WF of layers supported on mica, where the molecules are preferentially packed edge-on on the substrate, with the ultraviolet photoelectron spectroscopy microscopically measured WF of layers adsorbed on graphite, where the molecules should tend to assemble face-on at the surface. It appears that local WF studies are of paramount importance for understanding the electronic properties of active organic nanostructures, being therefore fundamental for the building of high-performance organic electronic devices, including field-effect transistors, light-emitting diodes and solar cells.     

Electronic structure of NPB and BCP molecules probed by x-ray emission spectroscopy

Soft x-ray absorption and emission spectroscopies have been employed to investigate the electronic structure and chemical bonding of two prototypical molecules, N,N(')-bis-(1-naphthyl)-N,N(')-diphenyl-1,1(')-biphenyl-4,4(')-diamine (NPB) and bathocuproine (BCP), which are frequently chosen because of their hole-transporting and hole-blocking properties, respectively. The resulting resonant C Kalpha x-ray emission spectra of these materials reveal different spectral features depending on the resonant excitation energy. According to the N absorption and emission spectra, the contribution of N atoms to the highest occupied and lowest unoccupied molecular orbitals is different for in NPB and in BCP. Detailed knowledge of these materials will allow tailoring charge transport properties of organic devices in order to develop high performance organic light-emitting diodes and photovoltaic cells.     

Oxidation properties of β-substituted pyrroles

Pyrroles represent building blocks of conjugated poly(heterocycles) which, as organic conductors, are potential materials for organic electronics. Oxidation of β-substituted pyrroles constitutes an important first step in the process of electropolymerization. Ionization energy and the electron spin density distribution are two the most important properties regarding monomers. These properties are studied as a function of electron-withdrawing and electron-donating substituents of pyrrole ring. Evolution of molecular structure, nature of bonding, and electronic density are studied as an effect of ionization process.     

Effective manipulation of the electronic effects and its influence on the emission of 5-substituted tris(8-quinolinolate) aluminum(III) complexes

The unique electron-transport and emissive properties of tris(8-quinolinolate) aluminum(III) (Alq(3)) have resulted in extensive use of this material for small molecular organic light-emitting diode (OLED) fabrication. So far, efforts to prepare stable and easy-to-process red/green/blue (RGB)-emitting Alq(3) derivatives have met with only a limited success. In this paper, we describe how the electronic nature of various substituents, projected via an arylethynyl or aryl spacer to the position of the highest HOMO density (C5), may be used for effective emission tuning to obtain blue-, green-, and red-emitting materials. The synthetic strategy consists of four different pathways for the attachment of electron-donating and electron-withdrawing aryl or arylethynyl substituents to the 5-position of the quinolinolate ring. Successful tuning of the emission color covering the whole visible spectrum (lambda=450-800 nm) was achieved. In addition, the photophysical properties of the luminophores were found to correlate with the Hammett constant of the respective substituents, providing a powerful strategy with which to predict the optical properties of new materials. We also demonstrate that the electronic nature of the substituent affects the emission properties of the resulting complex through effective modification of the HOMO levels of the quinolinolate ligand.     

Exciplex emission from electroluminescent ladder-type pentaphenylene oligomers bearing both electron- and hole-accepting substituents

We examine the photophysical properties of ladder-type pentaphenylenes, which have been prepared as prototypical "all-in-one" emissive materials bearing both electron-accepting (diaryloxadiazole) and electron-donating (triphenylamine) units. We find that donor-acceptor interactions are very dependent on the nature of the connectivity of these groups to the main pentaphenylene chain. When the oxadiazole and triphenylamine units were substituted on opposite sides of the pi-conjugated pentaphenylene chromophore, photoluminescence with long lifetimes typical of exciplex-like species was observed, while being significantly quenched by intermolecular charge separation between the substituents. By contrast, when the triphenylamine units were attached at the ends of the chromophore, no such effects were observed and a blue/green photoluminescence was obtained with very high quantum efficiency. In this latter configuration, evidence of ambipolar charge transport and a blue/green electroluminescence were additionally observed.     

Dipyrrin-based Complexes for Solution-processed Organic Solar Cells

Three dipyrrin-containing metal complexes and a boron dipyrromethene(BODIPY)-containing complex were designed and synthesized. The photophysical properties, electrochemical behaviours and photovoltaic performance were extensively investigated. Density functional theory calculations were also performed on those complexes. These complexes, together with electron-acceptor [6,6]-phenyl-C71-butyric acid methyl ester, were utilized for the fabrication of solution-processed bulk heterojunction solar cells as the electron-donor materials. The more efficient electron acceptor BODIPY segment renders a lower energy gap and a relatively better photovoltaic conversion efficiency of 0.58%. These results prove that BODIPY segment has a great potential for constructing efficient organic solar cell materials.     

Structural Fusion Yields Guest Acceptors that Enable Ternary Organic Solar Cells with 18.77 % Efficiency

The design and selection of a suitable guest acceptor are particularly important for improving the photovoltaic performance of ternary organic solar cells (OSCs). Herein, we designed and successfully synthesized two asymmetric silicon–oxygen bridged guest acceptors, which featured distinct blue-shifted absorption, upshifted lowest unoccupied molecular orbital energy levels, and larger dipole moments than symmetric silicon–oxygen-bridged acceptor. Ternary devices with the incorporation of 14.2 wt % these two asymmetric guest acceptors exhibited excellent performance with power conversion efficiencies (PCEs) of 18.22 % and 18.77 %, respectively. Our success in precise control of material properties via structural fusion of five-membered carbon linkages and six-membered silicon–oxygen connection at the central electron-donating core unit of fused-ring electron acceptors can attract considerable attention and bring new vigor and vitality for developing new materials toward more efficient OSCs.     

Novel bipolar host for highly efficient green,yellow, orange,red and deep-red phosphorescent organic light-emitting devices

A novel bipolar host tris(4-(pyrimidin-5-yl)phenyl)amine (TPMTPA) constructed by incorporating triphenylamine as the electron-donating core and pyrimidine as the electron-accepting peripheries was designed and synthesized. TPMTPA achieves excellent bipolar charge transport properties and has high enough triplet energy level to sensitize green, yellow, orange, red and deep-red phosphors. By using TPMTPA as a host, high performance green, yellow, orange, red and deep-red phosphorescent organic light-emitting devices (PhOLEDs) were demonstrated with maximum external quantum efficiencies of 20.4%, 17.6%, 15.1%, 15.3% and 15.7% respectively. These results suggested that TPMTPA is a versatile high performance host for PhOLEDs of different emission colors.     

Increasing the open circuit voltage of bulk-heterojunction solar cells by raising the LUMO level of the acceptor

We report the synthesis, characterization, and electrochemical properties of ten new fullerene derivatives for usage in organic solar cells. The phenyl ring of PCBM was substituted with electron-donating and electron-withdrawing substituents to study their influence on the LUMO level of the parent fullerene. We varied the LUMO level over a range of 86 mV and show a small but significant change of the open circuit voltage upon application in MDMO-PPV:methanofullerene bulk-heterojunction photovoltaic cells. [structure: see text].     

Effect of axial ligands on the photophysical properties of new silicon(IV) phthalocyanines

A series of axial di-substituted silicon(IV) phthalocyanines with electron-donating and electron-withdrawing properties were synthesized. The compounds were characterized by elemental analysis, ¹H NMR, IR, and ESI-MS. The effect of axial ligands on the photophysical properties of silicon phthalocyanines was studied by UV/Vis, steady-state and time-resolved fluorescence spectroscopic analyses. Compared with silicon phthalocyanines with electron-donating properties, silicon phthalocyanines with electron-withdrawing properties could expand the π-conjugation in the dyes, resulting in a redshift of Q bands, lower fluorescence emission intensity and fluorescence quantum yields, but increasing fluorescence lifetimes. These results strongly suggest that the molecular design of phthalocyanines is essential for construction of photoactive materials.