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1.
Advanced organic laser dyes exhibiting high solubility and bipolar behavior are developed based on a structure combining bis‐stilbene with carbazole (BSBCz). The materials show high photoluminescence quantum yields and large radiative rate constants in solutions, crystals, and blend and neat films. The introduction of alkyl groups significantly improves the solubility of BSBCz, and solution‐processed films of the alkyl‐substituted derivatives exhibit amplified spontaneous emission thresholds as low as 0.59 µJ cm?2, which is comparable to those of vacuum‐deposited BSBCz films. On the other hand, cyano‐substitution on BSBCz (BSBCz‐CN) increases electron‐accepting properties, resulting in a bathochromic shift of the emission wavelength and improved bipolar behavior. In a BSBCz‐CN‐doped film, a low ASE threshold of 0.63 µJ cm?2 is achieved, which is one of the lowest values for organic laser dyes with green emission. In addition, organic light‐emitting diodes based on BSBCz‐CN neat films exhibit external quantum efficiencies of 1.8% and could withstand injection of high current densities of up to 500 A cm?2 under pulse operation. These properties along with low excited‐state absorption cross sections make these materials an outstanding addition to the existing library of organic laser dyes, especially for consideration in electrically pumped lasers.  相似文献   

2.
A novel asymmetrically substituted dicyano‐tri‐tert‐butylphthalocyanine ((CN)2BuPc) with rectifying behavior has been synthesized. The morphology and conductive properties of (CN)2BuPc Langmuir–Blodgett (LB) films on mica and highly ordered pyrolytic graphite (HOPG) substrates were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), in air at 22 °C. The average area of each (CN)2BuPc molecule obtained from the AFM topography in situ is ca. 73.6 Å2, which is in good agreement with the result of ca. 74 Å2 obtained from the π–A isotherm curve of a LB film. This indicates that the molecules are standing edge‐on, tilted by 38° against the surface normal of the substrate. The conductive properties for the 7‐layer LB films of (CN)2BuPc were studied by STM with a tungsten tip. The asymmetric IV curve revealed a type of rectifying behavior for a negative and a positive bias. A feature model of the intramolecular and intermolecular charge transfer is presented. It not only interprets electron transfer from electron‐donor to electron‐acceptor molecules via a molecular “bridge”, but also the tunneling effect through intermolecular charge transfer.  相似文献   

3.
The synthesis via the Stille coupling of a new family of oligomers derived from benzo[b]thiophene is reported. Owing to their branched molecular structure lacking any symmetry element, these compounds display a low tendency to crystallization and better film‐forming properties than their linear counterparts. Spin‐coated films show photoluminescence efficiencies up to 50 %. Light‐emitting diodes with spin‐coated films as the active layers display markedly improved performance with respect to similar devices based on linear oligothiophenes, with luminance values up to more than 10 000 cd m–2. Semiempirical PM3 and ZINDO/S calculations provide insight into the molecular geometries and electron distribution of the frontier orbitals of the new compounds. Cyclic voltammetry data indicates that the transformation of the thienyl sulfur of benzo[b]thiophene to the corresponding thienyl‐S,S‐dioxide leads an increase in electron affinity by 0.5–0.7 V, analogous to that of the corresponding linear oligomers.  相似文献   

4.
Efficient synthesis of a series of terminally dicyanovinyl (DCV)‐substituted oligothiophenes, DCVnT 1–6, without solubilizing side chains synthesized via a novel convergent approach and their application as electron donors in vacuum‐processed m‐i‐p‐type planar and p‐i‐n‐type bulk heterojunction organic solar cells is described. Purification of the products via gradient sublimation yields thermally highly stable organic semiconducting materials in single crystalline quality which allows for X‐ray structure analysis. Important insights into the packing features and intermolecular interactions of these promising solar cell materials are provided. Optical absorption spectra and electrochemical properties of the oligomers are investigated and valuable structure–property relationships deduced. Photovoltaic devices incorporating DCVnTs 4–6 showed power conversion efficiencies up to 2.8% for planar and 5.2% for bulk heterojunction organic solar cells under full sun illumination (mismatch corrected simulated AM 1.5G sunlight). The 5.2% efficiency shown here represents one of the highest values ever reported for organic vacuum‐deposited single heterojunction solar cells.  相似文献   

5.
A series of novel acceptor–donor–acceptor oligothiophenes terminally substituted with the 1‐(1,1‐dicyanomethylene)‐cyclohex‐2‐ene (DCC) acceptor has been synthesized. Structural, thermal, optoelectronic, and photovoltaic properties of the π‐extended DCCnTs (n = 1–4) are characterized and contrasted to the trends found for the series of parent dicyanovinyl (DCV)‐substituted oligothiophenes DCVnT. The optoelectronic properties reveal the influence of the additional exocyclic, sterically fixed double bonds in trans‐configuration in the novel DCCnT derivatives. A close correspondence for derivatives with equal number of double bonds, that is, DCCnTs and DCV(n + 1)Ts, is identified. Despite having the same energy gap, the energy levels of the frontier orbitals, HOMO and LUMO, for the DCC ‐ derivatives are raised and more destabilized due to the aromatization energy of a thiophene ring versus two exocyclic double bonds indicating improved donor and reduced acceptor strength. DCC‐terthiophenes give good photovoltaic performance as donor materials in vacuum‐processed solar cells (power conversion efficiencies ≤ 4.4%) clearly outperforming all comparable DCV4T derivatives.  相似文献   

6.
Graphitic carbon nitride (g‐CN) is a promising heterogeneous metal‐free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants. Its catalytic performance is easily adjustable by modifying texture, optical, and electronic properties via nanocasting, doping, and copolymerization. However, simultaneous optimization has yet to be achieved. Here, a facile synthesis of mesoporous g‐CN using molecular cooperative assembly between triazine molecules is reported. Flower‐like, layered spherical aggregates of melamine cyanuric acid complex (MCA) are formed by precipitation from equimolecular mixtures in dimethyl sulfoxide (DMSO). Thermal polycondensation of MCA under nitrogen at 550 °C produces mesoporous hollow spheres comprised of tri‐s‐triazine based g‐CN nanosheets (MCA‐CN) with the composition of C3N4.14H1.98. The layered structure succeeded from MCA induces stronger optical absorption, widens the bandgap by 0.16 eV, and increases the lifetime of photoexcited charge carriers by twice compared to that of the bulk g‐CN, while the chemical structure remains similar to that of the bulk g‐CN. As a result of these simultaneous modifications, the photodegradation kinetics of rhodamine B on the catalyst surface can be improved by 10 times.  相似文献   

7.
The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F6TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F6TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm2 V?1 s1 being estimated from SCLC measurements for BTBT:F6TNAP and CBZ:F6TNAP cocrystals.  相似文献   

8.
We have designed and successfully synthesized star‐shaped oligothiophenes, which could be used as semiconducting materials for solution‐processible organic field‐effect transistors (FETs). By systematically changing the chemical structure of the star‐shaped oligothiophenes we obtained the structural requirements needed for making working FETs from them. UV‐vis fluorescence measurements showed that a molecule of the star‐shaped compounds under consideration is not a fully conjugated molecule, but it has three independently conjugated oligothienyl‐phenylene blocks. A possible scheme of molecular packing of the star‐shaped oligothiophenes in a lamellar structure was proposed and confirmed by atomic force microscopy (AFM) and X‐ray diffraction (XRD) measurements. Although the star‐shaped semiconductors show a somewhat lower mobility than their linear analogs, they possess better solubility and film‐forming properties, leading to improved spin‐coating processing. The best FETs were made by spin‐coating 1,3,5‐tris(5″‐decyl‐2,2′:5′,2″‐terthien‐5‐yl)benzene from a chloroform solution, which resulted in a mobility of 2 × 10–4 cm2 V –1s–1, a 102 on/off ratio at gate voltages of 0 V and –20 V, and a threshold voltage close to 0 V.  相似文献   

9.
A series of liquid‐crystalline (LC) π‐ ‐conjugated oligothiophenes bearing three or two alkoxy chains at their extremities has been designed and synthesized. These polycatenar oligothiophenes form various LC nanostructures including smectic, columnar, and micellar cubic phases. These properties depend on the number and length of the terminal alkoxy chains. The hole mobilities for the oligothiophenes have been measured. The layered smectic and columnar structures are capable of transporting holes, leading to mobilities of up to 0.01 cm2 V?1 s?1. The columnar LC assemblies have also been explored to produce linearly polarized light‐emission. Fine red polarized fluorescence is observed from a uniaxially aligned film of the oligothiophenes. The redox properties of the oligothiophenes both in solutions and in films have been examined. The oligothiophenes exhibit electrochromism upon applying an oxidative potential. The present design strategy is useful for fabricating a variety of functional electro‐active molecular assemblies.  相似文献   

10.
The highly photosensitive characteristics of organic thin‐film transistors (OTFTs) made using soluble star‐shaped oligothiophenes with four‐armed π‐conjugation paths, 4(HPBT)‐benzene and 4(HP3T)‐benzene molecules having a relatively high quantum yield, are reported. 4(HPBT)‐benzene‐based organic phototransistors (OPTs) exhibited high photosensitivity (~2500–4300 A W?1) even with low optical powers (~6.8–30 µW cm?2) at zero gate bias. The measured photosensitivity of the devices was much higher than that of inorganic single‐crystal Si‐based phototransistors, as well as that of other OPTs reported earlier. With the highly photosensitive characteristics of the 4(HPBT)‐benzene‐based OPTs, a high ratio of the on and off current switching of ~4 × 104 with low optical power and low gate bias was observed. The slow relaxation of the photoinduced charges and charge‐trapping phenomena at the interface could lead to a reproducible memory operation for 4(HPBT)‐benzene‐based OPTs.  相似文献   

11.
A novel family of soluble conjugated dendritic oligothiophenes (DOTs) as monodisperse 3D macromolecular architectures was characterized with respect to optical and redox properties in solution and in solid films. Band gaps of 2.5–2.2 eV, typical for organic semiconductors, were determined as well as HOMO/LUMO energy levels ideal for efficient electron transfer to acceptors such as [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) identifying them as suitable materials for solar cell applications. Solution‐processed bulk‐heterojunction solar cells using DOTs as electron donor and PCBM as acceptor were prepared and investigated. High open‐circuit voltages VOC of 1.0 V and power‐conversion efficiencies up to 1.72% were obtained for the DOT‐based devices. The higher generations DOTs provide the highest efficiencies. Based on the monodispersity of the DOTs, an analysis of the molar ratio between donor and acceptor in the blended film was possible leading to an optimal value of five to six thiophene units per PCBM.  相似文献   

12.
Organic crystals that combine high charge‐carrier mobility and excellent light‐emission characteristics are expected to be of interest for light‐emitting transistors and diodes, and may offer renewed hope for electrically pumped laser action. High‐luminescence‐efficiency cyano‐substituted oligo(p‐ phenylene vinylene) (CN‐DPDSB) crystals (η ≈ 95%) grown by the physical vapor transport method is reported here, with high mobilities (at ≈10?2 cm2 V?1 s?1 order of magnitude) as measured by time‐of‐flight. The CN‐DPDSB crystals have well‐balanced bipolar carrier‐transport characteristics (μhole≈ 2.5–5.5 × 10?2 cm2 V?1 s?1; μelectron ≈ 0.9–1.3 × 10?2 cm2 V?1 s?1) and excellent optically pumped laser properties. The threshold for amplified spontaneous emission (ASE) is about 4.6 μJ per pulse (23 KW cm?2), while the gain coefficient at the peak wavelength of ASE and the loss coefficient caused by scattering are ≈35 and ≈1.7 cm?1, respectively. This indicates that CN‐DPDSB crystals are promising candidates for organic laser diodes.  相似文献   

13.
Electron injection from the source–drain electrodes limits the performance of many n‐type organic field‐effect transistors (OFETs), particularly those based on organic semiconductors with electron affinities less than 3.5 eV. Here, it is shown that modification of gold source–drain electrodes with an overlying solution‐deposited, patterned layer of an n‐type metal oxide such as zinc oxide (ZnO) provides an efficient electron‐injecting contact, which avoids the use of unstable low‐work‐function metals and is compatible with high‐resolution patterning techniques such as photolithography. Ambipolar light‐emitting field‐effect transistors (LEFETs) based on green‐light‐emitting poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) and blue‐light‐emitting poly(9,9‐dioctylfluorene) (F8) with electron‐injecting gold/ZnO and hole‐injecting gold electrodes show significantly lower electron threshold voltages and several orders of magnitude higher ambipolar currents, and hence light emission intensities, than devices with bare gold electrodes. Moreover, different solution‐deposited metal oxide injection layers are compared. By spin‐coating ZnO from a low‐temperature precursor, processing temperatures could be reduced to 150 °C. Ultraviolet photoemission spectroscopy (UPS) shows that the improvement in transistor performance is due to reduction of the electron injection barrier at the interface between the organic semiconductor and ZnO/Au compared to bare gold electrodes.  相似文献   

14.
Sodium manganese hexacyanoferrate (NaxMnFe(CN)6) is one of the most promising cathode materials for sodium‐ion batteries (SIBs) due to the high voltage and low cost. However, its cycling performance is limited by the multiple phase transitions during Na+ insertion/extraction. In this work, a facile strategy is developed to synthesize cubic and monoclinic structured NaxMnFe(CN)6, and their structure evolutions are investigated through in situ X‐ray diffraction (XRD), ex situ Raman, and X‐ray photoelectron spectroscopy (XPS) characterizations. It is revealed that the monoclinic phase undergoes undesirable multiple two‐phase reactions (monoclinic ? cubic ? tetragonal) due to the large lattice distortions caused by the Jahn–Teller effects of Mn3+, resulting in poor cycling performances with 38% capacity retention. The cubic NaxMnFe(CN)6 with high structural symmetry maintains the structural stability during the repeated Na+ insertion/extraction process, demonstrating impressive electrochemical performances with specific capacity of ≈120 mAh g?1 at 3.5 V (vs Na/Na+), capacity retention of ≈70% over 500 cycles at 200 mA g?1. In addition, the TiO2//C‐MnHCF full battery is fabricated with an energy density of 111 Wh kg?1, suggesting the great potential of cubic NaxMnFe(CN)6 for practical energy storage applications.  相似文献   

15.
Defects at the surface and grain boundaries of metal–halide perovskite films lead to performance losses of perovskite solar cells (PSCs). Here, organic cyano‐based π‐conjugated molecules composed of indacenodithieno[3,2‐b]thiophene (IDTT) are reported and it is found that their cyano group can effectively passivate such defects. To achieve a homogeneous distribution, these molecules are dissolved in the antisolvent, used to initiate the perovskite crystallization. It is found that these molecules are self‐anchored at the grain boundaries due to their strong binding to undercoordinated Pb2+. On a device level, this passivation scheme enhances the charge separation and transport at the grain boundaries due to the well‐matched energetic levels between the passivant and the perovskite. Consequently, these benefits contribute directly to the achievement of power conversion efficiencies as high as 21.2%, as well as the improved environmental and thermal stability of the PSCs. The surface treatment provides a new strategy to simultaneously passivate defects and enhance charge extraction/transport at the device interface by manipulating the anchoring groups of the molecules.  相似文献   

16.
The field‐effect transistor (FET) and diode characteristics of poly(3‐alkylthiophene) (P3AT) nanofiber layers deposited from nanofiber dispersions are presented and compared with those of layers deposited from molecularly dissolved polymer solutions in chlorobenzene. The P3AT n‐alkyl‐side‐chain length was varied from 4 to 9 carbon atoms. The hole mobilities are correlated with the interface and bulk morphology of the layers as determined by UV–vis spectroscopy, transmission electron microscopy (TEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), and polarized carbon K‐edge near edge X‐ray absorption fine structure (NEXAFS) spectroscopy. The latter technique reveals the average polymer orientation in the accumulation region of the FET at the interface with the SiO2 gate dielectric. The previously observed alkyl‐chain‐length‐dependence of the FET mobility in P3AT films results from differences in molecular ordering and orientation at the dielectric/semiconductor interface, and it is concluded that side‐chain length does not determine the intrinsic mobility of P3ATs, but rather the alkyl chain length of P3ATs influences FET diode mobility only through changes in interfacial bulk ordering in solution processed films.  相似文献   

17.
Two new bipolar host molecules composed of hole‐transporting carbazole and electron‐transporting cyano ( CzFCN ) or oxadiazole ( CzFOxa )‐substituted fluorenes are synthesized and characterized. The non‐conjugated connections, via an sp3‐hybridized carbon, effectively block the electronic interactions between electron‐donating and ‐accepting moieties, giving CzFCN and CzFOxa bipolar charge transport features with balanced mobilities (10?5 to 10?6 cm2 V?1 s?1). The meta–meta configuration of the fluorene‐based acceptors allows the bipolar hosts to retain relatively high triplet energies [ET = 2.70 eV ( CzFOxa ) and 2. 86 eV ( CzFCN )], which are sufficiently high for hosting blue phosphor. Using a common device structure – ITO/PEDOT:PSS/DTAF/TCTA/host:10% dopants (from blue to red)/DPPS/LiF/Al – highly efficient electrophosphorescent devices are successfully achieved. CzFCN ‐based devices demonstrate better performance characteristics, with maximum ηext of 15.1%, 17.9%, 17.4%, 18%, and 20% for blue (FIrpic), green [(PPy)2Ir(acac)], yellowish‐green [m‐(Tpm)2Ir(acac)], yellow [(Bt)2Ir(acac)], and red [Os(bpftz)2(PPhMe2)2, OS1], respectively. In addition, combining yellowish‐green m‐(Tpm)2Ir(acac) with a blue emitter (FIrpic) and a red emitter (OS1) within a single emitting layer hosted by bipolar CzFCN , three‐color electrophosphorescent WOLEDs with high efficiencies (17.3%, 33.4 cd A?1, 30 lm W ?1), high color stability, and high color‐rendering index (CRI) of 89.7 can also be realized.  相似文献   

18.
Polymeric semiconductors are emerging as a kind of competitive photocatalysts for hydrogen evolution due to their well‐tunable structures, versatile functionalization, and low‐cost processibility. In this work, a series of conjugated porous polymers with substantial cyano‐substituted fully sp2‐carbon frameworks are efficiently synthesized by using electron‐deficient tricyanomesitylene as a key building block to promote an organic base‐catalyzed Knoevenagel condensation with various aldehyde‐substituted arenes. The resulting porous polymers feature donor‐acceptor structures with π‐extended conjugation, rendering them with distinct semiconducting properties. They possess hierarchically porous structures, nanoscale morphologies, and intriguing wettability. These promising physical characters, finely tailorable by varying the arene units, are essentially relevant to the abundant cynao substituents over the whole frameworks. The as‐prepared porous polymers exhibit excellent visible‐light‐driven photocatalytic activity for water‐splitting hydrogen evolution with apparent quantum yield up to 2.0% at 420 nm or 1.9% at 470 nm, among the highest values yet reported for porous polymer‐based photocatalysts, also representing the first example of such kinds of catalysts formed through a metal‐free‐catalyzed carbon–carbon coupling reaction.  相似文献   

19.
By using pyran‐containing donor–acceptor dyes as doping molecules in organic light‐emitting devices (OLEDs), we scrutinize the effects of charge trapping and polarization induced by the guest molecules in the electro‐active host material. Laser dyes 4‐(dicyanomethylene)‐2‐methyl‐6‐[2‐(julolidin‐9‐yl)phenyl]ethenyl]‐4H‐pyran (DCM2) and the novel 4‐(dicyanomethylene)‐2‐methyl‐6‐{2‐[(4‐diphenylamino)phenyl]ethenyl}‐4H‐pyran (DCM‐TPA) are used as model compounds. The emission color of these polar dyes depends strongly on doping concentration, which we have attributed to polarization effects induced by the doping molecules themselves. Their frontier orbital energy levels are situated within the bandgap of the tris(8‐hydroxyquinoline)aluminum (Alq3) host matrix and allow the investigation of either electron trapping or both electron and hole trapping. In the case of DCM‐TPA doping, we were able to show that electron trapping leads to a partial shift of the recombination zone out of the doped Alq3 region. To impede charge‐recombination processes taking place in the undoped host matrix, a charge‐blocking layer efficiently confines the recombination zone inside the doped zone and gives rise to increased luminous efficiency. For a doping concentration of 1 wt.‐% we obtain a maximum luminous efficiency of 10.4 cd A–1. At this doping concentration, the yellow emission spectrum shows excellent color saturation with CIE chromaticity coordinates x, y of 0.49 and 0.50, respectively. In the case of DCM2 the recombination zone is much less affected for the same doping concentrations, which is ascribed to the fact that both electrons and holes are being trapped. The experimental findings are corroborated with a numerical simulation of the doped multilayer devices.  相似文献   

20.
Wound infections caused by multidrug‐resistant (MDR) bacteria are hard to treat because of tolerance to existing antibiotics, repeated infection, and concomitant inflammation. Herein, zinc atom–doped g‐C3N4 and Bi2S3 nanorod heterojunctions (CN–Zn/BiS) are investigated for disinfection under near‐infrared light (NIR). The photocatalysis of CN–Zn/BiS is enhanced because of efficient charge separation during the interface electron field and increased oxygen adsorption capacity. Then, 99.2% antibacterial efficiency is shown toward methicillin‐resistant Staphylococcus aureus (MRSA) and 99.6% toward Escherichia coli under 10 min NIR irradiation. Meanwhile, a strategy for the combination of lapsed β‐lactam antibiotics with the photosensitizer CN–Zn/BiS is provided to kill MRSA by NIR without observable resistance, suggesting an approach to solve the problem of bacterial infection with NIR light penetrability and for exploiting new anti‐infection methods. The CN–Zn/BiS nanocomposite can also regulate genes and the inflammatory response through inflammatory factors (IL‐1β, IL‐6, TNF‐α, and iNOS) in vivo to accelerate tissue regeneration and thereby promote wound healing.  相似文献   

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