A Donor–Acceptor Polymer with a Peculiar Negative‐Charge‐“Trapping” Characteristic

Voltammetric and spectrophotometric measurements of poly(3,3″‐dipentoxy‐3′‐dicyanoethenyl‐2,2′:5′,2″‐terthiophene) (polyCN) films, in connection with other experimental evidence, reveal a normal oxidative, but a peculiar reductive behavior consisting of trapping of the negative charge during the cathodic scan. Another interesting property of polyCN films is the tendency to form strong intramolecular and intermolecular associations, probably charge‐transfer (CT) complexes. These properties could account for the fact that the photovoltaic performance does not improve when polyCN is blended with a polythiophene donor.     

Solution‐Processable Near‐Infrared–Responsive Composite of Perovskite Nanowires and Photon‐Upconversion Nanoparticles

Organolead halide perovskites (OHPs) have shown unprecedented potentials in optoelectronics. However, the inherent large bandgap has restrained its working wavelength within 280–800 nm, while light at other regions, e.g., near‐infrared (NIR), may cause drastic thermal heating effect that goes against the duration of OHP devices, if not properly exploited. Herein, a solution processable and large‐scale synthesis of multifunctional OHP composites containing lanthanide‐doped upconversion nanoparticles (UCNPs) is reported. Upon NIR illumination, the upconverted photons from UCNPs at 520–550 nm can be efficiently absorbed by closely surrounded OHP nanowires (NWs) and photocurrent is subsequently generated. The narrow full width at half maximum of the absorption of rare earth ions (Yb³⁺ and Er³⁺) has ensured high‐selective NIR response. Lifetime characterizations have suggested that Förster resonance energy transfer with an efficiency of 28.5% should be responsible for the direct energy transfer from UCNPs to OHP NWs. The fabricated proof‐of‐concept device has showcased perfect response to NIR light at 980 and 1532 nm, which has paved new avenues for applications of such composites in remote control, distance measurement, and stealth materials.     

DNA Lipoplex‐Based Light‐Harvesting Antennae

Natural light‐harvesting complexes are operated through the well‐designed self‐assembly of pigments with large protein complexes in a thylakoid lipid bilayer. However, a long‐range, directed transfer of excitation energy has not been achieved in artificial systems because the nanoscale arrangement of chromophores into stable micrometer‐scale structures is highly challenging. Here the multiscale assembly of chromophores for excited energy transfer through the arrangement of chromophores on nanoscale DNA templates followed by their incorporation into larger multilamellar lipid structures is reported. Single‐strand 10 nucleotide DNA molecules containing a terminal residue linked with three different chromophores are hybridized with their complementary 30 nucleotide matrix DNA strand. Due to the short DNA sequences, the energy transfer of the DNA‐templated chromophore arrays is limited at 4 °C. However, the incorporation of DNA‐templated chromophores into lipid‐DNA complexes dramatically increases both of the efficiencies and antenna effects of the single and two‐step energy transfers at room temperature through the structural stabilization and the secondary assembly of DNA between the interstitial spaces of multilamellar lipid structures. The findings suggest that the supramolecular alignment of DNA‐templated chromophores, which has never been explored previously, can be a very promising route toward directed, long‐range light harvesting.     

Red‐ to NIR‐Emitting,BODIPY‐Based,K+‐Selective Fluoroionophores and Sensing Materials

Optical sensing materials for the selective measurement of potassium ions (K⁺) in water are presented. The indicator dyes are based on an aza‐crown ether as a receptor and borondipyrromethenes (BODIPY) dyes as fluorophores. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer (PET) upon complexation with K⁺ ions. The family of new indicators possesses tuneable optical properties (green to red excitation, red to NIR emission) and PET efficiencies. They exhibit high brightness with quantum yields between 0.20 and 0.47 in the “on” state and a molar absorption coefficient between 30 000 and 290 000 m ^?1 cm^?1. The new indicator dyes are immobilized in biocompatible hydrogel matrices to obtain stable nonleaching and fast responding (t₉₀ ≈ 10 s) sensing materials for continuous measurements of potassium. They are realized in various formats such as planar optodes, fiber‐optic sensors, and water‐dispersible polymer‐based nanoparticles. Apart from fluorescence intensity measurements, self‐referenced read‐out of fluorescence decay time is demonstrated. All sensor materials display a high K⁺/Na⁺ selectivity and are not influenced by pH within the physiologically relevant range. Practical applicability of the materials is emphasized by application of a fiber‐optic sensor to quantification of K⁺ in serum, which shows excellent correlation with the reference measurements.     

Study on Two‐Coil and Four‐Coil Wireless Power Transfer Systems Using Z‐Parameter Approach

A wireless power transfer (WPT) system is usually classified as being of either a two‐coil or four‐coil type. It is known that two‐coil WPT systems are suitable for short‐range transmissions, whereas four‐coil WPT systems are suitable for mid‐range transmissions. However, this paper reveals that the two aforementioned types of WPT system are alike in terms of their performance and characteristics, differing only when it comes to their matching‐network configurations. In this paper, we first find the optimum load and source conditions using Z‐parameters. Then, we estimate the maximum power transfer efficiency under the optimum load and source conditions, and we describe how to configure the matching networks pertaining to both types of WPT system for the given optimum load and source conditions. The two types of WPT system show the same performance with respect to the coupling coefficient and load impedance. Further, they also demonstrate an identical performance in the two cases considered in this paper, that is, a strong‐coupled case and a weak‐coupled case.     

Deep‐Red/Near‐Infrared Electroluminescence from Single‐Component Charge‐Transfer Complex via Thermally Activated Delayed Fluorescence Channel

Formation of a single‐component charge‐transfer complex (SCCTC) is unveiled in solid state of an intermolecular charge‐transfer molecule 2‐(4‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenyl)anthracene‐9,10‐dione (PIPAQ). Intermolecular donor–acceptor interactions between two PIPAQ molecules is the primary driving force for self‐association and contributes to intermolecular charge transfer. The SCCTC character is fully verified by crystallographic, photophysical, electron spin resonance, and vibrational characterizations. The PIPAQ‐based SCCTC is first applied in light‐emitting devices as an emissive layer to realize efficient deep‐red/near‐infrared electroluminescence. This work provides new insights into SCCTC and represents an important step toward their applications in optoelectronic devices.     

Formation of charge‐transfer complexes significantly improves the performance of polymer solar cells based on PBDTTT‐C‐T: PC71BM

By adding appropriate proportions of nitrobenzene (C₆H₅NO₂) to the blended solution of poly{[4,8‐bis‐(2‐ethyl‐hexyl‐thiophene‐5‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl]‐alt‐[2‐(2′‐ethyl‐hexanoyl)‐thieno[3,4‐b]thiophen‐4,6‐diyl]}:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PBDTTT‐C‐T: PC₇₁BM), we substantially improved the power conversion efficiency from the best reported value of 7.48–8.88%. Experiments and simulations show that nitrobenzene and PBDTTT‐C‐T form stable coplanar charge‐transfer complexes through hydrogen bonds. Formation of the PBDTTT‐C‐T‐C₆H₅NO₂ complex simultaneously increases the external quantum efficiency. The underlying mechanisms of increased external quantum efficiency are attributed to the following: (i) higher lowest unoccupied molecular orbital (LUMO) of PBDTTT‐C‐T‐C₆H₅NO₂ for more efficient photoinduced electron transfer to the LUMO of PC₇₁BM and (ii) efficient quenching of fluorescence in the active layers due to formation of the PBDTTT‐C‐T‐C₆H₅NO₂ complex. This discovery clearly illustrates the potential of hydrogen‐bonded complexes as a new route for efficient polymer‐based photovoltaic devices. Copyright © 2014 John Wiley & Sons, Ltd.     

Near‐Infrared Light‐Emitting Diodes (LEDs) Based on Poly(phenylene)/Yb‐tris(β‐Diketonate) Complexes

Near‐infrared‐emitting electroluminescent (EL) devices using blue‐light‐emitting polymers blended with the Yb complexes Yb(DBM)₃phen (DBM = dibenzoylmethane), Yb(DNM)₃phen (DNM = dinaphthoylmethane), and Yb(TPP)L(OEt) (L(OEt) = [(C₅H₅)Co{P(O)Et₂}₃]^–) have been studied. EL devices composed of Yb(DNM)₃phen blended with PPP‐OR11 showed enhanced near‐IR output at 977 nm when compared to those fabricated with Yb(DBM)₃phen/PPP‐OR11 blends. The maximum near‐IR external efficiencies of the devices with Yb(DBM)₃phen and Yb(DNM)₃phen are, respectively, 7 × 10^–5 (at 6 V and at 0.81 mA mm^–2) and 4 × 10^–4 (at 7 V, and 0.74 mA mm^–2). The optimal blend composition for EL device performance consisted of PPP‐OR11 blended with 10–20 mol‐% Yb(DNM)₃phen. A device fabricated using Yb‐(TPP)L(OEt)/PPP‐OR11 showed significantly enhanced near‐IR output efficiency, and future efforts will focus on devices fabricated using porphyrin‐based materials.     

Symmetric Large‐Area Metal‐Molecular Monolayer‐Metal Junctions by Wedging Transfer

A method is described for fabricating and electrically characterizing large‐area (100–400 μm²) metal‐molecular monolayer‐metal junctions with a relatively high overall yield of ≈45%. The measurement geometry consists of ultra‐smooth (template‐stripped) patterned Au bottom electrodes, combined with ultra‐smooth top Au electrodes deposited using wedging transfer. The fabrication method is applied to the electrical characterization of Au‐alkanethiol self‐assembled monolayer‐Au junctions. An exponential decay of the current density is found for increasing the chain length of the alkanethiols, in agreement with earlier studies. The symmetric device geometry, and flexibility for contacting monolayers with various end groups are important advantages compared to existing techniques for electrically characterizing molecular monolayers.     

Aza[5]helicene Rivals N‐Annulated Perylene as π‐Linker of D−π−D Typed Hole‐Transporters for Perovskite Solar Cells

The superior role of helical π‐linkers is demonstrated for the design of donor?π linker?donor typed molecular semiconductors in perovskite solar cells (PSCs). Flat N‐annulated perylene (NP) and contorted aza[5]helicene (A5H) are side‐functionalized with methoxyphenyl and end‐capped with dimethoxydiphenylamine electron‐donor to afford two small‐molecule hole‐transporters J3 and J4. For methoxyphenyl functionalized π‐linkers, intermolecular π???π interactions in planar NP exist more extensively than those in helical A5H. However, for the dimethoxydiphenylamine derived hole‐transporters with high highest occupied molecular orbital energy levels, a part of the π???π interaction remains for J4 with A5H, while this desirable effect for charge transport is completely deprived for J3 with NP. Thus, the theoretically predicted hole mobility of J4 single‐crystal is even over two times higher than that of J3 one. Because of the larger size of the molecular aggregate, the hole mobility of the spin‐coated J4 thin film is also over three times as high as that of the J3 analog. Due to the reduced transport resistance and enhanced recombination resistance, PSCs with J4 exhibit a power conversion efficiency of 21.0% at standard air mass 1.5 global conditions, which is higher than that of 19.4% with J3 and that of 20.3% with spiro‐OMeTAD control.     

Depolarization Effects in Self‐Assembled Monolayers: A Quantum‐Chemical Insight

Many recent experimental studies have demonstrated that the deposition of a self‐assembled monolayer (SAM) made of polar molecules on a metal surface can significantly modulate its work function and hence the barrier for hole and electron injection in optoelectronic devices. The permanent dipole moment associated with the backbone of the molecules plays a key role in defining the amplitude and direction of the work‐function shift. We illustrate here via quantum‐chemical calculations performed on model systems that the dipole moment of molecules is significantly reduced going from the isolated state to the SAM. Such depolarization effects that are most often neglected thus reduce the work‐function shift and have to be taken in account to control and understand charge‐injection barriers in devices at a quantitative level.     

An efficient t‐out‐of‐n oblivious transfer for information security and privacy protection

In t‐out‐of‐n oblivious transfer (OT), the receiver can only receive t messages out of n messages sent by the sender, and the sender has no idea about which ones have been received. Majority of the existence of previous efficient OT schemes require t calls of 1‐out‐of‐n OT to construct the t‐out‐of‐n OT. Its computational requirements and bandwidth consumption are quite demanding. On the basis of the elliptic curves cryptography, we propose a new t‐out‐of‐n OT protocol for private information retrieval in this article. It is more suitable for the smart cards or mobile units. Copyright © 2013 John Wiley & Sons, Ltd.     

Near‐Infrared Electric Power Generation Through Sub‐Energy‐Gap Absorption in an Organic–Inorganic Composite

Exploitation of energy from the near‐infrared (NIR) region is one strategic approach for enhancing the performance of organic photovoltaic devices (OPVs). While effort has been mostly put toward developing materials with narrow energy gaps, here, a simple approach for harvesting NIR photons with wide‐energy‐gap materials by making use of their interactive charge‐transfer complex (CTC) is shown. It is shown using photoemission studies that the interface between molybdenum (VI) oxide and 5,6,11,12‐tetraphenylnaphthacene (MoO₃/rubrene) possesses an abrupt discontinuity in the vacuum level (VL), resulting in significantly overlapped electron wavefunctions and CTC formation. The CTC induces an intermediate state within the original energy gap of rubrene with energy of ≈1.3 eV, suggesting the feasibility of a charge transfer (CT) exciton generated upon NIR excitation. This is confirmed by generation of electric power OPVs with an active layer of MoO₃:rubrene composite under excitation with a NIR light source.     

Improved Hydrogen Production of Au–Pt–CdS Hetero‐Nanostructures by Efficient Plasmon‐Induced Multipathway Electron Transfer

The design of new functional materials with excellent hydrogen production activity under visible‐light irradiation has critical significance for solving the energy crisis. A well‐controlled synthesis strategy is developed to prepare an Au–Pt–CdS hetero‐nanostructure, in which each component of Au, Pt, and CdS has direct contact with the other two materials; Pt is on the tips and a CdS layer along the sides of an Au nanotriangle (NT), which exhibits excellent photocatalytic activity for hydrogen production under light irradiation (λ > 420 nm). The sequential growth and surfactant‐dependent deposition produce the three‐component Au–Pt–CdS hybrids with the Au NT acting as core while Pt and CdS serve as a co‐shell. Due to the presence of the Au NT cores, the Au–Pt–CdS nanostructures possess highly enhanced light‐harvesting and strong local‐electric‐field enhancement. Moreover, the intimate and multi‐interface contact generates multiple electron‐transfer pathways (Au to CdS, CdS to Pt and Au to Pt) which guide photoexcited electrons to the co‐catalyst Pt for an efficient hydrogen reduction reaction. By evaluating the hydrogen production rate when aqueous Na₂SO₃–Na₂S solution is used as sacrificial agent, the Au–Pt–CdS hybrid exhibits excellent photocatalytic activity that is about 2.5 and 1.4 times larger than those of CdS/Pt and Au@CdS/Pt, respectively.     

Hybrid CuTCNQ/AgTCNQ Metal‐Organic Charge Transfer Complexes via Galvanic Replacement vs Corrosion‐Recrystallization

This study reports a hybrid of two metal‐organic semiconductors that are based on organic charge transfer complexes of 7,7,8,8‐tetracyanoquinodimethane (TCNQ). It is shown that the spontaneous reaction between semiconducting microrods of CuTCNQ with Ag⁺ ions leads to the formation of a CuTCNQ/AgTCNQ hybrid, both in aqueous solution and acetonitrile, albeit with completely different reaction mechanisms. In an aqueous environment, the reaction proceeds by a complex galvanic replacement (GR) mechanism, wherein in addition to AgTCNQ nanowires, Ag⁰ nanoparticles and Cu(OH)₂ crystals decorate the surface of CuTCNQ microrods. Conversely, in acetonitrile, a GR mechanism is found to be thermodynamically unfavorable and instead a corrosion‐recrystallization mechanism leads to the decoration of CuTCNQ microrods with AgTCNQ nanoplates, resulting in a pure CuTCNQ/AgTCNQ hybrid metal‐organic charge transfer complex. While hybrids of two different inorganic semiconductors are regularly reported, this report pioneers the formation of a hybrid involving two metal‐organic semiconductors that will expand the scope of TCNQ‐based charge transfer complexes for improved catalysis, sensing, electronics, and biological applications.     

Restoration of Conductivity with TTF‐TCNQ Charge‐Transfer Salts

The formation of the conductive TTF‐TCNQ (tetrathiafulvalene–tetracyanoquinodimethane) charge‐transfer salt via rupture of microencapsulated solutions of its individual components is reported. Solutions of TTF and TCNQ in various solvents are separately incorporated into poly(urea‐formaldehyde) core–shell microcapsules. Rupture of a mixture of TTF‐containing microcapsules and TCNQ‐containing microcapsules results in the formation of the crystalline salt, as verified by FTIR spectroscopy and powder X‐ray diffraction. Preliminary measurements demonstrate the partial restoration of conductivity of severed gold electrodes in the presence of TTF‐TCNQ derived in situ. This is the first microcapsule system for the restoration of conductivity in mechanically damaged electronic devices in which the repairing agent is not conductive until its release.     

Photoinduced Electron Transfer in Dye‐Sensitized SnO2 Nanowire Field‐Effect Transistors

Electron transfer from excited dye molecules (chlorophyll or fluorescein) to a semiconductor is demonstrated by photoaction and photoluminescence spectra on field‐effect transistors consisting of dye‐sensitized individual SnO₂ nanowires. The photoaction spectrum shows a much better resolution for nanowires non‐covalently functionalized with dye molecules than for dyes deposited on SnO₂ nanoparticle‐films. Possible reasons for the deviation between the photoaction spectra and ordinary optical absorption spectra as well as for the current‐tail appearing along the falling edge are addressed. In dye‐sensitized nanowires, electron transfer from photo‐excited dyes to nanowires is analyzed by comparing gate‐voltage dependences in photoaction and photoluminescence spectra. The importance of this study is in the understanding of electron injection and recombination provided, as well as the performance optimization of nanowire‐based dye‐sensitized solar cells.