A Metalloregulated Four‐State Nanoswitch Controls Two‐Step Sequential Catalysis in an Eleven‐Component System

The nanomechanical switch 1 with its three orthogonal binding motifs—the zinc(II) porphyrin, azaterpyridine, and shielded phenanthroline binding station—is quantitatively and reversibly toggled back and forth between four different switching states by means of addition and removal of appropriate metal‐ion inputs. Two of the four switching stages are able to initiate catalytic transformations (ON1, ON2), while the two others shut down any reaction (OFF1, OFF2). Thus, in a cyclic four‐state switching process the sequential transformation A + B + C → AB + C → ABC can be controlled, which proceeds stepwise along the switching states OFF1→ON1 (click reaction: A + B → AB )→OFF2→ON2 (Michael addition: AB + C → ABC )→OFF1. Two consecutive cycles of the sequential catalysis were realized without loss in activity in a reaction system with eleven different components.     

In Situ Synthesis and Nonvolatile Rewritable‐Memory Effect of Polyaniline‐Functionalized Graphene Oxide

A new polyaniline (PANI)‐functionalized graphene oxide (GO‐PANI) was prepared by using an in situ oxidative graft polymerization of aniline on the surface of GO. Its highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), ionization potential (IP), and electron affinity (EA) values experimentally estimated by the onset of the redox potentials were ?5.33, ?3.57, 5.59, and 3.83 eV, respectively. A bistable electrical‐switching effect was observed in electronic device with the GO‐PANI film sandwiched between the indium tin oxide (ITO) and Al electrodes. This device exhibited two accessible conductivity states, that is, the low‐conductivity (OFF) state and the high‐conductivity (ON) state, and can be switched to the ON state under a negative electrical sweep, and can also be reset to the initial OFF state by a reverse (positive) electrical sweep. The ON state is nonvolatile and can withstand a constant voltage stress of ?1 V for 3 h and 10⁸ read cycles at ?1 V under ambient conditions. The nonvolatile nature of the ON state and the ability to write, read, and erase the electrical states, fulfill the functionality of a rewritable memory. An ON/OFF current ratio of more than 10⁴ at ?1 V achieved in this memory device is high enough to promise a low misreading rate through the precise control of the ON and OFF states. The mechanism associated with the memory effects was elucidated from molecular simulation results.     

Electrical bistability of organic devices with a polymeric thin film for nonvolatile data storage

In this study, organic memory devices with a single active layer between the two external electrodes were fabricated using an electron‐donor type conjugated polymer and an electron‐acceptor type small organic molecule. The active layer of the memory device was prepared by blending polystyrene, poly[10‐(2′‐ethylhexyl)phenothiazine‐3,7‐diyl], and tetracyanoquinodimethane in 1,2‐dichlorobenzene. The device initially showed a low‐conductance state (OFF state) in the low‐voltage range, and an abrupt current increase, corresponding to the transition to a high‐conductance state (ON state), occurred at a certain voltage (V_th). The ON state could be reverted to the OFF state by applying a voltage higher than V_th. The current ratio between the two states was about 10³ (up to 10⁵). After this transition, the device remained in the ON state even after the applied voltage was removed, and this indicated the nonvolatile characteristics of the device. There was no sharp current degradation in the OFF or ON states for 4500 s of continuous bias. The device‐to‐device performance fluctuation was measured, and the conduction mechanisms in the ON and OFF states were examined by fitting the data to well‐known theoretical models. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Push–Pull archetype of reduced graphene oxide functionalized with polyfluorene for nonvolatile rewritable memory

A solution‐processable PFTPA‐convalently grafted reduced graphene oxide (RGO‐PFTPA) was synthesized by the 1,3‐dipolar cycloaddition of azomethine ylide. Bistable electrical switching and nonvolatile rewritable memory effects were demonstrated in a sandwich structure of indium tin oxide/RGO‐PFTPA/Al. The switch‐on voltage of the as‐fabricated device was around ?1.4 V, and the ON/OFF‐state current ratio was more than 10³. The ON–OFF transition process is reversible because the application of a high enough positive voltage can induce the reverse transfer of electrons, reducing the conductivity back to its initial OFF state. Both the OFF and ON states are accessible and very stable under a constant voltage stress of ?1 V for up to 3 h, or under a pulse voltage stress of ?1 V for up to 10⁸ continuous read cycles (pulse period = 2 μs, pulse width = 1 μs). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Photoswitching of the antiferromagnetic coupling in an oxamato-based dicopper(II) anthracenophane

Thermally reversible photomagnetic (ON/OFF) switching behavior has been observed in a dinuclear oxamatocopper(II) anthracenophane upon UV light irradiation and heating; the two Cu(II) ions (S(Cu) = 1/2) that are antiferromagnetically coupled in the dicopper(II) metallacyclic precursor (ON state) become uncoupled in the corresponding [4+4] photocycloaddition product (OFF state), as substantiated from both experimental and theoretical studies.     

Dianionic Tris[oxalato(2—)]silicate and Tris[oxalato(2—)]germanate Complexes: Synthesis,Properties, and Structural Characterization in the Solid State and in Solution

Reaction of tetramethoxysilane with three molar equivalents of oxalic acid and two molar equivalents of 1‐(2‐hydroxyethyl)‐pyrrolidine or 1‐(2‐hydroxyethyl)piperidine in tetrahydrofuran yielded the λ⁶Si‐silicates 1‐(2‐hydroxyethyl)pyrrolidinium tris[oxalato(2—)]silicate ( 4 ) and 1‐(2‐hydroxyethyl)piperidinium tris[oxalato(2—)]silicate ( 5 ). The related germanium compounds 1‐(2‐hydroxyethyl)piperidinium tris[oxalato(2—)]germanate ( 6 ) and triethylammonium tris[oxalato(2—)]germanate ( 7 ) were synthesized analogously, starting from tetramethoxygermane and using three molar equivalents of oxalic acid and two molar equivalents of 1‐(2‐hydroxyethyl)piperidine or triethylamine. Compounds 4 — 7 were characterized by elemental analyses (C, H, N), single‐crystal X‐ray diffraction, solid‐state VACP/MAS NMR spectroscopy (²⁹Si), and solution NMR spectroscopy (¹H, ¹³C, ²⁹Si). The structural characterization was complemented by computational studies of the tris[oxalato(2—)]silicate dianion and the tris[oxalato(2—)]germanate dianion. In addition, the stability of compounds 4 — 7 in aqueous solution was studied by ¹³C NMR spectroscopy.     

A Solution‐Processable Donor–Acceptor Compound Containing Boron(III) Centers for Small‐Molecule‐Based High‐Performance Ternary Electronic Memory Devices

A novel small‐molecule boron(III)‐containing donor–acceptor compound has been synthesized and employed in the fabrication of solution‐processable electronic resistive memory devices. High ternary memory performances with low turn‐on (V_Th1=2.0 V) and distinct threshold voltages (V_Th2=3.3 V), small reading bias (1.0 V), and long retention time (>10⁴ seconds) with a large ON/OFF ratio of each state (current ratio of “OFF”, “ON1”, and “ON2”=1:10³:10⁶) have been demonstrated, suggestive of its potential application in high‐density data storage. The present design strategy provides new insight in the future design of memory devices with multi‐level transition states.     

Nonvolatile rewritable memory effects in graphene oxide functionalized by conjugated polymer containing fluorene and carbazole units

A new polymer, poly[{9,9-di(triphenylamine)fluorene}(9,9-dihexylfluorene)(4-aminophenylcarbazole)] (PFCz) was synthesized and used in a reaction with graphene oxide (GO) containing surface-bonded acyl chloride moieties to give a soluble GO-based polymer material GO-PFCz. A bistable electrical switching effect was observed in an electronic device in which the GO-PFCz film was sandwiched between indium-tin oxide (ITO) and Al electrodes. This device exhibited two accessible conductivity states, that is, a low-conductivity (OFF) state and a high-conductivity (ON) state, and can be switched to the ON state under a negative electrical sweep; it can also be reset to the initial OFF state by a reverse (positive) electrical sweep. The ON state is nonvolatile and can withstand a constant voltage stress of -1 V for 3 h and 10(8) read cycles at -1 V under ambient conditions. The nonvolatile nature of the ON state and the ability to write, read, and erase the electrical states, fulfill the functionality of a rewritable memory. The mechanism associated with the memory effects was elucidated from molecular simulation results and in-situ photoluminescence spectra of the GO-PFCz film under different electrical biases.     

The gas‐phase ligand exchange of copper and nickel acetylacetonate,hexafluoroacetylacetonate and trifluorotrimethylacetylacetonate complexes

The gas‐phase ligand‐exchange reactions between Cu(II) and Ni(II) complexes containing the acetylacetonate (acac), hexafluoroacetylacetonate (hfac), and trifluorotrimethylacetylacetonate (tftm) ligands were investigated using a triple quadrupole mass spectrometer. The gas‐phase mixed‐ligand products of [Cu(acac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ were formed following the co‐sublimation of either homo‐metal or hetero‐metal precursors. The gas‐phase formation of [Cu(acac)(tftm)]⁺, [Cu(hfac)(tftm)]⁺, [Ni(acac)(tftm)]⁺, and [Ni(hfac)(tftm)]⁺ complexes is reported herein for the first time. The corresponding fragmentation patterns of these species along with those of Cu(tftm)₂ and Ni(tftm)₂ are also presented. Mass‐selected ion‐neutral reactions were investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

Different Steric‐Twist‐Induced Ternary Memory Characteristics in Nonconjugated Copolymers with Pendant Naphthalene and 1,8‐Naphthalimide Moieties

Herein, novel random copolymers PMNN and PMNB were designed and synthesized, and the memory devices Al/ PMNN and PMNB /ITO both exhibited ternary memory performance. The switching voltages of the OFF–ON1 and ON1–ON2 transitions for both memory devices are around −2.0 and −3.5 V, respectively, and the ON1/OFF, ON2/ON1 current ratios are both up to 10³. The observed tristable electrical conductivity switching could be attributed to field‐induced conformational ordering of the naphthalene rings in the side chains, and subsequent charge trapping by 1,8‐naphthalimide moieties. More interestingly, by adjusting the connection sites of 1,8‐naphthalimide moieties to tune the steric‐twist effect, different memory properties were achieved ( PMNN showed nonvolatile write once, read many (WORM) memory behavior, whereas PMNB showed volatile static RAM (SRAM) memory behavior). This result will offer a guideline for the design of different high‐performance multilevel memory devices by tuning the steric effects of the chemical moieties.     

Synthesis of polyimides containing triphenylamine‐substituted triazole moieties for polymer memory applications

A series of thermally stable aromatic polyimides containing triphenylamine‐substituted triazole moieties ( AZTA‐PI )s were prepared and characterized. The glass transition temperatures (T_g) of the polyimides were found to be in the range of 262–314 °C. The polyimides obtained by chemical imidization had inherent viscosities of 0.25–0.44 dL g^?1 in N‐methyl‐2‐pyrrolidinone. The number average molecular weights (M_n) and weight average molecular weights (M_w) were 1.9–3.2 × 10⁴ and 3.2–5.6 × 10⁴, respectively, and the polydispersity indices (PDI = M_w/M_n) were in the range of 1.70–1.78. A resistive switching device was constructed from the 4,4′‐hexafluoroisopropylidenediphthalic dianhydride‐based soluble polyimide ( AZTA‐PIa ) in a sandwich structure of indium‐tin oxide/polymer/Al. The as‐fabricated device can be switched from the initial low‐conductivity (OFF) state to the high‐conductivity (ON) state at a switching threshold voltage of 2.5 V under either positive or negative electrical sweep, with an ON/OFF state current ratio in the order of 10⁵ at ?1 V. The device is able to remain in the ON state even after turning off the power or under a reverse bias. The nonvolatile and nonrewritable natures of the ON state indicate that the device is a write‐once read‐many times (WORM) memory. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Theoretical insights into the absorption and emission properties of blue luminescent copper(I) complexes based on the pyrazolyl‐pyridine ligands

The ground geometrical and electronic structures, charge transfer (CT) behaviors, absorption, and emission properties of the three copper(I) complexes [Cu(pypz)(POP)]⁺ (1) , [Cu(pympz)(POP)]⁺ (2) , and [Cu(pytfmpz)(POP)]⁺ (3) (pypz=1‐(2‐pyridyl)pyrazole, pympz=3‐methyl‐1‐(2‐pyridyl)pyrazole, and pytfmpz=3‐trifluoromethyl‐1‐(2‐pyridyl)pyrazole), have been investigated using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT). The vertical absorption energies of the all copper(I) complexes are well reproduced by TD‐DFT calculations based on the CT amount calculations. The triplet emission properties of the all copper(I) complexes were correctly evaluated at BMK/LANL2DZ/6‐31G* level of theory. In addition, the thermally activated delayed fluorescence properties of 1–3 were discussed in detail based on the spatial separation of the HOMO and LUMO and vertical excited energies. These theoretical insights should be expected to provide some guides for the design and synthesis of efficient luminescent copper(I) complexes. © 2014 Wiley Periodicals, Inc.     

Covalent Functionalization of Black Phosphorus with Conjugated Polymer for Information Storage

Major disadvantages of black phosphorus (BP) are its poor air‐stability and poor solubility in common organic solvents. The best way to solve this problem is to incorporate BP into a polymer backbone or a polymer matrix to form novel functional materials that can provide both challenges and opportunities for new innovation in optoelectronic and photonic applications. As a proof‐of concept application, we synthesized in situ the first highly soluble conjugated polymer‐covalently functionalized BP derivative (PDDF‐g‐BP) which was used to fabricate a resistive random access memory (RRAM) device with a configuration of Au/PDDF‐g‐BP/ITO. In contrast to PDDF without memory effect, PDDF‐g‐BP‐based device exhibits a nonvolatile rewritable memory performance, with a turn‐on and turn‐off voltages of +1.95 V and ?2.34 V, and an ON/OFF current ratio of 10⁴. The current through the device in both the ON and OFF states is still kept unchanged even at 200th switching cycle. The PDDF/BP blends show a very unstable memory performance with a very small ON/OFF current ratio.     

Remarkable solvent effects in the hydro‐ and solvothermal synthesis of copper‐1,10‐phenanthroline complexes

Compound {[Cu(II)/Cu(I)]₂(ophen)₄(Htpt)}^?2H₂O ( 1 ) was obtained by hydrothermal reaction. Compound 1 is a mixed‐valence copper coordination complex with a different coordination environment. The X‐ray structural analysis of 1 revealed two crystallographically independent dimeric [Cu₂(ophen)₂]⁺ units bridged by two µ₁‐carboxylate groups of the tpt ligand into a butterfly‐shaped molecule in the crystal structure. Compound [Cu(I)₃(CN)₃(phen)₃] ( 2 ) was synthesized using ethanol instead of water, and consisted of an infinite helix chain formed from [Cu(I)(phen)]⁺ units bridged by cyano groups. Copyright © 2007 John Wiley & Sons, Ltd.     

Shape‐Memory Platinum(II) Complexes: Intelligent Vapor‐History Sensor with ON–OFF Switching Function

A novel platinum(II)–diimine complex, [Pt(CN)₂(H₂dcphen)] ( 1 ; H₂dcphen=4,7‐dicarboxy‐1,10‐ phenanthroline), was synthesized and its vapochromic shape‐memory behavior was evaluated. The as‐synthesized amorphous purple solid, [Pt(CN)₂(H₂dcphen)]?2 H₂O ( 1 P ), exhibited vapochromic behavior in the presence of alcoholic vapors through transformation to a red, crystalline, porous, vapor‐adsorbed form, 1 R?vapor . The obtained 1 R?vapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vaporfree, porous 1 R?open could detect water or n‐hexane vapor, although these vapors could not induce 1 P ‐to‐ 1 R?vapor transformation, and 1 R?open could easily be converted to the initial 1 P by manual grinding. These results indicate that 1 is a new shape‐memory material that functions through formation and collapse of the porous framework with an emission change upon vapor‐adsorption and grinding; this enables it to exhibit vapor history and ON–OFF switching sensing functions.     

Semi-conductive,Switchable Dielectric and Photoluminescent Properties of Two High-Temperature Phase Transition Hybrids

Bistable switches (electrical switching between “ON” and “OFF” bistable states) have gradually developed into an ideal category of highly intelligent materials, due to their significant applications in optical technology, signal processors, data storage and other switchable media applications in the field of electrical devices. Here, we successfully designed and synthesized [(FC₆H₄C₂H₄NH₃)₂MCl₄]_n(FC₆H₄C₂H₄NH₃⁺)=deprotonated 4-fluoro- phenethylamine; M=Cd ( 1 ), Mn ( 2 )), which realized the coupling of thermo-dielectric switching characteristics, semi-conductor characteristics and photo-luminescent properties. DSC (differential scanning calorimetry) and dielectric measurements show that 1 is a sensitive dielectric bistable switch between the high dielectric (ON) and low dielectric (OFF) states. The temperature-variable single crystal structure shows that the both 1 and 2 undergo a high-temperature reversible phase transition around 383 K/380 K, which is caused by the order-disordered transformation of organic cations and the slight distortion of the inorganic framework. In particular, 1 shows outstanding switchable dielectric behavior and semiconducting properties. Further, 1 and 2 emit strong green and yellow luminescence at 527 and 595 nm, respectively.     

A Supramolecular Approach on Using Poly(fluorenylstyrene)‐block‐poly(2‐vinylpyridine):PCBM Composite Thin Films for Non‐Volatile Memory Device Applications

Supramolecular composite thin films of poly[4‐(9,9‐dihexylfloren‐2‐yl)styrene]‐block ‐poly(2‐vinylpyridine) (P(St‐Fl)‐b‐P2VP):[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) were prepared for write‐once‐read‐many times (WORM) non‐volatile memory devices. The optical absorption and photoluminescence results indicated the formation of charge transfer complexation between the P2VP block and PCBM, which led to the varied PCBM aggregated size and memory characteristics. The ITO/PCBM:(P(St‐Fl)‐b‐P2VP)/Al device exhibited the WORM characteristic with low threshold voltage (−1.6 to −3.2 V) and high ON/OFF ratio (10³ to 10⁵) by tuning the PCBM content. The switching behavior could be explained by the charge injection dominated thermionic emission in the OFF state and field‐induced charge transfer in the ON state. The present study provides a novel approach system for tuning polymer memory device characteristics through the supramolecular materials approach.

     

Gas‐phase ligand exchange of select transition‐metal acetylacetonate and hexafluoroacetylacetonate complexes

Gas‐phase ligand exchange reactions between M(acac)₂ and M(hfac)₂ species, where M is Cu(II) and/or Ni(II), were observed to occur in a double‐focusing reverse‐geometry magnetic sector mass spectrometer. The gas‐phase mixed ligand product, [M(acac)(hfac)]⁺, was formed following the co‐sublimation of either homo‐metal or hetero‐metal precursors. The gas‐phase formation of [Cu(acac)(hfac)]⁺ from hetero‐metal precursors is reported herein for the first time. The [Ni(acac)(hfac)]⁺ complex is also observed for the first time to form following the co‐sublimation of not only Ni precursors, but also from separate Ni and Cu precursors. The corresponding fragmentation patterns of these species are also presented, and the mixed metal mixed ligand product [NiCu(acac)₂(hfac)]⁺ is observed. Copyright © 2008 John Wiley & Sons, Ltd.     

Gas‐phase doubly charged complexes of cyclic peptides with copper in +1, +2 and +3 formal oxidation states: formation,structures and electron capture dissociation

Copper complexes with a cyclic D‐His‐β‐Ala‐L‐His‐L‐Lys and all‐L‐His‐β‐Ala‐His‐Lys peptides were generated by electrospray which were doubly charged ions that had different formal oxidation states of Cu(I), Cu(II) and Cu(III) and different protonation states of the peptide ligands. Electron capture dissociation showed no substantial differences between the D‐His and L‐His complexes. All complexes underwent peptide cross‐ring cleavages upon electron capture. The modes of ring cleavage depended on the formal oxidation state of the Cu ion and peptide protonation. Density functional theory (DFT) calculations, using the B3LYP with an effective core potential at Cu and M06‐2X functionals, identified several precursor ion structures in which the Cu ion was threecoordinated to pentacoordinated by the His and Lys side‐chain groups and the peptide amide or enolimine groups. The electronic structure of the formally Cu(III) complexes pointed to an effective Cu(I) oxidation state with the other charge residing in the peptide ligand. The relative energies of isomeric complexes of the [Cu(c‐HAHK + H)]²⁺ and [Cu(c‐HAHK ? H)]²⁺ type with closed electronic shells followed similar orders when treated by the B3LYP and M06‐2X functionals. Large differences between relative energies calculated by these methods were obtained for open‐shell complexes of the [Cu(c‐HAHK)]²⁺ type. Charge reduction resulted in lowering the coordination numbers for some Cu complexes that depended on the singlet or triplet spin state being formed. For [Cu(c‐HAHK ? H)]²⁺ complexes, solution H/D exchange involved only the N–H protons, resulting in the exchange of up to seven protons, as established by ultra‐high mass resolution measurements. Contrasting the experiments, DFT calculations found the lowest energy structures for the gas‐phase ions that were deprotonated at the peptide C_α positions. Copyright © 2012 John Wiley & Sons, Ltd.     

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

Two examples of a rare class of di‐radical azo‐anion complexes of 2‐(arylazo) pyridine with Ir^III carrier are introduced. Their electronic structures have been elucidated using a host of physical methods that include X‐ray crystallography, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. Room temperature magnetic moments of these are consistent with two nearly non‐interacting azo‐anion radicals. These displayed rich electrochemical properties consisting of six numbers of reversible and successive one electron CV‐waves. Redox processes occur entirely at the coordinated ligands without affecting metal redox state. Apart from reporting their chemical characterization, I‐V characteristics of these complexes in film state are investigated using sandwich‐type devices comprising of a thin film of 100–125 nm thickness placed between two gold‐plated ITO electrodes. These showed memory switching properties covering a useful voltage range with a reasonable ON/OFF ratio and also are suitable for RAM/ROM applications. I‐V characteristics of two similar complexes of Rh and Cr with identical ligand environment and electronic structure are also referred for developing an insight into the memory switching ability of Ir‐ and Rh‐ complexes on the basis of comparative analysis of responses of the respective systems. In a nutshell, thorough analysis of voltage driven redox dynamics and corresponding solid and solution state current responses of all the systems are attempted and there from an unexplored class of switching devices are systematically introduced.