Synthesis of Linear and Star-Shaped Poly[4-(diphenylamino)benzyl methacrylate]s by Group Transfer Polymerization and Their Electrical Memory Device Applications

Polymerization of Polar Monomers Mediated by Main-Group Lewis Acid-Base Pairs

The development of new or more sustainable, active, efficient, controlled, and selective polymerization reactions or processes continues to be crucial for the synthesis of important polymers or materials with specific structures or functions. In this context, the newly emerged polymerization technique enabled by main-group Lewis pairs (LPs), termed as Lewis pair polymerization (LPP), exploits the synergy and cooperativity between the Lewis acid (LA) and Lewis base (LB) sites of LPs, which can be employed as frustrated Lewis pairs (FLPs), interacting LPs (ILPs), or classical Lewis adducts (CLAs), to effect cooperative monomer activation as well as chain initiation, propagation, termination, and transfer events. Through balancing the Lewis acidity, Lewis basicity, and steric effects of LPs, LPP has shown several unique advantages or intriguing opportunities compared to other polymerization techniques and demonstrated its broad polar monomer scope, high activity, control or livingness, and complete chemo- or regioselectivity, as well as its unique application in materials chemistry. These advances made in LPP are comprehensively reviewed, with the scope of monomers focusing on heteroatom-containing polar monomers, while the polymerizations mediated by main-group LAs and LBs separately that are most relevant to the LPP are also highlighted or updated. Examples of applying the principles of the LPP and LP chemistry as a new platform for advancing materials chemistry are highlighted, and currently unmet challenges in the field of the LPP, and thus the suggested corresponding future research directions, are also presented.

Silyl Ketene Acetals/B(C₆F₅)₃ Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers

This work reveals the silyl ketene acetal (SKA)/B(C₆F₅)₃ Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C₆F₅)₃ indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C₆F₅)₃-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C₆F₅)₃-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C₆F₅)₃ is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL-b-PMBL, PMMBL-b-PMBL-b-PMMBL and random copolymers with the predicated molecular weights (Mn) and narrow molecular weight distribution (MWD).

Surface engineering to achieve organic ternary memory with a high device yield and improved performance

Organic memories fabricated on surface-engineered indium tin oxide show the highest ternary yield (82%) to date and better performance.

Squaraine molecules deposited on indium tin oxide (ITO) substrates modified with phosphonic acids crystalize more orderly than do those on untreated ITO. The as-fabricated electro-resistive memories show the highest ternary device yield observed to date (82%), a narrower switching voltage distribution, and better retention as well as resistance uniformity.

Organocatalyzed Group Transfer Polymerization

In contrast to the conventional group transfer polymerization (GTP) using a catalyst of either an anionic nucleophile or a transition-metal compound, the organocatalyzed GTP has to a great extent improved the living characteristics of the polymerization from the viewpoints of synthesizing structurally well-defined acrylic polymers and constructing defect-free polymer architectures. In this article, we describe the organocatalyzed GTP from a relatively personal perspective to provide our colleagues with a perspicuous and systematic overview on its recent progress as well as a reply to the curiosity of how excellently the organocatalysts have performed in this field. The stated perspectives of this review mainly cover five aspects, in terms of the assessment of the livingness of the polymerization, limit and scope of applicable monomers, mechanistic studies, control of the polymer structure, and a new GTP methodology involving the use of tris(pentafluorophenyl)borane and hydrosilane.

Synthesis, morphology, and electrical memory application of oligosaccharide-based block copolymers with π-conjugated pyrene moieties and their supramolecules

Transistor memory applications of maltoheptaose-block-poly(1-pyrenylmethyl methacrylate), and their supramolecules with (4-pyridyl)-acceptor-(4-pyridyl).

Electrically bistable and non-volatile memory devices based on p-toluenesulfonic-doped poly(triphenylamine)

The devices are bi-directionally switchable and have non-volatile WORM memory characteristics. They were used as promising candidates in security and data protection applications.

Pure white OLED based on an organic small molecule: 2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine

2,6-Di(1H-benzo[d]imidazol-2-yl)pyridine (DBIP) was synthesized. The single-crystal structure of DBIP was resolved. DBIP-based OLED was fabricated. The electroluminescence for the device corresponds to a pure white emission. In addition, thermal stability, UV-vis, photoluminescence and electrochemical behaviors of DBIP were investigated as well.

Synthesis and Morphology of Two Carbazole-Pyrazoline-Containing Polymer Systems and Their Electrical Memory Performance

A new atom-transfer radical polymerization (ATRP) initiator 4-[1-(2-dodecyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)-3-(4-nitrophenyl)-4,5-dihydro-1H-pyrazol-5-yl]phenyl 2-bromo-2-methylpropanoate (IN) as an electron acceptor (A) and a monomer 2-(9H-carbazole-9-yl)-ethyl methacrylate (MCz) as an electron donor (D) were simultaneously introduced into two different D-A polymer systems by using the end-functionalizing or blending method. The mass percentage of IN in the end-functionalized polymer PMCz-IN and the mixed polymer composite PMCz+IN were both controlled at approximately 1.0 wt %. The optical, electrochemical, and surface morphology properties of the two polymeric films prepared by means of spin-coating technology were comparatively investigated. Sandwich devices based on PMCz-IN and PMCz+IN demonstrated nonvolatile write-once-read-many-times memory (WORM) and volatile static random access memory (SRAM) characteristics, respectively, which were further verified by the Kelvin probe force microscopy (KPFM) measurements. The proposed memory mechanism could be attributed to the formation of a stable charge-transfer (CT) complex for PMCz-IN and an unstable CT complex for PMCz+IN. Furthermore, the different distribution of IN in the two polymeric films might be the main reason for the stability of the CT complex.

Metal complex modified azo polymers for multilevel organic memories

Multilevel organic memories have attracted considerable interest due to their high capacity of data storage. Despite advances, the search for multilevel memory materials still remains a formidable challenge. Herein, we present a rational design and synthesis of a class of polymers containing an azobenzene-pyridine group (PAzo-py) and its derivatives, for multilevel organic memory storage. In this design, a metal complex (M(Phen)Cl2, M = Cu, Pd) is employed to modify the HOMO-LUMO energy levels of azo polymers, thereby converting the memory state from binary to ternary. More importantly, this approach enables modulating the energy levels of azo polymers by varying the coordination metal ions. This makes the achievement of high performance multilevel memories possible. The ability to tune the bandgap energy of azo polymers provides new exciting opportunities to develop new materials for high-density data storage.

Organopolymerization of naturally occurring Tulipalin B: a hydroxyl-functionalized methylene butyrolactone

Naturally occurring, OH-containing, tri-functional Tulipalin B has been successfully polymerized by N-heterocyclic carbene and phosphazene superbase catalysts into polymers with M_n up to 13.2 kg mol⁻¹.

B(C6F5)3-catalyzed group transfer polymerization of alkyl methacrylates with dimethylphenylsilane through in situ formation of silyl ketene acetal by B(C6F5)3-catalyzed 1,4-hydrosilylation of methacrylate monomer

The B(C₆F₅)₃-catalyzed GTP of alkyl methacrylates using hydrosilane has been studied in this study.

Different interactions between a metal electrode and an organic layer and their different electrical bistability performances

Different electrical bistability performances were obtained by tuning metal electrodes.

High-performance nonvolatile organic transistor memory devices using the electrets of semiconducting blends

Organic nonvolatile transistor memory devices of the n-type semiconductor N,N'-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) were prepared using various electrets (i.e., three-armed star-shaped poly[4-(diphenylamino)benzyl methacrylate] (N(PTPMA)3) and its blends with 6,6-phenyl-C61-butyric acid methyl ester (PCBM), 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pen) or ferrocene). In the device using the PCBM:N(PTPMA)3 blend electret, it changed its memory feature from a write-once-read-many (WORM) type to a flash type as the PCBM content increased and could be operated repeatedly based on a tunneling process. The large shifts on the reversible transfer curves and the hysteresis after implementing a gate bias indicated the considerable charge storage in the electret layer. On the other hand, the memory characteristics showed a flash type and a WORM characteristic, respectively, using the donor/donor electrets TIPS-pen:N(PTPMA)3 and ferrocene:N(PTPMA)3. The variation on the memory characteristics was attributed to the difference of energy barrier at the interface when different types of electret materials were employed. All the studied memory devices exhibited a long retention over 10(4) s with a highly stable read-out current. In addition, the afore-discussed memory devices by inserting another electret layer of poly(methacrylic acid) (PMAA) between the BPE-PTCDI layer and the semiconducting blend layer enhanced the write-read-erase-read (WRER) operation cycle as high as 200 times. This study suggested that the energy level and charge transfer in the blend electret had a significant effect on tuning the characteristics of nonvolatile transistor memory devices.

Tunable electrical memory characteristics using polyimide:polycyclic aromatic compound blends on flexible substrates

Resistance switching memory devices with the configuration of poly(ethylene naphthalate)(PEN)/Al/polyimide (PI) blend/Al are reported. The active layers of the PI blend films were prepared from different compositions of poly[4,4'-diamino-4″-methyltriphenylamine-hexafluoroisopropylidenediphthalimide] (PI(AMTPA)) and polycyclic aromatic compounds (coronene or N,N-bis[4-(2-octyldodecyloxy)phenyl]-3,4,9,10-perylenetetracarboxylic diimide (PDI-DO)). The additives of large π-conjugated polycyclic compounds can stabilize the charge transfer complex induced by the applied electric field. Thus, the memory device characteristic changes from the volatile to nonvolatile behavior of flash and write-once-read-many times (WORM) as the additive contents increase in both blend systems. The main differences between these two blend systems are the threshold voltage values and the additive content to change the memory behavior. Due to the stronger accepting ability and higher electron affinity of PDI-DO than those of coronene, the PI(AMTPA):PDI-DO blend based memory devices show a smaller threshold voltage and change the memory behavior in a smaller additive content. Besides, the memory devices fabricated on a flexible PEN substrate exhibit an excellent durability upon the bending conditions. These tunable memory performances of the developed PI/polycyclic aromatic compound blends are advantageous for future advanced memory device applications.

A new europium(III) complex containing a neutral ligand of 2-(pyridin-2-yl)-1H-benzo[d]imidazole: thermal, electrochemical, luminescent properties

A new europium(III) complex i.e. Eu(ECTFBD)3PBI was synthesized, where ECTFBD and PBI are 4-(9-ethyl-9H-carbazol-3-yl)-1,1,1-trifluoro-4-oxobutan-2-olate anion and 2-(pyridin-2-yl)-1H-benzo[d]imidazole, respectively. Its IR, UV-Vis spectra, electrochemical, thermal properties as well as photoluminescent performances in solid state and in CH2Cl2 were investigated. Eu(ECTFBD)3PBI exhibited strong red emission without any emission from ECTFBD and PBI in solid state, but with a very weak emission from ECTFBD in CH2Cl2. We explored this difference of the luminesecences of Eu(ECTFBD)3PBI in solid state and in CH2Cl2 based on the excited triplet energy levels of ECTFBD and PBI.

Azo anion radical complex of rhodium as a molecular memory switching device: isolation, characterization, and evaluation of current-voltage characteristics

Two rare examples of azo anion diradical complexes of Rh(III) are reported. These complexes showed excellent memory switching properties with a large ON/OFF ratio and are suitable for RAM/ROM applications. Their electronic structures have been elucidated using a host of physical methods, including X-ray crystallography, variable-temperature magnetic susceptibility measurement, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. The results indicate a predominant triplet state description of the systems with two ferromagnetically coupled radicals.

Conjugated fluorene based rod-coil block copolymers and their PCBM composites for resistive memory switching devices

We report the fabrication and characterization of polymer resistive switching memory devices fabricated from conjugated rod-coil poly[2,7-(9,9-dihexylfluorene)]-block-poly(2-vinylpyridine) diblock copolymers (PF-b-P2VP) and their hybrids with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). PF(10)-b-P2VP(37) and PF(10)-b-P2VP(68)-based devices exhibited the volatile static random access memory (SRAM) characteristic with an ON/OFF current ratio up to 1 × 10(7), which was explained by the trapping/back transferring of charge carrier. PF(10)-b-P2VP(68) had a longer holding time in the ON state than PF(10)-b-P2VP(37) because of the delayed back transfer of trapping carriers originally from the longer P2VP blocks. The PCBM aggregated size in the composite thin films were effectively reduced by PF-b-P2VP compared to the homopolymer of PF or P2VP, because of the supramolecular charge transfer interaction, as evidenced by absorption and photoluminescence spectra. Their PCBM/PF-b-P2VP composite devices changed from the nonvolatile write-once-read-many-times (WORM) memory to the conductor behavior as the PCBM composition was increased. The electric-field induced charge transfer effect enabled the electrical bistable states for the applications in digital WORM memory device. The tunable memory characteristics through the block length ratio of block copolymers or PCBM composition provided the solution-processable charge storage nanomaterials for programmable high density memory device with a reducing bit cell size.