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     

Polycyclic arene‐based D–A polyimide electrets for high‐performance n‐type organic field effect transistor memory devices

We report the memory characteristics of n‐type N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide‐based organic field‐effect transistors (OFET) using a series of donor–acceptor (D–A) polyimide electrets of poly[4,4′‐diamino‐4″‐methyltriphenylamine‐hexafluoroisopropylidenediphthal imide] ( PI(AMTPA‐6FDA) ), poly[N,N‐bis‐(4‐aminophenyl)‐aminonaphthalene‐hexafluoroisopropylidenediphthalimide] ( PI(APAN‐6FDA) ), and poly[N,N‐bis‐(4‐aminophenyl)‐aminopyrene‐hexafluoroisopropylidenediphthalimide] ( PI(APAP‐6FDA) ). Among the polymer electrets, the OFET memory device based on PI(APAP‐6FDA) exhibits the largest memory window of 40.63 V and the best charge retention ability (maintained for over 10⁴ s with the ON/OFF current ratio about 10³) due to introducing polycyclic arene functionality of pyrene into the electron donating moiety. With the excellent carrier delocalization, pyrene successfully enhanced the charge storage ability and sustained the CT complex. Besides, PI(APAP‐6FDA)‐based OFET memory also performed well in the write‐read‐erase‐read tests for over 100 cycles. Our finding may provide a new approach for the preparation of high performance nonvolatile OFET memories with electrets of D–A polyimide systems. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 139–147     

Synthesis and properties of high‐performance functional polyimides containing rigid nonplanar conjugated tetraphenylethylene moieties

A simple diamine (TetraPEDA) containing rigid nonplanar conjugated tetraphenylethylene (TetraPE) moieties was designed and synthesized through Wittig–Horner and Suzuki coupling reactions. Four kinds of high‐performance functional polyimides (PI) were thus prepared by the polymerization of TetraPEDA and four dianhydrides, respectively. Because of the introduction of the aromatic rigid nonplanar TetraPE structure, the PI exhibited special fluorescent characteristics, as the maximum fluorescence emission of the four PI was observed at 425–505 nm in NMP solution and at 470–491 nm in film state. Also these organo‐soluble PI showed outstanding properties, such as low dielectric constant (even without fluorinated substituent), light color, high glass transition temperatures (382–443 °C) and thermal stability in air (T_d5% up to 565 °C), and excellent mechanical properties. The polymer memory devices with the configuration of indium tin oxide/PI/aluminum (ITO/PI/Al) exhibited distinct volatile memory characteristics of static random access memory, with an ON/OFF current ratio of 1 × 10⁴ to 1 × 10⁵. These functional PI showed attractive potential applications in the field of high performance flexible polymer photoconducting devices or fluorescent polymer memory devices. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Enhanced redox stability and electrochromic properties of aromatic polyamides based on N,N‐bis(4‐carboxyphenyl)‐N′,N′‐bis(4‐tert‐butylphenyl)‐1,4‐phenylenediamine

A new bis(triphenylamine)‐type dicarboxylic acid monomer, N,N‐bis(4‐carboxyphenyl)‐N′,N′‐bis(4‐tert‐butylphenyl)‐1,4‐phenylenediamine, was prepared by a well‐established procedure and led to a new family of redox‐active aromatic polyamides with di‐tert‐butyl‐substituted N,N,N′,N′‐tetraphenylphenylenediamine (TPPA) segments. The resulting polyamides were amorphous with good solubility in many organic solvents, and most of them could be solution cast into flexible polymer films. The polyamides exhibited high thermal stability with glass‐transition temperatures in the range of 247–293 °C and 10% weight‐loss temperatures in excess of 500 °C. They showed well‐defined and reversible redox couples during oxidative scanning, with a strong color change from a colorless or pale yellowish neutral form to green and blue oxidized forms. They had enhanced redox stability and electrochromic performance when compared with the corresponding analogs without tert‐butyl substituents on the TPPA unit. The polyamide with TPPA units in both the diacid and diamine components shows multicolored electrochromic behavior. A polyamide containing both the cathodic coloring anthraquinone chromophore and the anodic coloring TPPA chromophore has the ability to show red, green, and blue states, toward single‐component RGB electrochromics. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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.     

Growing poly(N‐vinylcarbazole) from the surface of graphene oxide via RAFT polymerization

A new approach on usage of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate (DDAT)‐covalently functionalized graphene oxide (GO) as reversible addition fragmentation chain transfer (RAFT) agent for growing of poly(N‐vinylcarbazole) (PVK) directly from the surface of GO was described. The PVK polymer covalently grafted onto GO has M_n of 8.05 × 10³, and a polydispersity of 1.43. The resulting material PVK‐GO shows a good solubility in organic solvents when compared to GO, and a significant energy bandgap of ～2.49 eV. Bistable electrical switching and nonvolatile rewritable memory effect, with a turn‐on voltage of about ?1.7 V and an ON/OFF state current ratio in excess of 10³, are demonstrated in the Al/PVK‐GO/ITO structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

High Performance Nonvolatile Transistor Memories Utilizing Functional Polyimide‐Based Supramolecular Electrets

We report pentacene‐based organic field‐effect transistor memory devices utilizing supramolecular electrets, consisting of a polyimide, PI(6FOH‐ODPA), containing hydroxyl groups for hydrogen bonding with amine functionalized aromatic rings (AM) of 1‐aniline (AM1), 2‐naphthylamine (AM2), 2‐aminoanthracene (AM3), and 1‐aminopyrene (AM4). The effect of the phenyl ring size and composition of AM1–AM4 on the hole‐trapping capability of the fabricated devices was investigated systematically. Under an operating voltage under ±40 V, the prepared devices using the electrets of 100 % AM1–AM4/PI ratios exhibited a memory window of 0, 8.59, 25.97, and 29.95 V, respectively, suggesting that the hole‐trapping capability increased with enhancing phenyl ring size. The memory window was enhanced as the amount of AM in PI increased. Furthermore, the devices showed a long charge‐retention time of 10⁴ s with an ON/OFF current ratio of around 10³–10⁴ and multiple switching stability over 100 cycles. This study demonstrated that the electrical characteristics of the OFET memory devices could be manipulated through the chemical compositions of the supramolecular electrets.     

Near‐infrared electrochromic poly(aryl ether)s based on isolated electroactive tetraphenyl‐p‐phenylenediamine moieties

A series of near‐infrared (NIR) electrochromic aromatic poly(aryl ether)s containing N,N,N′,N′‐tetraphenyl‐p‐phenylenediamine (TPPA) moieties in the backbone were prepared from the high‐temperature polycondensation reactions of a biphenol monomer, 2,5‐bis(diphenylamino)hydroquinone, with difluoro compounds. The obtained polymers were readily soluble in many organic solvents and showed useful levels of thermal stability associated with high glass‐transition temperatures (182–205 °C) and high char yields (higher than 40% at 800 °C in nitrogen). The polymer films showed reversible electrochemical oxidation with high contrast ratio both in the visible range and NIR region, and also exhibited high coloration efficiency (CE), low switching time, and stability for electrochromic operation. The polyether TPPA‐a thin film revealed good CE in visible (CE = 217 cm²/C) and NIR (CE = 192 cm²/C) region with reversible electroactive stability (over 500 times within 5% loss relative to its initial injected charge). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5378–5385, 2009     

Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides

Resistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX , with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine ( AMTPA ), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide ( NTCDI ) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide ( BTCDI ) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI . The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX . At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI . Combining these results and our previous study on perylenebisimide ( PBI ), we concluded that memory characteristics could be tailored by changing the conjugation length ( PBI > NTCDI > BTCDI ) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Fully transparent nonvolatile resistive polymer memory

We present a fully transparent nonvolatile resistive polymer memory device based on an anthracene‐containing partially aliphatic polyimide along with indium tin oxide (ITO) top and bottom electrodes. High transmittance of over 90% in the wavelength range of 400 to 800 nm is accomplished with an ITO/polyimide/ITO/glass device. The device shows unipolar write‐once‐read‐many times (WORM) memory behavior with an ON/OFF current ratio of ～2 × 10³, and the ratio remained without any significant degradation for over 10⁴ s. The memory behavior of the device is considered to be governed by trap‐controlled space‐charge limited conduction (SCLC) and local filament formation. Based on molecular simulation of the polyimide, the location of energy states is different from that in the conventional charge transfer (CT) mechanism. Despite the relatively low ON/OFF current ratio, our results can give insight into the development of fully transparent memory device. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 918–925     

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.     

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.

     

Novel triarylamine‐based alternating conjugated polymer with high hole mobility: Synthesis,electro‐optical,and electronic properties

Novel bi‐triphenylamine‐containing aromatic dibromide M3 , N,N‐bis(4‐bromophenyl)‐N′,N′‐dipheny‐l,4‐phenylenediamine, was successfully synthesized. The novel conjugated polymer P1 having number‐average molecular weight of 1.31 × 10⁴ was prepared via Suzuki coupling from the dibromide M3 and 9,9‐dioctylfluorene‐2,7‐diboronic acid bis(1,3‐propanediol) ester. Polymer P1 had excellent thermal stability associated with a high glass‐transition temperature (T_g = 141 °C). The hole‐transporting and UV‐vis‐near‐infrared electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the conjugated polymer films cast onto indium‐tin oxide‐coated glass substrates exhibited two reversible oxidation redox couples at E_1/2 values of 0.73 and 1.13 V versus Ag/Ag⁺ in acetonitrile solution. The hole mobility of the conjugated polymer P1 revealed ～10^?3 cm² V^?1 s^?1, which is much higher than that of other conjugated polymer systems. The observed UV‐vis‐near‐infrared absorption change in the conjugated polymer film P1 at applied potentials ranging from 0.00 to 1.23 V are fully reversible and associated with strong color changes from pale yellowish in its neutral form to green and blue in its oxidized form. Using a combination of experimental study and theoretical investigation, we proposed an oxidation mechanism based on molecular orbital theory, which explains the cyclic voltammetry experimental results well. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Hole‐transporting host‐polymer series consisting of triphenylamine basic structures for phosphorescent polymer light‐emitting diodes

A series of novel styrene derived monomers with triphenylamine‐based units, and their polymers have been synthesized and compared with the well‐known structure of polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine with respect to their hole‐transporting behavior in phosphorescent polymer light‐emitting diodes (PLEDs). A vinyltriphenylamine structure was selected as a basic unit, functionalized at the para positions with the following side groups: diphenylamine, 3‐methylphenyl‐aniline, 1‐ and 2‐naphthylamine, carbazole, and phenothiazine. The polymers are used in PLEDs as host polymers for blend systems with the following device configuration: glass/indium–tin–oxide/PEDOT:PSS/polymer‐blend/CsF/Ca/Ag. In addition to the hole‐transporting host polymer, the polymer blend includes a phosphorescent dopant [Ir(Me‐ppy)₃] and an electron‐transporting molecule (2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole). We demonstrate that two polymers are excellent hole‐transporting matrix materials for these blend systems because of their good overall electroluminescent performances and their comparatively high glass transition temperatures. For the carbazole‐substituted polymer (T_g = 246 °C), a luminous efficiency of 35 cd A^?1 and a brightness of 6700 cd m^?2 at 10 V is accessible. The phenothiazine‐functionalized polymer (T_g = 220 °C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well‐known polymer of N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A^?1 and a brightness of 2500 cd m^?2 (10 V). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3417–3430, 2010     

Fluorene based donor‐acceptor polymer electrets for nonvolatile organic transistor memory device applications

Fluorene based donor‐acceptor polyimides, including poly[bis‐(4‐aminophenyl)fluorene‐hexanediamide] [PA(BAP F‐AC)], poly[bis‐(4‐aminophenyl)fluorene‐hexafluoroisopropylidenediphthalimide] [PI(BAPF‐6FDA)], poly[bis‐(4‐aminophenyl)fluorene‐oxydiphthalimide] [PI(BAPF‐ODPA)], and poly[bis‐(4‐aminophenyl)fluorene‐1,2,4,5‐cyclohexanetetracarboxylic diimide] [PI(BAPF‐HPMDA)], as charge storage layer (electret) are employed for nonvolatile memory device applications. The polyimides are consisted of electron‐donating fluorene diamine moiety (BAPF) and neutral (AC and HPMDA) or electron‐accepting (6FDA and ODPA) moieties, respectively. The memory characteristics of these devices can be tuned from the EORM (erase once and read many times) behavior [PA(BAPF‐AC)], semi‐flash [PI(BAPF‐ODPA)], [PI(BAPF‐HPMDA)], to a flash type memory [PI(BAPF‐6FDA)]. The PI(BAPF‐6FDA) devices show the largest memory window of 77 V and a long retention time over 10⁴ s with a high I_on/I_off current ratio of 10⁸. This is attributed to the largest torsion angle of PI(BAPF‐6FDA) stabilizing charge transfer (CT) complexes. The write‐read‐erase‐read cycles were stably operated over 100 cycles. This work provides a new insight into the relationship between the CT effect and the nonvolatile memory behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 602–614     

Molecular Logic Gates and Switches Based on 1,3,4‐Oxadiazoles Triggered by Metal Ions

Organic molecular devices for information processing applications are highly useful building blocks for constructing molecular‐level machines. The development of “intelligent” molecules capable of performing logic operations would enable molecular‐level devices and machines to be created. We designed a series of 2,5‐diaryl‐1,3,4‐oxadiazoles bearing a 2‐(para‐substituted)phenyl and a 5‐(o‐pyridyl) group (substituent X=NMe₂, OEt, Me, H, and Cl; 1 a – e ) that form a bidentate chelating environment for metal ions. These compounds showed fluorescence response profiles varying in both emission intensity and wavelength toward the tested metal ions Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ and the responses were dependent on the substituent X, with those of 1 d being the most substantial. The 1,3,4‐oxadiazole O or N atom and pyridine N atom were identified as metal‐chelating sites. The fluorescence responses of 1 d upon metal chelation were employed for developing truth tables for OR, NOR, INHIBIT, and EnNOR logic gates as well as “ON‐OFF‐ON” and “OFF‐ON‐OFF” fluorescent switches in a single 1,3,4‐oxadiazole molecular system.     

Controlled helical orientation of carbazole in amino acid derived poly(N‐propargylamide)s

Novel L ‐alanine and L ‐glutamic acid derivatized, carbazole‐containing N‐propargylamides [N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide and N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] were synthesized and polymerized with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] (nbd = norbornadiene) as a catalyst to obtain the corresponding polymers with moderate molecular weights in high yields. Polarimetry, circular dichroism, and ultraviolet–visible spectroscopy studies revealed that both poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] and poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] took a helical structure with a predominantly one‐handed screw sense in tetrahydrofuran, CHCl₃, and CH₂Cl₂. The helix content of poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] could be tuned by heat or the addition of a protic solvent, and the helical sense of poly[N‐(9‐carbazolyl) ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] was inverted by heat in CHCl₃ or in mixtures of tetrahydrofuran and CH₂Cl₂. Poly[N‐(9‐carbazolyl) ethyloxycarbonyl‐L ‐alanine N′‐propargylamide] and poly[N‐(9‐carbazolyl)ethyloxycarbonyl‐L ‐glutamic acid‐γ‐benzyl ester N′‐propargylamide] also took a helical structure in film states. They showed small fluorescence in comparison with the monomers and redox activity based on carbazole. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 253–261, 2007     

Donor–Acceptor Oligoimides for Application in High‐Performance Electrical Memory Devices

Two new oligoimides, OI(APAP-6FDA) and OI(APAN-6FDA) , which consisted of electron‐donating N‐(4‐aminophenyl)‐N‐phenyl‐1‐aminopyrene ( APAP ) or N‐(4‐aminophenyl)‐N‐phenyl‐1‐aminonaphthalene ( APAN ) moieties and electron‐accepting 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride ( 6FDA ) moieties, were designed and synthesized for application in electrical memory devices. Such devices, with the indium tin oxide (ITO)/oligoimide/Al configuration, showed memory characteristics, from high‐conductance Ohmic current flow to negative differential resistance (NDR), with corresponding film thicknesses of 38 and 48 nm, respectively. The 48 nm oligoimide film device exhibited NDR electrical behavior, which resulted from the diffusion of Al atoms into the oligoimide layer. On further increasing the film thickness to 85 nm, the OI(APAP-6FDA) film device showed a reproducible nonvolatile “write once read many” (WORM) property with a high ON/OFF current ratio (more than ×10⁴). On the other hand, the device that was based on the 85 nm OI(APAN-6FDA) film exhibited a volatile static random access memory (SRAM) property. The longer conjugation length of the pyrene unit compared to that of a naphthalene unit was considered to be responsible for the different memory characteristics between these two oligoimides. These experimental results suggested that tunable switching behavior could be achieved through an appropriate design of the donor–acceptor oligoimide structure and controllable thickness of the active memory layer.     

Synthesis and properties of poly‐(2‐ethynylpyridinium bromide) having propargyl side chains

Poly‐(2‐ethynylpyridinum bromide) (PEPBP) having propargyl side chains was prepared by the direct polymerization of 2‐ethynylpyridine and propargyl bromide under mild reaction conditions without any initiator and catalysts. The polymerization proceeded well to give PEPBP with propargyl side chains in relatively high yields. Various spectral data for the polymer structure indicated that the conjugated polymer system having N‐propargylpyridinum substituent was formed. This ionic polymer was completely soluble in water, methanol, dimethylformamide, dimethyl sulfoxide, and N,N‐dimethylacetamide and well processable into thin homogeneous film. The photoluminescence intensity (λ_max = 760 nm) of this polymer increased as the temperature was increased. At 1 KHz and room temperature, this polymer has k′ = 2.9 and σ = 7.3 × 10^?10 (S/cm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3151–3158, 2001