Guey-Sheng Liou

Solution-processable triarylamine-based electroactive high performance polymers for anodically electrochromic applications

This review focused on high-performance polymers with anodically electrochromic triarylamine units built into main chains or as pendants. The main aim of the review is to present the most important and common trends regarding polymer synthesis from the point of view of the introduction of triarylamine moiety into polymer chains and to demonstrate how the polymer structures influence their properties, which leads them to be suitable for optoelectronic device construction. This review also covers a majority of the works in the recent decade involving the synthesis and characteristic evaluation of the resulting electrochromic polymers as well as their structural design by using the respective monomers.

Highly stable anodic green electrochromic aromatic polyamides: synthesis and electrochromic properties

A 4-methoxy-substituted triphenylamine containing the aromatic diamine, 4,4′-diamino-4″-methoxytriphenylamine (2), was synthesized by the caesium fluoride-mediated condensation of p-anisidine with 4-fluoronitrobenzene, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediate. A series of new polyamides with pendent 4-methoxy-substituted triphenylamine (TPA) units having inherent viscosities of 0.27–1.39 dL g−1 were prepared via the direct phosphorylation polycondensation of various dicarboxylic acids and the diamine (2). All the polymers were readily soluble in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into tough and flexible polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high softening temperature (242–282 °C), 10% weight-loss temperatures in excess of 470 °C, and char yields at 800 °C in nitrogen higher than 60%. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited reversible oxidation at 0.73–0.79 V versus Ag/AgCl in acetonitrile solution, and revealed excellent stability of electrochromic characteristics with a color change from colorless to green at applied potentials ranging from 0.00 to 1.05 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good green coloration efficiency (CE = 374 cm2 C−1) but also exhibited high contrast of optical transmittance change (ΔT %) up to 85% at 787 nm and 30% at 391 nm. After over 1000 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.

Novel high-Tg poly(amine-imide)s bearing pendent n-phenylcarbazole units : synthesis and photophysical, electrochemical and electrochromic properties

A new carbazole-derived, triphenylamine-containing aromatic diamine monomer, 4,4′-diamino-4″-N-carbazolyltriphenylamine, was successfully synthesized by the caesium fluoride-mediated condensation of N-(4-aminophenyl)carbazole with 4-fluoronitrobenzene, followed by palladium-catalyzed hydrazine reduction. A series of novel poly(amine-imide)s 6a–6g with pendent N-phenylcarbazole units having inherent viscosities of 0.17–0.56 dL g−1 were prepared from the newly synthesized diamine monomer and seven commercially available tetracarboxylic dianhydrides via a conventional two-step procedure that included a ring-opening polyaddition to give polyamic acids, followed by chemical or thermal cyclodehydration. The polymers of the series were amorphous and most of them could afford flexible, transparent, and tough films with good mechanical properties. All the poly(amine-imide)s had useful levels of thermal stability associated with high glass-transition temperatures (303–371 °C), 10% weight-loss temperatures in excess of 543 °C, and char yields at 800 °C in nitrogen higher than 60%. The poly(amine-imide)s 6e–6g exhibited a UV-vis absorption maximum at around 300 nm in NMP solution. The poly(amine-imide) 6g derived from an aliphatic dianhydride was optically transparent in the visible region and fluoresced violet–blue at 403 nm in NMP with 4.54% quantum yield higher than the wholly aromatic 6e and 6f. The hole-transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine-imide) films on an indium-tin oxide (ITO)-coated glass substrate exhibited a reversible oxidation wave at 1.05 V and an additional irreversible oxidation wave at 1.39 V versus Ag/AgCl in acetonitrile solution. The polymer films revealed excellent stability of electrochromic characteristics, with a color change from neutral pale yellowish to green doped form at applied potentials ranging from 0.00 to 1.15 V.

Highly flexible and optical transparent 6F-PI/TiO2 optical hybrid films with tunable refractive index and excellent thermal stability

In this study, a synthesis route was developed for preparing highly transparent novel polyimide-nanocrystalline-titania hybrid optical films with a relatively high titania content (up to 50 wt%) and thickness (20–30 μm) from a soluble polyimide 6F-poly(p-hydroxy-imide) (6FPI). It has been demonstrated that the introduction of bulky CF3 groups into polyimide backbones enhanced both solubility and optical transparency. Furthermore, the attachment of hydroxyl groups provided the organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide : hydroxyl groups. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films revealed excellent optical transparency in the visible range, good surface planarity, high thermally dimensional stability, and tunable refractive index. A three-layer anti-reflection coating based on the hybrid films was prepared and revealed a reflectance of less than 0.7% in the visible range, indicating its potential optical applications.

A novel molecularly imprinted polymer thin film as biosensor for uric acid

A novel amine-imide type conducting polymer, denoted as poly(PD-BCD), was molecularly imprinted on an indium-tin oxide (ITO) glass, with uric acid (UA) as the template and without any functional monomer. Intending to improve the imprinting efficiency, the polymer content was varied from 0.3 to 0.9wt% during the preparation of the molecularly imprinted polymer (MIP), thereby varying the thickness of the polymer film; the content of UA as the template was maintained to be the same for all the films. The sensitivities of the thus prepared MIP electrodes were calculated to be more than 3-fold, compared to those of the corresponding non-MIP (NMIP) electrodes, which were obtained through the same method, however, without adding UA during their preparation. A polymer content of 0.6wt% rendered the best performing MIP electrode, as judged by the imprinting efficiency and sensitivity of the electrode for UA. A linear relationship between steady-state currents and UA concentrations from 0 to 1.125mM was obtained for both types of the sensors. The sensitivities of the MIP and the NMIP electrodes made with 0.6wt% of polymer were calculated to be 24.72 and 6.63microAmM(-1)cm(-2), respectively. The limit of detection (LOD) for this MIP was found to be 0.3microM at a signal to noise ratio (S/N) of 3. This MIP electrode was used as a biosensor for the detection of UA in the presence of ascorbic acid (AA) in a sample containing these species in the same concentrations as those in a human serum. The selectivity of MIP electrode is higher than that of NMIP electrode, and the values are 28.76 and 8.85, respectively. The results are substantiated by using cyclic voltammetry (CV), linear sweep voltammetry, amperometry, and scanning electron microscopy.

Synthesis, luminescence and electrochromism of aromatic poly(amine–amide)s with pendent triphenylamine moieties

A new triphenylamine-containing aromatic dicarboxylic acid monomer, N,N-bis(4-carboxyphenyl)-N′,N′-diphenyl-1,4-phenylenediamine (2), was synthesized from the amination reaction between 4-aminotriphenylamine and 4-fluorobenzonitrile and subsequent alkaline hydrolysis of the dinitrile intermediate. A series of novel aromatic poly(amine–amide)s with triphenylamine units in the main chain and as the pendent group were prepared from the newly synthesized dicarboxylic acid and various aromatic diamines. These poly(amine–amide)s were amorphous and readily soluble in many organic solvents. All the polymers could be solution-cast into flexible films with good mechanical properties. They had excellent levels of thermal stability associated with high glass-transition temperatures (226–261 °C). These polymers exhibited strong UV–vis absorption bands at 350–365 nm in NMP solution. Their photoluminescence spectra showed maximum bands around 512–543 nm in the green region. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine–amide) 5a prepared from the dicarboxylic acid monomer 2 with a structurally similar diamine monomer N,N-bis(4-aminophenyl)-N′,N′-diphenyl-1,4-phenylenediamine (4a) exhibited four reversible oxidation redox couples in acetonitrile solution at E1/2 = 0.60, 0.80, 0.97 and 1.13 V, respectively. All the poly(amine–amide)s exhibited excellent reversibility of electrochromic characteristics by continuous five cyclic scans between 0.0 to 1.30 V, with a color change from the original pale yellowish neutral form to the green and then to blue oxidized forms.

Novel anodic electrochromic aromatic polyamides with multi-stage oxidative coloring based on N,N,N′,N′-tetraphenyl-p-phenylenediamine derivatives

A series of novel aromatic polyamides with pendent 4,4′-dimethoxy-substituted triphenylamine (TPA) units were prepared via the direct phosphorylation polycondensation from a new dicarboxylic acid monomer, N,N-bis(4-carboxyphenyl)-N′,N′-di(4-methoxyphenyl)-1,4-phenylenediamine (4), and various aromatic diamines. These polyamides were amorphous with good solubility in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into flexible polymer films. They had excellent levels of thermal stability associated with their relatively high glass-transition temperatures (233–308 °C). These polymers exhibited strong UV-vis absorption bands at 351–363 nm in NMP solution. Their photoluminescence spectra showed maximum bands around 450–504 nm. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide 6g prepared from the dicarboxylic acid monomer (4) with a structurally similar diamine monomer N,N-bis(4-aminophenyl)-N′,N′-di(4-methoxyphenyl)-1,4-phenylenediamine (5g) exhibited four reversible oxidation redox couples in acetonitrile solution at Eonset = 0.35, E1/2 = 0.64, 0.84, and 0.99 V, respectively. After over 3000 cyclic switches for green color, the films of polyamide 6g still showed excellent continuous cyclic stability of electrochromism.

Synthesis and properties of soluble aromatic polyimides from 2,2 '-bis(3,4-dicarboxyphenoxy)-1,1'-binaphthyl dianhydride and aromatic diamines

Aromatic tetracarboxylic dianhydride having crank and twisted noncopla- nar structure, 2,2*-bis(3,4-dicarboxyphenoxy)-1,1*-binaphthyl dianhydride, was syn- thesized by the reaction of 4-nitrophthalonitrile with 2,2*-dihydroxy-1,1*-binaphthyl, followed by alkaline hydrolysis of the intermediate bis(ether dinitrile) and subsequent dehydration of the resulting bis(ether diacid). Binaphthyl-2,2*-diyl-containing novel aromatic polyimides having inherent viscosities up to 0.67 dL/g were obtained by the one-step polymerization process starting from the bis(ether anhydride) and various aromatic diamines. All the polyimides showed typical amorphous diffraction patterns. Most of the polyimides were readily soluble in common organic solvents such as N,N- dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and pyridine. These aro- matic polyimides had glass transition temperatures in the range of 280-3507C, de- pending on the nature of the diamine moiety. All polymers were stable up to 4007C, with 10% weight loss being recorded above 4857C in air. q 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1937-1943, 1998

Novel triphenylamine-containing ambipolar polyimides with pendant anthraquinone moiety for polymeric memory device, electrochromic and gas separation applications

Novel electron-donating triphenylamine (TPA)-containing electroactive functional polyimides with electron-withdrawing pendant anthraquinone moiety were designed and prepared for memory devices, electrochromic and gas separation applications. These high-performance polymers exhibited two conductivity states and could be swept negatively with a high ON/OFF current ratio of 109. The ON state of OAQ-6FPI polyimide remained around 8 min after removing the applied voltage, while the AQ-6FPI polyimide quickly returned to the OFF state during the backward sweep in a dual sweep process, implying that devices based on OAQ-6FPI and AQ-6FPI reveal static random access memory (SRAM) and dynamic random access memory (DRAM) behaviors resulting from the isolated donor–acceptor (D–A) and non-isolated D–A structures, respectively. Meanwhile, the polymer films exhibited electrochromic characteristics with a color change from neutral colorless or pale yellowish to blue and green at applied potentials, ranging from 0.00 to 1.40 V. Furthermore, the presence of a bulky and carbonyl-containing anthraquinone unit could enhance effectively CO2 permeability coefficients (PCO2) and permeability selectivity (PCO2/PCH4) for these polyimide membranes in the range of 21.6–69.9 and 28.8–31.7, respectively, and permeability increased with higher efficiency by directly attaching the bulky group to the backbone than incorporating via a spacer.

Electrochemical characterization of small organic hole-transport molecules based on the triphenylamine unit

A series of substituted triphenylamine-containing organic compounds are synthesized and their hole-transport properties are examined by electrochemical and spectroelectrochemical methods. Several substituted tirphenylamines exhibited irreversible electron-transfer reactions both in the oxidative and reductive scan. On the other hand, the cyclic voltammograms of the p-phenylenediamine series are well defined. N,N 0 -bis(4-nitrophenyl)-N,N 0 -diphenyl-1,4-phenylenediamine (NPD) exhibited two reversible oxidation redox couples at +1.00 and +1.28 V vs. Ag/AgCl in dichloromethane solution. There is one reversible reduction redox couple at )1.12 V and one irreversible wave with Ep;c at )1.87 V. Cyano-substituted p-phenylenediamine (CPD) exhibited similar oxidation redox couples. Amino-substituted p-phenylenediamine (APD) is easier to oxidize than NPD and CPD. APD exhibits two reversible oxidation redox couples at +0.40 and +0.70 V and two extra irreversible oxidation waves at +1.26 and +1.52 V. Optically transparent thin-layer electrode (OTTLE) coupled with UV/Vis/NIR spectroscopy was used to examine the oxidation products of the above reactions. The electrogenerated cation and dication of the substituted p-phenylenediamine are very stable in the spectroelectrochemical studies. Oxidation of the compound APD exhibited a distinguished absorption pattern, which is different from those of compound NPD and compound CPD. 2003 Elsevier Science B.V. All rights reserved.