Coordinative Layer-by-Layer Assembly of Electrochromic Thin Films based on Metal Ion Complexes of Terpyridine-Substituted Polyaniline Derivatives

Abstract

Preparation, metal ion complexation, and coordinative assembly into organized electro-chromic films of a polyaniline derivative P1 substituted with tert-butyloxycarbonyl (boc) and terpyridine (tpy) substituent groups in alternating sequence are described. Cleavage of the boc groups after processing into thin films is also described. P1 is prepared upon Pd-catalyzed polycondensation of N-tert-butyloxycarbonyl-4,4'-dibromodiphenylamine and 4'(4-aminophenyl)-2,2':6,2''-terpyridine. The molecular weight is in the range of oligomers, the tetramer and pentamer being the most abundant species. P1 is soluble in common organic solvents. Solutions are pale yellow with blue or green fluorescence depending on the solvent. Fluorescence quantum yields up to 68% are found. P1 is able to complex divalent metal salts such as zinc(II) chloride, for example. Titration experiments indicate the formation of 2:1 tpy:metal ion complexes. Layer-by-layer (LbL) assembled films of metal ion complexes of P1 can be prepared, if negatively charged substrates are alternately dipped into solutions of metal(II) hexafluorophosphates and P1. Films of the zinc and nickel ion complex of P1 are lemon yellow in the neutral state and change color into greenish gray upon anodic oxidation, while Co-containing films are purple and change color into grayish blue upon oxidation. All color changes are reversible under ambient conditions. ATR-IR studies indicate that thermal treatment of the films at 180 °C, or acid treatment, e.g. with 5% aqueous trifluoroacetic acid solution, results in cleavage of the boc groups. P1 is transformed into the polyaniline derivative P2 with tpy substituent groups at every second N atom in the backbone. Films of metal ion complexes of P2 are also electrochromic albeit the colors differ slightly from those of P1. For example, the absorption maximum of the Zn-P2 film is at 456 nm, whereas it is at 446 nm for the corresponding Zn-P1 film. Prior to cleavage of the boc group, electrochromic switching times are 1.1 to 2.0 s for 30 to 40 nm thick films, while after the cleavage 0.5 to 1.2 s are found. The contrast is 13 to 19%, and not affected by the cleavage. Because of high stability, fast switching, and high contrast, the films might be useful as active materials in electrochromic devices.

Porous Carbons – Hyperbranched Polymers – Polymer Solvation

“…In addition, special derivatives of polyaniline [542] showed a multielectrochromic behavior ( Fig. 48) [543,544].…”

“…Electrochromic films based on metal-complexed polyaniline derivatives (reprinted with permission from[544]. Copyright 2012 American Chemical Society)…”

Covalent Layer‐by‐Layer Assembly Using Reactive Polymers

“…In addition, while conventional LbL processes for the assembly of PEMs are generally restricted to the use of aqueous solutions (owing to the limited solubility of many polyelectrolytes in solvents other than water), many materials useful for covalent LbL assembly are compatible with the use of organic solvents, including aprotic and less polar solvents, which can expand the range of substrates and interfaces on which films can be deposited. Finally, a particularly useful feature of these covalent approaches is that they often result in polymer multilayers containing residual, unreacted functional groups (either on the surface or in the interior of a film; e.g., Figure 15.1c) that can be exploited postfabrication, and under mild conditions, to covalently attach and/or create patterns of other functionalities using a wide range [112][113][114][115][116][117][118][119][120][121][122][123] of different chemical and biological agents ( Figure 15.1d). Although it is certainly not impossible to chemically functionalize or pattern the surfaces of conventional PEMs, the combination of increased film stability and chemical reactivity afforded by these reactive approaches can greatly facilitate postfabrication modification and, in general, opens the door to new opportunities for the design of functional surfaces and interfaces.…”

“…In addition, several recent reports also demonstrate the utility of metal-ligand interactions as a means of promoting LbL assembly. For example, interactions of various metal complexes with polymers bearing amine [112], carboxylic acid [113,114], salicylidene [115,116], and pyridine-containing [117][118][119][120][121] and palladium pincer-type [122,123] groups have been used to assemble metal complex crosslinked polymer films under a variety of different conditions. The metal-ligand bonds formed in these examples should be regarded as coordinate bonds rather than as covalent bonds.…”

“…These coordination-cross-linked films were stable to high temperatures and resisted degradation in polar solvents (e.g., EtOH, tetrahydrofuran (THF), and DMF) up to an order of magnitude longer than other common PEM films but could be disassembled in response to the addition of pyridine or other ligands via ligand/metal exchange. Maier et al demonstrated that films fabricated from terpyridine-functionalized polymers and one of several divalent metal salts displayed electrochromic behavior (e.g., where the color of the film was dependent on the metal ion in the film and could be quickly and reversibly switched between different colors by changing oxidation state) [121]. In general, the ability to incorporate metal centers into the structures of these films in well-defined ways (e.g., as stoichiometrically defined components of individual cross-links, as opposed to the ill-defined or random incorporation of metal complexes in an otherwise cross-linked multilayer) can provide unique opportunities for the design of responsive or erasable materials (e.g., films that disassemble in response to other metals or ligands), catalytic materials and membranes, electrical and photoelectric devices, and sensors.…”