Fast‐Switching Electrochromic Films of Zinc Polyiminofluorene‐Terpyridine Prepared Upon Coordinative Supramolecular Assembly

Abstract

Organic and inorganic materials with redox-controllable coloration and two or more stable valence states are of interest for applications in electrochromic and sensing devices. [1][2][3] Commercial applications require materials with film-forming properties, high stability, high contrast, and switching speed. Film formation can be achieved via spin-coating, solvent evaporation, electrochemical deposition, or layer-by-layer assembly.[4] The latter method is advantageous because it can be used to assemble ultrathin films of a variety of organic and inorganic compounds in a simple and inexpensive manner, with thickness control in the nanometer range.Previous work on preparation of electrochromic layer-by-layer assemblies was based on the use of polymers containing redoxactive viologen [5,6] or triphenylamine units, [7] conjugated polyelectrolytes, such as polythiophene derivatives [8][9][10] and polyaniline (PANI), [11] or colloidal solutions of Prussian Blue nanoparticles. [11,12] In most cases, film formation was brought about by alternating electrostatic assembly of electroactive components and nonactive counter-polyelectrolytes, utilizing the layer-by-layer technique first reported by Decher and coworkers. [13] Our contribution differs from the previous ones in that a crosslinked organic-inorganic coordination polymer is built up stepwise on a solid support, and no counter-polyelectrolyte is needed. The preparation method is similar to Decher's technique, in that the substrate is alternately dipped into two different solutions causing the sequential buildup of the polymer film at the substrate surface. However, in our case the two solutions contain a) a metal salt, such as zinc hexafluorophosphate, and b) a polymeric polytopic ligand, such as P1-2, which is composed of a polyiminofluorene backbone [14] with phenylterpyridine substituent groups attached to the nitrogen atom of the backbone. Synthesis and molecular structure are shown in Scheme 1a, and the self-assembly process is depicted in Scheme 2. The terpyridine (tpy) groups are capable of forming metal complexes of D 2d -symmetry with divalent zinc ions [15,16] (Scheme 1b). Due to the polytopic nature of the ligand P1-2, a network structure is formed, and the resulting coordination polymer is insoluble, so that it is easily immobilized at the substrate surface. Since the polytopic ligand is neutral, the buildup of the films proceeds exclusively via coordinative interactions. There is a similarity to the ''reactive self-assembly'' of previously reported films of coordination polymers, such as zinc bisquinoline, [17] metal tetrathiooxalates, [18] metal(IV)diphosphonates [19] metal hexacyanoferrates, [20] metal Schiff-base coordination polymers, [21] and others, [22,23] but in these cases the self-assembly is brought about by coordinative and electrostatic interactions simultaneously. There is also some analogy to functional metallo-supramolecular polyelectrolyte films and multilayers, reported by Kurth and coworkers.[24] However, in their work, first a line...

Layer-by-layer preparation of polyelectrolyte multilayer membranes for separation

“…Two strategies have been reported to incorporate metal ligand interactions into PEMMs, 1) utilization of metallo-supramolecular polymers as PE, and 2) utilization of the metal ligand interactions as driving force for LBL assembly. [41,42,43,44] In the first more classical approach, a charged metallo-supramolecular polymer is formed by the coordination of a bifunctional metal coordinating ligand with a metal ion to form a PE, which is subsequently used in LBL coating of multilayers with a classical anionic PE (figure 2). [45] Alternatively, the metal ligand coordination of cobalt or cupper ions have been utilized as driving force for the LBL assembly with poly(4-vinyl pyridine) (P4VP).…”

Synthesis, characterization and electrochromic properties of polyamides having triphenylamine derivatives

“…Electrochromic materials have attracted considerable attention in both academia and industry because of their potential application, such as reflectance mirrors, sunglasses, controllable aircraft canopies, smart windows, and electrochromic displays [3,6,7]. A variety of electrochromic materials have been reported [2,4,5,[8][9][10]: (1) transition metal oxides, such as WO 3 ; (2) small molecular dyes including organic or inorganic, such as viologens and Prussian blue; (3) conducting polymers, such as polyanilines, polypyrroles and polythiophenes, and (4) oxidizable organic polymers with triphenylamine derivatives.…”

Electrochromism Properties of Polyimides Possessing Triphenylamine Moieties with Different Substituents

“…In particular, electrochromic devices exhibit a reversible optical change in absorption or transmittance after being oxidized or reduced electrochemically by applying an external voltage using electrochromic materials, such as transition-metal oxides, inorganic coordination complexes, organic molecules, and conjugated polymers [6][7][8][9][10][11]. In general, studies of electrochromic materials focusing on the optical changes in the visible region have been useful for variable reflectance mirrors, sunglasses, controllable aircraft canopies, smart windows, and electrochromic displays [11].…”