Survey of Recent Advances in Molecular Fluorophores, Unconjugated Polymers, and Emerging Functional Materials Designed for Electrofluorochromic Use

In this review, recent advances that exploit the intrinsic emission of organic materials for reversibly modulating their intensity with applied potential are surveyed. Key design strategies that have been adopted during the past five years for developing such electrofluorochromic materials are presented, focusing on molecular fluorophores that are coupled with redox-active moieties, intrinsically electroactive molecular fluorophores, and unconjugated emissive organic polymers. The structural effects, main challenges, and strides toward addressing the limitations of emerging fluorescent materials that are electrochemically responsive are surveyed, along with how these can be adapted for their use in electrofluorochromic devices.

Synthesis and Characterization of Novel Triphenylamine-Containing Electrochromic Polyimides with Benzimidazole Substituents

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N'-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4'-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4'-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV-Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials.

Influence of 1:4;3:6-dianhydro-d- mannitol-based polyamide as an additive on morphology, permeability and antifouling performance of PES ultrafiltration membrane

A novel hydrophilic polyamide, PA-OH containing 1:4;3:6-dianhydro-d-mannitol (isomannide) fragment was synthesized and used as an additive to prepare a series of polyethersulfone (PES)/PA-OH hybrid membranes with different content of PA-OH by phase separation method. And the addition of PA-OH was expected to improve the hydrophilicity, permeability, and antifouling performance of the PES ultrafiltration (UF) membrane. The scanning electron microscopic and atomic force microscopic images showed that the addition of PA-OH greatly changed the morphology of membranes by increasing the porosity, pore size and pore density, and the hydrophilicity was also improved with the increased PA-OH content. Based on the UF experiment, when the PA-OH content was 3%, the fluxes of pure water and bovine serum albumin solution reached 213.1 and 92.6 L m−2 h−1, which were close to 1.5 times and 2 times those of the bare PES membrane, respectively. When the PA-OH content was 5%, the FRR1st reached 85.2%, which was distinctly higher than that of the compared PES/polyethylene glycol5% hybrid membrane of 74.3%. And the FRR2st of the PES/PA-OH5% hybrid membrane was still over 80%, which indicated its long-term antifouling performance. Thus, the PA-OH can be a candidate for the hydrophilic additives.

Novel organosoluble polyarylates based on diphenylamine-fluorene units

Two kinds of polyarylates with diphenylamine-fluorene units were synthesized from the bisphenol monomer “ N, N-di(4-hydroxyphenyl)-2-amino-9,9-dimethylfluorene” with two different benzenedicarbonyl chlorides. These polyarylates were highly soluble in N, N-dimethylacetamide, tetrahydrofuran, and chloroform and could be easily solution-cast into transparent films. Both of the polyarylates exhibited a couple of reversible redox with half-wave potentials in the range of 0.87–0.90 V. During the electrochromic process, the color of the film changed from colorless (neutral state) to grey green (oxidation state) with a high coloration efficiency of 242 cm2 C−1. Compared with the polyarylates prepared from terephthaloyl chloride, the polyarylates prepared from isophthaloyl chloride exhibited enhanced fluorescence because of the reduced charge-transfer effect. Furthermore, its fluorescence could be reversibly switched under the applied potentials.

Visible-to-NIR Electrochromic Device Prepared from a Thermally Polymerizable Electroactive Organic Monomer

A monomer (1) consisting of a benzothiadiazole core flanked by two triphenylamines and two styrene pendant moieties was prepared. The monomer was fluorescent with its emission spanning 145 nm in the visible, contingent on the organic solvent used for the measurement. In addition to its positive solvatochromism, the absolute fluorescence quantum yield (Φ_fl) was consistently >20% with values >80% being measured in hexane, toluene, diethyl ether, and toluene. 1 could be reversibly oxidized with an oxidation potential of 880 mV vs SCE. The monomer could be immobilized on ITO-coated glass substrates. The resulting 425 nm thick immobilized film (poly-1) was 15% thinner than the monomer coating deposited by spray- and spin-coating. The electroactive film did not delaminate from the electrode upon either washing or cycling electrochemically between its oxidized and neutral states. Its absorption at 460 nm bleached upon electrochemical oxidation with the formation of a strong absorption at 880 nm and in the NIR, similar to 1. The perceived reversible color change with applied potential switched between yellow and gray. The fluorescence intensity of poly-1 could be switched with applied potentials. A passive transmissive device prepared from poly-1 was both electrochromic and fluorochromic, exhibiting reversible color change and fluorescence quenching.