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Energy saving electrochromic windows from bistable low-HOMO level conjugated polymers

Energy saving electrochromic windows were established by controlling the interfacial charge transport using low-HOMO level ( 90 min) at the voltage-off state with a high color contrast (879 cm2 C−1).

Electrochemical Fluorescence Switching from a Patternable Poly(1,3,4‐oxadiazole) Thin Film

A highly soluble poly(1,3,4-oxadiazole) (POD) substituted with long alkyl chains was examined for electrochemical fluorescence switching. The high solubility of the polymers enabled a simple fabrication of an electrochemical cell, which showed reversible fluorescence switching between dark (n-doping) and bright (neutral) states with a maximum on/off ratio of 2.5 and a cyclability longer than 1000 cycles. Photochemical cleavage of the oxadiazole in POD allowed photo-patterning of the POD film upon exposure to UV source. The patterned POD films displayed patterned image reversibly under a step potential of +1.8/-1.8 V.

NIR electrochemical fluorescence switching from polymethine dyes

A polymethine dye was used as a fluorophore and an electroactive modulator in order to achieve reversible electrochemical fluorescence switching in the near infrared (NIR) region. An NIR emissive polymethine dye, 3H-indolium, 2-[2-[2-chloro-3-[2-[1,3-dihydro-3,3-dimethyl-1-(phenylmethyl)-2H-indol-2-ylidene]ethylidene]-5-(1,1-dimethylethyl)-1-cyclohexen-1-yl]ethenyl]-3,3-dimethyl-1-(phenylmethyl)-bromide (PM1), displayed high absorption and emission in the NIR region. In addition, it showed a relatively reversible electrochemical reaction between −0.5 and 1.1 V vs. Ag wire. In contrast, a keto group (CO) bridged polymethine analogue, 2,6-bis[2-(1,3-dihydro-1-hexyl-3,3-dimethyl-2H-indol-2-ylidene)ethylidene]-4-(1,1-dimethylethyl)cyclohexanone (PM2), showed an irreversible electrochemical reaction, possibly due to the keto group interrupting the full conjugation of the entire molecule in PM2. The reversible redox reaction of PM1 allowed electrochemical fluorescence switching in the NIR region for the first time. The NIR fluorescence switching was visually observable through a visible light cut-off filter with a cyclability of over 100.

Electrofluorescence switching of fluorescent polymer film

AbstractElectrofluorescence switching has attracted much research attention recently due to its potential applications in the areas of ion sensing, bio analysis, fluorescence imaging, and signaling recognition events. This review describes the chemical structure of electrofluorescent polymers their synthetic strategies, and their patterning characteristics. The designs of these polymers are based on fluorescence quenching through an energy transfer between a fluorophore and an acceptor, which is similar to various types of fluorescence-based sensors. Electrofluorescence devices were designed to demonstrate stable switching processes with different durations while measuring the photophysical properties. The patterning process has shown promise if used to create fluorescent displays, sensors, or for security document applications, but an investigation of patternable polymers and related mechanisms remains for future work.

NIR Electrofluorochromic Properties of Aza-Boron-dipyrromethene Dyes

The photophysical properties of near-infrared (NIR) emissive aza-boron-dipyrromethene (aza-BDP) dyes incorporating nitrofluorene and alkoxy decorations were intensively investigated. Their highly reversible one-electron reduction process showed characteristic electrofluorochromic (EF) properties in the NIR range, depending on the substituents. The nitrofluorene ethynyl-substituted (Type I) dyes showed smaller EF effects than the alkoxy-containing (Type II) dyes because of the difference in their intrinsic fluorescence contrast between the neutral and reduced states (radical anion). In addition, the Type II chromophores showed a larger diffusion coefficient for ion transport, which enhanced the EF contrast and the response time for the fluorescence change at a given step potential. With an optimized condition, the NIR EF ON/OFF ratio reached a value of 6.1 and a long cyclability over 1000 EF cycles between −0.4 V and +0.4 V switching potentials, with approximately 20% loss of the initial ON/OFF switching ratio. The NIR EF switching was visually observed through a visible light cut-off filter, featuring high fluorescence contrast.

Multi-color fluorescence switching with electrofluorochromic polymers

The multi-color switching of electrofluorochromism was examined from the thin electrofluorochromic (EF) films of polyfluorene (PFO) and poly(propylenedioxythiophene–phenylene) (P(ProDOT-Ph)). The PFO and P(ProDOT-Ph) films showed vivid blue and yellow fluorescence, respectively, at neutral state but their emission was quenched upon application of oxidation potential leading to ion radical states. The fluorescence from the polymer films was reversibly switched to vivid color when the films were returned to their neutral states. The EF color switching ratio (rc1/c2) between the fluorescent state (c1) and dark (c2) state for the yellow color EF device with P(ProDOT-Ph) film was about four times higher than that of the PFO. Because the two polymer films have different colors and working potentials, a multi-color switching device was fabricated by coating the P(ProDOT-Ph) and PFO films onto working and counter electrodes, respectively. The multi-color EF device showed fluorescence switching from blue (B) to white (W) to yellow (Y), and vice versa, depending on the applied potential. The rc1/c2 for yellow (c1) and blue (c2) switching (Y/B) was larger (9.71) than those for Y/W and W/B. Moreover, the EF switching for Y/B in the multi-EF device was also very effective and showed the largest EF efficiency (EEF = 3.82 × 106) among the EF color switching.

Electrofluorochromic Devices with Organic Dyes and Conjugated Polymers

Electrofluorochromic materials exhibit reversible switch of fluorescence emission by the applied potentials. This unique property is based on the electrochemistry of organic materials. Especially, electrofluorochromic organic dyes and conjugated polymers can be categorized into three types, depending on the distance between the electroactive moiety and the fluorescent core. The electrofluorochromic properties such as working potential, emission color, ON/OFF ratio, stability, and switching efficiency are summarized for each type of material. Also, the working principle of each type is introduced with suitable examples. Finally, some applications of electrofluorochromic materials are presented in the last part of this chapter. Although the reports on applications are still scarce until now, we believe that challenges in display or sensing applications will follow these pioneering researches.

Reversible multi-color electrofluorescence switching

The color of the electrofluorescence switching device was tuned to white by adding extra electroactive fluorophores with different emission colors. The reversible electrochemistry of fluorophores between neutral and anion radical was accompanied by fluorescence on and off, respectively, allowing fluorescence switching. Since the fluorophores have different emission color and also different redox potential, emission color could be further modified by quenching of the particular emission with precise voltage control. A reversible multicolor switching device was prepared by packing electroactive fluorophores blend of polymer electrolyte between ITO electrodes, and its emission color was examined with various fluorophore contents and potentials.

Photopatterning and electro-optical switching of redox active fluorescent polymers

The fluorescent poly(1,3,4-oxadiazole)s (POD) and polypyrene (PPy) were examined for electro-optic device. The fluorescence switching device prepared using poly(1,3,4-oxadiazole)s showed molecular structure-dependent switching properties depending on the para- or meta-linkage. Thin films of POD and PPy were prepared by solution process to give highly fluorescent film, of which emission intensity was switched on and off upon application of step potentials. Using a photochemical reaction, the thin films of POD and PPy were directly patterned to give a fluorescent pattern. An all solid state device containing the patterned films of POD and PPy was prepared using a solid polymer electrolyte layer. The device showed reversible fluorescence switching in response to external voltage applications. Patterning of the switching device in different dimension and scale will be demonstrated.