Conductivity Switching and Electronic Memory Effect in Polymers with Pendant Azobenzene Chromophores

Abstract

Electronic memory devices having the indium-tin oxide/polymer/Al sandwich structure were fabricated from polymers containing pendant azobenzene chromophores in donor-acceptor structures. The reversibility, or rewritability, of the high-conductivity (ON) state was found to be dependent on the terminal moiety of the azobenzene chromophore. While the polymers with electron-accepting terminal moieties (-Br or -NO2) in the pendant azobenzene exhibit write-once, read-many-times (WORM) type memory behavior, those with electron-donating terminal moieties (-OCH3) exhibit rewritable (FLASH) memory behavior. The WORM memory devices have low switching ("write") voltages below -2 V and high ON/OFF current ratios of about 10(4)-10(6). The polarity of the "write" voltage can be reversed by using an electrode with a higher work function than Al, thus excluding metallic filamentary conduction as a cause of the bistable switching phenomenon. The FLASH memory devices have low "write" and "erase" voltages of about -1.7 to -1.8 V and 2.0 to 2.2 V, respectively, and ON/OFF current ratios of about 10(3)-10(4). The electrical bistability observed can be attributed to charge trapping at the azobenzene chromophores, resulting in the charge-separated, high-conductivity state. The proposed mechanism is supported experimentally by a red shift and peak broadening in the UV-visible absorption spectra of the polymer films resulting from the OFF-to-ON electrical transition.

Highly UV‐Sensitive and Responsive Benzothiophene/Dielectric Polymer Blend‐Based Organic Thin‐Film Phototransistor

“…[ 26,27 ] In both cases, photoactive channel materials were completely or partially composed of the photochromic molecules, namely, oligomeric stilbenes containing EW/ED groups [ 26 ] and a polyester functionalized with pendant azobenzene moieties having EW/ ED groups. [ 27 ] The authors attributed the drain current modulation not only to the cis-trans isomerization of the photochromic moieties but also to the charge trapping of the photogenerated charge carriers by the EW/ED groups.…”

“…[ 26,27 ] In both cases, photoactive channel materials were completely or partially composed of the photochromic molecules, namely, oligomeric stilbenes containing EW/ED groups [ 26 ] and a polyester functionalized with pendant azobenzene moieties having EW/ ED groups. [ 27 ] The authors attributed the drain current modulation not only to the cis-trans isomerization of the photochromic moieties but also to the charge trapping of the photogenerated charge carriers by the EW/ED groups. The work recently published by our group, [ 28 ] demonstrated a successful engineering of such systems, utilizing a 2,7-dipentylbenzo[b]benzo [4,5]thieno [2,3-d]thiophene (BTBT-C5) and Disperse Red 1-functionalized poly(methyl methacrylate) (p-DR1).…”

Electrochemical Nanotransistor from Mixed‐Polymer Brushes

“…Their applications for controlled surface wettability, [6,7] thin-films permeability, [8,9] catalysis, [10] and particularly for assembling modified electrodes, [11] used in switchable sensors, [12] fuel cells, [13] and memory units, [14] resulted in novel materials, devices, and systems. [15,16] Recent integration of signal-responsive materials, functionalized switchable interfaces and biocomputing systems processing biochemical information resulted in the novel concept of biochemically controlled ''smart'' materials with built-in Boolean logic.…”

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

“…Additionally, many device applications demonstrated to date in covalent systems that benefit from photoresponsive azopolymers, such as photonic components, 67,164 organic lasers 165,166 and conductivity switching, [167][168][169] could benefit from employing the supramolecular materials for optimizing, e.g., the azobenzene content for the described application. Ionic bonding, on the other hand, is generally more stable thermally and temporally, whereas hydrogen-and halogenbonded small molecules are more susceptible to partial loss at higher temperatures or under vacuum drying.…”