Spiropyran‐Functionalized Polymer–Carbon Nanotube Hybrids for Dynamic Optical Memory Devices and UV Sensors

Abstract

easily processable (e.g., from solution and on flexible substrates), operate at low voltages, have long retention times, allow for a large number of distinguishable conductance states to be programmed, and should be easily readable and erasable in a controlled manner. [4] A wide range of organic semiconductors has been tested and employed for this purpose, often in field-effect transistor structures. [5] The operating mechanism usually depends on photoinduced charge trapping at the interface between the semiconductor and gate dielectric, thus leading to a threshold shift and a large ratio between the channel conductance before and after irradiatio n. [3c,6] A second possible route is mixing the semiconductor with a photochromic molecule that can act as a charge trap in one state but not the other and thus change the effective mobility of the semiconducting layer. [1a,7] A variety of light-switchable molecules were employed in such devices, e.g., diarylethenes or azobenz enes. [1a,8] Another well-known photochromic system is the spiropyran/merocyanine pair. [7d,9] Upon irradiation of spiropyran with ultraviolet (UV) light, its isomer merocyanine is formed. Merocyanine has a much higher dipole moment than spiropyran and due to its more extended π-conjugation absorbs light in the visible range. [9a] Heating as well as excitation with greenyellow light induces the reverse isomerization, which enables repeated switching between the two forms. One desirable application of such optical memory elements is wearable UV dosimeters that can track the total exposure to harmful ultraviolet radiation. [2,10] Practical devices of this kind require mechanical flexibility and low operating voltages. Ideally, these sensors should be blind to visible light and resettable, i.e., reusable. A variety of materials and sensor concepts have been explored in recent years including photoelectric (e.g., ZnO nanowire photodetectors) [11] and again photochromic (e.g., color change of a polyoxometalates) [12] sensors. Among them, mixed networks of single-walled carbon nanotubes (SWNTs) have been tested in photoelectric devices. Kim et al. found an increase of the resistance (by up to 50%) in a two-terminal device with a random network of SWNTs after UV exposure, which was caused by desorption of oxygen and thus decreased p-doping. [13] In general, nanomaterials such Nanohybrids of purified semiconducting single-walled carbon nanotubes and conjugated polymers with attached spiropyran moieties are created as photoresponsive materials for optical memory devices and ultraviolet (UV) light sensors. The hybrids respond to UV light exposure in air with photoisomerization of the spiropyran groups to merocyanine, resulting in significant and persistent p-doping of the nanotubes, as confirmed by photoluminescence quenching and trion emission. The increased carrier concentration after illumination and the inherently high mobility of carbon nanotubes enable an up to two orders of magnitude increased conductivity of the nanotube/polymer hybrid networks in s...

Asymmetric Dressing of WSe2 with (Macro)molecular Switches: Fabrication of Quaternary-Responsive Transistors

“…33 The charges related to zwitterionic MC may quench the PL via enhanced nonradiative Auger recombination, in agreement with previous works. 11 To cast light onto the electrical properties of the SP/WSe 2 hybrid, it has been integrated as channel material into FETs. The devices revealed an n-type behavior with electron mobility of 12.4 cm 2 V −1 s −1 , which is typical for back-gated WSe 2 FETs with nine atomic layers (Figure S12).…”

“…, transistors) as a mean to finely adjust their electrical characteristics, mainly via doping. − In addition, during the last five years considerable efforts have been dedicated to the incorporation of stimuli-responsive molecules, which are able to undergo precise nanoscale rearrangements in response to chemical or physical inputs, as fundamental building blocks in conventional electronic devices . Upon integration of such dynamic molecular systems, the external stimuli may act as an additional remote control to operate the target devices, endowing them with ad hoc properties for specific applications such as memories, , UV sensors, , synapse simulation, , and so on.…”

Novel Amphiphilic Polyfluorene-Graft-(Polymethacrylic Acid) Brushes: Synthesis, Conformation, and Self-Assembly

“…Moreover, PFs can be modified easily at C9 position for further synthesis of polymer brushes. The luminescent properties of polymer brushes with PF main chain make it possible to obtain materials for sensors, coating for electroluminescence and other applications [18][19][20][21][22][23].…”

Realizing fast photoinduced recovery with polyfluorene‐block‐poly(vinylphenyl oxadiazole) block copolymers as electret in photonic transistor memory devices

“…Besides, conjugated/insulating polymer blends-based electrets have attracted extensive interest to utilize photogating effect of conjugated polymers in the floating gate. We have reported memory devices comprising conjugated/insulating polymer blends with various conjugated polymers including poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly[{2,5-di(3 0 ,7 0 -dimethyloctyloxy)-1,4-phenylene-vinylene}co-{3-(4 0 -[3 00 ,7 00 dimethyloctyloxy] phenyl)-1,4-phenylenevinylene}-co-{3 0 -(3 0 -(3 0 ,7 0 -dimethyloctyloxy) phenyl) -1,4 phenyleneviny-lene}] (SY-PPV), poly[(9,9-din-octylfluorenyl-2,7-diyl)-alt-(benzo [2,1,3]thiadiazol-4,8-diyl)] (F8BT), and insulating polymers of polystyrene (PS) or poly(methyl methacrylate) (PMMA) [45][46][47][48][49][50][51][52][53][54][55] Despite the previous good achievements on the photoprogramming memory devices, limited work has been proposed about photoinduced recovery. 53,[56][57][58] Huang et al discovered that the interfacial contact between β-phase PFO and semiconducting layer could provide more trapping sites and effective tunneling resulting photo recovery in devices with 26% increased storage capacity in contrast to that used amorphous PFO electret.…”

“…Polyfluorenes are appeared to be a promising candidate not only as the emissive layer in light emitting diodes, but also as the memory behavior due to the desirable energy levels and charge-trapping ability in response to both electrical and photonic pulses. [45][46][47][48][49][50][51][52][53][54] The photonic FET memory device with electret of PFO/PS exhibited a high memory ratio (I ON /I OFF ) of over 10 6 and an ultrafast photoprogramming within 1 s, indicating the potential of conjugated polymers as photoactive material in photonic FET memory. 55 In the following research, a series of conjugated block copolymer (BCP) comprising PFO and PS, namely PFO-b-PS, was studied as an electret layer for a photonic transistor memory to overcome the obstacle of miscibility in the polymer blends.…”