Laser Patterning of Optically Reconfigurable Transistor Channels in a Photochromic Diarylethene Layer

Arylazopyrazole-modulated stable dual-mode phototransistors

High-performance organic devices with dynamic and stable modulation are essential for building devices adaptable to the environment. However, the existing reported devices incorporating light-activated units exhibit either limited device stability or subpar optoelectronic properties. Here, we synthesize a new optically tunable polymer dielectric functionalized with photochromic arylazopyrazole units with a cis-isomer half-life of as long as 90 days. On this basis, stable dual-mode organic transistors that can be reversibly modulated are successfully fabricated. The trans-state devices exhibit high carrier mobility reaching 7.4 square centimeters per volt per second and excellent optical figures of merit, whereas the cis-state devices demonstrate stable but starkly different optoelectronic performance. Furthermore, optical image sensors are prepared with regulatable nonvolatile memories from 36 hours (cis state) to 108 hours (trans state). The achievement of dynamic light modulation shows remarkable prospects for the intelligent application of organic optoelectronic devices.

Contributions of Light to Novel Logic Concepts Using Optoelectronic Materials

Instead of the current method of transmitting voltage or current signals in electronic circuit operation, light offers an alternative to conventional logic, allowing for the implementation of new logic concepts through interaction with light. This manuscript examines the use of light in implementing new logic concepts as an alternative to traditional logic circuits and as a future technology. This article provides an overview of how to implement logic operations using light rather than voltage or current signals using optoelectronic materials such as 2D materials, metal-oxides, carbon structures, polymers, small molecules, and perovskites. This review covers the various technologies and applications of using light to dope devices, implement logic gates, control logic circuits, and generate light as an output signal. Recent research on logic and the use of light to implement new functions is summarized. This review also highlights the potential of optoelectronic logic for future technological advancements.

Small-molecule ambipolar transistors

Ambipolar transistor properties have been observed in various small-molecule materials. Since a small energy gap is necessary, many types of molecular designs including extended π-skeletons as well as the incorporation of donor and acceptor units have been attempted. In addition to the energy levels, an inert passivation layer is important to observe ambipolar transistor properties. Ambipolar transport has been observed in extraordinary π-electron systems such as antiaromatic compounds, biradicals, radicals, metal complexes, and hydrogen-bonded materials. Several donor/acceptor cocrystals show ambipolar transport as well.

Future-Oriented Advanced Diarylethene Photoswitches: From Molecular Design to Spontaneous Assembly Systems

Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the building blocks to be manifested at the level of the entire system, beyond the DAE unit itself. This assembly-based strategy will bring many unexpected results that promote the design and manufacture of a new generation of advanced materials. Here, recent advances in the design and fabrication of diarylethene as a trigger in materials science, chemistry, and biomedicine are reviewed.

Molecular Approach to Engineer Two-Dimensional Devices for CMOS and beyond-CMOS Applications

Two-dimensional materials (2DMs) have attracted tremendous research interest over the last two decades. Their unique optical, electronic, thermal, and mechanical properties make 2DMs key building blocks for the fabrication of novel complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS devices. Major advances in device functionality and performance have been made by the covalent or noncovalent functionalization of 2DMs with molecules: while the molecular coating of metal electrodes and dielectrics allows for more efficient charge injection and transport through the 2DMs, the combination of dynamic molecular systems, capable to respond to external stimuli, with 2DMs makes it possible to generate hybrid systems possessing new properties by realizing stimuli-responsive functional devices and thereby enabling functional diversification in More-than-Moore technologies. In this review, we first introduce emerging 2DMs, various classes of (macro)molecules, and molecular switches and discuss their relevant properties. We then turn to 2DM/molecule hybrid systems and the various physical and chemical strategies used to synthesize them. Next, we discuss the use of molecules and assemblies thereof to boost the performance of 2D transistors for CMOS applications and to impart diverse functionalities in beyond-CMOS devices. Finally, we present the challenges, opportunities, and long-term perspectives in this technologically promising field.

Simultaneous Incorporation of Two Types of Azo-Groups in the Side Chains of a Conjugated D-A Polymer for Logic Control of the Semiconducting Performance by Light Irradiation

A new design strategy for photoresponsive semiconducting polymer with tri-stable semiconducting states is reported by simultaneous incorporation of tetra-ortho-methoxy-substituted azobenzene (mAzo) and arylazopyrazole (pAzo) in the side chains. The trans-to-cis transformations for mAzo and pAzo groups can sequentially occur within the polymer thin film after sequential 560 and 365 nm light irradiation. Remarkably, the trans-cis isomerization of mAzo and pAzo groups can modulate the thin film crystallinity. Accordingly, the performances of the resulting field-effect transistors (FETs) can be reversibly modulated, leading to tri-stable semiconducting states after sequential 560, 365, and 470 nm light irradiation. Therefore, the device performance can be logically controlled by light irradiation at three different wavelengths. In addition, with light irradiation and device current as the input and output signals, the three-value logic gate by using single FET device can be successfully mimicked.

Photochromic Behavior of ZnO/MoO3 Interfaces

ZnO/MoO₃ powder mixture exhibits a huge photochromic effect in comparison with the corresponding single oxides. The coloring efficiency of such combined material after UV-light irradiation was studied in terms of intensity, kinetics, and ZnO/MoO₃ powder ratio. Additionally, the incidence of the pretreatment step of the ZnO and MoO₃ powders under different atmospheres (air, Ar or Ar/H₂ flow) was analyzed. The huge photochromic effect discovered herein was interpreted as the creation of "self-closed Schottky barrier" at the solid/solid interfaces between the two oxides, associated with the full redox reaction which can be pictured by the equation ZnO_1-ε + MoO₃ → ZnO + MoO_3-ε. Remarkable optical contrast between virgin and color states as well as self-bleaching in dark allowing the reversibility of the photochromism is emphasized. From this first discovery, deeper characterization of the self-bleaching process shows that the photochromic mechanism is complex with a bleaching efficiency (possibility to come back to the virgin material optical properties without any deterioration) and a bleaching kinetics, which are both dependent on the coloring irradiation time. This demonstrates that the oxygen exchange through the Schottky interface proceeds in at least two convoluted steps: an anionic surface exchange allowing a reversibility of the redox reaction followed by bulk diffusion of the exchanged anions which are then definitively trapped. An emergent "negative photochromism effect" (i.e., photochromism associated with a self-bleaching instead of a darkening under irradiation) is observed after a long irradiation time.

A Conjugated Polymer Containing Arylazopyrazole Units in the Side Chains for Field-Effect Transistors Optically Tunable by Near Infra-Red Light

Optically tunable field-effect transistors (FETs) with near infra-red (NIR) light show promising applications in various areas. Now, arylazopyrazole groups are incorporated in the side chains of a semiconducting donor-acceptor (D-A) polymer. The cis-trans interconversion of the arylazopyrazole can be controlled by 980 nm and 808 nm NIR light irradiation, by utilizing NaYF₄ :Yb,Tm upconversion nanoparticles and the photothermal effect of conjugated D-A polymers, respectively. This reversible transformation affects the interchain packing of the polymer thin film, which in turn reversibly tunes the semiconducting properties of the FETs by the successive 980 nm and 808 nm light irradiation. The resultant FETs display fast response to NIR light, good resistance to photofatigue, and stability in storage for up to 120 days. These unique features will be useful in future memory and bioelectronic wearable devices.

Guiding Charge Transport in Semiconducting Carbon Nanotube Networks by Local Optical Switching

Photoswitchable, ambipolar field-effect transistors (FETs) are fabricated with dense networks of polymer-sorted, semiconducting single-walled carbon nanotubes (SWCNTs) in top-gate geometry with photochromic molecules mixed in the polymer matrix of the gate dielectric. Both hole and electron transport are strongly affected by the presence of spiropyran and its photoisomer merocyanine. A strong and persistent reduction of charge carrier mobilities and thus drain currents upon UV illumination (photoisomerization) and its recovery by annealing give these SWCNT transistors the basic properties of optical memory devices. Temperature-dependent mobility measurements and density functional theory calculations indicate scattering of charge carriers by the large dipoles of the merocyanine molecules and electron trapping by protonated merocyanine as the underlying mechanism. The direct dependence of carrier mobility on UV exposure is employed to pattern high- and low-resistance areas within the FET channel and thus to guide charge transport through the nanotube network along predefined paths with micrometer resolution. Near-infrared electroluminescence imaging enables the direct visualization of such patterned current pathways with good contrast. Elaborate mobility and thus current density patterns can be created by local optical switching, visualized and erased again by reverse isomerization through heating.

Geometrical Evolution and Formation of the Photoproduct in the Cycloreversion Reaction of a Diarylethene Derivative Probed by Vibrational Spectroscopy

The geometrical evolution of the reactant and formation of the photoproduct in the cycloreversion reaction of a diarylethene derivative were probed using time-resolved absorption spectroscopies in the visible to near-infrared and mid-infrared regions. The time-domain vibrational data in the visible region show that the initially formed Franck-Condon state is geometrically relaxed into the minimum in the excited state potential energy surface, concomitantly with the low-frequency coherent vibrations. Theoretical calculations indicate that the nuclear displacement in this coherent vibration is nearly parallel to that in the geometrical relaxation. Time-resolved mid-infrared spectroscopy directly detected the formation of the open-ring isomer with the same time constant as the decrease of the closed-ring isomer in the excited state minimum. This observation reveals that no detectable intermediate, in which the population is accumulated, is present between the excited closed-ring isomer and the open-ring isomer in the ground state.

Imidazole diarylethene switches: an alternative to acid-gated photochromism

Improving the photoactivity of imidazole diarylethenes by modifying their response sites in imidazole instead of appended aryl units is accomplished.

UV Radiation Cumulative Recording Based on Amorphous TiO2 Nanotubes

Ultraviolet (UV) photochromism is observed from natural light in amorphous TiO₂ nanotube arrays (NTAs) for the first time. Surface color of the NTAs film would change from light yellow to dark brown eventually, either under ultraviolet bulb irradiation or basking under natural sunlight. This photochromism is attributed to the appearance of Ti^3 + ions in the TiO₂ NTAs after UV illumination. Furthermore, a UV radiation cumulative dosimeter is designed and fabricated, consisting of a photochromic film and a colorimetric card, which convert invisible ultraviolet rays into visible color changes. This device helps people to understand intuitively how much UV radiation has been received in total from surrounding environments, which is of great importance for skin safety and public health.

Cyclization reaction dynamics of an inverse type diarylethene derivative as revealed by time-resolved absorption and fluorescence spectroscopies

Photocyclization reaction dynamics of an inverse type diarylethene derivative was investigated in alkane solutions by means of ultrafast laser spectroscopies. Femtosecond transient absorption spectroscopy showed that the Franck-Condon state formed by photoexcitation is geometrically relaxed to a transient species within 100 fs and subsequently the cyclization process takes place with a time constant of 36 ps. This time constant is much longer than those in normal type derivatives. Steady-state and time-resolved fluorescence measurements with the aid of quantum chemical calculations revealed that there exist three kinds of conformers, one parallel and two anti-parallel forms, in the ground state. One of the anti-parallel conformers undergoes the cyclization reaction, while the other two conformers are nonreactive species and their major relaxation processes are radiative decay and intersystem crossing into the triplet states. The triplet states thus formed no longer undergo the cyclization reaction in the late time region.

Structure and photochromism of 1-[2-methyl-5-phenyl-3-thienyl]-2-[2-methyl-5-(4-chlorophenyl)-3-thienyl]3,3,4,4,5,5-hexafluorocyclopent-1-ene, C27H16ClF6S2

C27H16ClF6S2, monclinic, P21/c (no. 14), a = 24.1193(5) Å, b = 9.2419(2) Å, c = 10.8343(2) Å, β = 96.1260(10)°, V = 2401.26(8) Å3, Z = 4, Rgt(F) = 0.0292, wRref(F2) = 0.0878, T = 100(2) K.

Self-Assembled Photochromic Molecular Dipoles for High-Performance Polymer Thin-Film Transistors

The development of high-performance multifunctional polymer-based electronic circuits is a major step toward future flexible electronics. Here, we demonstrate a tunable approach to fabricate such devices based on rationally designed dielectric super-lattice structures with photochromic azobenzene molecules. These nanodielectrics possessing ionic, molecular, and atomic polarization are utilized in polymer thin-film transistors (TFTs) to realize high-performance electronics with a p-type field-effect mobility (μ_FET) exceeding 2 cm² V^-1 s^-1. A crossover in the transport mechanism from electrostatic dipolar disorder to ionic-induced disorder is observed in the transistor characteristics over a range of temperatures. The facile supramolecular design allows the possibility to optically control the extent of molecular and ionic polarization in the ultrathin nanodielectric. Thus, we demonstrate a 3-fold increase in the capacitance from 0.1 to 0.34 μF/cm², which results in a 200% increase in TFT channel current.

Flexible small-channel thin-film transistors by electrohydrodynamic lithography

Small-channel organic thin-film transistors (OTFTs) are an essential component of microelectronic devices. With the advent of flexible electronics, the fabrication of OTFTs still faces numerous hurdles in the realization of highly-functional, devices of commercial value. Herein, a concise and efficient procedure is proposed for the fabrication of flexible, small-channel organic thin-film transistor (OTFT) arrays on large-area substrates that circumvents the use of photolithography. By employing a low-cost and high-resolution mechano-electrospinning technology, large-scale micro/nanofiber-based patterns can be digitally printed on flexible substrates (Si wafer or plastic), which can act as the channel mask of TFT instead of a photolithography reticle. The dimensions of the micro/nanochannel can be manipulated by tuning the processing parameters such as the nozzle-to-substrate distance, applied voltage, and fluid supply. The devices exhibit excellent electrical properties with high mobilities (∼0.62 cm² V^-1 s^-1) and high on/off current ratios (∼2.47 × 10⁶), and they are able to maintain stability upon being bent from 25 mm to 2.75 mm (bending radius) over 120 testing cycles. This electrohydrodynamic lithography-based approach is a digital, programmable, and reliable alternative for easily fabricating flexible, small-channel OTFTs, which can be integrated into flexible and wearable devices.

A fluorescent photochromic diarylethene based on naphthalic anhydride with strong solvatochromism

A diarylethene molecule consisting of an 1,8-naphthalic anhydride and two 2,5 dimethylthiophene which exhibits reversible fluorescence switching capacity as well as solvatochromism with red shift of the fluorescence maximum by more than 150 nm.

Solid-state photochromic behavior of pyrazolone 4-phenylthiosemicarbazones

Pyrazolone 4-phenylthiosemicarbazones show excellent solid-state photochromic properties, thermal stability and fatigue resistance upon the UV/Vis irradiation.