Hyun Ho Choi

In this study, we report a streamlined one-pot synthesis of a new series of ( E )-4-phenyl-2-(2-(pyren-1-ylmethylene)hydrazinyl)thiazole derivatives (4a–4o).

The molecular weight of a polystyrene gate dielectric tunes the surface glass transition and chain-end density at the buried interface, steering the nucleation, molecular orientation, and field-effect mobility of vacuum-deposited DNTT.

Aramid fibers are valued for their high strength, stiffness, and thermal stability, but their intrinsic chain rigidity restricts toughness and fatigue resistance. In this study, aramid copolymers containing heteroaromatic 6­(4-aminophenoxy)­pyridine-3-amine (APA) and extended aromatic 4,4′-bis­(4-aminophenoxy)­biphenyl (BABP) were synthesized by solution polycondensation and processed into fibers through wet spinning. The incorporation of APA improved ductility through dynamic hydrogen bonding, whereas BABP reinforced stiffness and strength through strong π–π stacking and rigid biphenyl alignment. The combination of these comonomers with 3,4′-oxidianiline (3,4′-ODA) further enhanced drawability and molecular orientation, resulting in a synergistic improvement in toughness and durability. Under cyclic loading, APA- and BABP-based fibers retained up to 78% and 64% of their initial tenacity, respectively, compared with 34% for the 3,4′-ODA fiber. Corresponding energy retention exceeded 50% in APA and 35% in BABP, accompanied by lower hysteresis losses. These results reveal that targeted comonomer design effectively balances strength, ductility, and fatigue resistance by tuning hydrogen bonding and π–π stacking. The findings provide molecular-level insights for developing next-generation aramid fibers capable of sustained performance in demanding mechanical and thermal environments.

Organic field-effect transistors (OFETs) require reliable micro- and nanoscale patterning of semiconducting layers, yet conjugated polymers have long been considered incompatible with photolithography due to dissolution and chemical damage from photoresist solvents. Here, we present a photolithography-compatible strategy based on doping-induced solubility conversion (DISC), demonstrated using poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). AuCl₃ doping reversibly modulates the benzoid/quinoid resonance balance, lamellar stacking, and π–π interactions, suppressing solubility during lithographic exposure, while dedoping restores the intrinsic electronic properties. Using this approach, micropatterns with linewidths as small as 2 µm were fabricated in diverse geometries—including line arrays, concentric rings, dot arrays, and curved channels—with high fidelity; quantitative analysis of dot arrays yielded mean absolute errors of 48–66 nm and coefficients of variation of 2.0–3.9%, confirming resolution and reproducibility across large areas. Importantly, OFETs based on patterned PBTTT exhibited charge-carrier mobility, threshold voltage, and on/off ratios comparable to spin-coated devices, despite undergoing multiple photolithography steps, indicating preservation of transport characteristics. Furthermore, the same DISC-assisted lithography was successfully applied to other representative p-type conjugated polymers, including P3HT and PDPP-4T, confirming the universality of the method. This scalable strategy thus combines the precision of established lithography with the functional advantages of organic semiconductors, providing a robust platform for high-density organic electronic integration in flexible circuits, biointerfaces, and active-matrix systems.

The controlled crystallization of organic semiconductors remains a key challenge for achieving reproducible performance in organic electronic devices. In this study, the influence of polymer interlayers on the polycrystalline growth of organic semiconductors was systematically investigated. Rubrene thin films deposited on UV-modified polystyrene interlayers exhibited spherulitic crystallization, with uniform orthorhombic domains forming exclusively on IPA-rinsed, crosslinked PS (PS-net). Polarized optical microscopy revealed a time-dependent nucleation-and-growth mechanism, while temperature-dependent studies identified a narrow 170–180 °C window for stabilizing orthorhombic domains. Surface morphology and surface energy analyses indicated that roughness and interfacial energy contribute partially, but cannot fully account for the observed crystallization behavior. Differential scanning calorimetry and solubility tests suggested that the thermal dynamics of the interlayer and the removal of chain-scission fragments play critical roles in enabling molecular diffusion and ordering. Taken together, these findings provide new insights into how polymer interlayers can be engineered to direct the crystallization pathways of small-molecule semiconductors, offering valuable guidance for the rational design of organic electronic materials. Graphical abstract Schematic illustration of rubrene film morphology on different polymer interlayers: amorphous rubrene on pristine PS (left) and well-developed spherulitic domains on crosslinked PS-net (right), highlighting the critical role of polymer interfacial structure in directing molecular crystallization.

Despite significant recent advancements in highly functional organic semiconductors (OSCs), the n ‐type OSCs reported to date lag behind their p ‐type counterparts in terms of long‐term environmental stability. As an alternative approach to n ‐type materials, a few p ‐type polymers have been shown to undergo dramatic transitions in their charge carrier polarity to n ‐type through transition metal‐incorporated Lewis acid doping. Although the concept of polarity switching is promising, its unclear chemical origin—particularly from a materials science perspective—limits its potential as an n ‐type counterpart. In this work, the chemical and structural mechanisms underlying the p ‐to‐ n polarity switching in a heavily doped conjugated polymer are elucidated. Using gold(III) chloride‐doped indacenodithiophene‐co‐benzothiadiazole (IDTBT) as a model system, doping‐induced thin‐film structural changes are investigated. Quantitative X‐ray photoelectron spectroscopy analysis of doped IDTBT films provides direct evidence of oxidation state changes in Au and Cl ions and confirms the covalent chlorination of the polymer backbone, establishing a direct correlation between the chemical doping mechanism and polarity switching. Finally, leveraging this polarity switching behavior, a p‐n homojunction organic diode is demonstrated with a rectification ratio of 10 ⁴ –10 ⁵ , highlighting the versatility and potential of this excessively p ‐doped n ‐type OSC system for tailoring charge transport properties.

Aramid copolymers have garnered significant interest due to their potential applications in extreme environments such as the aerospace, defense, and automotive industries. Recent developments in aramid copolymers have moved beyond their traditional use in high-strength, high-temperature resistant fibers. There is now a demand for new polymers that can easily be processed into thin films for applications such as electrical insulation films and membranes, utilizing the inherent properties of aramid copolymers. In this work, we demonstrate two novel aramid copolymers that are capable of polymerizing in polar organic solvents with a high degree of polymerization, achieved by incorporating flexible bis(4-aminophenoxy) benzene moieties into the chain backbone. The synthesized MBAB-aramid and PBAB-aramid have enabled the fabrication of exceptionally thin, clear films, with an average molecular weight exceeding 150 kDa and a thickness ranging from 3 to 10 μm. The dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) reveal that the thin films of MBAB-aramid and PBAB-aramid exhibited glass transition temperatures of 270.1 °C and 292.7 °C, respectively, and thermal decomposition temperatures of 449.6 °C and 465.5 °C, respectively. The mechanical tensile analysis of the 5 μm thick films confirmed that the tensile strengths, with elongation at break, are 107.1 MPa (50.7%) for MBAB-aramid and 113.5 MPa (58.4%) for PBAB-aramid, respectively. The thermal and mechanical properties consistently differ between the two polymers, which is attributed to variations in the linearity of the polymer structures and the resulting differences in the density of intermolecular hydrogen bonding and pi-pi interactions. The resulting high-strength, ultra-thin aramid materials offer numerous potential applications in thin films, membranes, and functional coatings across various industries.

Wearable technologies and flexible electronics have developed rapidly owing to the emergence of cutting-edge cross-disciplines. The flexibility and tunable properties of organic materials enable wearable sensory systems to adapt to complex surface deformations and detect physiological signals sensitively. The demand for high-performance strain sensors, to accurately detect complex movements and environmental changes, in wearable technology has increased notably. However, current sensors primarily detect strain in a single direction, which restricts their effectiveness in detecting multi-directional strains, such as in natural human movements or robotic joints. In this review, we examine the advances and future challenges that may arise in the development of strain sensors that can measure both the magnitude and direction of external tensile strain. Additionally, we examine the sensor materials (platform and sensing materials) required to develop a strain sensor to detect the direction of tension, structural research on strain sensors, and various application fields such as human motion detection and human–machine interaction via system integration. Finally, we discuss the prospects and current challenges involved in the development of direction-selective strain sensors for wearable smart electronic systems or electronic skin. This review should provide a comprehensive reference for future technologies.

Due to the increasing complexity in miniaturization of electronic devices, reconfigurable field-effect transistors (RFETs) have emerged as a solution. Although the foundational concepts of RFETs have matured over two decades, ongoing breakthroughs are needed to address challenges such as improving the device performance as well as achieving balanced symmetry between n-type and p-type transport modes with long-term stability. Herein, we present a nonvolatile WSe₂-based RFET that utilizes photoassisted interfacial charge trapping at the h-BN and SiO₂ interface. Unlike typical RFETs with two gate electrodes, our RFETs achieved polarity control with a single operating gate activated exclusively under white-light exposure. The threshold voltage was tunable, ranging from 27.4 (−31.6 V) to 0.9 (+19.5 V), allowing selective activation of n-type (p-type) operation at V_GS = 0 V. Additionally, our WSe₂-based RFETs show superior repeatability and long-term stability. Leveraging these advantages, various reconfigurable logic circuits were successfully demonstrated, including complementary inverters and switch circuits as well as pull-up and pull-down circuits, highlighting the potential of WSe₂ FETs for future advancements of integrated circuits.