Jongho Kim

Whispering‐gallery resonances provide a unique mechanism for light confinement through continuous rotational circulation, yet their realization in organic microcavities has been largely hindered by the thermodynamic tendency of small molecules to form solid faceted crystals. Here, we demonstrate that the phosphorescent complex tris(2‐phenylpyridine)iridium(III) (Ir(ppy) ₃ ) can be kinetically directed to self‐assemble into hollow hexagonal microtubes where the internal air void functions as a high‐contrast dielectric boundary for rotational optical confinement. These microtubes sustain robust whispering‐gallery modes (WGMs), confirmed via polarization‐resolved and spatially mapped photoluminescence to exhibit both azimuthal circulation and longitudinal propagation along the longitudinal axis. Unlike conventional Fabry–Pérot resonances that suffer from axial dissipation, the WGM coherence in these hollow architectures is preserved over extended propagation distances exceeding tens of micrometers. This persistence demonstrates that the tubular geometry enables complex 3D mode trajectories that effectively couple tight confinement with long‐range transport. Our results establish a lithography‐free strategy for engineering mode‐selective organic photonic devices, offering a versatile platform for coherent triplet‐exciton harvesting and high‐sensitivity optical sensing.

Near-infrared organic photodetectors (NIR-OPDs) are emerging as versatile platforms for flexible and low-cost optical sensing, yet achieving high-performance in the NIR region remains difficult remains challenging due to intrinsic trade-offs at both the material and device levels, due to the inherent balance required among bandgap narrowing, exciton dissociation, charge transport, and dark-current suppression. This review provides a concise overview of OPD operating mechanisms and the performance metrics governing sensitivity and noise. We highlight recent molecular-engineering strategies—core fluorination, asymmetric π-bridge design, fused-ring rigidification, and polymer backbone/side-chain tuning—that effectively enhance intermolecular ordering, reduce energetic disorder, and extend NIR absorption. Progress in all-polymer detectors and ambipolar phototransistors further demonstrates improved stability and broadened detection capability. Additionally, emerging applications, including NIR communication, biosignal monitoring, flexible imaging, and biometric recognition, showcase the expanding utility of NIR-OPDs. Remaining challenges include pushing detection beyond 1200 nm, simplifying synthesis, and improving long-term stability. Overall, advances in low-bandgap molecular design and device engineering continue to accelerate the practical adoption of NIR-OPDs.

Mechanoluminescence materials have emerged as promising candidates for haptic interface sensors due to their mechanically driven luminescent property. However, the inherently broad emission spectra of most mechanoluminescence materials hinder sharp signal generation and high spectral resolution. Here, a chromatic filtration strategy is suggested employing poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) as a conjugated polymer shell on copper‐doped zinc sulfide to achieve a highly refined and intensified signal. By selectively suppressing spectral components below 490 nm, the F8BT shell effectively narrows the emission bandwidth, yielding a full width at half maximum (FWHM) of 55 nm during the mechanoluminescence process. In particular, F8BT shell efficiently mitigates signal intensity loss, which can be ascribed to the chromatic filtration ability, through mechanoluminescence photon recycling performance. This dual functionality significantly reduces spectral noise in the blue region with high intensity, enhancing the resolution in actual powerless haptic controllers. The novel approach establishes a scalable framework for high‐resolution mechanoluminescence platforms, providing a versatile pathway toward next‐generation, power‐free stress‐sensing applications with unprecedented spectral precision and optical fidelity.

Recently, catechol-containing polymers have been extensively developed as promising materials for surgical tissue adhesives, wound dressing, drug delivery depots, and tissue engineering scaffolds. Catechol conjugation to the polymer backbone provides adhesive properties to the tissue and does not significantly affect the intrinsic properties of the polymers. An example of a catecholic polymer is catechol-conjugated hyaluronic acid. In general, hyaluronic acid shows excellent biocompatibility and biodegradability; thus, it is used in various medical applications. However, hyaluronic acid alone has poor mechanical and tissue adhesion properties. Catechol modification considerably increases the mechanical and underwater adhesive properties of hyaluronic acid, while maintaining its biocompatibility and biodegradability and enabling its use in several biomedical applications. In this review, we briefly describe the synthesis and characteristics of catechol-modified hyaluronic acid, with a specific focus on catechol-involving reactions. Finally, we discuss the basic concepts and therapeutic effects of catechol-conjugated hyaluronic acid for biomedical applications.

Polyacrylonitrile (PAN) is utilized as a precursor for the production of high-performance flame retarding fibers and is also widely used for clothing fibers. Herein, we report the flame retarding properties of catechol-containing PAN copolymers. The comonomer, dihydroxy styrene (DHS), was prepared from bio-derived caffeic acid (CA), which is a key intermediate in the biosynthesis of lignin. P(AN-co-DHS) and P(AN-co-CA) were synthesized by free radical polymerization. The effect of the comonomer structure on the stabilization of PAN copolymers was studied by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The catechol and acid groups of P(AN-co-DHS) and P(AN-co-CA) are effective at lowering the activation energy (E_a) for cyclization of the AN through an ionic mechanism. In CA copolymers, the acid-protected poly(acrylonitrile-co-methyl caffeate) (P(AN-co-MCA)) was found to be the most efficient in terms of E_a, the extent of reaction, and char fraction. The microscale combustion calorimetric analysis after thermal treatment (300 °C, 3 min) showed that the limiting oxygen index and heat release capacity of the P(AN-co-MCA₃) fiber were approximately 45% with V-0 of UL rating (superior to Nomex®) and 63 J g⁻¹ K⁻¹, respectively. This research demonstrates a simple, sustainable methodology for the production of environmentally friendly and high-performance flame retardants.