Jinsang Kim

Metal‐free purely organic phosphors (POPs) are attractive triplet emitters, but their room‐temperature phosphorescence (RTP) is often slow at milliseconds or longer because the radiative T ₁ →S ₀ transition is spin‐forbidden. Here, we introduce directional carbonyl orientation (DCO) as a packing‐aware conformational descriptor for understanding and designing fast metal‐free RTP. In brominated terephthalate derivatives, co‐directional carbonyl torsions are associated with fast RTP, whereas counter‐directional torsions are associated with slower RTP. Using two polymorphs of dimethyl dibromoterephthalate (MeBrTPA), we show that the co‐directional Form I emits blue RTP with Φ _phos = 24%, τ _phos = 15 µs, and an estimated k _r = 1.6 × 10 ⁴ s ⁻¹ , while the counter‐directional Form II is slower despite its higher quantum yield. State‐resolved TD‐DFT/SOC calculations further reveal that the difference cannot be described by direct S ₀ –T ₁ coupling alone, but instead reflects distinct state‐specific combinations of T ₁ –S _n SOC and S _n –S ₀ transition strength. Finally, translating the DCO‐favored geometry from crystal packing into molecular design, conformational locking in CyclicBrTPA produces fast blue RTP in amorphous PMMA. Together, these results establish DCO as a practical molecular design strategy for organizing favorable spin‐coupling geometries beyond a single crystal‐packing environment, while highlighting the continued importance of a sufficiently rigid environment for room‐temperature emission.

Metal‐free purely organic phosphors (POPs) are attractive triplet emitters, but their room‐temperature phosphorescence (RTP) is often slow at milliseconds or longer because the radiative T ₁ →S ₀ transition is spin‐forbidden. Here, we introduce directional carbonyl orientation (DCO) as a packing‐aware conformational descriptor for understanding and designing fast metal‐free RTP. In brominated terephthalate derivatives, co‐directional carbonyl torsions are associated with fast RTP, whereas counter‐directional torsions are associated with slower RTP. Using two polymorphs of dimethyl dibromoterephthalate (MeBrTPA), we show that the co‐directional Form I emits blue RTP with Φ _phos = 24%, τ _phos = 15 µs, and an estimated k _r = 1.6 × 10 ⁴ s ⁻¹ , while the counter‐directional Form II is slower despite its higher quantum yield. State‐resolved TD‐DFT/SOC calculations further reveal that the difference cannot be described by direct S ₀ –T ₁ coupling alone, but instead reflects distinct state‐specific combinations of T ₁ –S _n SOC and S _n –S ₀ transition strength. Finally, translating the DCO‐favored geometry from crystal packing into molecular design, conformational locking in CyclicBrTPA produces fast blue RTP in amorphous PMMA. Together, these results establish DCO as a practical molecular design strategy for organizing favorable spin‐coupling geometries beyond a single crystal‐packing environment, while highlighting the continued importance of a sufficiently rigid environment for room‐temperature emission.

The attachment of mussels relies on adhesive proteins rich in 3,4‐dihydroxyphenyl‐L‐alanine (DOPA) residues, which bind to surfaces underwater. Their broad‐spectrum adhesive behavior has inspired the development of many underwater adhesive and coating strategies based on catecholamine polymers (such as polydopamine); however, their complex coating processes and underlying molecular mechanisms (aggregation, deposition, and polymerization) are still not fully understood. Here, we study a set of six catecholamine building blocks to elucidate fundamental structure‐property relationships in mussel‐inspired underwater coatings. This set of molecules produced coatings with significant differences in morphology, conformality, and exposed functional groups at the surface, which are rationalized based on varying key molecular structure parameters. Based on comprehensive spectroscopic and microscopic characterization, we identified norepinephrine as a well‐balanced catecholamine building block for underwater coatings, providing both excellent morphological homogeneity as well as abundant reactive surface groups available for further post‐functionalization. Leveraging this reactivity, we explored polynorepinephrine (PNE) coatings as surface primers for substrate‐agnostic organic and inorganic surface functionalization via solution‐based polymer grafting and electroless deposition metallization processes. This approach produced PNE‐based underwater coatings with custom properties and functionality, including tunable surface chemistry, electrical conductivity, and magnetization, demonstrated on different substrate materials and for applications in wetting, electronics, and microrobotics.

Polydopamine (PDA) coatings have emerged as a versatile surface modification strategy owing to their substrate-independent coating capability and aqueous processability. However, the stability of conventional PDA coatings is primarily determined by weak cation-π interactions, which render them inherently unstable under strongly basic conditions or in highly polar aprotic solvents. This interaction-dominated nature fundamentally limits their chemical robustness and practical applicability. Here, we report a cation-π interaction-independent route for catechol-based coating strategy that replaces weak noncovalent interactions with chemically fixed covalent networks. By coupling catechol with diamine building blocks at pH 11, a cation-free condition, via a Michael addition reaction, we construct oligo(catechol)-diamine coatings in which C-N covalent linkages serve as the dominant structural backbone and driving force for coating formation. This reaction-driven, fast-coating strategy yields smooth, conformal ultrathin films that remain stable in strong bases (pH > 10), polar aprotic solvents, and nonpolar organic media. Importantly, the resulting coatings retain accessible primary amine groups at the surface, enabling postfunctionalization, while also significantly suppressing fluorescence quenching by tuning the diamine length. This fully aqueous, scalable approach provides a chemically robust and economically viable alternative to conventional PDA and silane-based coatings, offering a new framework for designing stable functional materials.

Purely organic phosphors have emerged as promising materials for various optical applications. Herein, we report a single-component organic phosphorescent crystal, 1,1′-(2,5-dibromoterephthaloyl)bis(glutarimide) (BrGlu), which exhibits fully reversible, pseudopolymorph-dependent phosphorescence color switching. Under standard crystallization conditions, BrGlu forms green-emitting crystal (G-crystal), while crystallization in the presence of CHCl₃ yields blue-emitting solvent-inclusion crystal (B-crystal). Notably, G-crystal converts into B-crystal upon exposure to CHCl_3, whereas the blue crystals revert to green upon heating, demonstrating a reversible phosphorescence-to-phosphorescence switching mechanism. Through a combination of experimental analyses and quantum chemical calculations, we elucidate the underlying mechanism governing this triplet emission color transformation: syn–anti conformational reorientation of bromine–carbonyl substituents: upon solvent inclusion, hydrogen bonding stabilizes the syn-rotamer to yield bright-blue phosphorescence, whereas gentle heating reverts the system to the anti-rotamer for green emission. Exploiting this property, we develop an advanced data encryption platform featuring a dual-layer security system—phosphorescence emission combined with thermal- or solvent-induced stimuli-response—significantly enhancing security in secure data encryption and anti-counterfeiting.

We developed a color-tunable CPP system via energy transfer in brominated CLCs, achieving high quantum yield, large dissymmetry, and helicity inversion through self-assembly.

Heparin-induced thrombocytopenia (HIT) is a serious side effect that occurs in patients undergoing heparin therapy. The known risk factor is the presence of antibodies created against platelet factor 4 and heparin complexes (PF4/heparin) in the blood, which activate platelet Fc receptors (FcγRIIA). Although immunoassays have been developed for HIT diagnosis, their specificity remains low (∼50%) due to the binding of nonpathogenic antibodies to the same antigen (PF4/heparin). As a result, a lack of rapid, highly sensitive, and selective diagnostic tests poses challenges for HIT treatment. In this study, we used monoclonal HIT-like KKO antibodies as a model and demonstrated a rapid biosensor based on quartz crystal microbalance (QCM) that effectively distinguishes the pathogenic (KKO) from nonpathogenic (RTO) antibodies within 10 min. Based on our key finding, KKO and RTO present clear binding affinity differences against FcγRIIA: RTO binds to FcγRIIA while KKO can bind to FcγRIIA only in the presence of PF4/heparin. The determined negative zeta potentials of proteins confirmed that the observed affinity differences toward FcγRIIA result from specific binding rather than nonselective electrostatic interactions. This highlights the potential use of FcγRIIA as an antigen instead of traditional PF4/heparin complexes. Although only a monoclonal HIT-like antibody was tested, the use of FcγRIIA to distinguish the binding patterns of KKO and RTO could be extended to the detection of human HIT antibodies.

Dilute magnetic doping in wide-bandgap semiconductors has attracted significant interest due to its potential for tailored optical, spintronic, and spin-photonic properties. While extensive research has explored the optical and magnetic properties of these doped systems, the exact nature of dopant-induced structural properties, particularly in high-quality single crystals, requires further investigation. Here, we demonstrate the synthesis of Mn²⁺-doped (BA)₂PbBr₄ (BA=butylammonium) single crystals with well-defined crystal habits and no grain boundaries, enabling controlled investigation into significant crystal deformation as a function of Mn²⁺ incorporation. Structural analysis provides compelling evidence of crystal distortion, manifested by a smooth transition from square nanoplatelets to parallelogram shapes with an in-plane shear distortion of up to ∼6° and an out-of-plane contraction of 9.7% for the highest 4.95% Mn²⁺ concentration. This magnitude of structural change significantly exceeds the typical range observed in doped semiconductors by an order of magnitude. We show, using density functional theory calculations, that the structural distortion upon doping is driven by a thermodynamic energy gain. Static and time-resolved photoluminescence spectroscopy confirms the successful incorporation of Mn²⁺ with characteristic emission at 600 nm with an approximate 0.3 ms radiative lifetime. The uniform incorporation of Mn²⁺ into the host medium is further corroborated by the hyperfine structure in an electron paramagnetic resonance spectrum and the paramagnetic response in superconducting quantum interference device measurements. These findings offer crucial insights into dopant-induced structural modifications, supporting the rational design of dilute magnetic semiconductors for spin-based information technologies.

Achieving high quantum yields for organic fluorophores in both solution and in the polycrystalline solid state is a significant yet challenging goal, as most fluorophores typically emit effectively in only one phase. In this study, we introduce 1,1’-(2,5-dimethoxyterephthaloyl)-bis(glutraimide) (TGlu), a novel ‘single benzene’-based organic fluorophore featuring an alkoxy donor and an N-acyl-glutarimide acceptor. TGlu achieves close-to-unity fluorescence quantum yields in both solution and in the polycrystalline state. Through systematic studies involving four additional structural analogues of TGlu, we unveiled that the acceptor group within the single benzene core plays a crucial steric and electronic role in achieving high fluorescence efficiency in both phases. Furthermore, we demonstrated the versatility of this new fluorophore in various applications. In solution, TGlu serves as a highly effective photocatalyst for photoinduced energy/electron transfer reversible addition−fragmentation chain-transfer polymerization while in its single-crystal form, TGlu exhibits highly efficient waveguiding properties.

Magnetic microrobots are attractive tools for operation in confined spaces due to their small size and untethered wireless operation, particularly in biomedical and environmental applications. Over years of development, many microrobot fabrication methods have been developed; however, they typically require costly specialized physical vapor deposition (PVD) vacuum instrumentation and present homogeneity and conformality coating problems (especially in complex 3D structures). Herein, a solution‐based polydopamine (PDA)‐assisted electroless deposition method is developed to deposit a superparamagnetic nickel thin film on microrobots. The multilayered functional film design comprises PDA as an adhesive primer and reducing agent, silver nanoclusters as catalysts, and a nickel magnetic top film, all deposited in a batch solution‐based process on glass and 3D‐printed polymer substrates. This multilayer magnetic coating is implemented and demonstrated in three magnetic microrobot archetypes, including arbitrarily‐shaped active particles, microrollers, and helical swimming microrobots, each using distinct actuation working mechanisms. Due to the material‐independent interfacial adhesive properties of PDA, this multilayer functionalization strategy can open up new magnetic microrobot fabrication schemes with a broad compatibility with materials and structures (including complex 3D‐printed polymer microstructures) and without the need for and limitations of PVD coating approaches.