Jung-Moo Heo

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.

From a molecular perspective, chirality is manifested in the intrinsic asymmetry of atomic arrangements that cannot be superimposed on their mirror images. Achiral molecules at nanometer scale can be assembled to have micron-scale chiral structures using physical stimuli, but the resulting chiral structures are often spatially limited, difficult to control over large areas, or unstable once the stimulus is removed. Here we show that a confined anisotropic molecular medium, derived from the nematic mesophase, undergoes a field-driven symmetry-breaking transition that generates micron-scale chiral structures. This approach provides a simple and scalable route to generate macroscopic chiral optical materials from molecularly symmetric precursors.

Flexible and transparent two-dimensional transition metal dichalcogenide-based non-contact triboelectric nanogenerators have attracted significant attention for next-generation intelligent electronics integrated with artificial intelligence and machine learning. However, conventional film-type transition metal dichalcogenides suffer from limited electric-field concentration owing to their intrinsically anisotropic polarizability originating from van der Waals gaps, resulting in weak electrostatic induction and restricted sensing performance. Here, we report photothermally dewetted dome-shaped WS2 synthesized via pulsed laser annealing for high-performance classifiable self-powered sensing systems. Finite-element simulations reveal that the curved morphology and internal void of dome-shaped WS2 effectively induce electric-field localization and enhanced electrostatic potential under non-contact conditions, contributing to improved signal uniformity. Consequently, the dome-shaped WS2-based non-contact triboelectric nanogenerator exhibits an open-circuit voltage of 4.25 V and a signal-to-noise ratio of 40.51 dB, significantly outperforming flat WS2 counterparts. Building upon the enhanced electrical response, a blur-free 4 x 4 self-powered d-WS2 pixel array was fabricated and integrated with support vector machine and convolutional neural network frameworks for polymer classification and spatial distribution recognition. The proposed system achieved classification accuracies of 97.74% and 95.94% for support vector machine- and convolutional neural network-based analyses, respectively, demonstrating the strong potential of morphology-engineered WS2 nanostructures for intelligent machine learning-assisted self-powered sensing systems.

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.

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.

Efficient light generation from triplet states of organic molecules has been a hot yet demanding topic in academia and the display industry. Herein, we propose a strategy for developing triplet emitter by creating heterostructures of organic chromophores and transition metal dichalcogenides (TMDs). These heterostructures emit microsecond phosphorescence at room temperature, while their organic chromophores intrinsically exhibit millisecond phosphorescence under vibration dissipation-free conditions. This enhancement in phosphorescence is indicative of significantly enhanced spin-orbit coupling efficiency through coupling with TMDs. Through detailed studies on these hybrids from various perspectives, we elucidate key features of each component essential for generating microsecond triplet emission, including 2H-TMDs with heavy transition metals and aromatic carbonyl with an ortho-hydroxy group. Our intriguing findings open avenues for exploring the universal applicability of fast and stable hybrid triplet emitters.

The construction of functional materials via the co-assembly of multimolecular systems has recently emerged as a fascinating topic. The co-assembled multicomponent could promote the evolution of supramolecular assemblies into a high-order nanoarchitecture with improved functional properties. We report the successful preparation of a dual-functional polydiacetylene (MCPDA-Tz-CA) having thermochromic and solvatochromic properties via facile co-assembly of MCDA-Tz and cyanuric acid (MCDA-Tz-CA) followed by ultraviolet-induced polymerization. Molecular packing patterns from powder X-ray diffraction and density functional theory calculations of molecular self-assembly processes confirm highly ordered co-assembled lamellar structures. MCPDA-Tz-CA showed excellent reversible thermochromism properties when the temperature was increased from 30 to 150 °C with a reversible blue-to-red color transition that could be detected by the naked eye. Also, MCPDA-Tz-CA displayed selective blue-to-red solvatochromism against dimethylformamide and dimethyl sulfoxide. Detailed investigations revealed that the enhanced thermochromic reversibility and solvatochromic selectivity could be attributed to the hydrogen-bonding interactions and the formation of a network structure in the MCDA-Tz/cyanuric acid co-assembly. Our research opens a promising route for improving the performance of functional materials via noncovalent multicomponent arrangements at the molecular level.

Circularly polarized phosphorescence (CPP) is increasingly recognized in materials science for its unique applications in optoelectronic devices, chiral recognition, and bioimaging. This study underscores a novel directed chiral self‐assembly strategy of purely organic phosphors into supramolecular nanostructures to achieve bright room‐temperature circularly polarized phosphorescence (RT‐CPP). RT‐CPP molecules are built on an aromatic carbonyl structure having also Br to mix (n,π*) and (π,π*) characters and to enable the heavy atom effect. Side chains are rationally designed to have strong hydrogen bonding, van der Waals interactions, and a chiral center for directed chiral self‐assembly into supramolecular nanostructures. The tightly packed resulting supramolecular nanostructures also impower efficient suppression of molecular motions, thereby minimizing non‐radiative decay and facilitating bright CPP emission at room temperature. The developed self‐assembled supramolecular structures exhibit RT‐CPP with the dissymmetry factor (g_lum) of ≈10⁻³, a high phosphorescence quantum yield of 4.1%, and a rapid triplet decay time of 180 microseconds. The presented molecular design principle enabling RT‐CPP from purely organic phosphors may pave the way for novel photonic materials.