Shigehiro Yamaguchi

Conspectus: Cell populations are inherently heterogeneous, and the molecular mechanisms that govern cellular plasticity and fate operate across broad spatial and temporal scales. Early signaling events emerge within seconds to minutes, whereas phenotypic transitions associated with differentiation, adaptation, and disease progression may unfold over hours, days, or longer. Elucidating these dynamic processes requires molecular imaging tools capable of quantitatively monitoring biochemical events with high spatial resolution, temporal precision, and molecular specificity in living systems. However, achieving this goal demands the integration of multiple design principles that are rarely realized within a single molecular platform. Therefore, the development of such tools remains a central challenge in chemical biology because molecular recognition, fluorescence signaling, organelle targeting, and photostability must be integrated within a single molecular architecture. In this Account, we present a historical overview of the evolution of our unique molecular imaging toolbox, tracing its development from fundamental studies of molecular recognition in artificial systems to multiplex visualization of organelle dynamics in living cells, and ultimately to their successful translation into bioimaging probes. Our early efforts established how hydrogen-bonding interactions at artificial lipid membrane interfaces can be exploited to enhance biomolecular recognition under aqueous conditions. These studies further revealed that tuning membrane mechanical properties provides a powerful strategy for discriminating structurally similar nucleotide targets and regulating selective molecular recognition. The principles derived from these artificial systems were subsequently extended to fluorescence sensing platforms for recognition of biologically relevant analytes. Building upon these molecular recognition strategies, we developed heteroatom-containing π-conjugated fluorophores in which phosphorus, sulfur, and nitrogen elements were strategically incorporated into ladder-type π-conjugated compounds to modulate electronic structure, fluorescence properties, and bioimaging performance. Systematic molecular engineering transformed these fluorophores from intracellular ion sensors into highly selective organelle-targeting probes and, ultimately, multiplex imaging platforms capable of simultaneously visualizing dynamic interactions among multiple subcellular compartments. Importantly, heteroatom engineering also enabled exceptional photostability, allowing long-term imaging of gradual cellular transitions that are inaccessible with conventional probes. A recurring theme throughout this work is the rational integration of molecular components to bridge chemical structure and biological function. Through precise tuning of fluorophore scaffolds, linker architectures, molecular recognition motifs, and organelle-targeting units, we established modular design principles that govern intracellular localization, selectivity, sensitivity, and imaging performance. These developments exemplify the importance of nanoarchitectonics, in which functional systems emerge through the hierarchical organization of atoms, molecules, supramolecular interactions, interfaces, and biomolecules. Looking forward, we envision next-generation imaging platforms that combine multiplexed sensing, adaptive functionality, and quantitative analysis to reveal the molecular basis of cellular plasticity across diverse biological systems. Such advances will provide critical spatiotemporal insights into disease onset, progression, and therapeutic response and contribute to the realization of precision medicine.

Diboron‐embedded heteroacenes with systematically varied central π‐skeletons and fusion modes were synthesized via one‐pot cyclative borylation using benzene, thieno[3,2‐ b ]thiophene, or dithieno[3,2‐ b :2′,3′‐ d ]thiophene cores, affording six derivatives with C _2h or C _2v symmetry. Their photophysical and electrochemical properties, including absorption and emission wavelengths and sequential reduction behavior during cyclic voltammetry, depend primarily on fusion mode rather than π‐core size. Single‐crystal analysis, in turn, revealed that molecular symmetry governs packing modes, where C _2h derivatives exhibited limited π‐overlap due to shielding by mesityl groups on both π‐faces, while C _2v derivatives formed efficient π–π stacking with large intermolecular overlap despite the presence of the bulky mesityl groups. Notably, one of the derivatives adopted a uniform columnar structure via continuous π–π stacking, establishing a design principle for solid‐state organization in boron‐embedded heteroacenes.

The P2X7 receptor (P2X7R) is an ATP-gated cation channel that plays an important role in inflammatory signaling, cancer progression, and immune regulation. Yet pharmacological tools that enable direct visualization of P2X7 receptor (P2X7R) expression in live biological systems remain limited. We report a near-infrared fluorescent P2X7R probe generated by conjugating the selective antagonist AZD9056 to a sulfonated phospha-rhodamine fluorophore. The resulting probe retains favorable photophysical properties after ligand conjugation, including absorption and emission beyond 700 nm, aqueous solubility, and sufficient brightness for fluorescence imaging. In a YO-PRO-1 dye-uptake assay, the conjugate preserved antagonistic activity at P2X7R, consistent with retained receptor engagement. Confocal microscopy revealed receptor-associated labeling in P2X7R-expressing cells, as evidenced by antibody colocalization and control experiments. The phospha-rhodamine scaffold also enabled multiphoton excitation, allowing visualization of probe-labeled cells and imaging in ex vivo mouse skin with low background and good photostability. Together, these results establish a small-molecule near-infrared probe for fluorescence imaging of P2X7R from single cells to intact tissue and highlight phospha-rhodamine fluorophores as useful scaffolds for targeted receptor imaging.

Thermally activated delayed fluorescence (TADF) emitters enable color‐pure, energy‐efficient organic light‐emitting diodes (OLEDs), yet many ultra‐narrowband designs rely on synthetically demanding boron incorporation. Here we discover boron‐free emitters that reconcile a robust nitrogen‐only polycyclic scaffold, Rec. 2020‐grade pure‐blue emission, and small singlet–triplet gaps (Δ E _ST ) conducive to TADF. We enumerated 19 518 13‐ring carbazole‐containing polycyclic aromatic hydrocarbons (Cz‐PAHs) and obtained quantum‐chemical reference values for ∼1000 molecules: emission energies and Δ E _ST at S ₁ ‐optimized geometries. A graph neural network enabled library‐wide prediction and revealed a pronounced negative correlation between emission energy and Δ E _ST ( R = −0.75), implicating configuration mixing in S ₁ and indicating that small‐gap candidates are enriched in the pure‐blue regime. Two selected Cz‐PAH emitters were synthesized and display deep‐blue, exceptionally narrow photoluminescence (full widths at half maximum 17–19 nm) with small experimental Δ E _ST (0.13–0.19 eV). OLEDs incorporating these emitters deliver narrowband blue electroluminescence ( λ _EL 456 and 481 nm); device A reaches chromaticity coordinates of (0.139, 0.069), close to the Rec. 2020 blue primary, whereas the sensitized device D achieves a maximum external quantum efficiency of 35.2%. Collectively, this work expands the boron‐free TADF design space and establishes an experimentally validated route to discovering high‐color‐purity organic emitters.

Thermally activated delayed fluorescence (TADF) emitters enable color‐pure, energy‐efficient organic light‐emitting diodes (OLEDs), yet many ultra‐narrowband designs rely on synthetically demanding boron incorporation. Here we discover boron‐free emitters that reconcile a robust nitrogen‐only polycyclic scaffold, Rec. 2020‐grade pure‐blue emission, and small singlet–triplet gaps (Δ E _ST ) conducive to TADF. We enumerated 19 518 13‐ring carbazole‐containing polycyclic aromatic hydrocarbons (Cz‐PAHs) and obtained quantum‐chemical reference values for ∼1000 molecules: emission energies and Δ E _ST at S ₁ ‐optimized geometries. A graph neural network enabled library‐wide prediction and revealed a pronounced negative correlation between emission energy and Δ E _ST ( R = −0.75), implicating configuration mixing in S ₁ and indicating that small‐gap candidates are enriched in the pure‐blue regime. Two selected Cz‐PAH emitters were synthesized and display deep‐blue, exceptionally narrow photoluminescence (full widths at half maximum 17–19 nm) with small experimental Δ E _ST (0.13–0.19 eV). OLEDs incorporating these emitters deliver narrowband blue electroluminescence ( λ _EL 456 and 481 nm); device A reaches chromaticity coordinates of (0.139, 0.069), close to the Rec. 2020 blue primary, whereas the sensitized device D achieves a maximum external quantum efficiency of 35.2%. Collectively, this work expands the boron‐free TADF design space and establishes an experimentally validated route to discovering high‐color‐purity organic emitters.

Supramolecular polymerization within living cells has emerged as a promising strategy for controlling cellular functions. Lipid droplets, intracellular organelles mainly composed of neutral lipids, provide low-polarity environments, yet their role in regulating supramolecular assembly pathways remains unclear. Here we show that triolein, a representative triacylglycerol featuring three ester groups and cis-9-octadecenyl chains, acts as an effective medium for kinetically controlled supramolecular polymerization. An alanine-based diamide-functionalized fluorophore forms supramolecular polymers in triolein through a nucleation-elongation mechanism, in which an initial nucleus triggers subsequent growth. Although the thermodynamic stability is comparable to that in di- n -butyl ether, a commonly used organic solvent, triolein suppresses spontaneous nucleation and inter-fiber bundling, creating a lag phase during which seeded polymerization guides monomers along a defined assembly pathway. Kinetic studies with ethyl oleate, a structural analogue of triolein, indicate that transient solute-solvent interactions contribute to the suppression of both nucleation and bundling events. This kinetic control enables stepwise seeded growth of multiblock nanostructures and establishes neutral lipids as functional media for the precision-controlled construction of supramolecular polymers.

Metal-free ionic liquids that exhibit intense fluorescence in the visible region of over 500 nm in the fluid state remain scarce. Although small π-conjugated frameworks combining electron-donating and electron-accepting groups represent a promising structural motif, such modifications often lead to fluorescence quenching in polar environments, including neat ionic liquids. Herein, we report fluorescent ionic liquids based on a phospholium containing a tetracyclic core. Incorporation of both an amino group and the phosphonium center in the same benzene ring prevents excessive spatial separation of HOMO and LUMO, thereby suppressing the increase in intramolecular charge-transfer character in the excited state. This push–pull architecture enables the ionic liquids to display bright yellow fluorescence with a large Stokes shift under neat conditions. Furthermore, bridging with a dialkylphosphonium unit effectively suppresses aggregation-induced quenching while lowering the glass transition temperature. The introduction of bulky counter anions, such as a tetrakis(3,5-bis(trifluoromethyl)phenyl)borate, further decreases the glass transition temperature by hindering π-core proximity and significantly increases the fluorescent quantum yield up to 0.64. A neat film of one derivative, doped with an additional red-emissive dye, exhibited red fluorescence through a Förster resonance energy transfer.

Incorporation of strongly accepting BMes ₂ (Mes = 2,4,6-trimethylphenyl) groups at the para -positions of a trigonal [CPh ₃ ] ⁻ framework leads to extensive delocalisation of the negative charge over the three aryl branches and onto the boron centres.

Coordination of a Lewis base to a tricoordinate boryl group generates a tetracoordinate species, thereby inverting the electronic character of the boryl substituents from electron‐accepting to electron‐donating. Utilizing this π‐umpolung strategy, we report temperature‐responsive fluorophores that emit in the near‐infrared (NIR) region. To achieve reversible π‐umpolung, we designed a diarylboryl unit in which two aryl rings are tethered by an alkenyl linker. This alkenyl‐strapped scaffold engages in a weak olefin–borane interaction and undergoes frustrated Lewis pair (FLP)‐type addition even with bulky neutral Lewis bases such as tricyclohexylphosphine (PCy ₃ ). When boryl groups are installed at both termini of 4,7‐di(2‐thienyl)‐2,1,3‐benzothiadiazole, coordination of PCy ₃ induces pronounced red‐shifts in the emission spectra. In polar acetonitrile, the emission maximum reaches 732 nm, entering the NIR region. This red shift arises from the strong σ‐donating character of the resulting tetracoordinate boron centers, which enhance intramolecular charge transfer (ICT) character in the excited state. Unlike conventional dimesitylborane–fluoride complexes, the FLP‐type adducts exhibit reversible, temperature‐dependent shifts in the dissociation/association equilibrium. Although the solvent polarity influences the equilibrium, modulation of phosphine Lewis basicity enables reversible dissociation even in polar media, allowing this system to display large emission changes spanning the visible to NIR region.

Coordination of a Lewis base to a tricoordinate boryl group generates a tetracoordinate species, thereby inverting the electronic character of the boryl substituents from electron‐accepting to electron‐donating. Utilizing this π‐umpolung strategy, we report temperature‐responsive fluorophores that emit in the near‐infrared (NIR) region. To achieve reversible π‐umpolung, we designed a diarylboryl unit in which two aryl rings are tethered by an alkenyl linker. This alkenyl‐strapped scaffold engages in a weak olefin–borane interaction and undergoes frustrated Lewis pair (FLP)‐type addition even with bulky neutral Lewis bases such as tricyclohexylphosphine (PCy ₃ ). When boryl groups are installed at both termini of 4,7‐di(2‐thienyl)‐2,1,3‐benzothiadiazole, coordination of PCy ₃ induces pronounced red‐shifts in the emission spectra. In polar acetonitrile, the emission maximum reaches 732 nm, entering the NIR region. This red shift arises from the strong σ‐donating character of the resulting tetracoordinate boron centers, which enhance intramolecular charge transfer (ICT) character in the excited state. Unlike conventional dimesitylborane–fluoride complexes, the FLP‐type adducts exhibit reversible, temperature‐dependent shifts in the dissociation/association equilibrium. Although the solvent polarity influences the equilibrium, modulation of phosphine Lewis basicity enables reversible dissociation even in polar media, allowing this system to display large emission changes spanning the visible to NIR region.