Faculty Profiles - YAMAGUCHI, Shigehiro

Papers - YAMAGUCHI, Shigehiro

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Organic phosphorescent polymorphs induced by various halogen bonds with stimuli-responsive single/dual phosphorescence switching Reviewed International coauthorship

Hao Liu, Wentao Liu, Naoki Ando, Shigehiro Yamaguchi, Hongyu Zhang

JOURNAL OF MATERIALS CHEMISTRY C Vol. 9 ( 8 ) page： 2738 - 2743 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Herein, we report the first example of two pure organic polymorphs with stimuli-responsive single/dual phosphorescence transformation. By analyzing the crystal structures and theoretical results, it could be understood that efficient intermolecular interactions could restrict the molecular movements and lock distinct molecular conformations, leading to different phosphorescence behaviors. Besides, single/dual phosphorescence could transform into each other by heating or under solvent vapor conditions. Considering such unique properties, logical sensors (AND gate and OR gate) were built by providing different emission colors as inputs. Our work provides not only important information for understanding the dual RTP mechanism but also unique stimuli-responsive pure organic phosphorescent materials to enrich material fields.

DOI： 10.1039/d0tc05468b

Dual Trapping of a Metastable Planarized Triarylborane pi-System Based on Folding and Lewis Acid-Base Complexation for Seeded Polymerization Reviewed

Heekyoung Choi, Soichiro Ogi, Naoki Ando, Shigehiro Yamaguchi

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 143 ( 7 ) page： 2953 - 2961 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

We report the kinetically controlled supramolecular polymerization of boron-containing p-conjugated molecules, which was enabled by a seeding method based on dual trapping of a metastable state by synergistic intramolecular hydrogen bonding and Lewis acid-based complexation. Planarized triarylborane-based 1, which bears a diamide chain with chiral alkyl groups, was synthesized. Upon cooling, the solution of monomer 1 afforded a supramolecular polymerization in a cooperative manner to form helical supramolecular nanostructures with intense J-type aggregate emission. In the presence of pyridine, the triarylborane moiety formed a Lewis acid-base complex, which enhances the stabilization of the metastable monomeric state. An assembly incompetent structure with a folded diamide chain conformation and a pyridine moiety axially coordinated to the boron atom is responsible for slowing the spontaneous aggregation. The seeding method was successfully applied to the solution to produce homogeneous nanofibers even at a high (millimolar-level) concentration. This unprecedented kinetic control via dual trapping provides an effective method to achieve seed-initiated polymerization under concentrated conditions.

DOI： 10.1021/jacs.0c13353

Twofold C-H Activation Enables Synthesis of a Diazacoronene-Type Fluorophore with Near Infrared Emission Through Isosteric Replacement Reviewed International coauthorship

Steffen Gressies, Masato Ito, Mika Sakai, Hiroshi Osaki, Ju Hyun Kim, Tobias Gensch, Constantin Daniliuc, Naoki Ando, Shigehiro Yamaguchi, Frank Glorius

CHEMISTRY-A EUROPEAN JOURNAL Vol. 27 ( 8 ) page： 2753 - 2759 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

The synthesis and photophysical properties of a soluble amide-embedded coronene is reported. The key step in this synthesis is the twofold C-H activation of diazaperylene by a rhodium(III)Cp* catalyst. This unprecedented structural motif shows intense fluorescence in the near infrared region with a small Stokes shift and a distinct vibronic structure, which exhibits a slight extent of negative solvatochromism. Comparison of this compound with some relevant compounds revealed the importance of the amide incorporation in the peripheral concave region including an angular position to retain high aromaticity reflecting that of parent coronene. Treatment of this compound with Lewis acid B(C6F5)(3) formed a bis-adduct, which exhibited enhanced aromaticity as a consequence of the increased double bond character of the amide C-N bonds.

DOI： 10.1002/chem.202004080

Dithieno[a,e]pentalenes: Highly Antiaromatic Yet Stable pi-Electron Systems without Bulky Substituents Reviewed

Junichi Usuba, Masahiro Hayakawa, Shigehiro Yamaguchi, Aiko Fukazawa

CHEMISTRY-A EUROPEAN JOURNAL Vol. 27 ( 5 ) page： 1482 - 1482 2021.1

Fused Thiophene-S,S-dioxide-Based Super-Photostable Fluorescent Marker for Lipid Droplets Reviewed

Masayasu Taki, Keiji Kajiwara, Eriko Yamaguchi, Yoshikatsu Sato, Shigehiro Yamaguchi

ACS MATERIALS LETTERS Vol. 3 ( 1 ) page： 42 - 49 2021.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Lipid droplets (LDs) are essential organelles in most eukaryotes, and tracking intracellular LD dynamics using synthetic small molecules is crucial for biological studies. However, only a limited number of fluorescent markers that satisfy all requirements, such as the selective staining of LDs, high photostability, and sufficient biocompatibility, have been developed. Herein, we report a series of donor-p-acceptor dyes based on the thiophene-containing fused polycyclic scaffold [1]benzothieno[3,2-b][1]benzothiophene (BTBT), in which either or both thiophene rings are oxidized into thiophene-S,S-dioxide to form an electron-accepting building block. Among these dyes, LAQ1 satisfied all the aforementioned requirements and allowed us to capture ultrasmall LDs on the endoplasmic reticulum (ER) membrane by stimulation emission depletion (STED) microscopy with a super-resolution below the diffraction limit of light. Moreover, the extremely high photostability of LAQ1 enabled recording the lipolysis of LDs and the concomitant lipogenesis, as well as long-term trajectory analysis of micro-LDs at the single-particle level in living cells.

DOI： 10.1021/acsmaterialslett.0c00451

Dithieno[a,e]pentalenes: Highly Antiaromatic Yet Stable pi-Electron Systems without Bulky Substituents

Junichi Usuba, Masahiro Hayakawa, Shigehiro Yamaguchi, Aiko Fukazawa

CHEMISTRY-A EUROPEAN JOURNAL Vol. 27 ( 5 ) page： 1638 - 1647 2021.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Dithieno[a,e]penalenes (DTPs) with various substituents were synthesized as a class of antiaromatic compounds. Annulation of thiophene rings imparts the pentalene moiety with high thermal stability even without bulky substituents, while retaining antiaromaticity. The higher magnitude of antiaromaticity in DTPs, in addition to the differences in the electronic structures of the fused aromatic rings, resulted in a narrower HOMO-LUMO gap than that of the corresponding dibenzo[a,e]pentalene analog, giving rise to red-shifted electronic absorption that reaches the near-infrared region. Moreover, systematic investigations on the solid-state packing structure revealed that DTPs prefer offset face-to-face packing motifs rather than face-centered pi-pi stacking. In particular, the thienyl-substituted DTP bearing hydrophilic side chains exhibited thermochromic behavior in polar solvents, which was ascribed to the formation of aggregates.

DOI： 10.1002/chem.202004244

Letters from Japan: Characteristic Approaches to Contemporary Organic Chemistry Open Access

Shigehiro Yamaguchi

ORGANIC LETTERS Vol. 22 ( 24 ) page： 9406 - 9407 2020.12

Hydrophobicity-driven folding and seeded polymerization of cystine-based dimeric diamides in aqueous media

Natsumi Fukaya, Soichiro Ogi, Midori Kawashiro, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 56 ( 85 ) page： 12901 - 12904 2020.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Seeded supramolecular polymerization of cystine-based dimeric diamides with aromatic substituents at the C- and N-termini was achieved in aqueous media. Theoretical and spectroscopic studies reveal that the terminal groups play crucial roles in slowing spontaneous assembly through formation of a folded conformation and guiding molecular alignment in the aggregated state.

DOI： 10.1039/d0cc05255h

Covalent Self-Labeling of Tagged Proteins with Chemical Fluorescent Dyes in BY-2 Cells and Arabidopsis Seedlings([OPEN]) Open Access

Ryu J. Iwatate, Akira Yoshinari, Noriyoshi Yagi, Marek Grzybowski, Hiroaki Ogasawara, Mako Kamiya, Toru Komatsu, Masayasu Taki, Shigehiro Yamaguchi, Wolf B. Frommer, Masayoshi Nakamura

PLANT CELL Vol. 32 ( 10 ) page： 3081 - 3094 2020.10

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS INC

Synthetic chemical fluorescent dyes promise to be useful for many applications in biology. Covalent, targeted labeling, such as with a SNAP-tag, uses synthetic dyes to label specific proteins in vivo for studying processes such as endocytosis or for imaging via super-resolution microscopy. Despite its potential, such chemical tagging has not been used effectively in plants. A major drawback has been the limited knowledge regarding cell wall and membrane permeability of the available synthetic dyes. Of 31 synthetic dyes tested here, 23 were taken up into BY-2 cells, while eight were not. This creates sets of dyes that can serve to measure endocytosis. Three of the dyes that were able to enter the cells, SNAP-tag ligands of diethylaminocoumarin, tetramethylrhodamine, and silicon-rhodamine 647, were used to SNAP-tag alpha-tubulin. Successful tagging was verified by live cell imaging and visualization of microtubule arrays in interphase and during mitosis in Arabidopsis (Arabidopsis thaliana) seedlings. Fluorescence activation-coupled protein labeling with DRBG-488 was used to observe PIN-FORMED2 (PIN2) endocytosis and delivery to the vacuole as well as preferential delivery of newly synthesized PIN2 to the actively forming cell plate during mitosis. Together, the data demonstrate that specific self-labeling of proteins can be used effectively in plants to study a wide variety of cellular and biological processes.Multicolor imaging with SNAP-tagged tubulin and monitoring of PIN2 endocytosis with a chemical dye demonstrate that specific self-labeling of proteins can be used effectively in plants.

DOI： 10.1105/tpc.20.00439

Magnetism of Topological Boundary States Induced by Boron Substitution in Graphene Nanoribbons Open Access

Niklas Friedrich, Pedro Brandimarte, Jingcheng Li, Shohei Saito, Shigehiro Yamaguchi, Iago Pozo, Diego Pena, Thomas Frederiksen, Aran Garcia-Lekue, Daniel Sanchez-Portal, Jose Ignacio Pascual

PHYSICAL REVIEW LETTERS Vol. 125 ( 14 ) page： 146801 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Graphene nanoribbons (GNRs), low-dimensional platforms for carbon-based electronics, show the promising perspective to also incorporate spin polarization in their conjugated electron system. However, magnetism in GNRs is generally associated with localized states around zigzag edges, difficult to fabricate and with high reactivity. Here we demonstrate that magnetism can also be induced away from physical GNR zigzag edges through atomically precise engineering topological defects in its interior. A pair of substitutional boron atoms inserted in the carbon backbone breaks the conjugation of their topological bands and builds two spin-polarized boundary states around them. The spin state was detected in electrical transport measurements through boron-substituted GNRs suspended between the tip and the sample of a scanning tunneling microscope. First-principle simulations find that boron pairs induce a spin 1, which is modified by tuning the spacing between pairs. Our results demonstrate a route to embed spin chains in GNRs, turning them into basic elements of spintronic devices.

DOI： 10.1103/PhysRevLett.125.146801

Long-Lived Charge-Transfer State from B-N Frustrated Lewis Pairs Enchained in Supramolecular Copolymers Open Access

Beatrice Adelizzi, Pongphak Chidchob, Naoki Tanaka, Brigitte A. G. Lamers, Stefan C. J. Meskers, Soichiro Ogi, Anja R. A. Palmans, Shigehiro Yamaguchi, E. W. Meijer

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 142 ( 39 ) page： 16681 - 16689 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The field of supramolecular polymers is rapidly expanding; however, the exploitation of these systems as functional materials is still elusive. To become competitive, supramolecular polymers must display microstructural order and the emergence of new properties upon copolymerization. To tackle this, a greater understanding of the relationship between monomers' design and polymer microstructure is required as well as a set of functional monomers that efficiently interact with one another to synergistically generate new properties upon copolymerization. Here, we present the first implementation of frustrated Lewis pairs into supramolecular copolymers. Two supramolecular copolymers based on p-conjugated O-bridged triphenylborane and two different triphenylamines display the formation of B-N pairs within the supramolecular chain. The remarkably long lifetime and the circularly polarized nature of the resulting photoluminescence emission highlight the possibility to obtain an intermolecular B-N charge transfer. These results are proposed to be the consequences of the enchainment of B-N frustrated Lewis pairs within 1D supramolecular aggregates. Although it is challenging to obtain a precise molecular picture of the copolymer microstructure, the formation of random blocklike copolymers could be deduced from a combination of optical spectroscopic techniques and theoretical simulation.

DOI： 10.1021/jacs.0c06921

A Near-Infrared Emissive pi-Conjugated Polymer Consisting of an Excited-State Intramolecular Proton Transfer Unit

Naoya Suzuki, Masayuki Wakioka, Fumiyuki Ozawa, Shigehiro Yamaguchi

ASIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 9 ( 9 ) page： 1326 - 1332 2020.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Near infrared (NIR)-emissive polymers are attractive luminescent materials due to their utilities in biological, optoelectronic, and telecommunication applications. Herein we report the use of a dialkylamine-strapped dithienylpyrrole (DTP) as an excited-state intramolecular proton transfer (ESIPT) building block for producing NIR-emissive pi-conjugated polymers. The study of a series of model compounds showed that the extension of pi-conjugation with a moderately electron-accepting comonomer unit, dithientyl-substituted thiazolo[5,4-d]thiazole (TzTz), effectively stabilizes the zwitterionic ESIPT state while increasing the oscillator strength for the electronic transition from the ESIPT state. Consequently, a polymer consisted of DTP and TzTz units exhibited a significantly red-shifted emission, exceeding 750 nm, from the ESIPT state in polar solvents.

DOI： 10.1002/ajoc.202000234

Phosphole-Oxide-Based Fluorescent Probe for Super-resolution Stimulated Emission Depletion Live Imaging of the Lysosome Membrane

Chenguang Wang, Masayasu Taki, Keiji Kajiwara, Junwei Wang, Shigehiro Yamaguchi

ACS MATERIALS LETTERS Vol. 2 ( 7 ) page： 705 - 711 2020.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Super-resolution imaging techniques have become increasingly important tools to visualize suborganelle structures and dynamic processes in living cells on the nanoscale. However, the utility of these imaging techniques is currently limited by the availability of advanced fluorescent probes that enable the specific labeling of the organelle of interest and provide the absorption/emission properties required for super-resolution imaging techniques. Herein, LysoPB Yellow is presented as a new small-molecule fluorescent probe that can selectivity stain the lysosomal membrane. Its outstandingly high photostability and long fluorescence lifetime are beneficial for its use in super-resolution stimulated emission depletion (STED) microscopy. A lysosomal membrane stained with LysoPB Yellow was successfully visualized by STED imaging in living cells with a full width at half maximum (FWHM) of 70 nm, which is substantially below the diffraction limit of light. Additionally, LysoPB Yellow displayed excellent retention ability and negligible cytotoxicity. Consequently, long-term time-lapse confocal imaging of living cells was successfully conducted, which demonstrates the practical utility of LysoPB Yellow in fluorescence imaging.

DOI： 10.1021/acsmaterialslett.0c00147

Effects of Amino Group Substitution on the Photophysical Properties and Stability of Near-Infrared Fluorescent P-Rhodamines

Marek Grzybowski, Masayasu Taki, Keiji Kajiwara, Shigehiro Yamaguchi

CHEMISTRY-A EUROPEAN JOURNAL Vol. 26 ( 35 ) page： 7912 - 7917 2020.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A series of phosphine oxide-bridged rhodamines (P-rhodamines) bearing various acyclic and cyclic amine moieties, including dimethyl- and diethylamine, azetidine, pyrrolidine and 7-azabicyclo[2,2,1]heptane (7ABH), have been synthesized. The photophysical properties as well as chemical and photostability of these dyes have been studied in detail. Among these dyes, the 7ABH-substituted dye shows stronger fluorescence in the near-infrared (NIR) region, relative to the other P-rhodamines. This dye could be applied to live-cell imaging, wherein lysosomes were selectively stained in a pH-independent manner. It was also found that the ring fusion of the amine moieties gives rise to remarkably redshifted spectra, with absorption and emission maxima at 770 and 820 nm, respectively, spectrally close to that of indocyanine green (ICG). Importantly, the ring-fused P-rhodamines showed much higher photostability than ICG, indicative of their promising utility as the NIR-emissive dyes.

DOI： 10.1002/chem.202000957

Multistep Photoisomerization of Dimesitylboron-Functionalized Stilbene Analogues

Yuxin Ge, Naoki Ando, Lijie Liu, Xiang Wang, Francoise Sauriol, Shigehiro Yamaguchi, Gang Wu, Suning Wang

ORGANIC LETTERS Vol. 22 ( 8 ) page： 3258 - 3262 2020.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Dimesitylboron-functionalized stilbene derivatives have been found to undergo an unusual regioselective photoisomerization upon irradiation at 365 nm. Using NMR to follow the photoreaction, the structures of key reaction intermediates and the final products were established. This photoisomerization occurs in four steps: trans-cis isomerization, Diels-Alder reaction, di-pi-methane rearrangement, and ring opening with [1,3]-H migration. This results in the formation of a rare structure with three fused five-membered rings and a six-membered one.

DOI： 10.1021/acs.orglett.0c01042

Donor-Acceptor Materials Exhibiting Thermally Activated Delayed Fluorescence Using a Planarized N-Phenylbenzimidazole Acceptor

Ethan R. Sauve, Jaesuk Paeng, Shigehiro Yamaguchi, Zachary M. Hudson

JOURNAL OF ORGANIC CHEMISTRY Vol. 85 ( 1 ) page： 108 - 117 2020.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

An N-phenylbenzimidazole constrained in a coplanar fashion with a methylene tether (IMAC) was designed and used to prepare a series of emitters exhibiting thermally activated delayed fluorescence (TADF). Four novel TADF emitters using 9,9-dimethylacridine, phenoxazine, phenothiazine, and bis(di-ptolylamino)carbazole as the donor group were designed and synthesized using IMAC as the acceptor. Additionally, two deepblue fluorescent emitters were prepared with carbazole and tercarbazole as the donor moieties. The twisted conformation between donor and acceptor in these molecules resulted in effective spatial separation of the HOMO and LUMO and small singlet-triplet energy gaps. Crystallographic properties, electronic structures, thermal stabilities, photophysical properties, and energy levels were studied systematically. Ultimately, these findings provide a promising opportunity for the design and synthesis of highly efficient TADF materials based on IMAC derivatives.

DOI： 10.1021/acs.joc.9b02283

Hydrophobicity and CH/pi-interaction-driven self-assembly of amphiphilic aromatic hydrocarbons into nanosheets Reviewed

Tsuyoshi Nishikawa, Hiroki Narita, Soichiro Ogi, Yoshikatsu Sato, Shigehiro Yamaguchi

CHEMICAL COMMUNICATIONS Vol. 55 ( 99 ) page： 14950 - 14953 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

The hydrophobicity and CH/pi-interaction-driven self-assembly of an amphiphile that contains a biphenylanthracene group furnishes two-dimensional aggregates in dilute aqueous solution. A windmill-shaped molecular packing structure that arises from multiple intermolecular CH/pi interactions of the aromatic hydrocarbons is the key motif for the self-assembly into micrometer-scale nanosheets.

DOI： 10.1039/c9cc08070h

[eta(5)-Cp*B-Mes](+): A Masked Potent Boron Lewis Acid

Hsi-Ching Tseng, Chao-Tang Shen, Kentaro Matsumoto, Ding-Nan Shih, Yi-Hung Liu, Shie-Ming Peng, Shigehiro Yamaguchi, Ya-Fan Lin, Ching-Wen Chiu

ORGANOMETALLICS Vol. 38 ( 22 ) page： 4516 - 4521 2019.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The chemistry of the boron cation has been revitalized in the past decade due to its newfound application in stoichiometric and catalytic organic reactions. To extend the frontier of boron cation catalysis, we came to discover that a mesityl-substituted eta(5)-Cp*-coordinated boron cation could serve as a powerful Lewis acid for organic catalytic transformations. The boron cation [Cp*B-Mes][B(C6F5)(4)] ([1] [B(C6F5)(4)]) stabilized in a boronium-like electronic structure binds to Et3PO readily and displays an acceptor number exceeding that of B(C6F5)(3) on the Gutmann-Beckett acidity scale. The steric and electronic stabilization exerted by the electron-donating Cp* renders the highly Lewis acidic boron cation an easy-to-handle catalyst for hydrodeoxygenation of aryl ketones at ambient temperature. The exceptional catalytic performance of [1](+) implies that the incorporation of a coordinatively flexible substituent at boron is critical in bringing catalytic activity and stability to boron cation catalysts.

DOI： 10.1021/acs.organomet.9b00671

The Effect of Branching on the One- and Two-Photon Absorption, Cell Viability, and Localization of Cationic Triarylborane Chromophores with Dipolar versus Octupolar Charge Distributions for Cellular Imaging Reviewed Open Access

Stefanie Griesbeck, Evripidis Michail, Florian Rauch, Hiroaki Ogasawara, Chenguang Wang, Yoshikatsu Sato, Robert M. Edkins, Zuolun Zhang, Masayasu Taki, Christoph Lambert, Shigehiro Yamaguchi, Todd B. Marder

CHEMISTRY-A EUROPEAN JOURNAL Vol. 25 ( 57 ) page： 13164 - 13175 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two-photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two-photon excited fluorescence (TPEF) live-cell imaging.

DOI： 10.1002/chem.201902461

Near-infrared fluorescein dyes containing a tricoordinate boron atom Open Access

Naoki Ando, Hiroki Soutome, Shigehiro Yamaguchi

CHEMICAL SCIENCE Vol. 10 ( 33 ) page： 7816 - 7821 2019.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Bora-fluoresceins (BFs), fluorescein analogues containing a tricoordinate boron atom instead of an oxygen atom at the 10-position of the fluorescein skeleton, were synthesized as a new family of fluorescein analogues. The deprotonated BFs exhibited absorption and fluorescence in the near-infrared region, which were significantly red-shifted relative to those of hitherto-known heteroatom-substituted fluorescein analogues on account of the orbital interaction between the tricoordinate boron atom and the fluorescein skeleton. BFs also showed multi-stage changes resulting from a Lewis acid-base equilibrium at the boron center in combination with a Bronsted acid-base equilibrium at the phenolic hydroxy group.

DOI： 10.1039/c9sc02314c

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