Search

Donor–π–acceptor fluorophores that consist of an electron‐donating amino group and an electron‐accepting triarylborane moiety generally exhibit substantial solvatochromism in their fluorescence while retaining high fluorescence quantum yields even in polar media. Herein, we report a new family of this compound class, which bears ortho‐P(=X)R2‐substituted phenyl groups (X=O or S) as a photodissociative module. The P=X moiety that intramolecularly coordinates to the boron atom undergoes dissociation in the excited state, giving rise to dual emission from the corresponding tetra‐ and tricoordinate boron species. The susceptibility of the systems to photodissociation depends on the coordination ability of the P=O and P=S moieties, whereby the latter facilitates dissociation. The intensity ratios of the dual emission bands are sensitive to environmental parameters, including temperature, solution polarity, and the viscosity of the medium. Moreover, precise tuning of the P(=X)R2 group and the electron‐donating amino moiety led to single‐molecule white emission in solution. [ABSTRACT FROM AUTHOR]

Olefin–borane π‐complexes have been postulated as intermediates for the addition of frustrated Lewis pairs (FLP) to olefins. In the present study, we have employed this weak interaction to modulate the electronic properties of boron‐based π‐electron materials. A series of donor–π–acceptor (D–π–A) fluorophores that contain an alkenyl‐bridged diarylboryl group is synthesized. A crystallographic analysis revealed that the olefin and boron moieties are held in close proximity. Upon addition of a Lewis base to a solution of these D–π–A fluorophores, an FLP‐type addition occurs with concurrent significant changes in the absorption and emission properties. The FLP‐type reaction shifts the reaction site from the Lewis‐acidic boron atom to a carbocationic center, and thereby even facilitates a reaction with bulky Lewis bases. For example, a tricyclohexylphosphine adduct thus generated exhibits temperature‐dependent reversible dissociation/association behavior. These results provide a design strategy for stimuli‐responsive emissive boron‐based materials. [ABSTRACT FROM AUTHOR]

Two kinds of planarized phenyldithienylboranes, which contain (CH3)2C‐ or CH2‐bridging moieties, were synthesized. The difference of the bridging moieties affects their packing structures and photophysical properties. In particular, the (CH3)2C‐bridged derivative exhibits a large Stokes shift, unusual for such planarized compounds, that results from a large structural relaxation in the excited state. A series of π‐extended derivatives was synthesized, among which a p‐(diphenylamino)phenyl‐substituted derivative shows large solvatochromism in the fluorescence spectra, while maintaining high quantum yields even in polar solvents. The Lewis acidity of the phenyldithienylborane derivatives was also assessed by titration with pyridine. The Lewis acidity of the boron center is affected not only by the difference in the steric bulk of the bridging moieties, but also by the electronic effect of the substituents introduced at remote positions relative to the boron atom. These results demonstrate the characteristic features of planarized phenyldithienylboranes as building blocks for boron‐based π‐electron materials. [ABSTRACT FROM AUTHOR]

Global staffing is a crucial factor for the success of the overseas operations of multinational corporations (MNCs). This study examines the contextual and organisational factors that affect the localisation of subsidiary staffing in the overseas operations of Japanese multinational companies. Using panel data containing more than 15 000 observations of Japanese overseas subsidiaries and a random‐effects logit model, we found that the cultural distance between the home country and the host country has a significant impact on the localisation of subsidiary staffing. In addition, the strategic importance of subsidiaries, as well as the local market orientation and business experiences in the host country, but not research and development (R&D) intensity of Japanese parent firms, have a significant impact on the localisation of foreign subsidiary staffing. We discuss the theoretical and practical implications of these findings. [ABSTRACT FROM AUTHOR]

We report on the fluorescence properties of a new class of emissive and stable π‐radicals that contain a boron atom at a position distant from the radical center. A fully planarized derivative exhibited an intense red fluorescence with high fluorescence quantum yields (ΦF >0.67) even in polar solvents. To elucidate the origin of this phenomenon, we synthesized another boron‐stabilized radical that contains a bulky aryl group on the boron atom. A comparison of these derivatives, as well as with conventional donor–π–acceptor (D–π–A)‐type emissive π‐radicals, unveiled several characteristic features in their photophysical properties. A theoretical analysis revealed that the SOMO–LUMO electronic transition generates an emissive D1 state. Unlike conventional D–π–A‐type π‐radicals, this state does not undergo significant structural relaxation. The boron‐stabilized π‐radicals demonstrated promising potential for organic light‐emitting diodes as an emitting material. [ABSTRACT FROM AUTHOR]

We report a new design strategy for an excited‐state intramolecular proton transfer (ESIPT) fluorophore that can be used in acidic media. A photobasic pyridine‐centered donor‐acceptor‐donor‐type fluorophore is combined with a basic trialkylamine "strap". In the presence of an acid, protonation occurs predominantly at the amine moiety in the ground state. A single‐crystal X‐ray diffraction analysis confirmed the formation of a pre‐organized intramolecular hydrogen‐bonded structure between the resulting ammonium moiety and the pyridine ring. Upon excitation, the intramolecular charge‐transfer transition increases the basicity of the pyridine moiety in the excited state, resulting in proton transfer from the amine to the pyridine moiety. Consequently, the fluorophore takes on a polymethine‐dye character in the ESIPT state, which gives rise to significantly red‐shifted emission with an increased fluorescence quantum yield. [ABSTRACT FROM AUTHOR]

Electron‐deficient heteroacenes that contain two tricoordinate boron atoms in their acene skeletons and planarized phenyl ether moieties at their periphery were synthesized via the borylation of silicon‐bridged precursors. X‐ray crystallographic analysis revealed quinoidal structures, which give rise to two‐step reversible redox processes for both the reduction and oxidation. These compounds exhibit intense absorption and sharp fluorescence bands with vibronic structures in the near‐infrared (NIR) region. These properties originate from the push–pull effect along the long axis of the molecule derived from the electron‐donating ether moieties and the electron‐accepting boron moieties. Of particular note is the NIR emission of the thienothiophene‐centered heteroacene, which has a maximum at 952 nm with a narrow band width of 309 cm−1 in cyclohexane. A Franck–Condon analysis revealed the crucial role of the sterically less‐hindered thienothiophene spacer in achieving this sharp emission band. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A B-phenyldibenzo[b,f]borepin planarized with two methylene bridges was synthesized. The structural constraint on the B-phenyl group resulted in a bathochromic shift of the absorption and fluorescence properties as well as enhanced Lewis acidity. A donor–π–acceptor type derivative based on this scaffold exhibited intense fluorescence irrespective of the solvent polarity. [ABSTRACT FROM AUTHOR]

Keywords: Boron; Donor-Acceptor Systems; Excited State; Fluorescence; Stimulus-Responsiveness EN Boron Donor-Acceptor Systems Excited State Fluorescence Stimulus-Responsiveness 1 1 1 06/20/23 20230626 NES 230626 B Dual-emissive b triarylborane-based donor- -acceptor fluorophores sensitive to environmental parameters, including temperature, solvent polarity, and viscosity of the medium, are reported by Shigehiro Yamaguchi and co-workers in their Research Article (e202303725). Boron, Donor-Acceptor Systems, Excited State, Fluorescence, Stimulus-Responsiveness Back Cover: Photodissociative Modules that Control Dual-Emission Properties in Donor- -Acceptor Organoborane Fluorophores (Angew. [Extracted from the article]

The intramolecularly coordinated B-X=P bond undergoes dissociation in the excited state, giving rise to bright emissions from the two different states. Boron, Donor-Acceptor Systems, Excited State, Fluorescence, Stimulus-Responsiveness Keywords: Boron; Donor-Acceptor Systems; Excited State; Fluorescence; Stimulus-Responsiveness EN Boron Donor-Acceptor Systems Excited State Fluorescence Stimulus-Responsiveness 1 1 1 06/20/23 20230626 NES 230626 B Dual-emissive b triarylborane-based donor- -acceptor fluorophores sensitive to environmental parameters, including temperature, solvent polarity, and viscosity of the medium, are reported by Shigehiro Yamaguchi and co-workers in their Research Article (e202303725). [Extracted from the article]

A new reaction mode for triarylboranes under photochemical conditions was discovered. Photoirradiation of dimesitylboryl-substituted (hetero)arenes produced spirocyclic boraindanes, where one of the C−H bonds in the ortho-methyl groups of the mesityl substituents was formally added in a syn fashion to a C−C double bond of the (hetero)aryl group. Quantum chemical calculations and laser flash photolysis measurements indicated that the reaction proceeds through a [1,6]-sigmatropic rearrangement. This behavior is reminiscent of the photochemical reaction mode of arylalkenylketones, thus demonstrating the isosteric relation between tricoordinate organoboron compounds and the corresponding pseudo-carbocationic species in terms of pericyclic reactions. Despite the disrupted π-conjugation, the resulting spirocyclic boraindanes exhibited a characteristic absorption band at relatively long wavelengths ( λ=370-400 nm). [ABSTRACT FROM AUTHOR]