Tomohiro AGOU

Abstract Two tris(2,4,6-trichlorophenyl)methyl (TTM)-type luminescent radicals, TTM-(3PCz)2 and TTM-(3PCz)3, bearing 2 and 3 9-phenylcarbazol-3-yl (3PCz) substituents, respectively, were synthesized and characterized. The photobleaching of these radicals was suppressed compared with that of previously reported TTM-type luminescent radicals, suggesting a favorable effect of the multiple electron-donating 3PCz groups on the photostability of the TTM-type radicals.

Abstract Dibenzo-1,4-heteraborins and their π-extended derivatives have been paid increased attention to because of their potential as optical and electronic functional materials such as organic electroluminescence emitters. Meanwhile, 1,4-heteraborin compounds with heteroaromatic ring systems have remained scarce, even though Liu et al. recently reported the synthesis, properties and functionalization of dithieno-1,4-thiaborins (DTTBs). In this work, DTTBs with 10H-phenothiazine-10-yl (Pz), 9H-carbazol-9-yl (Cz), and p-(Ph2N)C6H4 groups as electron-donating amino groups at the α-positions of the thiophene moieties were synthesized using palladium-catalyzed coupling reactions. X-Ray crystallographic analysis revealed the molecular structure of a DTTB substituted with Pz groups. This analysis showed that the two Pz moieties adopted extra- (quasi-axial) conformations. The Cz and p-(Ph2N)C6H4 substituted DTTBs showed red-shifted absorption and emission when compared to the original DTTBs. This shift is due to donor–acceptor interactions between the amino groups and the DTTB cores. The Pz-substituted DTTB exhibited dual fluorescence emissions, originating from the locally-excited (LE) and twisted intramolecular charge transfer (TICT) states. The intensity and nature of these emissions varied based on solvent polarity, temperature, and viscosity, suggesting the potential of the Pz-substituted DTTB to act as a fluorescent environment sensor.

Owing to their excellent fluorescence properties, coumarin derivatives have diverse applications in phototherapy and optoelectronics. Coumarin derivatives with a trifluoromethyl group at the 4-position have been extensively investigated; however, studies...

Functional molecules possessing photoluminescence (PL) and liquid-crystalline (LC) behaviors, known as photoluminescent liquid crystals, along with a small molecular structure, have attracted significant attention. Fluorinated tolane skeletons are small π-conjugated structures, which are promising candidates for such functional molecules. These structures were revealed to exhibit strong PL in solid state but no LC behavior. Based on a report on hydrogen-bonded dimer-type LC molecules of carboxylic acid, in this study, we designed and synthesized a series of fluorinated tolanecarboxylic acids (2,3,5,6-tetrafluoro-4-[2-(4-alkoxyphenyl)ethyn-1-yl]benzoic acids) as promising PLLC molecules. Evaluation of the LC behavior revealed that fluorinated tolanecarboxylic acids with a longer alkoxy chain than a butoxy chain exhibited nematic LC behavior. Additionally, fluorinated tolanecarboxylic acids showed intense PL in the solution and crystalline states. Notably, fluorinated tolanecarboxylic acid with an aggregated structure in the nematic LC phase also exhibited PL with a slight blue shift in PL maximum wavelength compared to the crystalline state. The present fluorinated tolanecarboxylic acid exhibiting PL and LC characteristics in a single molecule can be applied to thermoresponsive PL materials, such as a PL thermosensor.

Although dibenzo-fused 1,4-heteroaromatics are utilized as strongly reducing photocatalysts in organic synthesis and polymerization, they have rarely been employed in catalytic photooxidation. Moreover, to date, their boron-analogs, dibenzo-fused 1,4-azaborines (DBABs), have not been applied in photocatalysis despite their promising potential as photocatalysts. Accordingly, herein, aerobic photooxidation of triarylphosphines (Ar3P) was performed using DBABs as photocatalysts. The reaction smoothly proceeded in an aprotic solvent, and phosphine oxides were obtained in appropriate yields. Density functional theory calculations suggested that DBAB captured and activated phosphadioxirane intermediates, which were generated by the interaction of Ar3P with O-1(2), at the Lewis acidic boron center.

A novel π-conjugated tricarbocycle with a CF₂CF₂-containing cyclohexa-1,3-diene skeleton was revealed to show aggregation-induced enhancement emission, which would pave the way for novel solid-state fluorescence materials.

Dual-state emissive (DSE) luminophores, which can luminesce both in solution and in solid states, have recently attracted significant attention because of their broad applications. However, their development is difficult due to the difference in molecular design between solution- and solid-state luminophores. In this study, DSE luminophores based on unsymmetrical hexafluorocyclopentene-linked twisted π-conjugated structures carrying various substituents to tune the electron-density were designed and synthesized in a single-step reaction from heptafluorocyclopentene or perfluoro-1,2-diphenylcyclopentene derivatives. The twisted π-conjugated luminophores exhibited absorption in the UV region at approximately 330 nm, along with several signals in the high-energy region. Upon irradiating the luminophore solution (wavelength 330 nm), light-green to yellow photoluminescence (PL) was observed in the range of 422–471 nm with high PL efficiency. Theoretical calculations revealed that excitation from ground to excited states altered the structural shape of the luminophores from twisted to planar, leading to red-shifted PL and high PL efficiency (ΦPL). The intense blue PL exhibited by the luminophores in the crystalline state was attributed to their twisted molecular structures that suppressed non-radiative deactivation via the effective blocking of π/π stacking interactions.

Photoluminescent liquid crystals (PLLCs) have attracted significant attention owing to their broad applicability in thermosensing and PL switching. Extensive efforts have been made to develop bistolane-based PLLCs containing flexible units at both molecular terminals, and it has been revealed that their PL behavior can switch with the phase transition between the crystalline and LC phases. Although slight modulation of the flexible unit structure dramatically alters the LC and PL behaviors, few studies into the modification of the flexible units have been conducted. With the aim of achieving dynamic changes in their physical behaviors, we developed a family of bistolane derivatives containing a simple alkyl or a fluoroalkyl flexible chain and carried out a detailed systematic evaluation of their physical behaviors. Bistolanes containing a simple alkyl chain showed a nematic LC phase, whereas switching the flexible chain in the bistolane to a fluoroalkyl moiety significantly altered the LC phase to generate a smectic phase. The fluoroalkyl-containing bistolanes displayed a stronger deep blue PL than their corresponding non-fluorinated counterparts, even in the crystalline phase, which was attributed to the construction of rigid molecular aggregates through intermolecular F···H and F···F interactions to suppress non-radiative deactivation.

Light-emitting materials have received considerable attention because of their broad applications as substrates in bio-imaging and sensing components, light-emitting displays, and lighting devices. Herein, we developed fluorinated tolane and bistolane derivatives containing fluorinated aromatic rings and demonstrated their intense photoluminescence (PL) characteristics in crystalline powder states. We focused on molecules showing varied PL behavior with a change in the molecular aggregated structures. We synthesized novel fluorinated tolane dyads consisting of fluorinated tolane-based π-conjugated scaffolds and flexible alkylene linkages to control both the electron-density distribution and molecular aggregated states. Fluorinated tolane dyads connected with an alkylene linkage showed blue PL in a dilute solution, but the PL efficiency achieved was low. In contrast, the crystalline powder of tolane dyad substrates exhibited dual emission—relatively intense blue to deep blue PL—originating from monomer and aggregate emission. The PL behavior changed significantly with the alkylene linkage and the application of a mechanical stimulus to the crystalline powder sample. The fluorinated tolane dyads developed in this study could serve as stimulus-responsive photoluminescent materials suitable for optical applications.

A polycondensation of 1,4-dimethoxy-2,5-bis(trifluorovinyl)benzene (1) with bisphenols in the presence of K2CO3 afforded aromatic polymers 3 consisting of both the (E)- and (Z)-Ar-CF=CF-O-Ar' moieties in the main chains. The M-n and M-w values of polymer 3c prepared from bisphenol-AF were up to 6.62 x 10(4) and 1.29 X 10(5), respectively. The polymers 3 were transparent in the visible region (>400 nm) and exhibited good thermal stability (T-d5% > 320 degrees C). Fluorescence spectroscopy and X-ray diffraction analysis indicated the amorphous character of polymer 3c. The drop-cast film of 3c showed that the refractive indices and Abbe's number were comparable to those for widely used polymers having optical applications, such as polycarbonate and polystyrene.

Helicenes fused with hexafluorocyclopentene (HFCP) were synthesized by oxidative photocyclization of stilbene derivatives (the Mallory reaction). Of the newly-obtained fluorinated helicenes, the [7]helicenes bearing one- or three-HFCP units were structurally characterized by X-ray crystallographic analysis. The attempted synthesis of [9]helicene fused with three HFCP units resulted in the unexpected formation of a novel double helicene consisting of [4]- and [6]-helicenes sharing peripheral benzene rings. Optical properties and chiral resolutions of the newly obtained HFCP-substituted helicenes are also described.

Herein, a series of 1,2-disubstituted 3,3,4,4,5,5-hexafluorocyclopentene derivatives is synthesized from the commercially available octafluorocyclopentene via addition-elimination reactions, and their photophysical properties are investigated in detail. 1,2-Bis[2-(4-alkoxyaryl)ethyn-1-yl]-3,3,4,4,5,5-hexafluorocyclopentene exhibits UV-absorption at 345 nm in CH2Cl2 and deep blue photoluminescence (PL). The PL properties of these derivatives, including color and maximum wavelength (lambda(PL)), are strongly affected by the electron-density distribution induced by the electronic characteristics of the alkoxy-substituents at the 4-position of the benzene ring, with more electron-donating substituents resulting in a larger shift of lambda(PL) to longer wavelengths. Note that the present light-emitting pi-conjugated luminophores also exhibit relatively strong PL in the crystalline state, where lambda(PL) shifts can be introduced by modulation of the terminal alkoxy-chain length, resulting in different PL colors from light-blue to orange.

As one of the three primary colors, blue is significant for display and lighting applications and the development of blue-emitting molecules with high quantum efficiency, and color purity for organic light-emitting diodes (OLEDs) remains a key challenge. Herein, a new series of blue thermally activated delayed fluorescence (TADF) materials featuring π-extended ladder-oxaborin and thiaborin acceptors has been developed. Steady-state and time-resolved photophysical measurements revealed the advantages of the ladder-oxaborin emitter, including a tiny singlet–triplet energy splitting of 10 meV, an ideal photoluminescence quantum yield of 100%, and an ultrashort TADF lifetime of 780 ns. The TADF-OLEDs incorporating the ladder-oxaborin (deep-blue) and thiaborin (sky-blue) emitters achieved significantly high external electroluminescence quantum efficiencies of up to 20.1% and 25.9%, respectively, accompanied by suppressed efficiency roll-offs.

[2 + 3] Cycloaddition reaction of fluorine-containing alkynes with various 2-iodoaryl ketones in the presence of CoCl2(dppf) catalyst proceeded very smoothly to give the corresponding 2- or 3-fluoroalkylated indenols in 57-98% yields. These regioisomers could be successfully separated and obtained in a pure form. From X-ray crystallographic and NOESY analyses, major or minor regioisomers were determined as 3- or 2-fluoroalkylated indenols, respectively. (C) 2019 Elsevier Ltd. All rights reserved.

Herein, we prepared novel bent fluorine-containing donor-pi-acceptor (D-pi-A) molecules from commercially available octafluorocyclopentene using a facile two-step procedure, revealing that the above molecules absorb UV-light and exhibit yellow photoluminescence (PL) with high PL efficiencies (phi(PL)) in solution. The corresponding Stokes shifts exceeded 10 000 cm(-1), and the maximum PL wavelength (lambda(PL)) strongly depended on solvent polarity or intermolecular interactions in the solid state. On the basis of a Lippert-Mataga plot, PL was confidently assigned to radiative relaxation from an intramolecular charge-transfer excited state. Moreover, the synthesized luminophores showed intense PL even in the crystalline state and exhibited alkoxy chain length-dependent PL behavior (e.g., high phi(PL), lambda(PL) = 486-540 nm).

Organic luminescent materials have a wide range of practical applications, but the understanding of the relationship between molecular structure and luminescent behavior is lacking. Herein, we synthesized fluorinated bistolanes with an electron-donating alkoxy substituent at one terminal and an electron-withdrawing substituent at the other to realize systematic control of the electron-density distribution. Evaluation of the phase transition behavior revealed that most of the fluorinated bistolanes showed liquid-crystalline (LC) behavior, with the phase transition temperature depending on the terminal substituents. Additionally, the fluorinated luminophores displayed intense photoluminescence (PL) in solution and in their crystal phases. Remarkably, the PL color shifted dramatically depending on the dipole moment ((||)) along the long molecular axis; thus, PL tuning can be achieved through electronic modulation by precise control of the (||) of the luminophore. Interestingly, in the LC phases under thermal conditions, the maximum PL band shifted by 0.210 eV upon phase transition from the crystal to smectic A LC phases, indicating that PL tuning can also be achieved by controlling the aggregated structure. These results offer a new molecular design for easily tunable PL materials using the molecular properties or external stimuli for promising applications, including light-emitting displays and PL sensing materials.

In this study, we designed and synthesized novel pentafluorinated bistolane derivatives with 2-chloropentyl or 2-chlorohexyl flexible units as novel light-emitting liquid crystals (LELCs). By measuring the phase-transition behaviors, all derivatives were found to display liquid-crystalline (LC) phases during both heating and cooling processes. Among the novel bistolanes, the S- and R-configured derivatives exhibited a chiral nematic (N*) phase with a typical Grandjean optical texture. Interestingly, the chiral derivatives also exhibited a blue phase with a typical platelet texture in a narrow temperature range (2-4 degrees C). Photophysical measurements revealed that the 2-chloroalkoxy-substituted pentafluorinated bistolanes exhibited intense photoluminescence (PL) both in solution and in crystalline phases. The PL characteristics, especially the maximum PL wavelength, were found to switch sensitively during the heating and cooling cycles depending on the molecular aggregates through the crystal (Cr) ? N* phase transition. The 2-chloroalkoxy flexible units induced dynamic changes in the LC and PL properties, providing valuable insight into the potential of various LELCs as PL sensing materials.

An abbreviated synthesis of hexafluorocyclopentane-annulated 2,5-diarylfurans has been developed. 1,2-Dichloro-3,3,4,4,5,5-hexafluorocyclopentene was converted to corresponding polyfluorinated 1,2-diaroylalkenes, treatment of which with P(OEt)(3) afforded the polyfluorinated 2,5-diarylfurans. Solid-state photo-luminescence of the furan derivatives exhibited remarkable red-shifts compared to fluorescence emissions in solution, probably because of intermolecular interactions in the solid state. Comparisons of the optical and electrochemical data of the fluorinated furan derivatives with those of a non-fluorinated 2,5-diarylfuran suggest that the perfluorocycloalkane-annulation effectively enhances the electron-accepting ability of the 2,5-diarylfuran framework.