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Search Results (6)

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Keywords = bistolane

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15 pages, 19513 KiB  
Article
Effect of Fluoroalkyl-Substituent in Bistolane-Based Photoluminescent Liquid Crystals on Their Physical Behavior
by Shigeyuki Yamada, Yizhou Wang, Masato Morita, Qingzhi Zhang, David O’Hagan, Masakazu Nagata, Tomohiro Agou, Hiroki Fukumoto, Toshio Kubota, Mitsuo Hara and Tsutomu Konno
Crystals 2021, 11(4), 450; https://doi.org/10.3390/cryst11040450 - 20 Apr 2021
Cited by 4 | Viewed by 3519
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-Emitting Liquid Crystals (Volume II))
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11 pages, 1614 KiB  
Article
Electrorheological Effect of Gold Nanoparticles Coated with Fluorescent Mesogenic Groups Dispersed in Nematic Liquid Crystal
by Kosuke Kaneko, Kosuke Yamashita, Daiki Fujioka, Kimiyoshi Kaneko, Kiyomi Fuchigami, Takeshi Hashishin and Tomonori Hanasaki
Crystals 2021, 11(2), 192; https://doi.org/10.3390/cryst11020192 - 16 Feb 2021
Cited by 1 | Viewed by 2736
Abstract
The electrorheological (ER) properties of composite materials consisting of a nematic liquid crystal (LC) and gold nanoparticles (GNPs) coated with bistolane-based mesogenic groups were studied. The GNPs were coated by normal alkyl chains and the fluorescent LC compounds, of which the molecular structure [...] Read more.
The electrorheological (ER) properties of composite materials consisting of a nematic liquid crystal (LC) and gold nanoparticles (GNPs) coated with bistolane-based mesogenic groups were studied. The GNPs were coated by normal alkyl chains and the fluorescent LC compounds, of which the molecular structure was similar to that of the LC matrix. The dispersity of the GNPs in the nematic LC was investigated by polarizing optical microscopy (POM). In order to improve the ER effect of the composite, a simple strategy was investigated from the viewpoint of a material design in surface-modified GNPs by lateral substitution of the mesogenic groups. The presence of the GNPs in the nematic LC led to a slightly enhanced ER effect compared to that observed for only the nematic LC. This study demonstrates the potential of a hybrid system consisting of LCs and GNPs to yield a larger ER effect. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-Emitting Liquid Crystals (Volume II))
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16 pages, 2800 KiB  
Article
Fluorinated Tolane Dyads with Alkylene Linkage: Synthesis and Evaluation of Photophysical Characteristics
by Shigeyuki Yamada, Eiji Uto, Tomohiro Agou, Toshio Kubota and Tsutomu Konno
Crystals 2020, 10(8), 711; https://doi.org/10.3390/cryst10080711 - 18 Aug 2020
Cited by 7 | Viewed by 3549
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Recent Developments in Stimuli-Responsive Luminescent Materials)
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15 pages, 4333 KiB  
Article
Synthesis and Characterization of Photoluminescence Liquid Crystals Based on Flexible Chain-Bearing Pentafluorinated Bistolanes
by Shigeyuki Yamada, Masaya Sato and Tsutomu Konno
Crystals 2020, 10(7), 603; https://doi.org/10.3390/cryst10070603 - 11 Jul 2020
Cited by 2 | Viewed by 3908
Abstract
The liquid-crystalline (LC) and photophysical properties of molecules are very sensitive to their electronic and molecular aggregate structures. Herein, to shed light on the structure–property relationships of pentafluorinated bistolane-based photoluminescence (PL) liquid crystals (PLLCs) previously reported by our group, we synthesized pentafluorinated bistolanes [...] Read more.
The liquid-crystalline (LC) and photophysical properties of molecules are very sensitive to their electronic and molecular aggregate structures. Herein, to shed light on the structure–property relationships of pentafluorinated bistolane-based photoluminescence (PL) liquid crystals (PLLCs) previously reported by our group, we synthesized pentafluorinated bistolanes with variable flexible chains and evaluated their LC and photophysical properties. The incorporation of an oxygen atom (to afford a 2-methoxyethoxy unit) or an oxygen atom and a methyl group (to afford a 1-methoxyprop-2-oxy unit) into the flexible butoxy chain significantly decreased the temperature of the crystalline-to-LC phase transition, and a chiral nematic phase comprising helical molecular aggregates was observed for the chiral 1-methoxyprop-2-oxy group–bearing bistolane. The synthesized bistolanes exhibited strong blue PL in both solution and crystalline phases; the featuring PL characteristics were maintained in the LC phase (produced by the crystalline-to-LC phase transition) except for a slight PL color change. Thus, it was concluded that the PL behavior of pentafluorinated bistolanes can be modulated by the choice of a suitable flexible chain, and the obtained insights are believed to facilitate the application of PLLCs in thermosensing PL materials. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-Emitting Liquid Crystals (Volume II))
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16 pages, 5646 KiB  
Article
Luminescence Tuning of Fluorinated Bistolanes via Electronic or Aggregated-Structure Control
by Masato Morita, Shigeyuki Yamada, Tomohiro Agou, Toshio Kubota and Tsutomu Konno
Appl. Sci. 2019, 9(9), 1905; https://doi.org/10.3390/app9091905 - 9 May 2019
Cited by 14 | Viewed by 3751
Abstract
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 [...] Read more.
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 (μ||) along the long molecular axis; thus, PL tuning can be achieved through electronic modulation by precise control of the μ|| 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. Full article
(This article belongs to the Section Chemical and Molecular Sciences)
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16 pages, 4684 KiB  
Article
2-Chloroalkoxy-Substituted Pentafluorinated Bistolanes as Novel Light-Emitting Liquid Crystals
by Shigeyuki Yamada, Kazuya Miyano, Tomohiro Agou, Toshio Kubota and Tsutomu Konno
Crystals 2019, 9(4), 195; https://doi.org/10.3390/cryst9040195 - 6 Apr 2019
Cited by 10 | Viewed by 4139
Abstract
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. [...] Read more.
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 °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. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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