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Yoshio Furusho - One of the best experts on this subject based on the ideXlab platform.

  • supramolecular network polymers formed from polyamidine and carboxy terminated telechelic poly n butyl acrylate via amidinium Carboxylate Salt bridges
    Journal of Polymer Science Part A, 2016
    Co-Authors: Yoshio Furusho, Takeshi Endo, Keiko Higaki, Katsuhiro Kaetsu, Yuji Higaki, Ken Kojio, Atsushi Takahara
    Abstract:

    We have prepared the amidinium-Carboxylate Salt bridge-based supramolecular network polymers from a carboxy-terminated telechelic poly(n-butyl acrylate) and a linear polyamidine having N,N′-di-substituted acetamidine group in the main chain. FTIR measurements indicated that the Salt bridge was attributed to the three-dimensional network formation. Virtually, no fluidity was observed for the blend containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at −5 °C. For comparison, the supramolecular network polymers crosslinked by ammonium-Carboxylate Salt were prepared using a linear polyethyleneimine instead of the polyamidine. The blend with equimolar amounts of the carboxyl group and the secondary amino group showed liquid-like fluidity with a G′ value of about 0.01 MPa at −5 °C, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form, as evidenced by FTIR analysis. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2148–2155

  • supramolecular polymer gels formed from carboxy terminated telechelic polybutadiene and polyamidine through amidinium Carboxylate Salt bridge
    Journal of Polymer Science Part A, 2014
    Co-Authors: Yoshio Furusho, Takeshi Endo
    Abstract:

    In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium-Carboxylate Salt bridge, highlighting the difference from a well-established network system based on carboxylic acid and amine. We have prepared the amidinium-Carboxylate Salt bridge-based supramolecular polymer gels from a carboxy-terminated telechelic polybutadiene and a linear polyamidine having N,N′-di-substituted acetamidine group in the main chain. FTIR analysis along with Small angle X-ray scattering measurements indicated that the Salt bridge was attributed to the gelation through three-dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a Tgel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium-Carboxylate Salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid-like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without Salt formation, as evidenced by FTIR analysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1815–1824

  • photocontrolled template directed synthesis of complementary double helices assisted by amidinium Carboxylate Salt bridge formation
    Chemical Science, 2013
    Co-Authors: Junki Tanabe, Daisuke Taura, Hidekazu Yamada, Yoshio Furusho
    Abstract:

    The template-directed imine-bond forming reactions between chiral amidines or achiral carboxylic acids monomers bearing a formyl or an amino group at one end were remarkably accelerated 34- or 10-fold in chloroform in the presence of the corresponding optically inactive carboxylic acid dimer or optically active amidine dimer linked by a trans-azobenzene unit as the template, respectively. The cis-azobenzene-linked carboxylic acid template markedly slowed the monomer conversions, and hence a reversible photocontrolled dimerization was achieved by light-induced cis–trans isomerization upon alternative irradiation with UV and visible light.

  • synthesis of helically twisted 1 1 macrocycles assisted by amidinium Carboxylate Salt bridges and control of their chiroptical properties
    Organic and Biomolecular Chemistry, 2013
    Co-Authors: Yuji Nakatani, Yoshio Furusho
    Abstract:

    A series of optically active, helically twisted [1 + 1]macrocycles connected via o-, m-, and p-linkages (o-2, m-2, and p-2) was prepared from the corresponding linear duplexes stabilized by complementary amidinium–Carboxylate Salt bridges bearing two arms with terminal vinyl groups at both ends through the ring-closing metathesis reaction in the good yields of 67, 92, and 96%, respectively. The chiroptical properties of the macrocycles were dependent on the linker geometries and could be controlled by acid–base interactions and zinc coordination, the changes in which were detected by their CD and absorption spectral changes and fluorescence colors.

  • chiral amplification in double stranded helical polymers through chiral and achiral amidinium Carboxylate Salt bridges
    Polymer Journal, 2012
    Co-Authors: Wataru Makiguchi, Yoshio Furusho, Shinzo Kobayashi, Eiji Yashima
    Abstract:

    A series of m-terphenyl-based random copolymers of chiral and achiral amidines, and their complementary homopolymers of achiral carboxylic acids were prepared by the copolymerization of a p-diiodobenzene derivative, with the diethynyl monomers containing a chiral or achiral amidine group and a carboxyl group using the Sonogashira coupling reaction. The obtained chiral/achiral amidine copolymers assembled into a double-stranded helical structure upon complexation with the complementary achiral homopolymer of carboxylic acids through interstrand amidinium−Carboxylate Salt bridges. The complexes exhibited characteristic induced cotton effects in the π-conjugated main-chain chromophore regions, indicating that the interstrand duplexes possess a preferred-handed double-helical structure. The effect of the chiral and achiral amidine contents on the amplification of the helical chirality (‘the sergeants and soldiers effect’) during the interstrand double-helix formation was investigated by comparing the cotton effect patterns and intensities of the duplexes with those of the corresponding all-chiral amidine-based double-helical polymer. m-Terphenyl-based random copolymers of chiral and achiral amidines and its complementary homopolymer of achiral carboxylic acids self-assembled to form complementary double helices with a preferred-handed helical sense via interstrand amidinium–Carboxylate Salt bridges, thus showing induced cotton effects in the π-conjugated main-chain chromophore regions. A unique amplification of the helical chirality (‘the sergeants and soldiers effect’) was, for the first time, observed during the double-helix formation.

Eiji Yashima - One of the best experts on this subject based on the ideXlab platform.

  • chiral template directed regio diastereo and enantioselective photodimerization of an anthracene derivative assisted by complementary amidinium Carboxylate Salt bridge formation
    Journal of the American Chemical Society, 2017
    Co-Authors: Junki Tanabe, Daisuke Taura, Naoki Ousaka, Eiji Yashima
    Abstract:

    A series of optically active amidine dimers composed of m-terphenyl backbones joined by a variety of linkers, such as achiral and chiral p-phenylene and chiral amide linkers, were synthesized and used as templates for the regio- (head-to-tail (HT) or head-to-head (HH)), diastereo- (anti or syn), and enantioselective [4 + 4] photocyclodimerization of an achiral m-terphenyl-based carboxylic acid monomer bearing a prochiral 2-substituted anthracene at one end (1) through complementary amidinium–Carboxylate Salt bridges. The amidine dimers linked by p-phenylene linkages almost exclusively afforded the chiral syn-HT and anti-HH dimers at 25 °C, while those joined by amide linkers produced all four dimers. The p-phenylene-linked templates tended to enhance the syn-HT-photodimer formation at high temperatures with no significant changes in the product enantiomeric excess (ee), while the anti-HH-photodimer formation remarkably increased with the decreasing temperature accompanied by a significant enhancement of t...

  • Chiral Template-Directed Regio‑, Diastereo‑, and Enantioselective Photodimerization of an Anthracene Derivative Assisted by Complementary Amidinium–Carboxylate Salt Bridge Formation
    2017
    Co-Authors: Junki Tanabe, Daisuke Taura, Naoki Ousaka, Eiji Yashima
    Abstract:

    A series of optically active amidine dimers composed of m-terphenyl backbones joined by a variety of linkers, such as achiral and chiral p-phenylene and chiral amide linkers, were synthesized and used as templates for the regio- (head-to-tail (HT) or head-to-head (HH)), diastereo- (anti or syn), and enantioselective [4 + 4] photocyclodimerization of an achiral m-terphenyl-based carboxylic acid monomer bearing a prochiral 2-substituted anthracene at one end (1) through complementary amidinium–Carboxylate Salt bridges. The amidine dimers linked by p-phenylene linkages almost exclusively afforded the chiral syn-HT and anti-HH dimers at 25 °C, while those joined by amide linkers produced all four dimers. The p-phenylene-linked templates tended to enhance the syn-HT-photodimer formation at high temperatures with no significant changes in the product enantiomeric excess (ee), while the anti-HH-photodimer formation remarkably increased with the decreasing temperature accompanied by a significant enhancement of the product ee up to −86% at −50 °C. Temperature-dependent inversion of the chirality of the anti-HH dimer was observed when the chiral phenylene-linked amidine dimer was used and the product ee was changed from 22% at 50 °C to −86% at −50 °C. A similar enhancement of the enantioselectivity of the anti-HH dimer was also observed for the chiral amide-linked template, producing the anti-HH dimer with up to −88% ee at −50 °C. The observed difference in the regio-, diastereo-, and enantioselectivities due to the difference in the linker structures of the amidine dimers during the template-directed photodimerization of 1 was discussed on the basis of a reversible conformational change in the amidine dimers complexed with 1

  • chiral amplification in double stranded helical polymers through chiral and achiral amidinium Carboxylate Salt bridges
    Polymer Journal, 2012
    Co-Authors: Wataru Makiguchi, Yoshio Furusho, Shinzo Kobayashi, Eiji Yashima
    Abstract:

    A series of m-terphenyl-based random copolymers of chiral and achiral amidines, and their complementary homopolymers of achiral carboxylic acids were prepared by the copolymerization of a p-diiodobenzene derivative, with the diethynyl monomers containing a chiral or achiral amidine group and a carboxyl group using the Sonogashira coupling reaction. The obtained chiral/achiral amidine copolymers assembled into a double-stranded helical structure upon complexation with the complementary achiral homopolymer of carboxylic acids through interstrand amidinium−Carboxylate Salt bridges. The complexes exhibited characteristic induced cotton effects in the π-conjugated main-chain chromophore regions, indicating that the interstrand duplexes possess a preferred-handed double-helical structure. The effect of the chiral and achiral amidine contents on the amplification of the helical chirality (‘the sergeants and soldiers effect’) during the interstrand double-helix formation was investigated by comparing the cotton effect patterns and intensities of the duplexes with those of the corresponding all-chiral amidine-based double-helical polymer. m-Terphenyl-based random copolymers of chiral and achiral amidines and its complementary homopolymer of achiral carboxylic acids self-assembled to form complementary double helices with a preferred-handed helical sense via interstrand amidinium–Carboxylate Salt bridges, thus showing induced cotton effects in the π-conjugated main-chain chromophore regions. A unique amplification of the helical chirality (‘the sergeants and soldiers effect’) was, for the first time, observed during the double-helix formation.

  • synthesis of complementary double stranded helical oligomers through chiral and achiral amidinium Carboxylate Salt bridges and chiral amplification in their double helix formation
    Journal of the American Chemical Society, 2011
    Co-Authors: Masato Ikeda, Yoshio Furusho, Takashi Hasegawa, Eiji Yashima
    Abstract:

    A series of complementary molecular strands from 2-mer to 5-mer that are composed of m-terphenyl units bearing chiral/achiral amidine or achiral carboxyl groups linked via Pt(II) acetylide complexes were synthesized by sequential stepwise reactions, and their chiroptical properties on the double-helix formation were investigated by circular dichroism (CD) and 1H NMR spectroscopies. In CHCl3, the “all-chiral” amidine strands consisting of (R)- or (S)-amidine units formed preferred-handed double helices with the complementary achiral carboxylic acid strands through the amidinium−Carboxylate Salt bridges, resulting in characteristic induced CDs in the Pt(II) acetylide complex regions, indicating that the chiral substituents on the amidine units biased a helical sense preference. The Cotton effect patterns and intensities were highly dependent on the molecular lengths. The complementary double-helix formation was also explored using the chiral/achiral amidine strands with different sequences in which a chiral...

  • a hetero stranded double helix composed of m diethynylbenzene based complementary molecular strands stabilized by amidinium Carboxylate Salt bridges
    Chemical Communications, 2010
    Co-Authors: Yoshio Furusho, Hidekazu Yamada, Eiji Yashima
    Abstract:

    A hetero-stranded double helix with a controlled helix sense was designed and synthesized from an optically active dimeric amidine and its complementary achiral dicarboxylic acid strand with conjugated m-diethynylbenzene backbones, being stabilized by the Salt bridges.

Xiaoying Lü - One of the best experts on this subject based on the ideXlab platform.

  • Effects of different radio-opacifying agents on physicochemical and biological properties of a novel root-end filling material.
    PLOS ONE, 2018
    Co-Authors: Yao-zhong Chen, Xiaoying Lü
    Abstract:

    Background/Purpose Radio-opacity is an essential attribute of ideal root-end filling materials because it is important for clinicians to observe root canal filling and to facilitate the follow-up instructions. The novel root-end filling material (NRFM) has good cytocompatibility and physicochemical properties but low intrinsic radio-opacity value. To improve its radio-opacity value, three novel radio-opaque root-end filling materials (NRRFMs) were developed by adding barium sulphate (NRFM-Ba), bismuth trioxide (NRFM-Bi) and zirconium dioxide (NRFM-Zr) to NRFM, respectively. The purpose of this study was to identify the suitable radio-opacifier for NRFM through evaluating their physicochemical and biological properties, in comparison with NRFM and glass ionomer cement (GIC). Methods NRRFMs were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectrophotometry (FTIR). Physicochemical properties including setting time, compressive strength, porosity, pH variation, solubility, washout resistance, contact angle and radiopacity were investigated. Cytocompatibility of both freshly mixed and set NRRFMs was investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Alkaline phosphatase (ALP) activity assay and alizarin red staining were used to investigate the osteogenic differentiation potential of NRFM-Zr. Data were analyzed using two-way ANOVA (pH variation, solubility and ALP activity) and one-way ANOVA (for the other variables). Results (1) NRRFMs were primarily composed of hydroxyapatite, calcium Carboxylate Salt and the corresponding radio-opacity agents (barium sulphate, bismuth trioxide or zirconium dioxide). (2) Besides similar physicochemical properties in terms of setting time, pH variation, solubility, washout resistance and contact angle to NRFM, NRFM-Bi and NRFM-Zr exhibited lower porosity and greater compressive strength after being set for 7 days and their radio-opacity were greater than the 3 mm aluminium thickness specified in ISO 6876 (2001). (3) MTT assay revealed that freshly mixed and set NRFM-Zr presented better cell viability than NRFM-Ba and NRFM-Bi at 24 hours and 48 hours (P

  • effects of different radio opacifying agents on physicochemical and biological properties of a novel root end filling material
    PLOS ONE, 2018
    Co-Authors: Yao-zhong Chen, Xiaoying Lü
    Abstract:

    Background/Purpose Radio-opacity is an essential attribute of ideal root-end filling materials because it is important for clinicians to observe root canal filling and to facilitate the follow-up instructions. The novel root-end filling material (NRFM) has good cytocompatibility and physicochemical properties but low intrinsic radio-opacity value. To improve its radio-opacity value, three novel radio-opaque root-end filling materials (NRRFMs) were developed by adding barium sulphate (NRFM-Ba), bismuth trioxide (NRFM-Bi) and zirconium dioxide (NRFM-Zr) to NRFM, respectively. The purpose of this study was to identify the suitable radio-opacifier for NRFM through evaluating their physicochemical and biological properties, in comparison with NRFM and glass ionomer cement (GIC). Methods NRRFMs were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectrophotometry (FTIR). Physicochemical properties including setting time, compressive strength, porosity, pH variation, solubility, washout resistance, contact angle and radiopacity were investigated. Cytocompatibility of both freshly mixed and set NRRFMs was investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Alkaline phosphatase (ALP) activity assay and alizarin red staining were used to investigate the osteogenic differentiation potential of NRFM-Zr. Data were analyzed using two-way ANOVA (pH variation, solubility and ALP activity) and one-way ANOVA (for the other variables). Results (1) NRRFMs were primarily composed of hydroxyapatite, calcium Carboxylate Salt and the corresponding radio-opacity agents (barium sulphate, bismuth trioxide or zirconium dioxide). (2) Besides similar physicochemical properties in terms of setting time, pH variation, solubility, washout resistance and contact angle to NRFM, NRFM-Bi and NRFM-Zr exhibited lower porosity and greater compressive strength after being set for 7 days and their radio-opacity were greater than the 3 mm aluminium thickness specified in ISO 6876 (2001). (3) MTT assay revealed that freshly mixed and set NRFM-Zr presented better cell viability than NRFM-Ba and NRFM-Bi at 24 hours and 48 hours (P<0.05). (4) NRFM-Zr significantly enhanced ALP activity and calcium formation of human osteoblast-like Saos-2 cells when compared with negative group and GIC (P<0.05). Conclusion NRFM-Zr presents desirable physicochemical and biological properties, thus zirconium dioxide may be a suitable radio-opacifier for NRFM.

Junki Tanabe - One of the best experts on this subject based on the ideXlab platform.

  • chiral template directed regio diastereo and enantioselective photodimerization of an anthracene derivative assisted by complementary amidinium Carboxylate Salt bridge formation
    Journal of the American Chemical Society, 2017
    Co-Authors: Junki Tanabe, Daisuke Taura, Naoki Ousaka, Eiji Yashima
    Abstract:

    A series of optically active amidine dimers composed of m-terphenyl backbones joined by a variety of linkers, such as achiral and chiral p-phenylene and chiral amide linkers, were synthesized and used as templates for the regio- (head-to-tail (HT) or head-to-head (HH)), diastereo- (anti or syn), and enantioselective [4 + 4] photocyclodimerization of an achiral m-terphenyl-based carboxylic acid monomer bearing a prochiral 2-substituted anthracene at one end (1) through complementary amidinium–Carboxylate Salt bridges. The amidine dimers linked by p-phenylene linkages almost exclusively afforded the chiral syn-HT and anti-HH dimers at 25 °C, while those joined by amide linkers produced all four dimers. The p-phenylene-linked templates tended to enhance the syn-HT-photodimer formation at high temperatures with no significant changes in the product enantiomeric excess (ee), while the anti-HH-photodimer formation remarkably increased with the decreasing temperature accompanied by a significant enhancement of t...

  • Chiral Template-Directed Regio‑, Diastereo‑, and Enantioselective Photodimerization of an Anthracene Derivative Assisted by Complementary Amidinium–Carboxylate Salt Bridge Formation
    2017
    Co-Authors: Junki Tanabe, Daisuke Taura, Naoki Ousaka, Eiji Yashima
    Abstract:

    A series of optically active amidine dimers composed of m-terphenyl backbones joined by a variety of linkers, such as achiral and chiral p-phenylene and chiral amide linkers, were synthesized and used as templates for the regio- (head-to-tail (HT) or head-to-head (HH)), diastereo- (anti or syn), and enantioselective [4 + 4] photocyclodimerization of an achiral m-terphenyl-based carboxylic acid monomer bearing a prochiral 2-substituted anthracene at one end (1) through complementary amidinium–Carboxylate Salt bridges. The amidine dimers linked by p-phenylene linkages almost exclusively afforded the chiral syn-HT and anti-HH dimers at 25 °C, while those joined by amide linkers produced all four dimers. The p-phenylene-linked templates tended to enhance the syn-HT-photodimer formation at high temperatures with no significant changes in the product enantiomeric excess (ee), while the anti-HH-photodimer formation remarkably increased with the decreasing temperature accompanied by a significant enhancement of the product ee up to −86% at −50 °C. Temperature-dependent inversion of the chirality of the anti-HH dimer was observed when the chiral phenylene-linked amidine dimer was used and the product ee was changed from 22% at 50 °C to −86% at −50 °C. A similar enhancement of the enantioselectivity of the anti-HH dimer was also observed for the chiral amide-linked template, producing the anti-HH dimer with up to −88% ee at −50 °C. The observed difference in the regio-, diastereo-, and enantioselectivities due to the difference in the linker structures of the amidine dimers during the template-directed photodimerization of 1 was discussed on the basis of a reversible conformational change in the amidine dimers complexed with 1

  • Cobalt(II)-Salen-Linked Complementary Double-Stranded Helical Catalysts for Asymmetric Nitro-Aldol Reaction
    2016
    Co-Authors: Daisuke Taura, Junki Tanabe, Shogo Hioki, Naoki Ousaka
    Abstract:

    Double-helical, bimetallic chiral Co­(II)-salen complexes stabilized by chiral amidinium–Carboxylate Salt bridges efficiently catalyzed the asymmetric nitro-aldol (Henry) reaction, producing products with up to an 89% enantiomeric excess (ee); the reactivity and enantioselectivity were higher than those catalyzed by the corresponding single strands. The key role of the chiral double-helical framework for the supramolecular bimetallic catalysis has been revealed by a double-helical catalyst carrying achiral Co­(II)-salen units that promoted the Henry reaction, yielding the product with a 50%–45% ee, while the corresponding single strands showed poor or no enantioselectivity

  • photocontrolled template directed synthesis of complementary double helices assisted by amidinium Carboxylate Salt bridge formation
    Chemical Science, 2013
    Co-Authors: Junki Tanabe, Daisuke Taura, Hidekazu Yamada, Yoshio Furusho
    Abstract:

    The template-directed imine-bond forming reactions between chiral amidines or achiral carboxylic acids monomers bearing a formyl or an amino group at one end were remarkably accelerated 34- or 10-fold in chloroform in the presence of the corresponding optically inactive carboxylic acid dimer or optically active amidine dimer linked by a trans-azobenzene unit as the template, respectively. The cis-azobenzene-linked carboxylic acid template markedly slowed the monomer conversions, and hence a reversible photocontrolled dimerization was achieved by light-induced cis–trans isomerization upon alternative irradiation with UV and visible light.

Jonathan L Sessler - One of the best experts on this subject based on the ideXlab platform.

  • fluorescent supramolecular organic frameworks constructed by amidinium Carboxylate Salt bridges
    Chemistry: A European Journal, 2021
    Co-Authors: Hongqin Jiang, Jonathan L Sessler, Linhuang Xie, Zhiming Duan, Kunhua Lin, Vincent M Lynch, Hongyu Wang
    Abstract:

    We report here a set of fluorescent supramolecular organic frameworks (SOFs) that incorporate aggregation-induced emission (AIE) units within their frameworks. The fluorescent SOFs of this study were constructed by linking the tetraphenylethylene (TPE)-based tetra(amidinium) cation TPE4+ and aromatic diCarboxylate anions through amidinium-Carboxylate Salt bridges. The resulting self-assembled structures are characterized by fluorescence quantum yields in the range of 4.6∼14 %. This emissive behavior is ascribed to a combination of electrostatic interactions and hydrogen bonds that operate in concert to impede motions that would otherwise lead to excited state energy dissipation. Single-crystal X-ray diffraction analyses revealed that the length of the diCarboxylate anion bridges has a considerable impact on the structural features of the resulting frameworks. Nevertheless, all SOFs prepared in the context of the present study were found to display emissive features characteristic of TPE-based AIE luminogens with only a modest dependence on the structural specifics being seen. The SOFs reported here could be reversibly "broken up" and "reformed" in response to acid/base stimuli. This reversible structural behavior is consistent with their SOF nature.

  • amidinium Carboxylate Salt bridge mediated proton coupled electron transfer in a donor acceptor supramolecular system
    Organic chemistry frontiers, 2019
    Co-Authors: Xiaolei Ren, Xiaohua Wang, Yuren Sun, Xiaodong Chi, Daniel N Mangel, Hongyu Wang, Jonathan L Sessler
    Abstract:

    A supramolecular polymer, 3T-DPP, that undergoes photoinduced proton-coupled electron transfer was constructed by means of amidinium-Carboxylate Salt bridges that serve to link terthiophene electron donors and diketopyrrolopyrrole electron acceptors with a 1 : 1 binding constant of 1.13 × 105 M−1 in N-methyl pyrrolidone.

  • Photoinduced Electron Transfer from a Tetrathiafulvalene-Calix[4]pyrrole to a Porphyrin Carboxylate within a Supramolecular Ensemble
    2014
    Co-Authors: Christina M. Davis, Yuki Kawashima, Kei Ohkubo, Jong Min Lim, Dongho Kim, Shunichi Fukuzumi, Jonathan L Sessler
    Abstract:

    A supramolecular assembly is formed upon mixing millimolar concentrations of a tetrakis-tetrathiafulvalene calix[4]­pyrrole (TTF-C4P) and a porphyrin tetraethylammonium Carboxylate Salt in benzonitrile (PhCN). The TTF-C4P binds to the Carboxylate moiety of the porphyrin with a 1:1 stoichiometry and a binding constant of 6.3 × 104 M–1 in this solvent at 298 K. Laser photoexcitation of the supramolecular complex results in formation of the triplet charge-separated (CS) state composed of a radical cation of the TTF-C4P receptor and the radical anion of the porphyrin Carboxylate. These processes and the resulting states were characterized by means of transient absorption and electron spin resonance (ESR) spectroscopies. The rate constants corresponding to the forward and backward intramolecular electron-transfer (ET) processes were determined to be 2.1 × 104 and 3.6 × 102 s–1, respectively. The rate constants of intermolecular forward and backward electron transfer were also determined to be 4.4 × 108 and 9.8 × 108 M–1 s–1, respectively. The electronic coupling constant (V), 1.2 × 10–2 cm–1, and the reorganization energy (λ), 0.76 eV, for back electron transfer were evaluated from the temperature dependence of the rate constants of intramolecular electron transfer. The small V value indicates little spin-forbidden interaction between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and substantiates the long-lived CS lifetime. These results were corroborated by density function theory (DFT) calculations, which provided support for the conclusion that the HOMO and LUMO, located on a TTF moiety of the TTF-C4P and the porphyrin core, respectively, have little interaction though space