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Boron–Diindomethene (BDI) Dyes and Their Tetrahydrobicyclo Precursors—en Route to a New Class of Highly Emissive Fluorophores for the Red Spectral Range

Authors

  • Zhen Shen Dr.,

    1. Department of Chemistry, Faculty of Science, Ehime University, Matsuyama 790—8577, Japan, Fax: (+81) 899279590
    2. Present address: State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China
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  • Holger Röhr Dipl.-Phys.,

    1. Div. I.3 Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Strasse 11, 12489 Berlin, Germany, Fax: (+49) 308-104-5005
    2. Associated with: Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin, Takustrasse 3, 14195 Berlin, Germany
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  • Knut Rurack Dr.,

    1. Div. I.3 Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Strasse 11, 12489 Berlin, Germany, Fax: (+49) 308-104-5005
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  • Hidemitsu Uno Prof.,

    1. Integrated Center for Science, Faculty of Science, Ehime University, Matsuyama 790—8577, Japan
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  • Monika Spieles,

    1. Div. I.3 Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Strasse 11, 12489 Berlin, Germany, Fax: (+49) 308-104-5005
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  • Burkhard Schulz,

    1. Div. I.3 Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Strasse 11, 12489 Berlin, Germany, Fax: (+49) 308-104-5005
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  • Günter Reck Dr.,

    1. Div. I.3 Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Strasse 11, 12489 Berlin, Germany, Fax: (+49) 308-104-5005
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  • Noboru Ono Prof.

    1. Department of Chemistry, Faculty of Science, Ehime University, Matsuyama 790—8577, Japan, Fax: (+81) 899279590
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Abstract

The X-ray crystallographic, optical spectroscopic, and electrochemical properties of a newly synthesized class of boron–diindomethene (BDI) dyes and their tetrahydrobicyclo precursors (bc-BDP) are presented. The BDI chromophore was designed to show intensive absorption and strong fluorescence in an applicationary advantageous spectral range. Its modular architecture permits fusion of a second subunit, for example, a receptor moiety to the dye's core to yield directly linked yet perpendicularly prearranged composite systems. The synthesis was developed to allow facile tuning of the chromophore platform and to thus adjust its redox properties. X-ray analysis revealed a pronounced planarity of the chromophore in the case of the BDIs, which led to a remarkable close packing in the crystal of the simplest derivative. On the other hand, deviation from planarity was found for the diester-substituted bc-BDP benzocrown that exhibits a “butterfly”-like conformation in the crystal. Both families of dyes show charge- or electron-transfer-type fluorescence-quenching characteristics in polar solvents when equipped with a strong donor in the meso-position of the core. These processes can be utilized for signaling purposes if an appropriate receptor is introduced. Further modification of the chromophore can invoke such a guest-responsive intramolecular quenching process, also for receptor groups of low electron density, for example, benzocrowns. In addition to the design of various prototype molecules, a promising fluoroionophore for Na+ was obtained that absorbs and emits in the 650 nm region and shows a strong fluorescence enhancement upon analyte binding. Furthermore, investigation of the remarkable solvatokinetic fluorescence properties of the “butterfly”-like bc-BDP derivatives suggested that a second intrinsic nonradiative deactivation channel can play a role in the photophysics of boron–dipyrromethene dyes.

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