Environment-Sensitive Fluorophores with Benzothiadiazole and Benzoselenadiazole Structures as Candidate Components of a Fluorescent Polymeric Thermometer

Authors

  • Dr. Seiichi Uchiyama,

    Corresponding author
    1. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan), Fax: (+81) 3-58414768
    • Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan), Fax: (+81) 3-58414768
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  • Kohki Kimura,

    1. Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan), Fax: (+81) 277-30-1213
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  • Chie Gota,

    1. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan), Fax: (+81) 3-58414768
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  • Dr. Kohki Okabe,

    1. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan), Fax: (+81) 3-58414768
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  • Kyoko Kawamoto,

    1. Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan), Fax: (+81) 3-58414768
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  • Dr. Noriko Inada,

    1. Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192 (Japan)
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  • Dr. Toshitada Yoshihara,

    1. Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan), Fax: (+81) 277-30-1213
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  • Prof. Seiji Tobita

    Corresponding author
    1. Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan), Fax: (+81) 277-30-1213
    • Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515 (Japan), Fax: (+81) 277-30-1213
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Abstract

An environment-sensitive fluorophore can change its maximum emission wavelength (λem), fluorescence quantum yield (Φf), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge-transfer-type environment-sensitive fluorophores, DBThD-IA and DBSeD-IA, in which the oxygen atom of a well-established 2,1,3-benzoxadiazole environment-sensitive fluorophore, DBD-IA, has been replaced by a sulfur and selenium atom, respectively. DBThD-IA is highly fluorescent in n-hexane (Φf=0.81, λem=537 nm) with excitation at 449 nm, but is almost nonfluorescent in water (Φf=0.037, λem=616 nm), similarly to DBD-IA (Φf=0.91, λem=520 nm in n-hexane; Φf=0.027, λem=616 nm in water). A similar variation in fluorescence properties was also observed for DBSeD-IA (Φf=0.24, λem=591 nm in n-hexane; Φf=0.0046, λem=672 nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time-resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD-IA and DBSeD-IA. In addition, DBThD-IA exhibits a 10-fold higher photostability in aqueous solution than the original fluorophore DBD-IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry.

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