title: Environment-sensitive fluorophores with benzothiadiazole and benzoselenadiazole structures as candidate components of a fluorescent polymeric thermometer.
abstract: An environment-sensitive fluorophore can change its maximum emission wavelength (λ(em)), fluorescence quantum yield (Φ(f)), 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in which the oxygen atom of a well-established 2,1,3-benzoxadiazole environment-sensitive fluorophore, DBD-IA, has been replaced by a sulfur and selenium atom, respectively.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 (Φ(f) =0.81, λ(em) =537 nm) with excitation at 449 nm, but is almost nonfluorescent in water (Φ(f) =0.037, λ(em) =616 nm), similarly to DBD-IA (Φ(f) =0.91, λ(em) =520 nm in n-hexane; Φ(f) =0.027, λ(em) =616 nm in water). A similar variation in fluorescence properties was also observed for DBSeD-IA (Φ(f) =0.24, λ(em) =591 nm in n-hexane; Φ(f) =0.0046, λ(em) =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.
authors: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. seiichi@mol.f.u-tokyo.ac.jp
authors: Seiichi
authors: S
authors: Uchiyama
authors: Kohki
authors: K
authors: Kimura
authors: Chie
authors: C
authors: Gota
authors: Kohki
authors: K
authors: Okabe
authors: Kyoko
authors: K
authors: Kawamoto
authors: Noriko
authors: N
authors: Inada
authors: Toshitada
authors: T
authors: Yoshihara
authors: Seiji
authors: S
authors: Tobita
mesh_terms: D001393:Azoles / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D016566:Organoselenium Compounds / Q000737:chemistry*; D055668:Photochemical Processes; D013830:Thiadiazoles / Q000737:chemistry*
chemical_list: D001393:Azoles; D005456:Fluorescent Dyes; D016566:Organoselenium Compounds; D013830:Thiadiazoles; C042817:piaselenole; C015700:benzo-1,2,3-thiadiazole