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Environment‐Sensitive Fluorophores with Benzothiadiazole and Benzoselenadiazole Structures as Candidate Components of a Fluorescent Polymeric Thermometer
Author(s) -
Uchiyama Seiichi,
Kimura Kohki,
Gota Chie,
Okabe Kohki,
Kawamoto Kyoko,
Inada Noriko,
Yoshihara Toshitada,
Tobita Seiji
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200597
Subject(s) - fluorophore , fluorescence , photochemistry , quantum yield , chemistry , intersystem crossing , excited state , aqueous solution , fluorescence in the life sciences , solvent , materials science , analytical chemistry (journal) , organic chemistry , singlet state , optics , physics , nuclear physics
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in which the oxygen atom of a well‐established 2,1,3‐benzoxadiazole environment‐sensitive fluorophore, DBD‐IA, has been replaced by a sulfur and selenium atom, respectively.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.