Blue Fluorescence from BF2 Complexes of N,O-Benzamide Ligands

Synthesis, Structure, and Photophysical Properties

Minoru Yamaji, Shin Ichiro Kato, Kazuhiro Tomonari, Michitaka Mamiya, Kenta Goto, Hideki Okamoto, Yosuke Nakamura, Fumito Tani

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Small molecules having intense luminescence properties are required to promote biological and organic material applications. We prepared five types of benzamides having pyridine, pyridazine, pyrazine, and pyrimidine rings and successfully converted them into three types of the difluoroboronated complexes, Py@BAs, as novel blue fluorophores. Py@BA having a pyridine moiety (2-Py@BA) showed no fluorescence in solution, whereas Py@BAs of pyridazine and pyrazine moieties (2,3-Py@BA and 2,5-Py@BA, respectively) emitted blue fluorescence with quantum yields of ca. 0.1. Transient absorption measurements using laser flash photolysis of the Py@BAs revealed the triplet formation of 2,3- and 2,5-Py@BAs, while little transient signal was observed for 2-Py@BA. Therefore, the deactivation processes from the lowest excited singlet state of fluorescent 2,3- and 2,5-Py@BAs consist of fluorescence and intersystem crossing to the triplet state while that of the nonfluorescent Py@BA is governed almost entirely by internal conversion to the ground state. Conversely, in the solid state, 2-Py@BA emitted intense fluorescence with a fluorescence quantum yield as high as 0.66, whereas 2,3- and 2,5-Py@BAs showed fluorescence with quantum yields of ca. 0.2. The crystal structure of 2-Py@BA took a herringbone packing motif, whereas those for 2,3- and 2,5-Py@BAs were two-dimensional sheetlike. On the basis of the difference in crystal structures, the emission mechanism in the solid state was discussed.

Original languageEnglish
Pages (from-to)12514-12519
Number of pages6
JournalInorganic Chemistry
Volume56
Issue number20
DOIs
Publication statusPublished - Oct 16 2017

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Fluorescence
Ligands
fluorescence
ligands
Quantum yield
synthesis
Pyrazines
pyrazines
pyridines
Crystal structure
Benzamides
solid state
crystal structure
Fluorophores
Photolysis
internal conversion
pyrimidines
organic materials
Excited states
deactivation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Blue Fluorescence from BF2 Complexes of N,O-Benzamide Ligands : Synthesis, Structure, and Photophysical Properties. / Yamaji, Minoru; Kato, Shin Ichiro; Tomonari, Kazuhiro; Mamiya, Michitaka; Goto, Kenta; Okamoto, Hideki; Nakamura, Yosuke; Tani, Fumito.

In: Inorganic Chemistry, Vol. 56, No. 20, 16.10.2017, p. 12514-12519.

Research output: Contribution to journalArticle

Yamaji, Minoru ; Kato, Shin Ichiro ; Tomonari, Kazuhiro ; Mamiya, Michitaka ; Goto, Kenta ; Okamoto, Hideki ; Nakamura, Yosuke ; Tani, Fumito. / Blue Fluorescence from BF2 Complexes of N,O-Benzamide Ligands : Synthesis, Structure, and Photophysical Properties. In: Inorganic Chemistry. 2017 ; Vol. 56, No. 20. pp. 12514-12519.
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AU - Mamiya, Michitaka

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AU - Nakamura, Yosuke

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AB - Small molecules having intense luminescence properties are required to promote biological and organic material applications. We prepared five types of benzamides having pyridine, pyridazine, pyrazine, and pyrimidine rings and successfully converted them into three types of the difluoroboronated complexes, Py@BAs, as novel blue fluorophores. Py@BA having a pyridine moiety (2-Py@BA) showed no fluorescence in solution, whereas Py@BAs of pyridazine and pyrazine moieties (2,3-Py@BA and 2,5-Py@BA, respectively) emitted blue fluorescence with quantum yields of ca. 0.1. Transient absorption measurements using laser flash photolysis of the Py@BAs revealed the triplet formation of 2,3- and 2,5-Py@BAs, while little transient signal was observed for 2-Py@BA. Therefore, the deactivation processes from the lowest excited singlet state of fluorescent 2,3- and 2,5-Py@BAs consist of fluorescence and intersystem crossing to the triplet state while that of the nonfluorescent Py@BA is governed almost entirely by internal conversion to the ground state. Conversely, in the solid state, 2-Py@BA emitted intense fluorescence with a fluorescence quantum yield as high as 0.66, whereas 2,3- and 2,5-Py@BAs showed fluorescence with quantum yields of ca. 0.2. The crystal structure of 2-Py@BA took a herringbone packing motif, whereas those for 2,3- and 2,5-Py@BAs were two-dimensional sheetlike. On the basis of the difference in crystal structures, the emission mechanism in the solid state was discussed.

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