5 BODIPY Dyes and Their Analogues
167
value of the iodine derivative (R = I: ε = 15,400) is higher than that in the nonsubstituted derivative (99: ε = 6,600) maybe because of the electron-donating ability
of iodine. Introduction of iodine atoms does not lead to a large decrease in fluorescence quantum yield in solution (BODIQPy: 99: Φ f > 0.99, R = I: Φ f = 0.73).
The suppressed heavy atom effect is probably due to the strong electron-withdrawing
ability of the BODIQPy core. In the solid-state, the interactions between the carbonyl
oxygen and iodine enhance intermolecular interaction, which results in a decrease
in the Φ f value (BODIQPy: 99: Φ f = 0.60, R = I: Φ f = 0.02).
In the
5 NˆN type monoboron complexes, gelation-assisted piezochromism of
boron 2-(2
-pyridyl)imidazole complexes (BOPIMs) (Wang et al. 2017), dual emission of isoquinolinyl–pyrazolate boron complexes (Chen et al. 2019), EL properties of pyridyl–indolate-based (Liu et al. 2005b) and pyridyl–pyrrolide-based (Chen
et al. 2005) boron complexes, and solid-state fluorescence of BF 2 complexes of
dipyrrolylquinoxaline (BPQs) (Yu et al. 2015) are also reported.
For the
7 NˆN type monoboron complexes, 3H-pyrrolizine fused diazaborepin
DAB was synthesized in 2016 (Fig. 5.47h) (Li et al. 2016). In 2019, borondifluoride3,3-dimethyl-2-[2-(2-pyrrolyl)ethenyl] indoles (BOPYINs), simplified as DAB,
were also synthesized by Knoevenagel condensation of the 3H-indolium salt with
2-formylpyrrole followed by coordination with BF 3 ·OEt 2 (Zhang et al. 2019). In
the crystal form, 100 and 101 possess a nonplanar saddle-shape structure. When
compared with five (BOIMPY and BOPIM)-, six (BODIPY and aza-BODIPY)-,
and seven (DAB and BOPYIN)-membered ring NˆN boron complexes, the bond
angle of the N···B–N bond increases with the number of atoms in the core ring
based on Baeyer strain theory; 7-membered: ca. 110° > 6-membered: ca. 106° >
5-membered: ca. 96°. DAB and BOPYINs show a relatively larger Stokes shift.
Confocal images reveal BOPYINs are predominantly located in the perinuclear area
probably because of endocytic vesicles.
5.2.5 OˆO Type Organoboron Complex
Difluoroboron β-diketonates (BF 2 bdks) including difluoroboron dibenzoylmethane
(dbm) derivatives have received considerable attention because of their high fluorescence quantum yields, tuneable fluorescent properties, two-photon-excited fluorescence (TPEF) properties, mechanofluorochromic (MFC) properties, and room
temperature phosphorescence (RTP) properties (Fig. 5.48a) (Tanaka and Chujo 2015;
Chen et al. 2017a). Although BF 2 bdk was firstly reported in 1924 (Morgan and
Tunstall 1924), it did not attract much attention until recently. BF 2 bdks have high
stability towards oxygen and moisture. The absorption and fluorescence spectra of
BF 2 bdks tend to broaden, compared with those of BODIPY dyes in solution, probably because of the flexible structure of BF 2 bdks. Different from BODIPY dyes,
BF 2 bdks often show solid-state fluorescence.
167
value of the iodine derivative (R = I: ε = 15,400) is higher than that in the nonsubstituted derivative (99: ε = 6,600) maybe because of the electron-donating ability
of iodine. Introduction of iodine atoms does not lead to a large decrease in fluorescence quantum yield in solution (BODIQPy: 99: Φ f > 0.99, R = I: Φ f = 0.73).
The suppressed heavy atom effect is probably due to the strong electron-withdrawing
ability of the BODIQPy core. In the solid-state, the interactions between the carbonyl
oxygen and iodine enhance intermolecular interaction, which results in a decrease
in the Φ f value (BODIQPy: 99: Φ f = 0.60, R = I: Φ f = 0.02).
In the
5 NˆN type monoboron complexes, gelation-assisted piezochromism of
boron 2-(2
-pyridyl)imidazole complexes (BOPIMs) (Wang et al. 2017), dual emission of isoquinolinyl–pyrazolate boron complexes (Chen et al. 2019), EL properties of pyridyl–indolate-based (Liu et al. 2005b) and pyridyl–pyrrolide-based (Chen
et al. 2005) boron complexes, and solid-state fluorescence of BF 2 complexes of
dipyrrolylquinoxaline (BPQs) (Yu et al. 2015) are also reported.
For the
7 NˆN type monoboron complexes, 3H-pyrrolizine fused diazaborepin
DAB was synthesized in 2016 (Fig. 5.47h) (Li et al. 2016). In 2019, borondifluoride3,3-dimethyl-2-[2-(2-pyrrolyl)ethenyl] indoles (BOPYINs), simplified as DAB,
were also synthesized by Knoevenagel condensation of the 3H-indolium salt with
2-formylpyrrole followed by coordination with BF 3 ·OEt 2 (Zhang et al. 2019). In
the crystal form, 100 and 101 possess a nonplanar saddle-shape structure. When
compared with five (BOIMPY and BOPIM)-, six (BODIPY and aza-BODIPY)-,
and seven (DAB and BOPYIN)-membered ring NˆN boron complexes, the bond
angle of the N···B–N bond increases with the number of atoms in the core ring
based on Baeyer strain theory; 7-membered: ca. 110° > 6-membered: ca. 106° >
5-membered: ca. 96°. DAB and BOPYINs show a relatively larger Stokes shift.
Confocal images reveal BOPYINs are predominantly located in the perinuclear area
probably because of endocytic vesicles.
5.2.5 OˆO Type Organoboron Complex
Difluoroboron β-diketonates (BF 2 bdks) including difluoroboron dibenzoylmethane
(dbm) derivatives have received considerable attention because of their high fluorescence quantum yields, tuneable fluorescent properties, two-photon-excited fluorescence (TPEF) properties, mechanofluorochromic (MFC) properties, and room
temperature phosphorescence (RTP) properties (Fig. 5.48a) (Tanaka and Chujo 2015;
Chen et al. 2017a). Although BF 2 bdk was firstly reported in 1924 (Morgan and
Tunstall 1924), it did not attract much attention until recently. BF 2 bdks have high
stability towards oxygen and moisture. The absorption and fluorescence spectra of
BF 2 bdks tend to broaden, compared with those of BODIPY dyes in solution, probably because of the flexible structure of BF 2 bdks. Different from BODIPY dyes,
BF 2 bdks often show solid-state fluorescence.