156
Y. Kubota
λ max with a considerable decrease in the ε value. The Φ f of 47 also decreases with
increasing solvent polarity (cyclohexane: Φ f = 0.32, toluene: Φ f = 0.04, DCM <
0.001). Pyridone-, benzoindole-, and benzodithiophene-fused BODIPY dyes have
also been reported (48 (Didukh et al. 2019): λ max = 623 nm, 49 (Sarma et al. 2013):
λ max = 727 nm, 50 (Heyer et al. 2014): λ max = 655 nm, respectively) (Fig. 5.38b).
Other types of ring-fused BODIPY based on naphthalene (Yang et al. 2015; Ni
et al. 2016a), dihydronaphthalene (Wang et al. 2010), perylene (Jiao et al. 2011b),
anthracene (Zeng et al. 2011), coumarin (Bochkov et al. 2013), porphyrin (Jiao et al.
2011c), and others (Gobo et al. 2016; Wu et al. 2017a) have been reported.
Optical properties of ring-fused aza-BODIPY
Benzo[a]-fused aza-BODIPY 51 (Lu et al. 2011) shows a 71-nm redshifted λ max
compared with the corresponding BODIPY dye 18 (Figs. 5.34b and 5.39a). Incorporation of the dimethylamino group quenches the fluorescence in polar solvents (52
(Lu et al. 2011): F max = 830 nm, Φ f = 0.01 in DCM, F max = 796 nm, Φ f = 0.10 in
hexane) and results in a ratiometric pH response. The addition of TFA to a DCM of
52 leads to the formation of monoprotonated species (λ max = 771 nm) along with a
decrease in the absorption intensity. Further sequential addition of TFA causes the
quantitative formation of diprotonated species (λ max = 724 nm, F max = 745 nm) with
a gradual increase in the fluorescence intensity. 1,2-Naphtho[a]-fused aza-BODIPY
53 (Lu et al. 2011) shows more redshifted λ max .
Aza-BODIPY derivative 54 (Díaz-Moscoso et al. 2014) has a significantly
blueshifted λ max (439 nm) (Fig. 5.39b). Pyrazine-fused aza-BODIPY 55 (Liu et al.
2011) (λ max = 685 nm) shows a hypsochromic shift compared with 51 (Fig. 5.39c).
The pyrazine-fused derivative 55 can be used as a selective colorimetric and fluorometric sensor for NH 4
+ ; the addition of NH 4
+ to a THF solution of 55 results in
fluorescence quenching and an obvious colorimetric change from green to red-pink
probably because of the formation of H-aggregates.
Benzo[c,d]indole-based aza-BODIPY dyes with two fluorine atoms on the boron
atom 56 (λ max = 539 nm) show blueshifted λ max compared with that of the corresponding phenyl derivative 57 (λ max = 602 nm) (Fig. 5.39d) (Shimizu et al. 2015).
Thiophene-fused aza-BODIPY dyes (58: λ max = 767 nm, 59: λ max = 788 nm) show
sharp and intense absorption bands in the NIR region with very low absorptions in
the visible region (Fig. 5.39e) (Wu et al. 2014).
Phenanthrene-[a]-fused azaBODIPY 60 (Sheng et al. 2017a) (λ max = 745 nm)
has a near planar structure in the crystalline state and absorbs and fluoresces strongly
above 700 nm with excellent photostability (Fig. 5.39f). Phenanthrene-[b]-fused azaBODIPY 61 (Sheng et al. 2017b) (λ max = 804 nm) shows narrow absorption and
fluorescence band selectivity in the NIR region, large extinction coefficients, good
thermostability, and p-type transport character (hole mobility = 0.018 cm
2 V
−1 s
−1 ).
Annularly fused aza-BODIPY 62 (Sheng et al. 2018) has a wave conformation due
to the steric hindrance among the peripheral methoxy groups in the crystalline state.
Aza-BODIPY 62 (λ max = 878 nm) shows excellent spectral selectivity in the NIR
region (negligible absorption between 300 and 700 nm) with a narrow absorption
band, large extinction coefficient, and high photostability.
Y. Kubota
λ max with a considerable decrease in the ε value. The Φ f of 47 also decreases with
increasing solvent polarity (cyclohexane: Φ f = 0.32, toluene: Φ f = 0.04, DCM <
0.001). Pyridone-, benzoindole-, and benzodithiophene-fused BODIPY dyes have
also been reported (48 (Didukh et al. 2019): λ max = 623 nm, 49 (Sarma et al. 2013):
λ max = 727 nm, 50 (Heyer et al. 2014): λ max = 655 nm, respectively) (Fig. 5.38b).
Other types of ring-fused BODIPY based on naphthalene (Yang et al. 2015; Ni
et al. 2016a), dihydronaphthalene (Wang et al. 2010), perylene (Jiao et al. 2011b),
anthracene (Zeng et al. 2011), coumarin (Bochkov et al. 2013), porphyrin (Jiao et al.
2011c), and others (Gobo et al. 2016; Wu et al. 2017a) have been reported.
Optical properties of ring-fused aza-BODIPY
Benzo[a]-fused aza-BODIPY 51 (Lu et al. 2011) shows a 71-nm redshifted λ max
compared with the corresponding BODIPY dye 18 (Figs. 5.34b and 5.39a). Incorporation of the dimethylamino group quenches the fluorescence in polar solvents (52
(Lu et al. 2011): F max = 830 nm, Φ f = 0.01 in DCM, F max = 796 nm, Φ f = 0.10 in
hexane) and results in a ratiometric pH response. The addition of TFA to a DCM of
52 leads to the formation of monoprotonated species (λ max = 771 nm) along with a
decrease in the absorption intensity. Further sequential addition of TFA causes the
quantitative formation of diprotonated species (λ max = 724 nm, F max = 745 nm) with
a gradual increase in the fluorescence intensity. 1,2-Naphtho[a]-fused aza-BODIPY
53 (Lu et al. 2011) shows more redshifted λ max .
Aza-BODIPY derivative 54 (Díaz-Moscoso et al. 2014) has a significantly
blueshifted λ max (439 nm) (Fig. 5.39b). Pyrazine-fused aza-BODIPY 55 (Liu et al.
2011) (λ max = 685 nm) shows a hypsochromic shift compared with 51 (Fig. 5.39c).
The pyrazine-fused derivative 55 can be used as a selective colorimetric and fluorometric sensor for NH 4
+ ; the addition of NH 4
+ to a THF solution of 55 results in
fluorescence quenching and an obvious colorimetric change from green to red-pink
probably because of the formation of H-aggregates.
Benzo[c,d]indole-based aza-BODIPY dyes with two fluorine atoms on the boron
atom 56 (λ max = 539 nm) show blueshifted λ max compared with that of the corresponding phenyl derivative 57 (λ max = 602 nm) (Fig. 5.39d) (Shimizu et al. 2015).
Thiophene-fused aza-BODIPY dyes (58: λ max = 767 nm, 59: λ max = 788 nm) show
sharp and intense absorption bands in the NIR region with very low absorptions in
the visible region (Fig. 5.39e) (Wu et al. 2014).
Phenanthrene-[a]-fused azaBODIPY 60 (Sheng et al. 2017a) (λ max = 745 nm)
has a near planar structure in the crystalline state and absorbs and fluoresces strongly
above 700 nm with excellent photostability (Fig. 5.39f). Phenanthrene-[b]-fused azaBODIPY 61 (Sheng et al. 2017b) (λ max = 804 nm) shows narrow absorption and
fluorescence band selectivity in the NIR region, large extinction coefficients, good
thermostability, and p-type transport character (hole mobility = 0.018 cm
2 V
−1 s
−1 ).
Annularly fused aza-BODIPY 62 (Sheng et al. 2018) has a wave conformation due
to the steric hindrance among the peripheral methoxy groups in the crystalline state.
Aza-BODIPY 62 (λ max = 878 nm) shows excellent spectral selectivity in the NIR
region (negligible absorption between 300 and 700 nm) with a narrow absorption
band, large extinction coefficient, and high photostability.