5 BODIPY Dyes and Their Analogues
183
2002). When the starting phthalonitriles do not belong to the C 2v symmetry group,
SubPcs are formed as a mixture of C 1 and C 3 isomers; each of these isomers is a
racemic mixture of enantiomers (Claessens et al. 2002). The halogen atom in the
axial position can be easily displaced by oxygen, sulfur, nitrogen, and carbon nucleophiles (Guilleme et al. 2011). Kobayashi et al. reported the synthesis of unsymmetrical phthalocyanines by the reaction of the structurally distorted SubPc with 1,3diiminoisoindoline derivatives (Kobayashi et al. 1990). 167 shows a blueshifted Soret
band (B transition) (λ max = 307 nm, ε = ca. 40,000) and Q band (λ max = 565 nm, ε =
88,600) compared with those of phthalocyanines (Fulford et al. 2012). The blueshift
is due to the reduction in the number of π-electrons in the aromatic circuit from 18π
(phthalocyanines) to 14π (SubPcs) (Claessens et al. 2014). The relatively lower ε
value of SubPcs compared with that of phthalocyanines may be due to the nonplanar
structure. Although axial substituents have little effect on λ max , peripheral donor and
acceptor substituents tend to shift the Q band towards longer wavelengths (Claessens
et al. 2014). C 3 -Symmetric SubPc having peripheral nitro and tert-butyl groups is
resolved into two enantiomeric isomers by using an optically active HPLC column,
and their circular dichroism (CD) spectra are measured (Kobayashi and Nonomura
2002). Generally, SubPcs show a very small Stokes shift (typically around 10–15 nm),
and the Φ f values are typically around 0.2–0.5 (Claessens et al. 2014).
Subporphyrazine (SubPz), which is also called subtriazaporphyrin (SubTAP), is
less studied compared to SubPc (Fig. 5.62b) (Claessens et al. 2002, 2014; Shimizu
and Kobayashi 2014). In 2005, Torres et al. reported the synthesis of SubPzs by
a boron template cyclotrimerization of maleonitriles, which is a synthetic method
similar to that of SubPcs (Rodríuez-Morgade et al. 2005). 168 shows two intense
absorption bands at λ max = 295 (ε = 38,000) and 501 nm (ε = 40,000) corresponding to the Soret and Q transitions, respectively (Rodríuez-Morgade et al.
2005). SubPzs tend to show low Φ f values (typically less than 0.05) (Higashino
et al. 2013). Ring-fused SubPzs such as tri(benzo[b]thiopheno)subporphyrazine
(BTSubPz) (Shang et al. 2014), subazaphenalenephthalocyanine (SubAPPc) (Zhu
et al. 2010), and subnaphthalocyanine (SubNc) (Rauschnabel and Hanack 1995)
have also been reported.
Subtriazachlorin (SubTAC), which is sp
3 -hybridized SubPz, shows markedly split
Q bands which consist of a sharp band at 561 nm (ε = ca. 50,000) and a weak band
at 383 nm (ε = ca. 8,000) (Fig. 5.62c) (Shimizu et al. 2012). The low intensity of
the higher-energy Q band (λ max = 383 nm) can be ascribed to the configuration
interaction between the energetically close Soret band transition (λ max = 300 nm)
and the higher-energy Q band transition. Because the Q band absorptions mainly
comprise transitions from the HOMO to the LUMO and LUMO + 1, the observed
split nature of the Q band absorptions of SubTAC is considered to be due to the
non-degeneration of the LUMO and LUMO + 1 (Shimizu and Kobayashi 2014).
In 2006, Osuka et al. reported the first synthesis of benzosubporphyrin (BzSubP)
by the thermal self-condensation of 2-(3-oxo-2,3-dihydro-1H-isoindol-1-yl)acetic
acid in the presence of boric acid as a template (Inokuma et al. 2006). 169 has a
bowl-shaped geometry, and the depth of the bowl, which is defined as the distance
from the lowest edge of the macrocycle to the boron atom, is 2.33 Å. 169 shows a
183
2002). When the starting phthalonitriles do not belong to the C 2v symmetry group,
SubPcs are formed as a mixture of C 1 and C 3 isomers; each of these isomers is a
racemic mixture of enantiomers (Claessens et al. 2002). The halogen atom in the
axial position can be easily displaced by oxygen, sulfur, nitrogen, and carbon nucleophiles (Guilleme et al. 2011). Kobayashi et al. reported the synthesis of unsymmetrical phthalocyanines by the reaction of the structurally distorted SubPc with 1,3diiminoisoindoline derivatives (Kobayashi et al. 1990). 167 shows a blueshifted Soret
band (B transition) (λ max = 307 nm, ε = ca. 40,000) and Q band (λ max = 565 nm, ε =
88,600) compared with those of phthalocyanines (Fulford et al. 2012). The blueshift
is due to the reduction in the number of π-electrons in the aromatic circuit from 18π
(phthalocyanines) to 14π (SubPcs) (Claessens et al. 2014). The relatively lower ε
value of SubPcs compared with that of phthalocyanines may be due to the nonplanar
structure. Although axial substituents have little effect on λ max , peripheral donor and
acceptor substituents tend to shift the Q band towards longer wavelengths (Claessens
et al. 2014). C 3 -Symmetric SubPc having peripheral nitro and tert-butyl groups is
resolved into two enantiomeric isomers by using an optically active HPLC column,
and their circular dichroism (CD) spectra are measured (Kobayashi and Nonomura
2002). Generally, SubPcs show a very small Stokes shift (typically around 10–15 nm),
and the Φ f values are typically around 0.2–0.5 (Claessens et al. 2014).
Subporphyrazine (SubPz), which is also called subtriazaporphyrin (SubTAP), is
less studied compared to SubPc (Fig. 5.62b) (Claessens et al. 2002, 2014; Shimizu
and Kobayashi 2014). In 2005, Torres et al. reported the synthesis of SubPzs by
a boron template cyclotrimerization of maleonitriles, which is a synthetic method
similar to that of SubPcs (Rodríuez-Morgade et al. 2005). 168 shows two intense
absorption bands at λ max = 295 (ε = 38,000) and 501 nm (ε = 40,000) corresponding to the Soret and Q transitions, respectively (Rodríuez-Morgade et al.
2005). SubPzs tend to show low Φ f values (typically less than 0.05) (Higashino
et al. 2013). Ring-fused SubPzs such as tri(benzo[b]thiopheno)subporphyrazine
(BTSubPz) (Shang et al. 2014), subazaphenalenephthalocyanine (SubAPPc) (Zhu
et al. 2010), and subnaphthalocyanine (SubNc) (Rauschnabel and Hanack 1995)
have also been reported.
Subtriazachlorin (SubTAC), which is sp
3 -hybridized SubPz, shows markedly split
Q bands which consist of a sharp band at 561 nm (ε = ca. 50,000) and a weak band
at 383 nm (ε = ca. 8,000) (Fig. 5.62c) (Shimizu et al. 2012). The low intensity of
the higher-energy Q band (λ max = 383 nm) can be ascribed to the configuration
interaction between the energetically close Soret band transition (λ max = 300 nm)
and the higher-energy Q band transition. Because the Q band absorptions mainly
comprise transitions from the HOMO to the LUMO and LUMO + 1, the observed
split nature of the Q band absorptions of SubTAC is considered to be due to the
non-degeneration of the LUMO and LUMO + 1 (Shimizu and Kobayashi 2014).
In 2006, Osuka et al. reported the first synthesis of benzosubporphyrin (BzSubP)
by the thermal self-condensation of 2-(3-oxo-2,3-dihydro-1H-isoindol-1-yl)acetic
acid in the presence of boric acid as a template (Inokuma et al. 2006). 169 has a
bowl-shaped geometry, and the depth of the bowl, which is defined as the distance
from the lowest edge of the macrocycle to the boron atom, is 2.33 Å. 169 shows a