5 BODIPY Dyes and Their Analogues
133
(Kee et al. 2005). Additionally, the reaction of dipyrromethenium with a base such
as NEt 3 , and 1.8-bis(dimethylamino)naphthalene, a proton sponge, followed by
reaction with (C 6 F 5 )BF 2 , (C 6 F 5 ) 2 BCl, and bromoboraanthracene derivatives, gives
BF(C 6 F 5 )-, B(C 6 F 5 ) 2 - (Bonnier et al. 2009) and spiro (Yuan et al. 2017)-BODIPY
dyes, respectively (Fig. 5.16c). However, such direct boration has rarely been studied,
probably due to the instability and unavailability of organoboranes. Recently, direct
boron complexation of dipyrrin with air and moisture stable organotrifluoroborate
potassium salts (KBF 3 R) to yield BFR-BODIPY dyes has been reported (Fig. 5.16d)
(Sawazaki et al. 2018; Wang et al. 2019).
5.2.3.4 Relationship Between Absorption and Fluorescence
Wavelengths and Structure of BODIPY
The λ max and F max values of a BODIPY dye can be controlled by modifying its
substituents. Modification of the meso-substituent on the BODIPY core is an effective approach to change the absorption and fluorescence wavelengths. Introduction of an electron-donating group such as methylamino (λ max = 419 nm, F max =
463 nm) or methoxy (λ max = 452 nm, F max = 487 nm) groups causes a notable
hypsochromic shift when compared to a meso-unsubstituted derivative (λ max =
504 nm, F max = 511 nm) (Esnal et al. 2013) (Fig. 5.17a, b, d). Although mesounsubstituted BODIPY has a cyanine-like structure, meso-methylanimo and mesomethoxy substituted BODIPY dyes receive the contribution of hemicyanine and
merocyanine resonance structures, respectively (Fig. 5.17a). The hemicyanine and
merocyanine structures are cross-conjugated, which interrupts the push–pull conjugation of the cyanine structure between the two pyrrole rings, consequently causing
a spectral blueshift (Osorio-Martínez et al. 2012). The presence of methylthio group
at the meso-position leads to a slight blueshift of λ max (495 nm) and redshift of F max
(532 nm) compared to the moso-unsubstituted derivative (Fig. 5.17c). In the methylamino, methoxy and methylthio derivatives (λ max : 419–495 nm, F max : 463–532 nm,
Φ f : 0.70–0.84), methylation at both α positions led to a spectral redshift (λ max : 439–
531 nm, F max : 485–538 nm) and enhancement of the Φ f values (Φ f : 0.95–1.00). This
Fig. 5.17 Color tuning of BODIPY dyes by the modification of meso-substituent
133
(Kee et al. 2005). Additionally, the reaction of dipyrromethenium with a base such
as NEt 3 , and 1.8-bis(dimethylamino)naphthalene, a proton sponge, followed by
reaction with (C 6 F 5 )BF 2 , (C 6 F 5 ) 2 BCl, and bromoboraanthracene derivatives, gives
BF(C 6 F 5 )-, B(C 6 F 5 ) 2 - (Bonnier et al. 2009) and spiro (Yuan et al. 2017)-BODIPY
dyes, respectively (Fig. 5.16c). However, such direct boration has rarely been studied,
probably due to the instability and unavailability of organoboranes. Recently, direct
boron complexation of dipyrrin with air and moisture stable organotrifluoroborate
potassium salts (KBF 3 R) to yield BFR-BODIPY dyes has been reported (Fig. 5.16d)
(Sawazaki et al. 2018; Wang et al. 2019).
5.2.3.4 Relationship Between Absorption and Fluorescence
Wavelengths and Structure of BODIPY
The λ max and F max values of a BODIPY dye can be controlled by modifying its
substituents. Modification of the meso-substituent on the BODIPY core is an effective approach to change the absorption and fluorescence wavelengths. Introduction of an electron-donating group such as methylamino (λ max = 419 nm, F max =
463 nm) or methoxy (λ max = 452 nm, F max = 487 nm) groups causes a notable
hypsochromic shift when compared to a meso-unsubstituted derivative (λ max =
504 nm, F max = 511 nm) (Esnal et al. 2013) (Fig. 5.17a, b, d). Although mesounsubstituted BODIPY has a cyanine-like structure, meso-methylanimo and mesomethoxy substituted BODIPY dyes receive the contribution of hemicyanine and
merocyanine resonance structures, respectively (Fig. 5.17a). The hemicyanine and
merocyanine structures are cross-conjugated, which interrupts the push–pull conjugation of the cyanine structure between the two pyrrole rings, consequently causing
a spectral blueshift (Osorio-Martínez et al. 2012). The presence of methylthio group
at the meso-position leads to a slight blueshift of λ max (495 nm) and redshift of F max
(532 nm) compared to the moso-unsubstituted derivative (Fig. 5.17c). In the methylamino, methoxy and methylthio derivatives (λ max : 419–495 nm, F max : 463–532 nm,
Φ f : 0.70–0.84), methylation at both α positions led to a spectral redshift (λ max : 439–
531 nm, F max : 485–538 nm) and enhancement of the Φ f values (Φ f : 0.95–1.00). This
Fig. 5.17 Color tuning of BODIPY dyes by the modification of meso-substituent