5 BODIPY Dyes and Their Analogues
195
equation, k f is proportional to the integral of the molar extinction coefficient curve.
Thus, low ε values decrease the k f value, and consequently, the Φ f value decreases.
Because the S 0 to S 1 transition of 201 is predicted to be forbidden by the TDDFT
calculation (f = 0.00), the nonfluorescent property of the quinoid-type bisboron
complexes is probably because of the forbidden S 0 to S 1 transition that significantly
decreases the k f values. The cyclic voltammograms indicate that bisboron complex
201 is reduced to the corresponding aromatic dianion. The dianion and monoanion
of 201 show λ max at 414 and 520 nm, respectively. Although TDDFT results indicate
that the monoanion has λ max at 870 nm, NIR absorption is not observed because
of the limitations of the measuring instruments. The dianion of 201 has a benzene1,4-diol-based bisboron structure with two aromatic pyrrole moieties. The fact that
the S 0 to S 1 transition of the dianion is allowed predicts that it may show fluorescence because benzene-1,4-diol-based bisboron complexes 202, 204, and 205 show
fluorescence.
Benzene-1,4-diol-based bisboron complex 202 shows broad absorption at 461 nm
and fluorescence both in solution and the thin film state (Fig. 5.71a) (Zhang et al.
2009b). Bisboron complex 202 (T d5 = 378 °C) has a higher decomposition temperature with a 5% weight loss (T d5 ) compared to the corresponding monoboron complex
(T d5 = 247 °C). Simple double layer EL devices fabricated using 202 as both the
emitter and electron-transporting layers display good performance. Pyrene-based
bisboron complex 203 shows red fluorescence in the solid-state and behaves as
both an emitting and electron-transporting material in OLEDs (Fig. 5.71b) (Zhou
et al. 2010). In the benzene-1,4-diol-based bisboron complexes 204 and 205, the
two phenyl groups coordinated to each boron atom effectively keep the fluorophores
apart in the solid-state (Fig. 5.71c) (Li et al. 2011). Thus, bisboron complexes 204
and 205 exhibit solid-state fluorescence. OLEDs employing 204 or 205 as non-doped
emitters exhibit red and NIR electroluminescence. Salicylaldimine-based bisboron
complex 207 shows redshifted λ max compared with that of the structural isomer 206
(Fig. 5.71d) (Frath et al. 2016).
The photophysical properties of bis(boranil) complexes 208–210 can be easily
tuned in a wide range by variation of substituents (Fig. 5.72a) (Urban et al. 2017).
BF 2 –bridged azafulvene dimers are reported to be strong electron-accepting units
(Fig. 5.72b). Introduction of electron-donating groups enables the formation of D–
A–D chromophores to provide the intense NIR absorption (Shimogawa et al. 2018).
Especially, 213 with strong electron-donating groups shows an absorption maximum
at 922 nm in DCM, 914 nm in 1 wt% PMMA films, and 1066 and 1174 nm in neat
films. Because of the low-lying LUMO and moderate HOMO levels, BF 2 -bridged
azafulvene dimer 213 has a high photostability and strong resistance to oxidation.
Boron-fused double (Li et al. 2017a) helicene 214 shows two reversible reductions
and a low LUMO energy (Fig. 5.72c). It has been employed as a cathode active
material in lithium ion batteries and has shown moderate performance, capacity, and
cycle stability (Oda et al. 2019).
For OˆO type bisboron complexes, Ono et al. reported DHND-BF 2 (Ono et al.
2009) and QA-BF 2 (Moriya et al. 2019). DHND-BF 2 is the BF 2 complex of 6,11dihydroxy-5,12-naphthacenedione (DHND). The T d5 of DHND-BF 2 (325 °C) is
195
equation, k f is proportional to the integral of the molar extinction coefficient curve.
Thus, low ε values decrease the k f value, and consequently, the Φ f value decreases.
Because the S 0 to S 1 transition of 201 is predicted to be forbidden by the TDDFT
calculation (f = 0.00), the nonfluorescent property of the quinoid-type bisboron
complexes is probably because of the forbidden S 0 to S 1 transition that significantly
decreases the k f values. The cyclic voltammograms indicate that bisboron complex
201 is reduced to the corresponding aromatic dianion. The dianion and monoanion
of 201 show λ max at 414 and 520 nm, respectively. Although TDDFT results indicate
that the monoanion has λ max at 870 nm, NIR absorption is not observed because
of the limitations of the measuring instruments. The dianion of 201 has a benzene1,4-diol-based bisboron structure with two aromatic pyrrole moieties. The fact that
the S 0 to S 1 transition of the dianion is allowed predicts that it may show fluorescence because benzene-1,4-diol-based bisboron complexes 202, 204, and 205 show
fluorescence.
Benzene-1,4-diol-based bisboron complex 202 shows broad absorption at 461 nm
and fluorescence both in solution and the thin film state (Fig. 5.71a) (Zhang et al.
2009b). Bisboron complex 202 (T d5 = 378 °C) has a higher decomposition temperature with a 5% weight loss (T d5 ) compared to the corresponding monoboron complex
(T d5 = 247 °C). Simple double layer EL devices fabricated using 202 as both the
emitter and electron-transporting layers display good performance. Pyrene-based
bisboron complex 203 shows red fluorescence in the solid-state and behaves as
both an emitting and electron-transporting material in OLEDs (Fig. 5.71b) (Zhou
et al. 2010). In the benzene-1,4-diol-based bisboron complexes 204 and 205, the
two phenyl groups coordinated to each boron atom effectively keep the fluorophores
apart in the solid-state (Fig. 5.71c) (Li et al. 2011). Thus, bisboron complexes 204
and 205 exhibit solid-state fluorescence. OLEDs employing 204 or 205 as non-doped
emitters exhibit red and NIR electroluminescence. Salicylaldimine-based bisboron
complex 207 shows redshifted λ max compared with that of the structural isomer 206
(Fig. 5.71d) (Frath et al. 2016).
The photophysical properties of bis(boranil) complexes 208–210 can be easily
tuned in a wide range by variation of substituents (Fig. 5.72a) (Urban et al. 2017).
BF 2 –bridged azafulvene dimers are reported to be strong electron-accepting units
(Fig. 5.72b). Introduction of electron-donating groups enables the formation of D–
A–D chromophores to provide the intense NIR absorption (Shimogawa et al. 2018).
Especially, 213 with strong electron-donating groups shows an absorption maximum
at 922 nm in DCM, 914 nm in 1 wt% PMMA films, and 1066 and 1174 nm in neat
films. Because of the low-lying LUMO and moderate HOMO levels, BF 2 -bridged
azafulvene dimer 213 has a high photostability and strong resistance to oxidation.
Boron-fused double (Li et al. 2017a) helicene 214 shows two reversible reductions
and a low LUMO energy (Fig. 5.72c). It has been employed as a cathode active
material in lithium ion batteries and has shown moderate performance, capacity, and
cycle stability (Oda et al. 2019).
For OˆO type bisboron complexes, Ono et al. reported DHND-BF 2 (Ono et al.
2009) and QA-BF 2 (Moriya et al. 2019). DHND-BF 2 is the BF 2 complex of 6,11dihydroxy-5,12-naphthacenedione (DHND). The T d5 of DHND-BF 2 (325 °C) is