Chiral benzo-fused Aza-BODIPYs with optical activity extending into the NIR range

Article abstract of DOI:10.1016/j.dyepig.2016.07.039

Chiral benzo-fused aza-BODIPYs, namely N,N-difluoroboryl-[(dinaphtho[1,2-e:1′,2′-g]-1,4-dioxocine)-1-[N-(3-phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-1-ylidene)amine] (1) and N,N-difluoroboryl-[(dinaphtho[1,2-e:1′,2′-g]-1,4-dioxocine)-1-[(di

Full text of DOI:10.1016/j.dyepig.2016.07.039

Dyes and Pigments 134 (2016) 427e433
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Chiral benzo-fused Aza-BODIPYs with optical activity extending into
the NIR range
Lu Zhang, Luyang Zhao, Kang Wang, Jianzhuang Jiang*
Beijing Key Laboratory for Science and Application of Functional Molecular and Crystalline Materials, Department of Chemistry, University of Science and
Technology Beijing, Beijing 100083, China
a r t i c l e i n f o
a b s t r a c t
Chiral benzo-fused aza-BODIPYs, namely N,N-difluoroboryl-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-1-
[N-(3-phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-1-ylidene)amine] (1) and N,N-
difluoroboryl-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-1-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-N-(3-
phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-1-ylidene)amine] (2), have been synthe-
sized and spectroscopically characterized. Fusion of benzene moieties onto the BODIPY periphery in
combination with the introduction of peripheral chiral binaphthyl substituents renders the extension of
optical activity of resulting chiral benzo-fused aza-BODIPYs into the near-IR (NIR) range, representing the
first chiral BODIPYs with NIR optically activity. For comparative study, N,N-difluoroboryl-[N-(3-phenyl-
2H-isoindol-1-yl)-N-(3-phenyl-1H-isoindol-1-ylidene)amine] (0) was also prepared and characterized in
a similar manner.
Article history:
Received 29 June 2016
Received in revised form
26 July 2016
Accepted 30 July 2016
Available online 1 August 2016
Keywords:
Chirality
Aza-BODIPY
Near-infrared spectroscopy
© 2016 Elsevier Ltd. All rights reserved.
1. Introduction
and in particular the cellular and in vivo biological studies due to
the minimum photo-damage to biological samples and minimum
Boron dipyrromethenes (BODIPYs) are a special class of dipyr-
rolic conjugated molecular systems that have been widely studied
and applied in the field of biochemical labeling, fluorescent sensors,
and sensitizers for solar cells and laser dyes owning to their fasci-
nating physicochemical properties such as high fluorescence
quantum yields, narrow absorption and emission bands with high
intensities, reasonably long excited singlet state lifetime, and good
solubility and stability in common organic solvent systems [1,2].
The absorption and emission properties of BODIPYs can be easily
tuned through chemical modifications over the meso-carbon atom,
fluoride atoms of the BF2-group, and BODIPY periphery and core
[3]. Actually, replacement of the meso-carbon atom in the general
BODIPY dyes by nitrogen atom in combination with the fusion of
benzene moiety onto the pyrrole moieties of BODIPY chromophore
results in the benzo-fused aza-BODIPY compounds with extended
interference from background auto-fluorescence by biomolecules
in the living systems [5].
On the other hand, chirality has been one of the most fascinating
features commonly found in nature [6]. Due to the relatively easy
investigation by means of optical techniques, various chiral dyes
including
chiral
porphyrins
and
phthalocyanines/sub-
phthalocyanines have been designed and studied [7]. This is surely
true for the chiral BODIPY derivatives with the optical activity
limited in the UVevisible range [8]. However, chiral BODIPY de-
rivatives with the optical activity extending into the NIR region still
remain unreported thus far, to the best of our knowledge.
In this paper, chiral benzo-fused aza-BODIPYs, namely N,N-
difluoroboryl-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-1-[N-(3-
phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-1-
ylidene)amine] (1) and N,N-difluoroboryl-[(dinaphtho[1,2-e:10,20-
g]-1,4-dioxocine)-1-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-N-(3-
phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-1-
ylidene)amine] (2), have been synthesized and spectroscopically
characterized. Fusion of benzene moieties onto the BODIPY
periphery in combination with the introduction of peripheral
chiral binaphthyl substituents renders the extension of optical
activity of resulting chiral benzo-fused aza-BODIPYs into the
near-IR (NIR) range, representing the first chiral BODIPYs with
p-system and appearance of the electronic absorption and emis-
sion bands in the near-infrared (NIR) range [3b,4]. This in turn
endows such kind of benzo-fused aza-BODIPY dyes great applica-
tion potentials in fiber optic telecommunication, optical imaging,
* Corresponding author.
E-mail address: jianzhuang@ustb.edu.cn (J. Jiang).
http://dx.doi.org/10.1016/j.dyepig.2016.07.039
0143-7208/© 2016 Elsevier Ltd. All rights reserved.

428
L. Zhang et al. / Dyes and Pigments 134 (2016) 427e433
NIR optically activity. For comparative study, N,N-difluoroboryl-
[N-(3-phenyl-2H-isoindol-1-yl)-N-(3-phenyl-1H-isoindol-1-
ylidene)amine] (0) was also prepared and characterized in a
similar manner.
8H, a-benzo-H, binaphthyl-H). MALDI-TOF MS: an isotopic cluster
peaking at m/z 679.40; Calculated for C48H29N3O2, 679.23. Anal.
Calcd (%) for C48H29N3O2$CH3OH: C, 82.68; H, 4.67; N, 5.90; Found:
C, 82.51; H, 4.99; N, 5.80.
2. Experimental section
2.3. Synthesis of (R)/(S)-1
2.1. General remarks
Compound (R)/(S)-1a (68 mg, 0.1 mmol) was dissolved in
dichloroethane (2 mL), then diisopropylethylamine (88
0.5 mmol) was added. The mixture was stirred for 1 h and BF3$OEt2
(63 L, 0.5 mmol) was added at room temperature. This mixture
mL,
Column chromatography was carried out on silica gel (Merck,
Kieselgel 60, 70e230 mesh) with the indicated eluents. CH2Cl2 was
freshly distilled with CaH2 under nitrogen atmosphere. All other
reagents and solvents were used as received. The compounds (R)/
(S)-benzo[b]dinaphtho[2,1-e:10,20-g] [1,4]dioxocine-2,3- dicarboni-
trile were prepared according to the literature procedure [9].
The 1H NMR spectra and 1H-1H COSY spectra were recorded on a
Bruker DPX 400 spectrometer in CDCl3 with shifts referenced to
SiMe4 (0.00 ppm). Electronic absorption spectra were recorded on a
Hitachi U-4100 spectrophotometer. MALDI-TOF mass spectra were
taken on a Bruker BIFLEX III ultra-high resolution Fourier transform
ion cyclotron resonance (FT-IR) mass spectrometer with alpha-
cyano-4-hydroxy cinnamic acid as the matrix. Elemental analyses
m
was stirred at room temperature until complete conversion of the
starting material after ca. 5 h as monitored by thin layer chroma-
tography (TLC). The reaction mixture was then quenched with
water and extracted twice with dichloromethane (100 mL). Upon
drying over anhydrous Na2SO4, the organic layer was condensed in
vacuo and the crude product was purified by column chromatog-
raphy over silica gel using CH2Cl2/petroleum ether (1:1) as the
eluent to give a green band. Recrystallization from CH2Cl2 and
MeOH provided a green solid with the yield of 51.6 mg (71%). 1H
NMR (400 MHz, (CD3)2SO):
benzo-H, binaphthyl-H), 7.54e7.59 (m, 7H, binaphthyl-H, meta-H,
para-H), 7.62e7.64 (m, 2H, -benzo-H, binaphthyl-H), 7.67 (d, 1H,
d 7.42e7.48 (m, 6H, b-benzo-H, a-
were performed on an Elementar Vavio El
Ш
elemental analyzer.
a
Steady-state fluorescence spectroscopic studies and absolute fluo-
rescent quantum yields were performed on an Edinburgh In-
struments FLS920 fluorescence spectrometer with the excitation at
650 nm. Time-resolved fluorescence lifetime experiments were
performed by the time-correlated single-photon-counting (TCSPC)
technique on an Edinburgh Instruments FLS900 fluorescence
spectrometer. Electrochemical measurements were carried out
with a BAS CV-50W voltammetric analyzer. The reference electrode
was Agþ/Ag (a solution of 0.01 M AgNO3 and 0.1 M TBAP in
acetonitrile), which was connected to the solution by a Luggin
capillary whose tip was placed close to the working electrode. It
was corrected for junction potentials by being referenced internally
to the ferrocenium/ferrocene (Fcþ/Fc) couple [E1/2(Fcþ/
Fc) ¼ 0.501 V vs. SCE].
J ¼ 8.0 Hz, binaphthyl-H), 7.69 (d, 1H, J ¼ 8.0 Hz, binaphthyl-H), 7.72
(d, 1H, J ¼ 8.0 Hz, binaphthyl-H), 7.88 (m, 4H, ortho-H), 8.00 (s, 1H,
a-benzo-H), 8.06e8.08 (m, 2H, a-benzo-H, binaphthyl-H), 8.10 (d,
1H, J ¼ 8.0 Hz, binaphthyl-H), 8.12 (d, 1H, J ¼ 8.0 Hz, binaphthyl-H),
8.15 (d, 1H, J ¼ 8.0 Hz, binaphthyl-H). MALDI-TOF MS: an isotopic
cluster peaking at m/z 727.45; Calculated for C48H28BF2N3O2,
727.22. Anal. Calcd (%) for C48H28BF2N3O2$0.5CH2Cl2: C, 75.65; H,
3.80; N, 5.46; Found: C, 75.99; H, 4.01; N, 5.78.
2.4. Synthesis of (R)/(S)-2a
By employing the above-described procedure for Synthesis of
(R)/(S)-1a with (R)/(S)-benzo[b]dinaphtho[2,1-e:10,20-g] [1,4]dioxo-
cine-2,3-dicarbonitrile (410 mg, 1 mmol) instead of (R)/(S)-benzo
[b]dinaphtho[2,1-e:10,20-g]
[1,4]dioxocine-2,3-dicarbonitrile
2.2. Synthesis of (R)/(S)-1a
(410 mg, 1 mmol) and 1,2-Dicyanobenzene (128 mg, 1 mmol) as
starting material, compound 2a was obtained as a blue solid with
the yield of 21.6 mg (4.5%). 1H NMR (400 MHz, (CD3)2SO):
Phenyl magnesium bromide (3.0 mol/L in diethyl ether, 1 mL)
was added to a suspension of (R)/(S)-benzo[b]dinaphtho[2,1-e:10,20-
g] [1,4]dioxocine-2,3-dicarbonitrile (410 mg, 1 mmol) and 1,2-
Dicyanobenzene (128 mg, 1 mmol) in anhydrous diethyl ether
(10 mL) at 0 ꢀC under nitrogen. The reaction mixture was allowed to
warm to room temperature and stirred for additional 3 h. Then the
reaction mixture was evaporated to dryness and formamide
(30 mL) was added to the reaction system under nitrogen. The re-
action mixture was further heated at 150 ꢀC for 30 min. After being
cooled to room temperature, the mixture was diluted with
dichloromethane and washed with water and saturated NaCl (aq.).
Upon drying over anhydrous Na2SO4, the organic layer was
condensed in vacuo and the crude product was purified by column
chromatography over silica gel using CH2Cl2/petroleum ether (1:1)
as the eluent to give a blue band, which was further purified using
gel chromatography with CH2Cl2 as eluent to give the first blue
band as compound 2a, then the second blue band as compound 1a,
following by the third blue band as compound 0a. The following
recrystallization from CH2Cl2 and MeOH gave 0a as dark blue
powder (23.1 mg, 3.4%), 1a as dark blue powder (21.0 mg, 3.1%), 2a
as dark blue powder (9.5 mg, 1.4%). 1a:1H NMR (400 MHz,
d
7.48e7.53 (m, 10H, binaphthyl-H, para-H), 7.61e7.63 (m, 6H,
meta-H, -benzo-H), 7.69e7.73 (m, 4H, binaphthyl-H), 7.85 (d, 2H,
J ¼ 8.0 Hz, binaphthyl-H), 7.90 (d, 2H, J ¼ 8.0 Hz, binaphthyl-H),
8.15e8.17 (m, 6H, -benzo-H, ortho-H), 8.20e8.25 (m, 8H,
a
a
binaphthyl-H). MALDI-TOF MS: an isotopic cluster peaking at m/z
961.62; Calculated for C68H39N3O4, 961.29. Anal. Calcd (%) for
C
68H39N3O4$2CH3OH: C, 81.93; H, 4.62; N, 4.09; Found: C, 81.59; H,
4.97; N, 3.95.
2.5. Synthesis of (R)/(S)-2
By employing the above-described procedure for the synthesis
of (R)/(S)-1 with compound (R)/(S)-2a (96 mg, 0.1 mmol) instead of
(R)/(S)-1a (68 mg, 0.1 mmol) as starting material, compound 2 was
obtained as green solid with the yield of 67.6 mg (67%). 1H NMR
(400 MHz, (CD3)2SO:CDCl3 ¼ 3:1):
d
7.38e7.41 (m, 4H, binaphthyl-
H), 7.45 (m, 4H, binaphthyl-H,
a-benzo-H), 7.48e7.54 (m, 4H,
binaphthyl-H), 7.57e7.58 (m, 8H, binaphthyl-H, meta-H, para-H),
7.62 (d, 2H, J ¼ 8.0 Hz, binaphthyl-H), 7.67 (d, 2H, J ¼ 8.0 Hz,
binaphthyl-H), 7.87 (d, 2H, J ¼ 8.0 Hz, ortho-H), 7.92 (s, 2H,
a-
(CD3)2SO):
d
7.43e7.52 (m, 12H, binaphthyl-H, para-H,
b-benzo-H),
benzo-H), 8.00 (d, 2H, J ¼ 8.0 Hz, binaphthyl-H), 8.04e8.07 (m, 4H,
binaphthyl-H), 8.10 (d, 2H, J ¼ 8.0 Hz, binaphthyl-H). MALDI-TOF
MS: an isotopic cluster peaking at m/z 1009.65; Calculated for
7.56e7.60 (m, 5H, meta-H,
b
-benzo-H), 7.65e7.69 (m, 4H,
a-benzo-
H, binaphthyl-H), 7.80 (d, 2H, J ¼ 8.0 Hz, binaphthyl-H), 7.86 (d, 2H,
J ¼ 8.0 Hz, binaphthyl-H), 8.10e8.12 (m, 4H, ortho-H), 8.17e8.20 (m,
C
68H38BF2N3O4,
1009.29.
Anal.
Calcd
(%)
for

L. Zhang et al. / Dyes and Pigments 134 (2016) 427e433
429
C68H38BF2N3O4$0.5CH2Cl2: C, 78.18; H, 3.74; N, 3.99; Found: C,
binaphthyl group onto the benzene moiety of the benzo-fused 3,5-
78.42; H, 3.95; N, 3.79.
diaryl aza-BODIPY skeleton, the S0/S1 band slightly red-shifts to
717 nm for 1 due to the somewhat p-
p conjugation between the
peripheral oxygen atoms and the central BODIPY chromophore
[11]. As a consequence, further incorporation of the second
binaphthyl group onto the remaining benzene ring in the molecule
of 1 leads to further red-shift of the S0/S1 band to 722 nm for 2.
The CD spectra of the chiral fluorophores 1 and 2 are also dis-
played in Fig. 1 and Fig. S7 (Supporting Information). As can be
clearly seen, perfect mirror image CD spectra are observed in the
entire absorption region for both 1 and 2. The CD intensity for both
1 and 2 reaches up to 30 ꢁ 102 deg Mꢂ1 cmꢂ1, in line with that for
traditional optical active BODIPY chromophores [12]. In detail, the
CD signals of 1S is negative in the whole electronic absorption re-
gion, with significant S0/S1 band at ca. 717 nm, and S0/S2 band at
ca. 300 nm. In a similar manner, negative significant CD signals of
2S are observed at ca. 721 nm and 302 nm, belonging to S0/S1
band and S0/S2 band, respectively. In contrast, CD signals of both
1R and 2R are positive in the whole region with significant peaks at
719 nm and 300 nm for 1R, and 723 nm and 302 nm for 2R. Similar
to the reported binaphthyl-linked phthalocyanines and sub-
phthalocyanine [13], these intense CD signals of both 1 and 2 are
induced from the peripheral chiral binaphthyl units since the
central BODIPY chromophore is achiral while the CD of binaphthyl
units appears at wavelengths shorter than ca. 260 nm. Following
the mechanism of induced optical activity, the experimental phe-
nomenon that the CD intensity of S0/S2 band is much larger than
that of the S0/S1 band could be well explained on the basis of the
3. Results and discussion
3.1. Design and synthesis
(R)/(S)-Benzo[b]dinaphtho[2,1-e:10,20-g]
[1,4]dioxocine-2,3-
dicarbonitrile were prepared following published procedure [9].
Reaction of this precursor with 1,2-dicyanobenzene in the pres-
ence of phenyl magnesium bromide in formamide at 150 ꢀC
resulted in a mixture of N-(3-phenyl-2H-isoindol-1-yl)-N-(3-
phenyl-1H-isoindol-1-ylidene)amine (0a), (dinaphtho[1,2-e:10,20-
g]-1,4-dioxocine)-1-[N-(3-phenyl-2H-isoindole-1-yl)methylene]-
3-phenyl-1H-isoindol-1-ylidene)amine (1a), and (dinaphtho[1,2-
e:10,20-g]-1,4-dioxocine)-1-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)
-N-(3-phenyl-2H-isoindole-1-yl)methylene]-3-phenyl-1H-isoindol-
1-ylidene)amine (2a), Scheme S1 (Supporting Information). Gel
chromatography with CH2Cl2 as eluent afforded pure 0a, 1a, and 2a
in the yield of 3.4, 3.1, and 1.4%, respectively. Treatment of which
with diisopropylethylamine and BF3$OEt2 gave corresponding
benzo-fused 3,5-diaryl aza-BODIPY compounds including N,N-
difluoroboryl-[N-(3-phenyl-2H-isoindol-1-yl)-N-(3-phenyl-1H-iso-
indol-1-ylidene)amine] (0), N,N-difluoroboryl-[(dinaphtho[1,2-
e:10,20-g]-1,4-dioxocine)-1-[N-(3-phenyl-2H-isoindole-1-yl)methy-
lene]-3-phenyl-1H-isoindol-1-ylidene)amine] (1), and N,N-difluor-
oboryl-[(dinaphtho[1,2-e:10,20-g]-1,4-dioxocine)-1-[(dinaphtho[1,2-
e:10,20-g]-1,4-dioxocine)-N-(3-phenyl-2H-isoindole-1-yl)methy-
lene]-3-phenyl-1H-isoindol-1-ylidene)amine] (2) in the yield of
70, 71, and 67%, Scheme 1. Both 1 and 2 were characterized by 1H
NMR, 1H-1H COSY, and mass spectroscopies in addition to
elemental analysis, Figs. S1-S6 and Tables S1 and S2 (Supporting
Information). At the end of this section, it is worth noting that for
the ease of isolation both the symmetrical benzo-fused aza-
BODIPY precursors (0a, 2a) and derivatives (0, 2) could actually be
easily prepared with 1,2-dicyanobenzene or (R)/(S)-benzo[b]
dinaphtho[2,1-e:10,20-g] [1,4]dioxocine-2,3-dicarbonitrile instead
of mixed 1,2-dicyanobenzene and (R)/(S)-benzo[b]dinaphtho[2,1-
e:10,20-g] [1,4]dioxocine-2,3-dicarbonitrile as starting material
following the same reaction procedure as detailed above.
fact that the induced CD intensity is proportional to 1/(n2N nB2ODIPY
)
ꢂ
[14], where nN and nBODIPY are the frequencies of the absorption of
naphthalene and BODIPY, respectively. This is further supported by
the nearly two times of CD signal intensity for 2 with two chiral
binaphthyl groups in comparison with that for 1 with only one
chiral binaphthyl unit, Fig. 1 and Fig. S7 (Supporting Information).
To quantitatively evaluate the chiral dissymmetry of 1 and 2, the
anisotropic factor g was calculated according to the equation: g ¼
q/
(33$ε) [15]. The g factor values of 1 and 2 are summarized in
Table S4 (Supporting Information). As can be found, the g factor of
compound 1 is 1.4 ꢁ 10ꢂ4 for S0/S1 band and 12.8 ꢁ 10ꢂ4 for
S0/S2 band, which amounts to 2.6 ꢁ 10ꢂ4 and 16.4 ꢁ 10ꢂ4
,
respectively, for the S0/S1 and S0/S2 band of 2, indicating the
considerable chirality-induced ability of the binaphthyl unit. The g
factor of 2 is larger than that of 1, revealing the effect of the number
of binaphthyl units and confirming the induced chirality nature for
both 1 and 2.
3.2. Electronic absorption and circular dichroism (CD) spectroscopy
The electronic absorption spectra of 0e2 were recorded in
CH2Cl2 and the data are summarized in Table S3 (Supporting
Information). As shown in Fig. 1, Figs. S7, and S8 (Supporting
Information), an intense S0/S1 band appears at 712 nm for the
reference benzo-fused 3,5-diaryl aza-BODIPY compound 0 with a
shoulder band appearing at 655 nm. In addition, this compound
also exhibits a weak band at 309 nm due to the S0/S2 transition of
the BODIPY system [10]. Along with the incorporation of one
3.3. Electronic structures and theoretical investigation
In order to get further insight into electronic absorption and CD
spectra of 1 and 2, DFT and TD-DFT calculations were performed at
M06/6-311G(d) level [16]. The optimized molecular structures
Scheme 1. Schematic molecular structures of benzo-fused aza-BODIPYs.

430
L. Zhang et al. / Dyes and Pigments 134 (2016) 427e433
including both (R)- and (S)-enantiomers of both 1 and 2 are shown
in Fig. 2 and Fig. S9 (Supporting Information). The frontier molec-
ular orbital (MO) maps of 2S are shown in Fig. 3 and that of 1S in
Fig. S10 (Supporting Information). The excited states under TD-DFT
calculation and simulated absorption and CD spectra of 1 and 2 are
shown at the bottom of Fig. 1 and Fig. S7 (Supporting Information).
The electron transitions of significant excited states and corre-
sponding oscillator strength (f) and rotational strength (R) are
summarized in Table 1. As can be found, despite the slight over-
estimation of the vertical transition energies, the simulated
electronic absorption spectra of 1 and 2 are in good agreement with
the experimental results. The S0/S1 band absorptions are esti-
mated at 618 nm for 2S, 610 nm for 1S, and 600 nm for 0. The
S0/S1 band for all the three compounds is mainly contributed by
the electron transitions from HOMO/LUMO, which are located
mainly on the benzo-fused aza-BODIPY chromophore [4c,5a]. The
participation of peripheral oxygen atoms in the electron transitions
seems to result in the redshift of 1 and 2 in comparison with that for
0 due to the conjugation between oxygen atoms and the central
BODIPY chromophore according to the electron transition density
Fig. 1. Electronic absorption spectra and CD of 2 in CH2Cl2, and calculated absorption spectra and CD of 2S.

L. Zhang et al. / Dyes and Pigments 134 (2016) 427e433
431
Fig. 2. Simulated molecular structures of 2S and 2R.
Fig. 3. Partial molecular energy diagram and orbitals of 2S.

432
L. Zhang et al. / Dyes and Pigments 134 (2016) 427e433
Table 1
at ꢂ0.61 V. The potential difference between the first oxidation and
The calculated excited wavelength (l), oscillator strength (f), rotational strength (R),
the first reduction, which reflects the HOMO-LUMO gap, was found
to be 1.58 V for 0. This is also true for the counterparts 1 and 2 with
two quasi-reversible one-electron oxidations at þ1.39 and þ 0.97 V
and one quasi-reversible one-electron reduction at ꢂ0.58 V for 1
and two quasi-reversible one-electron oxidations at þ1.41
and þ 0.96 V and one quasi-reversible one-electron reduction
at ꢂ0.56 V for 2. Interestingly, along with the increase in the
number of binaphthyl group incorporated onto the benzo-fused
aza-BODIPY skeleton, the potential difference between the first
oxidation and the first reduction gets decreased from 1.58 V for 0 to
and electron transition compositions of important transitions for 0, 1S and 2S.
Compound
l
(nm)
f
R (length)a
Transition
compositionb
0
1
600
298
610
315
300
618
315
0.76
0.21
0.90
0.15
0.23
1.05
0.27
e
H/Lc
98%
92%
98%
94%
77%
98%
46%
49%
85%
7%
e
H/Lþ3
ꢂ36.34
ꢂ68.56
ꢂ32.56
ꢂ127.20
ꢂ557.90
H/L
Hꢂ1/Lþ1
H/Lþ6
H/L
Hꢂ2/Lþ2
Hꢂ1/Lþ1
H/Lþ9
H/Lþ12
2
1.55 V for 1 and 1.52 V for 2 due to the p-p conjugation between the
300
0.31
ꢂ34.77
peripheral oxygen atoms and the BODIPY chromophore. This result
is in line with the red-shift of the lowest energy absorption band of
these compounds in the same order.
a
The unit is 10ꢂ40 erg-esu-cm/Gauss.
The transition compositions with more than 5% contribution are listed.
H refers to HOMO, and L refers to LUMO.
b
c
4. Conclusion
difference plots, Table S5 (Supporting Information). This well re-
produces the experimental result. The band observed at 301 nm by
UVevis spectroscopy can be represented by the calculated transi-
tions at 315 nm and 300 nm with relatively large oscillator
strengths. However, the transition at 315 nm is composed by
HOMOꢂ2/LUMOþ2 and HOMOꢂ1/LUMOþ1 with electrons
localizing mainly on the binaphthyl units, while the transition at
301 nm is composed by HOMO/LUMOþ9, in which the electrons
locate mainly on the central BODIPY chromophore. As a conse-
quence, these two transitions exhibit essential different electronic
transition nature despite their close energies. This is also true for 1,
Table S6 (Supporting Information). The simulated CD spectra of 1S
and 2S also match well with the experimental ones in terms of both
the sign and relative intensity.
In conclusion, chiral benzo-fused aza-BODIPYs with optical ac-
tivity extending into the NIR range have been synthesized and
spectroscopically characterized for the first time. This will arouse a
wide range of interest in the design and synthesis of novel chiral
benzo-fused aza-BODIPY compounds due not only to their intrinsic
scientific importance but also their potential applications in bio-
logical measurements and cellular imaging.
Acknowledgement
Financial support from the National Key Basic Research Program
of China (No. 2013CB933402), the National Natural Science Foun-
dation of China (No. 21290174 and 21301017), Beijing Municipal
Commission of Education, and University of Science and Technol-
ogy Beijing is gratefully acknowledged.
3.4. Fluorescence spectra
Appendix A. Supplementary data
The steady-state fluorescence spectra of 0e2 were measured in
CH2Cl2 and toluene with corresponding data summarized in
Table S8 (Supporting Information). As shown in Fig. S12
(Supporting Information), the fluorescence emission spectra of
0e2 in CH2Cl2 display mirror-symmetrical bands relative to the
absorption spectra with almost the same Stokes shifts of ca.
590 cmꢂ1. The emission maxima of 0e2 appear at 744 nm, 749 nm,
and 754 nm, respectively, showing red-shift in comparison with
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2016.07.039.
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