The Diradical-Dication Strategy for BODIPY- and Porphyrin-Based Dyes with Near-Infrared Absorption Maxima from 1070 to 2040 nm

Article abstract of DOI:10.1002/chem.201804449

Four stable boron dipyrromethene (BODIPY)- and porphyrin-based bis-arylamine diradical dications were synthesized by two-electron oxidation of their neutral molecules. The two BODIPY-based dications have open-shell singlet ground states. UV/Vis absorption spectra of all four dications showed large redshifts in the NIR region compared to their neutral precursors with absorption maxima at 1274 and 1068 nm for the two BODIPY-based dications and 1746 and 2037 nm for the two porphyrin-based dications. Thus, two new types of NIR dyes with longer wavelengths are provided by the diradical-dication strategy, which can be applied for the generation of other NIR dyes with a range of different chromophores and auxochromes.

Full text of DOI:10.1002/chem.201804449

A Journal of
Accepted Article
Title: The Diradical-Dication Strategy for BODIPY- and Porphyrin-
Based Dyes with Near-Infrared Absorption Maxima from 1070 to
2040 nm
Authors: Xinping Wang, Houjia Wei, Rui Feng, Yong Fang, Lei Wang,
Chao Chen, Li Zhang, and Haiyan Cui
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
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to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
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To be cited as: Chem. Eur. J. 10.1002/chem.201804449
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The Diradical-Dication Strategy for BODIPY- and Porphyrin-Based
Dyes with Near-Infrared Absorption Maxima from 1070 to 2040 nm
Houjia Wei,† Rui Feng,†[a] Yong Fang, Lei Wang, Chao Chen, Li Zhang, Haiyan Cui,*
[a]
[a]
[a]
[a]
[a]
[a,b]
and
Xinping Wang*[a]
Abstract: Four stable BODIPY- and porphyrin-based bis(arylamine)
diradical dications were synthesized by two-electron oxidation of
their neutral molecules. The two BODIPY-based dications possess
open-shell singlet ground states. UV−Vis absorption spectra of all
the four dications show large red shift in the NIR region compared to
their neutral precursors with absorption maxima at 1274 nm and
Highly fused and conjugated porhyrins may reach long
wavelength absorption over 2000 nm but with tedious synthetic
procedure and low solubility.[2b,7] For years, many attempts have
also been made to develop diradicals of porphyrins with near-
infrared absorption. However, most of isolated porphyrin-based
diradicals are based on two fused porphyrin rings and exhibit
absorption wavelength shorter than 1400 nm.[8] Quite recently
monoporphyrin meso-oxy monoradicals were isolated with weak
and broad absorption bands in the range of 1100–1621 nm.[9]
By using weakly coordinating anions, we recently have
succeeded in stabilizing a series of diradicaloids including aryl-
bridged bis(triarylamine) dications, all of which exhibit distinct
absorption around 900 nm.[10] We speculate that BODIPY- or
porphyrin-based diradical dications with long-wavelength
absorptions could also be stabilized by employing such weakly
coordinating anions and bis(arylamino) groups. In this paper we
present four stable diradical dications with bridging moieties of
BODIPY or porphyrin. Two BODIPY-bridged dications (12+ and
1068 nm for the two BODIPY-based dications, while that at 1746 nm
and 2037 nm for the two porphyrin-based dications, respectively.
The work, thus, provides two novel types of NIR dyes at longer
wavelengths by the diradical-dication strategy, which may be applied
for the generation of other NIR dyes with a range of different
chromophores and auxochromes.
Introduction
Near-infrared (NIR) organic dyes with absorption spectral ranges
at long wavelength area especially above 1000 nm have
attracted intensive attention in light of their promising
22+
) show absorption at 1274 and 1068 nm, while the NIR
2+
2+
absorption of two porphyrin-bridged dications (3 and 4 ) falls
[
1]
applications in photonics, electronics and bio-imaging. In the
past few decades, numerous NIR dyes have been synthesized
and characterized by the extension of π-conjugation and the
introduction of a push-pull motif.[2] Recently, organic diradicals of
certain pro-aromatic and anti-aromatic π-conjugated systems in
singlet ground states exhibited small HOMO-LUMO gaps and
were demonstrated as NIR dyes.[1d,1e,3]
at 1746 and 2037 nm, respectively.
Results and Discussion
Boron dipyrromethenes (BODIPYs) are fascinating organic
dyes because of their outstanding optical properties, such as
intense absorption, high fluorescence quantum yields, and
excellent photostability.[4] Many BODIPY-based NIR dyes have
been isolated, but their absorption bands mostly exhibit around λ
=
700–900 nm. Very recently, two stable BODIPY-based organic
dyes with diradical character were reported to exhibit intense
absorption around 1100 nm.[5]
Similar to BODIPYs, porphyrins are another well-known class
of organic dyes, which are widespread both in nature and in
chemical laboratories.[6] Absorption maxima of the most isolated
monoporphyrins are located in the range of 500–1000 nm.
†
†
[
a]
H. Wei, R. Feng, Y. Fang, L. Wang, C. Chen, Dr. L. Zhang, Dr. H.
Cui, Prof. X. Wang
State Key Laboratory of Coordination Chemistry
School of Chemistry and Chemical Engineering
Collaborative Innovation Center of Advanced Microstructures
Nanjing University, Nanjing 210023 (China)
E-mail: xpwang@nju.edu.cn
[
b]
Dr. H. Cui
Institution Jiangsu Key Laboratory of Pesticide Science
College of Sciences
Nanjing Agricultural University, Nanjing 210095 (China)
E-mail: haiyancui555@163.com
These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.2017xxxxx.
[†
]
Scheme 1. Synthesis of dications 12+ and 22+
.
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1
and 2 were synthesized via Suzuki coupling reactions
symmetry approach was applied for open-shell singlet
calculations and spin contamination errors were corrected by
approximate spin-projection method.[15] Energy gaps, bond
lengths and their alterations (BLAs) in the average of bonds of
the optimized open-shell singlets (OS), closed-shell singlets
(CS), and pure diradical triplets (T) are listed in Table 1. From
12+ to 2 , the calculated energy difference between closed-shell
singlet and open-shell singlet (ΔECS-OS) increases, while ΔET-OS
decreases, revealing substituent dependence. BLA of the X-ray
structure is in good agreement with the open-shell singlet
configuration for 12+ (i.e. 1 -OS). Mülliken charge and spin
density distributions on peripheral aryl rings, nitrogen atoms, and
(
Scheme 1) by introducing triphenylamine groups (TPA) to
BODIPY (BDP) via attaching to the pyrrole rings on the 2,6-axis
to form the symmetrical donor–accepter–donor type of
structures DTPA–BDPs.[11a] Reactions of 1 and 2 with two equiv
of Ag[Al(OR ) ] (OR = OC(CF )
F 4 F 3 3
)[12] in fluorobenzene at room
temperature led to the formation of dications 1 and 22+ in high
2
+
2+
yields, respectively (Scheme 1). The dication salts
12+
F 4 F 4
·2[Al(OR ) ] and 2 ·2[Al(OR )
]- were isolated as dark purple
-
2+
powders. Both of them are air insensitive and stable for several
weeks at ambient temperature. These salts have been
characterized by electron paramagnetic resonance (EPR) and
UV-Vis spectroscopy, conjunction with DFT calculations.
·2[Al(OR )
F 4
]- was additionally studied by super conducting
quantum interference device (SQUID) measurements and
single-crystal X-ray diffraction.
2+
2
+
2+
bridging aryl rings in 1 –OS and 2 –OS dications also show
substituent dependence (Table S2 in the supporting information,
SI). The spin densities are mainly distributed on two triarylamine
12+
2
+
units (Figure 2a and 2b). Comparing to 2 –OS, the spin density
2
+
of 1 –OS is further delocalized to the bodipy ring.
Figure 1. Ellipsoid drawing of 12+ with 50% probability level. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å) and angles (deg):
C29–N2 1.404(5), C35–N2 1.426(6), C42–N2 1.417(5), C32–C19 1.471(6),
C19–C20 1.412(7), C18–C19 1.397(7), C17–C18 1.416(7), N1–C20 1.343(6),
N1–C17 1.400(6), N1–B1 1.554(6), B1–F37 1.390(5), C21–C17 1.393(6),
C21–C22 1.509(9), C29-N2-C42 121.2(3), C29-N2-C35 119.7(3), C42-N2-C35
119.0(3).
2
+
]- suitable for X-ray diffraction
Single crystals of 1 ·2[Al(OR
)
F 4
Figure 2. a) spin density, c) HOMO(α) and e) LUMO(α) of 12+-OS; b) spin
density, d) HOMO(α) and f) LUMO(α) of 22+–OS, calculated at the UB3LYP/6-
study were obtained from fluorobenzene. However, repeated
attempts to grow crystals of 2 ·2[Al(OR
of dication 1 is illustrated in Figure 1 with selected bond
parameters, some of which are given in Table 1. 1 ·2[Al(OR
crystalizes in the orthorhombic space group of P2 2. The two
nitrogen atoms N2 and N2' are nearly coplanar with their three
neighboring carbon atoms, respectively (the sum of angles at
the N2 atom = 359.9°). The dihedral angle between the bodipy
plane with Ar (Figure 1) is 53.7°, and that between Ar and Ar' is
2
+
]- failed. The structure
F
)
4
31G(d) level.
2
+
2
+
F 4
)
]-
The diradical character of 12+ and 22+ were further
characterized by EPR spectroscopy (Figure 3). The average g
factors are 2.0027 and 2.0011 for 12+ and 2 , respectively. The
EPR spectra have not been simulated because clear hyperfine
splitting was unobserved, but the forbidden half-field transition
1 1
2
2+
Δm
s
= ± 2 were clearly observed, indicating 12+ and 22+ are
7
3.4°. In the triphenylamine moieties, the average N–C bond
lengths (1.404(5) Å) to the bridged phenyl ring are shorter than
that to the peripheral aryl ring systems (N–Ar 1.422(6) Å), like
the previously reported bis(triarylamine)-type diradicals.[10] The
BLA value, reduced bond-length alteration of bridged phenyl
rings and identified as a signature of diradical character in
hydrocarbon diradicals and analogues,[10,13] in this work is the
difference between the average of C31–C32, C32–C33, C29–C30
diradical dications. The intensity of forbidden transition is largely
dependent on the distance between the two unpaired electrons,
so the weak half-field transition may derive from a large
separation of the two spins.
and C29–C34 bond lengths and the average of C30–C31 and C33
–
C
34 bond lengths of in bridging phenyl rings, as shown in the
scheme in Table 1. BLA (0.026) of 12+ is small and similar to the
reported phenyl-bridged di(triarylamine)-type diradicals.[10]
Geometry optimizations on 12+ and 22+ were performed at the
(
U)B3LYP/6-31G(d) level and the stationary points were
characterized by frequency calculations.[14] The broken-
Figure 3. The powder EPR spectra of 12+ (a) and 22+ (b) at 87.6 K.
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-
1
2 2
Table 1. Selected experimental and calculated bond lengths (Å), relative energy (kcal mol ), near-infrared absorption (nm) in solution (CH Cl .
) for 12+ and 22+
avg.
C
31–C32
, C32–C33,
λ
sol
ΔEX-OS[a]
avg. C19–C32
avg. C30–C31 and C33–C34
BLA[b]
avg. C29–N
avg. N–Ar
C
29–C30 and C29–C34
12+
1274
X-ray
CS[a,c]
OS[a,c]
T[a,c]
1.471
1.452
1.462
1.463
1.457
1.466
1.467
1.381
1.380
1.383
1.384
1.382
1.386
1.386
1.407
1.419
1.414
1.414
1.415
1.411
1.411
0.026
0.039
0.031
0.030
0.033
0.025
0.025
1.404
1.392
1.404
1.405
1.401
1.414
1.415
1.421
1.422
1.417
1.417
1.416
1.412
1.412
9.86
0
0.16
10.60
0
22+
1068
CS[a,c]
OS[a,c]
T[a,c]
0.04
[
C
(
a] X = CS (closed-shell singlet), OS (open-shell singlet), or T (triplet). [b] BLA = bond length alteration, i.e., the difference between the average of all C31–C32
32–C33, C29–C30 and C29–C34 bond lengths and the average of C30–C31 and C33–C34 bond lengths of in bridging phenyl rings. [c] Calculated at the level of
U)B3LYP/6-31G(d).
,
solvent molecules (Figure 4a). The results give a small singlet–
-1
triplet energy gap (ΔEST = – 0.07 kcal mol ), which agrees with
-1
the calculated value (– 0.16 kcal mol ) at the UB3LYP/6-31G(d)
level. It demonstrates that 12 has an open-shell singlet ground
state, which can be thermally excited to its triplet excited state at
room temperature as a result of the small singlet–triplet energy
gap. Unfortunately, SQUID measurements of 22+ could not be
well-fitted with Bleaney–Bowers equation, probably due to the
presence of some impurities. But the diagram (Figure S3 in SI)
+
2
+
is similar to that of 1 , indicating open-shell singlet ground state
2
+
of 2 .
Optical properties of these BODIPY-based diradical dications
were subsequently studied. Figure 4b shows the UV-Vis
2
+
2+
absorption spectra of dications 1 and 2 . In CH
12+ and 22+ displayed a broad absorption peak with rather strong
intensity in the near-infrared region (1 1274 nm, ε = 1.95 × 10
2 2
Cl solution,
2
+
4
-1
-1
2+
4
-1
-1
L·mol ·cm ; 2 1068 nm, ε = 1.82 × 10 L·mol ·cm ). With the
electron-donating ability of substituent enhanced, the absorption
peak in near-IR region was greatly blue-shifted, while the
absorption intensity slightly declined. TD-DFT calculations at the
UPBE1PBE/6-31G(d) level in combination with the Polarizable
Continuum Model (PCM) model[17] on the open-shell singlet
geometries of 12+ and 22+ indicate that the absorption in the
near-infrared region is ascribed to HOMO(α)–LUMO(α) (Figure
2c–2f) and HOMO(β)–LUMO(β) transitions (Table S3 and
Figures S4–S6 in SI), in accordance with the experimental
absorption. Comparing to organic mixed-valence radical
cations,[ the main difference should be the intrinsic transitions
contribution to the NIR absorption. For the organic mixed-
Figure 4. a) χ
M
T versus T curve in the SQUID measurements for the powder
of 12+ and the fitting plot obtained with the Bleaney–Bowers equation. b)
2+
2+
-5
-1
2 2
Absorption spectra of diradicals 1 and 2 (1 x 10 mol·L ) in CH Cl .
18]
The magnetic property of 12+ has also been determined by
SQUID measurements for 12+ in powder form at 5–300 K, which
can well conform to the Bleaney–Bowers equation,[16] and the
valence
systems,
the
lowest-energy
long-wavelength
absorptions, called intervalence charge-transfer (IVCT) bands,
discrepancy above 300 K may be caused by volatilization of
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are usually determined by HOMO–SOMO and SOMO–LUMO
electron transitions.[19] And the transitions of the NIR absorption
bands of our diradical dications are mainly assigned from HOMO
to LUMO, along with the intramolecular charge transfer from the
terminal group and BODIPY core to another triphenylamine
group.
atom in the diarylamine moieties is nearly coplanar with three
neighboring carbon atoms (sum angles 360° in 3 and 358° in 4).
The dihedral angles between the two planes are ca. 38.7° (for 3)
and 25.9° (for 4), and those between the planes of diarylamine
and porphyrin moieties are ca. 69.9° and 77.8°.
The reactions of 3 and 4 with Ag[Al(OR
F 4
) ] in the molar ratio
of 1 : 2 in CH Cl at room temperature resulted in the formation
2
2
2
+
2+
of diradical dications 3 and 4 , respectively (Scheme 2).
Unfortunately, single crystals of 32 and 42+ were not obtained
after repeated recrystallization. The powder EPR spectra at 87.6
+
2
+
-
2+
-
K of 3 ·2[Al(OR
S1 and S2 with g factors of 2.0034 (3 ) and 2.0036 (4 ). The
clearly observed forbidden half-field transitions (Δm = ±2)
indicate their diradical characters. The UV-Vis absorption
F 4 F 4
) ] and 4 ·2[Al(OR ) ] are shown in Figures
2
+
2+
s
spectra of dications 3 and 42+ are shown in Figure 6. 3 and
individually exhibit a broad absorption peak in the NIR region
32+ 1746 nm, ε = 1.21×10 L·mol ·cm ; 4 2037 nm, ε =
2+
2+
2
+
4
4
-1
-1
2+
(
1
4
-1
-1
2 2
.37×10 L·mol ·cm ) in CH Cl solution. The absorption peak
in near-IR region is obviously red-shifted along with the
increased electron-donating ability of substituent, but the two
NIR peaks of 32+ and 42+ show the similar absorption intensity.
Osuka group have recently reported a series of diradicals based
on porphyrin or porphyrin derivatives, the absorption maxima of
which are mostly located in the range of 1000–1400 nm.[
Scheme 2. Synthesis of diradical dication 32+ and 42+
.
8,21]
To extend this method for the generation of other types of
organic dyes and further explore the effect of bis(triarylamine)
diradical dications on the optical performance of chromophores,
we introduced diphenylamine groups (DPA) to porphyrin by
attaching them to the two methine carbons on the 5,15-meso
positions (Scheme 2). Consequently, compounds 3 and 4 were
synthesized as dark green solid by cross coupling.[11b] Their
identity were characterized by X-ray single-crystal analysis.
Figure 6. Absorption spectra of diradicals 3 (1.1 x 10-5 mol·L ) and 4 (1.8 x
2
+
-1
2+
-
5
-1
2 2
10 mol·L ) in CH Cl .
Conclusions
Figure 5. Ellipsoid drawing of 3 (a) and 4 (b) with 50% probability level.
Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg) in 3: Ni1–N1 1.930(2), Ni1–N2 1.938(2), N5–C1 1.430(3), N5–
C21 1.416(4), N5–C28 1.418(4), C28-N5-C21 122.7(2), C28-N5-C1 118.1(2),
C21-N5-C1 119.2(2). In 4: N2–Ni1 1.9284(18), N3–Ni1 1.9209(19), C5–N1
In summary, we have synthesized and characterized four air-
insensitive diradical dications of BODIPY- and porphyrin-based
dyes 12 – 4 . The four diradical dications show near-infrared
+
2+
absorptions at 1274 nm, 1068 nm, 1746 nm and 2037 nm in
1.414(3), C12–N1 1.420(3), C15–N1 1.429(3), C5-N1-C12 122.11(19), C5-N1-
CH
2
Cl
2
solution, respectively. Interestingly, the substituent
C15 117.94(19), C12-N1-C15 118.0(2).
effects for these two kinds of dyes are opposite, as the
2
+
absorption is blue-shifted for BODIPY-based dications from 1
2
+
to 2 , while that is red-shifted for porphyrin-based dications from
32+
and 4 . Rationalization of this behavior needs further deep
The structures of neutral 3 and 4 are shown in Figure 5,
along with selected bonding parameters. The bridging porphyrin
backbones between two nitrogen atoms are twisted in 3 and 4.
The average Ni–N bond length (1.9247Å) in 4 is slightly shorter
than that in 3 (1.934 Å), maybe resulting from the electron
donating MeO groups. The average C–N bond lengths (1.43 Å)
between porphyrin and diarylamine moiety are similar to the
reported 5,15-dicarbazole nickel porphyrins.[20] Each nitrogen
2+
studies in conjuction with detailed theoretical calculation. The
work presents guidance for approaching NIR dyes at longer
wavelengths using diradical-dication concept. Application of
such an approach to the generation of more novel NIR dyes
based on other chromophores is currently underway.
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3 3 3
), 2.55 (s, 6H, CH ), 1.31 (s, 6H, CH
); 13C NMR
H), 3.79 (s, 12H, CH
100.61 MHz, CDCl ) δ 156.06, 154.46, 147.75, 141.60, 140.95, 138.94,
35.75, 133.66, 130.76, 129.29, 129.03, 128.28, 126.90, 125.34, 119.85,
14.84, 55.63, 31.59, 30.33, 29.85, 13.64, 12.97; UV-vis (CH Cl ): ε (304
Experimental Section
(
1
1
3
General considerations: All experiments were carried out under a dry
oxygen-free nitrogen atmosphere using standard Schlenk techniques.
Solvents were dried by standard methods and freshly distilled prior to use.
2
2
4
-1
-1
4
-1
-1
nm) = 4.88 × 10 L·mol ·cm , ε (454 nm) = 1.33 × 10 L·mol ·cm , ε
(
552nm) = 4.63 × 104 L·mol ·cm ; HRMS (ESI-TOF) calculated for
-1
-1
The 1H NMR and 13C NMR spectra were recorded in solution of CDCl
using a Bruker Ultra Shield 400 MHz spectrometer in ppm downfield from
internal standard Me Si. EPR spectra were obtained using Bruker EMX
3
+
C59H53N2O
4
BF
2
Na [M+Na] : 953.4020, found: 953.4012.
4
Synthesis of neutral 3 and 4: Degassed THF (30 mL) was added to a
flask containing meso-bromo Ni(II) porphyrin, 4,4'-Dimethyldiphenylamine,
plus-6/1 X-band variable-temperature apparatus. UV-vis spectra were
recorded on Lambda 750 spectrometer. For the single crystal X-ray
structure analyses the crystals were each mounted on a glass capillary in
Pd-PEPPSI-IPent, and NaOtBu under
a nitrogen atmosphere. The
mixture was vigorously stirred at 60 °C for 48 h. Then the solvent was
concentrated and purified by silica gel column chromatography
perfluorinated oil and measured in a cold N
collected on Bruker D8 CMOS detectors at 123 K. The structures were
solved by direct methods and all refined on F2 with the SHELX-97
2
flow. The data were
(Petroleum ether/CH
2
Cl
2
, 2:1). Crystals were obtained by washing with
methanol and recrystallizing from CH
2
Cl /hexane.
2
software package. The positions of the H atoms were calculated and
considered isotropically according to a riding model. TPA-a and Pd-
PEPPSI-IPent were purchased from Adrich and used upon arrival. 2,6-
Compound 3: meso-bromo Ni(II) porphyrin (0.35 g, 0.5 mmol), 4,4'-
Dimethyldiphenylamine (0.49 g, 2.5 mmol), Pd-PEPPSI-IPent (63 mg,
Br
2
-BODIPY,11a TPA-b,22 meso-Br
2
-NiPorphyrin20 and Ag[Al(OR
F
)
4
]12
were synthesized according to the reported procedures. 3 and 4 were
synthesized by the method similar to Osuka et al’s.11b
0.08 mmol), and NaOtBu (0.24 g, 2.5 mmol); dark green needle crystals.
1
Yield: 0.42 g, 90%. H NMR (400 MHz, CDCl
3
) δ 9.02 (d, J = 5.0 Hz, 4H,
pyrr-H), 8.60 (d, J = 5.0 Hz, 4H, pyrr-H), 7.80 (d, J = 7.9 Hz, 4H, Ar-H),
7
8
.40 (d, J = 7.8 Hz, 4H, Ar-H), 7.10 (d, J = 8.5 Hz, 8H, Ar-H), 6.97 (d, J =
.5 Hz, Ar-H), 2.60 (s, 6H, CH ), 2.23 (s, 12H, CH
); 13C NMR (100.61
) δ 149.58, 145.55, 142.66, 137.65, 137.56, 133.59, 133.31,
30.79, 130.22, 129.79, 127.63, 122.25, 121.91, 119.29, 21.57, 20.74;
Synthesis of 4-borate-4,4-dimethoxytriphenylamine (TPA-b). n-BuLi
3
3
(23 mL, 1.6 M in hexanes) was slowly added to a solution of 4-bromo-
MHz, CDCl
1
UV-vis (CH
3
4
7
,4-dimethoxytriphenylamine (12.37 g, 32 mmol) in THF (100 ml) at -
8 °C. The resulting mixture was stirred at -78 °C for about one hour.
4
-1
-1
2
Cl
2
): ε (293 nm) = 5.83 × 10 L·mol ·cm , ε (397 nm) =
3 3
Then trimethyl borate (B(OCH ) ) (5 ml) was added and the solution was
4
-1
-1
4
-1
-1
11.23 × 10 L·mol ·cm , ε (467 nm) =7.68 × 10 L·mol ·cm , ε (549 nm)
stirred overnight at room temperature. After addition of HCl aqueous
solution (1 M, 250 ml), the solution turned to fluorescent·cyan-blue
immediately. After stirring at room temperature for about 3 hours and the
solvent was evaporated, and the resulting white solid was
chromatographed on silica gel with a mixture of Ethyl acetate and
1.47 × 104 L·mol ·cm , ε (607 nm) = 1.20 × 10 L·mol ·cm ; HRMS
-1
-1
4
-1
-1
=
+
(
ESI-TOF) calculated for C62
H N
51 6
Ni [M+H] : 937.3523, found: 937.3517.
Synthesis of 4: meso-bromo Ni(II) porphyrin (0.28 g, 0.4 mmol), 4,4'-
Dimethoxydiphenylamine (0.46 g, 2.0 mmol), Pd-PEPPSI-IPent (51 mg,
0.064 mmol), and NaOtBu (0.19 g, 2.0 mmol); dark green needle crystals.
Yield: 0.35 mg, 87%. 1H NMR (400 MHz, CDCl
4H, pyrr-H), 8.58 (d, J = 5.0 Hz, 4H, pyrr-H), 7.80 (d, J = 7.9 Hz, 4H, Ar-
H), 7.41 (d, J = 7.8 Hz, 4H, Ar-H), 7.13 (d, J = 9.1 Hz, 8H, Ar-H), 6.73 (d,
Petroleum ether (1:3, v:v) as the eluent. Removal of solvents afforded a
1
white solid (TPA-b) (3.91 g, 35%). H NMR (400 MHz, CDCl
3
): δ 7.94 (d,
J = 8.4 Hz, 2H, Ar-H), 7.11 (d, J = 8.5 Hz, 4H, Ar-H), 6.93 (d, J = 8.2 Hz,
H, Ar-H), 6.89 – 6.78 (m, 4H, Ar-H), 3.81 (s, 6H, CH ), 1.57 (s, br, 1H,
3
) δ 9.01 (d, J = 5.0 Hz,
2
3
OH).
3 3
), 2.60 (s, 6H, CH
); 13C NMR
J = 9.1 Hz, 8H, Ar-H), 3.71 (s, 12H, OCH
100.61 MHz, CDCl ) δ 153.82, 146.16, 145.60, 142.49, 137.58, 133.59,
33.20, 130.80, 127.67, 123.08, 122.64, 119.25, 114.61, 55.61, 21.57;
(
1
3
Synthesis of neutral
2
1 and 2: To a mixture of 2,6-Br -BODIPY,
Pd(PPh
3
)
4
, and TPA (TPA-a for 1 and TPA-b for 2) was added a
4
-1
-1
UV-vis (CH
2 2
Cl ): ε (292 nm) = 4.97 × 10 L·mol ·cm , ε (400 nm) =
degassed mixture of toluene (20 mL) and 2M Na
2
CO aqueous solution
3
0.33 × 104 L·mol ·cm , ε (478 nm) = 5.03 × 10 L·mol ·cm , ε (546
-1
-1
4
-1
-1
1
under a nitrogen atmosphere. The mixture was vigorously stirred at reflux
temperature for 12 h, and then the solvent was washed with water three
4
-1
-1
4
-1
-1
nm) = 0.98 × 10 L·mol ·cm , ε (625 nm) =1.13 × 10 L·mol ·cm ;
HRMS (ESI-TOF) calculated for C62
+
H
51
N
6
O
4
Ni [M+H] : 1001.3320, found:
times. The organic layer was collected, dried over anhydrous Na
2 4
SO ,
1001.3326.
and filtered. The filtrate was concentrated and purified by silica gel
column chromatography (Petroleum ether/CH
obtained as solid (0.46 g, 52%).
2 2
Cl , 2:1). Product was
Synthesis of dication salts: Under anaerobic and anhydrous conditions,
a mixture of neutral compound (1–4) and Ag[Al(OR ] in CH Cl (30 mL)
F
)
4
2
2
was stirred at room temperature overnight. The resultant solution was
filtered to remove the gray precipitate (Ag metal). The filtrate was then
concentrated and stored at -24 °C for 1 week to afford crystals or powder.
Compound 1: 2,6-Br
2
-BODIPY (0.49 g, 1.02 mmol), Pd(PPh
3
)
4
(0.11 g,
aqueous
0.06 mmol), TPA-a (0.71 g, 2.24 mmol) and 2M Na
2
CO
3
1
solution (20 mL); dark purple solid. Yield: 0.46 g, 52%. H NMR (400
MHz, CDCl ) δ 7.46 – 7.51 (m, 3H, Ar-H), 7.34 – 7.36 (m, 2H, Ar-H), 6.95
7.08 (m, 24H, Ar-H), 2.57 (s, 6H, CH ), 2.31 (s, 12H, CH ), 1.33 (s, 6H,
CH ) δ 154.45, 147.22, 145.32, 141.70,
). 13C NMR (100.61 MHz, CDCl
39.03, 135.71, 133.61, 132.81, 131.41, 130.83, 130.05, 129.31, 129.06,
3
12+·2[Al(OR
F 4
F 4
) )
]-: 1 (0.18 g, 0.30 mmol) and Ag[Al(OR
] (0.67 g, 0.62
Cl ): ε
–
3
3
3
3
mmol); dark purple crystals. Yield: 0.58 g, 77.4%. UV/Vis (CH
(1274 nm) = 1.95×10 L·mol ·cm .
2
2
4
-1
-1
1
1
28.26, 126.46, 124.96, 121.84, 20.97, 13.65, 12.99; UV-vis (CH
2
Cl
2
): ε
4
-1
-1
4
-1
-1
(308 nm) = 5.04 × 10 L·mol ·cm , ε (449 nm) = 1.17 × 10 L·mol ·cm ,
22+
]-: 2 (0.13 g, 0.20 mmol) and Ag[Al(OR
·2[Al(OR
F
)
4
F
)
4
] (0.47 g, 0.44
4
-1
-1
ε (547 nm) = 4.88 × 10 L·mol ·cm .
mmol); dark purple powder. Yield: 0.36 g, 69.2%. UV/Vis (CH
2
Cl ): ε
2
4
-1
-1
(1068 nm) = 1.82×10 L·mol ·cm .
Compound 2: 2,6-Br
2
-BODIPY (0.49 g, 1.02 mmol), Pd(PPh
3
)
4
(0.11 g,
0
.06 mmol), TPA-b (0.78 g,
2.24 mmol) and 2M Na CO
2
3
aqueous
32+
]-: 3 (0.047 g, 0.05 mmol) and Ag[Al(OR
F 4
) ] (0.113 g,
·2[Al(OR
F
)
4
1
solution (20 mL); dark purple solid. Yield: 0.43 g, 45%. H NMR (400
MHz, CDCl ) δ 7.45 – 7.50 (m, 3H, Ar-H), 7.33 – 7.35 (m, 2H, Ar-H), 7.06
7.09 (m, 8H, Ar-H), 6.89 – 6.95 (m, 8H, Ar-H), 6.82 – 6.84 (m, 8H, Ar-
0.105 mmol); gray brown powder. Yield: 0.057 g, 39.7%. UV/Vis
3
2 2
(CH Cl ): ε (1746 nm) = 1.21×10 L·mol ·cm .
4
-1
-1
–
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Chemistry - A European Journal
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42+
·2[Al(OR
)
]-: 4 (0.050 g, 0.05 mmol) and Ag[Al(OR
)
] (0.113 g, 0.105
S. Lee, J. M. Lim, D. Kim, A. Osuka, J. Am. Chem. Soc. 2015, 137,
2097.
F
4
F
4
mmol); reddish brown powder. Yield: 0.054 g, 36.8%. UV/Vis (CH
2
Cl ): ε
2
4
-1
-1
(2037 nm) = 1.37×10 L·mol ·cm .
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Keywords: diradical dications• dyes • near-infrared absorption •
BODIPY • porphyrins
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Entry for the Table of Contents
FULL PAPER
Two novel types of NIR dyes at
longer wavelengths from 1070 to
Houjia Wei, Rui Feng, Yong Fang,
Lei Wang, Li Zhang, Chao Chen,
Haiyan Cui,* and Xinping Wang*
2040 nm were synthesized and
isolated by the diradical-dication
strategy. The absorption is blue-
shifted for BODIPY-based
dications, while red-shifted for
porphyrin-based dications,
displaying an opposite substituent
effect.
Page No. – Page No.
The Diradical-Dication Strategy
for BODIPY- and Porphyrin-Based
Dyes with Near-Infrared
Absorption Maxima from 1070 to
2040 nm
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