Pyrrolopyrrole cyanines: Effect of substituents on optical properties

Article abstract of DOI:10.1002/ejoc.201100108

To tune their optical properties, a large variety of pyrrolopyrrole cyanines (PPCys) were synthesized with substitutedheteroaromatics such as quinoline, benzothiazole, and oxazole derivatives as terminal groups. Thus, a broad range of stable, highly fluorescing near-infrared (NIR) dyes with high absorptivities between 690 to 845 nm is accessible. The large number of newly synthesized compounds allows a detailed discussion of the correlation between molecular structure and the optical properties of the first electronic transition. Syntheses and optical properties of pyrrolopyrrole cyanines (PPCys) with different substituents at the terminal heteroaromatic moieties are described. The relationship between molecular structure and optical properties is discussed. By suitable substitution, the absorption and fluorescence maxima of the chromophore can be tuned in a range between 690 and 845 nm. Copyright

Full text of DOI:10.1002/ejoc.201100108

FULL PAPER
DOI: 10.1002/ejoc.201100108
Pyrrolopyrrole Cyanines: Effect of Substituents on Optical Properties
Georg M. Fischer,[a] Matthias K. Klein,[a] Ewald Daltrozzo,[a] and Andreas Zumbusch*[a]
Keywords: Chromophores / Dyes/pigments / Fluorescence / Heterocycles / Near-infrared dyes
To tune their optical properties, a large variety of pyrrolopyr-
role cyanines (PPCys) were synthesized with substituted
heteroaromatics such as quinoline, benzothiazole, and ox-
azole derivatives as terminal groups. Thus, a broad range of
stable, highly fluorescing near-infrared (NIR) dyes with high
absorptivities between 690 to 845 nm is accessible. The large
number of newly synthesized compounds allows a detailed
discussion of the correlation between molecular structure
and the optical properties of the first electronic transition.
(DPP) 1 and 2 equiv. of heteroaromatic acetonitrile (HAA)
2 after activation of the carbonyl groups of the DPP with
phosphoryl chloride. The resulting H-PPCys 3 can be stiff-
ened by exchanging the protons in the hydrogen bonds by
BF2 or BPh2, yielding BF2-PPCys 4 or BPh2-PPCys 5,
respectively (Scheme 1). The spectral properties of PPCys
are characterized by strong, narrow-band absorptions in the
NIR and very weak bands in the visible spectral range. The
stiffened PPCys fluoresce with quantum yields that are ex-
tremely high for NIR emission. So far, we have investigated
the influence of the heteroaromatic end groups and the
bridging BF2 and BPh2 groups on the spectral properties of
PPCys. The heterocyclic end groups introduced by HAAs 3
have the same influence on the optical properties as those
known for typical cyanine dyes, and show increasing ba-
thochromic shifts in the order: pyrimidine, benzoxazole,
pyridine, benzothiaole, quinoline, and quinoxaline.[5] The
energy difference between the absorption maxima of a BF2-
PPCy and a BPh2-PPCy with the same end group is almost
constant (ca. 1000 cm–1), irrespective of the nature of the
heterocycle.[4b] An alternative possibility to shift the optical
properties is the stepwise synthesis of asymmetric PPCys.
The photophysical properties, such as absorption and
fluorescence, of these compounds lie between those of the
corresponding symmetric derivatives.[6] With the exception
of bromine- and acetylene-substituted HAA, the acetoni-
triles used so far have only contained alkyl-substituted
groups. In this work, we present an investigation of the in-
fluence of the substitution pattern of HAAs 2 on the spec-
troscopic properties of the PPCys. In particular, substitu-
ents on the quinoline and benzothiazole HAAs were al-
tered, and a benzoxazole HAA was enlarged by benzannul-
ation of a benzene ring. We discuss the spectroscopic prop-
erties of the resulting PPCy dyes, which give important in-
sights into the photophysical behavior of this class of dyes.
Introduction
Much effort has recently been dedicated to the synthesis
of new dyes and fluorophores absorbing and emitting in the
near-infrared (NIR) spectral region. NIR fluorescence is ex-
ploited in imaging methods in biology and medicine. In this
context, working in the NIR region offers several advan-
tages over use of the visible spectral range, such as weak
absorption and low scattering of tissue, which leads to high
penetration depths and sensitive detection because of negli-
gible autofluorescence background.[1] In addition, NIR-ab-
sorbing dyes find broad applications in materials science.
Growing fields of interest are the use of organic dyes in
NIR light-emitting diodes, as sensitizers in dye-sensitized
solar cells, as selective NIR absorbers in paints to block
heat, or as antiforgery markers.[2] These applications have
provided motivation for the recent development of a broad
variety of new NIR fluorophores.[3]
In many of the aforementioned applications it is impor-
tant to match the optical properties of the dyes, such as
absorption and fluorescence maxima, bandshape or Stokes
shifts, to very specific requirements. To fine-tune the optical
molecular properties, a detailed understanding of the rela-
tionship between the structures and the properties of the
dyes is necessary.
In earlier work, we described the synthesis and spectro-
scopic characterization of pyrrolopyrrole cyanines (PPCy)
as a new class of NIR dyes and fluorophores.[4] PPCys are
obtained by condensation reaction of dioxopyrrolopyrrole
[a] Fachbereich Chemie, Universität Konstanz,
78457 Konstanz, Germany
Fax: +49-7531-883870
E-mail: andreas.zumbusch@uni-konstanz.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100108.
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A. Zumbusch et al.
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Scheme 1. Reagents and conditions (A = aromatic heterocycle): (a) anhydrous toluene (xylene)/POCl3, reflux; (b) CH2Cl2/diisopropylethyl-
amine, BF3·Et2O, reflux; (c) toluene/diisopropylethylamine, chlorodiphenylborane, reflux.
2d in 88% yield. The (6-chloro-4-phenylquinolinyl)acetoni-
Results and Discussion
trile 2c was synthesized by starting from quinolone 6
(Scheme 2, route B).[7] Compound 6 was chlorinated with
Synthesis
POCl3 to give 2-chloroquinoline 7,[7] which was further
The reaction pathway for PPCy formation is depicted in treated with the sodium salt of tert-butyl cyanoacetate to
Scheme 1. As shown in earlier work, para-octyloxy-substi- yield 8 in 88% yield. Saponification of 8 with formic acid
tuted DPP 1 was used to enhance the solubility of both and decarboxylation led to 2c in 84% yield.[8] Alternatively,
reactants and products.[4,6] The HAAs 2 were synthesized 2c could also be obtained in high yields from 8 by thermal
according to different strategies (Scheme 2). The 6-tert-but- elimination of isobutene and decarboxylation in vacuo. The
yl- and the 6-bromo-substituted quinoline derivatives 2a benzothiazole HAAs 2e–h were synthesized by starting
and 2b, respectively, were synthesized by chlorination of the from para-substituted aniline derivatives 9 (Scheme 2,
quinaldine and subsequent Kolbe nitrile reaction route C). In the first step, the anilines were converted into
(Scheme 2, route A).[4b,6] Derivative 2b was further modi- the corresponding 2-aminobenzothiazoles 10 by rhodan-
fied by introducing phenylacetylene at the 6-position by ation. Subsequent opening of the thiazol rings yielded the
Sonogashira coupling of 2b and phenylacetylene, affording 2-aminothiophenol derivatives 12. The tert-butyl and the
Scheme 2. Synthetic routes for heteroaromatic acetonitriles 2 (HAA).
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Optical Properties of Pyrrolopyrrole Cyanines
methoxy derivatives 10e[4b] and 10f[9] were opened by heat- Table 1. Spectroscopic data of the first electronic transition
(S0↔S1) of the H-PPCys 3, BF2-PPCys 4 and BPh2-PPCys 5.[a]
ing in the presence of potassium hydroxide. The thiomethyl
A
F
and the trifluoromethyl derivatives 12g and 12h were syn-
thesized in two steps by a milder method that allowed the
inclusion of more functionalities and gave higher yields. For
this purpose, the 2-aminobenzothiazoles 10 were deamin-
ated with isoamyl nitrite in tetrahydrofuran (THF), yielding
the benzothiazoles 11, which were subsequently treated
with hydrazine monohydrate in ethanol and led to 2-amino-
thiophenols 12.[10] Acidic condensation of malononitrile
with the 2-aminothiophenols 12e–h yielded the correspond-
ing benzothiazole HAAs 2e–h. The benzoxazole and the
naphthoxazole derivatives 2i and 2j were synthesized by
treating the 2-aminophenols with ethyl 2-cyanoacetimidate
hydrochloride[11] in dichloromethane. Subsequent treatment
with sodium hydroxide solution afforded the oxazole HAAs
(Scheme 2, route D).
The H-PPCys 3 were prepared as previously described
by condensation of DPP 1 and HAA 2 in the presence of
POCl3.[4] The derivatives 3b, 3c, and 3j are almost insoluble
in solvents such as chloroform or toluene and were there-
fore used for the complexation reactions without further
purification. The other H-PPCys were purified by column
chromatography. The BF2-PPCys 4 and the BPh2-PPCys 5
were synthesized according to previously described pro-
cedures.[4] With the exception of 4d, the boron derivatives
were much more soluble and could therefore be purified by
column chromatography more easily than the H-chelates 3.
PPCy λ00
ε00
f
λ00
Δν
ΦF
˜
A–F
[nm] [m–1 cm–1]
[nm]
[cm–1]
3a
3b
3c
3d
3e
3f
731
734
737
752
735
746
751
726
711
721
754
761
767
778
732
745
753
719
690
699
819
827
832
843
790
803
808
776
747
759
118000
0.71
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.59
0.49
0.50
0.45
0.69
0.32
0.28
0.62
0.57
0.35
0.53
0.52
0.56
0.36
0.48
0.25
0.26
0.60
0.54
0.31
[b]
[b]
–
–
–
–
[b]
[b]
166000
115000
106000
116000
130000
98000
0.91
0.74
0.71
0.77
0.73
0.65
3g
3h
3i
–
–
–
–
[b]
[b]
3j
–
–
4a
4b
4c
4d
4e
4f
205000
229000
237000
284000
190000
171000
165000
175000
135000
157000
256000
280000
293000
309000
221000
200000
196000
238000
164000
196000
0.83
0.85
0.92
1.0
772
775
781
791
749
763
773
738
712
720
831
837
843
855
803
817
827
785
762
771
250
250
250
250
300
300
350
350
500
400
150
150
150
150
200
200
250
150
250
200
0.82
0.80
0.85
0.74
0.73
0.76
0.76
0.78
0.82
0.91
0.76
0.76
0.82
0.74
0.73
0.79
4g
4h
4i
4j
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
[a] Conditions: chloroform, room temperature. λ00A: absorption
wavelength; ε00: molar decadic absorption coefficient; f: oscillator
Spectroscopic Properties
strength; λ00F: fluorescence wavelength; ΔνA–F: Stokes shift; ΦF:
˜
fluorescence quantum yield. [b] Not determined.
The 4-octyloxy-DPP 1 and ten different HAAs, namely,
four quinoline (2a–d), four benzothiazole (2e–h), and two
oxazole derivatives (2i and 2k), were used as starting mate-
rials. From these, ten H-PPCys 3 and their BF2 and BPh2
complexes 4 and 5, respectively, were synthesized. Their ab- are given in the Supporting Information. The trends within
sorption and fluorescence emission were recorded in chlo- the different series are discussed below.
roform solutions at room temperature, and the spectro-
scopic data of the longest-wavelength electronic transition absorption maximum is shifted bathochromically in the or-
of 3, 4, and 5 are summarized in Table 1. der: 6-tert-butyl (4a/5a), 6-bromo (4b/5b), 6-chloro-4-phenyl
Within the series of quinoline derivatives (Figure 1a), the
In general, within the series of 3, 4 and 5 with the same (4c/5c), and 6-(phenylethynyl) (4d/5d). In the same order,
HAA 2, the same trends already described were observed the intensity of the first electronic transition (ε00 and f) in-
upon complexation; sharpening of the vibronic bands, in- creases, for example, from 4a (ε00 = 205000 m–1 cm–1, f =
crease of the S0ǞS1 transition moment, and a significant 0.83) to 4d (ε00 = 284000 m–1 cm–1, f = 1.00). The halfwidth
shift of the Franck–Condon factors in favor of the 00 tran- of the 00 bands (4a–d: 500Ϯ20 cm–1; 5a–d: 420Ϯ10 cm–1)
sition. The difference between the absorption maxima of and the ratio of the intensity of the vibronic band ε01/ε00
BF2-PPCys 4 and BPh2-PPCys 5 remains almost constant (4a–d: 0.22Ϯ0.01; 5a–d: 0.13Ϯ0.01) remains almost con-
(1050 Ϯ 100 cm–1) even in the case of +M substituents at stant. By replacing the tert-butyl group, which has only an
the heteroaromatic moiety. This demonstrates that the in- inductive effect, by bromine or chlorine, which have +M
fluence of the BF2 and the BPh2 moieties is mainly σ-induc- effects, the chromophoric system is extended. Therefore, the
tive.[4]
resulting compounds have a higher transition dipole mo-
Within the series of BF2-PPCys 4 and BPh2-PPCys 5, ment. Compounds 4c/5c bear a phenyl group in the 4-posi-
the absorptions of the dyes exhibit similar bandshapes and tion as a second conjugating substituent, which can explain
fluorescence with high quantum yields. The Stokes shifts the more intense transition compared with those of 4b/5b.
are generally small, which suggests that, upon S0ǞS1 exci- The phenylethynyl moiety in 4d/5d extends the π-system
tation, the molecular geometry changes only slightly. Ab- considerably, leading to a significant increase of ε00 and f
sorption and fluorescence spectra of all derivatives 4 and 5 values compared with those of 4a/5a.
Eur. J. Org. Chem. 2011, 3421–3429
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A. Zumbusch et al.
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in the ε00 value but an increase in the oscillator strength. In
contrast, substitution of the tert-butyl group by the
strongly –I-effective trifluoromethyl group (4h/5h) leads to
a hypsochromic shift, a slight change in ε00 and a small
decrease of f. The halfwidths of the 00 bands of 4e/5e and
4h/5h are equal, whereas those of 4f/5f and 4g/5g are larger.
The Franck–Condon factors are shifted in favor of the 00
transition for the CF3 derivatives, whereas for the MeO and
MeS derivatives they are strongly shifted in favor of the 01
transition (ε01/ε00 for 4e: 0.27; 4f: 0.32; 4g: 0.33; 4h: 0.23;
5e: 0.20; 5f: 0.24; 5g: 0.25; 5h: 0.15). Compared with the
benzothiazole derivatives that have only I substituents, the
quantum yields of the MeO and MeS derivatives are ap-
proximately halved. These findings can be explained by a
steeper potential surface for the CF3 and a smoother one
for the MeO and MeS compounds compared with the tert-
butyl derivatives. The higher oscillator strengths of the
MeO and, especially, of the MeS derivatives compared with
the other benzothiazole PPCys can be explained by higher
transition dipole moments due to an extension of the π-
systems onto the substituents.
Expanding the π-system of benzoxazole PPCys (4i/5i) by
benzannulation to naphthoxazol PPCys 4j/5j led to a slight
bathochromic shift of 200 cm–1 and a more intense transi-
tion (BF2: f +5% and ε00 +16%; BPh2: f +8% and ε00
+20%). The absorption spectra are depicted in Figure 1c.
Whereas the halfwidths remain constant, the Franck–Con-
don factors are slightly shifted in favor of the 00 transition,
which is readily explained by the extension of the chromo-
phoric system (ε01/ε00 for 4i: 0.31; 4j: 0.28; 5i: 0.24; 5j: 0.23).
The benzannulation led to a higher transition dipole mo-
ment, but also led to a decrease in the quantum yields of
about 40%.
It is instructive to compare the linewidths of the purely
electronic 00 bands between absorption and emission spec-
tra (Figure 2). The main factor influencing the linewidth of
the bands is the potential function of the torsional vibration
of the heteroaromatic terminal groups. Vibrations of this
type have previously been assumed to represent a major re-
laxation pathway in PPCys.[4a] This interpretation is sup-
ported by the finding that the linewidths of the BF2-PPCys
are always broader than those of the respective BPh2-PPCys
compounds. Due to the steric hindrance of the BPh2
groups, the potentials are stiffer, which leads to narrower
bands and – because the oscillator strengths are almost un-
affected – to higher extinction coefficients of the BPh2-
PPCys. The linewidths of the 00 bands in absorption are
always smaller than in emission. This is particularly true for
the BF2-PPCys 4e, 4h, 4i, and 4j. We ascribe the broader
lines in emission to the fact that the torsional potentials are
stiffer in the ground than in the excited state.
Figure 1. Absorption of the PPCy dyes in chloroform at room tem-
perature: (a) quinoline derivatives, (b) benzothiazole derivatives, (c)
benzoxazole and naphthoxazole derivatives.
A variety of influences on the fluorescence quantum
yields can be described. No significant difference in quan-
tum yields is observed for the quinoline-, benzothiazole-,
Within the benzothiazole series (Figure 1b), substitution and benzoxazole-substituted derivatives. Only naphth-
of the 6-tert-butyl group (4e/5e) by the +M substituents oxazole as a terminal group led to a significant decrease.
MeO (4f/5f) and MeS (4g/5g) leads to a bathochromic shift The fluorescence quantum yields of the quinoline-contain-
of the absorption. The shift is accompanied by a decrease ing compounds 4a/5a, 4b/5b, and 4c/5c are similar, indicat-
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Optical Properties of Pyrrolopyrrole Cyanines
cessible with aza-aromatics having an extended π-system.
Further tuning of the optical properties can be achieved by
asymmetric substitution;[6] extension of both absorption
and emission up to and even beyond 1000 nm is attainable
by variation of the heterocycles used for bis-PPCy synthe-
ses.[12]
Experimental Section
General: Solvents were purified and dried according to standard
procedures. All commercially available reagents were used without
further purification unless otherwise noted. Column chromatog-
raphy was performed on Roth silica gel 60 (40–63 μm). All solvents
used for UV/Vis/NIR and fluorescence measurements were spectro-
scopic grade and were purchased from Fluka. NMR spectra were
recorded with a Bruker Avance III-400 (400 MHz) or a Bruker Av-
ance III-600 (600 MHz) spectrometer. The residual solvent peak
was used as internal reference (CHCl3: δ = 7.24 ppm; C2DHCl4: δ
= 5.91 ppm). For 1H NMR, multiplicity (s = singlet, d = doublet, t
= triplet, q = quartet, quint = quintet, m = multiplet) and coupling
constants are reported whenever possible. Structure and numbering
of the atoms for the assignment of the resonances are depicted
in the Supporting Information. MALDI-TOF mass spectra were
recorded with a Bruker Biflex III instrument in reflection mode or
a Bruker microflex; 2,5-dihydroxybenzoic acid (DHB) was used as
matrix. Elemental analysis was performed with a CHN analyser
Figure 2. Absorption and fluorescence emission spectra of BF2-
PPCy 4i and BPh2-PPCy 5i. The respective linewidths for the ab-
sorption are Δν00,A(4i) = 673 cm–1 and Δν00,A(5i) = 573 cm–1. The
˜
˜
corresponding values for the emission are Δν00,F(4i) = 1079 cm–1
˜
and ν00,F(5i) = 663 cm–1.
˜
ing that substitution on the quinoline moiety has little influ-
ence. However, a pronounced decrease was seen for the
phenylethynyl derivatives 4d/5d. For the benzothiazole-con- Vario EL from Elementar. Absorption and emission spectra were
recorded at ambient temperature by using 1 cm quartz cuvettes
(3 mL). UV/Vis/NIR absorptions were recorded with a Varian
spectrometer, model Cary 50; the spectra were processed with Spek-
win to calculate the oscillator strength.[13] Fluorescence spectra
were recorded with a self-assembled NIR fluorescence spectrometer
with a nitrogen-cooled Ge diode (Northcoast) as detector. Either a
diode laser (804 nm, 30 mW, model ACM30/1476 or 690 nm,
19 mW, model ACM19/1203) or an He–Ne laser (632.8 nm, 5 mW,
Spectra Physics model 105-1) were used for excitation. BF2-PPCy
(4a) (ΦF = 0.59 in CHCl3) and BPh2-PPCy (5a) (ΦF = 0.53 in
taining PPCys, no influence on the quantum yield was ob-
served for compounds with 6-(trifluoromethyl) or 6-tert-
butyl substitution. In contrast, substitution by π-donors,
such as methoxy, thiomethyl, and phenylethynyl groups, led
to a significant decrease in the fluorescence quantum yield.
No clear trend can be seen when the quantum yields for the
BF2-PPCys and their BPh2-PPCys counterparts are com-
pared. We interpret this as a result of two counteracting
influences; because torsional vibrations are seen as the main
cause of radiationless deactivation, a stiffer torsional poten- CHCl3) were used as references to determine the quantum yield.[4]
Synthesis and physical data of the reactants 1, 2a, 2e, 2i, BPh2Cl,[4]
tial – as observed for the BPh2-PPCys compared to the
BF2-PPCys – will lead to higher fluorescence quantum
and 2b[6] have already been published.
yield. The bathochromic shift for the BPh2-PPCys with re-
spect to the corresponding BF2-PPCys will, however, lead
to lower quantum yields because of better radiationless de-
activation, according to the energy gap law. As a result, an
increase or a decrease in the quantum yields upon replacing
the fluorine atoms by phenyl groups will occur, depending
on which of the two effects dominates.
tert-Butyl (2Z)-2-[6-Chloro-4-phenylquinolin-2(1H)-ylidene]-2-cy-
anoacetate (8):[8] To
solution of tert-butyl 2-cyanoacetate
a
(141.17 g, 150 mmol) and sodium tert-butoxide (96.1 g, 150 mmol)
in DMF (60 mL), 7[7] (13.7 g, 50 mmol) was added. After stirring at
105 °C for 3 h, the solution was cooled, DMF was removed under
reduced pressure, and a mixture of water (50 mL) and acetic acid
(2 mL) was added. The resulting solid was filtered, washed two
times with MeOH and filtered to give 8 (16.7 g, 44.0 mmol, 88%).
3
1H NMR (400 MHz, CDCl3): δ = 13.52 (s, 1 H, NH), 8.02 (d, J
4
3
= 9.0 Hz, 1 H, 8-H), 7.84 (d, J = 2.3 Hz, 1 H, 5-H), 7.68 (dd, J
4
Conclusions
= 9.0, J = 2.3 Hz, 1 H, 7-H), 7.50 (m, 5 H, PhH), 7.37 (s, 1 H, 3-
H), 1.57 (s, 9 H, tBu) ppm.
Many of the applications of NIR chromophores require
dyes with very specific spectral properties. For such fine-
tuning of the optical properties, we synthesized PPCys with
a variety of substituted heteroaromatics as end groups of
the chromophoric system. By using this approach, a broad
range of stable, highly fluorescing NIR dyes with high ab-
sorptivities between 690 and 845 nm is now available.
Shorter-wavelength-absorbing PPCys can be obtained with
monocyclic aza aromatics (pyridine, pyrimidines, pyrazine,
(6-Chloro-4-phenylquinolin-2-yl)acetonitrile (2c):[8] A solution of 8
(5.00 g, 13.19 mmol) in formic acid (140 mL) was stirred at 45 °C
for 1.5 h. The mixture was poured into an ice/ammonia solution,
and the resulting yellow solid was filtered and dried. Yield: 3.1 g
3
(11.1 mmol, 84%). 1H NMR (400 MHz, CDCl3): δ = 8.04 (d, J =
4
3
9.0 Hz, 1 H, 8-H), 7.86 (d, J = 2.3 Hz, 1 H, 5-H), 7.67 (dd, J =
4
9.0, J = 2.3 Hz, 1 H, 7-H), 7.54 (m, 3 H, PhH), 7.46 (m, 3 H, Ph,
3-H), 4.11 (s, 2 H, CH2) ppm. 13C NMR (100 MHz, CDCl3): δ =
150.60, 149.90, 147.03, 136.93, 133.42, 131.33, 131.32, 129.57,
or triazines), longer-wavelength-absorbing PPCys are ac- 129.33, 129.15, 126.80, 124.92, 120.88, 116.94, 27.57 ppm.
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A. Zumbusch et al.
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3
[6-(Phenylethynyl)quinolin-2-yl]acetonitrile (2d): Compound 2b SH) ppm. 13C NMR (100 MHz, CDCl3): δ = 150.47, 132.62 (q, J
3
1
(644 mg, 2.6 mmol) and phenylacetylene (850 mg, 8.32 mmol) were
dissolved in abs. THF (15 mL) and triethylamine (6 mL). The mix-
ture was degassed, and tetrakis(triphenylphosphane)palladium(0)
(150 mg, 0.13 mmol) and CuI (25 mg, 0.13 mmol) were added. The
mixture was heated to 60 °C overnight, cooled, added to CH2Cl2
(200 mL) and washed with H2O (250 mL), 1 m HCl (250 mL) and
again with H2O (2ϫ). The organic layer was dried with MgSO4,
and the solvent was removed. Column chromatography (CH2Cl2 Ǟ
CH2Cl2/ethyl acetate, 20:1) yielded 2d (615 mg, 2.29 mmol, 88%) as
a yellow solid. 1H NMR (400 MHz, CDCl3): δ = 8.23 (d, 3J =
= 4.0 Hz), 126.60 (q, J = 3.7 Hz), 124.48 (q, J = 271 Hz), 120.6
2
(q, J = 33.4 Hz), 114.42, 111.50 ppm.
[6-(Trifluoromethyl)benzothiazol-2-yl]acetonitrile (2h): Compound
12h (1.36 g, 7.18 mmol) and malononitrile (452 mg, 7.5 mmol) were
stirred in a mixture of glacial acetic acid (6 mL) and ethanol
(10 mL) at room temperature for 5 d. The mixture was added to
water (250 mL) and extracted with CH2Cl2. The combined organic
layers were washed with water, dried with MgSO4, and the solvent
was removed. Column chromatography (CH2Cl2) yielded 2h
(674 mg, 2.8 mmol, 39%) as a yellow solid. 1H NMR (400 MHz,
CDCl3): δ = 8.19 (m, 1 H, 7-H), 8.13 (m, 1 H, 4-H), 7.75 (m, 1 H,
5-H), 4.26 (s, 2 H, CH2) ppm. 13C NMR (100 MHz, CDCl3): δ =
161.79, 155.01, 135.82, 128.58 (q, 2J = 32.7 Hz), 124.18, 124.12 (q,
1J = 273 Hz), 124.02 (q, 3J = 3.5 Hz), 119.73 (q, 3J = 4.4 Hz),
114.60, 23.66 ppm.
8.5 Hz, 1 H, 4-H), 8.09 (d, J = 8.8 Hz, 1 H, 8-H), 8.03 (d, 4J =
3
3
4
1.7 Hz, 1 H, 5-H), 7.86 (dd, J = 8.8, J = 1.7 Hz, 1 H, 7-H), 7.57
(m, 3 H, 3-H, Ph), 7.37 (m, 3 H, Ph), 4.19 (s, 2 H, CH2) ppm. 13C
NMR (100 MHz, CDCl3): δ = 151.17, 147.12, 137.77, 133.34,
131.91, 130.97, 129.17, 128.91, 128.65, 127.17, 122.95, 122.53,
120.56, 116.83, 91.46, 88.82, 27.44 ppm.
2-(Naphtho[2,3-d]oxazol-2-yl)acetonitrile (2j): 2-Aminonaphthol
(1 g, 6.3 mmol; Sigma–Aldrich) and ethyl 2-cyanoacetimidate hy-
drochloride (983 mg, 6.6 mmol)[11] were heated to reflux in anhy-
drous CH2Cl2 (25 mL) for 60 h. The reaction mixture was diluted
with CH2Cl2 (25 mL) and washed twice with NaOH solution
(10%). The organic layer was dried with MgSO4. Removal of the
solvent yielded 2j (1.06 g, 5.1 mmol, 81%) as a grey solid. 1H NMR
(400 MHz, CDCl3): δ = 8.18 (s, 1 H), 7.98 (m, 2 H), 7.93 (s, 1 H),
7.51 (m, 2 H), 4.15 (s, 2 H, CH2) ppm. 13C NMR (100 MHz,
CDCl3): δ = 157.82, 150.00, 140.52, 132.07, 131.64, 128.91, 128.25,
126.37, 125.43, 118.43, 113.03, 107.14, 19.42 ppm.
(6-Methoxybenzothiazol-2-yl)acetonitrile (2f): 2-Amino-5-methoxy-
thiophenol (12f; 5.9 g, 38 mmol),[9] malononitrile (2.5 g, 38 mmol),
and glacial acetic acid (5 mL) were heated to reflux in acetonitrile
(30 mL) for 10 h. The acetonitrile was removed. Column
chromatography (petroleum ether/ethyl acetate, 2:1) yielded 2f
1
(1.5 g, 7.4 mmol, 20%). H NMR (400 MHz, CDCl3): δ = 7.89 (d,
4
3J = 9.0 Hz, 1 H, 4-H), 7.31 (d, J = 2.5 Hz, 1 H, 7-H), 7.09 (dd,
4
3J = 9.0, J = 2.5 Hz, 1 H, 5-H), 4.17 (s, 2 H, CH2), 3.87 (s, 3 H,
CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 158.47, 155.49,
147.55, 137.14, 124.10, 116.40, 115.19, 104.29, 56.06, 23.28 ppm.
[6-(Methylthio)benzothiazol-2-yl]acetonitrile
(2g):
2-Amino-5-
General Procedure for the Synthesis of H–PPCy Dyes 3: DPP 1
(1 mmol) and heteroarylacetonitrile 3 (2.5 mmol) were heated to
reflux in either anhydrous toluene or xylene (30 mL) under nitro-
gen. Phosphoryl chloride (8 mmol) was then added. The reaction
was monitored by UV/Vis/NIR spectroscopic analysis and thin-
layer chromatography. As soon as either 1 was used up or the con-
centration of the short-wavelength-absorbing by-products in-
creased, the reaction was stopped. The solvent and excess phos-
phoryl chloride were removed under vacuum, the crude product
was treated with methanol in an ultrasonic bath, and water was
added until a solid precipitated. The solid was collected by fil-
tration and washed with methanol until the filtrate became color-
less. If sufficiently soluble, the remaining solid was purified by col-
umn chromatography. Synthesis and physical data of 3a, 3e, and 3i
have been reported previously.[4]
(methylthio)benzenethiol (12g; 1.78 g, 10.4 mmol)[10] and malono-
nitrile (687 mg, 10.4 mmol) were stirred in a mixture of glacial
acetic acid (6 mL) and ethanol (10 mL) at room temperature for
2 d. The mixture was added to water (250 mL) and extracted with
CH2Cl2. The combined organic layers were washed with water,
dried with MgSO4, and the solvent was removed. Column
chromatography (petroleum ether/ethyl acetate, 4:1) yielded 2g
(1.54 g, 7 mmol, 67%) as a yellow solid. 1H NMR (400 MHz,
3
5
CDCl3): δ = 7.90 (dd, J = 8.9, J = 0.6 Hz, 1 H, 4-H), 7.70 (dd,
4J = 1.9, J = 0.6 Hz, 1 H, 7-H), 7.40 (dd, J = 8.6, J = 1.9 Hz, 1
H, 5-H), 4.19 (s, 2 H, CH2), 2.54 (s, 3 H, CH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 157.31, 150.91, 137.55, 136.38, 126.36,
123.56, 118.80, 115.00, 23.37, 16.57 ppm.
5
3
4
6-(Trifluoromethyl)benzothiazole (11h): Isoamyl nitrite (4.57 g,
39 mmol) was slowly added to a stirred solution of 6-(trifluoro-
methyl)benzothiazol-2-amine (10h; 3.86 g, 17.7 mmol)[14] in abs.
THF (30 mL). The mixture was heated to reflux for 30 min,
quenched with water, and extracted with ethyl acetate. The com-
bined organic layers were washed with water and brine, dried with
MgSO4, and the solvent was removed. Column chromatography
(CH2Cl2/petroleum ether, 6:1) yielded 11h (1.67 g, 8.2 mmol, 46%)
Compound 3b: The solubility of 3b in common solvents was too
low to allow purification by chromatography. The crude product
was digested in acetone, collected by filtration and washed with
acetone. Drying in air yielded 3b, which was pure enough to per-
form further reactions. 1H NMR (400 MHz, C2D2Cl4, 100 °C): δ
3
= 14.42 (s, 2 H, NH), 7.96 (d, J = 8.8 Hz, 2 H, 4-H), 7.90 (s, 2 H,
3
5-H), 7.77 (m, 8 H, AAЈ, 7-H, 8-H), 7.66 (d, J = 8.8 Hz, 2 H, 3-
1
as a yellow solid. H NMR (400 MHz, CDCl3): δ = 9.13 (s, 1 H,
3
H), 7.19 (m, 4 H, XXЈ), 4.16 (t, J = 6.6 Hz, 4 H, OCH2), 1.90 (m,
2-H), 8.25 (m, 1 H, 7-H), 8.21 (m, 1 H, 4-H), 7.74 (m, 1 H, 5-H)
ppm.
4 H, OCH2CH2), 1.42 [m, 4 H, O(CH2)2CH2], 1.5–1.3 (m, 16 H,
alkyl), 0.95 (m,
6 H, CH3) ppm. MALDI-MS: calcd. for
C56H54Br2N6O2 + 1 [M + H]+ 1003.3; found 1003.9.
2-Amino-5-(trifluoromethyl)benzenethiol (12h): A solution of 11h
(1.67 g, 8.2 mmol) and hydrazine monohydrate (3.08 g, 62 mmol)
in ethanol (20 mL) was heated to reflux for 1.5 h. The mixture was
added to a solution of acetic acid (6 mL) in water (200 mL) and
extracted with CH2Cl2. The combined organic layers were washed
with water and dried with MgSO4. Removal of the solvent yielded
12h (1.3 g, 7.18 mmol, 88%) as a yellow oil, which was used with-
out further purification. 1H NMR (400 MHz, CDCl3): δ = 7.61 (d,
Compound 3c: The solubility of 3c in common solvents was too low
to allow purification by chromatography. The crude product was
digested in acetone, collected by filtration and washed with acetone.
Drying in air yielded 3c, which was pure enough to perform further
reactions. MALDI-MS: calcd. for C68H62Cl2N6O2 + 1 [M + H]+
1065.4; found 1065.7.
3
4
4J = 1.6 Hz, 1 H, 6-H), 7.31 (dd, J = 8.5, J = 1.6 Hz, 1 H, 4-H), Compound 3d: Column chromatography (CH2Cl2) afforded 3d as a
3
1
6.73 (d, J = 8.5 Hz, 1 H, 3-H), 4.48 (s, 2 H, NH2), 2.93 (s, 1 H,
dark-green crystalline powder in 54% yield. H NMR (400 MHz,
3426
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 3421–3429

Optical Properties of Pyrrolopyrrole Cyanines
3
C2D2Cl4): δ = 14.45 (s, 2 H, NH), 7.84 (d, J = 8.9 Hz, 2 H, 4-H),
6.6 Hz, 4 H, OCH2), 1.89 (m, 4 H, OCH2CH2), 1.56 [m, 4 H,
7.76 (d, J = 1.7 Hz, 2 H, 5-H), 7.67 (m, 4 H, AAЈ), 7.61 (dd, 3J = O(CH2)2CH2], 1.5–1.3 (m, 16 H, alkyl), 0.96 (m, 6 H, CH3) ppm.
4
4
3
8.8, J = 1.7 Hz, 2 H, 7-H), 7.57 (d, J = 8.9 Hz, 2 H, 3-H), 7.53
UV/Vis/NIR (CHCl3): λmax (ε)
=
761 (229000), 689
(d, 3J = 8.8 Hz, 2 H, 8-H), 7.41 (m, 4 H, PhH), 7.24 (m, 6 H, PhH),
(48000 m–1 cm–1) nm. MALDI-MS: calcd. for C56H52B2Br2F4N6O2
7.13 (m, 4 H, XXЈ), 4.07 (t, J = 6.4 Hz, 4 H, OCH2), 1.82 (m, 4 [M + H]+ 1097.3; found 1097.9. C56H52B2Br2F4N6O2 (1098.49):
H, OCH2CH2), 1.47 [m, 4 H, O(CH2)2CH2], 1.4–1.2 (m, 16 H, calcd. C 61.23, H 4.77, N 7.65; found C 61.19, H 4.81, N 7.70.
alkyl), 0.85 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) =
3
Compound 4c: Column chromatography (CH2Cl2) afforded 4c as a
752 (166000), 681 (59000 m–1 cm–1) nm. C72H64N6O2 (1045.34):
green crystalline powder in 34% yield (relative to the crude product
calcd. C 82.73, H 6.17, N 8.04; found C 82.41, H 6.08, N 8.01.
1
3
3c). H NMR (400 MHz, C2D2Cl4): δ = 8.44 (d, J = 9.5 Hz, 2 H,
8-H), 7.68 (m, 6 H, 5-H, AAЈ), 7.56 (m, 2 H, 7-H), 7.55 (s, 2 H, 3-
H), 7.50 (m, 6 H, Ph), 7.38 (m, 4 H, Ph), 6.99 (m, 4 H, XXЈ), 3.99
Compound 3f: Column chromatography (CH2Cl2 to CH2Cl2/ethyl
acetate, 50:1) afforded 3f as a green crystalline powder in 19%
yield. 1H NMR (600 MHz, C2D2Cl4, 100 °C): δ = 7.70 (m, 4 H,
3
(t, J = 6.6 Hz, 4 H, OCH2), 1.75 (m, 4 H, OCH2CH2), 1.42 [m, 4
AAЈ), 7.68 (d, J = 8.8 Hz, 2 H, 4-H), 7.29 (d, 4J = 2.1 Hz, 2 H,
3
H, O(CH2)2CH2], 1.35–1.1 (m, 16 H, alkyl), 0.82 (m, 6 H, CH3)
3
4
7-H), 7.12 (m, 4 H, XXЈ), 7.03 (dd, J = 8.8, J = 2.1 Hz, 2 H, 5-
H), 4.10 (t, 3J = 6.4 Hz, 4 H, OCH2), 3.85 (s, 6 H, OCH3), 1.84
(m, 4 H, OCH2CH2), 1.51 [m, 4 H, O(CH2)2CH2], 1.45–1.25 (m,
16 H, alkyl), 0.91 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax
(ε) = 746 (106000), 676 (48000 m–1 cm–1) nm. MALDI-MS: calcd.
for C54H57N6O4S2 [M + H]+ 917.4; found 916.3. C54H56N6O4S2
(917.19): calcd. C 70.71, H 6.15, N 9.16, S 6.99; found C 70.57, H
6.18, N 9.00, S 7.09.
ppm. UV/Vis/NIR (CHCl3): λmax (ε)
= 767 (237000), 693
(51000 m–1 cm–1) nm. MALDI-MS: calcd. for C68H60B2Cl2F4N6O2
[M + H]+ 1161.4; found 1161.6. C68H60B2Cl2F4N6O2 (1161.78):
calcd. C 70.30, H 5.21, N 7.23; found C 70.36, H 5.37, N 7.28.
Compound 4d: The crude product was digested in methanol, col-
lected by filtration, and washed with methanol. Drying in air gave
4d in 86% yield as a green crystalline powder. 1H NMR (600 MHz,
3
3
C2D2Cl4, 100 °C): δ = 8.47 (d, J = 8.9 Hz, 2 H, 8-H), 8.01 (d, J
4
3
Compound 3g: Column chromatography (CH2Cl2 Ǟ CH2Cl2/ethyl
acetate, 100:1) afforded 3g as a green crystalline powder in 16%
yield. 1H NMR (400 MHz, C2D2Cl4): δ = 12.93 (s, 2 H, NH), 7.64
(m, 6 H, 4-H, AAЈ), 7.55 (d, J = 1.7 Hz, 2 H, 7-H), 7.28 (dd, J
= 8.5, 4J = 1.7 Hz, 2 H, 5-H), 7.08 (m, 4 H, XXЈ), 4.02 (t, 3J =
6.4 Hz, 4 H, OCH2), 2.48 (s, 6 H, SCH3), 1.78 (m, 4 H, OCH2CH2),
1.43 [m, 4 H, O(CH2)2CH2], 1.37–1.15 (m, 16 H, alkyl), 0.84 (m, 6
H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 751 (116000), 681
(52000 m–1 cm–1) nm. C54H56N6O2S4 (949.32): calcd. C 68.32, H
5.95, N 8.85, S 13.51; found C 67.95, H 5.81, N 9.00, S 13.57.
= 9.1 Hz, 2 H, 4-H), 7.83 (d, J = 1.7 Hz, 2 H, 5-H), 7.74 (dd, J
= 8.9, 4J = 1.7 Hz, 2 H, 7-H), 7.71 (d, J = 9.1 Hz, 2 H, 3-H), 7.68
3
(m, 4 H, AAЈ), 7.53 (m, 4 H, Ph), 7.33 (m, 6 H, Ph), 7.05 (m, 4 H,
XXЈ), 4.11 (t, 3J = 6.6 Hz, 4 H, OCH2), 1.86 (m, 4 H, OCH2CH2),
1.52 [m, 4 H, O(CH2)2CH2], 1.45–1.25 (m, 16 H, alkyl), 0.92 (m, 6
H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 778 (284000), 703
(59000 m–1 cm–1) nm. C72H62B2F4N6O2 (1140.93): calcd. C 75.80,
H 5.48, N 7.37; found C 75.54, H 5.55, N 7.51.
4
3
Compound 4f: Column chromatography (CH2Cl2) afforded 4f as a
green crystalline powder in 63% yield. 1H NMR (400 MHz,
Compound 3h: Column chromatography (CH2Cl2) afforded 3h as a
3
C2D2Cl4): δ = 7.87 (d, J = 9.2 Hz, 2 H, 4-H), 7.64 (m, 4 H, AAЈ),
green crystalline powder in 65% yield. 1H NMR (400 MHz,
4
3
4
7.16 (d, J = 2.4 Hz, 2 H, 7-H), 7.05 (dd, J = 9.2, J = 2.4 Hz, 2
H, 5-H), 7.03 (m, 4 H, XXЈ), 4.08 (t, 3J = 6.6 Hz, 4 H, OCH2),
3.83 (s, 6 H, OCH3), 1.84 (m, 4 H, OCH2CH2), 1.51 [m, 4 H,
O(CH2)2CH2], 1.45–1.25 (m, 16 H, alkyl), 0.91 (m, 6 H, CH3) ppm.
3
C2D2Cl4): δ = 12.91 (s, 2 H, NH), 7.89 (m, 2 H, 7-H), 7.80 (d, J
= 8.6 Hz, 2 H, 4-H), 7.92 (m, 6 H, 5-H, AAЈ), 7.06 (m, 4 H, XXЈ),
4.02 (t, J = 6.6 Hz, 4 H, OCH2), 1.79 (m, 4 H, OCH2CH2), 1.44
[m, 4 H, O(CH2)2CH2], 1.40–1.15 (m, 16 H, alkyl), 0.85 (m, 6 H,
CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 726 (130000), 659
(47000 m–1 cm–1) nm. C54H50B2F6N6O2S2 (1014.76): calcd. C 65.31,
H 5.07, N 8.46; found C 66.43, H 5.54, N 8.86.
3
UV/Vis/NIR (CHCl3): λmax (ε)
=
745 (171000), 674
(54000 m–1 cm–1) nm. MALDI-MS: calcd. for C54H54B2F4N6O4S2
1013.4 [M + H]+, 1035.4 [M + Na]+; found 1013.2, 1035.2.
C54H54B2F4N6O4S2 (1012.79): calcd. C 64.04, H 5.37, N 8.30;
found C 63.98, H 5.35, N 8.21.
Compound 3j: The solubility of 3j in common solvents was too low
to allow purification by chromatography. The crude product was
digested in acetone, collected by filtration, and washed with acet-
one. Drying in air yielded 3j, which was pure enough to perform
further reactions. MALDI-MS: calcd. for C60H56N6O4 + 1 [M +
H]+ 925.4; found 924.9.
Compound 4g: Column chromatography (CH2Cl2) afforded 4g as a
dark-green crystalline powder in 14% yield (relative to the crude
product 3g). 1H NMR (400 MHz, C2D2Cl4): δ = 7.78 (d, 3J =
4
8.8 Hz, 2 H, 4-H), 7.62 (m, 4 H, AAЈ), 7.49 (d, J = 1.7 Hz, 2 H,
7-H), 7.28 (dd, 3J = 8.8, 4J = 1.7 Hz, 2 H, 5-H), 7.00 (m, 4 H,
3
XXЈ), 4.00 (t, J = 6.6 Hz, 4 H, OCH2), 2.46 (s, 6 H, SCH3), 1.78
General Procedure for the Synthesis of BF2–PPCy Dyes 4: H-PPCy
dye 3 (1 mmol) and N,N-di-isopropylethylamine (20 mmol) were
heated to reflux in CH2Cl2 (100 mL). BF3·Et2O (40 mmol) was
added, and the mixture was heated to reflux for 10 min. The mix-
ture was washed with water and dried with MgSO4. After removal
of the solvent, the crude product was purified by column
chromatography. Synthesis and physical data of 4a, 4e, and 4i have
been previously reported.[4]
(m, 4 H, OCH2CH2), 1.43 [m, 4 H, O(CH2)2CH2], 1.37–1.15 (m,
16 H, alkyl), 0.84 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax
(ε) = 753 (165000), 683 (54000 m–1 cm–1) nm. MALDI-MS: calcd.
for C54H54B2F4N6O2S4 1045.3 [M
+
H]+; found 1044.8.
C54H54B2F4N6O2S4 (1044.91): calcd. C 62.07, H 5.21, N 8.04;
found C 61.70, H 5.36, N 8.16.
Compound 4h: Column chromatography (CH2Cl2) afforded 4h as a
green crystalline powder in 79% yield. 1H NMR (600 MHz,
C2D2Cl4, 118 °C): δ = 8.17 (m, 2 H, 4-H), 7.98 (m, 2 H, 7-H), 7.70
Compound 4b: The crude product was digested in methanol, col-
lected by filtration, and washed with methanol. Drying in air gave
4b in 74% yield (relative to the crude product 3b). 1H NMR
3
(m, 2 H, 5-H), 7.67 (m, 4 H, AAЈ), 7.05 (m, 4 H, XXЈ), 4.10 (t, J
3
(400 MHz, C2D2Cl4, 100 °C): δ = 8.42 (d, J = 9.5 Hz, 2 H, 8-H),
= 6.6 Hz, 4 H, OCH2), 1.84 (m, 4 H, OCH2CH2), 1.51 [m, 4 H,
O(CH2)2CH2], 1.45–1.15 (m, 16 H, alkyl), 0.91 (m, 6 H, CH3) ppm.
8.01 (d, J = 9.0 Hz, 2 H, 4-H), 7.89 (d, 4J = 2.2 Hz, 2 H, 5-H),
3
3
4
3
7.77 (dd, J = 9.5, J = 2.2 Hz, 2 H, 7-H), 7.75 (d, J = 9.0 Hz, 2 UV/Vis/NIR (CHCl3): λmax (ε)
=
719 (175000), 654
H, 3-H), 7.72 (m, 4 H, AAЈ), 7.08 (m, 4 H, XXЈ), 4.14 (t, 3J = (40000 m–1 cm–1) nm. C54H48B2F10N6O2S2 (1088.73): calcd.
C
Eur. J. Org. Chem. 2011, 3421–3429
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3427

A. Zumbusch et al.
FULL PAPER
59.57, H 4.44, N 7.72, S 5.89; found C 60.06, H 4.89, N 7.89, S
5.35.
Compound 5f: Column chromatography (CH2Cl2) afforded 5f as a
green crystalline powder in 72% yield. 1H NMR (400 MHz,
C2D2Cl4): δ = 7.13 (m, 8 H, PhH), 7.06 (m, 12 H, PhH), 6.92 (d,
Compound 4j: Column chromatography (CH2Cl2 Ǟ CH2Cl2/meth-
anol, 50:1) afforded 4j as a green crystalline powder in 6% yield
(relative to the crude product 3j). 1H NMR (600 MHz, C2D2Cl4,
100 °C): δ = 8.06 (s, 2 H, 4-H), 7.91 (m, 6 H, 5-H, 8-H, 9-H), 7.72
(m, 4 H, AAЈ), 7.53 (m, 4 H, 6-H, 7-H), 7.08 (m, 4 H, XXЈ), 4.12
3
4J = 2.6 Hz, 2 H, 7-H), 6.78 (d, J = 9.5 Hz, 2 H, 4-H), 6.53 (dd,
4
3J = 9.5, J = 2.6 Hz, 2 H, 5-H), 6.35 (m, 8 H, AAЈBBЈ), 3.85 (t,
3J = 6.7 Hz, 4 H, OCH2), 3.62 (s, 6 H, OCH3), 1.73 (m, 4 H,
OCH2CH2), 1.41 [m, 4 H, O(CH2)2CH2], 1.36–1.1 (m, 16 H, alkyl),
0.84 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 803
(200000), 721 (48500 m–1 cm–1) nm. MALDI-MS: calcd. for
C78H74B2N6O4S2 1244.5 [M + H]+, 1267.5 [M + Na]+; found
1244.1, 1267.1. C78H74B2N6O4S2 (1245.22): calcd. C 75.23, H 5.99,
N 6.75; found C 74.93, H 6.12, N 6.65.
3
(t, J = 6.6 Hz, 4 H, OCH2), 1.86 (m, 4 H, OCH2CH2), 1.53 [m, 4
H, O(CH2)2CH2], 1.45–1.3 (m, 16 H, alkyl), 0.92 (m, 6 H, CH3)
ppm. UV/Vis/NIR (CHCl3): λmax (ε)
= 699 (157000), 639
(45000 m–1 cm–1) nm. MALDI-MS: calcd. for C60H54B2F4N6O4
1021.4 [M + H]+, 1043.4 [M + Na]+; found 1020.8, 1042.9.
C60H54B2F4N6O4 (1020.74): calcd. C 70.60, H 5.33, N 8.23; found
C 69.84, H 5.48, N 8.20.
Compound 5g: Column chromatography (CH2Cl2/petroleum ether,
3:1) afforded 5g as an olive-green crystalline powder in 64% yield.
1H NMR (600 MHz, C2D2Cl4, 118 °C): δ = 7.32 (m, 2 H, 7-H),
7.22 (m, 8 H, PhH), 7.10 (m, 12 H, PhH), 6.86 (m, 2 H, 5-H), 6.81
General Procedure for the Synthesis of BPh2–PPCy Dyes 5: H-
PPCy 3 (1 mmol) and N,N-di-isopropylethylamine (3 mmol) were
heated to reflux in toluene. Chlorodiphenylborane (4.5 mmol) was
added, and the mixture was heated at reflux until the reaction was
complete (UV/Vis/NIR). The mixture was washed with water and
dried with MgSO4. After removing the solvent, the residue was
digested in methanol in an ultrasonic bath. The remaining solid
was separated by filtration, washed with methanol, and purified by
column chromatography. Synthesis and physical data of 5a, 5e, and
5i have been previously reported.[4]
3
(m, 2 H, 4-H), 6.46 (m, 4 H, AAЈ), 6.42 (m, 4 H, BBЈ), 3.94 (t, J
= 6.6 Hz, 4 H, OCH2), 2.36 (s, 6 H, SCH3), 1.78 (m, 4 H,
OCH2CH2), 1.48 [m, 4 H, O(CH2)2CH2], 145–1.15 (m, 16 H, alkyl),
0.92 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 808
(196000), 727 (48000 m–1 cm–1) nm. C78H74B2N6O2S4 (1277.34):
calcd. C 73.34, H 5.84, N 6.58; found C 73.18, H 5.91, N 6.58.
Compound 5h: Column chromatography (CH2Cl2/petroleum ether,
3:1) afforded 5h as a dark crystalline powder in 53% yield. 1H
NMR (400 MHz, C2D2Cl4): δ = 7.73 (d, 4J = 1.7 Hz, 2 H, 7-H),
7.20 (dd, 3J = 9.0, 4J = 1.7 Hz, 2 H, 5-H), 7.15 (m, 8 H, PhH),
Compound 5b: Column chromatography (CH2Cl2) afforded 5b as a
brown crystalline powder in 94% yield (relative to the crude prod-
3
1
3
7.09 (m, 12 H, PhH), 6.98 (d, J = 9.0 Hz, 2 H, 4-H), 6.38 (m, 8
uct 3b). H NMR (400 MHz, C2D2Cl4): δ = 7.99 (d, J = 9.7 Hz,
H, AAЈBBЈ), 3.86 (t, 3J = 6.7 Hz, 4 H, OCH2), 1.74 (m, 4 H,
OCH2CH2), 1.41 [m, 4 H, O(CH2)2CH2], 1.35–1.15 (m, 16 H,
alkyl), 0.85 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) =
776 (238000), 699 (37000 m–1 cm–1) nm. C78H68B2F6N6O2S2
(1321.16): calcd. C 70.91, H 5.19, N 6.36, S 4.85; found C 70.29,
H 5.60, N 6.27, S 5.23.
3
3
2 H, 8-H), 7.65 (d, J = 9.3 Hz, 2 H, 4-H), 7.52 (d, J = 9.3 Hz, 2
H, 3-H), 7.48 (d, J = 2.4 Hz, 2 H, 5-H), 7.20 (m, 8 H, PhH), 7.07
4
3
4
(dd, J = 9.7, J = 2.4 Hz, 2 H, 7-H), 7.04 (m, 12 H, PhH), 6.49
(m, 4 H, AAЈ), 6.04 (m, 4 H, XXЈ), 3.95 (t, 3J = 6.7 Hz, 4 H,
OCH2), 1.79 (m, 4 H, OCH2CH2), 1.45 [m, 4 H, O(CH2)2CH2],
1.4–1.1 (m, 16 H, alkyl), 0.85 (m, 6 H, CH3) ppm. UV/Vis/NIR
(CHCl3): λmax (ε) = 827 (280000), 742 (35000 m–1 cm–1) nm.
MALDI-MS: calcd. for C80H72B2Br2N6O2 1329.4 [M + H]+; found
1329.8. C80H72B2Br2N6O2 (1330.92): calcd. C 72.20, H 5.45, N
6.31; found C 72.09, H 5.34, N 6.28.
Compound 5j: Column chromatography (CH2Cl2) afforded 5j as a
turquoise crystalline powder in 53% yield (relative to the crude
1
product 3j). H NMR (400 MHz, C2D2Cl4): δ = 7.73 (m, 2 H, 8-
H), 7.68 (s, 2 H, 9-H), 7.48 (m, 2 H, 5-H), 7.36 (m, 2 H, 7-H), 7.31
(m, 2 H, 6-H), 7.21 (m, 8 H, PhH), 7.10 (m, 12 H, PhH), 6.70 (s,
Compound 5c: Column chromatography (CH2Cl2) afforded 5c as
red-brown crystalline powder in 40% yield (relative to the crude
product 3c). 1H NMR (400 MHz, C2D2Cl4): δ = 8.20 (d, 3J =
9.7 Hz, 2 H, 8-H), 7.46 (s, 2 H, 3-H), 7.40 (m, 6 H, PhH), 7.37 (d,
4J = 2.5 Hz, 2 H, 5-H), 7.26 (m, 12 H, PhH), 7.06 (m, 12 H, PhH),
6.96 (dd, 3J = 9.7, 4J = 2.5 Hz, 2 H, 7-H), 6.47 (m, 4 H, AAЈ), 6.04
(m, 4 H, XXЈ), 3.93 (t, 3J = 6.7 Hz, 4 H, OCH2), 1.78 (m, 4 H,
OCH2CH2), 1.44 [m, 4 H, O(CH2)2CH2], 1.4–1.1 (m, 16 H, alkyl),
0.85 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε) = 832
(293000), 746 (36000 m–1 cm–1) nm. MALDI-MS: calcd. for
3
2 H, 4-H), 6.64 (m, 4 H, AAЈ), 6.37 (m, 4 H, XXЈ), 3.84 (t, J =
6.6 Hz, 4 H, OCH2), 1.72 (m, 4 H, OCH2CH2), 1.40 [m, 4 H,
O(CH2)2CH2], 1.35–1.2 (m, 16 H, alkyl), 0.86 (m, 6 H, CH3) ppm.
UV/Vis/NIR (CHCl3): λmax (ε)
=
759 (196000), 687
(45000 m–1 cm–1) nm. C84H74B2N6O4 (1253.17): calcd. C 80.51, H
5.95, N 6.71; found C 80.40, H 6.13, N 6.84.
Supporting Information (see footnote on the first page of this arti-
cle): Absorption and fluorescence spectra of all dyes 4 and 5.
C92H80B2Cl2N6O2 1394.6 [M
+
H]+; found 1394.3.
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C 79.05, H 5.92, N 6.11.
Compound 5d: Column chromatography (CH2Cl2 Ǟ CH2Cl2/ethyl
acetate, 50:1) afforded 5d as a brown crystalline powder in 42%
yield (relative to the crude product 3d). 1H NMR (400 MHz,
C2D2Cl4): δ = 8.08 (d, 3J = 9.5 Hz, 2 H, 8-H), 7.71 (d, 3J = 9.5 Hz,
3
4
2 H, 4-H), 7.55 (d, J = 9.5 Hz, 2 H, 3-H), 7.51 (d, J = 1.8 Hz, 2
3
H, 5-H), 7.37 (m, 4 H, PhH), 7.24 (m, 14 H, PhH), 7.12 (dd, J =
9.5, 4J = 1.8 Hz, 2 H, 7-H), 7.04 (m, 12 H, PhH), 6.51 (m, 4 H,
3
AAЈ), 6.08 (m, 4 H, XXЈ), 3.97 (t, J = 6.6 Hz, 4 H, OCH2), 1.81
(m, 4 H, OCH2CH2), 1.49 [m, 4 H, O(CH2)2CH2], 1.42–1.2 (m, 16
H, alkyl), 0.86 (m, 6 H, CH3) ppm. UV/Vis/NIR (CHCl3): λmax (ε)
= 843 (309000), 756 (42000 m–1 cm–1) nm. C96H82B2N6O2 (1373.36):
calcd. C 83.96, H 6.02, N 6.12; found C 83.75, H 6.19, N 6.09.
3428
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: January 25, 2011
Published Online: May 24, 2011
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Eur. J. Org. Chem. 2011, 3421–3429
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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