Red-emitting dyes with photophysical and photochemical properties controlled by pH

Article abstract of DOI:10.1002/chem.201101123

New unsymmetrical zinc azaphthalocyanines, bearing one substituted aniline as a peripheral substituent, were prepared by using a statistical condensation approach. Both fluorescence and singlet oxygen quantum yields were extremely low in DMF (φ_F<0.01, φ_Δ<0.02, respectively), but increased after the addition of sulfuric acid, reaching values comparable to controls without aniline substituents (φ_F=0. 22-0.29, φ_Δ=0.40-0.59, respectively). This behavior was attributed to the deactivation of excited states by intramolecular charge transfer from a donor site (aniline), which was blocked after protonation in acidic media. In the protonated form, all of the compounds efficiently emitted light with λ_em in the region of 662-675 nm. The investigated compounds were anchored to dioleoylphosphatidylcholine (DOPC) unilamellar vesicles and showed response to buffer pH. They were highly fluorescent at low pH values and almost nonfluorescent in neutral solutions. The pK_a values were determined in DOPC vesicles and ranged between 2.2 and 4.2.

Full text of DOI:10.1002/chem.201101123

FULL PAPER
DOI: 10.1002/chem.201101123
Red-Emitting Dyes with Photophysical and Photochemical Properties
Controlled by pH
Veronika Novakova,[a] Miroslav Miletin,[b] Kamil Kopecky,[b] and Petr Zimcik*[b]
Abstract: New unsymmetrical zinc
azaphthalocyanines, bearing one substi-
tuted aniline as a peripheral substitu-
ent, were prepared by using a statistical
condensation approach. Both fluores-
cence and singlet oxygen quantum
yields were extremely low in DMF
(FF <0.01, FD <0.02, respectively), but
increased after the addition of sulfuric
acid, reaching values comparable to
controls without aniline substituents
(FF =0.22–0.29, FD =0.40–0.59, respec-
tively). This behavior was attributed to
the deactivation of excited states by in-
tramolecular charge transfer from a
donor site (aniline), which was blocked
after protonation in acidic media. In
the protonated form, all of the com-
pounds efficiently emitted light with
lem in the region of 662–675 nm. The
investigated compounds were anchored
to
dioleoylphosphatidylcholine
(DOPC) unilamellar vesicles and
showed response to buffer pH. They
were highly fluorescent at low pH
values and almost nonfluorescent in
neutral solutions. The pKa values were
determined in DOPC vesicles and
ranged between 2.2 and 4.2.
Keywords: dyes/pigments · fluores-
cence · liposomes · phthalocyanines ·
sensors · singlet oxygen
Introduction
mophore that quenches the excited states.[3,6,7] The wave-
length of excitation and emission of the dyes employed in
these applications are optimally over 640 nm, because of
deeper penetration of the light through tissues and the elim-
ination of possible autofluorescence of the endogenous
chromophores, for example hemoglobin.[1]
Changes in photophysical and photochemical parameters of
different dyes depending on the surrounding environment
has been widely utilized in last few decades for the develop-
ment of various sensors or imaging agents.[1,2] In particular,
reversibly switching between ON and OFF states based on
pH changes has recently gained attention in the visualiza-
tion or more selective treatment of tumors using photody-
namic therapy (PDT).[3–6] Generally, two mechanisms lead-
ing to the ON–OFF switching were recently used for the
design of new pH dependent probes. The first one employs
static quenching (OFF) between two molecules of a chro-
mophore[5] or between the chromophore and a quencher.[4]
The subsequent changes in the pH lead to an increase in the
distance between these dyes and the loss of quenching (ON
state). Another approach is based on photoinduced electron
transfer (PET) from amines to aromatic system of the chro-
Phthalocyanines (Pc) and their aza analogues, azaphthalo-
cyanines (AzaPc), are characterized by strong absorptions,
which are usually over 650 nm, good chemical stability, low
photobleaching, and sufficient quantum yields of fluores-
cence (FF) and singlet oxygen (FD).[8,9] Singlet oxygen pro-
duced after excitation of a photosensitizer is essential for
phototoxic effects in PDT.[10] For these reasons, Pc and
AzaPc represent ideal chromophore systems for the above-
mentioned applications. Despite this, the first and only Pc
with pH controlled photochemical and photophysical prop-
erties was developed only recently.[6,11] A likely explanation
for a lack of extensive studies in this area is that Pc macro-
cycles behave mostly as electron donors and not as accept-
ors.[12] The switching between ON and OFF states in sensors
is usually based on electron transfer from a donor (usually
amine) to an acceptor (a macrocycle dye), as in the case of
the silicon Pc substituted axially with aliphatic polyamine
chains.[6,11] Recently, we independently showed that intramo-
lecular charge transfer (ICT) from peripherally substituted
aromatic amines in AzaPc strongly influences FF and FD
values.[13,14] The ICT occurs when the donor amines are con-
jugated with AzaPc macrocycle. The ICT in AzaPc was also
shown to be easily controlled by environmental proper-
ties,[13,14] similarly as was observed for PET in porphyrinoid
systems.[15,16]
[a] Dr. V. Novakova
Department of Biophysics and Physical Chemistry
Faculty of Pharmacy in Hradec Kralove
Charles University in Prague
Heyrovskeho 1203, Hradec Kralove (Czech Republic)
Fax : (+420)495067167
[b] Dr. M. Miletin, Dr. K. Kopecky, Dr. P. Zimcik
Department of Pharmaceutical Chemistry and Drug Control
Faculty of Pharmacy in Hradec Kralove
Charles University in Prague
Heyrovskeho 1203, Hradec Kralove (Czech Republic)
Fax : (+420)495067167
E-mail: petr.zimcik@faf.cuni.cz
In the presented work, several new AzaPc compounds
which emit in the red portion of the UV/Vis spectrum were
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101123.
Chem. Eur. J. 2011, 17, 14273 – 14282
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14273

prepared, and their fluorescence and singlet oxygen produc-
tion with regards to pH is described. The aim of this work
was to develop compounds that extend the group of Pc and
AzaPc dyes to also be sensitive to lower pH values, which
may not be always achievable with strategies using more
basic aliphatic amines.[17] The sensitivity to lower pH that
occurs in lysosomes was recently successfully applied in the
imaging of viable cancer cells in vivo with BODIPY
(BODIPY=borondipyrromethene) antibody conjugates
with pKa values in the 4.4–5.8 range.[3]
in which substituents R1 and R2 are intended to modulate
the basicity of the donor. The substituent R3 is present only
for synthetic reasons and does not play an important role in
the mechanism of pH sensitivity.
The general methods leading to Pc and AzaPc core for-
mations employed cyclotetramerization of the correspond-
ing precursors, substituted phthalonitriles and pyrazine-2,3-
dicarbonitriles, respectively.[21] Because the compounds in-
volved in this study combined both Pc and AzaPc units, dif-
ferent synthetic routes had to be considered in the syntheses
of the precursors. The 5,6-disubstituted pyrazine-2,3-dicar-
bonitriles can be prepared either from 5,6-dichloropyrazine-
2,3-dicarbonitrile by nucleophilic substitution[22] or by con-
densation of the appropriate diketone with diaminomaleoni-
trile (DAMN).[23] The former procedure is suitable for the
alkylheteroatom-substituted pyrazines and was used for syn-
thesis of 6 (Scheme 1). The latter method was applied for
Results and Discussion
Synthesis: The design of the molecules was based on the fol-
lowing rational considerations. The photophysical and pho-
tochemical properties of AzaPc or Pc may be controlled by
PET or ICT as shown previously.[6,14] According to our expe-
rience, ICT, in which the donor is directly conjugated with
macrocyclic system, is more efficient than PET, in which the
electron must “jump” through space. In particular, the dis-
tance plays a crucial role in the PET quenching of the excit-
ed states.[18] The high efficiency of ICT is supported by the
fact that only one donor center in ICT is enough to efficient-
ly switch off the excited states.[14] Since the probes are in-
tended to be used at lower pH values, the substituted aniline
moiety with generally lower and substituent tunable pKa
values seems to be well suited to carry the donor. Besides
the pH sensitive moiety, bulky substituents should be intro-
duced to the periphery of the macrocycle to prevent a self-
aggregation that is a well-known phenomenon of planar aro-
matic systems and decreases the photophysical and photo-
chemical properties without any control. tert-Butylsulfanyl
substituents have been shown to efficiently inhibit the aggre-
gation both in organic solvents and liposomal mem-
branes.[19,20] Zinc(II) as the central cation is known to in-
crease triplet state lifetimes of Pc and AzaPc and gives the
macrocycle reasonable fluorescence and singlet oxygen
quantum yields.[8] All of the above-mentioned conditions
were combined into a model compound depicted in Figure 1
Scheme 1. Reaction conditions: i) POCl3, DMF, RT; ii) KCN, EtOH/
water, reflux; iii) Cu
ACHTUGNRTNE(NGNU CH3COO)2, NH4NO3, acetic acid, reflux; iv) acetic
acid, reflux; and v) NaOH/water, THF, (CH3)3CSH, RT.
ꢀ
the pyrazines with the substituents connected through C C
bonds (4a–c and 5) following the synthesis of the appropri-
ate diketones 3a–c (Scheme 1). Thus, Vilsmeier–Haack for-
mylation was used for the synthesis of the aldehyde 1b,[24]
which was then treated with nicotinaldehyde under benzoin
condensation conditions to form unsymmetrical acyloin 2b
in a moderate yield of 20% (Scheme 1). Similarly, commer-
cially available 1a gave acyloins 2a and 2c after condensa-
tion with benzaldehyde or nicotinaldehyde, respectively
(Scheme 1).[13] Oxidation of the acyloins with copper(II)
gave diketones 3a–c that reacted with DAMN to produce
the desired pyrazine-2,3-dicarbonitriles 4a–c. Similarly, the
Figure 1. Models of pH sensitive compounds investigated in this work.
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pH-Controlled Red-Emitting Dyes
FULL PAPER
condensation of benzil with DAMN gave compound 5
(Scheme 1).[25]
The electronic effects of benzene are dissimilar to a pyra-
zine ring and that is why different procedures had to be ap-
plied for the synthesis of 4-substituted phthalonitriles 9a
and 9b (Scheme 2). Thus, bromination of N,N-diethyl-3-
Scheme 3. Reaction conditions: i) Mg, butanol, reflux; ii) p-toluenesulfon-
ic acid, THF, RT; and iii) ZnACHTUNTRGNEUNG(CH3COO)2, DMF, reflux.
the ABBB congeners were isolated. The isolation of the de-
sired congener was performed in the metal-free form, be-
cause of strong tailing and overlapping of the fractions of
the metal complexes (both magnesium(II) and zinc(II)). The
last step involved chelation of zinc(II) into the center of the
complex by heating the metal-free derivative in DMF with
anhydrous zinc acetate. The overall yields of the statistical
condensation, isolation and metal exchange in AzaPc were
in a range of 7–14%. The symmetrical compound 15 was
prepared by simple cyclotetramerization of 6 as previously
described.[20] Compounds 15 and 16 were used as “always-
ON” controls. Since they did not contain a donor center for
ICT, they were expected not to respond to the pH changes.
Scheme 2. Reaction conditions: i) NBS, DMF, RT; ii) triisopropylborate,
THF, BuLi/hexane, ꢀ788C; and iii) K2CO3, [Pd
ACHTUNGTRENUN(NG PPh3)4], THF/water,
reflux.
methylaniline with N-bromosuccinimide (NBS) gave the
compound 7b in excellent yield of 93% (Scheme 2). Com-
pounds 7a (available commercially) and 7b were subse-
quently converted to phenylboronic acids 8a and 8b, which
underwent Suzuki coupling with 4-iodophthalonitrile to give
the desired 9a and 9b in good yields of 78 and 56%, respec-
tively (Scheme 2). Originally, we intended to include also 4’-
(diethylamino)-3’-methylbiphenyl-3,4-dicarbonitrile
(see
Supporting Information) into the study. However, all of the
tested routes to 4-halogeno-N,N-diethyl-2-methylaniline,
which is a key precursor of the substituted phenylboronic
acid, failed. These routes are widely discussed in the Sup-
porting Information and involved the bromination and iodi-
nation of N,N-diethyl-2-methylaniline with various agents or
several alkylation attempts of 4-bromo-2-methylaniline.
The above precursors were used for the synthesis of
AzaPc compounds 10–16 (Scheme 3). In the case of the un-
symmetrical Pc and AzaPc derivatives, two different units
(A and B) are involved in the cyclization. Their random
combination during the reaction gives a statistical mixture
consisting of AAAA, ABBB, ABAB, AABB, AAAB, and
BBBB congeners. The desired congener was then separated
by chromatographic methods. Although some selective
methods have been published,[26] statistical condensation still
remains a useful and reliable tool for preparation of the
ABBB congener.[27]
Photophysical and photochemical characterization: All of
the prepared AzaPc compounds showed absorption spectra
typical for Pc and AzaPc compounds with a high-energy B
band in region of 377–390 nm and a low-energy Q-band in
the region of 655–670 nm with two vibration bands in region
of 600–640 nm (Table 1, Figure 2). The absorption spectra
indicated the presence of only the monomeric form; no ag-
gregation was detected during the whole study in coordinat-
ing solvents (THF, DMF). Despite the unsymmetrical com-
position of the macrocycle, the Q-bands were not split
(Figure 2). This is due to similar electronic effects of the al-
kylsulfanyl and aryl substituents in the compounds 10–12
and 16. Only a broadening of the Q-band was observed in
the cases of 13 and 14 with one phthalonitrile moiety in the
macrocycle. In these cases, the unsymmetrical composition
of the macrocyclic core (three pyrazines and one benzene
ring) may influence the shape of the Q-band, but the posi-
tions of the Qx and Qy bands were apparently close to each
other, this leading to the broadening and not to splitting
(Figure 2). Conjugation of the lone-pair of the donor center
with a macrocyclic system was indicated by very small red-
shift of lmax of pH sensitive compounds (e.g., 10–12) when
compared with compounds without the donor (15, 16). This
Thus, the statistical condensation of the precursors 4a–c,
5, and 9a–b (A) with 6 (B, Scheme 3) in a 1:3 molar ratio in
butanol with magnesium(II) butoxide gave a statistical mix-
ture of the magnesium(II) complexes. Subsequent removal
of the central magnesium(II) by p-toluenesulfonic acid af-
forded metal-free dyes that were separated over silica, and
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P. Zimcik et al.
Table 1. Photophysical and photochemical data of compounds 10–16 in DMF and DMF with sulfuric acid (SA).
[d]
Absorption lmax
(DMF/DMF+SA)
Emission
lmax
FF
(DMF)
FF
(DMF+SA)[a]
FF
(toluene)
Factor of
increase
(FF)[b]
FD
(DMF)[c]
FD
ACHTUNGTRENNUNG
(DMF+SA)[a,c]
Factor of
increase
(FD)[b]
pKa
G
E
N
R
10
11
12
13
14
15
16
660/656
660/658
658/658
671/664
669/664
654/654
655/655
663
666
666
675
675
662
662
0.0036
0.0061
0.0050
0.0050
0.010
0.36
0.29
0.29
0.26
0.22
0.25
0.34
0.31
0.0032
0.0020
0.010
0.11
0.15
–
81
48
52
44
25
0.94
1.03
0.023
0.014
0.018
0.005
0.015
0.60
0.42
0.40
0.59
0.55
0.58
0.56
0.55
18
29
33
110
39
2.6
2.7
3.4
2.2
4.2
–
0.94
0.92
0.30
–
0.60
–
[a] DMF with 5% (v/v) sulfuric acid. [b] Calculated as follows: (value in DMF+SA)/(value in DMF). [c] ZnPc as reference in DMF (FD =0.56) or 15 as
reference in DMF+SA (FD =0.56). [d] Determined in DOPC liposomes.
Figure 3. Fluorescence emission spectra of 13 in DMF with the addition
of sulfuric acid up to 1% (lexc =603 nm). This represents typical behavior
of compounds 10–14. Inset: Dependence of FF value of 13 in DMF on
sulfuric acid added.
Figure 2. Absorption spectra of 11 (a), 14 (c) and 16 (g) in DMF.
Spectra were normalized to the same absorption in the Q-band. Inset:
Normalized absorption spectra of 11 in DMF (a) and DMF with 5%
sulfuric acid (c).
redshift was partially removed by protonation of the amino
moiety after the addition of sulfuric acid (5%) into the
DMF solution (Table 1, Figure 2 inset).
(Table 1). As mentioned above, the compounds were in the
monomeric form and, therefore, aggregation cannot account
for the low quantum yields. Stepwise addition of sulfuric
acid into solutions of 10–14 in DMF led to rapid increase of
the FF values as a consequence of inhibition of the ICT by
protonation of the peripheral amino groups (Figure 3,
Figure 4). A shift in the emission maxima or changes in the
In noncoordinating solvents, the peripheral amino sub-
stituents or pyridyl rings may be susceptible to coordination
with the central zinc(II) to form supramolecular assemblies.
The spectra in toluene (Supporting Information, Figure S3)
showed that this happened only when the whole macrocycle
was composed of pyrazine rings (compounds 10, 11, and 12).
The absorption spectra were typical for the formation of
slipped J-dimers recently described.[14,28] In the case of com-
pound 12, the spectra indicated an equilibrium between the
monomer and J-dimer, most likely due to steric hindrance
caused by methyl in the ortho-position on the peripheral
benzene ring. However, J-dimers were not detected in the
spectra of 13 and 14.
After excitation, the investigated compounds 10–16 in
DMF emitted fluorescence with emission maxima in region
of 663–675 nm, although the signal was very weak for com-
pounds 10–14. The fluorescence emission spectra were typi-
cal for Pc, AzaPc, and similar compounds (Figure 3).[29]
Fluorescence quantum yields (FF) of 10–14 in DMF (unsub-
stituted zinc(II) phthalocyanine (ZnPc) as reference,
FF(chloronaphthalene) =0.30[30]) were extremely low owing to ultra-
fast ICT that efficiently quenched the excited states
~
!
*
Figure 4. Dependence of FF values of 10 ( ), 12 (&), 14 ( ), and 15 (
)
in DMF on sulfuric acid added. Inset: enlarged part of the graph for com-
*
pounds 12 (&) and 14 ( ).
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pH-Controlled Red-Emitting Dyes
FULL PAPER
shapes of the emission spectra were not observed during the
titrations (Figure 3). All of the compounds reached a pla-
teau for the FF values, apparently after full protonation of
the aniline moiety when a donor center is no longer avail-
able for the ICT. It is worth noting that FF increased by
almost two orders of magnitude and reached the values
comparable with the always ON controls (see also Table 1).
Compounds 15 and 16 in DMF showed the high FF values
typical for ZnAzaPc. Very slow decreases in FF, which
became steep after approximately 15% of the sulfuric acid
was added to the solution, were observed upon acidification.
This behavior may be attributed to the protonation of azo-
methine nitrogen atoms as deduced from changes in the ab-
sorption spectra (see Supporting Information, Figure S2).
Protonation of these sites in the Pc or AzaPc macrocycles
has been widely discussed in previous works and was shown
to significantly decrease the fluorescence and singlet oxygen
quantum yields.[13,31] Similar to 15 and 16, protonation of the
azomethine nitrogen atoms was also detected for 10–14, but
at higher sulfuric acid concentrations (generally above 20%,
Figure 4). This does not represent an obstacle in the devel-
opment of pH sensitive dyes because the basicity of the azo-
methine nitrogen atoms is low, and these nitrogen atoms
were protonated only in strongly acidic media.
In toluene, a significant increase of FF, one order of mag-
nitude, was observed for compounds 13 and 14 (Table 1)
due to decreased feasibility of ICT in the less polar solvent,
which is consistent with the findings published in the litera-
ture.[14,15] A significant influence of the decreased polarity
was not observed in compounds 10 and 11 that formed J-
dimers in this noncoordinating solvent. Compound 12
showed only a moderate increase of FF due to equilibrium
between the monomer and J-dimer. The results indicated
that formation of J-dimers also deactivated the excited
states.
tonated at this concentration of sulfuric acid (Supporting In-
formation, Figure S1). For this reason, compound 15 was
used as the reference in DMF with 5% sulfuric acid. The
FD =0.56 was calculated on the basis of “factor of increase”
from fluorescence measurements (Table 1).
In order to mimic the pH sensitivity in a biologically rele-
vant environment, the investigated compounds were anch-
ored to dioleoylphosphatidylcholine (DOPC) large unila-
mellar vesicles (liposomes). Liposomes, particularly unila-
mellar, are considered to be simple models of biological
membranes.[35] That is why, DOPC large unilamellar vesicles
were prepared by the extrusion method, and compounds
10–16 were incorporated into a lipidic bilayer.[19] The de-
pendence of the fluorescence signal on the pH was mea-
sured in buffer solutions with pH values ranging from 2.6 to
7.4. It must be noted that the absorption spectra of AzaPc
in liposomes were of monomeric character, and J-dimers
contributions were not observed (Supporting Information,
Figure S4). Thus, the changes in fluorescence intensity can
be attributed solely to ICT and the block thereof after pro-
tonation. As anticipated, the pH sensitive compounds
became highly fluorescent at low pH levels and almost non-
fluorescent at higher pH levels. A quite steady fluorescence
signal which was not dependent on pH was detected for the
always ON controls (Figure 5). The factor of increase for
Singlet oxygen quantum yields were determined in DMF
using decomposition of a specific singlet oxygen scavenger,
diphenylisobenzofuran (DPBF), with ZnPc as a reference
(FD(DMF) =0.56[32]). Similar to what was observed for fluores-
cence in DMF, the FD of compounds 10–14 reached very
low values and the controls (15 and 16) showed values typi-
cal for ZnAzaPc.[33,34] After acidification (5% sulfuric acid
in solution), the FD values of all of the compounds were
comparable due to the inhibition of the ICT in the pH sensi-
tive derivatives (Table 1). Singlet oxygen production for the
pH sensitive derivatives increased several times (by a factor
of 18–110) upon changing the acidity of the solutions. The
concentration of the sulfuric acid was chosen on the basis of
the fluorescence experiments, in which 5% sulfuric acid in
DMF was shown to be enough to restore the fluorescence
quantum yields of all of the compounds (10–14) to normal,
and, at the same time, the changes could not be attributed
to significant protonation of azomethine nitrogen atoms
(Figure 4; Supporting Information, Figure S1). Despite this,
determination of the FD values in the acidified solution was
complicated by the stronger basicities of azomethine nitro-
gen atoms of the reference ZnPc, which was extensively pro-
~
Figure 5. Changes in the fluorescence intensity of compounds 12 ( ), 13
!
*
(
), 14 ( ), and 16 (&) in DOPC liposomes dependent on the pH of the
buffer. F is the fluorescence intensity at the actual pH, Fmax is the maxi-
mum value from all pH values for the respective compound (lexc
382 nm). The mean of three measurements is plotted, and error bars rep-
resent the standard deviation.
=
AzaPc (10–14) was generally over 20, but reached 70 for
compound 14. This increase suggests a good signal-to-noise
ratio between the ON and OFF states. The changes in fluo-
rescence intensities allowed the determination of the pKa of
the donor center by applying the Henderson–Hasselbalch
equation. The pKa values (Table 1) ranged between 2.2 and
4.2 and corresponded well with electron donating effects of
alkyl substituents on the aniline moiety. Compounds 12 and
14, containing the 4-(diethylamino)-2-methylphenyl substitu-
ent, belonged among the most basic in the study.
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P. Zimcik et al.
nide solution (1 mL) in ethanol (5 mL). The solution was heated at reflux
for 48 h. Ethanol was evaporated, and the mixture was extracted with
ethylacetate/water. The organic layer was dried over anhydrous Na2SO4
and evaporated. The crude product was purified over silica with ethylace-
tate as an eluent to yield a yellow oil (580 mg, 20%, 2b and 180 mg, 6%,
3b). 1H NMR (300 MHz, [D6]acetone): d=1.13 (t, J=7 Hz, 6H;
CH2CH3), 2.47 (s, 3H; CH3), 3.42 (q, J=7 Hz, 4H; CH2CH3), 6.07 (s,
Conclusion
Several new unsymmetrical ZnAzaPc compounds with ab-
sorption and emission maxima in the red portion of the UV/
Vis spectrum were synthesized from the corresponding pre-
cursors. Substituted anilino moieties in AzaPc served as the
donor for ICT, a process that efficiently quenched the excit-
ed states in DMF, leading to very low FD and FF values.
Protonation of the donor center by the addition of sulfuric
acid led to strong increases in both parameters and to values
that were comparable with always ON controls. All of the
compounds were incorporated into DOPC liposomes, and
AzaPc (10–14) showed fluorescence signal responses relative
to the pH of the buffer solution with pKa values in the
range 2.2–4.2. All of the above-mentioned measurements
unequivocally demonstrated that photophysical and photo-
chemical properties of the concerned compounds are easily
modified by acidification and that they may serve as sensors
or pH controlled photosensitizers in areas for which low pH
is appreciated and light activation at higher wavelengths de-
sirable.
1H; CHOH), 6.48–6.54 (m, 2H; ArH
5 Hz, 1H; ArH(aniline)), 7.68 (dt, J1 =8 Hz, J2 =2 Hz, 1H; ArH-
(pyridyl)), 7.85 (d, J=9 Hz, 1H; ArH(pyridyl)), 8.41 (dd, J1 =5 Hz, J2 =
2 Hz, 1H; ArH(pyridyl)), 8.64 ppm (d, J=2 Hz, 1H, ArH(pyridyl));
ACHTUNGTREN(NUNG aniline)), 7.26 (dd, J1 =8 Hz, J2 =
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
13C NMR (75 MHz, [D6]acetone): d=12.73, 23.30, 44.77, 73.64, 108.47,
114.75, 120.18, 124.32, 134.21, 135.14, 138.05, 144.32, 149.66, 149.93,
151.66, 197.56 ppm; IR (ATR): n˜ =2973, 2929, 1706, 1650, 1596, 1540,
1470, 1454, 1426, 1396, 1378, 1356, 1328, 1289, 1258, 1195, 1135, 1073,
1026, 1001, 965, 940, 843, 790, 753 cmꢀ1
.
1-[4-(Diethylamino)-2-methylphenyl]-2-(pyridin-3-yl)ethane-1,2-dione
(3b): Compound 2b (580 mg, 1.94 mmol), ammonium nitrate (195 mg,
2.43 mmol) and copper(II) acetate (3.5 mg, 0.019 mmol) were dissolved
in 80% (v/v) acetic acid (20 mL) and then heated to reflux for 2 h. The
mixture was concentrated and extracted three times with ethylacetate/
water. The organic layer was dried over anhydrous Na2SO4, and the sol-
vent was evaporated. The crude product was purified by column chroma-
tography over silica with ethylacetate as an eluent to yield a yellow oil
(507 mg, 88%). 1H NMR (500 MHz, [D6]DMSO): d=1.10 (t, J=7 Hz,
6H; CH2CH3), 2.61 (s, 3H; CH3), 3.42 (q, J=7 Hz, 4H; CH2CH3), 6.53
(dd, J1 =9 Hz, J2 =3 Hz, 1H; ArH
(aniline)), 7.36 (d, J=9 Hz, 1H; ArH
5 Hz, J3 =8 Hz, 1H; ArH(pyridyl)), 8.23 (dt, J1 =2 Hz, J2 =8 Hz, 1H;
ArH(pyridyl)), 8.86 (dd, J1 =5 Hz, J2 =2 Hz, 1H; ArH(pyridyl)),
8.99 ppm (dd, J1 =1 Hz, J2 =2 Hz, 1H; ArH
(pyridyl)); 13C NMR
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Experimental Section
G
ACHTUNGTRENNUNG
General: All of the organic solvents used were of analytical grade. Anhy-
drous butanol was stored over magnesium and distilled prior to use. All
of the chemicals for synthesis were obtained from established suppliers
(Aldrich, Acros, Merck) and used as received. Sulfuric acid used for titra-
tions was obtained from Penta (Czech Republic) and contained 96% sul-
furic acid and 4% water. Zinc phthalocyanine (ZnPc) was purchased
from Aldrich. TLC was performed on Merck aluminum sheets with silica
gel 60 F254. Merck Kieselgel 60 (0.040–0.063 mm) was used for column
chromatography. Melting points were measured on an Electrothermal
IA9200 Series Digital Melting Point apparatus (Electrothermal Engineer-
ing Ltd., Southend-on-Sea, Essex, Great Britain). Infrared spectra were
measured on a Nicolet Impact 400 IR spectrometer (KBr) or Nicolet
6700 (ATR mode). 1H and 13C NMR spectra were recorded on a Varian
Mercury Vx BB 300 or VNMR S500 NMR spectrometer. The reported
AHCTUNGTRENNUNG
(75 MHz, [D6]DMSO): d=12.56, 22.87, 44.10, 108.42, 114.21, 117.19,
124.64, 129.00, 136.60, 137.04, 144.19, 150.46, 151.74, 154.84, 192.23,
194.86 ppm; IR (ATR): n˜ =2974, 1680, 1639, 1587, 1537, 1460, 1405, 1378,
1354, 1309, 1269, 1224, 1205, 1169, 1138, 1078, 1049, 1027, 1014, 878, 843,
789, 766, 748 cmꢀ1
.
5-[4-(Diethylamino)-2-methylphenyl]-6-(pyridin-3-yl)pyrazine-2,3-dicar-
bonitrile (4b): Diaminomaleonitrile (237 mg, 2.2 mmol) was added to a
solution of 3b (500 mg, 1.7 mmol) in glacial acetic acid (15 mL). The mix-
ture was sonicated for 15 min and then heated to reflux for 48 h. The sol-
vent was evaporated. The crude product was purified over silica with eth-
ylacetate/chloroform 2:1 as an eluent and recrystallized in EtOH/H2O to
yield an orange-purple solid (370 mg, 60%). M.p. 174.4–175.68C;
1H NMR (300 MHz, [D6]acetone): d=1.14 (t, J=7 Hz, 6H; CH3), 2.84 (s,
3H; CH3), 3.42 (q, J=7 Hz, 4H; CH2CH3), 6.52–6.61 (m, 2H; ArH-
chemical shifts are given relative to SiACTHNUGTRNEG(UN CH3)4 and were locked to the
signal of the solvent. The elemental analysis was carried out on Automat-
ic Microanalyser EA1110CE (Fisons Instruments S.p.A., Milano, Italy).
The UV/Vis spectra were recorded using a Shimadzu UV-2401PC spec-
trophotometer. The fluorescence spectra were obtained by an AMINCO-
Bowman Series 2 luminescence spectrometer. Matrix assisted laser de-
sorption ionization - time of flight (MALDI-TOF) mass spectra were re-
corded in positive reflectron mode on a Voyager-DE STR mass spec-
trometer (Applied Biosystems, Framingham, MA, USA) in trans-2-[3-(4-
tert-butylphenyl)-2-methyl-2-propenylidene]-malononitrile as the matrix.
The instrument was calibrated externally with a five-point calibration
using Peptide Calibration Mix1 (LaserBio Labs, Sophia-Antipolis,
France). Electrospray ionization mass spectroscopic (ESI MS) experi-
ments were performed using LCQ Advantage Max (Thermo Finnigan,
San Jose, USA) equipped with an ESI source. The data were analyzed by
Thermo Finnigan Xcalibur software. Mass spectra of the samples were
obtained by direct infusion of each standard in a methanol (MeOH) and
water solution into the detector. The compounds 1b,[24] 4a, 4c (and their
intermediates 2a,c and 3a,c),[13] 5,[25,33] 6,[14,20] and 15[20] were prepared ac-
cording to the literature. Compounds 1a and 7a are available commer-
cially.
G
ACHTUNGTREN(NUNG aniline)), 7.40 (ddd, J1 =1 Hz, J2 =
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
E
ACHTUNGTRENNUNG
13C NMR (75 MHz, [D6]acetone): d=12.74, 20.60, 44.73, 110.11, 114.15,
114.81, 114.92, 122.36, 124.12, 129.97, 131.34, 133.40, 133.73, 137.29,
138.90, 150.24, 150.70, 151.69, 154.16, 158.28 ppm. IR (ATR): n˜ =2974,
2932, 2232, 1603, 1552, 1524, 1498, 1469, 1404, 1372, 1361, 1286, 1265,
1242, 1198, 1145, 1123, 1092, 1079, 1023, 1000, 949, 851, 829, 814,
787 cmꢀ1; MS-ESI: m/z (%): 369 (100) [M+H]+; MS/MS (49 eV): m/z
(%): 341 (100) [MꢀC2H4]+, 369 (4.5) [M+H]+; elemental analysis calcd
(%) for C22H20N6: C 71.72, H 5.47, N 22.81; found: C 71.79, H 5.72, N
23.29.
4-Bromo-N,N-diethyl-3-methylaniline (7b): NBS (2.2 g, 12 mmol) in
DMF (10 mL) was added dropwise to a solution of N,N-diethyl-3-methyl-
aniline (2 g, 12 mmol) in DMF (4 mL). After 5 min of stirring, water was
added (50 mL), and the mixture was extracted three times with ethylace-
tate. The organic layer was dried over anhydrous Na2SO4, and the solvent
was evaporated. The crude product was purified over silica with hexane/
ethyl acetate 100:3 as an eluent to yield a yellow oil (2.76 g, 93%);
1H NMR (500 MHz, CDCl3): d=1.16 (t, J=7 Hz, 6H; CH3CH2N), 2.36
(s, 3H; CH3), 3.33 (q, J=7 Hz, 4H; CH3CH2N), 6.40 (dd, J1 =9 Hz, J2 =
3 Hz, 1H; ArH), 6.56 (d, J=3 Hz, 1H; ArH) and 7.30 ppm (d, J=9 Hz,
1-[4-(Diethylamino)-2-methylphenyl]-2-hydroxy-2-(pyridin-3-yl)ethanone
(2b): This compound was prepared as published before for similar com-
pounds[13,36] by the condensation of pyridine-3-carboxaldehyde (1.89 g,
0.01 mmol) and 1b (2.6 g, 0.025 mmol) with 10% aqueous potassium cya-
14278
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14273 – 14282

pH-Controlled Red-Emitting Dyes
FULL PAPER
1H; ArH); 13C NMR (75 MHz, CDCl3): d=12.43, 23.40, 44.38, 109.82,
111.16, 114.08, 132.53, 137.98 and 147.03 ppm; IR (ATR): n˜ =2970, 2929,
2871, 1597, 1562, 1489, 1467, 1449, 1420, 1390, 1375, 1355, 1290, 1262,
1196, 1150, 1094, 1077, 1032, 1017, 921, 834 and 791 cmꢀ1; MS-ESI: m/z
(%): 242 (91) [M+H]+, 244 (100) [M+2+H]+.
6.62 (m, 2H; ArH), 7.06 (d, J=9 Hz, 1H; ArH), 7.67 (dd, J1 =8 Hz, J2 =
2 Hz, 1H; ArH), 7.75 (d, J=2 Hz, 1H; ArH), 7.78 ppm (d, J=8 Hz, 1H;
ArH); 13C NMR (75 MHz, CDCl3): d=12.54, 21.12, 44.28, 109.60, 112.07,
113.31, 115.47, 115.75, 115.86, 124.35, 130.91, 133.09, 133.69, 134.10,
136.08, 148.00, 148.21 ppm; IR (ATR): n˜ =2967, 2928, 2871, 2231, 1609,
1591, 1558, 1542, 1518, 1486, 1450, 1427, 1399, 1374, 1353, 1307, 1295,
1283, 1259, 1199, 1154, 1128, 1097, 1078, 1038, 917, 898, 852, 804,
784 cmꢀ1; elemental analysis calcd (%) for C19H19N3: C 78.86, H 6.62, N
14.52; found: C 78.30, H 6.88, N 14.53.
4-(Dimethylamino)phenylboronic acid (8a): 4-Bromo-N,N-dimethylani-
line 7a (1 g, 5 mmol) was dissolved in anhydrous THF (15 mL) under an
argon atmosphere and cooled to ꢀ788C. After cooling, a solution of
butyl lithium (BuLi, 3.44 mL, 5.5 mmol) in hexane (1.6m) was added
dropwise, and the solution was stirred at ꢀ788C for 60 min. Triisopropyl
borate (1.4 g, 7.5 mmol) was slowly added, and the solution turned
yellow. After stirring at ꢀ788C for 60 min, the solution was allowed to
slowly warm to RT. Water (15 mL) was added to the solution, and the
white precipitate that formed immediately after addition disappeared
after a few minutes. The pH was adjusted to 6 by using 18% (v/v) HCl,
and the solution was stirred for 18 h at RT. The organic layer was extract-
ed three times with 4% NaOH (10 mL). The water extracts were collect-
ed, and the pH was adjusted to 7 using concentrated HCl. The precipitate
that formed was collected and washed with water to obtain a pink solid
(275 mg, 33%). 1H NMR (300 MHz, [D6]DMSO): d=2.89 (s, 6H; CH3),
6.58–6.86 (m, 2H; ArH), 7.52–7.76 ppm (m, 2H, ArH); 13C NMR
(75 MHz, [D6]DMSO): d=39.98 (NCH3, overlapped by solvent residual
peak), 111.24, 116.10, 129.08, 135.64 ppm. The NMR spectroscopic data
were essentially the same as those given elsewhere.[37]
General procedure for the synthesis of AzaPc: Magnesium (28 equiv)
and a small crystal of iodine were heated to reflux for 3 h in anhydrous
butanol. Precursor A (1 equiv) and precursor B (3 equiv) were added all
at once or precursor B was divided into four parts and added subsequent-
ly within 2 h (mentioned for each compound below). The reflux contin-
ued for the next 6 h. The mixture was left to cool and was poured into
water/methanol/acetic acid 5:5:1 and stirred for 45 min at RT. The dark
solid was collected and washed thoroughly with water and slightly with
methanol. Part of the symmetrical magnesium(II) congener BBBB was
in some cases partially separated (and discarded) by column chromatog-
raphy over silica (mentioned for each compound below). Subsequently,
the mixture of AzaPc congeners (1 equiv) was dissolved in THF and
stirred at RT for 45 min with p-toluenesulfonic acid (20 equiv). The mix-
ture was concentrated, and water was added. The precipitate was collect-
ed and washed with 1% NaHCO3 and then with water. The product was
dried thoroughly. The desired congener (ABBB) was isolated by column
chromatography over silica using the eluents mentioned below. As the
final step, the solution of the metal-free ABBB congener (1 equiv) was
heated with anhydrous zinc(II) acetate (7 equiv) in DMF at 1608C for
2 h. Water was added, the precipitate was collected and washed thor-
oughly with water and slightly with methanol. The crude product was pu-
rified by column chromatography over silica. The pure compounds were
washed with methanol (10, 11) or were dissolved in a small amount of
pyridine and added dropwise to methanol (12, 13, and 16). The precipi-
tate was collected and put into a drying pistol to remove any residual sol-
vent. Compound 14 dissolves in methanol; therefore, the final purifica-
tion step was omitted.
4-(Diethylamino)-2-methylphenylboronic acid (8b): The same procedure
described for compound 8a was used but with 7b (3 g, 12 mmol), butyl
lithium (8.5 mL, 13.6 mmol) in hexane (1.6m), and triisopropyl borate
(3.5 g, 18 mmol) to a give brown solid (686 mg, 27%). M.p. >4008C’;
1H NMR (300 MHz, [D4]methanol): d=1.06 (t, J=7 Hz, 6H; CH2CH3),
2.20 (s, 3H; CH3), 3.27 (q, J=7 Hz, 4H; CH2CH3), 6.39 (d, J=7 Hz, 1H;
ArH), 6.43–6.50 (m, 1H; ArH), 6.93–7.01 (m, 1H; ArH); 13C NMR
(75 MHz, [D4]methanol): d=12.81, 22.02, 45.65, 111.36, 114.69, 129.99,
134.13, 139.66, 149.15 ppm. IR (ATR): n˜ =3332, 2972, 1600, 1580, 15447,
1498, 1391, 1374, 1355, 1295, 1274, 1199, 1176, 1146, 1093, 1076, 1030,
917, 822, 779 cmꢀ1; elemental analysis calcd (%) for C11H18BNO2: C
63.80, H 8.76, N 6.76; found C 64.20, H 8.54, N 6.77.
2-[4-(Dimethylamino)phenyl]-3-(phenyl)-9,10,16,17,23,24-hexakis(tert-bu-
tylsulfanyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninezinc(II) (10): Pre-
cursor A (4a, 90 mg, 0.28 mmol), precursor B (6, 254 mg, 0.83 mmol)
were added all at once. The other materials used were: Mg (188 mg,
7.74 mmol); the mobile phase for metal-free dye: toluene/chloroform/pyr-
idine 15:10:1 (Rf =0.24) and then toluene/chloroform/ethyl acetate 14:6:1
(Rf =0.33); mobile phase for zinc(II) complex: chloroform/acetone/pyri-
dine 20:3:1 (Rf =0.40). Green solid (28 mg, 8%); 1H NMR (300 MHz,
4’-(Dimethylamino)biphenyl-3,4-dicarbonitrile (9a): Compound 8a
(205 mg, 1.24 mmol) and 4-iodophthalonitrile (210 mg, 0.83 mmol) were
dissolved in THF (10 mL) together with a solution of K2CO3 (2m) in
water (1.49 mL, 2.98 mmol). The mixture was heated to 408C and tetra-
kis(triphenylphosphine)palladium(0) (96 mg, 0.083 mmol) was added.
The solution was heated at reflux for 3 h. After cooling, water (100 mL)
was add to the solution, and the mixture was extracted three times with
ethylacetate. The organic layer was dried over anhydrous Na2SO4, and
the solvent was evaporated. The crude product was purified over silica
with toluene/triethylamine 25:1 as an eluent and recrystallized from etha-
nol (EtOH) to obtain an orange solid (158 mg, 78%). M.p. 193.5–
195.88C; 1H NMR (300 MHz, CDCl3): d=3.06 (s, 6H; CH3), 6.82 (d, J=
[D5]pyridine): d=2.02 (s, 9H; SC
N
ACHTUGNTREN(UNNG CH3)3), 2.27 (s,
18H; SC(CH3)3), 2.28 (s, 18H; SCACHTNUGTRENNUNG
N
(m, 2H; ArH), 7.52–7.65 (m, 3H; ArH, overlapped by solvent residual
peak), 8.18–8.25 ppm (m, 4H; ArH); 13C NMR (75 MHz, [D5]pyridine):
d=29.98, 30.74, 30.79, 39.83, 51.19, 51.23, 51.29, 51.30, 51.45, 112.15,
124.03, 127.05, 128.92, 129.12, 130.88, 132.52, 135.99, 141.64, 144.98,
145.00, 145.18, 145.41, 145.47, 147.60, 149.28, 151.38, 151.53, 151.68,
151.71, 151.74, 151.85, 151.87, 152.06, 153.95, 154.85, 158.13, 158.16,
158.75, 158.76, 159.63, 159.72 ppm (some of the signals fused together);
IR (KBr): n˜ =3442, 2960, 2919, 2862, 1608, 1541, 1534, 1499, 1477, 1458,
1400, 1363, 1349, 1251, 1195, 1143, 1110, 975, 947, 847, 783, 754, 704,
693 cmꢀ1; UV/Vis (THF): lmax (e)=654 (273600), 628 sh, 595 (44500),
377 nm (154100 molꢀ1 m3 cmꢀ1); MS (MALDI-TOF): m/z: 1308 [M+H]+,
9 Hz, 2H, ArHACHTUNGTRENNUNG(aniline)), 7.49–7.54 (m, 2H; ArHCAHTUNGTRENN(UGN aniline)), 7.76 (d, J=
8 Hz, 1H; ArH), 7.85 (dd, J1 =8 Hz, J2 =2 Hz, 1H; ArH), 7.94 ppm (d,
J=2 Hz, 1H; ArH); 13C NMR (75 MHz, CDCl3): d=40.52, 111.67,
112.97, 115.78, 115.93, 116.24, 128.00, 129.60, 130.43, 133.80, 146.13,
150.94 ppm; IR (ATR): n˜ =2914, 2822, 2224, 1612, 1582, 1561, 1534, 1492,
1444, 1399, 1339, 1310, 1283, 1267, 1230, 1201, 1178, 1113, 1071, 999, 949,
881, 888, 838, 809, 755 cmꢀ1; elemental analysis calcd (%) for C16H13N3:
C 77.71, H 5.30, N 16.99; found: C 76.41, H 5.46, N 16.61.
4’-(Diethylamino)-2’-methylbiphenyl-3,4-dicarbonitrile (9b): Essentially
the same procedure as described for compound 9a was used but with 8b
(100 mg, 0.48 mmol), 4-iodophthalonitrile (81.3 mg, 0.32 mmol), a 2m so-
lution of K2CO3 in water (0.58 mL, 1.2 mmol), tetrakis(triphenylphosphi-
ne)palladium(0) (37 mg, 0.032 mmol). The reaction was heated at reflux
for 8 h. Water (100 mL) was added, and the mixture extracted three
times with ethylacetate. The organic layer was dried over anhydrous
Na2SO4, and the solvent was evaporated. The crude product was purified
over silica with toluene/chloroform 1:1 as an eluent and recrystallized
from EtOH/H2O to obtain an orange solid (78 mg, 56%). M.p. 99.5–
100.38C; 1H NMR (500 MHz, CDCl3): d=1.20 (t, J=7 Hz, 6H;
CH3CH2N), 2.29 (s, 3H; CH3), 3.40 (q, J=7 Hz, 4H; CH3CH2N), 6.55–
1330
[M+Na]+,
1346
[M+K]+,
1252
[M+HꢀC4H8]+,
1196
[M+Hꢀ2C4H8]+, 1140 [M+Hꢀ3C4H8]+; elemental analysis calcd (%) for
C62H69N17S6Zn·2H2O: C 55.32, H 5.47, N 17.69; found C 55.34, H 5.38, N
17.56.
2-[4-(Dimethylamino)phenyl]-3-(pyridin-3-yl)-9,10,16,17,23,24-hexakis-
AHCTUNGTRENGN(UN tert-butylsulfanyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninezinc(II)
(11): Precursor A (4c, 110 mg, 0.34 mmol) and precursor B (6, 315 mg,
1.03 mmol) were added all at once. The other materials used were: Mg
(230 mg, 9.47 mmol); mobile phase for magnesium(II) complex: toluene/
chlororform/pyridine 20:10:1 (Rf =0.08) and after symmetrical congener
BBBB was eluted mobile phase was changed to chloroform/pyridine 20:1
Chem. Eur. J. 2011, 17, 14273 – 14282
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14279

P. Zimcik et al.
(Rf =0.52); mobile phase for metal-free dye: chloroform/ethyl acetate 5:1
(Rf =0.35); mobile phase for zinc(II) complex: chloroform/THF 7:1.
(Rf =0.31). Green solid (33 mg, 7%); 1H NMR (300 MHz, [D5]pyridine):
added all at once. The other materials used were: Mg (468 mg,
19.26 mmol); water/methanol/acetic acid 5:5:1 was not added to the mix-
ture of magnesium complexes, but the butanol was evaporated and mix-
ture was extracted with chloroform. After that the procedure continued
according to general procedure; mobile phase for metal-free dye: tolu-
ene/chloroform/pyridine 15:5:0.3 (Rf =0.34); mobile phase for zinc(II)
complex: toluene/THF 100:5 (Rf =0.45). Green solid (95 mg, 13%);
1H NMR (300 MHz, [D5]pyridine): d=1.15 (t, J=7 Hz, 6H; NCH2CH3),
d=2.02 (s, 9H; SC
N
ACHTUGNTRENUN(GN CH3)3), 2.26 (s, 18H; SC-
N
ArH), (ddd, J1 =8 Hz, J2 =5 Hz, J3 =1 Hz, 1H; ArH) and 8.10–8.16 (m,
2H; ArH), 8.42 (dt, J1 =8 Hz, J2 =2 Hz, 1H; ArH), 8.91 (dd, J1 =5 Hz,
J2 =2 Hz, 1H, ArH), 9.63 ppm (dd, J1 =2 Hz, J2 =1 Hz, 1H, ArH);
13C NMR (75 MHz, [D5]pyridine): d=14.28, 22.94, 29.52, 29.61, 29.91,
29.98, 30.72, 30.77, 32.11, 39.80, 51.19, 51.22, 51.31, 51.46, 112.26, 126.37,
132.56, 137.70, 144.67, 145.03, 145.16, 145.44, 147.68, 151.44, 151.65,
151.89, 152.07, 158.28, 158.32, 158.80, 159.66 ppm (some of the signals
fused together); IR (KBr): n˜ =3441, 2923, 2853, 1737, 1608, 1544, 1529,
1460, 1362, 1255, 1142, 974, 783, 693 cmꢀ1; UV/Vis (THF): lmax (e)=655
(248000), 627 sh, 596 (38400), 480 sh, 377 nm (136700 molꢀ1 m3 cmꢀ1);
MS (MALDI-TOF): m/z: 1309 [M+H]+, 1331 [M+Na]+, 1347 [M+K]+;
elemental analysis calcd (%) for C61H68N18S6Zn·2H2O: C 54.39, H 5.39,
N 18.72; found C 54.33, H 5.54, N 17.53.
2.06 (s, 9H; SC
ACHTUTGNRENNGU(CH3)3), 2.18 (s, 9H; SCAHCTUNGTRNE(NUGN CH3)3), 1.08–1.14 (m, 36H; SC-
AHCTNUERTGGUN(NN CH3)3), 2.68 (s, 3H; CH3), 3.34 (q, J=7 Hz, 4H; NCH2CH3), 6.83–6.91
(m, 2H; ArH), 7.69 (d, J=9 Hz, 2H; ArH), 8.31 (d, J=8 Hz, 1H; ArH),
9.78 (d, J=7 Hz, 1H; ArH), 9.85 ppm (s, 1H; ArH); 13C NMR (75 MHz,
[D5]pyridine): d=12.89, 21.71, 30.61, 30.75, 30.80, 44.80, 51.05, 51.10,
51.31, 51.35, 51.44, 110.59, 114.29, 124.03, 129.30, 131.98, 132.43, 135.99,
136.70, 137.43, 140.19, 144.36, 144.38, 144.40, 144.51, 144.93, 145.25,
145.32, 145.78, 148.11, 151.67, 152.24, 152.39, 157.82, 157.86, 157.87,
157.90, 158.20, 158.22, 158.62, 159.10 ppm; IR (ATR): n˜ =2962, 2920,
1602, 1519, 1455, 1391, 1362, 1335, 1251, 1196, 1146, 1093, 1055, 1028,
976, 915, 846, 803, 781 cmꢀ1; UV/Vis (THF): lmax (e)=665 (185400), 601
(37200), 471 sh, 418 (38000) and 373 nm (142900 molꢀ1 m3 cmꢀ1); MS
(MALDI-TOF): m/z: 1271 [M]+, 1294 [M+Na]+, 1310 [M+K]+, 1243
[MꢀC2H4]+, 2542 [2M]+, 2565 [2M+Na]+, 2581 [2M+K]+; elemental
analysis calcd (%) for C61H73N15S6Zn: C 57.50, H 5.77, N 16.49; found: C
57.38, H 6.04, N 16.45.
2-[4-(Diethylamino)-2-methylphenyl]-3-(phenyl)-9,10,16,17,23,24-hexa-
kis(tert-butylsulfanyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyanine-
ACHTUNGTRENNUNGzinc(II) (12): Precursor A (4b, 250 mg, 0.68 mmol) and precursor B (6,
625 mg, 2.0 mmol) were added all at once. The other materials used
were: Mg (450 mg, 18.8 mmol); mobile phase for metal-free dye: chloro-
form/ethylacetate 10:1 (Rf =0.45); mobile phase for zinc(II) complex: tol-
uene/THF/pyridine 30:4:1 (Rf =0.29). Yield green solid (126 mg, 14%);
1H NMR (300 MHz, CDCl3/[D5]pyridine 3:1): d=0.88 (t, J=7 Hz, 6H;
2,3-BisACHTNUTRGNEUNG(phenyl)-9,10,16,17,23,24-hexakis(tert-butylsulfanyl)-1,4,8,11,-
15,18,22,25-(octaaza)phthalocyaninezinc(II) (16): Precursor A (5, 50 mg,
0.18 mmol) and precursor B (6, 163 mg, 0.53 mmol) were added all at
once. The other materials used were: Mg (121 mg, 5.0 mmol); mobile
phase for metal free dye: toluene/chloroform/pyridine 50:25:1 (Rf =0.18);
mobile phase for zinc(II) complex: chloroform/toluene/pyridine 50:25:1
(Rf =0.39). Green solid (24 mg, 11%); 1H NMR (300 MHz,
NCH2CH3), 1.74 (s, 9H; SC
ACHTUTNGRENNU(G CH3)3), 1.81 (s, 9H; SCACHTUNGTRENN(UGN CH3)3), 1.85 (s, 36H;
SC(CH3)3), 2.15 (s, 3H; ArCH3), 3.07 (q, J=7 Hz, 4H; NCH2CH3), 6.30–
ACHTUNGTRENNUNG
6.36 (m, 2H; ArH), 7.02 (ddd, J1 =8 Hz, J2 =5 Hz, J3 =1 Hz, 1H; ArH),
7.20–7.25 (m, 1H; ArH), 7.97 (dt, J1 =8 Hz, J2 =2 Hz, 1H; ArH), 8.34
(dd, J1 =5 Hz, J2 =2 Hz, 1H; ArH), 9.16 ppm (dd, J1 =2 Hz, J2 =1 Hz,
1H; ArH); 13C NMR (75 MHz, CDCl3/[D5]pyridine 3:1): d=11.89, 20.32,
29.90, 29.99, 30.05, 43.47, 50.48, 50.51, 50.60, 108.90, 112.83, 124.72,
132.40, 135.31, 136.38, 137.19, 143.78, 143.88, 143.92, 146.61, 147.57,
147.78, 149.77, 149.83, 150.40, 150.69, 150.85, 150.94, 150.97, 151.09,
151.15, 155.53, 157.51, 157.57, 157.84, 158.38, 158.45 ppm (some of the
signals overlapped); IR (ATR): n˜ =2963, 2919, 1606, 1519, 1479, 1453,
1398, 1362, 1349, 1248, 1144, 1109, 1092, 1059, 1024, 975, 953, 848, 782,
746 cmꢀ1; UV/Vis (THF): lmax (e)=653 (252100), 626 sh, 594 (39900),
376 nm (147800 molꢀ1 m3 cmꢀ1); MS (MALDI-TOF): m/z: 1350 [M]+,
1373 [M+Na]+, 1322 [MꢀC2H4]+, 1294 [Mꢀ2C2H4]+, 2701 [2M]+; ele-
mental analysis calcd (%) for C64H74N18S6Zn·2H2O: C 55.33, H 5.66, N
18.15; found C 55.26, H 5.60, N 18.05.
[D5]pyridine): d=2.01 (s, 18H; SCACHUTNGTREN(UNG CH3)3), 2.26 (s, 18H; SCACHTUGNTRENN(UNG CH3)3), 2.28
(s, 18H; SC(CH3)4), 7.49–7.55 (m, 6H; ArH; signal is overlapped by sol-
AHCTUNGTRENNUNG
vent residual peak), 8.08–8.13 ppm (m, 4H; ArH); 13C NMR (75 MHz,
[D5]pyridine): d=30.71, 30.76, 51.20, 51.30, 51.47, 128.79, 131.18, 140.50,
145.09, 145.18, 151.30, 154.46, 158.26, 159.78 ppm; IR (ATR): n˜ =2959,
2922, 2855, 1518, 1454, 1401, 1362, 1350, 1253, 1234, 1140, 1114, 1068,
1036, 974, 949, 848, 783 cmꢀ1; UV/Vis (THF): lmax (e)=650 (227200),
623 sh, 589 (29800), 478 sh, 377 nm (115900 molꢀ1 m3 cmꢀ1); MS
(MALDI-TOF): m/z: 1264 [M]+, 1287 [M+Na]+, 1303 [M+K]+, 2529
[2M]+.
Singlet oxygen measurements: All of the samples for both singlet oxygen
and fluorescence quantum yield determinations were further purified by
TLC to ensure absolute purity of the samples. The samples were eluted
over silica TLC plates (Silufol Kavalier Czechoslovakia, without fluores-
cence indicator) with eluents corresponding to the eluents used for the
purification of zinc(II) complexes of studied dyes. Corresponding parts of
the TLC were scrapped and AzaPc compounds were extracted from
silica using THF. Quantum yields of singlet oxygen (FD) were deter-
mined according to a previously published procedure[38] using the decom-
position of chemical trap 1,3-diphenylisobenzofuran (DPBF). Two sol-
vents were considered: DMF and DMF with 5% H2SO4 (v/v). Zinc
phthalocyanine (ZnPc) was used as a reference for DMF measurement
(FD =0.56 in DMF[32, 39]) and compound 15 for DMF with 5% H2SO4 be-
cause of the strong protonation of ZnPc under such conditions (Support-
ing Information, Figure S1). In detail, the procedure was as follows. A
stock solution of DPBF in DMF (2.5 mL, 5ꢁ10ꢀ5 m) was transferred into
a 10ꢁ10 mm quartz optical cell and bubbled with oxygen for 1 min. Sul-
furic acid (132 mL) was added (or not in the case of DMF measure-
ments), and the solution was mixed thoroughly and left to cool to RT
(10 min). A defined amount of concentrated stock solution of the tested
compound (10–16) in DMF (usually 30 mL) was then added. Absorbance
of the final solution in the Q band maximum was always about 0.1. The
solution was stirred and irradiated for defined times using a halogen
lamp (Tip, 300 W). Incident light was filtered through a water filter
(6 cm) and an orange HOYA G filter to remove heat and light under
506 nm, respectively. The decrease of DPBF in solution over the time of
irradiation was monitored at 415 nm (Supporting Information, Figure S5).
All of the experiments were performed three times, and the data present-
23-[4-(Dimethylamino)phenyl]-2,3,9,10,16,17-hexakis(tert-butylsulfanyl)-
1,4,8,11,15,18-(hexaaza)phthalocyaninezinc(II) (13): Precursor
A (9a,
200 mg, 0.81 mmol) and precursor B (6, 745 mg, 2.43 mmol) were added
in four parts over 2 h. The other materials used were: Mg (538 mg,
22.1 mmol); mobile phase for metal-free dye: toluene/chloroform/THF
10:3:0.3 (Rf =0.34); mobile phase for zinc(II) complex: toluene/THF
100:4 (Rf =0.40). Green solid (136 mg, 14%); 1H NMR (300 MHz,
[D5]pyridine): d=2.15 (s, 9H; SC
N
ACHTUGNTREN(UNNG CH3)3), 2.25 (s,
18H; SC(CH3)3), 2.27 (s, 18H; SCACHTNUGTRENNUNG
A
J=9 Hz, 2H; ArH), 8.18 (d, J=9 Hz, 2H; ArH), 8.55 (dd, J1 =8 Hz, J2 =
1 Hz, 1H; ArH), 9.79 (d, J=8 Hz, 1H; ArH), 10.04 ppm (s, 1H; ArH);
13C NMR (75 MHz, [D5]pyridine): d=30.75, 30.80, 40.15, 51.10, 51.31,
51.34, 113.53, 128.80, 128.84, 137.25, 140.94, 144.34, 144.38, 144.46, 144.52,
145.36, 151.05, 152.21, 152.36, 157.68, 157.87, 157.89, 158.20, 158.21,
159.17, 159.30 ppm (some of the signals fused together); IR (ATR): n˜ =
2960, 2918, 1602, 1523, 1479, 1446, 1390, 1362, 1333, 1249, 1192, 1144,
1111, 1092, 1057, 975, 915, 846, 811, 782, 774, 748 cmꢀ1; UV/Vis (THF):
lmax (e)=668 (189400), 612 (37000), 471 sh, 426 sh, 373 nm
(137800 molꢀ1 m3 cmꢀ1); MS (MALDI-TOF): m/z: 1229 [M]+, 1252
[M+Na]+, 1268 [M+K]+, 2458 [2M]+; elemental analysis calcd (%) for
C58H67N15S6Zn: C 56.54, H 5.48, N 17.05; found: C 57.06, H 5.56; N
16.74.
23-[4-(Diethylamino)-2-methylphenyl]-2,3,9,10,16,17-hexakis(tert-butyl-
sulfanyl)-1,4,8,11,15,18-(hexaaaza)phthalocyaninezinc(II) (14): Precursor
A (9b, 200 mg, 0.69 mmol) and precursor B (6, 477 mg, 1.56 mmol) were
14280
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14273 – 14282

pH-Controlled Red-Emitting Dyes
FULL PAPER
ed in the paper represent a mean of these three experiments. The esti-
mated error is ꢁ10%. All of the calculations were performed according
to a previously published procedure.[38]
to a thin film. All of the subsequent treatments, including swelling and
extrusion, were performed with the dye already incorporated into the
LUVETs (cdye =25 mm). The final lipid-to-dye ratio was 1000. The absorp-
tion spectra were measured after the appropriate dilution of the suspen-
sion of liposomes by a buffer of pH 7.4.
Fluorescence measurements: Fluorescence quantum yields (FF) were de-
termined by the comparative method[40] using ZnPc as a reference (FF =
0.30 in chloronaphthalene[30]). In the case of titrations with sulfuric acid,
a stock solution of the studied compound (10–16) in DMF (2.2 mL,
2.9 mm) was transferred to a quartz optical cell (10ꢁ10 mm), and a defi-
nite amount of concentrated sulfuric acid was added. The absorption and
emission spectra were collected. Both the reference and the sample were
excited at 603 nm (12–15) or at 596 nm (10, 11 and 16) for measurements
in DMF. The excitation wavelength in toluene was 605 nm for all of the
compounds. The FF was calculated using Equation (1) in which F is the
integrated area under the emission spectrum, A is absorbance at the exci-
tation wavelength, and n is the refractive index of the solvent. Super-
scripts R and S correspond to the reference and sample, respectively.
Acknowledgements
The work was supported by Czech Science Foundation, grant P207/11/
ˇ
ˇ
1200. The authors would like to thank Jirꢂ Kunes for the NMR measure-
ˇ
ˇ
ments, Vojtech Tambor, Petra Kovarꢂkovꢃ, and Ivana Pasꢃkovꢃ for the
MS measurements, and Pavel Berka for determination of the LUVETs
properties. A kind donation of the phospholipids by Lipoid GmbH is
gratefully acknowledged.
!
ꢀ
ꢁ
ꢀ
ꢁ
R
2
FS
FR
1 ꢀ 10ꢀA
nS
nR
FSF ¼ FRF
ð1Þ
S
1 ꢀ 10ꢀA
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sulfuric acid. The refractive index for solutions of the samples in DMF
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presented in Table 1 were performed three times and the data represent
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remove all traces of organic solvents.
A citrate-phosphate buffer
(2.5 mL) of the appropriate pH (2.6, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, or 7.4) was
added, and the lipids were removed from the flask walls by gentle shak-
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back and forth twenty-one times through two stacked polycarbonate fil-
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a LUVETs concentration of
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Received: April 12, 2011
Published online: November 3, 2011
14282
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Chem. Eur. J. 2011, 17, 14273 – 14282