Phenol-Substituted Tetrapyrazinoporphyrazines: pH-Dependent Fluorescence in Basic Media

Article abstract of DOI:10.1002/chem.201502533

Tetrapyrazinoporphyrazines (TPyzPzs) bearing one, two, four or eight 3,5-di(tert-butyl)-4-hydroxyphenol moieties were synthesized as zinc(II) complexes and metal-free derivatives. The deprotonation of the phenol using tetrabutylammonium hydroxide induced the formation of a strong donor for intramolecular charge transfer that switched OFF the red fluorescence (λ_F660 nm) of the parent zinc TPyzPzs. The changes were fully reversible for TPyzPzs with one to four phenolic moieties, and an irreversible modification was observed for TPyzPzs substituted with eight phenols. The sensors were anchored to lipophilic particles in water, and a pK_a approximately 12.5-12.7 was determined for the phenolic hydroxyl based on fluorescence changes in different buffers. In addition, a novel concept for fluorescence OFF-ON-OFF switching in metal-free TPyzPzs bearing phenolic moieties upon addition of specific amounts of base was demonstrated.

Full text of DOI:10.1002/chem.201502533

DOI: 10.1002/chem.201502533
Full Paper
&
Fluorescence |Hot Paper|
Phenol-Substituted Tetrapyrazinoporphyrazines: pH-Dependent
Fluorescence in Basic Media
[a]
[b]
[b]
[b]
ˇ ˇ
Veronika Novakova,* Miroslava Lµskovµ, Hana Vavrickovµ, and Petr Zimcik*
Abstract: Tetrapyrazinoporphyrazines (TPyzPzs) bearing one,
two, four or eight 3,5-di(tert-butyl)-4-hydroxyphenol moieties
were synthesized as zinc(II) complexes and metal-free deriva-
tives. The deprotonation of the phenol using tetrabutyl-
ammonium hydroxide induced the formation of a strong
donor for intramolecular charge transfer that switched OFF
the red fluorescence (lF ~660 nm) of the parent zinc TPyzPzs.
The changes were fully reversible for TPyzPzs with one to
four phenolic moieties, and an irreversible modification was
observed for TPyzPzs substituted with eight phenols. The
sensors were anchored to lipophilic particles in water, and
a pKa approximately 12.5–12.7 was determined for the phe-
nolic hydroxyl based on fluorescence changes in different
buffers. In addition, a novel concept for fluorescence OFF-
ON-OFF switching in metal-free TPyzPzs bearing phenolic
moieties upon addition of specific amounts of base was
demonstrated.
Introduction
fluorescence was switched ON upon binding of a cation or by
protonation in acidic pH. Similarly, amines have also been uti-
lized as donors in Pcs for the development of pH sensitive
photosensitizers in PDT.[12] The use of phenol or phenolate in
TPyzPzs or Pcs as the donor that can switch between ON and
OFF states in more basic pH or react in the presence of basic
cations has received limited attention[13] even though this type
of donor is often used in other types of fluorescent mole-
cules.[14] In particular, the 2,6-di(tert-butyl)phenol moiety has
been primarily studied as a substituent on a series of porphy-
rins for colorimetric detection.[15] A study on the use of the
phenol/phenolate couple for fluorescence sensing in TPyzPzs
that possess significant electron-deficient character, photosta-
bility and strong fluorescence in the red portion of the emis-
sion spectra[1a] is lacking.
Tetrapyrazinoporphyrazines (TPyzPzs) are the most widely in-
vestigated group of phthalocyanine (Pc) aza-analogues. In par-
ticular, TPyzPzs have received increasing attention in recent
years due to their promising fluorescent,[1] optical limiting,[2]
catalytic[3] and liquid crystalline properties[4] as well as their
ability to form nanoporous materials.[5] In addition, TPyzPzs are
able to efficiently produce singlet oxygen upon irradiation.[6]
Therefore, TPyzPzs have been investigated as photosensitizers
in photodynamic therapy (PDT) with good efficiency, which
has been confirmed in vitro on cells.[7] Aza-substitution in ben-
zene rings of Pcs imparts TPyzPz with significant electron defi-
cient properties,[8] which results in a macrocycle core that is
a good electron acceptor that can undergo intramolecular
charge transfer (ICT) or photoinduced electron transfer (PET)
after combination with a suitable donor moiety.[9] Both pro-
cesses can be utilized in sensing because they are competitive
relaxation pathways to fluorescence and can be easily switched
ON and OFF upon binding of an analyte.[1b,10]
The aim of this study was to investigate the possibility of
using a phenolate anion to act as a donor for ICT in TPyzPzs
and switch OFF their fluorescence. Zinc (1Zn–4Zn) and metal-
free (1H–4H) TPyzPzs (Figure 1) bearing one, two, four or
eight phenol moieties were synthesized and investigated to
elucidate the influence of the phenol/phenolate couple on the
resulting photophysics with the potential for switching be-
tween ON (phenol) and OFF (phenolate) states. To reduce or
eliminate undesirable aggregation of planar TPyzPz molecules,
the compounds were designed to contain bulky substituents
in both the nondonor (tert-butylsulfanyls) and donor moieties
(2,6-di(tert-butyl)phenol). Aggregation nonspecifically decreas-
es fluorescence and may lead to a misleading interpretation of
photophysical data. The data were compared with negative
controls 5H, 5Zn and 6Zn (Figure 1), which have a similar
structure but lack a phenol group.
Recently, a series of red fluorescent TPyzPz sensors for cat-
ions or pH detection have been reported.[1b,10,11] These sensors
contained various amines that serve as donors in ICT, and the
[a] Dr. V. Novakova
Department of Biophysics and Physical Chemistry
Faculty of Pharmacy in Hradec Kralove, Charles University in Prague
Heyrovskeho 1203, Hradec Kralove, 50005 (Czech Republic)
E-mail: veronika.novakova@faf.cuni.cz
ˇ ˇ
[b] M. Lµskovµ, H. Vavrickovµ, Dr. P. Zimcik
Department of Pharmaceutical Chemistry and Drug Control
Faculty of Pharmacy in Hradec Kralove, Charles University in Prague
Heyrovskeho 1203, Hradec Kralove, 50005 (Czech Republic)
E-mail: petr.zimcik@faf.cuni.cz
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502533.
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Figure 1. Structures of studied TPyzPzs.
Results and Discussion
azine was detected. A similar C-nucleophile behavior for this
phenol was reported during the synthesis of monosubstituted
phthalonitriles.[16] The second electron-deficient center in
monosubstituted 8 was further modified by nucleophilic sub-
stitution using bulky tert-butyl thiolate to afford precursor 9 in
77% yield. A different approach using condensation of a suit-
ably substituted diketone with diaminomaleonitrile was ap-
plied to synthesize pyrazine 13. First, 2,6-diisopropylphenol
was converted via a Duff reaction with methenamine to 10
(76% yield), which was alkylated by dimethylsulfate to 11
(79% yield). Subsequent benzoin condensation of aldehyde 11
in presence of the 5-(2-hydroxyethyl)-3,4-dimethylthiazolium
iodide catalyst yielded the corresponding acyloin. However,
this acyloin was unstable and gradually oxidized in solution
after the condensation and on silica during purification. There-
fore, this acyloin was directly oxidized to diketone 12 without
isolation, and the product was obtained in 21% yield from two
steps. Condensation of 12 with diaminomaleonitrile in acetic
acid afforded the required pyrazine precursor 13 in 34% yield.
The synthesis of symmetrical complexes 4H, 4Zn, 5H, and
5Zn was performed via magnesium butoxide induced cyclote-
Synthesis
The synthesis of TPyzPzs is typically performed using cyclote-
tramerization of precursors—suitably substituted pyrazine-2,3-
dicarbonitriles. The synthesis of precursors containing phenol
moieties started from commercially available 5,6-dichloropyr-
azine-2,3-dicarbonitrile. This compound was reported[13a] to un-
dergo nucleophilic substitution with 2,6-di(tert-butyl)phenol to
7 and 8. In our case, a slightly modified procedure was used
with 22 and 48% yields, respectively (Scheme 1).
Interestingly, 2,6-di(tert-butyl)phenol acts as a C-nucleophile
in this reaction. The O-nucleophilic center is sterically hindered
by bulky tert-butyl groups, and no phenoxy-substituted pyr-
tramerization of the corresponding precursors
7 or 13
(Scheme 2). The reaction primarily led to magnesium comp-
lexes 4Mg and 5Mg, which were subsequently demetalated
by p-toluenesulfonic acid (TsOH) to metal-free 4H and 5H. The
metal-free derivatives were converted to zinc complexes 4Zn
and 5Zn with Zn(CH3COO)2 in pyridine. Both the demetalation
reaction and complexation with the zinc cation were nearly
quantitative for both derivatives with the exception of the syn-
thesis of 4Zn, where only 54% yield was obtained due to
losses on the silica column during purification. The synthesis of
compound 6Zn has been previously reported.[17]
Unsymmetrical TPyzPzs were obtained by mixed cyclotetra-
merization (statistical condensation) of precursors 7 or 9 with
5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile induced by
magnesium butoxide (Scheme 2). This approach led to a mix-
ture of six different congeners (i.e., AAAA, AAAB, ABAB, AABB,
ABBB and BBBB) that were chromatographically separated.
However, the mixture of magnesium complexes was insepara-
Scheme 1. Synthesis of precursors for cyclotetramerization. i) 2,6-Di(tert-bu-
tyl)phenol (3 equiv), K2CO3, anhydr. MeCN, Ar, reflux, 24 h; ii) 2,6-di(tert-bu-
tyl)phenol (1.1 equiv), K2CO3, anhydr. MeCN, Ar, RT, 2.5 h; iii) 2-methylpro-
pane-2-thiol, pyridine, reflux, 1 h; iv) dimethylsulfate, THF, K2CO3, reflux, 21 h;
v) 5-(2-hydroxyethyl)-3,4-dimethylthiazolium iodide, DBU, anhydr. EtOH,
reflux, 3 h; vi) NH4NO3, Cu(CH3COO)2, AcOH, reflux, 4 h; vii) diaminomaleo-
nitrile, AcOH, reflux, 3 h.
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Figure 2. Normalized absorption and fluorescence emission (inset) spectra of
studied TPyzPz in THF. a) 1Zn (full line), 6Zn (dashed line). b) 4Zn (full line),
5Zn (dashed line). Emission spectra were corrected for detector response.
A single Q-band (e typically over 300000mÀ1 cmÀ1) was ob-
served for the zinc complexes, and due to lowered symmetry,
splitting was observed for the metal-free derivatives (see also
Figure S2 in the Supporting Information). All of the spectra in
THF as well as in other studied solvents (i.e., toluene, dioxane,
MeCN, DMF, DMSO, DMAC) exhibited the typical shape of
monomeric species and the presence of aggregates was not
detected at the studied concentrations (up to 5 mm). The effect
of the substituted phenyl rings and tert-butylsulfanyl substitu-
ents on the position of the Q-band was essentially the same
(Table 1). The only difference was a slight red shift of a few
nanometers as the number of phenols in the molecule in-
creased (Figure S3 in the Supporting Information), which may
be due to contributions from the hydroxyl lone pairs. There-
fore, the phenolic OH groups are conjugated to the TPyzPz
macrocycle despite the slight rotation of the phenyl rings from
the pyrazine plane, as shown in the recently reported X-ray
crystal structure of 7.[13a] The electronic coupling of the phenol-
ic hydroxyl with the TPyzPz core was also confirmed by the
significant increase in the n–p transition at approximately
500 nm in the absorption spectrum of 4Zn compared to that
of 5Zn (Figure 2b). The coupling is an essential requirement
for efficient ICT because the donor and acceptor must be in
conjugation.[9a]
Scheme 2. Synthesis of TPyzPzs. i) Mg, BuOH, reflux; ii) TsOH, THF, RT; iii) sep-
aration of congeners; iv) Zn(CH3COO)2, pyridine, reflux.
ble due to the strongly overlapping and tailing spots of the
congeners during TLC. The conversion to metal-free derivatives
by treating the mixture with TsOH enabled separation of the
individual congeners. In the metal-free form, nicely separated
round spots appeared during TLC, and 1H–3H were success-
fully isolated. TPyzPzs 2H and 3H were isolated from one reac-
tion, and the other possible congeners in this reaction ap-
peared as only minor products based on the weak spots that
were visible by TLC. The unsymmetrical metal-free TPyzPzs
were subsequently complexed nearly quantitatively by zinc
cations using Zn(CH3COO)2 in pyridine. It is important to note
that the A2B2 congener can potentially exist as two positional
isomers [i.e., adjacent (drawn on Figure 1, i.e., AABB type) and
opposite (i.e., ABAB type)] that are typically extremely difficult
to separate. The NMR spectroscopy data for 3Zn (Figure S1 in
the Supporting Information) confirmed that its structure can
be attributed primarily to the adjacent isomer based on the
presence of two equal sets of signals corresponding to all of
the protons. Only one signal for each of the protons would be
expected for the opposite isomer type, which appears to be
present as a very minor component.
Photophysical characterization
The fluorescence emission spectra (example for THF: Figure 2,
insets), which were obtained for all of the studied solvents,
mirrored the absorption spectra with only small Stokes shift.
The excitation spectra overlapped the absorption spectra,
which further confirmed the presence of only monomers and
excluded the influence of aggregation on the photophysical
data.
Absorption spectra
The absorption spectra for all of the studied compounds were
typical for TPyzPzs. These spectra were characterized by two
important bands including a high energy B-band (~375 nm)
and a low energy Q-band (~650 nm; Figure 2).
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for selected compounds in solvents with different polarities
(Table 2). The FF values for TPyzPzs without any phenol
groups (5Zn, 6Zn) were independent of the solvent polarity.
The FF values for 1Zn and 4Zn were fully comparable to
those of the controls (5Zn, 6Zn) in nonpolar solvents (dioxane,
toluene) where the ICT is not the preferred process. Because
the thermodynamic feasibility of ICT increases in polar sol-
vents, the quenching of excited states becomes more effective.
This behavior was observed as a drop in the fluorescence
quantum yields of 1Zn and 4Zn in solvents with a higher rela-
tive permittivity (er) with much steeper decrease for the latter
(compare, e.g., data in DMF, DMAC or DMSO). The experiments
supported the hypothesis that the phenolic hydroxyl is really
a donor for ICT in TPyzPzs but its effect is very weak and may
only have a significant effect on the deactivation process in
combination of a large number of phenolic groups (e.g., 4Zn)
and polar solvents. For comparison, the ICT in structurally simi-
lar TPyzPzs with only one diethylamino substituent as a donor
is way much stronger (e.g., FF(THF) =0.013, FF(MeCN) =0.0013)[9b]
than the effect of eight phenols in 4Zn. Therefore, the phenol
form was not excluded from use in the fluorescent form in the
phenol/phenolate pair.
Table 1. Absorption and photophysical data of studied TPyzPz in THF.[a]
[b]
[b]
Compound
lmax [nm]
lF [nm]
FF
FD
FF +FD
1H
2H
3H
4H
672, 642
673, 643
674, 647
675, 650
668, 639
651
651
653
654
648
676
678
677
663
673
658
658
659
661
654
656
0.036[c]
0.020[c]
0.006[c]
0.002
0.25
0.28
0.26
0.24
0.25
0.056
0.028
0.012
0.005
0.10
0.58
0.60
0.52
0.44
0.092
0.048
0.018
0.007
0.35
0.86
0.86
0.76
0.71
5H
1Zn
2Zn
3Zn
4Zn
5Zn
6Zn
0.32
0.30
0.56
0.55
0.88
0.85
650
[a] Absorption maximum at the Q-band (lmax), fluorescence emission max-
imum (lF), fluorescence quantum yield (FF), singlet oxygen quantum
yield (FD). [b] With unsubstituted ZnPc in THF as reference (FF =0.32,
FD =0.53). [c] FF(1H) in MeCN=0.005, FF(2H) in MeCN=0.002, FF(3H) in
MeCN=0.002
The photophysical data were primarily collected for all of
the compounds to characterize the properties of the phenol
form (i.e., the ON state in the potential sensor). Both the fluo-
rescence (FF) and singlet oxygen quantum yields (FD) in THF
were determined by comparative methods using unsubstituted
ZnPc as a reference. The data are summarized in Table 1. The
fluorescence and singlet oxygen production represent two
major deactivation pathways for the excited states of TPyzPzs.
The sum of these quantum yields (FF +FD) in TPyzPzs reaches
typical values close to 1 when no other relaxation pathways
are available.[9a] The FF +FD sum in THF for the zinc com-
plexes without any possible donors (5Zn, 6Zn) and those with
just one (1Zn) and two (2Zn) phenolic groups were compara-
ble (i.e., typically more than 0.85). However, a decrease in the
FF +FD sum of more than 10% was observed for 3Zn and
4Zn bearing four and eight phenolic groups, respectively. The
FF +FD sum for the metal-free derivatives in this study was
unusually low (Table 1). This observation, which is not yet well
explained, is typical for various metal-free TPyzPz irrespective
of the presence or absence of donors for ICT/PET on the pe-
riphery of the macrocycle[1a] and is apparently not connected
with the ICT from peripheral substituents. Despite the low
values in the metal-free derivatives, the same trend with a de-
crease in the FF +FD sum as the number of phenolic groups
increased was observed (Table 1).
Table 2. Fluorescence quantum yields (FF) and fluorescence emission
maxima (lF) of studied TPyzPz in solvents of different polarity.[a,b,c]
Solvent
er
1Zn
4Zn
5Zn
6Zn
dioxane
toluene
THF
2.2
2.4
7.4
36.7
37.5
37.8
48.9
0.25 (659)
0.25 (662)
0.28 (658)
0.16 (664)
0.22 (661)
0.14 (664)
0.04 (666)
0.26 (661)
–
0.27 (654)
–
0.27 (658)
0.27 (660)
0.30 (656)
0.23 (662)
0.23 (659)
0.26 (661)
0.26 (664)
[d]
[d]
0.25 (661)
0.017 (668)
0.15 (665)
0.013 (668)
0.002 (670)
0.32 (654)
0.25 (663)
0.24 (661)
0.26 (663)
0.30 (664)
DMF
MeCN
DMAC
DMSO
[a] Expressed as FF (lF [nm]). [b] Relative permittivity of the solvent (er),
N,N-dimethylacetamide (DMAC), acetonitrile (MeCN). [c] With unsubstitut-
ed ZnPc in THF as reference (FF =0.32). [d] Insoluble in toluene.
ON-OFF switching of fluorescence
The conversion of phenol to phenolate by deprotonation in
basic media was expected to induce a strong donor center in
the molecule, which should be able to efficiently quench the
excited states. Therefore, this effect may be used for switching
OFF the fluorescence of TPyzPzs in basic media. This premise
was tested using titration experiments with tetrabutylammoni-
um hydroxide (TBAH) in acetonitrile (MeCN). Stepwise addition
of TBAH (up to 500 mm) into a solution containing 1Zn–3Zn
(1 mm) induced small hypso- and hypochromic shifts of the ab-
sorption Q-band (Figure 3a, and Figures S5 and S6 in the Sup-
porting Information). Simultaneously, the fluorescence intensity
decreased with no changes in the shape of the emission spec-
tra (Figure 3a, inset). The progress of the changes in the ab-
sorption and emission spectra corresponded to each other and
stopped when 1Zn–3Zn were fully deprotonated on the phe-
nolic hydroxyls (Figure 3c, and Figures S5 and S6). Excess
TBAH did not lead to any further changes (Figure 3b). Acidifi-
The smaller FF +FD sum for TPyzPzs bearing more phenol
groups may indicate that phenol also acts as a weak donor for
ICT in these molecules. Indeed, phenols have been reported to
serve as donors for ICT or PET processes in various fluoro-
phores.[18] However, in the design of fluorescence sensors, the
phenol form in the phenol/phenolate pair is expected to be
the fluorescent one (i.e., in ON state). From this point of view,
any excessive quenching of fluorescence by a phenolic hydrox-
yl donor would reduce the usability of this pair in sensing ap-
plications, especially in more polar solvents as both PET and
ICT are more efficient in polar solvents.[19] Therefore, the influ-
ence of the phenolic hydroxyl on the photophysical properties
in the ON state was investigated by determining the FF values
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cation of the solution at the end of the titration by addition of
excess acetic acid resulted in the full recovery of both the ab-
sorption spectra and fluorescence intensity (Figures S4–S6 in
the Supporting Information).
The changes in the absorption spectra or FF values of con-
trols 5Zn and 6Zn after addition of TBAH were negligible (Fig-
ure 3c and f). A very small red shift (~3 nm) of the Q-band and
a slight decrease in the FF values were observed after the first
addition of TBAH, and then, the spectral shape and fluores-
cence intensity remained constant as the amount of TBAH in-
creased. Both the Q-band and FF returned to their original
shape and values after acidification. These small changes may
be explained in terms of the complexation of the hydroxyl
anion to the central zinc cation after the first addition of TBAH
and its removal after acidification. This behavior also most
likely occurs for 1Zn–4Zn but the effect on the properties is
small and obscured by the changes induced by the formation
of the phenolate ion (Figure 4).
Similarly, the titrations of 4Zn containing eight donor cen-
ters induced a decrease in the fluorescence intensity. However,
the absorption spectra exhibited a different behavior than
1Zn–3Zn. The hypso- and hypochromic shift of the Q-band
continued with increasing amounts of TBAH even when the
fluorescence reached a minimum. Ultimately, a completely dif-
ferent absorption spectrum was obtained at large excesses of
TBAH (Figure 3d and e). Notably, acidification of the solution
at the end of the titration of 4Zn with acetic acid did not re-
store the FF value (Table 3), and the absorption spectrum was
less intense in the Q-band and blue shifted by 7 nm (Figure 3e
and Figure S4 in the Supporting Information). This result sug-
gests an irreversible change in the structure of 4Zn. Any at-
tempt to characterize the product mixture (e.g., by mass spec-
trometry) failed. However, a reasonable explanation was pre-
sented by Clarkson et al., who observed similar broad and flat
absorption spectra after addition of TBAH and a hypsochromic
shift after subsequent acidification for metal-free Pcs substitut-
ed with four 2,6-di(tert-butyl)phenol moieties.[16a] The 2,6-
di(tert-butyl)phenol moieties may undergo oxidation to qui-
none and/or other well-known transformations including the
formation of endoperoxides and/or aromatic ring contrac-
tion.[20] Alternatively, the oxidation of the 2,6-di(tert-butyl)phe-
nol moiety to ortho-quinone may also be involved, as recently
suggested by a study on porphyrins meso-substituted with 2,6-
di(tert-butyl)phenols.[21]
Compounds 1Zn–3Zn bear suitable structural features for
anchoring in the lipophilic particles in water with the hydro-
phobic moiety (TPyzPz with tBuS substituents) buried in the
hydrophobic core and with the more hydrophilic phenol ori-
ented out of the particle. This arrangement also allows for the
assessment of the sensing potential in water-based medium
and determination of the pKa. Compound 4Zn was not includ-
ed in these experiments due to the irreversible changes ob-
served after addition of base (see above). Therefore, 1Zn–3Zn
and control 6Zn were integrated into particles in a microemul-
sion prepared from medium-chain triglycerides (MCT) stabi-
lized with the Cremophor EL emulsifier, and their responses to
different pH values of the buffer were evaluated. It is impor-
tant to note that the TPyzPzs 1Zn, 2Zn and 6Zn were incor-
porated into particles in a monomeric form based on the
shape of their absorption spectra (Figure S7 in the Supporting
Figure 3. Changes in the absorption spectra of: a) 1Zn, and b) 4Zn in MeCN (c=1 mm) after addition of TBAH (up to 240 mm). Insets a,d): corresponding
changes in the fluorescence emission spectra (lexc =603 and 597 nm for 1Zn and 4Zn, respectively). Spectra of: b) 1Zn, and e) 4Zn in MeCN (c=1 mm)
before (full line) and after addition of TBAH (c=240 mm, complete deprotonation; dashed line) and after addition of a large excess of TBAH (dotted). All of
the absorption spectra were corrected for dilution. c,f) Dependence of FF(0)/FF on the concentration of TBAH in the solution for 1Zn (c, open symbols), 4Zn
(f, open symbols), 5Zn (f, full symbols) and 6Zn (c, full symbols). The addition of excess acetic acid that neutralized TBAH is indicated by the arrows (c, f).
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protonation of the central NH groups led us to evaluate the
novel concept of sensing based on OFF-ON-OFF switching.
The concept was tested on 1H in MeCN (1 mm). After the ad-
dition of a small amount of TBAH, the absorption spectra
changed from a split Q-band to a single unsplit one (Figure S8
in the Supporting Information). This change is indicative of de-
protonation of both central NH groups.[22] The deprotonation
was accompanied by a 2.5-times increase in the fluorescence
(Figure 5). The [1H]/[TBAH] ratio was 2 for the break point of
the change in the absorption and fluorescence spectra
(Figure 5, inset), and this result further supports the simultane-
ous deprotonation of both central NH groups, which is typical
of TPyzPzs and structurally similar Pcs.[22b,23] Further addition of
a small amount of TBAH did not change the spectra or the flu-
orescent properties. However, addition of larger amounts (over
10 mm) induced spectral changes similar to those observed
during titration of 1Zn upon deprotonation of phenol with
TBAH (Figure S9 in the Supporting Information). The phenol
deprotonation in 1H was also accompanied by a decrease in
its fluorescence (Figure 5). Similar changes were also observed
for 2H and 3H (Figures S10 and S11 in the Supporting Infor-
mation). This result confirmed that the switching between
OFF-ON-OFF states was driven by the addition of specific
amounts of base. Metal-free TPyzPzs are in the OFF state in
their neutral form, switched ON after addition of a small
amount of base (TBAH) due to deprotonation of the central
NH groups and switched OFF after addition of a larger amount
of base, which deprotonates the phenolic group (Figure 5).
Table 3. Fluorescence quantum yields (FF) in MeCN and pKa values in mi-
croemulsions of studied TPyzPz.[a,b]
[c]
[d]
[f]
FF(phenol)
FF(phenolate)
FF(AcOH)
Decrease[e]
pKa
1Zn
2Zn
3Zn
4Zn
5Zn
6Zn
0.22
0.18
0.17
0.15
0.24
0.23
0.015
0.03
0.0030
0.0026
0.22
0.24
0.22
0.20
0.09
0.25
0.25
15
6
57
58
1.1
1.2
12.5
12.6
12.7
–
–
–
0.20
[a] Tetrabutylammonium hydroxide (TBAH), acetic acid (AcOH).
[b] [TPyzPz]=1 mm. [c] Fully deprotonated form ([TBAH]=240 mm).
[d] After acidification ([AcOH] ~120 mm) of the solution of fully deproton-
ated form. [e] Calculated as follows: FF(phenol)/FF(phenolate). [f] Deter-
mined in microemulsion made from MCT/Cremophor EL in water.
Figure 4. Dependence of the FF value on the pH of the buffer solution for
1Zn (dots, full line), 2Zn (open triangles, dashed line), 3Zn (open squares,
dotted line) and 6Zn (full triangles) incorporated in the microemulsion. Sym-
bols represent experimental data, and the lines are the best fit.
Information) and the perfect match with the corresponding ex-
citation spectra. Compound 3Zn slightly aggregated (Fig-
ure S7c). A change in the buffer pH from 9 to 13 induced simi-
lar changes in the absorption spectra of 1Zn–3Zn as seen in
MeCN upon titration with TBAH. The fluorescence signal de-
creased at a higher pH due to the deprotonation of the phe-
nolic OH (Figure 4). No changes were detected for control
6Zn, which did not contain a phenol, over the studied pH
range. FF of 1Zn and 2Zn in the microemulsion in the ON
state (below pH 11) reached values of 0.15 and 0.14 (compara-
ble to FF =0.19 of 6Zn in a microemulsion), respectively, and
these values decreased by more than 1 order of magnitude at
pH 13. However, the initial FF value for 3Zn was only 0.02,
which was most likely due to the aggregation of this TPyzPz in
the microemulsion. The pKa values, which were determined
from the dependence of FF on the pH of the buffer, were simi-
lar for all of the sensor compounds (1Zn–3Zn) and reached
values of approximately 12.5–12.7 (Table 3). Interestingly, the
pKa value corresponded well to the calculated value for 2,6-
di(tert-butyl)phenol (pKa =12.16, calculated using ACD/Labs
Software V11.02).
OFF-ON-OFF switching of fluorescence
Figure 5. Concept of OFF-ON-OFF switching. Changes in the fluorescence of
1H in MeCN upon addition of TBAH; c(1H)=1 mm, lexc =600 nm,
lem =669 nm. Inset: enlarged part of the graph at lower TBAH concentra-
tions.
The low fluorescence of metal-free TPyzPz and the results from
several experiments where the fluorescence increased after de-
Chem. Eur. J. 2015, 21, 14382 – 14392
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Manchester, UK) based on Q-TOF. The chromatography for this HR
MS measurement was performed using an Acquity UPLC BEH300
C4 (2.1”50 mm, 1.7 mm) column with isocratic elution consisting
of MeCN and 10 mm ammonium formate buffer at a pH of 3
(90:10) and a flow rate of 0.4 mLminÀ1. Electrospray ionization was
operated in positive mode. The ESI spectra were recorded in the
range 200–2000 m/z using glu-fibrinopeptide B as a lock mass ref-
erence and sodium iodide for calibration. Slightly modified proce-
dures to syntheses of compounds that have already been pub-
lished (7, 8, 10, 11) are mentioned in the Supporting Information.
Synthesis of compound 6Zn was performed according to literature
and is not reported here.[17]
Conclusion
In conclusion, new metal-free and zinc complexes of TPyzPzs
bearing phenol(s) as peripheral substituents were synthesized.
The deprotonation of phenol to phenolate by TBAH induced
a strong donor center for intramolecular charge transfer in the
molecule, leading to a significant decrease in the FF values of
the zinc complexes. The changes induced by addition of base
led to irreversible modification of 4Zn bearing eight phenolic
moieties. However, fully reversible switching was observed for
1Zn–3Zn bearing up to four phenols. 1Zn–3Zn were also suc-
cessfully anchored into the lipophilic core of a MCT microemul-
sion, their fluorescence responded well to changes in the
buffer pH, and the pKa was determined to be 12.6. This study
confirmed that TPyzPzs bearing phenol moieties may be suita-
ble sensors for basic media and should stimulate future re-
search in this area (e.g., manipulation of the acidic properties
of the donor by suitable substitution patterns). The advantage
of the TPyzPzs for use in sensing applications is their strong
absorption (lmax >650 nm, e>300000mÀ1 cmÀ1) and emission
in the red portion of the spectrum (lem >655 nm). Living tis-
sues are more permeable at these wavelengths, and the light
is less scattered. In addition, autofluorescence of endogenous
chromophores is reduced. A novel fluorescence off-on-off
switch using metal-free TPyzPzs bearing phenolic moieties
based on the addition of specific amounts of base was demon-
strated for the first time.
Synthesis and characterization
Synthesis
of
2-[3,5-di(tert-butyl)-4-hydroxyphenyl]-
3,9,10,16,17,23,24-heptakis(tert-butylsulfanyl)-
1,4,8,11,15,18,22,25-(octaaza)phthalocyanine (1H): Magnesium
turnings (680 mg, 28 mmol) were refluxed with a small crystal of
iodine in anhydr. butanol (65 mL) for 3 h. After completion of the
magnesium butoxide formation, compound 9 (423 mg, 1 mmol)
and 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile[24] (918 mg,
3 mmol) were added, and the refluxing was continued for an addi-
tional 19 h. After cooling, the entire reaction was poured into a mix-
ture (300 mL) consisting of MeOH/water/acetic acid (10:10:1, v/v)
and stirred at RT for 30 min. The precipitate was collected and
washed thoroughly with water and air-dried. Then, the mixture of
magnesium congeners was demetalated. The entire product mix-
ture was dissolved in CHCl3 (50 mL), and TsOH monohydrate (1.9 g,
10 mmol) dissolved in THF (50 mL) was added. The mixture was
stirred at RT for 4 h. The solvent was evaporated, and the residue
was washed with water. The crude product was purified by column
chromatography on silica with toluene/CHCl3 (3:1) as the eluent,
and the second intense green fraction was collected. The purified
product was washed gently with MeOH to yield a dark green solid.
Experimental Section
General
1
Yield 90 mg (7%). H NMR (300 MHz, CDCl3, 258C, TMS): d=8.38 (s,
2H; ArH), 5.66 (s, 1H; OH), 2.14 (s, 27H, SCCH3), 2.11 (s, 18H,
SCCH3), 2.10 (s, 18H, SCCH3), 1.68 (s, 18H, ArCCH3) and À1.73 ppm
(s, 2H, NH); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=160.67,
160.31, 159.81, 159.16, 159.10, 156.03, 155.19, 135.54, 128.79,
127.78, 124.44, 123.96, 51.85, 51.75, 51.71, 51.64, 51.61, 50.85,
34.82, 30.79, 30.67, 30.57, 30.52, 30.18, 29.69 ppm (some aromatic
carbon signals were not detected); IR (ATR): n˜ =3630 (OH), 3302
(centr NH), 2957, 2901, 1522, 1452, 1362, 1313, 1279, 1232, 1141,
1081, 1011, 971 cmÀ1; UV/Vis (THF, 1 mm): lmax (e)=673 (135100),
642 (110000), 621 (36700), 590 (26100), 480 (49400), 367 nm
(103500 molÀ1 cmÀ1 L); MS (MALDI): m/z: 1342.4 [M]+, HR MS (ESI):
m/z 1343.5281 [M+H]+, calcd for C66H87N16OS7: 1343.5288.
All organic solvents used for synthesis were of analytical grade. An-
hydrous butanol for cyclotetramerization was freshly distilled from
magnesium. All chemicals for synthesis were purchased from certi-
fied suppliers (Sigma–Aldrich, TCI Europe, Acros, Merck) and used
as received. 5,6-Dichlorpyrazine-2,3-dicarbonitrile was obtained
from TCI Europe, unsubstituted zinc phthalocyanine was obtained
from Sigma–Aldrich. TLC was performed on Merck aluminum
sheets coated 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 Engineeering, Southend-on-Sea,
Essex, Great Britain). The infrared spectra were obtained on a Nico-
1
let 6700 spectrometer in ATR mode. H and 13C NMR spectra were
Synthesis
of
2-[3,5-di(tert-butyl)-4-hydroxyphenyl]-
recorded on a Varian Mercury Vx BB 300 NMR spectrometer or
VNMR S500 NMR spectrometer. Chemical shifts are given relative
to Si(CH3)4 and were locked to the signal of the solvent. The UV/Vis
spectra were recorded using a Shimadzu UV-2600 spectrophotom-
eter. The steady-state fluorescence spectra were measured using
an AMINCO-Bowman Series 2 luminescence spectrometer. The
MALDI-TOF mass spectra were recorded in positive reflectron
mode on a 4800 MALDI TOF/TOF mass spectrometer (AB Sciex, Fra-
mingham, MA, USA) in trans-2- [3-(4-tert-butylphenyl) -2-methyl-2-
propenylidene] -malononitrile as a matrix. The instrument was cali-
brated externally with a five-point calibration using a peptide cali-
bration Mix1 kit (LaserBio Laboratories, Sophia-Antipolis, France).
High resolution mass spectra (HR MS) were measured using
a UHPLC system Acquity UPLC I-class (Waters, Millford, USA) cou-
pled to a high resolution mass spectrometer Synapt G2Si (Waters,
3,9,10,16,17,23,24-heptakis(tert-butylsulfanyl)-
1,4,8,11,15,18,22,25-(octaaza)phthalocyaninato zinc(II) (1Zn):
Metal-free 1H (35 mg, 26 mmol) was dissolved in pyridine (2 mL)
and anhydr. Zn(CH3COO)2 (48 mg, 0.26 mmol) was added. The mix-
ture was refluxed for 1 h. The solvent was evaporated, and the resi-
due was washed with water. The crude product was purified by
column chromatography on silica with toluene/CHCl3 1:1 as the
eluent. The purified product was washed gently with MeOH to
afford dark green solid. Yield 34 mg (93%). 1H NMR (300 MHz,
CDCl3/[D5]pyridine, 258C, TMS): d=8.53 (s, 2H; ArH), 7.04 (s, 1H;
OH), 2.27 (s, 27H, SCCH3), 2.25 (s, 18H, SCCH3), 2.23 (s, 9H, SCCH3),
2.21 (s, 9H, SCCH3), 1.79 ppm (s, 18H, ArCCH3); 13C NMR (75 MHz,
CDCl3/[D5]pyridine, 258C, TMS): d=159.84, 159.02, 158.55, 158.51,
158.29, 156.50, 154.79, 151.97, 151.64, 151.54, 151.50, 151.43,
151.11, 146.85, 145.19, 144.85, 144.68, 144.59, 144.57, 144.55,
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137.00, 129.29, 127.78, 51.52, 51.49, 51.46, 51.41, 50.76, 35.21,
31.07, 30.96, 30.88, 30.83, 30.78, 29.88 ppm (some aromatic carbon
signals were not detected); IR (ATR): n˜ =2968, 2915, 1518, 1477,
1454, 1391, 1362, 1321, 1252, 1146, 976 cmÀ1; UV/Vis (THF, 1 mm):
lmax (e)=651 (290900), 591 (39100), 378 nm (148900 molÀ1 cmÀ1 L);
MS (MALDI): m/z: 1404.3 [M]+. HR MS (ESI): m/z 1405.4415 [M+H]+,
calcd for C66H85N16OS7Zn: 1405.4423.
Synthesis of 2,3,9,10-tetrakis[3,5-di(tert-butyl)-4-hydroxyphen-
yl]-16,17,23,24-tetrakis (tert-butylsulfanyl)-1,4,8,11,15,18,22,25-
(octaaza)phthalocyanine (3H): The compound was isolated as the
third most intense green fraction from the column chromatogra-
1
phy in the synthesis of 2H. Yield (142 mg, 7%). H NMR (500 MHz,
CDCl3/[D5]pyridine, 258C, TMS): d=8.26 (s, 4H; ArH), 8.14 (s, 4H;
ArH), 6.81 (s, 2H; OH), 6.75 (s, 4H; OH), 2.30 (s, 18H, SCCH3), 2.29
(s, 18H, SCCH3), 1.71 (s, 36H, ArCCH3), 1.67 (s, 36H, ArCCH3),
À1.02 ppm (s, 2H, NH); 13C NMR (125 MHz, CDCl3/[D5]pyridine,
258C, TMS): d=157.11, 155.56, 141.61, 137.42, 137.07, 131.36,
129.20, 128.48, 128.42, 128.21, 126.70, 125.50, 51.71, 51.57, 35.02,
35.00, 31.06, 30.90, 30.77, 30.72, 30.69 ppm (some aromatic carbon
signals were not detected); IR (ATR): n˜ =3630 (OH), 3301 (centr
NH), 2959, 2926, 2873, 1522, 1443, 1393, 1361, 1319, 1282, 1235,
1148, 1113, 1081, 1023, 986, 970 cmÀ1; UV/Vis (THF, 1 mm): lmax (e)=
675 (134000), 646 (102400), 620 (37900), 593 (27500), 483
(41600), 374 nm (93300 molÀ1 cmÀ1 L); MS (MALDI): m/z: 1690.7
[M]+. HR MS (ESI): m/z 1691.8831 [M+H]+, calcd for C96H123N16O4S4:
1691.8791.
Synthesis
of
2,3-bis[3,5-di(tert-butyl)-4-hydroxyphenyl]-
9,10,16,17,23,24-hexakis(tert-butylsulfanyl)-1,4,8,11,15,18,22,25-
(octaaza)phthalocyanine (2H): Magnesium turnings (803 mg,
33 mmol) were refluxed with a small crystal of iodine in anhydr.
butanol (65 mL) for 3 h. After completion of the magnesium butox-
ide formation, compound 7 (638 mg, 1.2 mmol) and 5,6-bis(tert-bu-
tylsulfanyl)pyrazine-2,3-dicarbonitrile (1.09 g, 3.6 mmol) were
added, and the refluxing was continued for an additional 6 h. After
cooling, the entire reaction was poured into a mixture (300 mL)
consisting of MeOH/water/acetic acid (10:10:1, v/v) and stirred at
RT for 30 min. The precipitate was collected and washed thorough-
ly with water and air-dried. Then, the mixture of magnesium con-
geners was demetalated. The entire product mixture was dissolved
in THF (100 mL), and TsOH monohydrate (2.3 g, 12 mmol) dissolved
in THF (50 mL) was added. The mixture was stirred at RT for 4 h.
The solvent was evaporated, and the residue was washed with
water. The crude product was purified by gradient column chroma-
tography on silica with toluene/CHCl3 (3:1) up to 1:1 as the eluent,
and the second intense green fraction (Rf =0.16 in toluene/CHCl3
(3:1); Rf =0.27 in toluene/CHCl3 1:1) was collected (2H). The third
most intense green fraction (Rf =0.05 in toluene/CHCl3 3:1; Rf =
0.12 in toluene/CHCl3 1:1) was also collected (3H). Both fractions
were repurified by repeated column chromatography using tolu-
ene/CHCl3 (3:1) as the eluent. After evaporation of the pure frac-
tions, the obtained dark green solids were washed gently with
a small amount of hexane. Yield of 2H: 340 mg (21%). 1H NMR
(500 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=8.29 (s, 4H; ArH),
6.86 (s, 2H; OH), 2.29 (s, 18H, SCCH3), 2.25 (s, 18H, SCCH3), 2.23 (s,
18H, SCCH3), 1.70 (s, 36H, ArCCH3), À1.80 ppm (s, 2H, NH);
13C NMR (125 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=160.66,
160.33, 159.13, 156.05, 155.70, 137.42, 131.35, 128.17, 51.88, 51.85,
51.63, 35.00, 30.98, 30.80, 30.72 ppm (some aromatic carbon sig-
nals were not detected); IR (ATR): n˜ =3630 (OH), 3295 (centr NH),
2959, 2919, 1518, 1444, 1362, 1317, 1233, 1142, 1081, 1015,
972 cmÀ1; UV/Vis (THF, 1 mm): lmax (e)=674 (153600), 643 (121800),
Synthesis of 2,3,9,10-tetrakis[3,5-di(tert-butyl)-4-hydroxyphen-
yl]-16,17,23,24-tetrakis(tert-butylsulfanyl)-1,4,8,11,15,18,22,25-
(octaaza)phthalocyaninato zinc (3Zn): The same method used for
the synthesis of 1Zn was applied but starting from 3H (100 mg,
5.9 mmol) and anhydr. Zn(CH3COO)2 (76 mg, 41 mmol). Mobile
phase: toluene/CHCl3/THF 20:10:1. Yield 100 mg (96%). 1H NMR
(300 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=8.21 (s, 4H; ArH),
8.05 (s, 4H; ArH), 6.85 (s, 2H; OH), 6.75 (s, 2H; OH), 2.27 (s, 18H,
SCCH3), 2.25 (s, 18H, SCCH3), 1.63 (s, 36H, ArCCH3), 1.61 ppm (s,
36H, ArCCH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=159.06,
158.34, 156.12, 155.55, 155.36, 151.70, 151.59, 151.35, 147.83,
144.82, 144.65, 137.53, 137.22, 131.64, 130.97, 128.17, 127.86,
51.44, 51.40, 34.91, 34.89, 31.07, 30.83, 30.66, 30.63 ppm (some aro-
matic carbon signals were not detected); IR (ATR): n˜ =3632 (OH),
2958, 2927, 2871, 1599, 1535, 1443, 1391, 1360, 1320, 1254, 1240,
1200, 1145, 1105, 1026, 1042, 980 cmÀ1; UV/Vis (THF, 1 mm): lmax
(e)=653 (280 300), 593 (37 400), 380 (133900 molÀ1 cmÀ1 L); MS
(MALDI): m/z: 1752.6 [M]+. HR MS (ESI): m/z 1753.7892 [M+H]+,
calcd for C96H121N16O4S4Zn: 1753.7926.
Synthesis of 2,3,9,10,16,17,23,24-octakis[3,5-di(tert-butyl)-4-hy-
droxyphenyl]-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninato
magnesium(II) (4Mg): Magnesium turnings (316 mg, 13 mmol)
were refluxed with a small crystal of iodine in anhydr. butanol
(65 mL) for 3 h. After completion of the magnesium butoxide for-
mation, compound 7 (1 g, 1.86 mmol) was added, and the reflux-
ing was continued for an additional 19 h. After cooling, the entire
reaction was poured into a mixture (300 mL) consisting of MeOH/
water/acetic acid (10:10:1, v/v) and stirred at RT for 30 min. The
precipitate was collected and washed thoroughly with water and
MeOH. The crude product was purified by column chromatography
on silica with CHCl3/THF (20:1) as the eluent. The purified product
was dissolved in a minimal amount of CHCl3 and dropped into
hexane. A fine precipitate was collected and dried to yield a dark
green solid. Yield 714 mg (71%). 1H NMR (300 MHz, CDCl3/
[D5]pyridine, 258C, TMS): d=8.03 (s, 16H; ArH), 1.61 ppm (s, 144H,
CH3); 13C NMR (75 MHz, CDCl3/[D5]pyridine, 258C, TMS): no signals
were detected. IR (ATR): n˜ =3630 (OH), 2956, 1636, 1437, 1393,
1355, 1319, 1239, 1198, 1159, 11010, 1004 cmÀ1; UV/Vis (THF, 1 mm):
lmax (e)=657 (364900), 596 (45600), 465 (27000), 391 nm
(171000 molÀ1 cmÀ1 L); MS (MALDI): m/z: 2177.1 [M]+. HR MS (ESI):
m/z 2178.3208 [M+H]+, calcd for C136H169MgN16O8: 2178.3154.
619
(43300),
590
(30400),
481
(53700),
370 nm
(110200 molÀ1 cmÀ1 L); MS (MALDI): m/z: 1458.5 [M]+. HR MS (ESI):
m/z 1459.6466 [M+H]+, calcd for C76H99N16O2S6: 1459.6456.
Synthesis
of
2,3-bis[3,5-di(tert-butyl)-4-hydroxyphenyl]-
9,10,16,17,23,24-hexakis(tert-butylsulfanyl)-1,4,8,11,15,18,22,25-
(octaaza)phthalocyaninato zinc (2Zn): The same method used for
the synthesis of 1Zn was applied but starting from 2H (280 mg,
0.19 mmol) and anhydr. Zn(CH3COO)2 (246 mg, 1.34 mmol). Mobile
phase: CHCl3. Yield 229 mg (78%). 1H NMR (300 MHz, CDCl3/
[D5]pyridine, 258C, TMS): d=8.22 (s, 4H; ArH), 6.87 (s, 2H; OH),
2.263 (s, 18H, SCCH3), 2.256 (s, 18H, SCCH3), 2.247 (s, 18H, SCCH3),
1.63 ppm (s, 36H, ArCCH3); 13C NMR (75 MHz, CDCl3/[D5]pyridine,
258C, TMS): d=158.93, 158.53, 158.31, 155.58, 155.30, 151.58,
151.53, 151.44, 151.38, 147.35, 144.83, 144.66, 144.55, 137.43,
131.28, 127.93, 123.84, 51.49, 51.43, 51.40, 34.91, 31.07, 30.85,
30.83, 30.63 ppm; IR (ATR): n˜ =3632 (OH), 2960, 2919, 1519, 1445,
1392, 1362, 1320, 1250, 1141, 1106, 976 cmÀ1; UV/Vis (THF, 1 mm):
lmax (e)=651 (308900), 591 (40400), 380 (148500 molÀ1 cmÀ1 L); MS
(MALDI): m/z: 1520.4 [M]+. HR MS (ESI): m/z 1521.5571 [M+H]+,
calcd for C76H97N16O2S6Zn: 1521.5591.
Synthesis of 2,3,9,10,16,17,23,24-octakis[3,5-di (tert-butyl)-4-hy-
droxyphenyl]-1,4,8,11,15,18,22,25-(octaaza)phthalocyanine (4H):
Magnesium complex 4Mg (175 mg, 80 mmol) was dissolved in THF
Chem. Eur. J. 2015, 21, 14382 – 14392
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ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
(10 mL), and TsOH monohydrate (153 mg, 0.8 mmol) dissolved in
THF (10 mL) was added. The mixture was stirred at RT for 4 h. The
solvent was evaporated, and the residue was washed with water.
The crude product was purified by column chromatography on
silica with CHCl3/THF (50:1) as the eluent. The purified product was
washed thoroughly with hexane. A fine precipitate was collected
and dried to afford a black solid. Yield 159 mg (92%). 1H NMR
(300 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=8.07 (s, 16H; ArH),
6.78 (bs, 8H, OH), 1.64 (s, 144H, CH3), À0.69 ppm (bs, 2H, NH);
13C NMR (75 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=158.0, 155.7,
146.2, 137.5, 131.0, 128.2, 34.9, 30.7 ppm (one aromatic carbon was
not detected); IR (ATR): n˜ =3633 (OH), 3301 (NH), 2955, 2871, 1635,
1598, 1541, 1434, 1400, 1353, 1319, 1255, 1238, 1223, 1150, 1110,
[D5]pyridine, 258C, TMS): d=157.8, 155.7, 146.7, 142.3, 135.6, 127.3,
62.4, 26.8, 24.2 ppm (one aromatic carbon was not detected). IR
(ATR): n˜ =3305 (NH), 2964, 2870, 2829, 1633, 1543, 1460, 1364,
1311, 1286, 1225, 1200, 1169, 1011 cmÀ1; UV/Vis (THF, 1 mm): lmax
(e)=668 (146400), 639 (121700), 612 (41200), 588 (31800), 470
(42400), 369 nm (113700 molÀ1 cmÀ1 L); MS (MALDI): m/z: 2043.1
[M]+; HR MS (ESI): m/z 2044.2190 [M+H]+, calcd for C128H155N16O8:
2044.2208.
Synthesis of 2,3,9,10,16,17,23,24-octakis(3,5-diisopropyl-4-me-
thoxyphenyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninato
zinc(II) (5Zn): Zinc complex 5Zn was prepared in the same way as
4Zn from metal-free 5H (35 mg, 17 mmol) and anhydr.
Zn(CH3COO)2 (32 mg, 0.17 mmol). Toluene/CHCl3/THF (25:25:1) was
used as the eluent for column chromatography, and the final prod-
uct was only washed with MeOH. Yield 32 mg (97%). 1H NMR
(300 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=7.79 (s, 16H; ArH),
3.84 (s, 24H, OCH3), 3.53–3.36 (m, 16H, CH), 1.25 ppm (d, J=6.8 Hz,
96H, CH3); 13C NMR (75 MHz, CDCl3/[D5]pyridine, 258C, TMS): 156.4,
155.3, 151.7, 148.3, 142.0, 135.9, 127.2, 62.3, 26.6, 24.1 ppm; IR
(ATR): n˜ =3962, 2870, 2831, 1633, 1537, 1461, 1369, 1310, 1286,
1236, 1197, 1168, 1099, 1061, 1012 cmÀ1; UV/Vis (THF, 1 mm): lmax
(e)=648 (330600), 588 (42000), 375 nm (153200 molÀ1 cmÀ1 L); MS
(MALDI): m/z: 2105.0 [M]+; HR MS (ESI): the compound did not
ionize sufficiently in ESI.
1015 cmÀ1
; UV/Vis (THF, 1 mm): lmax (e)=676 (174500), 650
(128300), 621 (47200), 599 (38400), 519 (45600), 384 nm
(118400 molÀ1 cmÀ1 L); MS (MALDI): m/z: 2155.2 [M]+; HR MS (ESI):
m/z 2156.3438 [M+H]+, calcd for C136H171N16O8: 2156.3460. The
data corresponded well with those published by Hill et al.[13a]
Synthesis of 2,3,9,10,16,17,23,24-octakis[3,5-di(tert-butyl)-4-hy-
droxyphenyl]-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninato
zinc(II) (4Zn): Metal-free 4H (78 mg, 36 mmol) was dissolved in pyr-
idine (5 mL) and anhydr. Zn(CH3COO)2 (66 mg, 0.36 mmol) was
added. The mixture was refluxed for 1 h. The solvent was evaporat-
ed, and the residue was washed with water. The crude product
was purified by column chromatography on silica with CHCl3/THF
(25:1) as the eluent. The purified product was washed thoroughly
with hexane. A fine precipitate was collected and dried to afford
Synthesis of 5-tert-butylsulfanyl-6-[3,5-di(tert-butyl)-4-hydroxy-
phenyl]pyrazine-2,3-dicarbonitrile (9): Compound
8
(1 g,
2.7 mmol) was dissolved in pyridine (30 mL) to yield a red solution.
2-Methylpropan-2-thiol (292 mg, 365 mL, 3.2 mmol) was added, and
the mixture was refluxed for 1 h. The solvent was removed under
reduced pressure, and the solid residue was washed with water
and air-dried. The crude product was purified by column chroma-
tography on silica with hexane/ethylacetate (15:1) as the eluent.
The purified product was crystallized from chloroform/hexane to
yield yellow crystals. Yield 0.88 g (77%); m.p. 143.7–144.68C;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.67 (s, 2H; ArH), 5.69 (s,
1H; OH), 1.62 (s, 9H, SCCH3), 1.48 ppm (s, 18H, CH3); 13C NMR
(75 MHz, CDCl3, 258C, TMS): d=162.5, 157.1, 156.2, 136.1, 127.8,
126.8, 126.1, 125.1, 113.7, 113.6, 51.3, 34.6, 30.1, 29.5 ppm; IR (ATR):
a
black solid. Yield 43 mg (54%). 1H NMR (300 MHz, CDCl3/
[D5]pyridine, 258C, TMS): d=8.06 (s, 16H; ArH), 7.49 (s, 8H, OH),
1.63 ppm (s, 144H, CH3); 13C NMR (75 MHz, CDCl3/[D5]pyridine,
258C, TMS): d=34.4, 30.1 ppm (aromatic carbon signals were not
detected). IR (ATR): n˜ =3639 (OH), 2956, 2871, 1635, 1601, 1540,
1440, 1356, 1318, 1238, 1159, 1103, 1005 cmÀ1; UV/Vis (THF, 1 mm):
lmax (e)=654 (325500), 595 (42300), 460 (28300), 384 nm
(147800 molÀ1 cmÀ1 L); MS (MALDI): m/z: 2217.1 [M]+; HR MS (ESI):
m/z 2218.2534 [M+H]+, calcd for C136H169N16O8Zn: 2218.2595.
Synthesis of 2,3,9,10,16,17,23,24-octakis(3,5-diisopropyl-4-me-
thoxyphenyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyaninato
magnesium(II) (5Mg): Magnesium complex 5Mg was prepared in
the same way as 4Mg from magnesium (86 mg, 3.5 mmol) and
precursor 13 (257 mg, 0.5 mmol). CHCl3/THF (50:1) was used as the
eluent for column chromatography, and the final product was only
washed with hexane without dissolving in CHCl3. Yield 137 mg
(53%). 1H NMR (300 MHz, CDCl3/[D5]pyridine, 258C, TMS): d=7.83
(s, 16H; ArH), 3.89 (s, 24H, OCH3), 3.50 (hept, J=6.8 Hz, 16H, CH),
1.31 ppm (d, J=6.8 Hz, 96H, CH3); 13C NMR (75 MHz, CDCl3/
[D5]pyridine, 258C, TMS): d=156.0, 155.3, 151.2, 148.9, 142.1, 136.1,
127.3, 62.4, 26.7, 24.3 ppm. IR (ATR): n˜ =2962, 2871, 2828, 1632,
1536, 1462, 1366, 1311, 1286, 1254, 1236, 1197, 1168, 1099, 1061,
1013 cmÀ1; UV/Vis (THF, 1 mm): lmax (e)=651 (385400), 624 (43600),
591 (46400), 383 nm (176100 molÀ1 cmÀ1 L); MS (MALDI): m/z:
2065.0 [M]+; HR MS (ESI): m/z 2066.1924 [M+H]+, calcd for
C128H153MgN16O8: 2066.1902.
n˜ =2963, 2874, 2225 (CN), 1489, 1379, 1363, 1222, 1139, 999 cmÀ1
.
Synthesis of 1,2-bis(3,5-diisopropyl-4-methoxyphenyl)ethane-
1,2-dione (12): Benzaldehyde 11 (6.6 g, 30 mmol) was dissolved in
absolute EtOH (75 mL), and 5-(2-hydroxyethyl)-3,4-dimethylthiazoli-
um iodide (427 mg, 1.5 mmol) and 1,8-diazabicyclo[5.4.0]undec-7-
ene (227 mg, 227 mL, 1.5 mmol) were added. The reaction was
heated under reflux for 3 h, and the color changed from red to
yellow-orange. The solvent was removed under reduced pressure,
and the residue was suspended in water. The suspension was ex-
tracted three times with ethyl acetate, and the organic layers were
dried over anhydr. Na2SO4 and evaporated to dryness. The acyloin
was directly oxidized to a diketone after dissolution in acetic acid
(50 mL) using Cu(CH3COO)2 (30 mg, 0.16 mmol) and NH4NO3 (1.4 g,
17.5 mmol). The mixture was refluxed for 4 h, and the solvent was
evaporated under reduced pressure. The residue was suspended in
water and extracted three times with ethyl acetate. The organic
layers were dried over anhydr. Na2SO4 and evaporated to dryness.
The crude product was purified by column chromatography on
silica with toluene/CHCl3 (4:1) as the eluent. The purified product
was crystallized from CHCl3/hexane (the crystals appeared after
couple of days in the freezer) to yield colorless crystals. Yield 1.4 g
(21%); m.p. 162.6–163.98C; 1H NMR (300 MHz, CDCl3, 258C, TMS):
d=7.75 (s, 4H, ArH), 3.80 (s, 6H, OCH3), 3.34 (hept, J=6.9 Hz, 4H,
CH), 1.24 ppm (d, J=6.9 Hz, 24H, CH3); 13C NMR (75 MHz, CDCl3,
258C, TMS): d=194.1, 160.5, 142.9, 129.8, 126.7, 62.3, 26.7,
Synthesis of 2,3,9,10,16,17,23,24-octakis(3,5-diisopropyl-4-me-
thoxyphenyl)-1,4,8,11,15,18,22,25-(octaaza)phthalocyanine (5H):
Metal-free complex 5H was prepared in the same way as 4H from
magnesium complex 5Mg (88 mg, 43 mmol) and TsOH monohy-
drate (82 mg, 0.43 mmol). Toluene/CHCl3/THF (25:25:1) was used as
the eluent for column chromatography, and the final product was
only washed with MeOH. Yield 77 mg (88%). 1H NMR (300 MHz,
CDCl3/[D5]pyridine, 258C, TMS): d=7.84 (s, 16H; ArH), 3.88 (s, 24H,
OCH3), 3.49 (hept, J=6.9 Hz, 16H, CH), 1.30 (d, J=6.9 Hz, 96H,
CH3), À0.77 ppm (bs, 2H, NH); 13C NMR (75 MHz, CDCl3/
Chem. Eur. J. 2015, 21, 14382 – 14392
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14390
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
23.8 ppm; IR (ATR): n˜ =2966, 2931, 2871, 1663 (CO), 1593, 1461,
1418, 1364, 1305, 1163, 1112, 1005 cmÀ1
Preparations of the microemulsions
.
Compounds 1Zn–3Zn and 6Zn (0.25 nmol), Cremophor EL (BASF,
72 mg) and medium-chain triglycerides (MCT, Ecogreen oleochemi-
cals, meeting specifications of Ph.Eur.) (29 mg) were dissolved in
THF. The solvent was evaporated under reduced pressure, and the
flask was maintained under deep vacuum (5 mbar) for 30 min at
408C to remove all traces of solvent. Then, water was added to
a total volume of 5.0 mL, and the mixture was thoroughly shaken
on a vortex and orbital shaker. The particles were characterized
using a photon correlation spectroscope Zetasizer Nano-ZS (Mal-
vern, UK). Their size was determined to be approximately 300 nm.
The microemulsion was stable for at least two weeks without any
significant change in the particle size.
Synthesis of 5,6-bis (3,5-diisopropyl-4-methoxyphenyl)pyrazine-
2,3-dicarbonitrile (13): Dione 12 (1.4 g, 2.7 mmol) was dissolved in
acetic acid (25 mL), and diaminomaleonitrile (1.4 g, 13 mmol) was
added. The mixture was refluxed for 3 h, and then, the solvent was
evaporated under reduced pressure. The residue was extracted
with acetone and filtered, and the filtrate was evaporated. The
crude product was purified by column chromatography on silica
with hexane/ethyl acetate (9:1) as the eluent. The purified product
was crystallized from CHCl3/hexane to afford fine yellow needles.
Yield 555 mg (34%); m.p. 241.0–242.38C; 1H NMR (500 MHz,
[D6]acetone, 258C, TMS): d=7.27 (s, 4H, ArH), 3.72 (s, 6H, OCH3),
3.28 (hept, J=6.9 Hz, 4H, CH), 1.07 ppm (d, J=6.9 Hz, 24H, CH3);
13C NMR (125 MHz, [D6]acetone, 258C, TMS): d=157.38, 157.36,
143.04, 133.21, 130.54, 127.05, 114.88, 62.54, 27.14, 24.06 ppm; IR
(ATR): n˜ =2964, 2873, 2240 (CN), 1603, 1516, 1474, 1382, 1327,
Acknowledgements
1301, 1279, 1250, 1194, 1167, 1102, 1003 cmÀ1
.
The work was financially supported by the Czech Science
ˇ
ˇ
Foundation (14-02165P). The authors wish to thank Jirí Kunes
Singlet oxygen and fluorescence quantum yields
ˇ
for NMR spectroscopy measurements, Juraj Lenco for MALDI-
TOF measurements and Lucie Novµkovµ for HR MS data.
For singlet oxygen and fluorescence determination as well as the
titration experiments, the dye samples were purified by preparative
TLC on Merck aluminum sheets coated with silica gel 60 F254 to
ensure high purity. Both the FD and FF values were determined
by comparative methods[25] using unsubstituted zinc phthalocya-
nine (ZnPc) as a reference (FD(THF) =0.53,[26] FF(THF) =0.32[1a]). All of
the experiments were performed in triplicate, and the data repre-
sent the means of the measurements (estimated error Æ10%). For
FF determination, the sample and reference were excited at
599 nm, and the absorbance at the Q-band maximum was main-
tained at less than 0.05 to avoid the inner filter effect. The emission
spectra were corrected for the instrument response. The FF values
were corrected for the refractive indices of the appropriate sol-
vents.
Keywords: azaphthalocyanines · fluorescence · intramolecular
charge transfer · pH sensors · phthalocyanines
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Received: June 29, 2015
Published online on August 26, 2015
Chem. Eur. J. 2015, 21, 14382 – 14392
www.chemeurj.org
14392
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim