Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues

Article abstract of DOI:10.1039/c2dt31403g

Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or

Full text of DOI:10.1039/c2dt31403g

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PAPER
Effect of intramolecular charge transfer on fluorescence and singlet oxygen
production of phthalocyanine analogues†
Lenka Vachova,a Veronika Novakova,b Kamil Kopecky,a Miroslav Miletina and Petr Zimcik*a
Received 28th June 2012, Accepted 12th July 2012
DOI: 10.1039/c2dt31403g
Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc
complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two
dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The
dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable
decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties
were compared to corresponding macrocycles that do not bear any donor centers. The data showed high
feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this
deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of
non-donor peripheral substituents on ICT was also described. The results imply that
tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in
applications based on ICT.
Presented work is focused on synthesis and investigation of
photophysical and photochemical properties of compounds
Introduction
Phthalocyanines (Pcs) and their aza-analogues azaphthalocya-
nines are synthetic dyes that have been extensively studied due
to their unique optical, physical, electronic, spectral and struc-
tural properties.1 Recently, they attracted also great attention in
the field of dye-sensitized solar cells,2 fluorescent probes3,4 and
photodynamic therapy.5 A long-lived excited state and high
quantum yield of fluorescence or singlet oxygen are, in general,
advantageous in these applications. On the other hand, an inter-
esting phenomenon of ultrafast intramolecular charge transfer
(ICT) was recently shown to be responsible for quenching of the
excited states in tetrapyrazinoporphyrazines (TPyzPz), a type of
azaphthalocyanines.6 This discovery opened a door for new
applications of these macrocyclic dyes in quenching of fluor-
escence in DNA-hybridization probes7 or as molecular sensors
(e.g. pH-sensitive8). The effect of ICT was studied in detail
for TPyzPz but similar processes were recently described also
for Pc.9,10
bearing donor centers for ICT and containing different macro-
cycle ring and peripheral substituents. The aim is to compare the
efficiency of ICT in these compounds and to discuss their poten-
tial to be further investigated as efficient quenchers of fluor-
escence or sensors.
Results and discussion
Design of the compounds
The structures of the compounds (Scheme 1) were designed to
contain two donor centers (aminosubstituents) in order to allow
high feasibility of ICT. ICT in compounds with only one donor
center is highly sensitive to properties of environment6 (e.g.
polarity, acidity) that may interfere with proper interpretation of
the results. The substituents on the studied derivatives were
chosen to be bulky to limit aggregation of planar molecules that
could lead to misinterpretation of the data. One carboxy group
was introduced to the molecule in order to allow simple binding
of prospective derivatives to biomolecules or other suitable
modifiers in future.7
The porphyrazine ring was fused with three benzene and one
pyrazine rings (5 and 6) or contains only pyrazine rings (i.e.
TPyzPz) in the case of 7. Compounds 6 and 7 contained the
same substituents and differed only in the macrocyclic core. This
series allows comparison between macrocycle types without the
influence of peripheral substitution (compounds 6 and 7) and
between peripheral substituents without influence of the macro-
cycle ring (5 and 6). Symmetrical compounds 8–10 without any
aDepartment of Pharmaceutical Chemistry and Drug Control, Faculty of
Pharmacy in Hradec Kralove, Charles University in Prague,
Heyrovskeho 1203, 50005, Hradec Kralove, Czech Republic.
E-mail: petr.zimcik@faf.cuni.cz; Fax: +420 495067167;
Tel: +420 495067257
bDepartment of Biophysics and Physical Chemistry, Faculty of
Pharmacy in Hradec Kralove, Charles University in Prague,
Heyrovskeho 1203, 50005 Hradec Kralove, Czech Republic
†Electronic supplementary information (ESI) available: NMR spectra,
MS (MALDI-TOF) spectra, absorption, emission and excitation spectra.
See DOI: 10.1039/c2dt31403g
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Scheme 1 Synthesis of the investigated compounds. Reaction conditions: (i) Mg, I2, butanol, reflux, (ii) TFA or pTSA, chloroform, rt,
(iii) Zn(CH3COO)2, pyridine, reflux.
donor center were used as negative controls where no ICT can
occur.
Synthesis
Mixed cyclotetramerization (also known as statistical conden-
sation11) is the simplest method for the synthesis and isolation of
unsymmetrical Pc and TPyzPz of the AAAB type despite the
fact that several selective approaches were developed.12 Thus,
treatment of a mixture of precursors A (1, 2, or 3) and B (com-
pound 4) with magnesium butoxide in butanol gave a mixture of
six congeners, from which congeners of ABBB type were separ-
ated on silica to afford 5Mg–7Mg in reasonable yields of 7–15%
(Scheme 1). In order to increase the amount of the AAAB con-
gener in the statistical mixture, the ratio of starting material was
set to 3 : 1 (A : B) and the precursor A was added in three por-
Fig. 1 Normalized absorption spectra of 5Zn (black, dotted), 6Zn
(red, full) and 7Zn (blue, dashed) in THF.
tions due to the lower reactivity of compound 4. The isolation
was facilitated by the presence of a polar substituent (carboxy
group) that led to a good separation of the congeners on TLC
Absorption spectra
Absorption spectra in THF were consistent with the structures
and contained high energy B-band (in area 350–390 nm) and
low energy Q-band (in area 650–695 nm) with clearly marked
vibrational bands (Fig. 1). The shape of the spectra was typical
for monomeric species in solution, no aggregates were detected
during all photophysical and photochemical measurements. In
general, unsymmetrical composition of the macrocycle is indi-
cated by splitting of the Q-band. The metal-free derivatives 5H,
6H and 7H were characterized by strong splitting between the
Qx- and Qy-bands due to lowered symmetry because of the pres-
ence of central hydrogens (see ESI, Fig. S16†). The symmetry of
the porphyrazine ring was lowered also in metal complexes
5Mg–7Mg and 5Zn–7Zn due to the presence of different iso-
indole units. However, only the absorption spectra of compounds
5Mg and 5Zn showed hardly-noticeable splitting of the Q-band
with distinct retention factors. Despite this, purification on the
silica column had to be repeated several times to obtain pure
product. Magnesium complexes were demetalated using strong
organic acid and the metal free derivatives 5H–7H were con-
verted to zinc complexes using zinc acetate in pyridine to afford
5Zn–7Zn. The synthesis of metal complexes of compounds
8–10 was described elsewhere.4 All analyses confirmed unequi-
vocally the structure of the isolated congeners (see ESI, Fig. S1–
S15†). Interestingly, compounds 5Mg, 5H and 5Zn were extre-
mely light sensitive and decomposed rapidly in solution or on
TLC. For this reason, the solutions and silica columns were
strictly protected from light by aluminum foil. In agreement with
this observation, extensive photodecomposition was recently
found for structurally similar 8Mg and 8Zn with high photo-
bleaching quantum yields.4
11652 | Dalton Trans., 2012, 41, 11651–11656
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Table 1 Photophysical and photochemical data for studied compounds in THF
b
b
c
c
Designationa
Q-band λmax (nm)
λem (nm)
Stokes shift (cm−1
)
ΦF
ΦΔ
ΦF(N)/ΦF(D)
ΦΔ(N)/ΦΔ(D)
5Zn
5Mg
6Zn
6Mg
7Zn
7Mg
8Znd
8Mgd
9Znd
9Mgd
10Znd
10Mgd
D
D
D
D
D
D
N
N
N
N
N
N
678
680
689
690
654
655
675
677
697
699
649
651
682
684
696
698
662
660
680
681
707
709
656
658
87
86
0.15
0.35
0.071
0.062
0.0045
0.0087
0.29
0.52
0.16
0.23
0.35
0.37
0.23
0.10
0.043
0.030
0.013
0.61
0.26
0.68
0.23
0.55
0.30
1.9
1.5
2.3
3.7
78
61
—
—
—
—
—
—
1.7
1.1
6.6
5.4
19
22
—
—
—
—
—
—
146
166
185
116
109
87
203
202
164
163
0.53
a D = compound contains donor centers, N = compound does not contain a donor center. b Mean of three independent measurements, estimated error
15%. c Calculated by dividing the quantum yield of a compound without a donor center (N) by the quantum yield of the corresponding compound
with donor centers (D), corresponding pairs: 5 and 8, 6 and 9, 7 and 10. d Data from ref. 4.
(Fig. 1 and ESI, Fig. S17†), the metal complexes of 6 and 7
remained unsplit.
The positions of the Q-band maxima were also influenced by
the composition of the macrocycle and peripheral substituents
(Table 1). Considering the central metal, a very small red-shift of
the maximum (approximately 1–2 nm) can be observed for mag-
nesium complexes if compared with zinc derivatives. On the
other hand, an almost 35 nm red shift was detected when three
pyrazine rings in the macrocycle were exchanged for benzene
rings (compare compounds 6 and 7). Pc in general are always
red-shifted for about 48 nm if compared with TPyzPz (compare
the corresponding metal complexes of 9 and 10 (Table 1)).4,13 In
the case of compounds 6 and 7, only three pyrazines were
exchanged for benzene rings in the macrocycle core when going
from 7 to 6, which corresponds to a 36 nm calculated red shift.
Fig. 2 Emission spectra of 5Zn (black, dotted), 6Zn (red, full) and
7Zn (blue, dashed) in THF. Absorbance at the excitation wavelength
(λexc = 612 nm) was the same for all compounds. Inset: normalized
This observation is in agreement with previously published data
and indicates that the position of the Q-band can be considered
as an additive parameter that depends on the composition of the
emission spectra.
macrocycle.14 Focusing on the influence of peripheral substi-
tution (comparison between 5 and 6), an important red-shift
(about 10 nm) was observed for the alkylsulfanyl derivative.
motion that may deactivate the excited states. For this reason,
these derivatives are not suitable for investigation of the
influence of structure on ICT due to another relaxation channel
and therefore were not included in the photophysical and photo-
Fluorescence and singlet oxygen production
chemical study. Data obtained for compounds 5Mg–7Mg, 5Zn–
7Zn and corresponding symmetrical derivatives without the
donor center (8Mg–10Mg and 8Zn–10Zn) are mentioned in
Table 1. As anticipated, very low ΦF values below 0.01 were
obtained for compounds 7Mg and 7Zn due to efficient ICT. The
values are almost two orders of magnitude lower than for corre-
sponding compounds without the donor centers (10Mg and
10Zn). This confirmed previous observations that ICT is a
highly efficient relaxation pathway of excited states in this type
of macrocycle.6 ΦF values of compounds that are structurally
closer to Pc (5 and 6) were much higher than for compounds 7,
however; still several times lower than for the corresponding
derivatives without any donor center. The moderate (for com-
plexes 6) or only minimal (for complexes 5) decrease of fluor-
escence after the introduction of donor centers indicates that ICT
The fluorescence was measured in THF after excitation at
Q-band. Fluorescence emission spectra mirrored the absorption
spectra with only small Stokes shift (Table 1). The shape of the
spectra were typical for TPyzPz, Pc and related compounds
(Fig. 2). The signal was very weak for 7Zn and 7Mg. The exci-
tation spectra (see ESI, Fig. S17†) superimposed the absorption
spectra confirming the origin of the signal and presence of only
monomeric species. Thus, the observed low ΦF values of com-
pounds containing donor centers (see below) cannot be attributed
to aggregation. The fluorescence quantum yields were deter-
mined in THF with unsubstituted ZnPc in 1-chloronaphthalene15
(ΦF = 0.30) as a reference. The data were collected only for the
metal complexes. Metal-free TPyzPz are, in general, character-
ized by low fluorescence and singlet oxygen quantum yields.4
An apparent reason may be enhanced vibrational and rotational
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is a far less efficient deactivation process in this type of macro-
cycle. The results are in agreement with observations of ICT in
Pc where only a moderate decrease of ΦF values was observed
after the introduction of one to four donor centers.10
Experimental
General
All organic solvents used were of analytical grade. All chemicals
for the synthesis were obtained from established suppliers
(Aldrich, Acros, Merck, TCI Europe) and used as received. 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. 1H and 13C NMR spectra were recorded on
Varian Mercury Vx BB 300 spectrometer or VNMR S500 NMR
spectrometer. Chemical shifts reported are relative to Me4Si and
were locked to the signal of a solvent. The UV-vis spectra were
recorded using a Shimadzu UV-2401PC spectrophotometer. The
fluorescence spectra were obtained by an AMINCO-Bowman
Series 2 luminescence spectrometer. MALDI-TOF mass spectra
were recorded in a positive reflectron mode on a Voyager-DE
STR mass spectrometer (Applied Biosystems, Framingham,
MA, USA) in trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-prope-
nylidene]malononitrile as the matrix. The instrument was cali-
brated externally with a five-point calibration using Peptide
Calibration Mix1 (Laser-Bio Labs, Sophia-Antipolis, France).
Synthesis of precursors 1,19 2,20 320 and 47 and metal complexes
8–104 was performed according to the literature.
Singlet oxygen quantum yields were determined in THF with
ZnPc in THF16 (ΦΔ = 0.53) as a reference. The results summar-
ized in Table 1 indicated similar dependencies as outlined above
for fluorescence. The largest decrease in singlet oxygen pro-
duction after the incorporation of two donor centers into the mol-
ecule was observed for compounds 7, followed by complexes 6
and only minimal influence of ICT was detected in derivatives 5.
The obtained results indicated that high feasibility of ICT may
be closely connected with TPyzPz macrocycles. The macrocycle
that is structurally closer to Pc seems to be less suitable for this
deactivation process (compare 6 and 7). Also, peripheral substi-
tuents not involved in ICT may play an important role as shown
on metal complexes of 5 and 6. The explanation for all the
observed results may be related to strong electron-deficient pro-
perties of TPyzPz macrocycles if compared with Pc as shown by
Donzello et al.17 TPyzPz are easier to reduce as documented by
literature data: the first reduction potential for (SC6H13)8ZnPc
(analogue to 9Zn) in CH2Cl2 is reported −0.79 V,18 for TPyzPz
10Zn in pyridine −0.58 V6 and for octa(2-pyridyl)ZnTPyzPz
even −0.34 V (in pyridine17). In the case of the observed deacti-
vation process, the macrocycle ring is the acceptor while a per-
ipheral amino substituent is the donor of the electrons. The more
electron-deficient the macrocycle is the more feasibly ICT can be
anticipated. This may explain the differences between com-
pounds 6 and 7. Moreover, strongly electron-donating peripheral
substituents (e.g. 2,5-diisopropylphenoxy substituents in com-
pounds 5) may further decrease the electron-accepting properties
of the ring and as a consequence also the feasibility of ICT. The
photophysical and photochemical parameters of such com-
pounds will therefore remain close to similar derivatives without
the donor centers.
General procedure for synthesis of 5Mg–7Mg
Magnesium (28 eq.), and a small crystal of iodine were refluxed
in anhydrous butanol for 3 h. After that time, compound 4
(1 eq.) was added. The second precursor (1, 2 or 3, 3 eq.) was
added in three equal portions during next hour and a half and
heating was continued for the next 20 h. The mixture was cooled
down in the air, the solvent was evaporated under reduced
pressure, aqueous acetic acid (50% (v/v)) was added and the sus-
pension was stirred for 30 min. The dark solid was filtered,
washed with aqueous acetic acid and water and air-dried. The
mixture of the congeners was separated by column chromato-
graphy on silica (eluents are mentioned below) to obtain mag-
nesium complexes 5Mg–7Mg as green solids.
Conclusions
In conclusion, magnesium, metal-free and zinc complexes of
three unsymmetrical derivatives of porphyrazine were syn-
thesized from two different precursors using a statistical conden-
sation approach. The compounds contained two peripheral
amino substituents, the donors in ICT. Ultrafast ICT was respon-
sible for the considerable decrease of both fluorescence and
singlet oxygen quantum yields of these macrocycles if compared
with corresponding compounds without any donor center. The
strong influence of both macrocycle character and peripheral
substituents on ICT was confirmed. The more efficient ICT pro-
ceeds in TPyzPz macrocycles and therefore they are more suit-
able for future development of different molecular sensors and
quenchers of fluorescence based on ICT. High efficiency of the
ICT is required in these applications in order to obtain a suffi-
ciently quenched “OFF” state. Macrocycles that are structurally
closer to Pc seem to be less suitable for these applications unless
substituted by electron withdrawing substituents that may
enhance the electron accepting properties of the whole
macrocycle.
Compound 5Mg. Starting amounts: 1 (1440 mg, 3 mmol), 4
(350 mg,
1 mmol), eluent: chloroform–acetone–methanol
(20 : 1 : 1), yield: 200 mg (11%). λmax (THF, 1 μM)/nm 680
(ε/dm3 mol−1 cm−1 148 300), 608 (24 600), 363 (80 950). δH
(300 MHz, pyridine-d5) 9.05 (s, 1H, ArH-Pc), 8.98 (s, 1H,
ArH-Pc), 8.75–8.65 (m, 4H, ArH-Pc), 8.47 (d, J = 8.4 Hz, 2H,
ArH-phenylamino), 7.97–7.85 (m, 4H, ArH-phenoxy),
7.77–7.40 (m, 14H, ArH-phenoxy), 7.08 (d, J = 8.4 Hz, 2H,
ArH-phenylamino), 3.90–3.41 (m, 19H, CH, N–CH2, N–CH3),
1.58–1.00 (m, 78H, CH3). δC (75 MHz, pyridine-d5) 169.15,
155.26, 155.15, 155.00, 154.70, 153.20, 152.01, 151.26, 151.23,
151.19, 151.13, 142.25, 142.10, 141.81, 140.86, 134.24, 134.17,
133.76, 133.70, 133.66, 133.57, 131.22, 127.43, 127.30, 125.73,
125.58, 116.88, 108.15, 108.10, 107.89, 44.24, 37.89, 28.00,
24.31, 22.81, 13.27, some aromatic signals were not detected.
m/z (MALDI TOF) 1814.81 [M]+, 1837.80 [M + Na]+, 1853.77
[M + K]+.
11654 | Dalton Trans., 2012, 41, 11651–11656
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were not detected. m/z (MALDI TOF) 1792.76 [M]+, 1815.72
Compound 6Mg. Starting amounts: 2 (730 mg, 2.4 mmol), 4
(280 mg, 0.8 mmol), eluent: chloroform–acetone–methanol
(20 : 1 : 1), yield: 75 mg (7%). λmax (THF, 1 μM)/nm 690 (ε/dm3
mol−1 cm−1 229 800), 623 (38 800), 373 (86 900). δH
(300 MHz, pyridine-d5) 10.21 (s, 1H, ArH-Pc), 10.19–10.15 (m,
4H, ArH-Pc), 10.14 (s, 1H, ArH-Pc), 8.45 (d, J = 8.2 Hz, 2H,
ArH-phenylamino), 7.21–7.17 (m, 2H, ArH-phenylamino), 3.91
(s, 3H, N–CH3), 3.79 (q, J = 7.1 Hz, 4H, N–CH2), 1.64 (s, 18H,
CH3), 1.63–1.60 (m, 18H, CH3), 1.58 (s, 9H, CH3), 1.50 (s, 9H,
CH3), 1.15 (t, J = 7.1 Hz, 6H, NCH2CH3). δC (75 MHz, pyri-
dine-d5) 168.99, 155.25, 155.17, 154.96, 154.68, 154.42,
153.81, 152.84, 151.01, 146.85, 146.39, 142.85, 142.21, 142.13,
141.80, 141.70, 141.39, 139.08, 138.98, 138.95, 138.80, 132.84,
132.18, 131.60, 131.50, 131.44, 131.36, 131.16, 124.75, 117.20,
48.78, 48.73, 48.69, 48.63, 44.03, 39.03, 31.39, 13.28, some
aromatic signals were not detected. m/z (MALDI TOF) 1286.39
[M]+, 1309.38 [M + Na]+, 1325.35 [M + K]+.
[M + Na]+, 1831.70 [M + K]+.
Compound 6H. Starting amount: 6Mg (42 mg, 0.033 mmol),
eluent: chloroform–acetone–methanol (20 : 1 : 1), yield: 40 mg
(97%). λmax (THF, 1 μM)/nm 715 (ε/dm3 mol−1 cm−1 143 800),
684 (130 500), 655 (46 000), 624 (33 900), 549 (21 000), 352
(79 700). δH (500 MHz, pyridine-d5) 10.00 (s, 1H, ArH-Pc),
9.98 (s, 1H, ArH-Pc), 9.91 (s, 1H, ArH-Pc), 9.90 (s, 1H,
ArH-Pc), 9.88 (s, 1H, ArH-Pc), 9.81 (s, 1H, ArH-Pc), 8.61 (d, J
= 8.4 Hz, 2H, ArH-phenylamino), 7.49 (d, J = 8.4 Hz, 2H, ArH-
phenylamino), 4.04 (s, 3H, N–CH3), 3.89–3.78 (m, 4H, N–
CH2), 1.76 (s, 9H, CH3), 1.75 (s, 9H, CH3), 1.74 (s, 9H, CH3),
1.72 (s, 9H, CH3), 1.66 (s, 9H, CH3), 1.59 (s, 9H, CH3),
1.21–1.14 (m, 3H, NCH2CH3), −0.65 (s, 2H, NH). δC
(125 MHz, pyridine-d5) 168.90, 153.35, 144.14, 143.82, 143.47,
143.04, 142.12, 131.39, 119.04, 49.13, 49.06, 48.99, 48.90,
48.78, 48.66, 43.84, 39.74, 31.48, 31.47, 31.43, 31.42, 13.13,
some aromatic signals were not detected. m/z (MALDI TOF)
1264.40 [M]+.
Compound 7Mg. Starting amounts: 3 (460 mg, 1.5 mmol), 4
(175 mg, 0.5 mmol), eluent: chloroform–acetone–methanol
(40 : 2 : 1), yield: 96 mg (15%). λmax (THF, 1 μM)/nm 655
(ε/dm3 mol−1 cm−1 189 500), 595 (30 700), 382 (119 900). δH
(300 MHz, pyridine-d5) 8.51 (d, J = 8.2 Hz, 2H, ArH), 7.24 (d,
J = 8.2 Hz, 2H, ArH), 3.99 (s, 3H, N–CH3), 3.85–3.74 (m, 4H,
N–CH2), 2.31–2.16 (m, 45H, CH3), 2.12 (s, 9H, CH3),
1.30–1.20 (m, 6H, NCH2CH3). δC (75 MHz, pyridine-d5)
158.13, 145.47, 131.22, 117.88, 51.31, 51.27, 51.21, 51.17,
44.42, 38.45, 30.76, 13.40, some aromatic signals were not
detected. m/z (MALDI TOF) 1292.40 [M]+, 1315.38 [M + Na]+,
1331.36 [M + K]+.
Compound 7H. Starting amount: 7Mg (60 mg, 0.05 mmol),
eluent: toluene–chloroform–pyridine (8 : 10 : 1), yield: 56 mg
(94%). λmax (THF, 1 μM)/nm 674 (ε/dm3 mol−1 cm−1 106 300),
648 (90 900), 618sh, 593 (31 000), 551 (27 800), 474 (40 800),
366 (101 700). δH (300 MHz, pyridine-d5) 12.60 (s, 2H, NH),
8.62 (d, J = 8.6 Hz, 2H, ArH), 7.54 (d, J = 8.6 Hz, 2H, ArH),
4.27 (s, 3H, N–CH3), 3.99 (q, J = 7.2 Hz, 4H, N–CH2), 2.30 (s,
9H, CH3), 2.26 (s, 18H, CH3), 2.23 (s, 27H, CH3), 1.45–1.36
(m, 6H, NCH2CH3). δC (75 MHz, pyridine-d5) 168.92, 159.64,
159.56, 159.39, 159.14, 158.48, 158.44, 152.75, 147.61, 145.07,
144.83, 131.25, 126.23, 119.24, 51.93, 51.91, 51.43, 51.38,
51.30, 44.69, 39.18, 30.82, 30.72, 13.56, some aromatic signals
were not detected. m/z (MALDI TOF) 1270.42 [M]+, 1293.41
[M + Na]+, 1309.38 [M + K]+.
General procedure for synthesis of 5H–7H
The magnesium complex (5Mg, 6Mg or 7Mg, 1 eq.) was dis-
solved in chloroform and stirred at rt for 1 h with acid (p-tolue-
nesulfonic acid in THF for 5Mg, trifluoroacetic acid for 6Mg
and 7Mg, 15 eq.). Thereafter, the solvents were evaporated
under reduced pressure, the crude product was washed with
water and purified by column chromatography (eluents are men-
tioned below) to obtain a green solid.
General procedure for synthesis of 5Zn–7Zn
Metal-free derivatives 5H–7H (1 eq.) were dissolved in pyridine
and anhydrous zinc acetate (15–20 eq.) was added. The mixture
was put into a preheated oil bath to 130 °C and stirred at this
temperature for 2.5 h. After this time, solvent was removed
under reduced pressure and the dark solid washed thoroughly
with water. Finally, the product was purified by column chrom-
atography on silica (eluents are mentioned below) to obtain a
green solid.
Compound 5H. Starting amount: 5Mg (154 mg,
0.084 mmol), eluent: chloroform–acetone–methanol (80 : 2 : 1),
yield: 103 mg (68%). λmax (THF, 1 μM)/nm 700 (ε/dm3 mol−1
cm−1 59 800), 662 (50 600), 637 (24 600), 606(13 700), 506
(7200), 353 (42 700). δH (300 MHz, pyridine-d5) 9.01 (s, 1H,
ArH-Pc), 8.94 (s, 1H, ArH-Pc), 8.68–8.63 (m, 4H, ArH-Pc),
8.52 (d, J = 8.8 Hz, 2H, ArH-phenylamino), 7.94 (t, J = 7.8 Hz,
4H, ArH-phenoxy), 7.75 (d, J = 7.8 Hz, 8H, ArH-phenoxy),
7.70–7.52 (m, 6H, ArH-phenoxy), 7.21–7.15 (m, 2H, ArH-phe-
nylamino), 3.91–3.67 (m, 10H, CH), 3.66–3.56 (m, 7H, N–CH2,
N–CH3), 3.45–3.30 (m, 2H, CH), 1.58–1.20 (m, 72H, CHCH3),
1.20–1.11 (m, 6H, NCH2CH3), −0.71 (s, 2H, NH). δC (75 MHz,
pyridine-d5) 169.06, 152.53, 152.09, 152.04, 151.92, 151.84,
149.23, 142.17, 142.07, 142.04, 142.00, 141.77, 141.32, 134.80,
132.37, 131.73, 131.23, 127.62, 127.51, 127.34, 125.86, 125.83,
125.73, 125.43, 125.13, 117.72, 108.13, 107.93, 44.26, 38.20,
28.03, 27.82, 27.78, 24.31, 23.04, 13.19, some aromatic signals
Compound 5Zn. Starting amount: 5H (88.2 mg, 0.05 mmol),
eluent: chloroform–acetone–methanol (20 : 1 : 1), yield: 42 mg
(46%). λmax (THF, 1 μM)/nm 678 (ε/dm3 mol−1 cm−1 201 900),
607 (34 200), 359 (96 100). δH (500 MHz, pyridine-d5) 9.04 (s,
1H, ArH-Pc), 8.97 (s, 1H, ArH-Pc), 8.74–8.64 (m, 4H, ArH-Pc),
8.49 (d, J = 8.4 Hz, 2H, ArH-phenylamino), 7.95–7.88 (m, 4H,
ArH-phenoxy), 7.77–7.46 (m, 14H, ArH-phenoxy), 7.10 (d, J =
8.4 Hz, 2H, ArH-phenylamino), 3.85–3.66 (m, 12H, CH), 3.62
(q, J = 7.0 Hz, 4H, N–CH2), 3.55 (s, 3H, N–CH3), 1.57–1.06
(m, 78H, CH3). δC (125 MHz, pyridine-d5) 169.15, 155.15,
155.03, 154.90, 154.58, 153.89, 153.16, 152.07, 151.39, 151.36,
151.33, 151.29, 151.24, 149.35, 148.88, 145.82, 145.63, 142.26,
142.15, 142.12, 142.11, 141.82, 140.53, 135.99, 133.85, 133.77,
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 11651–11656 | 11655

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133.33, 133.29, 133.23, 133.15, 131.22, 127.50, 127.45, 127.34,
127.28, 125.77, 125.74, 125.66, 125.60, 124.38, 117.03, 108.28,
108.05, 108.00, 107.76, 44.31, 37.92, 28.02, 24.62, 22.90,
13.29, some aromatic signals were not detected. m/z (MALDI
TOF) 1854.63 [M]+, 1877.61 [M + Na]+, 1893.59 [M + K]+.
plates were scraped off, the sample was extracted from the silica
with THF, filtered and the solvent was evaporated.
Acknowledgements
The work was supported by Charles University in Prague
(projects GAUK 68110/2010 and SVV 265 001). Authors are
grateful to Jiří Kuneš for NMR measurements and to Vojtěch
Tambor for measurements of MS spectra.
Compound 6Zn. Starting amount: 6H (31.3 mg,
0.025 mmol), eluent: chloroform–acetone–methanol (20 : 1 : 1),
yield: 21 mg (62%). λmax (THF, 1 μM)/nm 689 (ε/dm3 mol−1
cm−1 267 800), 622 (45 300), 365 (97 100). δH (300 MHz, pyri-
dine-d5) 10.21 (s, 1H, ArH-Pc), 10.17 (s, 2H, ArH-Pc), 10.16 (s,
2H, ArH-Pc), 10.14 (s, 1H, ArH-Pc), 8.47 (d, J = 8.7 Hz, 2H,
ArH-phenylamino), 7.22 (d, J = 8.7 Hz, 2H, ArH-phenylamino),
3.94 (s, 3H, N–CH3), 3.81 (q, J = 7.1 Hz, 4H, N–CH2), 1.66 (s,
18H, CH3), 1.64 (s, 9H, CH3), 1.63 (s, 9H, CH3), 1.60 (s, 9H,
CH3), 1.51 (s, 9H, CH3), 1.21–1.14 (m, 6H, NCH2CH3). δC
(75 MHz, pyridine-d5) 168.95, 155.41, 155.31, 155.13, 154.81,
154.59, 153.97, 152.94, 151.26, 146.64, 146.41, 143.13, 142.41,
142.33, 142.31, 141.90, 141.52, 141.35, 138.49, 138.38, 138.33,
138.19, 132.64, 131.90, 131.36, 130.82, 117.40, 48.85, 48.83,
48.78, 48.74, 48.67, 44.06, 39.09, 31.38, 31.35, 13.26, some
aromatic signals were not detected. m/z (MALDI TOF) 1326.28
[M]+, 1349.25 [M + Na]+.
Notes and references
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Compound 7Zn. Starting amount: 7H (40 mg, 0.03 mmol),
eluent: chloroform–acetone–methanol (40 : 2 : 1), yield: 37 mg
(88%). λmax (THF, 1 μM)/nm 654 (ε/dm3 mol−1 cm−1 177 100),
594 (29 500), 377 (108 500). δH (300 MHz, pyridine-d5) 8.53 (d,
J = 8.7 Hz, 2H, ArH), 7.29 (d, J = 8.7 Hz, 2H, ArH), 4.03 (s,
3H, N–CH3), 3.84 (q, J = 7.1 Hz, 4H, N–CH2), 2.29–2.22 (m,
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158.40, 158.16, 158.05, 153.01, 152.41, 152.22, 151.91, 151.35,
151.11, 150.99, 150.72, 150.70, 147.03, 146.25, 145.34, 145.12,
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Quantum yields of singlet oxygen formation (ΦΔ) and fluor-
escence (ΦF) were measured in THF using the comparative
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0.53 in THF,16 ΦF = 0.30 in chloronaphthalene15). Excitation
wavelength for ΦF determination was set to 612 nm. Details on
the methods can be found elsewhere.4 No changes in the shape
or intensity of the absorption bands of tested dyes were observed
within the course of the experiments. All the samples used for
quantum yields determinations were further purified on silica
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11656 | Dalton Trans., 2012, 41, 11651–11656
This journal is © The Royal Society of Chemistry 2012