Study of multiporphyrin compounds as colorimetric sitting-atop metal complexes: Synthesis and photophysical studies

Article abstract of DOI:10.1002/cplu.201500386

Mono-, di-, tri-, and hexaporphyrin derivatives were synthesized and their sensorial ability toward Na⁺, Li⁺, Ca²⁺, Cu²⁺, Ni²⁺, Co²⁺, Fe³⁺, Zn²⁺, Cd²⁺, Hg²⁺, Ag⁺, Cr³⁺, Pb²⁺, and Al³⁺ was explored by absorption and emission spectroscopy and ¹H NMR spectroscopy. For all of the studied porphyrin derivatives the most significant spectral changes were observed upon addition of Zn²⁺, Cd²⁺, Cu²⁺, Co²⁺, Pb²⁺, Hg²⁺, and Fe³⁺, which resulted in a color change from red to green. When the remaining metal ions were tested, no significant changes were observed. The results reveal, as expected, the formation of mononuclear complexes for porphyrin 4, dinuclear complexes for diporphyrin 7, and trinuclear complexes for triporphyrins 9 and 10. In addition, complexes of type M₆L were determined for hexaporphyrin 8. The NMR spectroscopy studies suggest that the interaction with the metals occurs with the formation of sitting-atop complexes. This study also shows that the sensitivity increases with increasing number of coordination sites, with the most pronounced case observed for Hg²⁺. The lowest value of detectable concentration of 0.05 μm for Hg²⁺ was achieved for hexaporphyrin 8. Sensitive subjects: Mono-, di-, tri-, and hexaporphyrin derivatives (see compound 4 in the figure) were synthesized and their sensorial ability towards metal ions was studied. It was found that they showed an increased sensitivity to Hg²⁺ ions. The NMR spectroscopy studies suggest that the interaction with the metal ions occurs with the formation of sitting-atop complexes.

Full text of DOI:10.1002/cplu.201500386

DOI: 10.1002/cplu.201500386
Full Papers
Study of Multiporphyrin Compounds as Colorimetric
Sitting-Atop Metal Complexes: Synthesis and
Photophysical Studies
Joana I. T. Costa,[a] Elisabete Oliveira,*[b, c, d] Hugo M. Santos,[b, c] Augusto C. TomØ,*[a]
Maria G. P. M. S. Neves,[a] and Carlos Lodeiro[b, c]
Mono-, di-, tri-, and hexaporphyrin derivatives were synthe-
sized and their sensorial ability toward Na+, Li+, Ca2+, Cu2+
formation of mononuclear complexes for porphyrin 4, dinu-
clear complexes for diporphyrin 7, and trinuclear complexes
for triporphyrins 9 and 10. In addition, complexes of type M6L
were determined for hexaporphyrin 8. The NMR spectroscopy
studies suggest that the interaction with the metals occurs
with the formation of sitting-atop complexes. This study also
shows that the sensitivity increases with increasing number of
coordination sites, with the most pronounced case observed
for Hg2+. The lowest value of detectable concentration of
0.05 mm for Hg2+ was achieved for hexaporphyrin 8.
,
Ni2+, Co2+, Fe3+, Zn2+, Cd2+, Hg2+, Ag+, Cr3+, Pb2+, and Al3+
was explored by absorption and emission spectroscopy and
1H NMR spectroscopy. For all of the studied porphyrin deriva-
tives the most significant spectral changes were observed
upon addition of Zn2+, Cd2+, Cu2+, Co2+, Pb2+, Hg2+, and
Fe3+, which resulted in a color change from red to green.
When the remaining metal ions were tested, no significant
changes were observed. The results reveal, as expected, the
Introduction
Over the past two decades, various synthetic strategies have
been developed to make multiporphyrin oligomers, including
directly linked multiporphyrin systems, oligoporphyrins with
fused p systems, and arrays bearing rigid and flexible spacers.[1]
In this context, different types of covalently linked porphyrin
arrays with linear, cyclic, and cross-linked geometries have
been synthesized. These multiporphyrin systems are of para-
mount interest because of their potential application in
a range of areas such as electronics, materials, catalysis, and
medicine.[2]
which generates the corresponding metalloporphyrins. In
nature, the most common metalloporphyrin is the heme
group of hemoproteins, which contains an iron ion chelated
by the four nitrogen atoms of the macrocycle. Generally, the
supramolecular coordination chemistry of metalloporphyrins is
dominated by the use of small metal ions, such as Zn2+, Mg2+
,
Al3+, Ru2+, and Rh3+, that are able to coordinate into the N-
core of the free-base macrocycle affording highly stable com-
plexes.[3] Owing to the high stability of porphyrins, their optical
and electrochemical properties, and their ability to coordinate
with different types of metal ions, these macrocycles are often
integrated into functional materials or devices as fluorescent
and colorimetric metal-responsive chemosensors. In fact, por-
phyrins show remarkable photophysical properties to be used
as fluorophores, with strong fluorescence, large Stokes shifts,
and relatively long excitation (>400 nm) and emission
(>600 nm) wavelengths[4,5] that minimize the effects of the
background fluorescence. Other pyrrolic compounds, including
linear oligopyrroles,[6] calixpyrroles,[7] and contracted or ex-
panded porphyrins[8] have also been extensively used for ion
sensing (both for anions and metal ions).
The size of the host cavity of the porphyrin macrocycle, and
the presence of NH groups in free-base porphyrins, allows the
binding of a large variety of analytes, such as metal ions,
[a] J. I. T. Costa, Dr. A. C. TomØ, Dr. M. G. P. M. S. Neves
Department of Chemistry & QOPNA
University of Aveiro, 3810-193 Aveiro (Portugal)
E-mail: actome@ua.pt
[b] Dr. E. Oliveira, Dr. H. M. Santos, Dr. C. Lodeiro
BIOSCOPE group, UCIBIO-REQUIMTE
Chemistry Department, Faculty of Sciences and Technology
University NOVA of Lisbon, 2829-516 Caparica (Portugal)
E-mail: ej.oliveira@fct.unl.pt
Among the various analytical detection techniques, optical
detections using spectrophotometric and spectrofluorimetric
measurements are the most convenient methods for real-time
monitoring of environmental, biological, and industrial samples
owing to the low cost, versatility, and accessibility.[9]
[c] Dr. E. Oliveira, Dr. H. M. Santos, Dr. C. Lodeiro
Proteomass Scientific Society
Madan Parque, Rua dos Inventores
2825-182 Caparica (Portugal)
[d] Dr. E. Oliveira
The detection of heavy-metal ions, such as Hg2+, Cd2+, and
Pb2+ are of interest for environmental and health-related
issues.[10,11] These metals are pollutants and extremely toxic,
thereby altering the biological activity of important constitu-
ents of living cells.[12–15] Other important metals, such as zinc(II),
Veterinary Science Department and CECAV
University of Trµs-os-Montes and Alto Douro
5001-801 Vila Real (Portugal)
Supporting information and ORCID(s) from the author(s) for this article
are available on the WWW under http://dx.doi.org/10.1002/
cplu.201500386.
ChemPlusChem 2016, 81, 143 – 153
143
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
copper(II), and iron(III), are of particular interest owing to their
significant functions in biological and environmental fields.[16,17]
Therefore, the construction of efficient and specific lumines-
cent chemosensors for heavy and transition-metal ions consti-
tute an active area of research.
In recent years, the development of metal-ion probes based
on porphyrins[18] or other ligands[19] has attracted considerable
attention. With regard to the metal complexation of porphyr-
ins, it was reported recently that free-base porphyrin–coumarin
conjugates show a strong colorimetric effect (color change
from purple to yellow) and an unprecedented sensitivity for
Scheme 1. Synthesis of the meso-[4-(pentafluorophenyloxy)phenyl]-
porphyrins 4–6.
Hg2+ [20]
range of monomeric porphyrin derivatives in the presence of
several metal ions, such as Ag+, Cu2+, Zn2+, Cd2+, and Hg2+
.
However, Moura et al. reported the behavior of a wide
.
(pentafluorophenyloxy)phenyl]-15,20-diphenylporphyrin
(5)
Some of those porphyrin derivatives revealed selectivity to
specific metal ions.[21–24]
and 5,15-bis[4-(pentafluorophenyloxy)phenyl]-10,20-diphenyl-
porphyrin (6) were obtained in 53 and 43% yields, respectively,
from the corresponding porphyrins 2 and 3. The structures of
Herein, we present the synthesis of several multiporphyrin
derivatives (covalently linked) and the study of their interaction
with metal ions. The aim of this study was to find how the
number of porphyrin units and the geometry of the multipor-
phyrin systems can affect the coordination of metal ions. In
particular, we were interested in examining whether the pres-
ence of several coordinated metal ions at fixed (or almost
fixed) short distances may induce unusual chemical or photo-
physical properties. The sensing ability of the porphyrin deriva-
1
compounds 5 and 6 were confirmed by their mass, and H, 19F,
1
and 13C NMR spectra. Compared with the H NMR spectra of
1
porphyrins 2 and 3, the H NMR spectra of compounds 5 and
6 show small shifts to higher frequencies of the signals corre-
sponding to the protons of the substituted phenyl groups.
The syntheses of the new multiporphyrin compounds 8–10
are outlined in Schemes 2–4. The reaction of 5-[4-(pentafluoro-
phenyloxy)phenyl]-10,15,20-triphenylporphyrin (4) with 5-(4-
hydroxyphenyl)-10,15,20-triphenylporphyrin (1), in DMF, in the
presence of sodium hydride, for two hours at room tempera-
ture, afforded diporphyrin 7 in 74% yield. When diporphyrin 7
tives towards metal ions (Na+, Li+, Ca2+, Cu2+, Ni2+, Co2+
,
Fe3+, Zn2+, Cd2+, Hg2+, Ag+, Cr3+, Pb2+, Al3+) was analyzed by
absorption and emission spectroscopy and the results show
that increasing the number or porphyrin units results in higher
sensitivity for the metal, mainly for Hg2+. The NMR spectrosco-
py studies confirmed that the interaction with the metals
occurs through the formation of sitting-atop complexes.
Results and Discussion
Synthesis
The new multiporphyrin derivatives were prepared by chemical
modification of the mono- and bis(4-hydroxyphenyl)porphyrins
1, 2, and 3, which were obtained from the reaction of pyrrole
and mixtures of benzaldehyde and 4-hydroxybenzaldehyde, in
appropriate proportions, in acetic acid and nitrobenzene at
reflux.[25]
The isomeric porphyrins 2 and 3, obtained in the same reac-
tion, were separated by column chromatography (silica gel)
using a mixture of chloroform–methanol (98:2) as eluent. The
most abundant isomer (the one with the lower Rf) was identi-
1
fied as porphyrin 2. The H NMR spectra of the two isomers
show distinct signals for the b-pyrrolic protons: a clear AB
system (8H-b) is observed for porphyrin 3 (the isomer with
higher symmetry), whereas two multiplets (4H-b each) are ob-
served for porphyrin 2.
The reaction of porphyrin 1 with hexafluorobenzene was
carried out in N,N-dimethylformamide (DMF), in the presence
of sodium hydride, and afforded 5-[4-(pentafluorophenyl-
oxy)phenyl]-10,15,20-triphenylporphyrin (4) in 85% yield
(Scheme 1).[25] By using
a
similar approach, 5,10-bis[4-
Scheme 2. Synthesis of diporphyrin 7 and hexaporphyrin 8.
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
144
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
was treated with five equivalents of mono(4-hydroxy-
phenyl)porphyrin 1, in the presence of sodium hydride, for five
days at 808C, hexaporphyrin 8 was obtained in 30% yield as
the main product.
try of these molecules. In the case of hexaporphyrin 8, no sig-
nals were observed in the 19F NMR spectrum. The mass spec-
trum of diporphyrin 7 shows the expected [M+H]+ ion at m/z
1407.5 but the mass spectrum of hexaporphyrin 8 shows only
peaks corresponding to fragments of the molecule. Both mass
spectra of triporphyrins 9 and 10 show the [M+H]+ ion at m/z
2199.6.
The angular and linear triporphyrin derivatives 9 and 10
were obtained from the reaction between the corresponding
bis(pentafluorophenyloxyphenyl)porphyrins
5
and
6
and
mono(4-hydroxyphenyl)porphyrin 1 (Schemes 3 and 4). Both
Photophysical properties
The absorption, emission, and excitation spectra of porphyrin
4 and multiporphyrin derivatives 7–10 were measured in solu-
tions in chloroform (ca. 10À5–10À6 m) at 295 K and the main
photophysical data are summarized in Table S1 in the Support-
ing Information. Figure 1 shows the photophysical characteri-
zation of compounds 4 and 8, as representative examples.
Scheme 3. Synthesis of the angular triporphyrin 9.
reactions were carried out in DMF in the presence of potassi-
um carbonate for 48 hours at 508C. The new compounds were
obtained, respectively, in 62 and 53% yield. The use of sodium
hydride in these reactions led to lower yields.
The structures of the new multiporphyrin compounds 7, 8,
9, and 10 were unambiguously established from their mass
and UV/Vis and NMR (1H, 13C, and 19F) spectra. The 19F NMR
spectra of diporphyrin 7 and triporphyrins 9 and 10 show only
one signal at about d=À177 ppm, which confirms the symme-
Figure 1. Absorption, normalized emission, and excitation spectra of com-
pounds 4 (A) and 8 (B) in chloroform. ([4]=2.0”10À6 m, [8]=7.0”10À7 m;
lexc(4)=lexc(8)=515 nm, lemiss(4)=648 nm, lemiss(8)=650 nm, T=295 K, rela-
tive standard deviation (RSD) of the values measured was below 10%,
n=3).
Scheme 4. Synthesis of the linear triporphyrin 10.
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
145
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
The multiporphyrin compounds exhibit the typical features
of p–p* transitions of monomeric free-base porphyrins, which
show an intense Soret band at 415–420 nm and four Q bands
between 514 and 642 nm. The emission spectra were recorded
upon excitation at the Q band to avoid re-absorption phenom-
ena, and, as a result, all compounds show two bands centered
at about 650 and 714–716 nm. The overlap between the ab-
sorption and excitation spectra indicates the absence of emis-
sive impurities. The multiporphyrin compounds showed Stokes
shifts between 7 and 9 nm.
The relative fluorescence quantum yields (f) were deter-
mined by using an internal reference method with respect to
cresyl violet and the values of f vary between 1 and 2.1%
(Table S1 in the Supporting Information). The low fluorescence
efficiency of these porphyrin derivatives may be related to
a modification of the planarity of the macrocycles leading to
a reduction of the mobility of the p electrons.[26] The results
show that increasing the number of porphyrin units does not
produce significant changes in the photophysical properties of
the compounds.
Metal binding studies
The sensorial ability of porphyrin 4 and multiporphyrin deriva-
tives 7–10 towards alkaline, alkaline-earth, transition, and post-
transition metal ions such as Na+, Li+, Ca2+, Cu2+, Ni2+, Co2+
,
Fe3+, Zn2+, Cd2+, Hg2+, Ag+, Cr3+, Pb2+, and Al3+ was evaluat-
ed by the titration of the ligands (in chloroform) with small
amounts of the metal ions. These experiments were monitored
by absorption and emission spectroscopy at 295 K. For all of
the studied porphyrin derivatives the most significant changes
were obtained for Zn2+, Cd2+, Cu2+, Co2+, Pb2+, Hg2+, and
Fe3+ ions. No significant changes were observed for the other
metal ions tested.
Figure 2. Spectrophotometric (A, C, E) and spectrofluorimetric (B, D, F) titra-
tions of porphyrin 4 (CHCl3) with Zn2+, Cd2+, and Cu2+ ions (CH3CN). The
insets represent the absorption at 415 and 440 nm (A, C, E) and the normal-
ized fluorescence intensity at 600 and 648 nm (B) and at 648 nm (D, F)
([4]=2.0”10À6 m, lexc =515 nm, T=295 K, relative standard deviation (RSD)
of the values measured was below 10%, n=3).
Titration with Zn2+, Cd2+, Cu2+, and Co2+
The addition of Zn2+, Cd2+, Cu2+, and Co2+ to porphyrin 4 re-
sulted in similar spectral changes. As representative examples,
Figure 2 shows the spectral behavior of compound 4 upon ad-
dition of Zn2+ (A, B), Cd2+ (C, D), and Cu2+ (E, F). The spectra
of this porphyrin with Co2+ are gathered in Figure S23 in the
Supporting Information.
The addition of Zn2+ induces a decrease in the absorbance
at 415 nm and an increase at 440 nm. These changes of the
Soret band are accompanied by a decrease of the Q band at
515 nm and a small increase at about 550 nm; a new band is
formed at about 660 nm. The observed bathochromic shift
[Dl=25 nm (Soret) and Dl=35 nm (Q band)] and the forma-
tion of the new absorption band at longer wavelength can be
attributed to the coordination of the metal ion to the nitrogen
atoms of the porphyrin macrocycle without deprotonation (as
confirmed by the NMR spectroscopic titration studies dis-
cussed below).
0)(0–1)[27] is accompanied by an increase of a new band at
600 nm. This band can be attributed to a metal-to-ligand
charge transfer[24] and reveals the formation of a new fluoro-
phore from the metal–porphyrin association.
In the titration of porphyrin 4 with Cd2+ ions, the redshifts
of the Soret band (from 415 to 440 nm) and of the Q band
(from 515 to 552 nm), and the formation of two well-defined
isosbestic points at 426 and 536 nm, indicate the presence of
new species in solution. Relative to the emission spectra, only
a decrease in the emission intensity at 648 (60%) and 714 nm
(30%) was detected. The titrations with Cu2+ and Co2+ ions
induce spectral changes similar to those observed for Cd2+
,
but in both cases total quenching was observed in the emis-
sion spectra. These results reveal that there are probably differ-
ent interactions between the metal ions and the free electrons
of the porphyrin nitrogen atoms.
For porphyrin derivatives 7–10, their interactions with the
metal ions under discussion are dependent of the number of
porphyrin units (see Figures S24 and S26 in the Supporting In-
formation). Diporphyrin 7 and triporphyrins 9 and 10 are more
In relation to the changes in the excited state, a quenching
of the emission intensity in the two bands centered at 648 and
714 nm due to free-base porphyrin emission Q(0–0) and Q(0–
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
146
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
reactive to Zn2+ and Cu2+. However, hexaporphyrin 8 is less re-
Titrations with Hg2+
active to these metal ions (see Figure 6 below).
The Hg2+ ion is considered to be one of the most toxic metal
ions. This is due to the fact that its inorganic form can be con-
verted by bacteria into the highly toxic methylmercury. Howev-
er, due to its catalytic effect on the complexation to other
metal ions, such as Cu2+ and Zn2+, the first studies reported
involved metalloporphyrins containing Hg2+ ions.[28,29] Being
a heavy-metal ion, Hg2+ acts as a fluorescence quencher by
means of a spin–orbit coupling effect, producing “turn off” sys-
tems.[30,31] The addition of Hg2+ induces, for all the studied por-
phyrin derivatives, a redshift of the Soret band from 415–420
to 440 nm, as well as the appearance of a new band at
660 nm; these alterations are indicative of metal complexation.
The absorption titrations of porphyrin 4, diporphyrin 7, and
hexaporphyrin 8 with Hg2+ are shown in Figure 4A, C, E, re-
spectively. The spectra of the other porphyrin systems can be
found in the Supporting Information (Figures S27 and S28).
As expected, in the emission spectra, a quenching of the
emission intensity at 648–650 nm is visualized for all com-
Titrations with Pb2+ and Fe3+
The addition of Pb2+ to the studied porphyrin derivatives
leads to a decrease of the absorptions at 415–420 nm and at
515 nm and an increase of the ones at 440 and 552 nm. These
changes are accompanied by the formation of isosbestic
points at about 426 and 536 nm, as shown in Figure 3A for
Figure 3. Spectrophotometric (A, C) and spectrofluorimetric (B, D) titrations
of compounds 4 and 7 (CHCl3) with Pb2+ and Fe3+ (CH3CN), respectively.
The insets represent the absorption at 415 and 440 nm (A, C) and the nor-
malized fluorescence intensity at 648 nm (B) and at 650 and 685 (D)
([4]=2.0”10À6 m, [7]=1.0”10À6 m, lexc =515 nm, T=295 K, relative standard
deviation (RSD) of the values measured was below 10%, n=3).
compound 4. In relation to the emission spectra, a quenching
in the emission intensity at 648–650 nm is detected for por-
phyrin 4 (Figure 3B), diporphyrin 7, and hexaporphyrin 8 (see
Figures S24 and S25 in the Supporting Information). However,
in triporphyrins 9 and 10 a new small emissive band at
690 nm develops (see Figures S26 and S28 in the Supporting
Information). For the interaction of Fe3+ with the porphyrin de-
rivatives, a decrease of the bands at 415–420 and 515 nm and
an increase at 440 and 552 nm are observed in all the absorp-
tion spectra, as exemplified in Figure 3C for compound 7. For
diporphyrin 7 and triporphyrin 9, upon addition of Fe3+
,
quenching of the emission intensity at 650 nm is observed,
but a new emissive band appears at 685 nm. The photophysi-
cal spectra resulting from the titration of the other porphyrins
with Pb2+ and Fe3+ are compiled in the Supporting Informa-
tion (Figures S24–S28).
Figure 4. Spectrophotometric (A, C, E) and spectrofluorimetric (B, D, F) titra-
tions of compounds 4, 7, and 8 (CHCl3) with Hg2+ (CH3CN). The insets repre-
sent the absorption at 415 and 440 nm (A, C) and at 420 and 440 nm (E) and
the normalized fluorescence intensity at 648 nm (B) and at 650 nm (D, F).
([4]=2.0”10À6 m, [7]=1.0”10À6 m, [8]=7.0”10À7 m, lexc =515 nm, T=295 K,
relative standard deviation (RSD) of the values measured was below 10%,
n=3).
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
147
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
pounds (Figure 4B,F) except diporphyrin 7, for which a new
band at 690 nm is observed.
Table 1. Stability constants and stoichiometries for the complexes
formed with porphyrin derivatives 4 and 7–10 (in CHCl3) and Zn2+, Cd2+
,
Cu2+, Co2+, Pb2+, Hg2+, and Fe3+ ions (CH3CN); s is an estimate of the
average experimental error and is presented in the Supporting Informa-
tion.
Overall, the absorption spectra show that the addition of
Hg2+ or the other above-mentioned metals to the studied por-
phyrin derivatives leads to the appearance of a new band at
approximately 660 nm, which results in a color change from
red to green. This color change and the disappearance of the
emission signal (Figure 5) is a clear indication of the formation
of metal complexes.
Compd.
Interaction (M/L)
Ælogb (abs)
Ælogb (emis)
s
s
Zn2+ (1:1)
Cd2+ (1:1)
Cu2+ (1:1)
Co2+ (1:1)
Pb2+ (1:1)
Hg2+ (1:1)
Fe3+ (1:1)
5.0Æ0.1
8.2Æ0.1
5.2Æ0.1
8.5Æ0.1
5.4Æ0.1
6.7Æ0.1
4.9Æ0.1
5.2Æ0.1
7.9Æ0.1
5.7Æ0.1
8.3Æ0.1
4.8Æ0.1
6.5Æ0.1
5.6Æ0.1
4
Zn2+ (2:1)
Cu2+ (2:1)
Pb2+ (2:1)
Hg2+ (2:1)
Fe3+ (2:1)
10.1Æ0.1
11.5Æ0.1
10.7Æ0.1
12.2Æ0.1
11.1Æ0.1
10.5Æ0.1
12.0Æ0.2
11.3Æ0.1
13.6Æ0.1
10.8Æ0.1
7
8
Figure 5. Images of chloroform solutions of porphyrin 4 and porphyrin 4
with Hg2+ as viewed (A) by the naked eye and (B) under a UV lamp
(lexc =365 nm).
Pb2+ (6:1)
Hg2+ (6:1)
Fe3+ (6:1)
36.2Æ0.1
38.1Æ0.1
32.9Æ0.1
39.1Æ0.1
40.2Æ0.1
32.8Æ0.1
Zn2+ (3:1)
Cu2+ (3:1)
Pb2+ (3:1)
Hg2+ (3:1)
Fe3+ (3:1)
18.7Æ0.1
17.2Æ0.1
17.6Æ0.1
17.4Æ0.1
16.4Æ0.1
19.5Æ0.1
17.8Æ0.1
18.9Æ0.1
19.8Æ0.1
16.2Æ0.1
Stability constants and stoichiometry
9
The stoichiometry of the metal complexes formed in solution
and the corresponding stability constants were determined by
using the HypSpec program.[32] The main data are gathered in
Table 1 and the results show the formation of mononuclear
complexes for porphyrin 4, dinuclear complexes for diporphyr-
in 7, and trinuclear complexes for triporphyrins 9 and 10. In ac-
cordance with this trend, complexes of the type M6L were de-
termined for hexaporphyrin 8.
Pb2+ (3:1)
Hg2+ (3:1)
17.9Æ0.1
26.4Æ0.1
19.3Æ0.1
28.8Æ0.1
10[a]
[a] The behavior of porphyrins 9 and 10 with Zn2+, Cu2+, and Fe3+ is sim-
ilar.
An increasing of the stability constants with an increasing
number of the coordination sites was observed, with the high-
est constant being obtained for hexaporphyrin 8 with logb
ꢀ32–40. The results show that each porphyrin unit in the mul-
tiporphyrin derivatives acts as an independent coordination
site. Because of this, the logarithm of the overall stability con-
stants corresponds to “n times log(b)”, in which n is the
number of porphyrin units and b the stability constant of mon-
omeric porphyrin 4. For example, the stability constants for
the Pb2+ ion with dinuclear (7), trinuclear (9 and 10), and hexa-
nuclear (8) porphyrins are about twice, thrice, and six times as
much as the constants for monomer 4.
In Table 1 only the final association constants are presented.
However, since intermediate complexes may be formed during
the titrations, these intermediate complexes and constants are
indicated in the Supporting Information. The final stoichiome-
try was confirmed by the Job’s plot method and the main re-
sults are also presented in the Supporting Information (Fig-
ure S29).
Comparative fluorescence response of chemosensors
In addition to the type of donor atoms present within the mac-
rocycle in which metal complexation occurs, parameters such
as the cavity size, shape, conformation, topology, and rigidity
of the macrocycle are very important because they influence
the kinetics and the thermodynamic properties of the corre-
sponding metal complexes. Moreover, the chelate and macro-
cyclic effects must be taken into account.[33,34] Figure 6 shows
the normalized fluorescence intensity of porphyrin 4, dipor-
phyrin 7, angular triporphyrin 9, and hexaporphyrin 8 upon ad-
dition of one, two, three, and six equivalents, respectively, of
Na+, Li+, Ca2+, Cu2+, Ni2+, Co2+, Fe3+, Zn2+, Cd2+, Hg2+, Ag+,
Cr3+, Pb2+, Al3+ ions.
For monomer 4, the highest stability constants were ob-
tained with Cd2+ and Co2+. However, with the increase of por-
phyrin units this behavior changes and the highest stability
values were obtained for the heavy-metal ions Pb2+ and Hg2+
.
On comparing triporphyrins 9 and 10, the highest association
constant for the Hg2+ ion was obtained for the linear form 10
(logb(emis) 28.8 versus 19.8). These values indicate that the
angular triporphyrin forms complexes with Hg2+ ions that are
less stable than those formed with the linear isomer. This is
probably due to repulsion between the metal ions coordinated
to the neighboring terminal porphyrin units. In contrast, in the
linear triporphyrin all porphyrin units are well separated, which
produces more stable complexes.
Careful inspection of Figure 6 reveals that the porphyrin de-
rivatives have high quenching properties with transition and
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
148
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
post-transition metal ions, and are practically unaffected by
alkali and alkaline-earth metal ions. With an increasing number
of coordination sites, the quenching is most pronounced in
the case of Hg2+, as well as Al3+. Monomer 4, upon addition
of one equivalent of metal ion, shows pronounced changes
with Pb2+, Cu2+, Zn2+, Cd2+, Hg2+, Co2+, and Fe3+. The coordi-
nation sphere has a tendency to be octahedral owing to the
presence of acetonitrile or nitrate anions. However, in the ab-
sence of a crystalline structure to verify it, this fact cannot be
confirmed.
NMR spectroscopic titrations
To shed light on the system, and to better understand the
metal complexation in the porphyrin core, several 1H NMR
spectroscopic titrations were performed. The experiment in-
volved the successive addition of small volumes of a solution
of Hg(OTf)2 in CD3CN to solutions of the porphyrin derivatives
in CDCl3. After each addition of Hg2+ a H NMR spectrum was
1
acquired. Since all porphyrin derivatives revealed a similar be-
1
havior, only the H NMR spectroscopic titration of porphyrin 4
Consequently, we might expect that hexaporphyrin 8, with
six coordination sites, should be able to detect lower amounts
of the toxic heavy-metal ion Hg2+. To confirm this fact, the
minimal detectable concentration of this metal ion by porphy-
rin 4 and hexaporphyrin 8 was determined. The limit of detec-
tion (LOD) by absorption at 440 nm was 0.022Æ0.006 and by
emission at 650 nm was 1.143Æ0.146 (normalized). Through
these values, the minimal detectable concentrations of 0.26
and 0.09 mm by absorption at 440 nm, and of 0.20 and 0.05 mm
by emission at 650 nm were obtained for compounds 4 and 8,
respectively.
The interaction of compounds 4, 7, 9, and 10 with Hg2+ in
the gas phase was studied by MALDI-TOF-MS (see the Experi-
mental Section). Peaks corresponding to the following species
were identified in the mass spectra at m/z (found):
797.2 [4+H]+, 991.2 [(4À2H)Hg+H]+, 1407.5 [7+H]+,
2199.7 [9+H]+, 2199.7 [10+H]+.
is shown in Figure 7 as a representative example (the remain-
1
ing H NMR spectroscopic titrations are shown in the Support-
1
ing Information). It is evident from the H NMR spectra that, as
soon Hg2+ is added to the solution, the initial signal corre-
sponding to the resonance of the NH protons of the free-base
porphyrin (a sharp singlet at dꢀÀ2.8 ppm) becomes broader
and two new signals start to appear at dꢀÀ1.8 ppm. With the
increasing amount of Hg2+ (more than 1 equiv) the signal at
dꢀÀ2.8 ppm disappears completely. The resonances of the b-
pyrrolic and phenyl protons are also shifted due to the pres-
ence of Hg2+: whereas the signal of the b-pyrrolic protons (at
dꢀ8.85 ppm) is shifted upfield, the signals corresponding to
the phenyl protons are shifted downfield. These results show
unequivocally that the interaction of the metal ion with the
free-base porphyrin does not lead to the deprotonation of the
inner NH groups and induces a distortion of the macrocycle
(as a consequence, the planarity and the ring current are re-
1
duced). A similar effect was observed in the H NMR spectra of
Figure 6. Normalized fluorescence emission of compounds 4 (A), 7 (B), 8 (C), and 9 (D) in CHCl3 upon addition of 1, 2, 3, and 6 equivalents, respectively, of
Na+, Li+, Ca2+, Cu2+, Ni2+, Co2+, Fe3+, Zn2+, Cd2+, Hg2+, Ag+, Cr3+, Pb2+, Al3+ ions (CH3CN) ([4]=2.0”10À6 m, [7]=[9]=1.0”10À6 m, [8]=5.0”10À7 m,
lexc =515 nm, T=295 K, RSD of the values measured was below 10%, n=3).
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
149
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
Experimental Section
Materials and methods
General: 1H, 13C, and 19F NMR spectra were recorded on Bruker
Avance 300 (300.13, 75.47, and 282.38 MHz, respectively) and 500
spectrometers (500.13 MHz for 1H and 125.76 MHz for 13C). CDCl3
was use as solvent and tetramethylsilane (TMS) as internal refer-
ence. The chemical shifts are expressed in d (ppm) and the cou-
pling constants (J) in Hertz (Hz). Mass spectra were recorded using
a MALDI TOF/TOF 4800 Analyzer (Applied Biosystems MDS Sciex),
with CHCl3 as solvent and 3-nitrobenzyl alcohol (NBA) as matrix.
High-resolution mass spectra (HRMS) were recorded on an APEXQe
FT-ICR (Bruker Daltonics, Billerica, MA) mass spectrometer using
CHCl3 as solvent. The UV/Vis spectra were recorded on a JASCO V-
650 spectrophotometer using CHCl3 as solvent. Preparative thin-
layer chromatography (TLC) was carried out on 20”20 cm glass
plates coated with silica gel (0.5 mm thick). Column chromatogra-
phy was carried out using silica gel (Merck, 35–70 mesh). Analytical
TLC was carried out on precoated sheets with silica gel (Merck 60,
0.2 mm thick). Solvents were purified or dried according to the lit-
erature procedures.[37]
Figure 7. 1H NMR spectra of porphyrin 4 (7.5”10À3 m) in CDCl3 with the ad-
dition of 0 to 3 equiv of Hg2+ in CD3CN.
Materials: NaBF4, Li(OTf)2, Ca(OTf)2, Cu(OTf)2, Ni(OTf)2, Co(OTf)2,
Zn(OTf)2, Cd(OTf)2, Hg(OTf)2, Pb(OTf)2, Ag(OTf)2, Fe(NO3)3·9H2O,
Al(NO3)3·9H2O, and Cr(NO3)3·9H2O were purchased from Strem
Chemicals, Sigma–Aldrich, or Solchemar. All these chemicals were
used as supplied. The solvents were obtained from Panreac and
Riedel-de-Häen and were used as received or distilled and dried by
using standard procedures. The solutions of the salts were pre-
pared in acetonitrile, except for Al(NO3)3·9H2O and Cr(NO3)3·9H2O
for which DMSO was used as solvent.
Figure 8. 1H NMR spectra of porphyrin 4 (7.5”10À3 m) in CDCl3 with the ad-
dition of 0 to 4 equiv of Zn2+ in CD3CN.
porphyrin 4 upon addition of Zn2+ (Figure 8). From Figures 7
and 8 it is also clear that Zn2+ has a lower interaction than
Hg2+ since upon addition of one equivalent of metal ion in
the case of Zn2+ about 50% of the porphyrin remains as the
free base (signal at dꢀÀ2.8 ppm). These two experiments are
new examples of the formation of sitting-atop complexes in
meso-tetraarylporphyrins.[35,36]
Spectrophotometric and spectrofluorimetric measurements: UV/
Vis absorption spectra were recorded with a JASCO V-650 spectro-
photometer and the fluorescence emission with a HORIBA Scientif-
ic FLUOROMAX-4 spectrofluorimeter. Chloroform was used as sol-
vent. The linearity of the fluorescence emission versus the concen-
tration was checked for the concentration used. A correction for
the absorbed light was performed in the case of absorbance (A)
values higher than 0.2 at the excitation wavelength. For the photo-
physical characterization of compounds 4 and 7–10 stock solutions
(ca. 10À3 m) were prepared in chloroform. The stock solutions were
then diluted to 10À5–10À6 m.
Conclusion
The interaction of five porphyrin derivatives, containing one to
six coordination sites, with Na+, Li+, Ca2+, Cu2+, Ni2+, Co2+
,
Fe3+, Zn2+, Cd2+, Hg2+, Ag+, Cr3+, Pb2+, and Al3+ was evaluat-
ed by the titration of the ligands (in chloroform) with solutions
of the metal salts in acetonitrile. In all porphyrin derivatives
Titrations of compounds 4 and 7–10 were carried out by adding
microliter amounts of standard solutions of the metal ions (in ace-
tonitrile) to the ligand (in chloroform). All measurements were per-
formed at 295 K. Luminescence quantum yields were measured
using a solution of cresyl violet in ethanol (fF =0.54).[38,39]
the most significant changes were observed for Zn2+, Cd2+
,
Cu2+, Co2+, Pb2+, Hg2+, and Fe3+. No significant changes were
observed for the other metal ions. In the presence of the
above metals, the porphyrin derivatives show a colorimetric
behavior, with a color change from red to green. The results
show that each porphyrin unit in the multiporphyrin deriva-
tives acts as an independent coordination site, whereas the
logarithm of the overall stability constants corresponds to “n
times log(b)”, in which n is the number of porphyrin units and
b the stability constant of the monomeric porphyrin 4.
For the Job plot experiments, stock solutions of the com-
pounds (A) (CHCl3) and the metal ions (B) (CH3CN) were prepared.
For a fixed volume of 3 mL, a series of solutions containing a fixed
total number of moles, but varying the concentration of each com-
ponent A and B was prepared.[40]
Determination of the limit of detection (LOD): The LOD, or detec-
tion limit, is the lowest concentration level that can be determined
to be statistically different from a blank. For the determination of
the LOD, ten different measurements of a solution containing the
selected probe were collected without addition of any metal ion
(yblank). The LOD was determined by the formula [Eq. (1)]:
Increasing the number of porphyrin units led to higher sta-
bility values for the heavy-metal ions Pb2+ and Hg2+, and the
triporphyrin derivative with linear geometry (10) produced
more-stable complexes with Hg2+ than the angular one (9).
The lowest detectable concentration of 0.05 mm (Hg2+) was ob-
tained with hexaporphyrin 8.
LOD ¼ ydl ¼ yblank þ 3 std
ð1Þ
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
150
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
J=4.8 Hz, 8H; H-b); UV/Vis (CHCl3): lmax (%): 419 (100), 515 (7), 551
(5), 591 (4), 648 nm (4); MS (MALDI): m/z: 647.2 [M+H]+.
in which ydl =signal detection limit and std=standard devia-
tion. Additionally, small amounts of Hg2+ were added to a solu-
tion of porphyrin 4 (or hexaporphyrin 8) to determine the min-
imal detectable concentration out of the LOD value.
5-[4-(Pentafluorophenyloxy)phenyl]-10,15,20-triphenylporphyr-
in (4): This compound was prepared by treating porphyrin 1 with
hexafluorobenzene as previously described.[25]
MALDI-TOF-MS studies: The MALDI-MS analyses were performed
with a MALDI-TOF-TOF-MS model Ultraflex II Bruker, Germany,
equipped with a nitrogen laser. Each spectrum represents the ac-
cumulation of 5”50 laser shots. The reflection mode was used.
The ion source and flight tube pressure were less than 1.80”10À7
and 5.60”10À8 torr, respectively. The MALDI mass spectra were re-
corded by using the conventional sample preparation method for
MALDI-MS. The metal ion solution (1 mL) was put on the sample
holder on which the porphyrinic compounds had been previously
spotted. The sample holder was inserted in the ion source. The
chemical reaction between the compounds and the metal ions oc-
curred in the holder and complexed species were produced. The
porphyrin derivatives were dissolved in chloroform and the metal
salts in acetonitrile. a-Cyano-4-hydroxycinnamic acid (CHCA) was
used as the matrix.
5,10-Bis[4-(pentafluorophenyloxy)phenyl]-15,20-diphenylpor-
phyrin (5): An excess amount of sodium hydride (ꢀ50 mg) was
added to a solution of porphyrin 2 (50.0 mg, 77 mmol) in dry DMF
(2 mL) and the mixture was heated at 708C for ten minutes under
a nitrogen atmosphere. Hexafluorobenzene (1 mL, 8.7 mmol) was
then added and the mixture was maintained at that temperature
for four hours. After cooling to room temperature, the reaction
mixture was neutralized with a saturated aqueous citric acid solu-
tion and the resulting porphyrin was extracted with dichlorome-
thane. The organic layer was washed with water, dried with
Na2SO4, and the solvent was evaporated under reduced pressure.
The residue was purified by column chromatography on silica gel
using dichloromethane/petroleum ether (2:1) as the eluent. The
major fraction afforded porphyrin 5 (40 mg, 53% yield) after recrys-
tallization from chloroform/methanol. M.p. >3008C; 1H NMR
(300 MHz, CDCl3): d=À2.82 (s, 2H), 7.34 (d, 4H; J=8.6 Hz), 7.71–
7.79 (m, 6H), 8.14–8.22 (m, 8H), 8.81–8.86 ppm (m, 8H); 19F NMR
(282 MHz, CDCl3): d=À185.15 (dt, J=22.0 and 4.8 Hz, 4F), À182.93
(t, J=22.0 Hz, 2F), À176.97 ppm (dd, J=22.0 and 4.8 Hz, 4F);
13C NMR (75 MHz, CDCl3): d=113.76, 118.71, 120.43, 126.71, 127.78,
130.39–131.84, 134.55, 135.68, 137.91, 142.02, 157.02 ppm; MS
(MALDI): m/z: 979.2 [M+H]+; HRMS-ESI(+): m/z calcd for
C56H29F10N4O2 [M+H]+: 979.2125; found: 979.2101; calcd for
Synthetic procedures
5-(4-Hydroxyphenyl)-10,15,20-triphenylporphyrin (1): Porphyrin
1 was obtained from the reaction of pyrrole (4 equiv) and a mixture
of benzaldehyde (3 equiv) and 4-hydroxybenzaldehyde (1.2 equiv)
in acetic acid and nitrobenzene at reflux, as previously described.[25]
Compounds 1–3 were recently prepared by deacetylation of the
corresponding (4-acetyloxyphenyl)porphyrins.[41]
C56H28F10N4O2 [M]+ : 978.2047; found: 978.2041; UV/Vis (CHCl3): lmax
C
(loge)=418 (5.3), 515 (3.8), 550 (3.6), 590 (3.5), 641 nm (3.4).
5,10-Bis(4-hydroxyphenyl)-15,20-diphenylporphyrin (2)
5,15-Bis(4-hydroxyphenyl)-10,20-diphenylporphyrin (3):
and
4-Hy-
5,15-Bis[4-(pentafluorophenyloxy)phenyl]-10,20-diphenylpor-
phyrin (6): An excess amount of sodium hydride (ꢀ50 mg) was
added to a solution of 3 (50.0 mg, 77 mmol) in dry DMF (2 mL) and
the mixture was heated at 708C for ten minutes under a nitrogen
atmosphere. Hexafluorobenzene (1 mL, 8.7 mmol) was then added
and the mixture was maintained at that temperature for four
hours. Workup was performed as described above. The residue
was purified by column chromatography on silica gel using di-
chloromethane/petroleum ether (2:1) as the eluent. The major frac-
tion afforded porphyrin 6 (32 mg, 43% yield) after recrystallization
from chloroform/methanol. M.p. >3008C; 1H NMR (300 MHz,
CDCl3): d=À2.82 (s, 2H), 7.34 (d, 4H; J=8.6 Hz), 7.72–7.81 (m, 6H),
8.14–8.22 (m, 8H), 8.83 and 8.86 ppm (AB, 8H; J=4.9 Hz); 19F NMR
(282 MHz, CDCl3): d=À185.16 (dt, J=21.8, 4.5 Hz, 4F), À182.94 (t,
J=21.8 Hz, 2F), À176.97 ppm (dd, J=21.8, 4.5 Hz, 4F); 13C NMR
(75 MHz, CDCl3): d=113.75, 118.78, 120.36, 126.72, 127.80, 130.41–
131.97, 134.56, 135.68, 137.90, 141.99, 157.01 ppm; MS (MALDI):
m/z: 979.2 [M+H]+; HRMS-ESI(+): m/z calcd for C56H29F10N4O2
[M+H]+: 979.2125; found: 979.2109; UV/Vis (CHCl3): lmax (loge)=
418 (5.3), 513 (3.9), 550 (3.6), 589 (3.5), 642 nm (3.5).
droxybenzaldehyde (2.90 g, 23.8 mmol) and benzaldehyde
(1.98 mL, 19.5 mmol) were added to a mixture of glacial acetic acid
(200 mL) and nitrobenzene (150 mL) at reflux. Pyrrole (3.00 mL,
43.2 mmol) was then added dropwise over 20 min and the mixture
was heated at reflux for a further 1.5 hours. After cooling to room
temperature, the acetic acid and the nitrobenzene were distilled
under reduced pressure. The crude material was taken into chloro-
form and submitted to column chromatography (silica gel) using
a mixture of chloroform–petroleum ether (1:1) as eluent. The first
fraction was identified by TLC as 5,10,15,20-tetraphenylporphyrin
(TPP). A second fraction, identified as the mono(4-hydroxyphenyl)-
porphyrin 1, was then eluted with chloroform. A third fraction con-
taining the two isomeric porphyrins 2 and 3 was eluted using
a mixture of chloroform–methanol (98:2). This fraction was submit-
ted to a new column chromatography (silica gel) using a mixture
of chloroform–methanol (98:2) as eluent, which allowed the sepa-
ration of the two isomeric porphyrins (the one with higher Rf was
identified as porphyrin 3). Evaporation of the solvent and recrystal-
lization of both porphyrins from chloroform/petroleum ether gave
2 (600 mg, 9%) and 3 (320 mg, 5% yield).
Diporphyrin 7: An excess amount of sodium hydride (12 mg) was
added to a solution of 1 (23.7 mg, 38 mmol) in dry DMF (2 mL) and
the mixture was stirred under a nitrogen atmosphere for ten mi-
nutes at room temperature. Porphyrin 4 (20.0 mg, 25 mmol) was
then added and the mixture was stirred for two hours. The workup
was identical to that described above. The residue was purified by
column chromatography on silica gel using dichloromethane/pe-
troleum ether (1:1) as the eluent. The major fraction afforded com-
pound 7 (26 mg, 74% yield). M.p. >3008C; 1H NMR (300 MHz,
CDCl3): d=À2.80 (s, 4H), 7.45 (d, 4H; J=8.6 Hz), 7.70–7.77 (m,
18H), 8.17–8.23 (m, 16H), 8.83 (s, 8H) 8.86 ppm (s, 8H); 19F NMR
1
Porphyrin 2: H NMR (300 MHz, CDCl3) d=À2.81 (s, 2H; NH), 5.23
(brs, 2H; OH), 7.19 (d, J=8.5 Hz, 4H; 5,10-C6H4-m-H), 7.70–7.79 (m,
6H; 15,20-Ph-m,p-H), 8.05 (d, J=8.5 Hz, 4H; 5,10-C6H4-o-H), 8.15–
8.23 (m, 4H; 15,20-Ph-o-H), 8.81–8.83 (m, 4H; H-b), 8.85–8.87 ppm
(m, 4H; H-b); UV/Vis (CHCl3): lmax (%)=419 (100), 516 (7), 553 (5),
590 (5), 647 nm (5); MS (MALDI): m/z: 647.2 [M+H]+.
1
Porphyrin 3: H NMR (300 MHz, CDCl3): d=À2.79 (s, 2H; NH), 5.20
(brs, 2H; OH), 7.20 (d, J=8.4 Hz, 4H; 5,15-C6H4-m-H), 7.72–7.81 (m,
6H; 10,20-Ph-m,p-H), 8.07 (d, J=8.4 Hz, 4H; 5,15-C6H4-o-H), 8.21
(dd, J=7.3 and 1.9 Hz, 4H; 10,20-Ph-o-H), 8.84 and 8.87 ppm (AB,
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
151
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
(282 MHz, CDCl3): d=À177.01 ppm (s, 4F); 13C NMR (126 MHz,
CDCl3): d=113.76, 113.91, 118.70, 120.23, 125.28, 126.69, 127.73,
128.21, 129.02, 130.60–131.68, 134.55, 135.73, 137.94, 142.08,
157.15 ppm; MS (MALDI): m/z: 1407.4 [M+H]+; HRMS-ESI(+): m/z
calcd for C94H59F4N8O2 [M+H]+: 1407.4692; found: 1407.4732; calcd
for C94H60F4N8O2 [M+2H]2+ 704.2382; found: 704.2378; UV/Vis
(CHCl3): lmax (loge): 415 (5.7), 514 (4.5), 550 (4.3), 588 (4.2), 642 nm
(4.1).
Acknowledgements
Thanks are due to Fundażo para a CiÞncia e a Tecnologia (FCT/
MEC), European Union, QREN, FEDER, and COMPETE for funding
the project PTDC/QEQ-QOR/1273/2012, the QOPNA research unit
(FCT UID/QUI/00062/2013; FCOMP-01-0124-FEDER-037296), and
the Portuguese NMR Network. J.I.T.C., E.O., and H.M.S. are grate-
ful to FCT for their Doctoral and Postdoctoral fellowships SFRH/
BD/75242/2010, SRFH/BPD/72557/2010, and SFRH/BPD/73997/
2010, respectively. The authors also thank PROTEOMASS Scientific
Society (Portugal), UCIBIO: UID/Multi/04378/2013 and REQUIMTE-
FCT PEst-C/EQB/LA0006/2013 for general funding.
Hexaporphyrin 8: An excess amount of sodium hydride (14 mg)
was added to a solution of 1 (22.4 mg, 36 mmol) in dry DMF
(1.5 mL) and the mixture was heated at 808C for ten minutes
under a nitrogen atmosphere. Diporphyrin 7 (10.0 mg, 7 mmol) was
then added and the mixture was maintained at 808C for five days.
Workup was identical to that described above. The residue was pu-
rified by preparative TLC using dichloromethane/petroleum ether
(1:1) as the eluent. A pink major fraction was eluted followed by
precursor 1. The major product was identified as 8 (8 mg, 30%
Keywords: colorimetry
porphyrinoids · sensors
·
fluorescence
·
mercury
·
1
yield). M.p. >3008C; H NMR (300 MHz, CDCl3): d=À2.75 (s, 12H),
7.69 (d, J=8.6 Hz, 12H;), 7.72–7.79 (m, 54H), 8.21–8.27 (m, 48H),
8.85 (s, 24H), 8.87 and 8.96 ppm (AB, 24H; J=4.8 Hz); 13C NMR
(75 MHz, CDCl3): d=114.74, 119.63, 120.14, 126.68, 127.70, 128.21,
129.02, 130.34–131.90, 134.56, 135.79, 136.50, 142.17, 157.10 ppm;
UV/Vis (CHCl3): lmax (loge)=420 (6.0), 514 (4.8), 551 (4.5), 590 (4.4),
641 nm (4.3).
[1] a) D. Kim, A. Osuka, Acc. Chem. Res. 2004, 37, 735–745; b) N. Aratani, D.
Kim, A. Osuka, Acc. Chem. Res. 2009, 42, 1922–1934; c) A. M. V. M. Per-
eira, M. G. P. M. S. Neves, J. A. S. Cavaleiro, C. Jeandon, J.-P. Gisselbrecht,
S. Choua, R. Ruppert, Org. Lett. 2011, 13, 4742–4745; d) Q. Ouyang, Y.-Z.
Zhu, C.-H. Zhang, K.-Q. Yan, Y.-C. Li, J.-Y. Zheng, Org. Lett. 2009, 11,
5266–5269; e) M. Akita, S. Hiroto, H. Shinokubo, Angew. Chem. Int. Ed.
2012, 51, 2894–2897; Angew. Chem. 2012, 124, 2948–2951; f) O. Locos,
Triporphyrin 9: A solution of 5 (20.0 mg, 20 mmol), 1 (32.2 mg,
51 mmol, 2.5 equiv), and potassium carbonate (16.9 mg, 122 mmol,
6 equiv) in DMF (2 mL) was stirred under a nitrogen atmosphere at
508C for 48 hours. After cooling to room temperature, the reaction
mixture was diluted with dichloromethane and washed with water.
The organic phase was dried with Na2SO4 and the solvent was
evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel using dichloromethane/pe-
troleum ether (1:1) as the eluent. The major fraction afforded com-
pound 9 (28 mg, 62% yield). M.p. >3008C; 1H NMR (300 MHz,
CDCl3): d=À2.79 (s, 6H), 7.46 (dd, J=8.6 and 1.6 Hz, 8H), 7.72–
7.76 (m, 24H), 8.19–8.23 (m, 24H), 8.83–8.86 ppm (m, 24H);
19F NMR (282 MHz, CDCl3): d=À177.00 ppm (s, 8F); 13C NMR
(75 MHz, CDCl3): d=113.73, 118.68, 118.80, 120.22, 120.27, 120.38,
126.68, 127.72, 130.35–132.04, 134.54, 135.72, 137.82, 137.90,
141.99, 142.04, 157.12 ppm; MS (MALDI): m/z: 2199.6 [M+H]+;
HRMS-ESI(+): m/z calcd for C144H88F8N12O4 [M+2H]2+: 1100.3456;
found: 1100.3463; UV/Vis (CHCl3): lmax (loge)=420 (5.9), 515 (4.6),
550 (4.3), 589 (4.2), 641 nm (4.1).
ˇ ´
L. B. Basic, J. C. McMurtrie, P. Jensen, D. P. Arnold, Chem. Eur. J. 2012, 18,
5574–5588; g) H. L. Anderson, Chem. Commun. 1999, 2323–2331;
h) I. A. Maretina, Russ. J. Gen. Chem. 2009, 79, 1544–1581; i) A. C. Cunha,
A. T. P. C. Gomes, V. F. Ferreira, M. C. B. V. Souza, M. G. P. M. S. Neves, A. C.
TomØ, A. M. S. Silva, J. A. S. Cavaleiro, Synthesis 2010, 510–514; j) H.-W.
Jiang, S. Ham, N. Aratani, D. Kim, A. Osuka, Chem. Eur. J. 2013, 19,
13328–13336; k) P. S. S. Lacerda, A. M. G. Silva, A. C. TomØ, M. G. P. M. S.
Neves, A. M. S. Silva, J. A. S. Cavaleiro, A. L. Llamas-Saiz, Angew. Chem.
Int. Ed. 2006, 45, 5487–5491; Angew. Chem. 2006, 118, 5613–5617; l) W.
Maes, J. Vanderhaeghen, S. Smeets, C. V. Asokan, L. M. V. Renterghem,
F. E. Du Prez, M. Smet, W. Dehaen, J. Org. Chem. 2006, 71, 2987–2994;
m) Y. Pareek, M. Ravikanth, Chem. Eur. J. 2012, 18, 8835–8846; n) T.
Tanaka, A. Osuka, Chem. Soc. Rev. 2015, 44, 943–969.
[2] a) T. M. Wilson, T. Hori, M.-C. Yoon, N. Aratani, A. Osuka, D. Kim, M. R.
Wasielewski, J. Am. Chem. Soc. 2010, 132, 1383–1388; b) T. Zhang, X.
Zhu, W.-K. Wong, H.-L. Tam, W.-Y. Wong, Chem. Eur. J. 2013, 19, 739–
748; c) J. Melomedov, J. R. Ochsmann, M. Meister, F. Laquai, K. Heinze,
Eur. J. Inorg. Chem. 2014, 1984–1987; d) H. Yoon, J. M. Lim, H.-C. Gee,
C.-H. Lee, Y. H. Jeong, D. Kim, W.-D. Jang, J. Am. Chem. Soc. 2014, 136,
1672–1678; e) P. C. Ray, P. Bonifassi, J. Leszczynski, J. Phys. Chem. A
2008, 112, 2870–2879; f) X. Wang, H. Wang, Y. Yang, Y. He, L. Zhang, Y.
Li, X. Li, Macromolecules 2010, 43, 709–715; g) S. A. Chavan, W. Maes,
L. E. M. Gevers, J. Wahlen, I. F. J. Vankelecom, P. A. Jacobs, W. Dehaen,
D. E. De Vos, Chem. Eur. J. 2005, 11, 6754–6762; h) G. Garcia, F. Ham-
merer, F. Poyer, S. Achelle, M.-P. Teulade-Fichou, P. Maillard, Bioorg. Med.
Chem. 2013, 21, 153–414; i) O. Mongin, M. Sankar, M. Charlot, Y. Mir, M.
Blanchard-Desce, Tetrahedron Lett. 2013, 54, 6474–6478.
[3] I. Beletskaya, V. S. Tyurin, A. Y. Tsivadze, R. Guilard, C. Stern, Chem. Rev.
2009, 109, 1659–1713.
[4] Y.-Q. Weng, F. Yue, Y.-R. Zhong, B.-H. Ye, Inorg. Chem. 2007, 46, 7749–
7755.
[5] C.-Y. Li, X.-B. Zhang, Y.-Y. Dong, Q.-J. Ma, Z.-X. Han, Y. Zhao, G.-L. Shen,
R.-Q. Yu, Anal. Chim. Acta 2008, 616, 214–221.
Triporphyrin 10: A solution of 6 (20.0 mg, 20 mmol), 1 (32.2 mg,
51 mmol, 2.5 equiv), and potassium carbonate (16.9 mg, 122 mmol,
6 equiv) in DMF (2 mL) was stirred under a nitrogen atmosphere at
508C for 48 hours. Workup was as described above. The residue
was purified by column chromatography on silica gel using di-
chloromethane/petroleum ether (1:1) as the eluent. The major frac-
tion afforded compound 10 (24 mg, 53% yield). M.p. >3008C;
1H NMR (300 MHz, CDCl3): d=À2.80 (s, 6H), 7.45 (d, J=8.5 Hz, 8H),
7.68–7.79 (m, 24H), 8.19–8.23 (m, 24H), 8.83 (s, 12H), 8.86 ppm (s,
12H); 19F NMR (282 MHz, CDCl3): d=À176.99 ppm (s, 8F); 13C NMR
(75 MHz, CDCl3): d=113.73, 113.88, 118.68, 118.88, 120.22, 126.28,
127.72, 128.11, 129.02, 130.36–132.14, 132.86, 132.90, 134.15,
134.54, 135.72, 137.90, 141,97, 142.05, 157.12 ppm; MS (MALDI): m/
z: 2199.6 [M+H]+; HRMS-ESI(+): m/z calcd for C144H88F8N12O4
[6] a) Y. Ding, Y. Tang, W. Zhu, Y. Xie, Chem. Soc. Rev. 2015, 44, 1101–1112;
b) Y. Ding, X. Li, T. Li, W. Zhu, Y. Xie, J. Org. Chem. 2013, 78, 5328–5338;
c) Y. Ding, T. Li, W. Zhu, Y. Xie, Org. Biomol. Chem. 2012, 10, 4201–4207.
[7] a) C.-H. Lee, H. Miyaji, D.-W. Yoon, J. L. Sessler, Chem. Commun. 2008,
24–34; b) A. S. F. Farinha, M. R. C. Fernandes, A. C. TomØ, Sens. Actuators
B 2014, 200, 332–338; c) A. S. F. Farinha, A. C. TomØ, J. A. S. Cavaleiro,
Tetrahedron Lett. 2010, 51, 2184–2187; d) A. S. F. Farinha, A. C. TomØ,
J. A. S. Cavaleiro, Tetrahedron 2010, 66, 7595–7599.
[M+2H]2+
(loge)=420 (5.8), 514 (4.6), 550 (4.3), 589 (4.2), 641 nm (4.2).
: 1100.3465; found: 1100.3449; UV/Vis (CHCl3): lmax
[8] a) Y. Pareek, M. Ravikanth, T. K. Chandrashekar, Acc. Chem. Res. 2012, 45,
1801–1816; b) J. M. M. Rodrigues, A. S. F. Farinha, P. V. Muteto, S. M.
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
152
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Papers
Woranovicz-Barreira, F. A. A. Paz, M. G. P. M. S. Neves, J. A. S. Cavaleiro,
A. C. TomØ, M. T. S. R. Gomes, J. L. Sessler, J. P. C. TomØ, Chem. Commun.
2014, 50, 1359–1361; c) F. Figueira, A. S. F. Farinha, A. C. TomØ, J. A. S.
Cavaleiro, F. A. A. Paz, J. P. C. TomØ, J. Porphyrins Phthalocyanines 2014,
18, 824–831; d) B. M. Rambo, J. L. Sessler, Chem. Eur. J. 2011, 17, 4946–
4959; e) S. Saito, A. Osuka, Angew. Chem. Int. Ed. 2011, 50, 4342–4373;
Angew. Chem. 2011, 123, 4432–4464; f) R. Misra, T. K. Chandrashekar,
Acc. Chem. Res. 2008, 41, 265–279.
[23] N. M. M. Moura, C. Nunez, S. M. Santos, M. A. F. Faustino, J. A. S. Cava-
leiro, M. G. P. M. S. Neves, J. L. Capelo, C. Lodeiro, ChemPlusChem 2013,
78, 1230–1243.
[24] N. M. M. Moura, C. Nunez, S. M. Santos, M. A. F. Faustino, J. A. S. Cava-
leiro, F. A. A. Paz, M. G. P. M. S. Neves, J. L. Capelo, C. Lodeiro, Chem. Eur.
J. 2014, 20, 6684–6691.
[25] J. P. C. TomØ, M. G. P. M. S. Neves, A. C. TomØ, J. A. S. Cavaleiro, A. F. Men-
donÅa, I. N. Pegado, R. Duarte, M. L. Valdeira, Bioorg. Med. Chem. 2005,
13, 3878–3885.
[26] K. K. Rohatgi-Mukherjee, Fundamentals of Photochemistry, Wiley Eastern
Limited, Calcutta, 1992.
[9] a) B. Wang, E. V. Anslyn, Chemosensors: Principles, Strategies and Applica-
tions; John Wiley & Sons, Inc., Singapore, 2011; b) C. Lodeiro, F. Pina,
Coord. Chem. Rev. 2009, 253, 1353–1383.
[10] Y. Yang, J. Jiang, G. Shen, R. Yu, Anal. Chim. Acta 2009, 636, 83–88.
[11] C. Y. Li, X.-B. Zhang, L. Qiao, Y. Zhao, C.-M. He, S.-Y. Huan, L.-M. Lu, L.-X.
Jian, G.-L. Shen, R.-Q. Yu, Anal. Chem. 2009, 81, 9993–10001.
[12] D. W. Boening, Chemosphere 2000, 40, 1335–1351.
[27] Z. X. Han, H. Y. Luo, X. B. Zhang, R. M. Kong, G. L. Shen, R. Q. Yu, Spectro-
chim. Acta Part A 2009, 72, 1084–1088.
[28] H. Baker, P. Hambrigth, L. Wagner, L. Ross, Inorg. Chem. 1973, 12, 2200–
2211.
[13] F. Di Natale, A. Lancia, A. Molino, M. Di Natale, D. Karatza, D. Musmarra,
J. Hazard. Mater. 2006, 132, 220–225.
[14] W. Zheng, M. Aschner, J.-F. Ghersi-Egea, Toxicol. Appl. Pharmacol. 2003,
192, 1–11.
[15] C. N. Glover, D. Zheng, S. Jayashankar, G. D. Sales, C. Hogstrand, A.-K.
Lundebye, Toxicol. Sci. 2009, 110, 389–400.
[16] P. Roy, K. Dhara, M. Manassero, J. Ratha, P. Banerjee, Inorg. Chem. 2007,
46, 6405–6406.
[29] M. Tabata, W. Miyata, N. Nahar, Inorg. Chem. 1995, 34, 6492–6496.
[30] E. Oliveira, J. Lorenzo, A. Cid, J. L. Capelo, C. Lodeiro, J. Photochem. Pho-
tobiol. A 2013, 269, 17–26.
[31] E. Oliveira, C. Nunez, B. Rodriguez-Gonzalez, J. L. Capelo, C. Lodeiro,
Inorg. Chem. 2011, 50, 8797–8798.
[32] P. Gans, A. Sabatini, A. Vacca, Talanta 1996, 43, 1739–1753.
[33] F. A Cotton, G. Wilkinson, Advanced Inorganic Chemistry, 5th ed., Wiley,
New York, 1988, pp. 735–738.
[17] G. Crivat, K. Kikuchi, T. Nagano, T. Priel, M. Hershfinkel, I. Sekler, N. Rose-
nzweig, Z. Rosenzweig, Anal. Chem. 2006, 78, 5799–5804.
[18] a) J. K. Choi, G. Sargsyan, A. M. Olive, M. Balaz, Chem. Eur. J. 2013, 19,
2515–2523; b) Y. Lv, M. Cao, J. Li, J. Wang, Sensors 2013, 13, 3131–
3141; c) T. Chaudhuria, M. Banerjeeb, A. Ghoshb, A. Panb, S. G. Neogi,
Luminescence 2011, 26, 747–753; d) C.-Y. Li, F. Xu, Y.-F. Li, Spectrochim.
Acta Part A 2010, 76, 197–206; e) W. Lin, L. Yuan, L. Long, C. Guo, J.
Feng, Adv. Funct. Mater. 2008, 18, 2366–2372; f) H.-Y. Luo, J.-H. Jiang,
X.-B. Zhang, C.-Y. Li, G.-L. Shen, R.-Q. Yu, Talanta 2007, 72, 575–581.
[19] a) M. Formica, V. Fusi, L. Giorgi, M. Micheloni, Coord. Chem. Rev. 2012,
256, 170–192; b) G. Ambrosi, E. Borgogelli, M. Formica, V. Fusi, L. Giorgi,
M. Micheloni, E. Rampazzo, M. Sgarzi, N. Zaccheroni, L. Prodi, Sens. Ac-
tuators B 2015, 207, 1035–1044.
[34] D. K. Cabbiness, D. W. Margerum, J. Am. Chem. Soc. 1969, 91, 6540–
6541.
[35] E. B. Fleischer, F. Dixon, Bioinorg. Chem. 1977, 7, 129–139.
[36] Y. Inada, Y. Sugimoto, Y. Nakano, Y. Itoh, S. Funahashi, Inorg. Chem.
1998, 37, 5519–5526.
[37] W. L. F. Armarego, D. D. Perrin, Purification of Laboratory Chemicals,
4th ed., Butterworth-Heinemann, Oxford, 1996.
[38] I. B. Berlman, Handbook of Fluorescence Spectra of Aromatic Molecules,
2nd ed., Academic Press, New York, 1971.
[39] M. Montalti, A. Credi, L. Prodi, M. T. Gandolfi, Handbook of Photochemis-
try, 3rd ed., Taylor & Francis, Boca Raton, FL, 2006.
[40] J. S. Renny, L. L. Tomasevich, E. H. Tallmadge, D. B. Collum , Angew.
Chem. Int. Ed. 2013, 52, 11998–12013; Angew. Chem. 2013, 125, 12218–
12234.
[20] C. I. M. Santos, E. Oliveira, J. C. J. M. D. S. Menezes, J. F. B. Barata, M. A. F.
Faustino, V. F. Ferreira, J. A. S. Cavaleiro, M. G. P. M. S. Neves, Tetrahedron
2014, 70, 3361–3364.
[41] N. Furuta, T. Mizutani, Thin Solid Films 2014, 556, 174–180.
[21] N. M. M. Moura, C. Nunez, M. A. F. Faustino, J. A. S. Cavaleiro,
M. G. P. M. S. Neves, J. L. Capelo, C. Lodeiro, J. Mater. Chem. C 2014, 2,
4772–4776.
[22] N. M. M. Moura, C. Nunez, S. M. Santos, M. A. F. Faustino, J. A. S. Cava-
leiro, M. G. P. M. S. Neves, J. L. Capelo, C. Lodeiro, Inorg. Chem. 2014, 53,
6149–6158.
Manuscript received: August 28, 2015
Accepted Article published: && &&, 0000
Final Article published: November 25, 2015
ChemPlusChem 2016, 81, 143 – 153
www.chempluschem.org
153
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim