Synthesis, characterization and near-infrared photoluminescent studies of diethyl malonate appended mono-porphyrinate lanthanide complexes

Article abstract of DOI:10.1039/b208987b

A new unsymmetrical diethyl malonate appended porphyrin and its Yb³⁺, Er³⁺ and Nd³⁺ complexes prepared and characterized by elemental analysis, NMR, IR, UV-visible and mass spectral methods. The results revealed that the p

Full text of DOI:10.1039/b208987b

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Synthesis, characterization and near-infrared photoluminescent
studies of diethyl malonate appended mono-porphyrinate
lanthanide complexes
Hong-Shan He,a,c Zhi-Xin Zhao,a Wai-Kwok Wong,*a King-Fai Li,b Jian-Xin Mengd and
Kok-Wai Cheaha,b
a Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong,
Hong Kong
b Department of Physics, Hong Kong Baptist University, Waterloo Road, Kowloon Tong,
Hong Kong
c Department of Applied Chemistry, National Huaqiao University, Quanzhou 362011,
P. R. China
d Department of Chemistry, Jinan University, Guangzhou, 510275, P. R.. China
Received 13th September 2002, Accepted 9th December 2002
First published as an Advance Article on the web 5th February 2003
A new unsymmetrical diethyl malonate appended porphyrin and its Yb3ϩ, Er3ϩ and Nd3ϩ complexes were prepared
and characterized by elemental analysis, NMR, IR, UV-visible and mass spectral methods. The results revealed
that the porphyrinate behaved as a tri-deprotonated hexadentate ligand with the appended diethyl malonate group
coordinated to the lanthanide ion as an anion. Photoluminescent studies showed that the porphyrin ring transferred
the absorbed visible light to the metal ions, which led to emission characteristic of the lanthanide ions in the near-
infrared region. The factors affecting the emission intensity were also investigated.
complexes, [Ln(TMPP)(LOEt)] (Ln = Yb or Er; LOEt = (η5-C5H5)-
Introduction
Ϫ
Co[P(᎐O)(OEt) ] anion), and demonstrated that porphyrin
᎐
2 3
Trivalent rare earth ions are known for their unique optical
properties such as line-like emission bands and relatively long
luminescence lifetimes.1 These unique properties have drawn
considerable interest for their potential application as fluor-
escence imaging agents.2 Direct excitation of lanthanide ions,
however, is difficult because of the forbidden nature of their
electronic transitions.3 To overcome this problem, the lumin-
escent lanthanide ions are usually encapsulated by an organic
chromophore (often referred to as an “antenna chromophore”),
the excitation of which, followed by energy transfer, causes the
sensitized luminescence of the metal ion.4,5 Most of the investi-
gations in the field of luminescent lanthanide complexes have
been devoted to the Eu3ϩ, Tb3ϩ, Dy3ϩ and Sm3ϩ compounds,6–13
which emit in the visible spectral region and are used as
sensors8 and as luminescent labels in fluoroimmuno-assays.6
Recently, there has been increasing interest in complexes of
could absorb and transfer the visible light to lanthanide ions,
which led to NIR emission.29
Tailed metalloporphyrins have attracted considerable atten-
tion for the various kinds of functions the tailed group exhib-
ited. The pendant group that is linked to the porphyrin ring via
amide or ether linkage can act as an axial ligand in biochemical
mimicking of cytochrome P-450 or as an interaction site in
molecular recognition.30–33 However, no β-diketonato appended
porphyrin and its lanthanide complex have been reported due
to the limitations of the traditional method for the preparation
of porphyrinate complexes. Recently we reported a new syn-
thetic method for the preparation of cationic monopor-
phyrinate lanthanide complex [Ln(Por)(H2O)3]Cl via the inter-
action of Ln[N(SiMe3)2]3ؒx[LiCl(THF)3] with porphyrin free
base (H2Por).34 However for lanthanide ions with large ionic
radii, we were unable to isolate stable cationic lanthanide por-
phyrinate complexes. As most β-diketonates can coordinate to
lanthanide ions and form stable lanthanide complexes with the
porphyrinate dianion,26,35 we propose that stable complexes
should be obtained if β-diketonate was appended to the
appropriate position of the porphyrin ring through an alkyl
chain. In this paper, we report the synthesis and characteriz-
ation of diethyl malonate (DEM) appended porphyrin and its
Yb3ϩ, Er3ϩ and Nd3ϩ complexes. The results revealed that the
lanthanide complexes were quite stable due to the coordin-
ation of the diethyl malonate group. Photoluminescence studies
showed that the porphyin ring could act as an efficient
photosensitizer.
Yb3ϩ, Nd3ϩ, and Er3ϩ 12–20
which have emission bands ranging
,
from 880 to 1550 nm. These lanthanide() complexes, which
emit in the near-infrared (NIR) region, a region where bio-
logical tissues and fluids are relatively transparent, are promis-
ing probes for fluoroimmuno-assays.17a Furthermore they also
have potential applications in optical amplification18a,21 and in
laser system.19c
Porphyrin, a highly conjugated system that absorbs strongly
in the UV-visible region, can act as an antenna for photolumin-
escence. Their transition metal complexes as photo-sensitizers
have been widely investigated.22–25 However, there are relatively
few studies on lanthanide porphyrinate complexes, especially
on monoporphyrinate lanthanide complexes, even though the
monoporphyrinate lanthanide complexes were reported early in
1974.26 The first report on porphyrins as sensitizers for Yb3ϩ ion
appeared in 1990,27 and their properties were only briefly
studied. Eleven years later, Korovin et al.28 reported the photo-
physical properties of Yb3ϩ complexes of crown ether linked
porphyrin and found that the luminescence of the complex was
completely quenched in the presence of alkali metal ions.
Recently we reported the synthesis and near-infrared lumin-
escent properties of bimetallic monoporphyrinate lanthanide
Results and discussion
Synthesis and characterization of appended porphyrin
The diethyl malonate appended porphyrin free base, 5-[2-(5,5Ј-
ethoxycarbonyl)pentoxy]phenyl-10,15,20-triphenylporphyrin
[o-DEM(H)-C4-O-TPPH2], was prepared as shown in Scheme 1.
5-(2-Hydroxylphenyl)-10,15,20-triphenylporphyrin
(o-OH-
TPPH2) was prepared conveniently from the condensation of
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
980

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Scheme 1 Synthetic route for o-DEM(H)-C4-O-TPPH2 and its lanthanide complexes.
o-hydroxybenzaldehyde, benzaldehyde and pyrrole in a molar
chloroform solution. The relative intensities of the four Q
ratio of 3 : 1 : 4 in propionic acid.31 Interaction of o-OH-TPPH2
with an excess amount of 1,4-dibromobutane in dry DMF in
the presence of anhydrous K2CO3 gave 5-(2-(4-bromobutyl)-
bands are typical of an etio-type porphyrin free base (inset of
Fig. 1).37 In its FAB (positive) mass spectrum, peaks corre-
sponding to [M ϩ H]ϩ, [M Ϫ CO2Et]ϩ and [M Ϫ (CH2)4-
CH(CO2Et)2]ϩ were observed at 845, 771 and 629 respectively.
Furthermore, the electrospray ionization high-resolution mass
spectrum (ESI-HRMS) in methanol (positive mode) shows the
[M ϩ H]ϩ peak at m/z 845.3672 (C55H49N4O5 requires 845.3702)
confirming that the diethyl malonate group has appended to the
phenyl)-10,15,20-triphenylporphyrin
(o-Br-C4-O-TPPH2),
which then reacted with diethyl malonate in the presence of a
slight excess of sodium methoxide in dry DMF to give
o-DEM(H)-C4-O-TPPH2 in high yield.
The purple porphyrin free base, o-DEM(H)-C4-O-TPPH2, is
stable in the air and soluble in most organic solvents except in
methanol and hexane. The UV-visible absorption spectrum of
the compound (Fig. 1) is almost identical to that of 5,10,15,20-
tetraphenylporphyrin (H2TPP).36 The Soret and Q bands
were observed at 418 and 516, 550, 589, 645 respectively in
1
porphyrin free base. Its H NMR spectrum (Fig. 2) confirmed
that the diethyl malonate has connected to the porphyrin via the
-(CH2)4- chain at its methylene position. The chemical shift of
the NH protons of the porphyrin ring was observed at δ Ϫ2.77,
which is identical to that of H2TPP. Peaks at δ 3.88, 1.04, 0.51
and 1.53 are attributed to the protons in a, b, c and d positions
(Scheme 1) of the four -CH2- groups, respectively. The chemical
shifts of the protons of the diethyl malonate moiety have
changed greatly. The chemical shifts of the protons in the two
-CH3 groups, two -OCH2 groups and one -CH are at δ 0.89, 3.70
and 2.55, respectively. These are more up-field than those of
free diethyl malonate (δ 1.28, 4.21 and 3.36 for -CH3, -OCH2
and -CH2 groups, respectively). It is known that the porphyrin
ring can produce a ring current, which can make the chemical
shifts of the protons closer to the ring center more up-field.38
Fig. 1 UV-VIS spectra of DEM-C4-TPP (solid line) and its Er3ϩ
complex (dashed line) in CHCl3. Inset shows the corresponding plots
for an etio-type porphyrin free base.
Fig. 2 1H NMR spectrum of o-DEM-C4-O-TPPH2 in CDCl3.
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
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Our previous investigations31,32 on various kinds of heterocyclic
base appended porphyrins and their transition metal complexes
also confirmed that the chemical shifts of protons in hetero-
cyclic bases appended in the ortho position of the phenyl group
were more up-field than those in meta or para positions due to
their closer location to the porphyrin ring center. So the large
changes of chemical shifts of the protons in diethyl malonate to
high field indicate that the group is close to the ring center. In
fact, this conformation is quite favorable for the coordination
of the diethyl malonate to lanthanide ions.
porphyrinate behaved as a tri-deprotonated hexadentate ligand
with the appended diethyl malonate group coordinated to the
lanthanide ion as an anion. Complexes 1–3 show similar frag-
mentation patterns in their mass spectra. The electrospray
ionization high-resolution mass spectra (positive mode) of the
complexes in methanol shows mass peaks at m/z correspond-
ing to [Ln(o-DEM-C4-O-TPP) ϩ H]ϩ and its fragment ion
[Ln(o-DEM-C4-O-TPP) Ϫ C2H4 ϩ H]ϩ. For instance, the Er3ϩ
complex exhibited mass peaks at m/z 1010.2809 and 982.2499
which deviate by less than 5 ppm from the theoretical peak
match values of 1010.2805 for the elemental composition of
[Er(o-DEM-C4-O-TPP) ϩ H]ϩ and 982.2493 for [Er(o-DEM-
C4-O-TPP) Ϫ C2H4 ϩ H]ϩ. The observed isotope distribution
patterns of these peaks also match the expected theoretical
signals. Elemental analyses suggested that the complexes should
be formulated as [Ln(o-DEM-C4-O-TPP)(H2O)]. The presence
of a water molecule is indicated by the IR spectra of the com-
plexes, which show vO-H at around 3444 cmϪ1. It is not uncom-
mon for lanthanide complexes with coordination number 6 or
lower to have solvent molecules coordinated to the metal
centres raising their coordination number to 7, 8 or 9.40 Thus,
for compounds 1–3, it is very likely that the water molecule is
coordinated to the metal centre. This is further supported by
luminescent studies (vide infra), which show that the lumin-
escent intensity of the complexes varies with the solvents.
Attempts to grow single crystals of compounds 1–3 suitable for
X-ray diffraction studies were unsuccessful. However, based on
the above spectroscopic evidence, the structure of compounds
1–3 (shown in Scheme 1) can be considered as a 7 coordinated
species with four N of the porphyrinate and three O (two from
the appended diethyl malonate anion and one from water)
coordinated to the metal centre.
Synthesis and characterization of lanthanide porphyrinate
complexes
Recently, we established a new synthetic method for the prepar-
ation of cationic lanthanide porphyrinate complexes [Ln(Por)-
(H2O)3]Cl via the interaction of Ln[N(SiMe3)2]3ؒx[LiCl(THF)3]
(Ln = Yb3ϩ, Er3ϩ and Y3ϩ) with porphyrin free base.34 Further-
more, we demonstrated that these cationic porphyrinate com-
plexes were good precursors for the preparation of other
lanthanide porphyrinate complexes. For instance, [Ln(Por)-
(H2O)3]Cl reacted with anionic tripodal ligands to form novel
neutral seven coordinated porphyrinate complexes.29 However,
with lighter lanthanide ions, such as Nd3ϩ which has a larger
ionic radius, the [Nd(Por)(H2O)3]Cl complex which was only
observed spectroscopically, was rather unstable and decom-
posed rapidly via de-metallation to regenerate the porphyrin
free base upon exposure to air and moisture. However, when the
diethyl malonate appended porphyrin was used, we were able to
obtain complexes 1–3.
Interaction of the porphyrin free base o-DEM(H)-C4-O-
TPPH2 with an excess amount of Ln[N(SiMe3)2]3ؒx[LiCl-
(THF)3] (Ln = Yb, Er or Nd) in refluxing bis(2-methoxyethyl)
ether gave purple air stable lanthanide porphyrinate complexes
(1 Yb, 2 Er or 3 Nd) (Scheme 1). Complexes 1–3 were quite
stable toward moisture and could be purified by column chro-
matography on silica gel. The complexes were soluble in chloro-
form, dichloromethane, THF and methanol but insoluble in
hexane. The electronic absorption spectra of complexes 1–3
were characteristic of regular-normal metalloporphyrins36
(Fig. 1) and similar to that of [Ln(TPP)(acac)].26 After com-
plexation the number of Q bands of the porphyrin ring (four
for porphyrin free base) reduced to two bands at 552 and 589
nm (see inset of Fig. 1). This is in agreement with Gouterman’s
four-orbital model,39 which predicts that due to an increase in
symmetry, the four Q bands of the porphyrin free base will be
reduced to two upon the formation of a metalloporphyrin. In
the absorption spectra of regular metalloporphyrins, there are
two Q bands between 500 and 600 nm. The lower-energy band
(α band) is the electronic origin Q(0,0) of the lowest singlet
excited state S1. The second band (β band) is its vibrational
overtone and is labeled as Q(1,0). The relative intensities of
these bands can be a qualitative yardstick of just how stable is
the metal complexed to the four porphyrinic nitrogen atoms.
Thus, when the intensity of the α band is greater than that of
the β band, the metal forms a stable complex with the por-
phyrin; whereas when α < β, the metal is easily displaced by
protons.37 The α/β relative intensity ratios for complexes 1–3 are
Complexes 1–3 are quite stable in air, which, we believe, can
only be attributed to the coordination of the appended diethyl
malonate anion. This makes us believe that the second ligand is
crucial for the preparation of stable monoporphyrinate lan-
thanide complexes, particularly those metals with large ionic
radii. In fact our recent results show that anionic tripodal
ligands such as (η5-C H )Co[P(᎐O)(OEt) ] anion and hydro-
Ϫ
᎐
5
5
2 3
tris(1-pyrazoly1)borate, could be used to stabilize mono-
porphyrinate complexes of lanthanide ions (e.g. Nd3ϩ and
Sm3ϩ) with large ionic radii.41
Photophysical studies of complexes
The photophysical properties of compounds 1–3 have been
examined and are summarized in Table 1. The room temper-
ature solution electronic absorption and emission spectra of
compounds 1–3 in the UV-VIS region are almost identical and
characteristic of intra-ligand transitions of normal por-
phyrinate complexes.36 Fig. 1 shows the absorption spectrum of
1, and Fig. 3 shows the emission (excited at 422 nm) and excit-
ation (monitored at 650 nm) spectra of 1. The excitation spec-
trum closely resembles the absorption spectrum. The absorp-
tion bands at 422, 552 and 589 nm and emission peak at 650 nm
(τ = 5.1 ns and Φem = 0.15 × 10Ϫ3 for 1; τ = 3.3 ns and Φem
0.98 × 10Ϫ4 for 2; τ = 8.9 ns and Φem = 5.02 × 10Ϫ3 for 3) can be
assigned to the intra-ligand π π* transitions of the por-
=
0.26, 0.19 and 0.17, respectively. In the IR spectra, the vC᎐O
,
phyrinate ligand. The quantum efficiency of the metallo-
porphyrin is much lower than that of the appended porphyrin
free base (Φem = 3.56 × 10Ϫ2). Other than the visible emission,
compounds 1–3 also exhibit emissions corresponding to the
lanthanide() ion in the near-infrared (NIR) region (Fig. 4).
These NIR emissions are very similar to those reported for
which appeared at 1735 cmϪ1 for the appended porphyrin free
base, was shifted to 1698 cmϪ1 indicating that the C᎐O group
᎐
had coordinated to the lanthanide ions. This is in accordance
with the literature reported [Ln(TPP)(acac)] compound.26 Con-
ductivity measurements showed that the complexes were non-
conducting in chloroform and methanol indicating that the
complexes were neutral. Treatment of a methanol solution
of the complexes with an aqueous solution of AgNO3 did not
give any AgCl precipitation indicating that there was no
chloride (whether as a coordinated ligand or as an anion) pres-
ent in the complexes. The above observations indicate that the
Yb3ϩ, Er3ϩ and Nd3ϩ 17a,20
centred at 980 and 1544 nm can be assigned to the 2F5/2
transition of Yb3ϩ and 4I13/2 4I15/2 transition of Er3ϩ, respect-
ively. For 3, the emission peaks centred at 853 and 890 nm can
be assigned to 4F3/2 4I9/2 and 1074 nm to 4F3/2 4I11/2 transi-
tions of Nd3ϩ. The excitation spectra for the NIR emission of 1
.
For 1 and 2, the emission peaks
2F7/2
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
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Table 1 Photophysical data of compounds 1, 2 and 3a
Compound
Absorption: λmax/nm [log(ε/dm3 molϪ1 cmϪ1)]
Excitation: λexc/nm
Emission: λem/nm (τ, Φem × 103)b, c
1
2
3
422 (5.88), 552 (4.55)
589 (3.96)
422 (5.71), 551 (4.31)
589 (3.58)
422 (5.68), 551(4.28)
594 (3.52)
422
422
422
650 (5.1 ns, 0.15)
980 (2.43 µs)
650 (3.3 ns, 0.098)
1544d
650 (8.9 ns, 5.02)
853e
a Photophysical measurements were made in CHCl3 solution at room temperature. b Quantum yields were determined relative to [Ru(bipy)3]Cl2 in air-
equilibrated water (Φ = 0.028). c Due to the limitations of the instrument, we were unable to determine the quantum yields of the NIR luminescence
of compounds 1, 2 and 3. d Due to the limitations of the instrument, we were unable to measure the lifetime of the NIR luminescence of compound
2. e Compound 3 decomposes upon irradiation with N2 laser at 337 nm. Thus, its NIR luminescence lifetime could not be measured.
Fig.
5
NIR luminescence spectrum (solid line) and excitation
spectrum (dashed line), monitored at 980 nm, of 1 in CHCl3.
Fig. 3 Emission spectrum (a) and excitation spectrum (b), monitored
at 650 nm, of 1 in CHCl3.
Fig. 6 Schematic energy diagram of diethyl malonate appended
lanthanide complexes. The arrows indicate the excitation mechanism of
lanthanide ions by the porphyrin sensitizer (S0
by intersystem crossing and energy transfer).
S1 transition followed
of the sensitization process is depicted in Fig. 6. Generally the
energy transfer from an antenna to lanthanide ions is con-
sidered to take place through the triplet state of the antenna
and its singlet state has little contribution to the sensitization
Fig. 4 NIR luminescence spectra of complexes 1–3 in CHCl3.
process. Excitation of the π
π* transitions of the por-
and 3 are very similar. Fig. 5 shows the NIR emission and exci-
tation spectra of 1. The excitation band of 1 in chloroform
solution at 298 K (monitored at 980 nm) is observed at 560 nm,
which almost coincides with its visible absorption band at 552
nm. This clearly shows that the excitation of the Yb3ϩ ion
phyrinate produced the singlet S1 state, which via intersystem
crossing transferred part of its energy to the triplet T1 state. The
T1 state then transferred its energy to the lanthanide metal ions,
which led to NIR emission.17a,42
The photoluminescence intensity of the complexes is quite
different under the same conditions (Fig. 4). The NIR emission
intensities of the Yb3ϩ and Nd3ϩ complexes are an order of
magnitude stronger than that of the Er3ϩ complex. As the lan-
thanide ions are in the same environment, we can conclude that
this difference stems from the different energy transfer effi-
ciency of porphyrin to the lanthanide ions. The luminescence of
lanthanide ions was heavily affected by the kinds of solvent
used. Research showed that OH oscillators, e.g. in bound water
molecules, OH-containing solvents, could quench the lumines-
cence.43 Fig. 7 shows the luminescence of complex 1 in different
originates from the π
π* transitions of the porphyrinate
antenna and excitation of the porphyrin is the photophysical
pathway leading to the observable NIR luminescence. The NIR
luminescence lifetime of 1 is 2.43 µs and is much longer than the
lifetime of the porphyrinate emission. Due to the limitations of
our equipment, we were unable to measure the excitation
(monitored at 1544 nm) spectrum and the NIR luminescence
lifetime of 2. 3 decomposed upon irradiation with an N2 laser at
337 nm, and therefore its NIR luminescence lifetime could not
be measures. A simple photophysical model for the description
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
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Electronic absorption spectra in the UV-VIS region were
recorded on a Hewlett Packard 8453 UV-Visible spectro-
photometer, steady-state visible fluorescence and PL excitation
spectra on a Photon Technology International (PTI) Alphascan
spectrofluorimeter and visible decay spectra on a pico-N2 laser
system (PTI Time Master) with λexc = 337 nm. NIR emission
was detected by a liquid nitrogen cooled InSb IR detector (EG
& G) with a preamplifier and recorded by a lock-in amplifier
system as the third harmonic, the 355 nm line of a Nd:YAG
laser (Quantel Brilliant B) was used as the excitation source and
also to pump the OPO (Opotek MagicPrism VIR) to provide a
continuously tunable laser source from 410–670 nm with a
pulse-width of 4 ns. NIR decay spectra were detected by an
Oriel 77343 photomultiplier and monitored by a HP54522A
500 MHz oscilloscope. Quantum yields were computed accord-
ing to the literature method44 using [Ru(bipy)3]Cl2 as the refer-
ence standard (Φ = 0.028 in air-equilibrated water).45 To avoid
any second-order light reaching the detector, 710 and 830 nm
cutoff filters were used where applicable. The complexes in dif-
ferent solutions were analyzed in quartz cells with concen-
tration 2 × 10Ϫ5 M. The power on the cell was 1 W and all
spectra were corrected for the detector response.
Fig.
7
Photoluminescence of 1 in different solvents at room
temperature.
solvents. The results revealed that an OH-rich solvent, for
example MeOH, had a slight effect on their emission. However,
we found that DMF could enhance the emission intensity,
which, we believe, could only be attributed to the substitution
of coordinated H2O by DMF. This is supported by the electro-
spray ionization high-resolution mass spectrum of a DMF
solution of 1 in MeOH, which exhibits a peak at m/z 1162.4081
corresponding to (M Ϫ H2O ϩ 2DMF ϩ H)ϩ (C61H60N6O7Yb
requires 1162.3923). Furthermore, in the IR spectrum of the
resultant porphyrinate complex obtained by removing the
solvent of a DMF solution of 1, the vO-H at 3446 cmϪ1 had
disappeared and a new peak at 1664 cmϪ1, which probably
corresponded to the vC᎐O of coordinated DMF, was observed.
Thus, the above spectro᎐scopic data support the conclusion that
the coordinated H2O molecule of 1 has been substituted by
DMF when dissolved in DMF.
Preparation of porphyrin free bases
5-(2-Hydroxylphenyl)-10,15,20-triphenylporphyrin
(o-OH-
TPPH2). This compound was prepared by a modification of
the literature method.23 A solution of benzaldehyde (5.5 cm3,
54 mmol) and o-hydroxybenzaldehyde (3.7 cm3, 35 mmol) in
propionic acid (250 cm3) was heated to reflux with mechanical
stirring. Then freshly distilled pyrrole (5.0 cm3, 72 mmol) in
propionic acid (50 cm3) was added slowly to the solution in
half an hour. Upon cooling to room temperature, methanol
(300 cm3) was added to the reaction mixture. The resultant solu-
tion was kept in a refrigerator overnight. Filtration gave about
1.3 g of crude product, which was redissolved in a minimum
amount of chloroform and chromatographed on a silica gel
column with dichloromethane as eluent. The second band gives
the desired o-OH-TPPH2. Yield: 1.10 g, 5%. UV-VIS data in
CHCl3, 20 ЊC, λmax/nm: 418, 516, 550, 589 and 645. FAB-MS
(ϩve mode) m/z: 631 (M ϩ H)ϩ.
Conclusion
In this paper, we have described the detailed synthesis and char-
acterization of a novel diethyl malonate appended porphyrin
and its lanthanide() complexes [Ln(o-DEM-C4-O-TPP)-
(H2O)] (Ln3ϩ = Yb3ϩ, Er3ϩ and Nd3ϩ). Spectroscopic evidence
suggests that the structures of these complexes can be con-
sidered as 7 coordinated species with four N of the porphyrin-
ate and three O (two from the appended diethyl malonate anion
and one from water) coordinated to the metal centre. We fur-
ther show that the diethyl malonate appended porphyrin can
behave as a tri-deprotonated hexadentate ligand to encapsulate
and stabilize lanthanide metal ions with large ionic radii. Photo-
luminescence studies showed that the porphyrin ring could
act as an antenna for the near-infrared emission of lanthanide
ions. Better donating solvents could enhance the luminescence
efficiency by replacing the coordinated water molecule.
5-(2-(4-Bromobutyl)phenyl)-10,15,20-triphenylporphyrin (o-
Br-C4-O-TPPH2). To a suspension of o-OH-TPPH2 (0.50 g,
0.8 mmol) and anhydrous K2CO3 in dry DMF was added 2 cm3
of 1,4-dibromobutane, the mixture was stirred at room temper-
ature and the progress of the reaction was monitored by TLC.
After 24 h, chloroform (100 cm3) was added to the reaction
mixture, which was then washed with water (6 × 50 cm3) until
all of the DMF and potassium carbonate were removed. The
organic phase was evaporated to dryness in vacuo and the resi-
due was re-dissolved in chloroform/hexane (v/v, 1 : 1) and
chromatographed on a silica gel column using chloroform/
hexane (v/v, 5 : 1) as eluent. The first band gave the product
o-Br-C4-O-TPPH2. Yield: 0.58 g, 95%.1H NMR (in CDCl3):
δ Ϫ2.76 (s, 2H), 8.83–8.78 (m, 8H), 8.24–8.19 (m, 6H), 8.04–
8.02 (m, 2H), 7.38–7.21 (m, 11H), 3.92 (s, 2H), 2.39 (s, 2H), 1.13
(s, 2H), 0.82 (s, 2H). UV-VIS data in CHCl3, 20 ЊC, λmax/nm:
419, 515, 550, 589 and 645. FAB-MS (ϩve mode) m/z: 765
(M ϩ H)ϩ for 79Br.
Experimental
Procedures
All reactions were carried out in an atmosphere of dry nitrogen.
Solvents were dried by standard procedures, distilled and
deaerated prior to use. All chemicals used were of reagent
grade, obtained from Aldrich Chemical Company and, where
appropriate, degassed before use. The IR spectra (KBr pellets)
were recorded on a Nicolet Nagba-IR 550 spectrometer and
NMR spectra on a Varian INOVA 400 spectrometer. Elemental
analyses were performed by the Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences. Low-resolution mass
spectra were obtained on a Finnigan MAT SSQ-710 in FAB
(positive) mode. Electrospray ionization high-resolution mass
spectra (ESI-HRMS) were recorded on a QSTAR mass
spectrometer.
5-[2-(5,5Ј-Ethoxycarbonyl)pentoxy]phenyl-10,15,20-triphenyl-
porphyrin [o-DEM(H)-C4-O-TPPH2]. Sodium methoxide
(1.0 g, 18.5 mmol) was added to a solution of diethyl malonate
(2.8 cm3, 18.5 mmol) in DMF (50 cm3) and the resulting
suspension was stirred under nitrogen at 60ЊC until the solu-
tion was clear. Then a solution of o-Br-C4-O-TPPH2 (0.3 g,
0.4 mmol) in DMF (5.0 cm3) was added slowly to the solution
in 30 min. The mixture was stirred further for about 2 h. Upon
cooling to room temperature, the reaction mixture was diluted
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
984

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with chloroform (100 cm3) and washed with water (6 × 50 cm3).
The organic layer was dried over anhydrous Na2SO4 and
filtered. The solvent of the filtrate was removed in vacuo and
the residue was redissolved in 5 cm3 of chloroform/hexane (v/v,
5 : 1) and chromatographed on silica gel using chloroform/
hexane (v/v, 5 : 1) as eluent. The second band gives the desired
compound o-DEM(H)-C4-O-TPPH2 after re-crystallization in a
chloroform/methanol solution. Yield: 0.30 g, 89%. M.p. 108–
110 ЊC. IR (cmϪ1, in KBr): 3462 w, 3312w, 2962m, 1746m,
1728s, 1600m, 1471m, 1441m, 1356m, 1261s, 1094s, 1024s, 964s,
C55H46N4O5Er requires 1010.2805), 982.2499 ([M Ϫ H2O Ϫ
C2H4 ϩ H]ϩ, C53H42N4O5Er requires 982.2493). Anal. found
(calc.) for C55H47N4O6ErؒCH3OHؒH2O: C, 62.55 (62.43); H,
5.09 (4.96); N, 5.00 (5.20%).
[NdIII(o-DEM-C4-O-TPP)(H2O)] 3. Anhydrous NdCl3 (0.40
g, 1.6 mmol) was used. Yield: 0.27 g, 90%. M.p. > 300 ЊC. IR
(cmϪ1, in KBr): 3451s, 2960w, 2924m, 2862w, 1703m, 1625m,
1594s, 1574s, 1481s, 1450s, 1268m, 1207m, 989vs, 803s, 757s,
710s. UV-VIS in CHCl3, 20 ЊC, λmax/nm [log(ε/dm3 molϪ1 cmϪ1
)
1
800vs, 749m, 729m, 701s. H NMR (CDCl3): δ Ϫ2.77 (s, 2H),
in parentheses]: 419 (5.68), 550 (4.28), 594 (3.52). Fluorescence
data in CHCl3, 20 ЊC, λexc/nm: 422; λem/nm: 650, 715, 853, 890,
1074; Φem = 5.02 × 10Ϫ3; τ = 8.9 ns (650 nm). FAB-MS (ϩve
mode) m/z: 984 (M Ϫ H2O ϩ H)ϩ for 142Nd. ESI-HRMS
(ϩve mode, in CH3OH) m/z: 986.2526 ([M Ϫ H2O ϩ H]ϩ,
C55H46N4O5Nd requires 986.2581) and 958.2322 ([M Ϫ H2O Ϫ
C2H4 ϩ H]ϩ, C53H42N4O5Nd requires 958.2267). Anal. found
(calc.) for C55H47N4O6Nd: C, 66.02 (65.78); H, 4.84 (4.72); N,
5.65 (5.58%).
8.83–8.78 (m, 8H), 8.26–8.18 (m, 6H), 7.98–7.96 (m, 2H), 7.78–
7.71 (m, 9H), 7.34–7.28 (m, 2H), 3.87 (t, 2H), 3.69 (m, 4H), 2.55
(s, 1H), 1.26 (t, 2H), 1.01 (s, 2H), 0.87 (m, 6H), 0.48 (s, 2H).
UV-VIS in CHCl3, 20 ЊC, λmax/nm [log(ε/dm3 molϪ1 cmϪ1
)
in parentheses]: 419 (5.63), 514 (4.26), 548 (3.87), 590 (3.71),
649 (3.78). Fluorescence data in CHCl3, 20 ЊC, λexc/nm: 425,
514, 544, 594; λem/nm: 652, 715; Φem = 3.56 × 10Ϫ2; τ = 9.4 ns
(652 nm). FAB-MS (ϩve mode) m/z: 845 (M ϩ H)ϩ, 771
(M Ϫ CO2Et)ϩ and 629 [M Ϫ (CH2)4CH(CO2Et)2]ϩ. ESI-
HRMS (ϩve mode, in CH3OH) m/z: 845.3672 [(M ϩ H)ϩ,
C55H49N4O5 requires 845.3702]. Anal. found (calc.) for C55H48-
N4O5ؒ1.5H2O: C, 75.92 (75.75); H, 5.91 (5.90); N, 6.26 (6.43%).
Acknowledgements
The work described in this paper was partially supported by a
grant from the Research Grants Council of the Hong Kong
Special Administrative Region, China (HKBU 2023/00P) and a
grant from the Hong Kong Baptist University (FRG/99-00/
II-92, FRG/01-02/I-16).
Preparation of lanthanide complexes
Compounds 1–3 were prepared with the same procedure. A
typical procedure is given for 1.
[YbIII(o-DEM-C4-O-TPP)(H2O)] 1. A solution of n-BuLi
(1.6 M, 3.0 cm3, 4.8 mmol) in hexane was added dropwise over
a period of 10 min to a solution of (Me3Si)2NH (0.78 g,
4.8 mmol) in THF (15 cm3), the reaction mixture was allowed to
stirred at room temperature for 2 h, then transferred slowly to
a suspension of anhydrous YbCl3 (0.44 g, 1.6 mmol) in THF
(10 cm3). After stirring at room temperature for 24 h, the mix-
ture was concentrated to ca. 5 cm3 and filtered. The filtrate
was added to a solution of o-DEM(H)-C4-O-TPPH2 (0.25 g,
0.30 mmol) in bis(2-methoxyethyl) ether (5 cm3). The resultant
solution was refluxed for 24 h. Upon cooling to room temper-
ature, chloroform (50 cm3) was added to the solution and fil-
tered. The filtrate was washed with water (5 × 30 cm3), dried
over anhydrous Na2SO4 and filtered. The organic layer was
evaporated to dryness in vacuo and the residue was redissolved
in chloroform and chromatographed on silica gel using chloro-
form/methanol (v/v, 5 : 1) as eluent. The second band gave the
References
1 W. D. Horrocks, Jr. and M. Albin, Progress in Inorganic Chemistry,
ed. S. J. Lippard, John Wiley & Sons, 1984, vol. 31, p. 1104.
2 Bioanalytical Applications of Labelling Technologies, ed. I. Hemmilä,
T. Stählberg and P. Mottram, Wallac Oy, Turku, Finland, 1994.
3 (a) R. Reinfeld and C. H. Jørgensen, Lasers and Excited States of
Rare Earths, Springer-Verlag, Berlin, 1977; (b) K. A. Gschneider, Jr.
and L. Eyring, Handbook on the Physics and Chemistry of Rare
Earths, North-Holland, Amsterdam, 1979, vol. 15.
4 N. Sabbatini, M. Guardigli and J.-M. Lehn, Coord. Chem. Rev.,
1993, 123, 201.
5 A. Beeby, R. S. Dickins, S. FitzGerald, L. J. Govenlock, C. L.
Maupin, D. Parker, J. P. Riehl, G. Silligardi and J. A. G. Williams,
Chem. Commun., 2000, 1183.
6 M. Elbanowski and B. Makowska, J. Photochem. Photobiol. A,
1996, 99, 85.
7 F. J. Steemers, W. Verboom, D. N. Reinhoudt, E. B. Van der Tol and
J. W. Verhoeven, J. Am. Chem. Soc., 1995, 117, 9408.
8 (a) D. Parker, Coord. Chem. Rev., 2000, 205, 109; (b) M. P. Lowe and
D. Parker, Inorg. Chim. Acta, 2001, 317, 163; (c) M. P. Lowe,
D. Parker, O. Reany, S. Aime, M. Botta, G. Castellano, E. Gianolio
and R. Pagliarin, J. Am. Chem. Soc., 2001, 123, 7601; (d ) D. Parker,
R. S. Dickins, H. Puschmann, C. Crossland and J. A. K. Howard,
Chem. Rev., 2002, 102, 1977.
9 (a) C. Edder, C. Piguet, J.-C. G. Bünzli and G. Hopfgartner, J. Chem.
Soc., Dalton Trans., 1997, 4657; (b) M. Elhabiri, R. Scopelliti,
J.-C. G. Bünzli and C. Piguet, J. Am. Chem. Soc., 1999, 121, 10747;
(c) G. Zucchi, A.-C. Ferrand, R. Scopelliti and J.-C. G. Bünzli,
Inorg. Chem., 2002, 41, 2459; (d ) J.-C. G. Bünzli and C. Piguet,
Chem. Rev., 2002, 102, 1897.
10 X.-P. Yang, C.-Y. Su, B.-S. Kang, X.-L. Feng, W.-L. Xiao and
H.-Q. Liu, J. Chem. Soc., Dalton Trans., 2000, 3253.
11 M. Xiao and P. R. Selvin, J. Am. Chem. Soc., 2001, 123, 7067.
12 S. I. Klink, L. Grave, D. N. Reinhoudt, F. C. J. M. van Veggel,
M. H. V. Werts, G. A. J. Geurts and J. W. Hofstraat, J. Phys. Chem.
A, 2000, 104, 5457.
13 V. Vicinelli, P. Ceroni, M. Maestri, V. Balzani, M. Gorka and
F. Vögtle, J. Am. Chem. Soc., 2002, 124, 6461.
14 A. Beeby, R. S. Dickins, S. Faulkner, D. Parker and J. A. G.
Williams, Chem. Commun., 1997, 1401.
15 W. D. Horrocks, Jr., J. P. Bolender, W. D. Smith and R. M.
Supkowski, J. Am. Chem. Soc., 1997, 119, 5972.
16 M. I. Gaiduk, V. V. Grigoryants, A. F. Mironov, V. D. Rumyantseva,
V. I. Chissov and G. M. Sukhin, J. Photochem. Photobiol. B, 1990, 7,
15.
desired complex 1. Yield: 0.29 g, 95%. M.p. > 300 ЊC. IR (cmϪ1
,
in KBr): 3446m, 2955m,2918m, 2867m, 1739m, 1698m, 1615m,
1594s, 1439s, 1263s, 1196s, 1113m, 1072m, 989s, 798vs, 756s,
710s, 658m. UV-VIS in CHCl3, 20 ЊC, λmax/nm [log(ε/dm3 molϪ1
cmϪ1) in parentheses]: 422 (5.88), 552 (4.55), 589 (3.96). Fluor-
escence data in CHCl3, 20 ЊC, λexc/nm: 422; λem/nm: 650, 715,
980; Φem = 0.15 × 10Ϫ3; τ = 5.1 ns (650 nm), 2.43 µs (980 nm).
FAB-MS (ϩve mode) m/z: 1016 (M Ϫ H2O ϩ H)ϩ for 174Yb.
ESI-HRMS (ϩve mode, in CH3OH) m/z: 1016.2826 ([M Ϫ H2O
ϩ H]ϩ, C55H46N4O5Yb requires 1016.2867), 988.2494 ([M Ϫ
H2O Ϫ C2H4 ϩ H]ϩ, C53H42N4O5Yb requires 988.2553). Anal.
found (calc.) for C55H47N4O6Yb: C, 63.94 (63.95); H, 4.47
(4.59); N, 5.63 (5.42%).
[ErIII(o-DEM-C4-O-TPP)(H2O)] 2. Anhydrous ErCl3 (0.44 g,
1,6 mmol) was used. Yield: 0.30 g, 92%. M.p. > 300 ЊC. IR
(cmϪ1, in KBr): 3441m, 2975m, 2924m, 2851m, 1698m, 1620m,
1600m, 1574m, 1445m, 1331m, 1264s, 1103s, 1015s, 798vs,
700m. UV-VIS in CHCl3, 20 ЊC, λmax/nm [log(ε/dm3 molϪ1
cmϪ1) in parentheses]: 422 (5.71), 551 (4.31), 589 (3.58). Fluor-
escence data in CHCl3, 20 ЊC, λexc/nm: 422; λem/nm: 650, 715,
1544; Φem = 0.98 × 10Ϫ4; τ = 3.3 ns (650 nm). FAB-MS
(ϩve mode) m/z: 1008 (M Ϫ H2O ϩ H)ϩ for 166Er. ESI-HRMS
(ϩve mode, in CH3OH) m/z: 1010.2809 ([M Ϫ H2O ϩ H]ϩ,
17 (a) M. H. V. Werts, J. W. Hofstraat, F. A. J. Geurts and J. W.
Verhoeven, Chem. Phys. Lett., 1997, 276, 196; (b) M. H. V. Werts,
D a l t o n T r a n s . , 2 0 0 3 , 9 8 0 – 9 8 6
985

View Article Online
J. W. Verhoeven and J. W. Hofstraat, J. Chem. Soc., Perkin Trans. 2,
2000, 433; (c) M. H. V. Werts, R. H. Woudenberg, P. G. Emmerink,
R. van Gassel, J. W. Hofstraat and J. W. Verhoeven, Angew. Chem.,
Int. Ed., 2000, 39, 4542; (d ) B. H. Bakker, M. Goes, N. Hoebe,
H. J. van Ramesdonk, J. W. Verhoeven, M. H. V. Werts and
J. W. Hofstraat, Coord. Chem. Rev., 2000, 208, 3.
27 M. I. Gaiduk, V. V. Gridoryants, A. F. Mironov, V. D. Rumyantseva,
V. I. Chissov and G. M. Sukhin, J. Phochem. Photobiol. B, 1990, 7,
15.
28 Y. Korovin, Z. Zhilina, N. Kuzmin, S. Vodzinsky and Y. Ishkov,
J. Porphyrins Phthalocyanines, 2001, 5, 481.
29 W. K. Wong, A. X. Hou, J. P. Guo, H. S. He, L. L. Zhang, W. Y.
Wong, K. F. Li, K. W. Cheah, F. Xue and T. C. W. Mak, J. Chem.
Soc., Dalton Trans., 2001, 3092.
30 B. Meunier, Chem. Rev., 1990, 29, 2734.
31 H. S. He, B. S. Fang, J. W. Huang and L. N. Ji, Transition Met.
Chem., 2000, 35, 365.
32 H. S. He, J. W. Huang and L. N. Ji, Synth. React. Inorg. Met-Org.
Chem., 2001, 31, 17–29.
18 (a) M. P. Oude Wolbers, F. C. J. M. van Veggel, F. G. A. Peters,
E. S. E. van Beelen, J. W. Hofstraat, F. A. J. Geurts and D. N.
Reinhoudt, Chem. Eur. J., 1998, 4, 772; (b) S. I. Klink, H. Keizer
and F. C. J. M. van Veggel, Angew. Chem., Int. Ed., 2000, 39,
4319; (c) S. I. Klink, P. Oude Alink, L. Grave, F. G. A. Peters,
J. W. Hofstraat, F. A. J. Geurts and F. C. J. M. van Veggel, J. Chem.
Soc., Perkin Trans. 2, 2001, 363.
19 (a) Y. Hasegawa, Y. Kimura, K. Murakoshi, Y. Wada, J. Kim,
N. Nakashima, T. Yamanaka and S. Yanagida, J. Phys. Chem.,
1996, 100, 10201; (b) Y. Wada, T. Okubo, M. Ryo, T. Nakazawa,
Y. Hasegawa and S. Yanagida, J. Am. Chem. Soc., 2000, 122, 8583;
(c) Y. Hasegawa, T. Ohkubo, K. Sogabe, Y. Kawamura, Y. Wada,
H. Nakashima and S. Yanagida, Angew. Chem., Int. Ed., 2000, 39,
357.
20 W. K. Wong, H. Liang, W. Y. Wong, Z. Cai, K. F. Li and K. W.
Cheah, New J. Chem., 2002, 26, 275.
21 (a) L. H. Slooff, A. Polman, M. P. Oude Wolbers, F. C. J. M. van
Veggel, D. N. Reinhoudt and J. W. Hofstraat, J. Appl. Phys., 1998,
83, 497; (b) L. H. Slooff, A. Polman, S. I. Klink, G. A. Hebbink,
L. Grave, F. C.J. M. van Veggel, D. N. Reinhoudt and J. W.
Hofstraat, Opt. Mater., 2000, 14, 101.
33 R. A. Ghiladi and K. D. Karlin, Inorg. Chem., 2002, 41, 2400.
34 W. K. Wong, L. L. Zhang, W. T. Wong, F. Xue and T. C. W. Mak,
J. Chem. Soc., Dalton Trans., 1999, 615.
35 W. Horrocks Dew, Jr., R. F. Venteicher, C. A. Spilburg and
B. L. Vallee, Biochem. Biophys. Res. Commun., 1975, 64, 317.
36 K. Kalyanasundaram, Photochemistry of Polypyridine and Porphyrin
Complexes, Academic Press, London, 1992, p. 376.
37 L. R. Milgrom, The Colours of Life: An Introduction to The
Chemistry of Porphyrins and Related Compounds, Oxford University
Press, Oxford, 1997, p. 85.
38 Q. Z. Ren, J. W. Huang, X. B. Peng and L. N. Ji, J. Mol. Cat. A:
Chem., 1999, 148, 9.
39 M. Gouterman, in The Porphyrins, ed. D. Dolphin, Academic Press,
New York, 1978, vol. III, ch. 1.
22 T. Yamamoto, N. Fukushima, H. Nakajima, T. Maruyama and
I. Yamaguchi, Macromolecules, 2000, 33, 5988.
23 N. V. Tkachenko, C. Guenther, H. Imahori, K. Amki, Y. Sakata,
S. Fukuzumi and H. Lemmetyinen, Chem. Phys. Lett., 2000, 326,
344.
40 F. A. Cotton, G. Wilkinson, C. A. Murillo and M. Bochmann,
Advanced Inorganic Chemistry, 6th edn., Wiley-Interscience,
New York, 1999, p. 1110.
41 H. S. He, Z. X. Zhao, J. P. Guo, W. K. Wong, K. F. Li and K. W.
Cheah, unpublished results.
24 A. Prodi, M. Indelli, M. T. Kleverlaan, J. Cornelis, F. Scandola,
E. Alessio, T. Gianferrara and L. G. Marzilli, Chem. Eur. J., 1999, 5,
2668.
25 R. A. Kipp, Y. Q. Li, J. A. Jerald and R. H. Schmehl, J. Photochem.
Photobiol. A, 1999, 121, 27.
26 C. P. Wong, R. F. Venteicher and W. D. Horrock, Jr., J. Am. Chem.
Soc., 1974, 96, 7149.
42 Y. Kawamura, Y. Wada and S. Yanagida, Jpn. J. Appl. Phys., 2001,
40, 350.
43 A. Beeby, I. M. Clarkson, R. S. Dickins, S. F. Aulkner, A. Parker,
L. Royle, A. S. de Sousa, J. A. G. Williams and M. Woods., J. Chem.
Soc., Perkin Trans. 2, 1999, 493.
44 C. A. Parker and W. T. Rees, Analyst (London), 1960, 85, 587.
45 K. Nakamaru, Bull. Chem. Soc. Jpn., 1982, 55, 2697.
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