Full text of DOI:10.1070/MC2002v012n04ABEH001638

Mendeleev Commun., 2002, 12(4), 151–152
Luminescence of ytterbium in binuclear bis(porphyrin) complexes
a
a
b
b
b
Yurii V. Korovin,* Natalia V. Rusakova, Zinaida I. Zhilina, Yurii V. Ishkov, Sergey V. Vodzinsky and
a
Vladimir P. Dotsenko
a
A. V. Bogatsky Physico-Chemical Institute, National Academy of Sciences of Ukraine, 65080 Odessa, Ukraine.
Fax: +38 0482 652 012; e-mail: physchem@paco.net
b
I. I. Mechnikov Odessa National University, 65026 Odessa, Ukraine. Fax: +38 0482 235 214; e-mail: jvi@te.net.ua
1
0.1070/MC2002v012n04ABEH001638
Binuclear complexes of ytterbium with four asymmetric bis(porphyrins) have been obtained, and their spectral and luminescence
properties have been investigated.
Ytterbium porphyrins are promising IR-luminescence probes in
Table 2 Luminescence characteristics of the binuclear bis(porphyrins)
1
,2
complexes of ytterbium (295 K).
biomedical practice. However, there is almost no data on
lanthanide complexes with covalently bound dimeric (or bis)
3
Position of
porphyrins. Synthetic dimeric porphyrins are good model sys-
Complexa
T-levels,
F×103 b
t/µsc
F t–1/10–3 s–1
tems for studying electron-transfer processes and the redox,
catalytic and optical properties of the porphyrin chromophore
–
1
E/cm
4
(Yb)2-1
12980
12950
12995
12960
12890
12935
12920
4.1
5.4
2.7
3.5
4.2
5.1
6.0
3.7
4.6
5.1
0.80
0.81
0.73
0.76
0.82
0.88
0.93
as a main constituent of important biological systems. We
(
(
(
Yb) -2
2
studied the spectral and luminescence properties of binuclear
ytterbium complexes with four asymmetric bis(porphyrins)
Yb) -3
2
Yb) -4
2
(
Figure 1). The synthesis of the complexes was described pre-
Yb-TPP
Yb-T3PyP
Yb-T4PyP
5
viously.
7.8
10.1
8.9
10.9
6
The complexes were prepared by a modified method through
the interaction of a 15 to 20-fold excess of Yb(acac) (acac is
3
aDMF solutions (c = 2×10–5 mol dm ). l = 425 nm; luminescence spectra
–3
b
exc
acetylacetone as an extra ligand) and free porphyrin base 1–4
in 1,2,4-trichlorobenzene on boiling under argon for 20–25 h
depending on porphyrin. The purity of the compounds was
c
were corrected with a standard lamp. Errors are ±10%.
nescence (F) of YbIII ions in complexes (Zn tetraphenyl-
porphyrin as a standard compound, F = 0.03 in ethanol) and
luminescence lifetime (t) were determined as described else-
1
controlled by UV, IR and H NMR spectroscopy. The com-
plexation with two metal centres was confirmed by the absorp-
tion spectra and elemental analysis data. The spectra of metal-
free porphyrins (Specord M40 UV-VIS spectrophotometer)
were characterised by the presence of an intense split Soret
band and four Q-bands (I–IV) (Table 1). The ratio of the inten-
sities of the Q-bands allowed us to assign these spectra to the
etio type: IV > III > II > I. It is known that the splitting (i.e., the
ratio between the intensities of short-wave and long-wave com-
ponents) of the Soret band in dimeric porphyrins can give
8
where.
The 4f luminescence of YbIII ions in the test complexes is
observed at 960–1010 nm (lmax = 980 nm, F ® F transi-
tion) on the excitation in a wide spectral range (~300–600 nm).
The highest efficiency was detected on excitation at the maximum
of the Soret band. The similarity of the excitation spectra of
the 4f luminescence of Yb in porphyrin complexes to their
absorption spectra [Figure 2, (Yb) –1 complex as an example]
indicates that ytterbium ions take energy from the organic
2
2
5/2
7/2
III
2
7
qualitative information on their structure. The above ratios in
the considered dimers are practically equal. This fact suggests
an isotropic (intermediate between parallel and perpendicular)
7
interlocation of porphyrins chromophores. Almost synchronous
changes in the spectra of all complexes were observed as com-
pared to the spectra of free bases. Thus, the spectra of complexes
consist of two Q-bands different in intensity and a broadened
Soret band with no splitting.
Luminescence was excited with a Xe-150 xenon lamp and
3+
a Nd :YAG laser (a SDL-1 spectrofluorimeter equipped with a
photon-counting system and an attachment for phosphorescence
measurements was used). The relative quantum yields of lumi-
Table 1 Absorption spectra of bis(porphyrins) 1–4 and their ytterbium
complexes in DMF solutions (c = 2×10–5 mol dm ).
–3
lmax/nm (log e)
Ligand/
Complex Soret
Q-bands
band
I
II
III
IV
1
419 (5.25)/ 646 (3.91) 590 (3.99) 550 (4.08) 514 (4.30)
25 (5.27)
423 (5.30)
419 (5.80)/ 646 (4.33) 591 (4.40) 550 (4.57) 515 (4.89)
26 (5.85)
424 (5.86)
414 (5.54)/ 645 (3.92) 589 (4.05) 549 (4.27) 514 (4.53)
27 (5.53)
426 (5.56)
415 (5.64)/ 644 (4.01) 588 (4.14) 548 (4.28) 513 (4.60)
26 (5.63)
423 (5.70)
4
(
Yb) -1
595 (426) 557 (4.72)
2
2
4
(
Yb) -2
598 (4.71) 559 (5.23)
2
3
4
(
Yb) -3
596 (4.42) 558 (4.90)
2
4
4
(
Yb) -4
597 (4.39) 558 (4.95)
2
Figure 1 Structure of the ligands.
–
151 –

Mendeleev Commun., 2002, 12(4), 151–152
9
methods for structurally similar complexes. Evidently, the dif-
ference in distances explains the higher luminescence charac-
teristics of p-phenylene derivatives. Note that analogous energy-
transfer processes were observed before in dinuclear lanthanide
complexes with p-tert-butylcalix[8]arene10 at almost the same
metal–metal distances. It should be noted that the value of F/t
indicates that the quantum efficiency of intramolecular energy
transfer in the test complexes is high (higher than that in Yb
3
2
1
0
.5
.5
.5
.5
8
crown-porphyrins ). The almost quenched molecular lumi-
nescence (manifested in non-metal porphyrins as two weakly
structured bands in the regions 610–645 nm and 690–720 nm)
proves this fact. Moreover, the quantum yields of the 4f lumi-
III
nescence of Yb ions and the luminescence lifetime are the
highest.11
2
References
1
M. I. Gaiduk, V. V. Grigoryants, A. F. Mironov, V. D. Rumyantseva,
V. I. Chissov and G. M. Sukhin, J. Photochem. Photobiol., 1990, 7, 15.
A. Beeby, R. S. Dickins, S. Fitzgerald, L. J. Govenlock, C. L. Maupin,
D. Parker, J. P. Riehl, G. Siligardi and J. A. Gareth Williams, Chem.
Commun., 2000, 1183.
1
2
400
500
l/nm
Figure 2 Electronic (1) absorption and (2) excitation spectra of (Yb) -1
600
3
A. G. Coutsolelos, G. K. Tsikalos, C. P. Raptopoulou and A. Terzis,
Abstracts of the 1st International Conference on Porphyrins and
Phthalocyanines, Dijon, 2000, p. 380.
2
–
5
–3
(
2×10 mol dm in DMF; lan = 980 nm).
4
5
6
7
8
9
The Porphyrin Handbook, eds. K. M. Kadish, K. M. Smith and
R. Guillard, Academic Press, New York, 1999, vol. 6.
Yu. V. Ishkov, Z. I. Zhilina and S. V. Vodzinsky, Zh. Org. Khim., 2000,
moiety of the complex molecule [the energies of the triplet
–
1
levels (T) of dimeric porphyrins are ~13000 cm ].
III
The characteristics of the 4f luminescence of Yb in the
complexes are given in Table 2. For comparison, data for
complexes with meso-tetraphenylporphyrin (TPP) and meso-
tetra[3(4)-pyridil]porphyrin (T3PyP and T4PyP) are given. The
data suggest that the luminescence in monomeric and dimeric
complexes is somewhat higher in p-pyridil derivatives [e.g.,
Yb–T4PyP, (Yb) –2, (Yb) –4] than in m-pyridil derivatives
3
6, 609 (Russ. J. Org. Chem., 2000, 26, 641).
C. P. Wong, R. F. Venteicher and W. de W. Horrocks, Jr., J. Am. Chem.
Soc., 1974, 96, 7149.
T. Nagata, A. Osuka and K. Maruyama, J. Am. Chem. Soc., 1990, 112,
3054.
Yu. Korovin, Z. Zhilina, N. Rusakova, V. Kuz’min, S. Vodzinsky and
Yu. Ishkov, J. Porphyrins Phthalocyanines, 2001, 5, 481.
S. Eriksson, B. Källebring, S. Larsson, J. Martensson and O. Wennerström,
Chem. Phys., 1990, 146, 165.
2
2
[
e.g.,Yb–T3PyP, (Yb) –1, (Yb) –3]. However, we believe that
2 2
the fact that 4f luminescence efficiency in dimers is somewhat
lower than that in monomeric complexes is more important.
The reason is the resonance Yb–Yb interaction, which manifests
itself in spite of a rather long distance between two lanthanide
centres. With the use of molecular mechanics calculations (the
1
1
0 P. Froidevaux and J. C. G. Bünzli, J. Phys. Chem., 1994, 98, 532.
1 M. P. Tsvirko, S. B. Meskova, V. Ya. Venchikov and D. V. Bolshoi,
Opt. Spektrosk., 1999, 87, 950 (in Russian).
+
MM method, the HYPERCHEM 5.1 program) we found that
the Yb–Yb distance in m-phenylene derivatives (Yb) –3 and
2
(
Yb) –4 is equal to 10.8±0.1 Å. The Yb–Yb distance in p-phe-
2
nylene derivatives (Yb) –1 and (Yb) –2 is 12.0±0.1 Å. These
results are in good agreement with data obtained by other
2
2
Received: 12th July 2002; Com. 02/1964
–
152 –