Angewandte
Chemie
tBu
protonated ligand H {(PyrO) tacn} was characterized by X-
lanthanide complexes [{( ArO) tacn}Ln] (Ln = Sm, Eu,
Lu).
3
3
3
1
13
[6a]
ray diffraction analysis and H NMR, C NMR, UV/Vis, and
luminescence spectroscopy (Figures S1–S3 in the Supporting
Information). In luminescent lanthanide complexes, energy
levels of the lowest singlet and triplet ligand-centered excited
states are crucial factors determining the photoinduced
properties and can be estimated by measuring the photo-
physical properties of the gadolinium(III) complexes with the
Figure 3a displays the UV/Vis absorption spectrum of 1 in
THF at room temperature. The absorption bands at 288, 366,
384, and 405 nm (e = 8.90 ꢀ 10 , 7.27 ꢀ 10 , 8.38 ꢀ 10 , 10.35 ꢀ
4
4
4
[6h,11]
newly developed ligands.
Reaction of H {(PyrO) tacn} with Gd(OTf) in acetone/
3
3
3
THF at room temperature led to the formation of the
gadolinium(III) complex 1 as a yellow powder (76%,
Scheme 1, see the Supporting Information).
Yellow crystals suitable for X-ray diffraction analysis were
grown from a saturated THF/AcOEt solution of 1 at room
temperature. The obtained crystals consist of four complexes
1, five THF molecules, and three AcOEt molecules per
asymmetric unit. The solid-state molecular structure of one of
the four crystallographically independent complexes 1 in the
crystals of 41·5THF·3AcOEt is depicted in Figure 2. The
trivalent gadolinium ion in 1 is coordinated by three nitrogen
and four oxygen atoms. The coordination polyhedron of the
seven-coordinate gadolinium ion can be described as face-
capped octahedron, in which the oxygen atom of THF caps
the triangular face formed by the oxygen atoms of the
3
ꢀ
{
(PyrO) tacn} ligand. The observed geometry of 1 is similar
3
ꢀ
6
Figure 3. a) UV/Vis absorption spectrum of 1 (7.0ꢀ10 m). b) Cor-
to that of the reported trivalent uranium complex with an
ꢀ7
tBu
rected luminescence spectra of 1 (3.1ꢀ10 m) in nondegassed (blue)
and degassed (red) THF at room temperature (l =285 nm).
N O3 hexadentate trianionic ligand [{( ArO) tacn}U-
3
3
[
6f]
tBu
3ꢀ
ex
(
CH CN)]
({( ArO) tacn} = {(CH tBu C H O) -
3 2 2 6 2 3
3
3
ꢀ
C H N } ) rather than those of the corresponding trivalent
6
12
3
4
ꢀ1
ꢀ1
1
0 m cm , respectively) are mainly corresponding to the
p!p* transition of the hydroxypyrenato moieties. The
absorption bands are slightly red-shifted relative to those of
H {(PyrO) tacn} (Figure S2 in the Supporting Information).
3
3
[
7]
Under the excitation of 1 at l < 405 nm, blue emission
ex
was observed in nondegassed THF at room temperature
Figure 3b, blue). Owing to the small Stokes shift and short
emission lifetime (t), the blue emission can be assigned to the
(
max
fluorescence from an intraligand excited state (lem
4
=
[
12,13]
12 nm, t < 50 ms, quantum yield (F) = 0.01; Figure S3).
[7]
Surprisingly, continuous irradiation of 1 at l < 405 nm
irr
induces a change of the emission color from blue to red at
room temperature. The obtained spectrum (Figure S4 in the
Supporting Information, black dots), in which the original
max
fluorescence band (lem = 412 nm) is still observed with the
same F, is identical to the emission spectrum of 1 in degassed
THF at room temperature (Figure 3b, red). The red color
originates mainly in a new emission band from 600 to 850 nm
max
(
lem = 625 nm, t = 430 ms, F = 0.12; Figure S5 in the Sup-
porting Information). The red emission is quenched by O and
2
goes back to the blue fluorescence only. On the basis of these
results, the photoinduced red emission can be assigned to the
Figure 2. An ORTEP drawing of gadolinium(III) complex 1. One of the
four independent complexes in the crystals of 41·5THF·3AcOEt is
shown. Hydrogen atoms and cocrystallized solvent molecules (THF
and AcOEt) are omitted for clarity; thermal ellipsoids are at the 50%
probability level. Selected bond distances [ꢁ] and angles [8]: Gd1–
N1=2.555(4), Gd1–N2=2.621(3), Gd1–N3=2.604(4), Gd1–O1=
[
13]
phosphorescence from an intraligand excited state.
The
excitation spectra monitored at 460 and 625 nm (fluorescence
and phosphorescence, respectively) are identical to the
absorption spectrum of 1 (Figure S6a and S6b in the
Supporting Information). Thus, the luminescence photo-
chromism is based on the fluorescence and room-temperature
2
.216(3), Gd1–O2=2.189(3), Gd1–O3=2.219(3). Gd1–O4=2.447(3),
N1-Gd1-N2=68.40(9), N1-Gd1-N3=68.58(11), N2-Gd1-N3=
6
6.56(11), O1-Gd1-O2=111.08(11), O1-Gd1-O3=118.34(9), O2-Gd1-
[
18]
3+
O3=115.01(11).
phosphorescence of 1. The heavy-atom effect of the Gd ion
Angew. Chem. Int. Ed. 2013, 52, 8722 –8725
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8723