Reversible luminescence modulation in photochromic europium(III) complex having triangle terthiazole ligands

Article abstract of DOI:10.1246/cl.2007.372

Luminescent Eu^III complex having photochromic ligand is synthesized, and its reversible control of the luminescent properties based on photochromic reaction was demonstrated. Copyright

Full text of DOI:10.1246/cl.2007.372

3
72
Chemistry Letters Vol.36, No.3 (2007)
Reversible Luminescence Modulation in Photochromic Europium(III) Complex
Having Triangle Terthiazole Ligands
ꢀ
ꢀ
Tetsuya Nakagawa, Kazuhiko Atsumi, Takuya Nakashima, Yasuchika Hasegawa, and Tsuyoshi Kawai
Graduate School of Materials Science, Nara Institute of Science and Technology,
8916-5 Takayama, Ikoma 630-0192
(Received November 29, 2006; CL-061407; E-mail: hasegawa@ms.naist.jp; tkawai@ma.naist.jp)
Luminescent EuIII complex having photochromic ligand is
synthesized, and its reversible control of the luminescent proper-
ties based on photochromic reaction was demonstrated.
with a photochromic unit, tris(hexafluoroacetylacetonato)-
bis[4,5-bis(5-methyl-2-phenylthiazolyl)-2-phenylthiazole]euro-
pium(III), [Eu(HFA)3(THIA)2] (2a) was synthesized with a
photochromic ligand, 4,5-bis(5-methyl-2-phenyltiazolyl)-2-
phenylthiazole (THIA, 1a), which is an analogue of photochro-
5
Development of luminescent molecule is an active area of
1
mic triangle-terthiophene. The reversible luminescent control
III
photofunctional material chemistry. Especially, the construc-
III
of the Eu complex based on the photochromic reaction is
successfully demonstrated.
tion of photofunctionalized lanthanide(III) (Ln ) complexes
showing strong luminescence is currently of great interest be-
cause of their characteristic luminescence with narrow emission
band and ideal four level transitions. These characteristic prop-
erties of the lanthanide(III) complexes allow them to be the prac-
tical candidate for various applications in organic laser, lumines-
THIA, 1a was prepared by cross-coupling reaction of 4,5-
dibromo-2-phenylthiazole and 5-methyl-2-phenyl-4-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolane-2-yl)thiazole. 1a was purified
by column chromatography (alumina, hexane:ethyl acetate =
10:1) and recrystallized from hexane. The molecular structure
2
1
cent displays and plastic optical devices. The reversible change
III
of 1a was characterized by H NMR, ESI-Mass, and X-ray struc-
6
of the luminescence properties of Ln complex may open some
unique photonic applications such as a photoswitching laser and
luminescent devices. In the present paper, we study on a lumi-
ture analysis. Detailed photochromic properties will be reported
5
b
elsewhere. [Eu(HFA)3(THIA)2] (2) was prepared by reaction
7
of [Eu(HFA)3(H2O)2] with 1a in methanol/chloroform mixed
solution under reflux. Obtained powder was washed with chloro-
III
nescent Ln complex having photochromic molecule as a pho-
III
toresponsive ligand for reversible change of Ln luminescence.
Photochromic molecules have been widely studied as photo-
switching units for controlling various properties of molecules
form and hot hexane for several times. 2a was also characterized
1
8
by H NMR, ESI-Mass, IR, and elemental analysis. The coordi-
III
nation of 1a to Eu ion was confirmed by the chemical shifts
1
3
and polymers. The fluorescence of photochromic transition-
metal complexes has also been modulated by changes of the
and broadening of the H NMR signals of 2a. From elemental
III
analysis and ESI-Mass spectroscopy, the Eu complex 2a was
determined to be [Eu(HFA)3(THIA)2]. The emission quantum
yield of 2a excited at 465 nm was determined by standard proce-
4
MLCT energy levels of the complexes. In order to realize rever-
III
sible control of Ln luminescence, we designed novel photo-
chromic terarylene derivative as the photoresponsive ligand with
7
dure with an integrating sphere. The emission lifetime was de-
5
a
relatively high photochromic performance as a photo-switch-
ing unit. The colored closed-ring isomers of terarylene deriva-
tives show characteristic absorption band at around 600 nm.
termined by using a Nd:YAG laser and a dye laser (coumarin
460: ꢀex ¼ 465 nm) as the pulsed excitation light source.
Colorless solution of open-ring isomer 1a turned blue upon
irradiation with UV light (ꢀ ¼ 365 nm). The blue color disap-
peared after irradiation with visible light (ꢀ > 440 nm). 1a
showed no absorption band in visible range, and a new absorp-
tion band appeared at 591 nm upon irradiation with UV light,
which corresponds to the formation of 1b (closed-ring isomer).
III
III
Therefore, the luminescence of Ln , especially Eu , is expect-
ed to be efficiently quenched when the photochromic unit is
converted from the colorless open-ring form to the closed-ring
form upon UV light irradiation, resulting in change of the
emission intensity.
In this letter, luminescent LnIII complex having photochro-
1
1b was isolated by HPLC and characterized by H NMR meas-
6
III
mic ligand is reported for the first time. An Eu complex
urements.
Absorption spectral change of 2a upon irradiation with UV
light (ꢀ ¼ 365 nm) are shown in Figure 1. Photochromic behav-
ior of 2a is similar to that of ligand 1a. A new absorption band
and an isosbestic point were observed at 591 and 330 nm for the
photochromic reactions of 2, which coincided with those of 1a.
UV
S
N
S N
N
N
Vis
N
N
S
S
S
S
1
1
a
1b
In the H NMR measurement, signals of free photochromic
ligand (both open-ring isomer 1a and closed-ring isomer 1b)
were not observed after irradiation with UV light at 365 nm.
Similar photochromic behavior was also observed in PMMA
film. These results indicate the formation of 2b without dissoci-
ation of the photochromic ligands, 1a nor 1b. Because of char-
acteristic feature of lanthanide(III) complex, optical properties
of organic ligands in the complex roughly coincide with those
of the free ligands. One may evaluate maximum conversion of
S
S
N
CF3
CH
N
CF3
CH
N
N
UV
Vis
N
O
O
O
S
Eu(III)
S
Eu(III)
O
N
S
CF3
S
CF3
3
3
2
2a
2
2b
Scheme 1.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.3 (2007)
373
cant in comparison with that at 592 nm (modulation efficien-
cy = 64%). Since both emission lines originate from the same
(
a)
5
excited state D0, the change in the emission profile would be
attributed to not only the energy-transfer quenching, but to
change in the symmetry of the coordination structure around
III
the Eu center, which will be discussed in detail elsewhere.
A large change in emission intensity at the photostationary
state was not observed with continuous irradiation of 465 nm,
where both bleached and colored ligands scarcely absorb the
irradiation light. The low photochromic sensitivity against the
excitation light leads to quasi-nondestructive read-out capabili-
1
1
ty as the optical recording materials. The photochromic lantha-
nide complex is expected to be a novel photofunctional molecule
with unique photoswitching properties.
(
b)
References and Notes
1
G. Blasse, B. C. Grabmaier, in Luminescent Materials,
Spring-Verlag, New York, 1994.
2
a) J. Kido, H. Hayase, K. Hongawa, K. Nagai, K. Okuyama,
Appl. Phys. Lett. 1994, 65, 2124. b) Y. Hasegawa, M.
Yamamuro, Y. Wada, N. Kanehisa, Y. Kai, S. Yanagida, J.
Phys. Chem. A 2003, 107, 1697.
3
a) T. Koshido, T. Kawai, K. Yoshino, Synth. Met. 1995, 73,
257. b) G. M. Tsivgoulis, J. M. Lehn, Angew. Chem., Int. Ed.
Engl. 1995, 34, 1119. c) T. Kawai, T. Sasaki, M. Irie, Chem.
Commun. 2001, 711. d) T. B. Norsten, N. R. Branda, J. Am.
Chem. Soc. 2001, 123, 1784. e) M. Irie, T. Fukaminato,
T. Sasaki, N. Tamai, T. Kawai, Nature 2002, 420, 759.
f) T. Fukaminato, T. Sasaki, T. Kawai, N. Tamai, M. Irie,
J. Am. Chem. Soc. 2004, 126, 14843.
ꢂ4
Figure 1. (a) Absorption (concn: 1:4 ꢁ 10 M, optical path
length: 1 mm, intervals of the measurements: 30 s) and (b) emis-
sion spectral changes of [Eu(HFA)3(THIA)2] under irradiation
ꢂ3
with 365 nm light in dioxane. (concn: 1:2 ꢁ 10 M, optical path
length: 1 mm, intervals of the measurements: 2 s) 7F0– D2
5
(
465 nm) was excited for the luminescence measurements. Inset:
reversible change of the emission intensity at 614 nm with the
alternative irradiation cycles of UV ( ) and visible ( ) light.
4
a) B. Z. Chen, M. Z. Wang, Y. Q. Wu, H. Tian, Chem. Com-
mun. 2002, 1060. b) V. W.-W. Yam, C.-C. Ko, N. Zhu,
J. Am. Chem. Soc. 2004, 126, 12734. c) P. Belser, L.
De Cola, F. Hartl, V. Adamo, B. Bozic, Y. Chriqui, V. M.
Iyer, R. T. F. Jukes, J. Kuhni, M. Querol, S. Roma, N.
Salluce, Adv. Funct. Mater. 2006, 16, 195.
the coordinating ligand under UV (365 nm) light irradiation to
be about 70% under assumption of same extinction coefficient
III
of the coordinating 1b in the colored Eu complex at the photo-
stationary state as that of free 1b. We, thus, expect 2b,
[
Eu (HFA)3(1b)2] as well as [Eu(HFA)3(1b)(1a)] as the colored
photoproducts.
In order to characterize the luminescence modulation in
5
6
a) T. Kawai, T. Sasaki, M. Irie, Chem. Commun. 2004, 72.
b) T. Nakashima, K. Atsumi, S. Kawai, T. Nakagawa, Y.
Hasegawa, T. Kawai, in contribution.
III
Eu complexes, the emission spectra shown in Figure 1b were
7
1
1a: H NMR (300 MHz, CDCl3) ꢁ 2.11 (s, 3H), 2.52 (s, 3H),
5
III
measured under excitation at 465 nm ( F0– D2: excited at Eu
ion), at this wavelength absorbance is less than 0.1 even in the
7
.33 (m, 3H), 7.43 (m, 6H), 7.80 (m, 2H), 7.93 (m, 2H), 8.07
1
þ
(m, 2H). ESI-Mass (m=z) 508.1 (M + H). 1b: H NMR
300 MHz, CDCl3) ꢁ 2.10 (s, 3H), 2.12 (s, 3H), 7.50 (m,
9
colored state. The emission bands were observed at 579, 592,
5
(
7
5
and 614 and are attributed to the f–f transitions D0– F0, D0–
9
H), 7.92 (m, 2H), 8.05 (m, 4H).
7
5
7
F1, D0– F2, respectively. The emission quantum yield and
the emission lifetime of 2a excited at 465 nm were found to be
7
8
a) Y. Hasegawa, Y. Kimura, K. Murakoshi, Y. Wada, J.-H.
Kim, N. Nakashima, T. Yamanaka, S. Yanagida, J. Phys.
Chem. 1996, 100, 10201.
3
.6% and 0.4 ms, respectively.
III
The emission of the Eu complex was suppressed after UV
2a: Anal. Found: C, 48.32; H, 2.70; N, 4.76%. Calcd. for
.
light irradiation as also shown in Figure 1b. The emission inten-
sity at the photostationary state (614 nm) was about 30% of
the original intensity. The reversible changes in emission inten-
sity at 614 nm with the alternative irradiation cycles of UV
C73H45N6O6S6F18Eu H2O: C, 48.54; H, 2.62; N, 4.65%.
1
H NMR (300 MHz, CDCl3) ꢁ 2.11 (s, 3H), 2.53 (s, 3H),
7
.42 (m, 9H), 7.80–8.10 (m, 6H). ESI-Mass (m=z) 1581.07
þ
(
M ). IR (KBr) 3421 w, 3062 m, 3024 m, 1654 s, 1558 m,
¼ 7:4 ꢁ
(
ꢀ ¼ 365 nm) and visible light (ꢀ > 440 nm) are shown in
1531 m, 1475 s, 1255 s, 1205 s, 1146 s. "
3
15nm
4
ꢂ1
ꢂ1
Figure 1 (inset). The emission intensity change with the photo-
chromic reactions can be repeated for many times reversibly.
The quenching effect in the colored state seems to be attributed
10 M cm .
Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa, Y. Kai,
9
S. Yanagida, J. Phys. Chem. A 2003, 107, 1697.
10 P. R. Selvin, T. M. Rana, J. E. Hearst, J. Am. Chem. Soc.
1994, 116, 6029.
11 E. Murguly, T. B. Norsten, N. R. Branda, Angew. Chem., Int.
Ed. 2001, 40, 1752.
5
to the resonance energy transfer from the D0 excited state to the
1
0
ligand in the colored closed-ring form. It should also be noted
that the decrease in the emission intensity at 614 nm of the col-
ored state (modulation efficiency = 70%) is much more signifi-
Published on the web (Advance View) February 3, 2007; doi:10.1246/cl.2007.372