Up-conversion luminescent switch based on photochromic diarylethene and rare-earth nanophosphors

Article abstract of DOI:10.1039/b809021a

We have demonstrated a novel and unique route to a highly efficient luminescent switch with nondestructive readout capability by utilizing photochromic diarylethene and up-conversion LaF₃:Yb,Ho nanophosphors. The Royal Society of Chemistry.

Full text of DOI:10.1039/b809021a

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Up-conversion luminescent switch based on photochromic diarylethene
and rare-earth nanophosphorsw
Zhiguo Zhou, He Hu, Hong Yang, Tao Yi,* Kewei Huang, Mengxiao Yu,
Fuyou Li* and Chunhui Huang
Received (in Cambridge, UK) 28th May 2008, Accepted 7th July 2008
First published as an Advance Article on the web 12th August 2008
DOI: 10.1039/b809021a
We have demonstrated a novel and unique route to a highly
efficient luminescent switch with nondestructive readout capabi-
lity by utilizing photochromic diarylethene and up-conversion
LaF3:Yb,Ho nanophosphors.
light into emission at visible wavelengths via the sequential
absorption of two or more low energy photons.7 Different
colours of visible light can be obtained from different up-
conversion nanophosphors when excited by the same IR
laser.8 Compared with the conventional down-conversion
luminescent materials, UCNPs show very low background
fluorescence, minimal photo damage, deep penetration and
so on. In addition, UCNPs generate large anti-Stokes shifts of
up to 500 nm, which results in well-separated emission and
excitation bands. For this reason they have already recently
received significant attention for possible uses in bioassay and
bioimaging.9 Recently, our group reported a versatile syn-
thetic strategy for carboxylic acid-functionalized UCNPs and
applied it as a highly sensitive DNA sensor.10 In the present
paper, we have employed a DTE derivative (compound 1,11
Scheme 1) in LaF3:Yb,Ho loaded poly(methyl methacrylate)
(PMMA) film, and demonstrated an up-conversion lumines-
cent switch by an intermolecular energy transfer process12
from UCNPs to the closed state of 1.
Photochromic materials such as spiropyrans, fulgides and
azobenzenes have recently attracted significant attention from
both the fundamental and practical points of view for their
potential applications as optical memory devices and
switches.1 Diarylethene derivatives (DTEs) are the most pro-
mising candidates because of their notable irreversible thermal
photochromic behaviour, high photoisomerization quantum
yields and outstanding fatigue resistance.2 For practical ap-
plications in high density data storage systems, nondestructive
readout capability is indispensable. So far, several attempts
have been made to achieve this. In general, the objective is the
synthesis of photochromic materials with a gated photochro-
mic system in which two different kinds of stimuli such as
thermal–optical, magneto–optical or electrical–optical can
read the memory non-destructively.3 Another approach is to
use the readout light which should not induce any photo-
chromic reactions.4 Among various types of signal outputs
such as fluorescence, infrared, refractive index, electric con-
ductance and so on, fluorescent emission is one of the most
promising signal modes owing to its high sensitivity, high
resolution and high contrast. Many different classes of fluo-
rescent DTEs have been obtained in which fluorescent chro-
mophores are covalently attached to DTEs5 or doped in the
polymer films of DTEs.6 It is a requirement that DTEs (in
both the open and closed states) should have zero absorbance
at the fluorescence excitation wavelength, so generating no
photochromic reactions during the fluorescence readout pro-
cess. Despite this simple strategic principle for the nondestruc-
tive readout process, few suitable material systems have been
found so far due to the inherent limitation of the Stokes’ shift
in conventional fluorescent fluorophores.
The LaF3:Yb,Ho was synthesized by a modified hydrother-
mal process.13 These nanophosphors have been characterized
by transmission electron microscopy (TEM) and powder
X-ray diffraction (XRD) analyses. The representative TEM
image of the as-prepared LaF3:Yb,Ho clearly showed very
uniform nanocrystals, with an average diameter of about
30 nm (Fig. 1). From the powder X-ray diffraction pattern
(Fig. S1 in ESIw), we can see that the as-prepared Yb/Ho co-
doped LaF3 nanocrystals displayed the pure hexagonal LaF3
phase (JCPDS card 72-1435). LaF3:Yb,Ho also has high
crystallinity, contributing to the strong luminescence.
1 underwent a reversible photocyclization reaction under
alternating illumination by ultraviolet and visible light, dis-
playing a new absorption band centred at 560 nm in THF
solution.11 The hybrid system 1/LaF3:Yb,Ho loaded into
PMMA film performed a reversible photochromic reaction
similar to that of the isolated species 1. The open form of 1 on
the film showed an absorption located at 340 nm. Upon
irradiation by UV light (365 nm), a new absorption band
centred at 560 nm appeared in a photostationary state (PSS,
Fig. 2). On the other hand, the PSS converted to the open-ring
form upon irradiation with visible light of wavelength greater
than 450 nm.
Up-conversion rare-earth nanophosphors (UCNPs) consist-
ing of certain lanthanide dopants embedded in a crystalline
host lattice can convert low energy near-infrared excitation
Department of Chemistry & Laboratory of Advanced Materials,
Fudan University, Shanghai, 200433, PR China.
E-mail: yitao@fudan.edu.cn. E-mail: fyli@fudan.edu.cn;
Fax: +86-21-55664621; Tel: +86-21-55664185
w Electronic supplementary information (ESI) available: Experimental
details and XRD profiles. See DOI: 10.1039/b809021a
The up-conversion luminescence of 1/LaF3:Yb,Ho-loaded
PMMA film pumped with 980 nm diode lasers shows a green
colour (Fig. 2 inset), with the emission peaks mainly located at
540 and 645 nm, corresponding to energy transfer from the
ꢀc
This journal is The Royal Society of Chemistry 2008
4786 | Chem. Commun., 2008, 4786–4788

View Article Online
Scheme 1 Principle and confocal luminescence images of the up-conversion luminescent switch consisting of 1/LaF3:Yb,Ho-loaded PMMA film.
Before (left), and after (right) irradiation with 365 nm light for 30 min, lex = 980 nm.
absorbance in the near-infrared region, so this nondestructive
up-conversion luminescent switch process, excited by
near-infrared light (980 nm), is performed perfectly. This is
confirmed by the confocal luminescence images of
1/LaF3:Yb,Ho-loaded PMMA film before and after UV light
irradiation (Scheme 1).
To make the intermolecular energy transfer process in
PMMA film more effective, the ratio of 1 to LaF3:Yb,Ho was
optimized. The up-conversion luminescence spectra of
1/LaF3:Yb,Ho-loaded PMMA films were measured after the
photochromic reaction, with the weight of LaF3:Yb,Ho fixed
and that of 1 was varied. As shown in Fig. 3(a), upon irradiation
with UV light, the up-conversion luminescent intensity at
Fig. 1 TEM image of LaF3:Yb,Ho.
Fig.
2 UV-visible absorption spectra of 1/LaF3:Yb,Ho-loaded
PMMA film before (dashed line) and after (solid line) irradiation with
365 nm light for 30 min, and the normalized up-conversion lumines-
cence spectra of the prepared film (dotted line, lex = 980 nm). Inset
shows the image of the up-conversion emission of the film.
5
5
5
excited states S2 and F5 to the ground state I8, respectively
(Fig. 2).14 It is obvious that the up-conversion luminescence of
LaF3:Yb,Ho significantly overlaps the absorption band of the
PSS of 1 (Fig. 2) and therefore can be effectively quenched by
the PSS of 1 through an intermolecular energy transfer
process12 from UCNPs (energy donor) to the closed state of
1 (energy acceptor) upon irradiation with UV light. Scheme 1
shows the fundamental principle of the up-conversion lumi-
nescent switch. What is more important is that 1 has zero
Fig. 3 (a) Up-conversion luminescence spectra of 1/LaF3:Yb,Ho loaded
PMMA films in the PSS with different weight ratio of 1 to LaF3:Yb,Ho
(1 : UCNP = 0 : 1, 1 : 4, 1 : 2, 1 : 1, 1.5 : 1, 2 : 1, 3 : 1 and
4 : 1, respectively). Inset graph shows the change of up-conversion
luminescence at 540 nm as a function of weight ratio of 1 to LaF3:Yb,Ho;
(b) Up-conversion luminescence spectra of 1/LaF3:Yb,Ho (4 : 1) loaded
PMMA film after different irradiation times with 365 nm light
(time interval: 0, 5, 10, 20, 40, 60, 120, 240, 360, 600, 1200, 1800 s,
lex = 980 nm).
ꢀc
This journal is The Royal Society of Chemistry 2008
Chem. Commun., 2008, 4786–4788 | 4787

View Article Online
High Technology Program of China (2006AA03Z318), and
Shanghai Leading Academic Discipline Project (B108).
Notes and references
1 (a) B. L. Feringa, Molecular Switches, Wiley-VCH, 2001; M. Irie,
Chem. Rev., 2000, 100, 1685–1716; (b) Y. Yokoyama, Chem. Rev.,
2000, 100, 1741–1754; (c) F. M. Raymo and M. Tomasulo, Chem.
Soc. Rev., 2005, 34, 327–336; (d) W. F. Yuan, L. Sun, H. H. Tang,
Y. Q. Wen, G. Y. Jiang, W. H. Huang, L. Jiang, Y. L. Song, H.
Tian and D. B. Zhu, Adv. Mater., 2005, 17, 156–160.
2 (a) H. Tian and S. G. Yang, Chem. Soc. Rev., 2004, 33, 85–97; (b)
S. Kawata and Y. Kawata, Chem. Rev., 2000, 100, 1777–1788; (c)
M. Irie, S. Kobatake and M. Horichi, Science, 2001, 291,
1769–1772; (d) M. Irie, T. Fukaminato, T. Sasaki, N. Tamai and
T. Kawai, Nature, 2002, 420, 759–760; (e) K. Uchida, M. Saito, A.
Murakami, T. Kobayashi, S. Nakamura and M. Irie, Chem.–Eur.
J., 2005, 11, 534–542.
3 (a) T. Tsujioka, Y. Hamada, K. Shibata, A. Taniguchi and T.
Fuyuki, Appl. Phys. Lett., 2001, 78, 2282–2284; (b) K. Uchida, M.
Saito, A. Murakami, S. Nakamura and M. Irie, Adv. Mater., 2003,
15, 121–125; (c) J. Areephong, W. R. Browne, N. Katsonis and B.
L. Feringa, Chem. Commun., 2006, 3930–3932.
Fig. 4 Nondestructive readout capability of 1/LaF3:Yb,Ho-loaded
PMMA film in the open state (&) and in the PSS state (’), lex
980 nm. Inset graph shows the modulated up-conversion luminescence
intensity at 540 nm of the PMMA film during alternating UV and visible
light irradiation.
=
540 nm decreased as the proportion of 1 increased. The up-
conversion luminescent intensity levelled off when the ratio was
above 3 : 1. The maximum difference of up-conversion lumines-
cent intensity before and after UV irradiation was up to a factor
20, which is a sufficiently high contrast for information storage
with luminescence mode. In addition, the change of up-conver-
sion luminescent intensity at 540 nm with variation of irradia-
tion time by UV light was also investigated on a film of
1/LaF3:Yb,Ho (4 : 1). After irradiation for 30 min, the
up-conversion luminescent spectra remained stable.
4 (a) S. J. Lim, J. W. Seo and S. J. Park, J. Am. Chem. Soc., 2006,
128, 14542–14547; (b) G. Y. Liang, S. Wang, W. F. Yuan, L. Jiang,
Y. L. Song, H. Tian and D. B. Zhu, Chem. Mater., 2006, 18,
235–237; (c) C. C. Corredor, Z. L. Huang and K. D. Belfield, Adv.
Mater., 2006, 18, 2910–2914; (d) S. Z. Xiao, Y. Zhou, M. X. Yu, T.
Yi, Y. F. Zhou, F. Y. Li and C. H. Huang, Chem. Commun., 2007,
4758–4760; (e) S. L. Lim, B. K. An and S. Y. Park, Macromole-
cules, 2005, 38, 6236–6239; (f) T. Nakagawa, K. Atsumi, T.
Nakashima, Y. Hasegawa and T. Kawai, Chem. Lett., 2007, 36,
372–373.
5 (a) V. W. W. Yam, C. C. Ko and N. Y. Zhu, J. Am. Chem. Soc.,
2004, 126, 12734–12735; (b) T. A. Golovkova, D. V. Kozlov and
D. C. Neckers, J. Org. Chem., 2005, 70, 5545–5549; (c) M. Bossi, V.
Belov, S. Polyakova and S. W. Hell, Angew. Chem., Int. Ed., 2006,
45, 7462–7465; (d) J. Folling, S. Polyakova, V. Belov, A.
Blaaderen, M. L. Bossi and S. W. Hell, Small, 2008, 4, 134–142.
6 (a) S. Murase, M. Teramoto, H. Furukawa, Y. Miyashita and K.
Horie, Macromolecules, 2003, 36, 964–966; (b) D. V. Kozlov and F.
N. Castellano, J. Phys. Chem. A, 2004, 108, 10619–10622; (c) Y.
Chen and N. Xie, J. Mater. Chem., 2005, 15, 3229–3232.
7 F. Auzel, Chem. Rev., 2004, 104, 139–173.
8 (a) E. Downing, L. Hesselink, J. Ralston and R. Macfarlane,
Science, 1996, 273, 1185–1189; (b) S. Heer, O. Lehmann, M. Haase
and H. U. Gudel, Angew. Chem., Int. Ed., 2003, 42, 3179–3182; (c)
S. Heer, K. Kompe, H. U. Gudel and M. Haase, Adv. Mater.,
2004, 16, 2102–2104; (d) O. Ehlert, R. Thomann, M. Darbandi and
T. Nann, ACS Nano, 2008, 2, 120–124.
9 (a) F. V. Rijke, H. Zijlmans, S. Li, T. Vail, A. K. Raap, R. S.
Niedbala and H. J. Tanke, Nat. Biotechnol., 2001, 19, 273–276; (b)
L. Y. Wang, R. X. Yan, Z. Y. Huo, L. Wang, J. H. Zeng, J. Bao,
X. Wang, Q. Peng and Y. D. Li, Angew. Chem., Int. Ed., 2005, 44,
6054–6057; (c) L. Y. Wang and Y. D. Li, Chem. Commun., 2006,
2557–2558; (d) S. F. Lim, W. S. Ryu, N. Khanarian, C. K. Tung,
D. Tank and R. H. Austin, Nano Lett., 2006, 6, 169–174.
10 Z. G. Chen, H. L. Chen, H. Hu, M. X. Yu, F. Y. Li, Q. Zhang, Z.
G. Zhou, T. Yi and C. H. Huang, J. Am. Chem. Soc., 2008, 130,
3023–3029.
As shown in Fig. 4 inset, the up-conversion luminescent
switch had good reversibility with alternating UV (365 nm)
and visible light (4450 nm) irradiation for many cycles. The
reversible changes can be used in a repeated ‘‘write-erase’’
process. To investigate its nondestructive readout capability,
1/LaF3:Yb,Ho-loaded PMMA film was continuously irra-
diated by the 980 nm diode laser. The strong irradiation of
980 nm (800 mw) induced no discernible changes of up-
conversion luminescence both in the ‘‘switch on’’ and ‘‘switch
off’’ state. After irradiation with the 980 nm laser for 48 h, the
increase of up-conversion luminescence was less than 2%
when 1 was in the open form, and the decrease was less than
1% when 1 was in the photostationary state. This is attributed
to the negligible absorbance of 1 at 980 nm in both the open
and PSS states. Thus, the present system affords a good
example of nondestructive readout capability.
In summary, by combination of the organic photochromic
DTE and upconversion LaF3:Yb,Ho nanophosphors,
a
hybrid switchable system has been obtained. Because DTE
has negligible absorbance at 980 nm in both the open form and
the PSS, whereas LaF3:Yb,Ho nanophosphors can emit visible
luminescence by excitation at 980 nm due to the large anti-
Stokes’ shift, a novel and unique route to a highly efficient
nondestructive optical memory can be developed in this DTE/
LaF3:Yb,Ho hybrid nanosystem via an intermolecular energy
transfer process.
11 Z. G. Zhou, H. Yang, M. Shi, S. Z. Xiao, F. Y. Li, T. Yi and C. H.
Huang, ChemPhysChem, 2007, 8, 1289–1292.
12 (a) P. Zhang, S. Rogelj, K. Nguyen and D. Wheeler, J. Am. Chem.
Soc., 2006, 128, 12410–12411; (b) K. Kuningas, T. Rantanen, T.
Ukonaho, T. Lovgen and T. Soukka, Anal. Chem., 2005, 77,
7348–7355; (c) K. Kuningas, T. Ukonaho, H. Pakkila, T.
Rantanen, J. Rpsenberg, T. Lovgen and T. Soukka, Anal. Chem.,
2006, 78, 4690–4696.
13 X. Wang, J. Zhuang, Q. Peng and Y. D. Li, Nature, 2005, 437,
121–124.
14 F. Lahoz, I. R. Martin and A. Briones, J. Appl. Phys., 2004, 95,
2957–2962.
This work was supported by the National Science Founda-
tion of China (20571016, 20501006, 20775017 and 20771027),
Shanghai Sci. Tech. Comm. (06J14016, 06QH14002), National
ꢀc
This journal is The Royal Society of Chemistry 2008
4788 | Chem. Commun., 2008, 4786–4788