Homometallic Ln(III)-complexes from an ILCT ligand with sensitized vis-NIR emission, excitation-dependent PL color tuning and white-light emission

Article abstract of DOI:10.1039/c8tc00458g

A facilely available zwitterionic ligand, 1,1′-(1,4-phenylenebis(methylene))dipyridin-4(1H)-one (PBPO), has been designed to bear intraligand charge transfer (ILCT) energy states. PBPO was used to assemble two series of Ln(iii) complexes with either 2D (6,3)-hcb network (LIFM-24(Ln), Ln = Pr, Nd, and Sm), or 1D loop-and-chain (LIFM-25(Ln), Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) polymeric structures, as determined by the radius of the lanthanide ions. Highly efficient photoluminescence (PL) in the visible to near-infrared (NIR) regions can be obtained in these Ln-complexes, due to the extended energy transfer from both the triplet and ILCT states of the zwitterionic ligand. Among these complexes, LIFM-24(Pr) and LIFM-25(Dy) display excitation-dependent color tunable luminescence and white-light emission based on the combination of ligand-centered (LC) and metallic-centered (MC) emissions. Uniquely, a strict linear relationship was established between the excitation wavelength and the emission CIE (Commission Internationale de L'Eclairage) coordinates in a wide color range (orange to blue for LIFM-24(Pr), and yellow to blue for LIFM-25(Dy)), thereby providing prototype models for programmable PL color tuning and white-light emission, which are rarely achievable in homometallic Ln-complexes.

Full text of DOI:10.1039/c8tc00458g

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Journal Name
RSCPublishing
ARTICLE
Homometallic Ln(III)-complexes from ILCT ligand
with sensitized vis-NIR emission, excitation-
dependent PL color tuning and white-light emitting
Cite this: DOI: 10.1039/x0xx00000x
Wei-Ming Liao,a Chao-Jie Li,a Xiangwen Wu,b Jian-Hua Zhang,a Zheng Wang,a Hai-Ping Wang,a
Ya-Nan Fan,a Mei Pan,*a and Cheng-Yong Sua
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
A facilely available zwitterionic ligand, 1,1'ꢀ(1,4ꢀphenylenebis(methylene))dipyridinꢀ4(1H)ꢀ
www.rsc.org/
one (PBPO), has been designed to bear intraligand charge transfer (ILCT) energy states.
PBPO was applied to assemble two series of Ln(III) complexes with either 2D (6,3)ꢀhcb
network (LIFMꢀ24(Ln), Ln = Pr, Nd, and Sm), or 1D loopꢀandꢀchain (LIFMꢀ25(Ln), Ln =
Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) polymeric structures, which are decided by lanthanide
ions radius. Highly efficient photoluminescence (PL) in visible to nearꢀinfrared (NIR)
regions can be obtained in these Lnꢀcomplexes, due to the extended energy transfer from
both triplet and ILCT states of the zwitterionic ligand. Among which, LIFMꢀ24(Pr) and
LIFMꢀ25(Dy) manifest excitationꢀdependent color tunable luminescence and whiteꢀlight
emission based on the combination of ligandꢀcentered (LC) and metallicꢀcentered (MC)
emission. Uniquely, strict linear relationship is established between the excitation
wavelength and emission CIE (Commission Internationale de L'Eclairage) coordinates in a
long color range (orange to blue for LIFMꢀ24(Pr), and yellow to blue for LIFMꢀ25(Dy)),
which provides prototype models for programmable PL color tuning and white light emitting,
which are rarely achievable in homometallic Lnꢀcomplexes.
potential applications, such as complexes from Nd3+/Yb3+
(biological imaging), Er3+ (optical fibers), Pr3+, Sm3+, Dy3+, and
Introduction
Tm3+ (both vis and NIR emissions), etc.8ꢀ10 This might be due to
the relatively weak emission of these Lnꢀcomplexes by inefficient
energy transfer from the ligands triplet states.11 To solve this
problem, designing reasonable ligands including extended energy
levels, which can match the various accepting levels of different
lanthanide ions, might enhance energy transfer efficiency to the
lanthanide centers, and provide a promising method to achieve
highly sensitized emission in both visible and NIR regions.12ꢀ14
Recently, our group reported a series of Lnꢀcomplexes from monoꢀ,
biꢀ, and triꢀpodal zwitterionic ligands, and it indicated that the
ligands could highly sensitize all of the investigated lanthanide ions,
which was ascribed to the extended intraligand charge transfer
(ILCT) plus triplet energy states in these ligands can better fit the
accepting fꢀlevels of different lanthanide ions, and provide more
broad energy tansfer and sensitization pathway to the lanthanide
centers.15ꢀ17
Recently, Lanthanide metalꢀorganic complexes have attracted
growing attention not only for the novel structural diversity but also
for the advanced applications in optics,1,2 adsorption and
separation,3, 4 proton conductivity,5, 6 heterogeneous catalyst,7 etc.
Especially, Lnꢀcomplexes were used to synthesize distinctive
luminescent materials for their large Stokes shift, excellent
quantum yield, and long lifetime. Among which, Eu3+ and Tb3+
complexes have been investigated and reported in a plenty of works
as multiꢀfunctional materials owing to the strong red and green
photoluminescence, respectively. While some other lanthanide
complexes have been less studied, despite of their uniquely
Single component white light emitting (SCꢀWLE) and
photoluminescence color tuning are important in various fields
such as displaying, imaging, sensing and antiꢀcounterfeiting, etc.18ꢀ
20
To attain this purpose, a common method was to introduce
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different types of lanthanide ions, such as Eu3+ and Tb3+, into the
same metalꢀorganic framework.21ꢀ23 Among all of the SCꢀWLE Lnꢀ
complexes, only a few were based on homometallic examples, such
as Sm3+, Eu3+, Dy3+, and Pr3+ꢀcomplexes.10, 24ꢀ27 Therefore, it is still
desirable to develop novel homometallic Lnꢀcomplexes with SCꢀ
WLE and PL color tuning properties, for their advantages of great
6.5 mmol) was added into ethanol (30 ml) and refluxed for 4 hours,
and then 1,4ꢀbis(bromomethyl)benzene (0.88 g, 3 mmol) was
added and another reaction for 24 h was conducted under the same
condition. After the reaction, colorless and transparent solution was
obtained with solid filtered, ethanol was evaporated until white
product was precipitated, into which 100 ml ethyl ether was
injected and great amount of white precipitates were acquired after
filtering. The product was dried under vacuum for more than 24 h
reproducibility, simple preparation process, and ease of operation.19,
28, 29
1
Herein, we synthesized a new bipodal zwitterionic ligand, 1,1'ꢀ
(1,4ꢀphenylenebis(methylene))dipyridinꢀ4(1H)ꢀone (PBPO), which
possesses the attributes of good solubility, strong coordination
ability with lanthanide ions, separated charge distribution and
potential ILCT property. Lnꢀcomplexes in two series of
coordination structures were synthesized and investigated by the
visible or/and NIR PL spectra, and it indicated that PBPO ligand
could sensitize all of the explored lanthanide ions efficiently.
Uniquely, SCꢀWLE and linearly PL color tuning could be obtained
both in Prꢀ and Dyꢀ homometallic complexes by varying the
excitation wavelengths.
before use (Scheme 1). Yield: 76%. H NMR (400 MHz, D2O, 25
°C, Fig. S1): δ 7.79ꢀ7.64 (m, 4H), 7.12 (s, 4H), 6.50ꢀ6.29 (m, 4H),
5.08 (s, 4H).
Scheme 1 Synthetic route for PBPO ligand.
Syntheses of the LnꢀComplexes
LIFMꢀ24(Ln), [Ln2(PBPO)4(NO3)6] (Ln = Pr, Nd, and Sm): A
mixture of PBPO (0.03 mmol) ligand in water (1 ml) was added to
a solution of Ln(NO3)3·xH2O (0.02 mmol, x = 3ꢀ6) in acetone (3
ml). The solution was stirred for 30 min. Slow diffusion of acetone
into the filtrate over 10 days afforded block crystals suitable for
single crystal Xꢀray diffraction. Yield: 67ꢀ70%.
Experimental
Materials and methods
All chemicals were of AR grade attained from commercial sources
and used as purchased without further purification. 1H NMR
spectra were recorded on Bruker Avance 400 NMR spectrometer.
Thermogravimetric analysis (TGA) curves were conducted on a
NETZSCH TG 209 thermal analyzer from room temperature to 800
oC with a heating rate of 10 oC/min. Powder Xꢀray diffraction
(PXRD) data were measured on a Bruker D8 ADVANCE
diffractometer (Cu Kα, λ = 1.54178 Å) at 40 kV, 30 mA. The UVꢀ
Vis absorption spectra were collected on a Shimadzu UVꢀ250PC
spectrophotometer with a variable wavelength between 200 and
800 nm. The data of photoluminescence spectra, and decay lifetime
were measured on EDINBURGH FLS980 spectrophotometer with
the samples inside two clamped quartz pieces.
LIFMꢀ25(Ln),
[Ln(PBPO)2(NO3)2]·0.5PBPO·(NO3)·solvents
(Ln = Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb): These complexes were
obtained by a similar method mentioned above but using the
corresponding lanthanide salts for instead. Yield: 63ꢀ69%.
Results and discussion
Crystal Structures
The series of LIFMꢀ24(Ln) isomorphous complexes were
obtained by slow diffusion of acetone into the mixture of PBPO
and Ln(NO3)3 (Ln = Pr, Nd, and Sm). LIFMꢀ24 (Pr) was taken as a
representative and the singleꢀcrystal Xꢀray diffraction data was
collected. It indicated that LIFMꢀ24 (Pr) crystallized in the triclinic
space group Pꢀ1 (Table 1). And the asymmetric unit included one
Crystallography
Both singleꢀcrystal diffraction data of LIFMꢀ24(Pr) and LIFMꢀ
25(Eu) were collected from an Agilent Gemini
S Ultra
ꢀ
Pr3+ ion, two PBPO ligands, and three coordinated NO3 (Fig. 1a).
diffractometer with the Enhance Xꢀray Source of CuꢀKα radiation
(λ = 1.54178 Å) at 293 K or 173 K. Absorption corrections were
applied using multiscan technique. Both of the structures were
solved by direct method of SHELXS and refined against F2 using
the SHELXL programs. The nonꢀhydrogen atoms were treated with
anisotropic parameters, while H atoms were placed in calculated
positions and refined using a riding model. Crystallographic data
and structural refinement information were listed in Table 1.
Crystallographic data for the structures reported in this paper have
been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication no. CCDC 1819541ꢀ1819542.
ꢀ
The Pr3+ center was 10ꢀcoordinated by three chelated NO3 anions
and four oxygen atoms from the PBPO ligands, which resulted in a
2D flat structure with (6,3) hcbꢀnetwork (Fig. 1b and c).
Accordingly, this (6,3) hcbꢀnetworks were packed into an ABAB
fashion in the crystal lattice (Fig. 1d). Similarly, the Ndꢀ and Smꢀ
complexes could be synthesized in this strategy, and all of them
showed almost the same result in PXRD patterns, which suggested
the isomorphous structure of LIFMꢀ24(Ln) (Fig. S2). The LIFMꢀ
25(Ln) series of isomorphous complexes (Ln = Eu, Gd, Tb, Dy, Ho,
Er, Tm, and Yb) were prepared in a similar method but resulted in
different crystal structures. Taking LIFMꢀ25(Eu) as an example, it
crystallized into orthorhombic space group Pbca. And the
asymmetric unit included one Eu3+ ions, two PBPO ligands, two
Syntheses of the ligand
ꢀ
ꢀ
1,1'ꢀ(1,4ꢀphenylenebis(methylene))dipyridinꢀ4(1H)ꢀone
(PBPO): K2CO3 (1.6 g, 12 mmol) and 4ꢀhydroxypyridine (0.627 g,
coordinated NO3 ions, one uncoordinated NO3 ion and three
coordinated water molecules (Fig. 1e). The Eu3+ ion was 8ꢀ
2 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C8TC00458G
coordinated by four oxygen atoms from the PBPO ligands and two
chelated NO3ꢀ anions, linking into 1D coordinated chain (Fig. 1f
and g). According to the PXRD patterns of LIFMꢀ25 series of
complexes, they all indicated the isomorphous structures (Fig. S3).
fashion (d), and LIFMꢀ25(Eu): asymmetric unit (e), aꢀaxis view
(f), and 1D loopꢀandꢀchain (g). All of the hydrogen atoms and
solvent molecules were omitted for clarity.
From the above analysis, we can see that the coordination
environment of Ln3+ center and obtained networks were decided by
the ionic radii of lanthanide ions. To the large ions of Pr3+, Nd3+,
and Sm3+, the coordinated number of lanthanide center was 10 and
it resulted in a (6,3)ꢀhcb network. To the small ions of Eu3+, Gd3+,
Tb3+, Dy3+, Ho3+, Er3+, Tm3+, and Yb3+, the lanthanide center adopt
8ꢀcoordinated geometry and linking four PBPO ligands into a 1D
loopꢀandꢀchain. Furthermore, all of the lanthanide ions were
coordinated by ligands and NO3ꢀ ions but without water molecules,
which might help to enhance the sensitization efficiency of
lanthanide ions.30
Table 1 Crystallographic data for complexes LIFMꢀ24(Pr) and
LIFMꢀ25(Eu).
LIFMꢀ24(Pr)
C72H64N14O26Pr2
1823.20
293
LIFMꢀ25(Eu)
C45H40N8O17Eu
1116.82
173
Formula
F.w.
T (K)
Crystal system
Space group
triclinic
Pꢀ1
orthorhombic
Pbca
a (Å)
b (Å)
c (Å)
α
10.0807(3)
11.0770(5)
32.5012(13)
91.153(4)
94.746(3)
91.904(3)
3613.7(2)
2
22.1509(4)
16.0378(7)
27.6728(12)
90
90
90
9830.81(8)
8
1.509
Thermal stability of LnꢀComplexes
The thermogravimetric analyses (TGA) of LIFMꢀ24(Pr) and
LIFMꢀ25(Ho) were carried out and the results were shown in Fig.
S4. To LIFMꢀ24(Pr), no obvious weight loss until the
decomposition of the framework appeared at about 330 oC,
indicating of good thermal stability (Fig. S4a). To LIFMꢀ25 (Ho),
there was a 10.2% weight loss occurred when heated from room
temperature to 325 oC, which indicated the loss of one acetone and
three water molecules (cacl. 10.7%). Another weight loss of 19.8%
appeared from 325 to 366 oC, suggesting the decomposition of
β
γ
V (Å3)
Z
Dc (g cmꢀ3)
1.676
11.027
ꢀ
(mmꢀ1)
9.816
F(000)
1840
4520
R1 (>2σ)
wR2(all data)
GOF
0.0604
0.1970
1.076
0.0530
0.1545
1.144
ꢀ
three NO3 ions (cacl. 19.7%). Then the obvious weight loss from
400 oC should be ascribed to the collapse of metalꢀligand
framework.
Visible and NIR emissions
Luminescence property of PBPO ligand was investigated and
the excitation and emission spectra were shown in Fig. S5. PBPO
showed a broad excitation from 300 to 400 nm, ascribing to the
S0→1S1* and S0→ILCT excited state.15, 16 When excited at 355 nm,
the emission peak of PBPO was at about 420 nm showing blue
1
*
light emitting, which should be ascribed to the ligandꢀbased S1
state emission. As obtained from the phosphorescence spectrum of
LIFMꢀ25(Gd) at 77 K (Ex=305 nm), the emission broad peak was
from 425 to 650 nm (Fig. S6), and the decay lifetime was tested to
be 2.7 ms (503 nm), showing phosphorescence nature compared
with the lifetime of 1.1 ms detected at RT. As a result, the
combined ILCT plus triplet energy levels of PBPO was determined
to be between 15385 and 23809 cmꢀ1 (420 to 650 nm). This value
was suitable to most of the lanthanide excited states, including Pr3+
(3P0, 21000 cmꢀ1), Nd3+ (4F3/2, 11666 cmꢀ1), Eu3+ (5D0, 17500 cmꢀ1),
Tb3+ (5D4, 20400 cmꢀ1), Dy3+ (4F9/2, 22200 cmꢀ1), Sm3+ (4G5/2
,
17730 cmꢀ1), and Yb3+ (4F5/2, 10250 cmꢀ1), and might result in
highly sensitized visible to NIR emission by efficient energy
transfer from ligand to lanthanide,17 as shown below.
The luminescence of Lnꢀcomplexes achieved from lanthanide
ions and PBPO ligand were therefore investigated (Fig. S7). It
indicated that the PBPO ligand could sensitize all of the explored
lanthanide ions to emit the characteristic f→f transitions in visible
or NIR regions. Meanwhile, the decay lifetimes of Lnꢀcomplexes
were measured and shown in Table 2 for comparison. In visible
Fig. 1 Crystal structures of LIFMꢀ24(Pr): asymmetric unit (a), 2D
(6,3)ꢀhcb network (b), simplified topology (c), ABAB packing
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region, the emission peaks of LIFMꢀ24(Pr) should be assigned to
*n.d. = no detected.
the Pr3+ transitions of 3P0 → 3H4 (486 nm), 3P0 → 3H5 (543 nm), 1D2
3
3
3
→ 3H4 (596 nm), P0 → 3H6 (612 nm), P0 → 6F2 (641 nm), and P0
PBPO ligand can sensitize the lanthanide ions emission not
only in visible region but also NIR region, as shown in Fig. S7 and
the photophysical data were summarized in Table 2. In detail, the
emission bands of LIFMꢀ24(Pr) centered at 855, 1010 and 1420
nm were assigned to the 1D2 → 3F2,1D2 → 3F2 and 1D2 → 1G4,
respectively.36 And the decay lifetime detected at 1010 nm was
determined to be 4.9 ꢁs, which was quite shorted than that in
visible region. LIFMꢀ24(Nd) has the NIR emission peaks at 896,
1055 and 1326 nm, which correspond to the Nd3+ transitions of
6
→ F3 (698 nm), respectively. And the luminescence lifetime was
determined to be 61 ꢁs at the most efficiently sensitized 641 nm. To
LIFMꢀ24(Sm), the sharp peaks at 562, 596, 643 and 703 should be
ascribed to the Sm3+ transitions of 4G2/5 → 6HJ (J = 5/2, 7/2, 9/2 and
11/2, respectively. And the luminescence lifetime detected at 643
nm was found to be 65 ꢁs, which was a rather better value with
comparison to some previous Lnꢀcomplexes.31,32 To LIFMꢀ25(Eu),
the red luminescence consisted of peaks at 586, 594, 616, 655, and
5
7
4
698 nm corresponds to the Eu3+ transitions of D0 → FJ (J = 0, 1,
2, 3 and 4, respectively). The highest peak 616 nm was detected to
obtain the decay lifetime of 1056 ꢁs. Similarly, to LIFMꢀ25(Tb),
the green luminescence was combined by the peaks at 487, 545,
588 and 625 nm which were assigned to the transitions of Tb3+ 5D4
→ 7FJ (J = 0, 1, 2 and 3, respectively). The rather long lifetimes of
LIFMꢀ25(Eu, 1056 ꢁs) and LIFMꢀ25(Tb, 1092 ꢁs) could be
compared to many other reported Lnꢀcomplexes.33ꢀ35 To LIFMꢀ
4F3/2 → IJ (J = 9/2, 11/2, and 13/2, respectively). LIFMꢀ24(Sm)
showed the peaks at 788, 875, 895, 940, 1020, and 1166 nm
corresponding to the Sm3+ transitions of G2/5
4
→
6H13/2, and
4G2/5→6FJ (J = 1/2, 3/2, 5/2, 7/2, and 9/2). Its value of decay
lifetime at 940 nm was high to 66 ꢁs which was almost identical to
that in visible region (65 ꢁs), suggesting the good sensitization to
Sm3+ by PBPO ligand in NIR region. LIFMꢀ25(Dy) showed major
peaks at 836, 928, 995 and 1163 nm which should be ascribed to
4
6
4
6
4
6
25(Dy), corresponding to the Dy3+ transitions of F9/2 → H15/2
,
the Dy3+ transitions of F9/2 → H7/2+6F9/2, F9/2 → H5/2，4F9/2
→
4F9/2 → H13/2, F9/2 → H11/2 and F9/2 → H9/2, the emission peaks
were found at 480, 575, 660 and 750 nm, respectively. The lifetime
was measured and determined to be 43 ꢁs by detecting at 575 nm,
which is among the best for the rarely reported Dyꢀcomplexes
compared with earlier literatures.17, 26 The luminescence spectrum
of LIFMꢀ25(Tm) was also investigated, when excited at 330 nm,
the emission peaks at 796 nm in visible region was found, which
should be ascribed to the Tm3+ transition of 3H4→3H6.
6F7/2 and F9/2 → F5/2, respectively. The lifetime determined to be
38 ꢁs, a little bit shorter comparing with that in visible region (43
ꢁs). Four major emission peaks of LIFMꢀ25(Ho) was found at 810,
975, 1183 and 1480 nm. And these peaks were corresponding to
5F4 → 5I7，5F5 → 5I7，5I6 → 5I8 and 5F5 → 5I6, respectively. LIFMꢀ
25(Er) displayed two emission peaks at 816 and 1533 nm which
6
4
6
4
6
4
6
can be attributed to Er3+ transitions of 4I9/2 →4I15/2 and 4I13/2 →4I15/2
,
respectively. To LIFMꢀ25(Tm) complex, the Tm3+ transitions of
3
3
3
3
3H4 → H6, H5 → H6 and F4 → 3H4 charactered at 796, 1226 and
1550 nm, respectively. The lifetimes of LIFMꢀ25(Ho), LIFMꢀ
25(Er), LIFMꢀ25(Tm) were determined to be 1.9, 1.2 and 2.8 ꢁs,
Table 2 Photophysical properties of Lnꢀcomplexes from PBPO
ligand (solid state, 298 K).
τobs (ꢁs)a
respectively. The NIR peaks detected at 982 and 1030 nm for
LIFMꢀ25(Yb) should be assigned to the transition of F5/2 → 2F7/2
Its lifetime (determined to be 17 ꢁs) was quite high comparing to
some other reported cases.37
Complex
λmax (nm) and assignment
2
.
LIFMꢀ24(Pr)
641 (3P0
1010 (1D2
1055 (4F3/2→4I11/2
643 (4G5/2→6H9/2
→
3F3)
3F4)
61
→
4.9
2.8
65
Color tuning and whiteꢀlight emitting
LIFMꢀ24(Nd)
LIFMꢀ24(Sm)
)
)
Among the above investigated Lnꢀcomplexes, LIFMꢀ24(Pr)
and LIFMꢀ25(Dy) were found to be able to produce direct tunable
and white light emission by varying the excitation wavelength. For
LIFMꢀ24(Pr), the emission spectra were explored by excitation
varying from 300 to 360 nm, showing different emitting colors and
intensity. When excited at high energy wavelength, for example
290 nm, almost only emission of Pr3+ fꢀf transition was found,
resulting in orange color light (Fig. 2). It suggested that all of the
absorbed energy at this wavelength was transferred from PBPO
ligand to lanthanide center efficiently. This can be further proven
by the excitation spectra of LIFMꢀ24(Pr) monitored by 430 nm
(based on ligand emission) and 641 nm (based on Pr3+ emission) in
Fig. S8. When excited at 290ꢀ300 nm, the ligand emission was
negligible, but Pr3+ emission could happen efficiently. However,
when excited at lower energy wavelength between 300 and 350 nm,
two new broad emission peaks were detected covering from 400 to
600 nm. These two peaks should be ascribed to ILCT and Pr3+ꢀ
affected ligand emissions. It indicated that the energy transfer from
ligand to Pr3+ was incomplete, resulting in a combined spectra of
940 (4G5/2→6F5/2
616 (5D0→7F2)
545 (5D4→7F5)
)
66
LIFMꢀ25(Eu)
LIFMꢀ25(Tb)
LIFMꢀ25(Dy)
1056
1092
43
575 (4F9/2→ 6H13/2
)
839 (4F9/2 → 6H7/2+6F9/2
980 (5F5→5I6)
)
38
LIFMꢀ25(Ho)
LIFMꢀ25(Er)
LIFMꢀ25(Tm)
1.9
1.2
n.d.*
2.8
17
1533 (4I13/2→4I15/2
796 (3H4→3H6)
1226 (3H5→3H6)
)
LIFMꢀ25(Yb)
982 (2F5/2→2F7/2
)
a The data of photophysical properties written in nonꢀitalicized text
represent visibleꢀlight emission, while those in italicized text
represent NIR emission.
4 | J. Name., 2012, 00, 1-3
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ARTICLE
DOI: 10.1039/C8TC00458G
Pr3+ꢀbased fꢀf and ligandꢀbased ILCT emission. Especially, when
excited at 330 and 345 nm, pink and white light emission could be
obtained. CIE coordinates of this white light emission was (0.34,
0.30), with correlated color temperature (CCT) and color rendering
index (CRI) of 5468 K and 98, respectively. It emphasized LIFMꢀ
24(Pr) a potential whiteꢀlight material and could be applied in some
applications, for example barcode module.10 Further, when excited
at even lower energy wavelength, no efficient energy transfer
appeared from ligand to Pr3+, thus the ILCT emission of ligand was
dominant, leading to blue light emission. On this basis, a series of
CIE coordinates were obtained from emission spectra excited at
various wavelengths from 300 to 360 nm, which showed a linear
relationship.
light (0.33, 0.33). Its CCT and CRI were 5461 K and 97,
respectively. Accordingly, a series of CIE coordinates were
obtained from emission spectra excited at various wavelengths
from 290 to 360 nm, which also showed a good linear relationship
(Fig. 3b). Based on this, materials and devices with programmable
PL color tuning strategies can be established. For example, in a
typical fluorescent plate model designed from LIFMꢀ24(Pr) and
LIFMꢀ25(Dy) as shown in Fig. 3c, by swapping the excitaion
wavelengths controllable by a computer program, continuously
varied displaying color can be achieved. Compared with other
models, the PL color tuning herein is dependent on programmable
switch of different exciting wavelengths applied on a homometallic
Lnꢀcomplex material, which is more reliable, practicable and
reproducible.
Fig. 2 Tunable and white light emission of LIFMꢀ24(Pr) at room
temperature. Photoꢀexcited images (a) and emission spectra (c)
excited at 290 (orange), 330 (pink), 345 (white), and 355 (blue) nm,
respectively. (b) CIE coordinates of the emission spectra at the
excitation wavelength from 300 to 360 nm (the excitation
wavelength interval was 3 nm).
Fig. 3 Tunable and white light emission of LIFMꢀ25(Dy) at room
temperature. Emission spectra (a) excited at 290, 320, 339, and 360
nm, respectively. (b) CIE coordinates of the emission spectra at the
excitation wavelength from 300 to 360 nm (the excitation
wavelength interval was
3 nm). (c) Schemiatic model for
excitationꢀdependent fluorescent plate made from LIFMꢀ24(Pr)
and LIFMꢀ25(Dy).
The emission spectra of LIFMꢀ25(Dy) were also measured at
different excitation wavelengths (Fig. 3). When excited at high
energy wavelength below 310 nm, only Dy3+ꢀbased emission was
found, leading to a yellow color light. This resulted from the
efficient energy transfer from PBPO ligand to Dy3+ center similar
to the case of LIFMꢀ25(Pr), which was proved by the excitation
spectrum (Fig. S9). And when the wavelength increased from 320
to 360 nm, white light could be obtained from the combination of
ligandꢀbased and Dy3+ꢀbased emissions. Especially, when the
excitation wavelength was 339 nm, the white light with CIE
coordinates of (0.32, 0.33) was quite near to that of standard white
Conclusions
In summary, a zwitterionic ligand PBPO with ILCT property
was used to assemble eleven Lnꢀcomplexes which crystallized in
two series of coordination structures. The ligand can sensitize both
visible and NIR emissions in these Lnꢀcomplexes efficiently.
Especially, two singeꢀcomponent homometallic Lnꢀcomplexes,
LIFMꢀ24(Pr) and LIFMꢀ25(Dy) show color tunable and whiteꢀ
light emission from the combination of ligandꢀbased and
lanthanideꢀbased emissions when excited at appropriate wavelength.
This journal is © The Royal Society of Chemistry 2012
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ARTICLE
Journal Name
DOI: 10.1039/C8TC00458G
A good linear relationship is established between the excitation
wavelength and CIE coordinate, which has not been reported for
homometallic Lnꢀcomplexes before. This provides new
opportunities for designing photoluminescent materials and devices
with programmable PL color tuning strategies, which can be
potential for further applications in displaying, sensing, and antiꢀ
counterfeiting.
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Conflicts of interest
There are no conflicts to declare.
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Journal of Materials Chemistry C
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DOI: 10.1039/C8TC00458G
Table of contents entry
Homometallic Ln(III)-complexes with sensitized
vis-NIR emission, excitation-dependent PL color
tuning and white-light emitting from an ILCT ligand.