Unusual Aggregation/Gelation-Induced Phosphorescence of Propeller-Type Binuclear Platinum(II) Enantiomers

Article abstract of DOI:10.1002/ejic.201600839

Three binuclear cyclometalated Pt^IIcomplexes, [(ppy)Pt(μ-SA)Pt(ppy)] (ppy = 2-phenylpyridine, SA: salicylaldehyde azine), have been synthesized and characterized. Owing to the blockage of the intramolecular rotation of the bridging SA ligands, all three complexes exhibit propeller-type enantiomers and aggregation-induced phosphorescence (AIP). Interestingly, one complex with –NEt₂groups instead of long alkyl chains, amide, urea peptides, cholesterol, sugar, or steroidal groups was found to show strong phosphorescence enhancement gated by the gelation process. This unusual gelation behavior is rarely encountered, as the metallogel has no intermolecular hydrogen bonding or Pt–Pt interactions. We attribute the driving force of this gelation-induced phosphorescence (GIP) to the propeller-type structure, optimally balanced solubility of –NEt₂groups, enantiomer-induced π–π stacking interactions, and strong multiple intermolecular H–C, H–O, and H–H interactions.

Full text of DOI:10.1002/ejic.201600839

DOI: 10.1002/ejic.201600839
Communication
Phosphorescent Metallogels
Unusual Aggregation/Gelation-Induced Phosphorescence of
Propeller-Type Binuclear Platinum(II) Enantiomers
Fei Gou,[a] Jinghui Cheng,[a] Xiaohong Zhang,[a] Guangyu Shen,[a] Xiangge Zhou,[a] and
Haifeng Xiang*[a]
Abstract: Three binuclear cyclometalated PtII complexes, ment gated by the gelation process. This unusual gelation be-
[(ppy)Pt(μ-SA)Pt(ppy)] (ppy = 2-phenylpyridine, SA: salicylalde- havior is rarely encountered, as the metallogel has no intermo-
hyde azine), have been synthesized and characterized. Owing lecular hydrogen bonding or Pt–Pt interactions. We attribute
to the blockage of the intramolecular rotation of the bridging the driving force of this gelation-induced phosphorescence
SA ligands, all three complexes exhibit propeller-type enantio- (GIP) to the propeller-type structure, optimally balanced solubil-
mers and aggregation-induced phosphorescence (AIP). Interest- ity of –NEt2 groups, enantiomer-induced π–π stacking interac-
ingly, one complex with –NEt2 groups instead of long alkyl tions, and strong multiple intermolecular H–C, H–O, and H–H
chains, amide, urea peptides, cholesterol, sugar, or steroidal interactions.
groups was found to show strong phosphorescence enhance-
Introduction
tions,[8] have also been widely used to promote molecular self-
Self-assembled supramolecular gels (low-molecular-weight ge-
assembly and gelation.
lators), including organogels[1] and metallogels,[2] have been
PtII complexes have been investigated extensively in the past
considered to be one of the most interesting soft and smart
two decades because of their interesting phosphorescence
materials due to their ability to construct polymeric structures
properties.[2,9] Unlike another class of phosphorescent octa-
from small molecules through non-covalent interactions.
hedral d6 IrIII complexes, square-planar d8 PtII complexes are far
Among them, luminescent π-conjugated supramolecular gels
more likely to encounter the problem of “aggregation-caused
(π-gels) have attracted intense interest for some of their promis-
quenching” (ACQ) of their emission,[9,10] because they easily
ing applications in optoelectronics and optical sensors.[1e,1f,2c,2d]
form dimers not only through intermolecular π–π stacking in-
The basic principle of designing these π-gels is the incorpora-
teractions but also through PtII–PtII interactions in high concen-
tion of some side functional groups such as long alkyl chains,
trations, in the solid state, or in gels. Therefore, in order to solve
amide, urea peptides, cholesterol, sugar, or steroidal groups into
the ACQ problem, much effort has recently been made to de-
the π-conjugated aromatic core. The presence of a π-conju-
gated core that is in favor of intermolecular π–π stacking inter-
actions is a key requirement for the design of π-gels. The side
velop aggregation-induced-emission (AIE)-active materials and
supramolecular gels.[1e,11] Up to now, most of the reported AIE-
active PtII complexes or metallogels are mononuclear PtII com-
functional groups are capable of forming intermolecular
plexes.[1e,2c,11e] Komiya et al.[8f] recently demonstrated some re-
hydrogen bonding, securing the balanced hydrophobic interac-
markable binuclear PtII complexes that are linked by non-conju-
tions and solubility, and facilitating van der Waals interactions,
gated long heptyl spacers and exhibit gelation-induced phos-
which are essential for gelation. Sometimes, however, these
phorescence (GIP) through chiral aggregations, intermolecular
bulky non-conjugated side groups are normally inactive and
π–π stacking, and Pt–Pt interactions. Herein we present three
undesirable for optoelectronic applications. Until recently, some
rigid π-gels[1] with –CF3 groups,[3] aromatic side chains,[4]
methyl ester groups,[5] triphenylamine groups,[6] and –CN
groups[7] have been demonstrated to exhibit gelation without
intermolecular hydrogen bonding. For metallogels,[2] intermo-
lecular metal–metal interactions, and especially PtII–PtII interac-
[a] College of Chemistry, Sichuan University
Chengdu, 610041, China
E-mail: xianghaifeng@scu.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejic.201600839.
Scheme 1. Synthesis of complexes 1–3.
Eur. J. Inorg. Chem. 2016, 4862–4866
4862 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
novel highly-conjugated, neutral, and soluble binuclear PtII ecules to orient and assemble. Thus, we tried many different
complexes (1–3), [(ppy)Pt(μ-SA)Pt(ppy)] (ppy: 2-phenylpyridine, ways to grow single crystals of 1–3. For 1, we always failed to
SA: salicylaldehyde azine) (Scheme 1), which exhibit propeller- obtain single crystals but had powders instead. Fortunately,
type enantiomers and unusual aggregation/gelation-induced after dozens of attempts, we obtained suitable single crystals
phosphorescence (AIP/GIP) properties.
of 2 and 3 for X-ray crystallographic structure determination by
a slow diffusion/evaporation of CH2Cl2/hexane solution and
slow evaporation of ethyl acetate solution, respectively. The sin-
gle-crystal X-ray diffraction structures of 2 and 3 are depicted
Results and Discussion
Our research work focuses on the synthesis and luminescence in Figures 2, S4, S5 and Figures 3, S6, S7, respectively.
properties of salicylaldehyde-based Schiff bases.[12] The reason
why we chose the ppy ligand is that ppy-based PtII complexes
are highly phosphorescent and [(ppy)Pt(μ-Cl)2Pt(ppy)]
(Scheme 1) is an ideal precursor to prepare bis-cyclometalated
PtII complexes.[9,13] The bis-bidentate-bridging SA ligands
were adopted because of their simple, highly conjugated, and
rotatable structures (Scheme 1) that would help to achieve
AIE.[10b,12f] Complexes 1–3 were synthesized in a straightfor-
ward manner according to Scheme 1 (see the Supporting Infor-
mation for a description of the synthesis procedures). Com-
pounds 1 and 2 are weakly soluble in CH2Cl2, benzene, and THF
but not soluble in water, ether, ethanol, or hexane. Compound
3 has a much better solubility in CH2Cl2 and benzene. Com-
plexes 1–3 have reasonable thermal stabilities (1 has a Td of
about 250 °C; see Figure S1 in the Supporting Information).
The UV/Vis absorption and phosphorescence properties of
1–3 are presented in Table S1, Figure 1, and Figure S1. As ex-
pected, they are non-emissive in pure dilute CH2Cl2, benzene,
or THF, as the intramolecular rotations of the bridging SA ligand
provide a possible way to non-radiatively annihilate its excited
states. Nonetheless, their aggregates either in THF/water or in
the solid state (Figures 1 and S2) exhibit strong yellow-red
phosphorescence, revealing their AIP. The phosphorescence
quantum yields of the powders of 1, 2, and 3 are 10.5, 14.0, and
7.5 %, respectively. They also have very short phosphorescence
decay lifetimes of 0.79, 1.23, and 1.44 μs, respectively (Fig-
ure S3). Moreover, when a hole-transport polymer polyvinyl-
carbazol (PVK) is doped with 1, 2, or 3,[14] the phosphorescence
of the resultant films is stronger than that of the corresponding
powders. All the aforementioned findings indicate that com-
pounds 1–3 are suitable for applications in phosphorescent or-
Figure 2. Single-crystal X-ray diffraction structure and packing of molecules
ganic light-emitting diodes (OLEDs).
of 2: (a) side view; (b) packing (H atoms are omitted); (c,d) intermolecular
interactions of the two closest enantiomers [a = 2.7844 Å, b = 2.9459 Å, c =
2.8566 Å, d = 2.7803 Å, e = 2.7085 Å, f = 2.6169 Å, g = 2.5737 Å, h = 2.9393 Å,
i = 2.9639 Å, j = 2.9647 Å, k = 2.8314 Å]; (e) enantiomers of 2.
In dilute organic solution, it is obvious that the N–N single
bond in the SA ligand is rotatable, which provides a possible
way to non-radiatively annihilate its excited states and results
in the absence of luminescence for 2 solution. In the solid state,
however, many strong intermolecular interactions (less than
3.0 Å) including HAr–CAr (2.7085 Å), HAr–CC=N (2.7844 Å), HAr–Pt
(2.9459 Å), HAr–Ophenol (2.7803 Å), HOMe–HAr (2.5737, 2.6169, and
2.9639 Å), HOMe–CAr (2.8314 and 2.9393 Å), and HOMe–Ophenol
(2.9647 Å) are found between the two closest molecules of 2
(Figure 2c and d). These strong intermolecular interactions elim-
inate the rotation of N–N single bond and –OMe groups. More-
Figure 1. Photographs in room light and 360 nm UV light: (a)
2
(1.0 × 10–6 mol L–1) in THF/water (left, fwater = 90 vol %) and in THF (right);
(b) powders of 1, 2, and 3 (from left to right); (c) casting films of 1, 2, and 3
(from left to right) in PVK (ca. 5 wt.-%). (d) Normalized emission spectra of
powders of 1–3.
Molecular structures and arrangements of atoms play a key over, since 2 has a propeller-type structure (dihedral angles 73.3
role in AIE. Non-covalent interactions frequently assist the mol- and 106.7°) (Figure 2a), there is no face-to-face π–π stacking
Eur. J. Inorg. Chem. 2016, 4862–4866
www.eurjic.org
4863
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
ligand charge transfer (3MLCT) emission. The AIP of mono-
nuclear [(ppy)Pt(SA)] was attributed to “restricted distortion of
excited-state structure” in a previous publication.[13c]
For 3, it should be noted that the methyl C atom in one of
the –NEt2 groups might appear above or below the neighbor-
ing C atom with the same percent probability of 50 % (Fig-
ure S6), due to the disorder of the –NEt2 group in the single-
crystal structures. Such disorder is quite common in terminal
alkyl groups.[15] Molecules of 3 appear to have a much more
serious packing-induced distortion (Figure 3a) than those of 2.
The four dihedral angles of 3 are 66.9, 84.5, 62.3, and 125.5°. The
shortest intramolecular and intermolecular PtII–PtII distances are
4.7645 and 5.3338 Å, respectively. Molecules of 3 also have two
enantiomers (Figure S7) that pack together more closely than
enantiomers of 2 through stronger multiple intermolecular in-
teractions (2.3775–2.8926 Å, Figure 3b and c). On the other
hand, enantiomers of 3 induce strong face-to-face intermolec-
ular π–π stacking interactions (d = 3.3 Å, Figure 3d and e),
which is consistent with the fact that the phosphorescence
quantum yield of powders of 3 (7.5 %) is lower than that of
powders of 2 (14 %).
It is unexpected that gels were always obtained when we
used various organic solvents to grow single crystals of 3. Com-
pound 3 contains two –NEt2 groups, and it thus has a much
better solubility in CH2Cl2 and benzene than 1 and 2. 1 mL of
CH2Cl2 can dissolve at least 50 mg of 3 but at most 5.0 mg of
1 and 2. Good solubility would promote molecules of 3 to form
a gel prior to precipitation or crystallization. As shown in
Table S2, compound 3 can form metallogels in pure organic
solvents benzene and toluene and mixed solvents CHCl3/n-hex-
ane and THF/cyclohexane when its concentration is more than
1.0 wt.-%. For example, the so-called “inverted test tube”
method was used as a visual technique to test the gelation of
a solution of 3 (2.0 wt.-% in benzene) after heating or ultrasonic
irradiation (Figure 4). For 3, the gelation procedure (cooling of
Figure 3. Single-crystal X-ray diffraction structure and packing of molecules
of 3: (a) side view; (b, c) intermolecular interactions of the two closest
enantiomers [a = 2.6493 Å, b = 2.8926 Å, c = 2.8727 Å, d = 2.7993 Å, e =
2.8741 Å, f = 2.5206 Å, g = 2.5815 Å, h = 2.7666 Å, i = 2.3775 Å, j = 2.6596 Å,
k = 2.7256 Å, l = 2.7358 Å]; (d) top and (e) side views of the face-to-face π–
π stacking interactions (H atoms and –NEt2 groups are omitted).
interaction (Figures S4 and S5) between the two closest 2 mol-
ecules. The shortest intramolecular and intermolecular PtII–PtII
distances are 4.7125 and 7.7452 Å, respectively, which indicates
that there is no strong PtII–PtII interaction, either. Intermolecular
π–π stacking and PtII–PtII interactions are normally in the range
3.0–3.5[10b,12f,12g] and 3.2–3.7 Å,[9d] respectively. The absence of
intermolecular π–π stacking and PtII–PtII interactions are benefi-
cial in preventing the formation of dimers. Finally, the phos-
phorescence of 2 is induced by the synergistic effects of the
restricted intramolecular rotation and the absence of dimers.
Since the N–N single bond cannot rotate freely in the solid
state, it is not surprising to observe two enantiomers in the
single crystals of 2 (Figure 2c–e). No low-energy absorption
bands (at wavelengths above 470 nm) even at high concentra-
tions (Figure S8) and weak solvent effects (Figure S9) were ob-
served, which might exclude the possibility of triplet metal-to-
Figure 4. (a) Dissolution of 3 (2.0 wt.-% in benzene) after heating at 80 °C.
(b–e) Formation of metallogels after cooling the solution to room tempera-
ture [(c) under 360 nm UV light]. (f) Heating/cooling cycles of 3-based metal-
logels (emission intensity at 570 nm). (g) SEM image of xerogels obtained
from 3-based metallogels. (h) TEM and SAED (inset) images of xerogels ob-
tained from 3-based metallogels.
Eur. J. Inorg. Chem. 2016, 4862–4866
www.eurjic.org
4864
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
the hot solution into metallogels) is very fast (about 5 min), semble in three steps (Figure 5c) through strong enantiomer-
and the resultant metallogels are thermoreversible, transparent induced intermolecular interactions, such as H–C, H–O, H–H,
(Figure 4), and stable for several months. Compound 3 is nearly and π–π stacking interactions (Figure 3c and d), to form nano-
non-emissive in solution, whereas its metallogels exhibit much fiber structures during gelation. It is obvious that there is no
stronger phosphorescence, which suggests that 3 is a promis- intermolecular hydrogen bonding and Pt–Pt interaction. Due to
ing GIP-active material for photoactive nanostructured devices. their amorphous structures, no diffraction pattern was observed
However, 1 and 2 cannot form gels under the various condi- in the XRPD measurement of powders of 1–3.
tions studied.
Morphological analysis was carried out with transmission
electron microscopy (TEM) and scanning electron microscopy
(SEM) to investigate the microstructure of xerogels obtained
Conclusion
We have developed a straightforward way to prepare a new
from 3-based metallogels. SEM (Figure 4g) and TEM (Figure 4h)
analyses of xerogels reveal that molecules of 3 can self-assem-
class of binuclear cyclometalated PtII enantiomers. Owing to
their propeller-type structures, they exhibit unusual aggrega-
tion/gelation-induced phosphorescence through strong multi-
ple intermolecular interactions, such as H–C, H–Pt, H–O, and H–
H interactions, rather than intermolecular hydrogen bonding
and Pt–Pt interactions. Moreover, intermolecular π–π stacking
interactions between two enantiomers can be well tuned by
their chemical structures to induce the formation of gels.
ble to form a well-defined three-dimensional nanofiber network
with diameters and lengths of hundreds of nanometers and
several micrometers, respectively, which could account for the
high viscosity of 3 at this concentration in benzene.
To gain insight into how molecules of 3 pack into fibrous
self-assemblies, the wide-angle X-ray powder diffraction (XRPD)
and selected area electron diffraction (SAED) patterns of 3-
based xerogels were examined. The XRPD pattern of 3-based
xerogels shows one sharp diffraction peak and one weak and
broad diffraction peak (Figure 5a), which correspond to d-spac-
ing values of 9.8 and 3.9–3.4 Å, respectively. The spacing of
9.8 Å is consistent with the results obtained from single-crystal
X-ray diffraction of molecules of 3, which indicates that mol-
ecules of 3 have tight, interlaced packing (the size of a molecule
of 3 is 7.8 × 17.8 Å, Figures 5b and S10). The spacing of 3.9–
3.4 Å is attributed to strong intermolecular π–π stacking inter-
Experimental Section
Experimental Details are given in the Supporting Information.
CCDC 1483625 (for 2) and 1479017 (for 3) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre.
actions between two enantiomers (Figures 3d and 5b). The Acknowledgments
XRPD d-spacings of 9.8 and 3.9–3.4 Å are also in accordance
with those obtained from SAED measurements (9.6 and 3.3 Å,
Figure 4h). Therefore, we propose that molecules of 3 self-as-
This work was supported by the National Natural Science Foun-
dation of China (no. 21372169). We acknowledge the compre-
hensive training platform of the specialized laboratory of the
College of Chemistry, Sichuan University, for material analysis.
Keywords: Platinum · Gels · Luminescence ·
Supramolecular chemistry · Binuclear enantiomers
[1] a) P. Terech, R. G. Weiss, Chem. Rev. 1997, 97, 3133–3159; b) J. H. van Esch,
B. L. Feringa, Angew. Chem. Int. Ed. 2000, 39, 2263–2266; Angew. Chem.
2000, 112, 2351–2354; c) N. M. Sangeetha, U. Maitra, Chem. Soc. Rev.
2005, 34, 821–836; d) J. W. Steed, Chem. Commun. 2011, 47, 1379–1383;
e) Z. J. Zhao, J. W. Y. Lam, B. Z. Tang, Soft Matter 2013, 9, 4564–4579; f)
S. S. Babu, V. K. Praveen, A. Ajayaghosh, Chem. Rev. 2014, 114, 1973–
2129; g) X. D. Yu, L. M. Chen, M. M. Zhang, T. Yi, Chem. Soc. Rev. 2014,
43, 5346–5371; h) S. Datta, S. Bhattacharya, Chem. Soc. Rev. 2015, 44,
5596–5637.
[2] a) M. O. M. Piepenbrock, G. O. Lloyd, N. Clarke, J. W. Steed, Chem. Rev.
2010, 110, 1960–2004; b) J. Y. Zhang, C. Y. Su, Coord. Chem. Rev. 2013,
257, 1373–1408; c) A. Y. Y. Tam, V. W. W. Yam, Chem. Soc. Rev. 2013, 42,
1540–1567; d) V. W. W. Yam, V. K. M. Au, S. Yu, L. Leung, Chem. Rev. 2015,
115, 7589–7728.
[3] a) B. K. An, D. S. Lee, J. S. Lee, Y. S. Park, H. S. Song, S. Y. Park, J. Am.
Chem. Soc. 2004, 126, 10232–10233; b) B. K. An, S. H. Gihm, J. W. Chung,
C. R. Park, S. K. Kwon, S. Y. Park, J. Am. Chem. Soc. 2009, 131, 3950–3957;
c) J. W. Chung, S. J. Yoon, S. J. Lim, B. K. An, S. Y. Park, Angew. Chem. Int.
Ed. 2009, 48, 7030–7034; Angew. Chem. 2009, 121, 7164–7168.
[4] T. Ishi-I, T. Hirayama, K. Murakami, H. Tashiro, T. Thiemann, K. Kubo, A.
Mori, S. Yamasaki, T. Akao, A. Tsuboyama, T. Mukaide, K. Ueno, S. Mataka,
Langmuir 2005, 21, 1261–1268.
Figure 5. (a) XRPD of xerogels obtained from 3-based metallogels (2.0 wt.-%
in benzene). (b) Single-crystal X-ray diffraction packing of molecules of 3. (c)
Proposed molecular packing diagram of 3-based metallogels.
Eur. J. Inorg. Chem. 2016, 4862–4866
www.eurjic.org
4865
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[5] I. Hisaki, H. Shigemitsu, Y. Sakamoto, Y. Hasegawa, Y. Okajima, K. Nakano,
N. Tohnai, M. Miyata, Angew. Chem. Int. Ed. 2009, 48, 5465–5469; Angew.
Chem. 2009, 121, 5573–5577.
[6] X. F. Zhang, R. Lu, J. H. Jia, X. L. Liu, P. C. Xue, D. F. Xu, H. P. Zhou, Chem.
Commun. 2010, 46, 8419–8421.
Wang, G. X. Zhang, D. Q. Zhang, D. B. Zhu, B. Z. Tang, J. Mater. Chem.
2010, 20, 1858–1867; d) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Soc. Rev.
2011, 40, 5361–5388; e) J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam,
B. Z. Tang, Chem. Rev. 2015, 115, 11718–11940.
[12] a) L. Zhou, P. Y. Cai, Y. Feng, J. H. Cheng, H. F. Xiang, J. Liu, D. Wu, X. G.
Zhou, Anal. Chim. Acta 2012, 735, 96–106; b) L. Zhou, Y. Feng, J. H.
Cheng, N. Sun, X. G. Zhou, H. F. Xiang, RSC Adv. 2012, 2, 10529–10536;
c) J. H. Cheng, K. Y. Wei, X. F. Ma, X. G. Zhou, H. F. Xiang, J. Phys. Chem.
C 2013, 117, 16552–16563; d) J. H. Cheng, Y. H. Zhang, X. F. Ma, X. G.
Zhou, H. F. Xiang, Chem. Commun. 2013, 49, 11791–11793; e) J. H. Cheng,
X. F. Ma, Y. H. Zhang, J. Y. Liu, X. G. Zhou, H. F. Xiang, Inorg. Chem. 2014,
53, 3210–3219; f) X. F. Ma, J. H. Cheng, J. Y. Liu, X. G. Zhou, H. F. Xiang,
New J. Chem. 2015, 39, 492–500; g) J. H. Cheng, Y. X. Li, R. Sun, J. Y. Liu,
F. Gou, X. G. Zhou, H. F. Xiang, J. Liu, J. Mater. Chem. C 2015, 3, 11099–
11110; h) J. H. Cheng, F. Gou, X. H. Zhang, G. Y. Shen, X. G. Zhou, H. F.
Xiang, Inorg. Chem. 2016, 55, 9221–9229.
[13] a) J. Brooks, Y. Babayan, S. Lamansky, P. I. Djurovich, I. Tsyba, R. Bau, M. E.
Thompson, Inorg. Chem. 2002, 41, 3055–3066; b) A. A. Rachford, F. N.
Castellano, Inorg. Chem. 2009, 48, 10865–10867; c) S. J. Liu, H. B. Sun, Y.
Ma, S. G. Ye, X. M. Liu, X. H. Zhou, X. Mou, L. H. Wang, Q. Zhao, W. Huang,
J. Mater. Chem. 2012, 22, 22167–22173.
[7] S. J. Yoon, J. H. Kim, J. W. Chung, S. Y. Park, J. Mater. Chem. 2011, 21,
18971–18973.
[8] a) M. Shirakawa, N. Fujita, T. Tani, K. Kaneko, S. Shinkai, Chem. Commun.
2005, 4149–4150; b) A. Y. Y. Tam, K. M. C. Wong, V. W. W. Yam, J. Am.
Chem. Soc. 2009, 131, 6253–6060; c) A. Y. Y. Tam, K. M. C. Wong, V. W. W.
Yam, Chem. Eur. J. 2009, 15, 4775–4778; d) W. Lu, Y. Chen, V. A. L. Roy,
S. S. Y. Chui, C. M. Che, Angew. Chem. Int. Ed. 2009, 48, 7621–7625;
Angew. Chem. 2009, 121, 7757–7761; e) T. Tu, W. W. Fang, X. L. Bao, X. B.
Li, K. H. Dotz, Angew. Chem. Int. Ed. 2011, 50, 6601–6605; Angew. Chem.
2011, 123, 6731–6735; f) N. Komiya, T. Muraoka, M. Iida, M. Miyanaga,
K. Takahashi, T. Naota, J. Am. Chem. Soc. 2011, 133, 16054–16061; g) K. Y.
Liu, L. Y. Meng, S. L. Mo, M. M. Zhang, Y. Y. Mao, X. H. Cao, C. H. Huang,
T. Yi, J. Mater. Chem. C 2013, 1, 1753–1762; h) X. S. Xiao, W. Lu, C. M.
Che, Chem. Sci. 2014, 5, 2482–2488; i) J. L. L. Tsai, T. T. Zou, J. Liu, T. F.
Chen, A. O. Y. Chan, C. Yang, C. N. Lok, C. M. Che, Chem. Sci. 2015, 6,
3823–3830.
[9] a) J. A. G. Williams, Top. Curr. Chem. 2007, 281, 205–268; b) J. A. G. Willi-
ams, S. Develay, D. L. Rochester, L. Murphy, Coord. Chem. Rev. 2008, 252,
2596–2611; c) Y. Feng, J. H. Cheng, L. Zhou, X. G. Zhou, H. F. Xiang,
Analyst 2012, 137, 4885–4901; d) H. F. Xiang, J. H. Cheng, X. F. Ma, X. G.
Zhou, J. J. Chruma, Chem. Soc. Rev. 2013, 42, 6128–6185; e) K. Li, G. S. M.
Tong, Q. Wan, G. Cheng, W. Y. Tong, W. H. Ang, W. L. Kwong, C. M. Che,
Chem. Sci. 2016, 7, 1653–1673.
[10] a) J. B. Birks, Photophysics of Aromatic Molecules, Wiley, New York, 1970;
b) X. F. Ma, R. Sun, J. H. Cheng, J. Y. Liu, F. Gou, H. F. Xiang, X. G. Zhou,
J. Chem. Educ. 2016, 93, 345–350.
[14] a) Y. You, C. G. An, D. S. Lee, J. J. Kim, S. Y. Park, J. Mater. Chem. 2006,
16, 4706–4713; b) C. A. Strassert, C. H. Chien, M. D. G. Lopez, D. Kourkou-
los, D. Hertel, K. Meerholz, L. D. Cola, Angew. Chem. Int. Ed. 2011, 50,
946–950; Angew. Chem. 2011, 123, 976–980; c) Y. Z. Zheng, A. S. Bat-
sanov, M. A. Fox, H. A. Al-Attar, K. Abdullah, V. Jankus, M. R. Bryce, A. P.
Monkman, Angew. Chem. Int. Ed. 2014, 53, 11616–11619; Angew. Chem.
2014, 126, 11800–11803.
[15] a) P. Knuuttila, Acta Chem. Scand. A 1982, 36, 541–545; b) A. Adams, J. M.
Guss, C. A. Collyer, Biochemistry 1999, 38, 9221–9233.
[11] a) J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X.
Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun. 2001, 1740–1741; b) Y.
Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332–4353; c) M.
Received: July 13, 2016
Published Online: September 30, 2016
Eur. J. Inorg. Chem. 2016, 4862–4866
www.eurjic.org
4866
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim