Giant Concentric Metallosupramolecule with Aggregation-Induced Phosphorescent Emission

Article abstract of DOI:10.1021/jacs.0c06680

Fluorescent metallosupramolecules have received considerable attention due to their precisely controlled dimensions as well as the tunable photophysical and photochemical properties. However, phosphorescent analogues are still rare and limited to small structures with low-temperature phosphorescence. Herein, we report the self-assembly and photophysical studies of a giant, discrete metallosupramolecular concentric hexagon functionalized with six alkynylplatinum(II) bzimpy moieties. With a size larger than 10 nm and molecular weight higher than 26000 Da, the assembled terpyridine-based supramolecule displayed phosphorescent emission at room temperature. Moreover, the supramolecule exhibited enhanced aggregation-induced phosphorescent emission compared to the ligand by tuning the aggregation states through intermolecular interactions and significant enhancement of emission to CO2 gas.

Full text of DOI:10.1021/jacs.0c06680

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Giant Concentric Metallosupramolecule with Aggregation-Induced
Phosphorescent Emission
Yiming Li,∥ Gui-Fei Huo,∥ Bingqing Liu, Bo Song, Yuan Zhang, Xiaomin Qian, Heng Wang,
Guang-Qiang Yin, Alexander Filosa, Wenfang Sun, Saw Wai Hla, Hai-Bo Yang, and Xiaopeng Li*
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ABSTRACT: Fluorescent metallosupramolecules have received considerable attention
due to their precisely controlled dimensions as well as the tunable photophysical and
photochemical properties. However, phosphorescent analogues are still rare and limited
to small structures with low-temperature phosphorescence. Herein, we report the self-
assembly and photophysical studies of a giant, discrete metallosupramolecular
concentric hexagon functionalized with six alkynylplatinum(II) bzimpy moieties.
With a size larger than 10 nm and molecular weight higher than 26 000 Da, the
assembled terpyridine-based supramolecule displayed phosphorescent emission at room
temperature. Moreover, the supramolecule exhibited enhanced aggregation-induced
phosphorescent emission compared to the ligand by tuning the aggregation states
through intermolecular interactions and significant enhancement of emission to CO2
gas.
metal complexes.24 For instance, Cd(II) was frequently
assembled with tpy to construct fluorescent supramolecules,25
among which characteristic aggregation-induced emission
(AIE)12a,26 was observed. Recent examples further employed
tpy building blocks to construct phosphorescent metal-
lopolymers.27 Among the luminophores, square-planar Pt(II)
motifs have received considerable attention because of their
unique photophysical and electrochemical properties.28 These
complexes exhibit phosphorescence brought by the heavy-
atom effect with tunable emission wavelengths and life-
times.28b,29 Also, Pt(II) luminophores are prone to have
strong intermolecular Pt···Pt interaction,30 which can manip-
ulate their aggregations and enable emission through the
aggregation-induced phosphorescent emission (AIPE) effect,31
a variant of AIE. More importantly, Pt(II) complexes are
thermodynamically stable and kinetically inert.28a Thus, such
features facilitate the synthesis of tpy building blocks with
Pt(II) luminophores for further coordination-driven self-
assembly.
INTRODUCTION
■
Discrete metallosupramolecules obtained via coordination-
driven self-assembly have emerged as a class of materials to
bridge the gap between small molecules and polymers1 on
account of the precisely controlled dimensions that provide an
ideal platform for investigations of structure−property−
function relationships.2 Among the various functions, the
luminescence of metallosupramolecules has a wide range of
applications in sensing,3 photocatalysis,4 bioimaging,5 light
harvesting,6 phototherapy7 and so on.8 Emissive metal-
losupramolecules have been constructed mainly through the
following three strategies: (i) introducing the luminophores
into the scaffolds;9 (ii) attaching the luminophores on the
backbone as accessories;7c,10 and (iii) encapsulating lumino-
phores in the cavity of the structures through host−guest
chemistry.8f,11 Generally, the luminophores include small
organic motifs, such as tetraphenylethylene,12 boron-dipyrro-
methene (BODIPY),5b,13 triphenylamine,14 pyrene,15 and
perylene diimide,16 as well as emissive metal complexes
containing Ru(II),17 Eu(III),18 Ir(III),6a,10,19 Pt(II),20 and
Au(I).21 Among these emissive metallosupramolecules, how-
ever, phosphorescent analogues are still rare and mainly limited
to small structures with low-temperature phosphorescen-
ce.18d,20a,21a,22
On the basis of a previous study, we speculated the
combination of AIPE-active Pt(II) components with tpy-based
emissive supramolecules could create a synergy by which the
emissive properties of individual components could be retained
Received: June 21, 2020
2,2′:6′,2′′-Terpyridine (tpy), as one of the most intensively
investigated building blocks, has been widely used in
constructing sophisticated metallosupramolecular architectures
with well-defined sizes, shapes, and geometries.23 With weak
luminescence, tpy has been functionalized with many
luminophores to tune the emissive properties of corresponding
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A

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Scheme 1. Synthesis of Ligand L and Self-Assembly of Metallosupramolecule S
Figure 1. 1H NMR spectra of (a) L in CDCl3, (b) A in CDCl3, and (c) S in CD3CN. Broad signals of L were attributed to the strong aggregation in
solution.
and the hybrid supramolecular architectures could even display
superior AIPE compared to the individual components.
According to this speculation, we designed a giant but discrete
metallosupramolecular concentric hexagon (S) functionalized
with six Pt(II) bzimpy (bzimpy = 2,6-bis(benzimidazole-2′-yl)
pyridine) motifs. In the design, a terminal alkynyl group was
employed to install the Pt(II) motif with a stable and rigid
Pt(II)−alkynyl bond for further self-assembly. Also, we
introduced multiple hydrophilic ethylene glycol chains into
bzimpy moieties on the periphery and a long alkyl chain (C12)
into the interior to tune the aggregation through balancing the
overall hydrophobicity/hydrophilicity. With a size larger than
10 nm and a molecular weight higher than 26 000 Da, the
assembled tpy-based supramolecule containing six Pt(II)
centers displayed phosphorescent emission with a lifetime of
218 ns at room temperature. By synergistically combining
AIPE from Pt(II) luminophores and AIE features from
Cd(II)−tpy assemblies, the functionalized supramolecule S
exhibited significantly enhanced AIPE compared to the ligand
L. Via tuning the aggregation states of the functionalized ligand
L and S, their AIPE behaviors were carefully investigated.
More interestingly, further enhancement of phosphorescent
emission was observed in both L and S when purged by CO2
gas. As such, this system is expected to find practical
applications, such as gas sensing.
RESULTS AND DISCUSSION
■
In the synthesis of building block L, Scheme 1, tetratopic tpy-
pyridinium salt precursor A was synthesized using a modified
procedure as previously reported.23h A terminal alkynyl group
was introduced into the backbone of A in order to further
functionalize the metallosupramolecule, including installation
B
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of the following Pt(II) motif with the stable and rigid Pt(II)−
alkynyl bond. The detailed synthesis procedures for A (Scheme
S2) and chloroplatinum(II) bzimpy precursor P (Scheme S3)
are described in the Supporting Information (SI). The final
alkynylplatinum(II) bzimpy ligand L was synthesized by
bridging P and A in the presence of a catalytic amount of
copper(I) iodide and triethylamine in DMF solution under N2
atmosphere.
All of the ligands and precursors were fully characterized by
multidimensional nuclear magnetic resonance (NMR), includ-
1
ing H, 13C, 2D correlation spectroscopy (2D COSY), and/or
nuclear Overhauser effect spectroscopy (NOESY), as well as
electrospray ionization mass spectrometry (ESI-MS) (see
details in SI). It is noteworthy that the proton resonance of
ligand L showed very broad signals in CDCl3 (Figure 1a), as
well as in CD3CN (Figure S38). In contrast, the proton
resonance for the Pt(II) free precursor A displayed sharp
signals (Figure 1b). All of these results suggested that L was
highly prone to aggregate in solutions through intermolecular
Pt···Pt and π−π interactions.32
The self-assembly of S was achieved by treating L with
Cd(NO3)2 in a stoichiometric ratio of 1:2, followed by
counterion exchange with excess NH4PF6 to give S as a yellow
Figure 2. (a) ESI-MS and (b) TWIM-MS plots of S.
1
precipitate in a high yield. The H NMR spectrum of the
supramolecule (Figure 1c) showed much sharper signals
compared with the spectrum of L, indicating weaker
aggregation of S owing to the bulky size of the octahedral
coordination of the ⟨tpy−Cd(II)−tpy⟩ unit that reduced the
intermolecular Pt···Pt interactions. Two characteristic singlets
with an integration ratio of 1:1 were observed at 9.00 and 8.97
ppm, respectively, which were assigned to the tpy-H3′,5′
protons of the inner and outer layer, excluding formation of
polymeric species. Compared with those of A, the tpy-H3′,5′
signals of S showed a diagnostic downfield shift (ca. 0.3 ppm)
while the tpy-H6,6″ peaks exhibited a significantly upfield shift
(ca. 0.7 ppm), indicating complexation of tpy units with
Cd(II). Diffusion ordered spectroscopy (DOSY) NMR of S
revealed a narrow band with diffusion coefficient log D =
−9.20 at 298 K (Figure S50), suggesting formation of a
discrete structure. All of the assignments were further
supported by 2D COSY and NOESY spectra (Figures S45−
S49).
of the metallosupramolecules with high resolution, ultrahigh-
vacuum-low-temperature-scanning tunneling microscopy
(UHV-LT-STM) was also applied.23k,34 Ultrahigh vacuum
provided a clean and neat environment to minimize noise, and
low temperature would reduce thermal motion, thus leading to
a higher resolution. A very dilute solution of S was drop casted
on a Ag(111) substrate followed by cooling down to 4 K. Due
to the octahedral coordination and high electron density
around the metal center, the STM imaging showed six elliptic
bright dots corresponding to ⟨tpy−Cd(II)−tpy⟩ units, which
depicted the framework of a hexagonal structure (Figure 3d−
f). Within the magnified image, the shape and direction of each
elliptic-shaped lobe can be distinctly observed. Note that each
dot was attributed to the fusion of signals from two ⟨tpy−
Cd(II)−tpy⟩ units in the two layers because of the short
distance between them. Moreover, the double-layered scaffold
without Pt(II) motifs was measured to have a diameter of ∼8
nm and a height of ∼10 Å (Figure 3f−h), which agreed well
with the theoretical modeling (Figure 3a). In sharp contrast to
the bright lobes of ⟨tpy−Cd(II)−tpy⟩ units in STM measure-
ment, Pt atoms did not exhibit strong signals. We speculated
that the bulky ⟨tpy−Cd(II)−tpy⟩ unit with octahedral
coordination geometry might lift the entire organic moieties
off the substrate, as well as the end groups of alkynyl−Pt
bzimpy. Therefore, the square-planar Pt(II) center could have
less contact with the surface, leading to the loss of tunneling
current.
After the structural characterization, the emission properties
of S, L, and the precursors A and P were investigated in
acetonitrile solutions (mixed with 5% CH2Cl2 for A) at room
temperature. The normalized emission spectra are shown in
Figure 4a, and the emission parameters, including emission
wavelengths and lifetimes, are listed in Table S1. The
emissions of P, L, and S exhibited large Stokes shifts (>200
nm) with respect to their corresponding absorption bands
(Figure S64)35 and were prone to oxygen quenching. In
addition, the recorded emission lifetimes of L and S deduced
from the decay traces were 270 and 218 ns, respectively
(Figure 4b and 4c), which are longer than those of general
In addition, electrospray ionization-mass spectrometry (ESI-
MS) and traveling wave ion mobility-mass spectrometry
(TWIM-MS)33 were used to characterize the functionalized
supramolecule. A series of peaks with continuous charges from
13+ to 24+ was observed in ESI-MS (Figure 2a) due to the
−
successive loss of PF6 counterions. After deconvolution, the
molecular weight was calculated as 26 301 Da, corresponding
t o
t h e
c h e m i c a l
c o m p o s i t i o n
o f
C1188H1152N108O102Pt6Cd12P36F216. The experimental isotope
pattern of each charge state agreed well with the corresponding
simulated peak (Figure 2a inset, Figure S63). Moreover, only
one set of signals was observed from TWIM-MS, indicating
that there was no other structural conformer or isomer for the
assembled structure (Figure 2b).
To further study the structure of the supramolecule,
transmission electron microscopy (TEM) was utilized to
verify the size and shape of S. The supramolecules were
observed as a dispersion of individual uniform dots (Figure
3b). The average size of the particles was in good agreement
with the theoretical diameter calculated by molecular modeling
(Figure 3a and 3c). In order to directly visualize the structure
C
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Figure 4. (a) Normalized emission spectra of P and A (λex = 390 nm)
and L and S (λex = 370 nm) in N2 deoxygenated acetonitrile (with 5%
CH2Cl2 for A) at room temperature (c = 1 × 10−5 mol/L). Emission
lifetime decay traces of (b) L and (c) S.
fluorescence. These features implied a nature of room-
temperature phosphorescence through the emission from the
triplet excited states.
The emission spectra of P, L, and S resembled each other
with essentially the same energy and similar vibronic
progressions, indicating the same/similar original emitting
excited states. The vibronic spacing between the band maxima
(ca. 567 nm) and the shoulder (ca. 606 nm) was
approximately 1135 cm−1, which is in accordance with the
stretching mode of the aromatic rings.35 Also, broad tails were
observed in L and S compared to P due to the metal-metal-to-
ligand charge transfer(3MMLCT) excited states from the Pt···
Pt and π−π stacking interactions.32 In view of the similar
structural component in these three complexes, i.e., bzimpy, a
similar [(N^N^N)PtCl]+ complex was reported in the
literature, we attribute the observed emission originating
36
3
from the metal-perturbed π,π* emission of the bzimpy.
Pt(II)-contained precursor P exhibited short-lived emission of
18 ns (Figure S65). This phenomenon could be ascribed to the
presence of a thermally accessible low-lying metal-centered
3
nonemissive d,d state, which provided an additional decay
3
pathway and quenched the ligand-localized π,π* emission.
This is a common feature in many other [(N^N^N)PtCl]+
complexes.37 When the Cl ligand in P was replaced by the
acetylide ligand in L, the electron-donating ability of the
acetylide ligand lifted up the 3d,d state with a negligible impact
on the energy of the 3π,π* state. This separated the
Figure 3. TEM and STM imaging of S. (a) Molecular modeling of S
(ethylene glycol and alkyl chains were omitted for clarity). (b) TEM
image of S. (c) Magnified TEM image of S. (d) Large area STM
image of S showing the presence of two supramolecules (imaging
parameters: Vt = 2.5 V and It = 35 pA). (e) Magnified image of a
single supramolecule. (f) STM image of S with molecular modeling
overlay (imaging parameters: Vt = 2.5 V and It = 29 pA). (g and h)
STM line profiling measurements were performed along the green
and blue dashed lines shown in f.
3
3
nonemissive d,d state from the emitting π,π* state further
and consequently improved the emission in L. Introduction of
heavy-atom Cd(II) during the self-assembly of L into S could
induce intersystem crossing (a competing nonradiative thermal
process with the radiative decay path) from T1 to S0.
Meanwhile, the weak ligand field strength of the Cd(II) ion
3
would narrow the energy gap between the nonemissive d,d
D
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Figure 5. Emission spectra of L and S. (a) Emission spectra of ligand L in nondeoxygenated acetonitrile/water solvent (λex = 370 nm, c = 3.5 μM).
(b) Emission spectra of S in nondeoxygenated acetonitrile/water solvent (λex = 370 nm, c = 0.6 μM). (c) Emission intensity of L and S at 567 nm
with different fractions of water in nondeoxygenated acetonitrile/water solution. (d) Phosphorescent emission spectra of L with N2 deoxygenated
acetonitrile/water solvent (λex = 370 nm, c = 3.5 μM). (e) Phosphorescent emission spectra of S with N2 deoxygenated acetonitrile/water solvent
(λex = 370 nm, c = 0.6 μM). (f) Emission intensity of L and S at 567 nm with different fractions of water in N2 deoxygenated acetonitrile/water
solution. (g) Emission photographs of L in nondeoxygenated acetonitrile/water with various water fractions. (h) Emission photographs of S in
nondeoxygenated acetonitrile/water with various water fractions. (i) Emission photographs of L in N2 deoxygenated acetonitrile/water with various
water fractions (under 365 nm UV lamp). (j) Emission photographs of S in N2 deoxygenated acetonitrile/water with various water fractions (under
365 nm UV lamp).
3
state and the emitting π,π* state, which would decrease the
lifetime of S. Interestingly, S still retained a relatively long
lifetime of 218 ns. It is worth noting that these phosphorescent
properties are quite unique for such a giant supramolecule with
a diameter of 10 nm.
fractions of poor solvent (i.e., water) to investigate the AIPE
effects. Since both L and S have installed multiple ethylene
glycol chains for enhanced solubility in aqueous solutions, they
did not show immediate precipitation with a high fraction of
water. When the fraction of water was increased, the UV−vis
absorption spectra of both L and S (Figure S67) displayed a
rise in the absorption tail around 480 nm, indicating growth of
To investigate the intermolecular interactions within ligands
and supramolecules, temperature-dependent emission studies
were performed (Figure S66). The spectra of both L and S
showed that with the elevation of the temperature, the
intensity of the emission decreased dramatically as the
noncovalent interactions could become negligible at high
temperature.38 These results suggested the existence of Pt···Pt
interactions in both ligand L and supramolecule S at room
temperature. Indeed, formation of aggregations by Pt···Pt
interactions brought the restriction of an intramolecular
rotation (RIR) effect at low temperature26d,e and immobilized
the luminophores on the molecules, leading to the enhance-
ment of emission.
30d,39
3
the MMLCT transition due to Pt···Pt interaction
Both the ligand L and the supramolecule S showed weak
emission in pure acetonitrile with increasing fraction of water
as the poor solvent; S exhibited stronger emission in its
aggregation state due to the cooperative effect from the Pt(II)
motif and ⟨tpy−Cd(II)−tpy⟩ units (Figure 5a and 5b).
Furthermore, in the deoxygenated solvent without oxygen
quenching for the phosphorescence, supramolecule S exhibited
significantly enhanced AIPE compared to ligand L, i.e., the
maximum in emission intensity reached 3.1-fold enhancement
for S but only 1.3-fold increase for L (Figure 5b and 5e). In
addition, the AIPE behavior was well maintained along with
the increasing fraction of water from 0% to 50%. However,
Further detailed photophysical studies of L and S were
performed in acetonitrile/water mixed solvents with various
E
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Figure 6. TEM images of L and S aggregates. TEM images of the aggregates of L formed in acetonitrile/water mixtures containing (a) 20%, (b)
40%, (c) 60%, and (d) 80% water and aggregates of S formed in acetonitrile/water mixtures containing (e) 20%, (f) 40%, (g) 60%, and (h) 80%
water. (i) Proposed formation of sheet-like aggregates by L. (j) Proposed Pt···Pt interaction and π−π stacking between ligands with face-to-face
direction. (m) Worm-like aggregates of S. (k) Unfavorable face-to-face stacking. (l) Proposed head-to-tail Pt···Pt interaction bridging
supramolecules without ring stacking.
further increasing the poor solvent fraction (from 60% to 90%)
resulted in a decrease of the phosphorescent intensity. Due to
the poor solubility of L and S in water, we observed large
aggregates formed in the solutions with high water fractions
after the deoxygenating process. Also, precipitate formation
caused the decrement of phosphorescent intensity.
For further comparison and investigation of the AIPE
mechanism, supramolecule C without Pt(II) motif was
constructed (see detailed characterization in Figures S39−
S44, S61, and S62) by assembling A and Cd(II) directly
(Scheme S4). The emission enhancement was also observed
by increasing the fraction of water (Figure S69a), suggesting
the AIE feature of Cd(II)−tpy-based supramolecules. How-
ever, C exhibited a short-lived emission of less than 5 ns, and
no further enhancements were observed with deoxygenated
solvent (Figure S69b), indicating that this emission was
fluorescence only.
brought about a weaker enhancement for S and L, i.e., 3.1- and
1.3-fold increase, respectively. We speculated that CO2 might
have weak interactions with Pt(II),40 since CO2 has a kinetic
diameter of 3.3 Å, which is very close to the ideal distance
between Pt atoms in the Pt···Pt interaction (3.5 Å). As such,
CO2 might strengthen the Pt···Pt interactions between
supramolecules with a higher RIR effect, leading to an
increased emission. In addition, S exhibited more significant
responses to different gases than L, perhaps due to the
cooperative effect of multiple Pt(II) centers within the large
supramolecular architectures. This property may lead to a
potential application for gas sensing.41
Morphology studies of aggregates were generally used for
evaluating aggregation behaviors and investigating the AIE or
AIPE mechanism. Dynamic light scattering (DLS) and TEM
were utilized to further elucidate the relationship between the
luminescent properties and the aggregation of the ligand L and
supramolecule S. The DLS results (Figure S71) showed the
average hydrodynamic diameters (Dh) of the aggregations of L
and S were increased with the increment of the water fraction.
Also, the TEM images (Figure 6a−d) showed that L
aggregated into a layered nanosheet structure in acetonitrile/
water, and the size of the sheet was increased with the
Interestingly, variations in emission spectra were observed
using different gases to deoxygenate the solvent (Figure S70).
It was found that CO2 can further trigger substantial
enhancements in emission intensity compared with the results
in nondeoxygenated solvent (ca. 5.5-fold increase in the case of
S, and 1.8-fold increase in the case of L). For comparison, N2
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increment of water portion. In contrast, S aggregated into
worm-like structures (Figure 6e−h). With the increase of the
water fraction, the length of the worm-like aggregates extended
and finally became a cross-linked structure. These results
agreed well with the AIPE effect observed in acetonitrile/water
solvent.
concentration. Our endeavors expand the scope of discrete
phosphorescent materials into dimensions beyond 10 nm and
will shed light on the development of novel phosphorescent
materials that combine the advantages from small molecules
and polymers, i.e., precise functions, a high level of
sophistication, and facile device fabrication.
It is interesting to observe the tremendously different
aggregation morphologies of L and S. To gain further insight
into the aggregation mechanism, different solvent mixtures
were used to investigate their aggregation behaviors.
Compared with the layered structure observed in the
CH3CN/water system, L formed spherical aggregates with
diameters around 100 nm in DMF/Et2O solution, and larger
spherical structures could be observed in the DMF/i-Pr2O
system (Figure S72). The difference between the sheet and the
sphere is possibly due to the long hydrophobic/hydrophilic
chains decorated on the inner and outer rims of the ligand
performing differently in aqueous/nonaqueous solutions.
According to the observation, we postulated that both the
Pt···Pt interaction and π−π stacking might work simulta-
neously to organize ligand L with a face-to-face direction
(Figure 6j).
In a sharp contrast, after coordinating with Cd(II), the
metallosupramolecule S did not aggregate into spherical/
layered morphologies as L or a tubular structure as the
unfunctionalized concentric hexagons.23h Instead, the amor-
phous worm-like structure was the only morphology observed
in several different solvent systems (Figure S73). We
speculated that the entire concentric hexagon core played an
essential role in regulating the aggregating behavior of the Pt−
Pt interaction and determining the final morphology of the
hierarchical self-assembly. Since the ideal distance between the
Pt atoms in the Pt···Pt interaction is reported to be around 3.5
Å,42 the bulky octahedral coordination of ⟨tpy−Cd(II)−tpy⟩
with a height of 10 Å, as measured from STM, can effectively
prohibit formation of π−π stacking and block the Pt−Pt
interaction from the face-to-face orientation (Figure 6k) but
force the Pt−Pt interaction to a head-to-tail way (Figure 6l).
The emissive behavior of individual components (Pt and tpy)
was retained in supramolecule S, which displayed enhanced
phosphorescent properties during aggregation than individual
components.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c06680.
■
sı
Synthetic details; ligands and complexes characterization
1
including H NMR, 13C NMR, 2D COSY, 2D NOESY,
ESI-MS, TWIM-MS, UV−vis, TEM (PDF)
Compound 14 (CIF)
AUTHOR INFORMATION
Corresponding Author
■
Xiaopeng Li − College of Chemistry and Environmental
Engineering, Shenzhen University, Shenzhen 518055, China;
orcid.org/0000-0001-9655-9551; Email: xiaopengli@
szu.edu.cn
Authors
Yiming Li − College of Chemistry and Environmental
Engineering, Shenzhen University, Shenzhen 518055, China;
Department of Chemistry, University of South Florida, Tampa,
Florida 33620, United States
Gui-Fei Huo − Shanghai Key Laboratory of Green Chemistry
and Chemical Processes, Department of Chemistry, East China
Normal University, Shanghai 200062, China
Bingqing Liu − Department of Chemistry and Biochemistry,
North Dakota State University, Fargo, North Dakota 58105,
United States
Bo Song − Department of Chemistry, Northwestern University,
Evanston, Illinois 60208, United States
Yuan Zhang − Department of Physics, Old Dominion University,
Norfolk, Virginia 23529, United States
Xiaomin Qian − Department of Chemistry, University of South
Florida, Tampa, Florida 33620, United States
Heng Wang − College of Chemistry and Environmental
Engineering, Shenzhen University, Shenzhen 518055, China
Guang-Qiang Yin − College of Chemistry and Environmental
Engineering, Shenzhen University, Shenzhen 518055, China
Alexander Filosa − Department of Chemistry, University of
South Florida, Tampa, Florida 33620, United States
Wenfang Sun − Department of Chemistry and Biochemistry,
North Dakota State University, Fargo, North Dakota 58105,
United States; orcid.org/0000-0003-3608-611X
Saw Wai Hla − Nanoscience and Technology Division, Argonne
National Laboratory, Lemont, Illinois 60439, United States
Hai-Bo Yang − Shanghai Key Laboratory of Green Chemistry
and Chemical Processes, Department of Chemistry, East China
Normal University, Shanghai 200062, China; orcid.org/
0000-0003-4926-1618
CONCLUSIONS
■
In summary, a giant but discrete concentric metallosupramo-
lecule with six well-arrayed alkynyl−platinum(II) bzimpy
groups was assembled through rational design to enrich the
library of phosphorescent metallosupramolecules, which still
remain in its infancy. The cyclic structure was clearly visualized
by STM imaging at submolecular resolution. With the Pt(II)
motifs installed, the functionalized ligand and the metal-
losupramolecule exhibited room-temperature phosphorescence
with lifetimes of 270 and 218 ns, respectively. With the AIE
enhancement from the ⟨tpy−Cd(II)−tpy⟩ coordination,
supramolecule S exhibited conspicuously stronger AIPE
compared to ligand L. In addition, both the ligand and the
supramolecule exhibited significant responses to CO2 gas,
indicating the potential existence of weak interaction between
gas molecules and aggregates. Regarding the aggregation
behaviors driven by intermolecular interactions, the ligand
could aggregate into layered and spherical structures in
different solvent systems, while the supramolecule could only
aggregate into a worm-like structure and gel at high
Complete contact information is available at:
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Author Contributions
∥Y.L. and G.-F. H. contributed equally.
Notes
The authors declare no competing financial interest.
G
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ACKNOWLEDGMENTS
■
This research was supported by Shenzhen University and the
University of South Florida. Use of the Center for Nanoscale
Materials, an Office of Science user facility, was supported by
the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences, under Contract No. DE-AC02-
06CH11357.
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