Construction and luminescence property of a highly ordered 2D self-assembled amphiphilic bidentate organoplatinum(II) complex

Article abstract of DOI:10.1039/c6ra03553a

Rod-coil shaped amphiphilic bidentate dichloro(phenanthroline)platinum(ii) complexes, 1-Pt and 2-Pt, which possess different hydrophilic lateral chains on one side of an identical aromatic rod core, are synthesized. 1-Pt first forms dimers then arranges into well-defined two-dimensional (2D) films consisting of highly ordered molecular arrays both from methanol and on substrate. 2-Pt, as a building-block, yields micrometer-sized rigid 2D sheets without formation of an initial dimer. Red luminescence of the film is induced by self-assembly of nonemissive 1-Pt molecules, whereas sheets based on nonemissive 2-Pt gives weak yellow emission. These results indicate that the coil-rod ratio plays an important role in the structure and optical properties of these self-assemblies. Moreover, the film on the substrate at the macroscopic scale, exhibits multi-stimuli responsiveness, which predicts its application in smart chemosensing devices and probes.

Full text of DOI:10.1039/c6ra03553a

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Construction and luminescence property of
a highly ordered 2D self-assembled amphiphilic
Cite this: RSC Adv., 2016, 6, 27360
bidentate organoplatinum(II) complex†
a
a
a
a
b
*
Yunjie Xiang, Wenjing Li, Yuxi Fang, Dengqing Zhang, Xianying Li
ac
*
and Wusong Jin
Rod-coil shaped amphiphilic bidentate dichloro(phenanthroline)platinum(II) complexes, 1-Pt and 2-Pt,
which possess different hydrophilic lateral chains on one side of an identical aromatic rod core, are
synthesized. 1-Pt first forms dimers then arranges into well-defined two-dimensional (2D) films
consisting of highly ordered molecular arrays both from methanol and on substrate. 2-Pt, as
a building-block, yields micrometer-sized rigid 2D sheets without formation of an initial dimer. Red
luminescence of the film is induced by self-assembly of nonemissive 1-Pt molecules, whereas sheets
based on nonemissive 2-Pt gives weak yellow emission. These results indicate that the coil-rod ratio
plays an important role in the structure and optical properties of these self-assemblies. Moreover, the
film on the substrate at the macroscopic scale, exhibits multi-stimuli responsiveness, which predicts its
application in smart chemosensing devices and probes.
Received 7th February 2016
Accepted 4th March 2016
DOI: 10.1039/c6ra03553a
www.rsc.org/advances
usually utilized.4 In this regard, we used another simple strategy,
facile solution processable self-assembly approach, to increase
PtII/PtII and/or p–p interactions between Pt(diimine)Cl2 to
Introduction
The square-planar bidentate platinum(II) complexes have attracted
much attention because of their particularly appealing photo-
physical and photochemical properties.1 These appealing proper-
ties are not observed in tetrahedral and octahedral metal
complexes, since the forces, such as PtII/PtII and/or p–p between
two molecules2 can be facilitated by cofacial molecular interactions
in these platinum(II) complexes. The bidentate dichloro(diimine)
platinum(II) complexes [Pt(diimine)Cl2], in which the chlorine
atom as an auxiliary ligand, is one of a useful building blocks for
constructing luminescent materials.3 However, Pt(diimine)Cl2
complexes are oen found to be nonemissive in solution at room
temperature because the molecules are extremely distorted at the
low-lying d–d excited states in contrast to the ground state, which
leads to nonradiative decay.1a To improve their emissive proper-
ties, either the cultivation of crystals, which induces the
emission by enhancing PtII/PtII and/or p–p interactions between
Pt(diimine)Cl2, or substitution of the auxiliary Cl with other
groups, such as a strong s-donor and a strong p-acceptor, is
induce luminescence. In the self-assembling process, PtII/PtII
and/or p-p interactions are convenient to be modulated by
external inuences, which is benecial to generating the excellent
luminescent materials. To date, there have been few examples of
materials with induced luminescence by efficient self-assembly of
bidentate Pt(diimine)Cl2.
On the other hand, luminescent organoplatinum(II) 2D
materials, such as lms, are promising candidates as active
layers for chemosensing and organic electronic devices.5
Their structures and luminescence properties are governed by
PtII/PtII and/or p–p interactions through control of the
packing of molecules.6 Construction of such noncovalently
linked quasi-2D structures are regarded as of interest because
during self-assembly of small molecules into such structures at
the nanoscopic or molecular levels, precise control of the
bilateral intermolecular interactions is necessary but still
remains a longstanding challenge.7 Without elaborate design of
the building blocks, many defects are usually formed, leading to
ill-dened and/or nonemissive lms. Considering photo-
luminescence and application, the presence of highly ordered
arrays by PtII/PtII and/or p–p interactions is essential to avoid
unexpected agglomerates.8 Despite some luminescent nano-
objects of organoplatinum(II) that have been constructed by
crystallization, a facile solution-processable 2D material is more
realistic for application. Up to now, reports on the preparation
of highly ordered lms based on Pt(diimine)Cl2 with induced
luminescence are still limited.
aState Key Laboratory for Modication of Chemical Fibers and Polymer Materials,
College of Chemistry, Chemical Engineering and Biotechnology, Donghua University,
2999 North Renmin Road, Songjiang, Shanghai 201620, P. R. China
bSchool of Environmental Science and Engineering, Donghua University, 2999 North
Renmin Road, Songjiang, Shanghai 201620, P. R. China. E-mail: seanlee@dhu.edu.cn
cKey Laboratory of Natural Resources of Changbai Mountain & Functional Molecules
(Yanbian University), Ministry of Education, Park Road 977, Yanji, 133002, P. R.
China. E-mail: wsjin@dhu.edu.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra03553a
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Scheme 1 Reaction scheme of the designed amphiphilic bidentate dichloro(phenanthroline)platinum(II) complexes, 1-Pt and 2-Pt.
Amphiphiles composed of rigid hydrophobic rod and
hydrophilic coil segments are useful scaffolds for constructing
switchable hierarchical structures responding to the selected
conditions.9 The volume fraction of rod to coil segments, the
Results and discussion
Synthesis of amphiphilic rod–coil Pt(Phen)Cl2 complexes
Target amphiphilic rod–coil 1-Pt and 2-Pt were synthesized
cross-sectional area of the coil segment, or the shape of the rigid
segment, greatly inuence the molecules to form diversely
structured nanomaterials.10 Amphiphiles consisting of rational
coil and aromatic rod segments which could arrange side-by-
side have the tendency to grow in two dimensions to form
ordered self-assemblies.11 In the present study, we synthesize
novel amphiphilic bidentate platinum(II) complexes 1-Pt and
2-Pt (Scheme 1). These complexes possess the same planar
phenanthroline (Phen) aromatic rod but a different coil region.
1-Pt possesses four lateral triethylene glycol (OTEG) chains
whereas 2-Pt contains two hydrophilic OTEG segments. 1-Pt
molecules are successfully constructed into highly ordered
microscopic and macroscopic 2D lms from solution and on
substrate with induced red luminescence by self-assembly. In
the 2D lms, the molecular motion which results in non-
radiative decay inducing the luminescence quenching is ach-
ieved to be restrained. Compared with the weakly emissive
sheets of 2-Pt, this work provides insight into the molecular
structure–optical property relationships of organoplatinum(II)
2D self-assemblies at the molecule level.
following the synthetic route shown in Scheme 1. 1,10-Phe-
nanthroline hydrate reacted with Br2 to prepare brominated
phenanthroline 7. Compound
7 was oxidized to yield
3,8-dibromo-1,10-phenanthroline-5,6-dione 8. Compound
9
and 10 with different side chain was prepared by reaction
of compound 8 with 2-bromomethyl-1,3-bis{2-[2-(2-methoxy-
ethoxy)ethoxy]ethoxy}propane
5 and 1-(2-(2-methoxyethoxy)
ethoxy)-2-bromoethane 6, respectively. Compound 9 reacted
with biphenyl-4-ylboronic acid to afford 1. Amphiphilic rod–coil
1-Pt was obtained through reaction of 1 with K2PtCl4. 2-Pt was
synthesized following the similar reaction route as 1-Pt from
compound 10 by reacting with biphenyl-4-ylboronic acid and
further with K2PtCl4.
2D self-assembly of Pt(Phen)Cl2 with induced luminescence
from methanol solution
In CH2Cl2 and THF, the amphiphilic 1-Pt molecule, with four
exible side chains, formed a nonemissive transparent solution
owing to their relatively high solubility in these solvents.
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Fig. 1 (a) Emission spectra of 1-Pt with different concentrations of 1.0 ꢁ 10ꢂ7, 1.0 ꢁ 10ꢂ6, 5.0 ꢁ 10ꢂ6, 1.0 ꢁ 10ꢂ5, 5.0 ꢁ 10ꢂ5, 5.0 ꢁ 10ꢂ4, 6.0 ꢁ
10ꢂ4, 1.0 ꢁ 10ꢂ3, and 1.3 ꢁ 10ꢂ3 M, and (b) emission spectra of 2-Pt with different concentrations of 1.0 ꢁ 10ꢂ6, 5.0 ꢁ 10ꢂ6, 1.0 ꢁ 10ꢂ5, 1.0 ꢁ
10ꢂ4, 5.0 ꢁ 10ꢂ4, and 9.0 ꢁ 10ꢂ4 M in methanol, pass length ¼ 1 cm, lex ¼ 388 nm, slit width ¼ 3. Inset (a) luminescent photo of 1-Pt complex and
inset (b) photo of 2-Pt luminescence at concentration of 5.0 ꢁ 10ꢂ4 in methanol at room temperature irradiated by UV light at 365 nm.
Whereas, in water, 1-Pt did not exhibit a good solubility and 419 nm originated from the singlet metal to ligand charge
formed an orange luminescent precipitate (Fig. S1†). Interest- transfer (1MLCT) and the triplet metal to ligand or triplet metal
ingly, from methanol, 1-Pt formed a self-assembly with a red to metal to ligand charge transfer (3MLCT/3MMLCT), respec-
emission at high concentration (Fig. 1a inset).
tively. These bands arose from the coordination of ligand 1 with
Typically, the suspended methanol solution of 1-Pt was PtII.12 A dimerization plot for the monomer–dimer equilibrium
heated to 65 ꢀC, resulting a transparent yellow solution without was performed, which yielded a linear plot with an R2 of 0.9988
emission under irradiation with UV light at 365 nm. Upon (Fig. 2a and b). The results indicated the existence of dimer
cooling down to 25 ꢀC, the yellow suspension emitting red arising from metal–metal and/or p–p interactions.13 A weakly
emission was gradually formed within a few minutes. At a dilute emissive band centered at 667 nm in the luminescence spec-
concentration (1.0 ꢁ 10ꢂ6 M), self-assembly was not achieved trum (Fig. S3-b†) appeared, which was attributed to the pres-
and the solution was nonemissive (Fig. S2†). In the electronic ence of the dimer.14 In the concentration range from 1.0 ꢁ 10ꢂ7
absorption spectrum (Fig. S3-a†), the band at 376 nm and to 5.0 ꢁ 10ꢂ5 M (Fig. 1a), two emission bands appeared at
Fig. 2 (a) UV-vis spectra of 1-Pt complex in methanol with the concentrations of 1.0 ꢁ 10ꢂ6, 2.5 ꢁ 10ꢂ6, 5.0 ꢁ 10ꢂ6, 1.0 ꢁ 10ꢂ5, 2.5 ꢁ 10ꢂ5, and
5.0 ꢁ 10ꢂ5 M, and (c) UV-vis spectra of 2-Pt complex in methanol at the concentrations of 1.0 ꢁ 10ꢂ6, 2.5 ꢁ 10ꢂ6, 5.0 ꢁ 10ꢂ6, 7.5 ꢁ 10ꢂ6, 1.0 ꢁ
10ꢂ5, 2.5 ꢁ 10ꢂ5, 5.0 ꢁ 10ꢂ5, and 7.5 ꢁ 10ꢂ5 M (arrow shows spectra with increasing concentration). (b) Dimerization plot for a monomer–dimer
equilibrium of 1-Pt in methanol at 328 nm, R2 for the fitting of linear line is 0.9988. (d) Nonlinear dimerization plot for 2-Pt in methanol at 391 nm.
Inset (a) and (c) are the corresponding zoomed-in UV-vis spectra.
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438 nm from the monomer and 667 nm from the dimer spectra (Fig. 1b), which indicated that the molecular arrange-
respectively. With an increasing concentration, the intensity of ment of this yellow luminescent 2-Pt was different from that of
the monomeric band initially increased and then decreased red emissive 1-Pt. The SEM micrograph displayed that the
when the concentration reached to 5.0 ꢁ 10ꢂ5 M, which indi- sample consisted of large amounts of rigid 2D sheets in
cated the disappearance of monomer, while the band arising micrometer length and width (Fig. 3d). Differing from 1-Pt, the
from the dimer15 exhibited an increased intensity and a gradual TEM image did not exhibit ordered arrays in the sheets (Fig. 3e
blue-shi. From 5.0 ꢁ 10ꢂ4 M to 1.3 ꢁ 10ꢂ3 M, the dimeric and f). Combined with the former result of the nonlinear
band centered at 667 nm blue-shied to 614 nm,16 which were dimerization plot (Fig. 2d), it was concluded that the rigid 2D
assignable to the formation of the self-assembly by further sheets arranged by 1-Pt without formation of initial dimer. This
aggregation of dimers. In above aggregate, the free rotation of might arise from the quick precipitation of 2-Pt with relatively
the molecules can be suppressed to reduce the inefficient low solubility from methanol. These results demonstrated the
radiation,17 in order to tune them from being quenched to critical role of the molecular structure, especially, the ratio of
emissive. Scanning electronic micrograph (SEM) of an air-dried lateral coil to rod, both in the formation of highly ordered
suspension sample of 1-Pt from methanol (5.0 ꢁ 10ꢂ4 M) on structure and corresponding optical properties.
a silicon wafer surface, showed a wrinkled 2D lm with
X-ray diffraction (XRD) was used to study more details about
micrometer size (Fig. 3a). Transmission electronic microscopy the packing models and the luminescence mechanism. The
(TEM) indicated the multilayer structure of the lm (Fig. 3b). XRD prole (Fig. 4b) of the 1-Pt lm on a quartz surface showed
ꢀ
˚
Interestingly, the magnied TEM micrograph showed that each that the d-spacings of 28.85, 16.16 and 9.50 A (2q < 10 ) in the
layer was consisted of a highly ordered array of equidistant, ratio of 1 : 2 : 3 indicated the formation of lamellar structure.
parallel line-like architectures with spacing of 0.3–0.4 nm From the density functional theory (DFT) calculation results of
˚
(Fig. 3c).
1-Pt, the width of the 1-Pt head part was 6.91 A (Fig. S4†) along
˚
In contrast, 2-Pt, bearing two exible hydrophilic side the b axis. A spacing of 9.50 A, much bigger than the width of
chains, easily precipitated from methanol, which was attributed one molecular head and smaller than twice of them, indicated
to the reduced solubility and hydrophilicity. The yellow emis- that two 1-Pt partially overlapped together. The peak with a d-
˚
sive precipitate of 2-Pt was obtained from a dilute methanol spacing of 3.82 A in the wide-angle X-ray diffraction (WAXD)
solution (1.0 ꢁ 10ꢂ6 M) by a similar heating and cooling pattern, corresponding to the Pt/Pt distance along c axis or
process. For 2-Pt, no dimer was formed, which was indicated by p–p stacking, indicated Pt/Pt or p–p interactions between two
the nonlinear dimerization plot (Fig. 2c and d). With increasing overlapped 1-Pt molecules. These results demonstrated that two
concentration, the corresponding dimeric band at 620–700 nm 1-Pt molecules stacked upon each other in a head-to-head
did not appeared in the concentration-dependent luminescence manner with partial overlap, and the tails extended to the outer,
Fig. 3 (a) SEM, (b) TEM and (c) magnified TEM image of the 1-Pt film. (d) SEM, (e) TEM and (f) magnified TEM image of the sample of 2-Pt. SEM and
TEM samples were prepared by drop-casting solution onto the silicon wafer and copper grid, respectively.
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Fig. 4 (a) Molecular packing model in 2D film of 1-Pt. (b) WAXD and SAXD profiles (inset) of 1-Pt 2D film which was prepared from methanol by
drop-casting in heating and cooling process.
to form a dimer, probably due to the steric hindrance of lateral
2D self-assembly of Pt(Phen)Cl2 on substrate
˚
coils. A spacing of 22.87 A, smaller than the length of one dimer
For practical application, the construction of luminescent
organometallic lms with highly ordered nanostructures on
substrate is desired. 1-Pt is not only able to build 2D lm from
methanol solution but also on substrate. For example, a hot
along the a axis, suggested that dimers might overlap side-by-side
˚
with a center-to-center (Pt-to-Pt) distance of 22.87 A between two
dimers to form 1D structure along the a axis (Fig. 4a).18 This
conguration subsequently assembled into a 2D monolayer
ꢀ
transparent methanol solution (65 C) of amphiphilic 1-Pt, ob-
˚
through weak p–p or Pt/Pt interactions (3.99 A in WAXD pattern)
tained by heating the suspension sample (5.0 ꢁ 10ꢂ4 M), was cast
on a quartz surface and then cooled to 25 ꢀC, upon spontaneous
evaporation of methanol, to form yellow macroscopic lm in
a few minutes (Fig. 5a). Electronic absorption spectrum of the
lm (Fig. 5c) showed a band at 429 nm arising from
3MLCT/3MMLCT.3,12,13,19 The red-shied band, compared with
that at 419 nm of its hot transparent solution, implied stronger
intermolecular interactions in the lm than in solution state. The
zoomed-in TEM image demonstrated that the lm was composed
of highly ordered arrays with width of 0.3–0.4 nm (Fig. 5d), which
was identical to the lm obtained from the methanol suspension
by heating and cooling process. By drop-casting, 1-Pt easily
constructed highly ordered 2D lm with red luminescence on
substrate (Fig. 5b). On the contrary, by drop-casting a hot (65 ꢀC)
methanol solution of 2-Pt (5.0 ꢁ 10ꢂ4 M) on quartz surface,
a yellow bulk lm (Fig. S7-a†) exhibiting weak yellow-brown
emission (Fig. S7-b†) was obtained.
along the c axis, which is in accordance with the spacing described
in the magnied TEM image (Fig. 3c).18 The calculated thickness of
˚
the monolayer was about 44.52 A. The atomic force microscopy
(AFM) image of the lm (Fig. S5†), prepared by diluted
solution (1.0 ꢁ 10ꢂ6 M), showed that the height of the layers was in
4.0–5.5 nm, in agreement with the calculated value, which
conrmed the existence of monolayer structure. Such monolayer
further cross-connected in a tail-to-tail method along the b axis to
form lamellar structure, in which the center-to-center distance of
˚
the monolayers is 28.85 A (Fig. 4a). These results suggested that
the Pt/Pt and/or p–p interactions were enhanced and/or the
motion of molecules were restrained by the dense packing of
amphiphilic 1-Pt molecules in the 2D self-assembly to induce red
luminescence. Whereas, for 2D sheets of 2-Pt with two hydrophilic
˚
tails, XRD patterns (Fig. S6†) showed d-spacings of 17.52 A and
ꢀ
˚
8.77 A (2q < 10 ) in the ratio of 2 : 1, which may suggest the
formation of lamellar structure. But, in combination with the
results of TEM micrograph, the 2D sheets were formed without
highly ordered arrays. These results indicated the importance of
the molecular structure in the packing model and luminescence
properties of these 2D self-assemblies.
Multi-stimuli responsiveness of the 1-Pt lm
Self-assembled square-planar platinum(II) complexes are
sensitive to environmental factors such as temperature,
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Fig. 6 (a) Diverse luminescence colors of the macroscopic film of 1-Pt
on a quartz substrate after exposure to Vocs with different polarities.
(b) Responsiveness of the film to acetic acid. (c) Luminescence color
changes of the red emissive film triggered by temperature.
devices. Whereas, the lm of 2-Pt only exhibited acid respon-
siveness and inconspicuous vapoluminescence (Fig. S11†). In
contrast to 1-Pt, the acidic quenched emission of the 2-Pt lm
was irreversible even aer removal of acetic acid (Fig. S12†).
Fig. 5 (a) Yellow-colored photograph and (b) red luminescence
photograph (lex ¼ 365 nm) of a 1-Pt film prepared by drop-casting the
hot methanol solution (5.0 ꢁ 10ꢂ4 M) on a quartz substrate and then
cooling it to room temperature (RT). (c) Electronic absorption spectra
of hot methanol solution (5.0 ꢁ 10ꢂ4 M) of 1-Pt (dotted line) and film
(solid line). (d) TEM micrograph of the film which was manufactured by
drop-casting the heated methanol solution (5.0 ꢁ 10ꢂ4 M) on a copper
grid and cooling to RT.
Conclusions
In summary, amphiphilic dichloro(phenanthroline)platinum(II)
complexes, 1-Pt and 2-Pt, with different hydrophilic coil chains
and the same lateral aromatic rod, are synthesized. 1-Pt
successfully self-assembled in highly ordered 2D lm from
methanol solution. The close packing of molecules in this 2D
lm enhanced the PtII/PtII and p–p interactions leading to the
induced red emission. Whereas, 2-Pt, with less hydrophilic coil,
formed weak yellow luminescent 2D sheets. Moreover,
the macroscopic lm of 1-Pt can be efficiently gained by
drop-casting the hot solution on the quartz substrate. By
adjusting the lateral coil of platinum(II) complexes, the struc-
ture, optical property and multi-stimuli-responsiveness of these
2D self-assemblies can be modulated. Our work may offer
intriguing potential for development of intelligent 2D chemo-
sensing materials.
pressure, pH and vapor, resulting in a change of the original
color or luminescence, which are benecial for use as sensor.20
Distinct from most single or dual stimuli-responsive organo-
platinum materials, the red luminescent lm of 1-Pt showed
multi-stimuli-responsiveness to volatile organic compounds
(Vocs), acids, and temperature (Fig. 6). When 1-Pt lm was
exposed to Vocs, its emissive color changed within a few
seconds irreversibly (Fig. 6a). The luminescence color was
converted differently which was due to different changes of
intermolecular interactions induced by Vocs with variable
polarity in the lm.21 Furthermore, the lm can respond to
acidic stimuli in a few seconds. The vapor of strong acids, such
as HCl, triuoromethanesulfonic acid, and triuoroacetic acid,
quenched the luminescence unrecoverably (Fig. S8†). Acetic
acid can also quench the luminescence of the lm in seconds.
Aer removal of acetic acid by evaporation, the emission was
switched on again (Fig. 6b), which may indicate the different
responsive mechanism from the mentioned strong acids.
Thermoresponsiveness was another property of this lm. The
emission was gradually quenched with increasing temperature
from 25 to 110 ꢀC, lower than the decomposition temperature of
1-Pt at 306 ꢀC (obtained by TG analysis; Fig. S9†), attributed to
changes of the PtII/PtII and/or p–p interactions.22 The lumi-
nescence of the lm was turned on again by cooling it to room
temperature (Fig. 6c). The TEM image of the cooled lm
(Fig. S10†) showed the similar ordered array as observed before
heating up to 110 ꢀC (Fig. 3c). These results demonstrate the
potential for applications in chemical sensing and smart
Experimental section
General
Unless otherwise noted, all commercial reagents were used as
received without further purication. Methallyl dichloride (98%,
GC) was purchased from TCI (Tokyo Chemical Industry) and
methanol (99.9%, GC) was purchased from Adamas Reagent,
Ltd. Tetrahydrofuran (THF) was reuxed over a mixture of
sodium and benzophenone under argon and distilled just before
use. Dichloromethane/CH2Cl2 (DCM) was dried over CaH2
under argon and freshly distilled prior to use. 1H NMR and 13C
NMR spectra were recorded on a Bruker model Bruker AV-400
spectrometer, operating at 400 and 101 MHz, respectively.
Matrix-assisted laser desorption ionization time-of-ight mass
spectrometry (MALDI-TOF MS) was performed on an AB Sciex
model AB Sciex 4800 Plus MALDI TOF/TOF analyzer, using
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dithranol as a matrix. Electronic absorption spectra were recor- cooling to room temperature, the solution was poured into
ded on a PERSEE model TU-1901 spectrophotometer, using water and extracted with DCM. The organic layer was dried over
a quartz cell of 1 cm path length. Luminescent spectroscopy was anhydrous MgSO4. The solvent was removed by Rotavapor, and
conducted using a quartz cell of 1 cm path length on a HORIBA the crude product was then puried by ash column chroma-
Scientic model Fluoromax-4 spectrophotometer. Scanning tography (SiO2, PE/EA ¼ 1/1, v/v), giving the product 5 as
electron microscopy (SEM) was performed on a HITACHI model colorless liquid. Yield: 1.5 g (65%). 1H NMR (400 MHz, CDCl3):
S-4800 FE-SEM electron microscope operating at 5 kV. Trans- d (ppm) 3.68–3.45 (m, 30H), 3.38 (s, 6H), 2.31–2.23 (m, 1H). 13
C
mission electron micrographs (TEM) were recorded on a JEOL NMR (101 MHz, CDCl3): d (ppm) 72.1, 70.8, 70.7, 70.6, 70.2, 59.2,
Model JEM-2100/2100 electron microscope operating at 200 kV. 41.5, 33.6. HRMS (FAB): calcd for C18H37O8Br [M + H]+: m/z ¼
Atomic force microscopy (AFM) was performed on a Bruker 461.1750, found: 461.1744.
model Dimension Icon microscope.
Synthesis of 1-(2-(2-methoxyethoxy)ethoxy)-2-bromoethane
(6). The solution of CBr4 (6.56 g, 20 mmol) in dry DCM (5 mL)
was slowly added into the solution of triethylene glycol mono-
methylether (1.64 g, 10 mmol) in dry DCM (15 mL). The reaction
Synthesis of compounds
Synthesis of 3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}-2-({2- mixture was cooled to 0 ꢀC under argon atmosphere. Triphenyl
[2-(2-methoxyethoxy)ethoxy]ethoxy}-methyl)propene (3). NaH phosphine (5.24 g, 20 mmol) in DCM (5 mL) ꢀwas added drop-
(19.2 g, 0.8 mol) and methallyl dichloride (13.5 g, 0.11 mol) in wise to the mixture. Then it was stirred at 50 C for 12 h. Aer
freshly distilled dry THF (200 mL) were placed in a dry round- cooling to room temperature, the solution was poured into
bottom ask under an argon atmosphere. Then triethylene water and extracted with DCM. The organic layer was dried over
glycol monomethylether (37.24 g, 0.23 mol) was added inside anhydrous MgSO4. The solvent was removed by Rotavapor, and
dropwise. The mixture was stirred for 15 min at room temper- the crude product was then puried by ash column chroma-
ꢀ
ature and then heated up to 65 C to react for 12 hours. Aer tography (SiO2, PE/EA ¼ 5/1), giving the product 6 as colorless
1
cooling to room temperature, the reaction mixture was liquid. Yield: 1.6 g (70%). H NMR (400 MHz, CDCl3): d (ppm)
quenched with water and extracted with DCM. The organic layer 3.81 (t, J ¼ 6.3 Hz, 2H), 3.70–3.64 (m, 6H), 3.58–3.54 (m, 2H),
was then dried over anhydrous MgSO4. The solvent was then 3.47 (t, J ¼ 6.3 Hz, 2H), 3.39 (s, 3H). 13C NMR (101 MHz, CDCl3):
removed by Rotavapor. The residue was quickly and simply d (ppm) 30.3, 59.0, 70.5, 70.6, 71.2, 71.9. ESI mass: calcd for
puried by column chromatography (SiO2, hexane/acetone/ C7H15BrO3 [M + H]+: m/z ¼ 227.03, found: 227.05. Anal. calcd for
CH2Cl2/EtOH ¼ 5/2/3/0.5, v/v) to give compound 3 as liquid. The C7H15BrO3: C, 37.02; H, 6.66. Found: C, 36.92; H, 6.57.
compound 3 can be used in the next step without further
purication.
Synthesis of 3,8-dibromo-1,10-phenanthroline (7). A solution
of 1,10-phenanthroline hydrate (2 g, 10 mmol) in nitrobenzene
Synthesis of 3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}-2-({2- (4 mL) was heated to 140 ꢀC under argon atmosphere. Then
[2-(2-methoxyethoxy)ethoxy]ethoxy}-methyl)propanol
(4). bromine (0.77 mL, 15 mmol) in 2 mL nitrobenzene was added
Compound 3 (3.3 g, 8.86 mmol) in freshly distilled dry THF (25 inside dropwise. The mixture was stirred at 140 ꢀC for 48 hours.
mL) was placed in a dry round-bottom ask under argon and Aer adding the same equivalent of bromine, it continued to
cooled to 0 ꢀC in an ice bath. BH3 (1 M, 16.5 mL) in THF (20 mL) react for 48 hours. The reaction mixture was cooled to room
was added slowly inside. The reaction mixture was stirred at temperature, and treated with aqueous ammonia solution, then
0
ꢀC for 2 hours. Then it was quenched with NaOH aqueous extracted with DCM. The organic layer was dried over anhy-
solution (3 M, 16.5 mL) and stirred for 15 min, followed by drous MgSO4. The solvent was removed by Rotavapor, and the
adding 30% H2O2 aqueous solution (16.5 mL). The obtained crude product was then puried by ash column chromatog-
mixture was stirred at room temperature for 30 min more and raphy (SiO2, CH2Cl2/EA ¼ 10/15), giving the product 7 as white
1
saturated with K2CO3, then extracted with DCM. The organic solid. Yield: 1.22 g (36%). H NMR (400 MHz, CDCl3): d (ppm)
layer was dried over anhydrous MgSO4 and the solvent was 9.24 (s, 2H), 8.47 (s, 2H), 7.80 (s, 2H). 13C NMR (101 MHz,
removed by Rotavapor. Purication of the residue by silica gel CDCl3): d (ppm) 151.69, 144.15, 137.70, 129.70, 126.99, 120.35.
ash column chromatography (SiO2, EA/CH3OH ¼ 15/1, v/v) HRMS (MALDI-TOF): calcd for C12H6Br2N2 [M + K]+: m/z ¼
yielded 3.0 g of 4 (87%) as colorless liquid; 1H NMR (400 MHz, 374.8535, found: 374.6033.
CDCl3): d (ppm) 3.68 (t, J ¼ 5.6 Hz, 1H, –OH), 3.60–3.47 (m,
Synthesis of 3,8-dibromo-1,10-phenanthroline-5,6-dione (8).
30H), 3.32 (s, 6H), 2.10–2.04 (m, 1H). 13C NMR (101 MHz, Solid KBr (4.3 g, 36.3 mmol) was placed in a two-necked ask
CDCl3): d (ppm) 72.1, 71.0, 70.8, 70.75, 70.7, 70.68, 70.6, 63.6, equipped with a condenser. The ask was placed in an ice bath,
59.2, 41.4. HRMS (FAB): calcd for C18H38O9 [M + H]+: m/z ¼ and then concentrated H2SO4 (98%, 6 mL) was added inside
399.2594, found: 399.2601.
dropwise, followed by the addition of concentrated HNO3 (68%,
Synthesis of 2-bromomethyl-1,3-bis{2-[2-(2-methoxyethoxy) 7.4 mL). 7 (1.22 g, 3.63 mmol) was dissolved in the concentrated
ethoxy]ethoxy}propane (5). The solution of CBr4 (3.28 g, 10 H2SO4 (10 mL) and then added dropwise to the pre-cooled
mmol) in dry DCM (5 mL) was slowly added into the solution of mixture. The resulting mixture was stirred for 20 min at room
compound 4 (2.0 g, 5 mmol) in dry DCM (15 mL). The reaction temperature and then for 3 h at 80 ꢀC. Aer cooled down to
mixture was cooled to 0 ꢀC under argon atmosphere. Triphenyl room temperature, this mixture was poured into ice (100 g) and
phosphine (2.62 g, 10 mmol) in DCM (5 mL) was added drop- neutralized to pH z 7 with aqueous ammonia solution (25%).
wise into the mixture. Then it was stirred at 50 ꢀC for 12 h. Aer The gained solution was then extracted with DCM. The organic
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layer was dried over anhydrous MgSO4. The solvent was 2.60 (m, 2H). 13C NMR (101 MHz, CDCl3): d (ppm) 147.32,
removed by Rotavapor, and the crude product was then puried 143.46, 142.35, 139.60, 138.32, 137.17, 134.11, 131.23, 129.03,
by ash column chromatography (SiO2, CH2Cl2), giving the 128.23, 128.05, 127.20, 127.10, 73.04, 71.87, 70.75, 70.56, 70.49,
product 8 as yellow solid. Yield: 1.02 g (77%). 1H NMR (400 70.44, 69.33, 59.05, 40.84. HRMS (MALDI-TOF): calcd for
MHz, CDCl3): d (ppm) 9.14 (d, J ¼ 2.3 Hz, 2H), 8.61 (d, J ¼ 2.4 Hz,
C
72H96N2O18[M + H]+: m/z ¼ 1277.6736, found: 1278.2584; for 2,
2H). 13C NMR (101 MHz, CDCl3): d (ppm) 177.13, 157.60, 150.47, 1H NMR (400 MHz, CDCl3): d (ppm) 9.41 (s, 2H), 9.09 (s, 2H),
139.53, 128.44, 123.58. MALDI-TOF mass: calcd for 7.91 (d, J ¼ 8.1 Hz, 4H), 7.82 (d, J ¼ 8.1 Hz, 4H), 7.69 (d, J ¼ 7.6
C
12H4Br2N2O2 [M + H]+: m/z ¼ 366.87, found: 367.71. Anal. calcd Hz, 4H), 7.51 (s, 4H), 7.42 (t, J ¼ 7.4 Hz, 2H), 4.55 (s, 4H), 3.89 (s,
for C12H4Br2N2O2: C, 39.17; H, 1.10; N, 7.61. Found: C, 39.21; H, 4H), 3.72–3.67 (m, 4H), 3.58 (t, J ¼ 4.8 Hz, 4H), 3.52–3.48 (m,
1.29; N, 7.52.
4H), 3.45–3.40 (m, 4H), 3.29 (s, 6H). 13C NMR (101 MHz, CDCl3):
Synthesis of 5,6-bis[2-(2,5,8,11-tetraoxadodec-1-yl)-4,7,10,13- d (ppm) 147.26, 143.10, 141.85, 140.01, 136.90, 135.30, 130.12,
tetraoxatetradec-1-yl]oxy]-3,8-dibromo-1,10-phenanthroline (9) 128.96, 128.06, 127.99, 127.85, 127.09, 126.95, 73.19, 71.82,
and 5,6-bis[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]-3,8-dibromo- 70.63, 70.57, 70.52, 70.23, 58.97. HRMS (MALDI-TOF): calcd for
1,10-phenanthroline (10). Compound 8 (200 mg, 0.55 mmol),
Bu4NBr (116 mg, 0.36 mmol), Na2S2O4 (575 mg, 3.3 mmol), and
C
50H52N2O8 [M + H]+: m/z ¼ 809.3802, found: 808.9722.
Synthesis of compound 1-Pt and 2-Pt. A mixture of 1 (70 mg,
compound 5 (1.26 g, 2.73 mmol) or compound 6 (617 mg, 2.73 0.055 mmol) or 2 (44.49 mg, 0.055 mmol) and K2PtCl4 (25.03
mmol) in the mixture solvent H2O/THF (4/8 mL) were stirred mg, 0.060 mmol) in C2H5OH (35 mL) was stirred under reux
under argon atmosphere at room temperature. Then KOH for 36 h at argon atmosphere. Aer cooling to room tempera-
aqueous solution (462 mg, 8.25 mmol) in 4 mL H2O was added ture, the reaction mixture was evaporated. It was dissolved into
inside. The mixture was stirred at 80 ꢀC for 2 days. Aer cooling CH2Cl2 and reprecipitated by methanol. The gained product
to room temperature, the solution was poured into water and was further puried by thin layer chromatography (SiO2,
extracted with DCM. The organic layer was dried over anhy- CH2Cl2/methanol ¼ 25/1 or CH2Cl2/methanol ¼ 35/1). Yield: 50
drous MgSO4. The solvent was removed by Rotavapor, and the mg of 1-Pt (60%) or 25 mg of 2-Pt (43%) respectively. For 1-Pt, 1H
crude product was then puried by ash column chromatog- NMR (400 MHz, CDCl3): d (ppm) 9.60 (s, 2H), 9.01 (s, 2H), 7.69
raphy (SiO2, CH2Cl2/acetone ¼ 3/1 or EA), giving the product 9 (dd, J ¼ 17.2, 8.1 Hz, 8H), 7.53 (d, J ¼ 7.3 Hz, 4H), 7.43–7.35 (m,
or 10 as colorless liquid. Yield: 325 mg of 9 (53%) or 240 mg of 6H), 4.50 (d, J ¼ 5.2 Hz, 4H), 3.79 (d, J ¼ 5.7 Hz, 8H), 3.64 (d, J ¼
10 (67%) respectively. For 9, 1H NMR (400 MHz, CDCl3): d (ppm) 4.6 Hz, 8H), 3.57 (d, J ¼ 4.7 Hz, 32H), 3.51–3.46 (m, 8H), 3.33 (s,
9.06 (s, 2H), 8.71 (d, J ¼ 1.7 Hz, 2H), 4.26 (d, J ¼ 5.6 Hz, 4H), 3.71 12H), 2.66–2.58 (m, 2H). 13C NMR (101 MHz, CDCl3): d (ppm)
(t, J ¼ 5.4 Hz, 8H), 3.65–3.58 (m, 40H), 3.52–3.48 (m, 8H), 3.34 (s, 145.27, 144.70, 144.21, 141.90, 139.35, 137.03, 134.26, 130.88,
12H), 2.51 (dt, J ¼ 11.6, 5.8 Hz, 2H). 13C NMR (101 MHz, CDCl3): 128.96, 128.62, 127.90, 127.89, 126.90, 73.21, 71.88, 70.65,
d (ppm) 150.07, 142.45, 141.09, 133.03, 127.49, 120.81, 72.43, 70.56, 70.47, 69.39, 58.99, 40.83. HRMS (MALDI-TOF): calcd for
71.88, 70.64, 70.57, 70.48, 70.45, 69.26, 58.99, 40.70. HRMS
C
72H96Cl2N2O18Pt [M
+
K]+: m/z
¼
1580.53200, found:
(MALDI-TOF): calcd for C48H78Br2N2O18 [M + K]+: m/z ¼ 1581.51974; for 2-Pt, 1H NMR (400 MHz, CDCl3): d (ppm) 9.30 (d,
1167.3253, found: 1166.8026; for 10, 1H NMR (400 MHz, CDCl3): J ¼ 1.6 Hz, 2H), 9.17 (d, J ¼ 1.8 Hz, 2H), 7.60 (dd, J ¼ 19.8, 8.4 Hz,
d (ppm) 9.09 (d, J ¼ 1.5 Hz, 2H), 8.88 (d, J ¼ 1.9 Hz, 2H), 4.46– 8H), 7.45 (dd, J ¼ 6.5, 3.0 Hz, 4H), 7.38–7.34 (m, 6H), 4.74 (dd, J
4.42 (m, 4H), 3.84–3.80 (m, 4H), 3.70 (s, 8H), 3.66–3.63 (m, 4H), ¼ 4.9, 2.9 Hz, 4H), 3.99–3.94 (m, 4H), 3.75–3.70 (m, 4H), 3.61–
3.54–3.51 (m, 4H), 3.35 (s, 6H). 13C NMR (101 MHz, CDCl3): 3.57 (m, 4H), 3.50 (dd, J ¼ 5.8, 3.2 Hz, 4H), 3.42 (dd, J ¼ 5.7, 3.2
d (ppm) 150.35, 142.09, 141.97, 132.89, 127.52, 120.47, 72.87, Hz, 4H), 3.29 (s, 6H). 13C NMR (101 MHz, CDCl3): d (ppm)
71.86, 70.66, 70.58, 70.11, 58.98. HRMS (MALDI-TOF): calcd for 145.05, 144.69, 144.30, 141.85, 139.36, 136.77, 134.13, 131.34,
C
26H34Br2N2O8 [M + K]+: m/z ¼ 699.0319, found: 700.6271.
128.95, 128.86, 127.81, 126.88, 73.77, 71.86, 70.59, 70.53, 70.48,
Synthesis of compound 1 and 2. [Pd(PPh3)4] (26 mg, 0.022 58.99, 31.52, 31.45, 30.20, 29.70. HRMS (MALDI-TOF): calcd for
mmol, 10%) and 2 mol Lꢂ1 aqueous K2CO3 (3.6 mL) were added
C
50H52Cl2N2O8Pt [M
+
Na]+: m/z
¼
1096.26462, found:
into the mixture solution of 9 (250 mg, 0.221 mmol) or 10 (200 1097.58805.
mg, 0.302 mmol) and biphenyl-4-ylboronic acid (218 mg, 1.11
mmol or 299 mg, 1.51 mmol) in toluene (20 mL or 25 mL). The
resulting mixture was stirred under argon atmosphere at 110 ꢀC
for 24 h. The solvent was removed in vacuo and the residue was
dissolved in DCM. The organic layer was dried over MgSO4 and
then concentrated by Rotavapor. The residue was puried by
ash column chromatography (SiO2, CH2Cl2/acetone ¼ 2/1 or
CH2Cl2/CH3OH ¼ 40/1), giving the product 1 as green solid or 2
as white solid. Yield: 120 mg of 1 (43%) or 138 mg of 2 (57%)
respectively. For 1, 1H NMR (400 MHz, CDCl3): d (ppm) 9.38 (s,
Methods
The monomer–dimer equilibrium. KMM and Kpp for complex
1-Pt in methanol were determined in the concentration range of
1.0 ꢁ 10ꢂ6 to 5.0 ꢁ 10ꢂ5 M using the equation23 as shown in the
following,
ꢀ
ꢁ
pffiffiffiffi
½Cꢃ
1
2
2Kpp
pffiffiffiffi pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
¼
þ
þ
A
3MM 3MMKMM
3MMKMM
A
2H), 9.03 (s, 2H), 7.91 (d, J ¼ 7.9 Hz, 4H), 7.85 (d, J ¼ 8.0 Hz, 4H), where [C] is the concentration, A is the absorbance at a partic-
7.70 (d, J ¼ 7.6 Hz, 4H), 7.52 (t, J ¼ 7.4 Hz, 4H), 7.43 (t, J ¼ 7.1 Hz, ular wavelength, 3MM is the extinction coefficient (constant) of
2H), 4.40 (d, J ¼ 5.2 Hz, 4H), 3.77 (d, J ¼ 5.7 Hz, 8H), 3.62 (d, J ¼ the MMLCT band. KMM and Kpp are the equilibrium constants
4.5 Hz, 8H), 3.56 (s, 32H), 3.48 (d, J ¼ 4.9 Hz, 8H), 3.32 (s, 12H), of dimerization due to metal–metal and p–p interactions
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respectively by assuming that there are two dimerization
processes as shown below:
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Soc., 2004, 126, 3551–3558; (b) M. Lee, B. K. Cho, Y. G. Jang
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Y. Yao, X. Chi, Y. Zhou and F. Huang, Chem. Sci., 2014, 5,
2778–2782; (d) X. Yan, S. Li, T. R. Cook, X. Ji, Y. Yao,
J. B. Pollock, Y. Shi, G. Yu, J. Li, F. Huang and P. J. Stang,
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Kpp
*
2Pt )
ðPt2Þpp
KMM
*
2Pt )
ðPt2Þ
MM
DFT calculations. The geometry optimization of Pt(Phen)Cl2
was performed with Gaussian 09 (Rev. D. 01) by DFT method
using B3LYP functional and the 6-311G* and LANL2DZ basis
sets.24
Acknowledgements
This work was supported by National Foundation of Natural
Science in China (No. 21172035 and No. 21302018), Research
Fund for the Doctoral Program of Higher Education of China
(No. 2012007511001 and No. 20120075120017), NRFM-K-12-01,
The Science and Technology Commission of Shanghai Munic-
ipality (No. 12JC1400200) and Fundamental Research Funds for
the Central University (15D210505 and 15D110566).
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