Shape-persistent (Pt-salphen)2 phosphorescent coordination frameworks: Structural insights and selective perturbations

Article abstract of DOI:10.1002/chem.201300421

The development of molecular frameworks derived from binuclear platinum(II) aromatic Schiff base (salphen) complexes and their supramolecular chemistry have been undertaken. A series of axially rotating (Pt-salphen)₂ luminophores, tethered in a

Full text of DOI:10.1002/chem.201300421

FULL PAPER
DOI: 10.1002/chem.201300421
Shape-Persistent (Pt-salphen)2 Phosphorescent Coordination Frameworks:
Structural Insights and Selective Perturbations
Zhengqing Guo, Shek-Man Yiu, and Michael C. W. Chan*[a]
Abstract: The development of molecu-
lar frameworks derived from binuclear
platinum(II) aromatic Schiff base (sal-
phen) complexes and their supramolec-
ular chemistry have been undertaken.
A series of axially rotating (Pt-sal-
phen)2 luminophores, tethered in a co-
facial manner by a rigid linker (xan-
thene, 1; dibenzofuran, 2; biphenylene,
3), was synthesized in which the O-
ing interactions, as well as contrasting
syn (1) and anti (3) configurations, for
the (Pt-salphen)2 moiety. All com-
plexes are luminescent in solution at
room temperature. Their photophysical
and solvatochromic properties have
been examined, and the emissions are
assigned to mixed triplet O(p)/Pt(d)!
tum yields of 1 and 3, relative to 2, are
ascribed to enhanced intramolecular p-
stacking interactions. Photophysical
changes and selective responses to
metal ions (particularly Pb2+
) have
been investigated by using various
spectroscopic methods and DFT calcu-
lations, and through comparative stud-
ies with control complexes. A plausible
binding mechanism is proposed based
p*ACTHNUTRGNE(UNG diimine) excited states. The red-
shifted fluid emissions and lower quan-
A
on occupation of the OACTHNGUTERNNU(G salphen)-bind-
nable for guest-binding. The molecular
structures of 1 and 3 have been deter-
mined by X-ray crystallography, reveal-
ing intra- and intermolecular p-stack-
ing cavity, which induces perturbation
of intramolecular p–p interactions, and
hence the self-quenching and emission
properties, of the (Pt-salphen)2 unit.
Keywords: luminescence · pi inter-
actions · platinum · sensors · supra-
molecular chemistry
Introduction
recognition properties.[20] Although attention has been fo-
cused on organic hosts and fluorescent versions have been
developed,[21] it is evident that transition-metal-based sys-
tems can engender advantages such as tunable, well-defined
coordination geometries, and visible-light reporting. The re-
lated development of molecular tweezers,[22] clips, grippers,
and related p-stacked host systems exhibiting interesting
recognition, electronic and chiroptical characteristics have
been described.[23]
We initiated a program to develop phosphorescent molec-
ular hosts and assemblies, based on a modular design ap-
proach encompassing coordinatively unsaturated transition-
metal-(p-organic) phosphorescent units (thus enabling axial
substrate-binding interactions and signaling without interfer-
ence from organic/background fluorescence) and a rigid,
robust, and readily derivatizable supporting framework (that
would link components and maintain structural integrity),
with the aim of engendering molecular topologies with un-
usual photophysical and sensing properties. New classes of
shape-persistent mono-,[24] bi-[25] and polynuclear[26] PtII coor-
dination frameworks and materials, bearing integrated fea-
tures that allow the reporting of molecular-level perturba-
tions and events, have been developed. Our underlying ob-
jective is to devise new strategies to modulate, control, and
signal the molecular motion in these systems, paving the
way towards new functionalities and the realization of lumi-
nescent machines.
The design and development of new functional molecular
architectures is a core motivation in coordination and supra-
molecular chemistry.[1] Multidentate Schiff bases have been
prominent in this regard,[2] and considerable efforts have
been made to utilize these diverse building blocks in the
construction of macrocycles[3] and metalated host mole-
cules,[4] and to study their ion binding and transport proper-
ties[5] as well as aggregation and self-assembly[6] into supra-
molecular entities and nanostructures.[7,8] In recent years,
the guest-binding abilities of multinuclear chiral hosts[9] and
new transformations mediated by cooperative and biomi-
metic catalysts[10,11] have also been highlighted.
In the context of this work, the photophysical[12] and elec-
tronic[13] characteristics (and materials applications[14] and
catalytic role[15]) of bis(metal-Schiff base) complexes have
been investigated, and several of these systems have exploit-
ed the inherently rigid, planar nature of p-systems. More
generally, design strategies evolved from molecular phenom-
ena such as rigidification[16] and restricted rotation/confor-
mation[17] in crowded aromatic architectures have been ex-
plored in search of desirable electronic,[18] catalytic[19] and
[a] Dr. Z. Guo, Dr. S.-M. Yiu, Dr. M. C. W. Chan
Department of Biology and Chemistry, City University of Hong Kong
Tat Chee Avenue, Kowloon, Hong Kong (P.R. China)
E-mail: mcwchan@cityu.edu.hk
We are currently focused on creating congested molecular
scaffolds derived from platinum(II) luminophores supported
by aromatic Schiff bases. The incorporation of phosphores-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300421.
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cent metal-organic moieties such as Pt-salphen (H2-sal-
phen=N,N’-bis(salicylidene)-1,2-phenylenediamine) into su-
(C1) with K2PtCl4 in the presence of K2CO3 in DMSO at
758C. Regarding the rigid backbones, the substituted xan-
thene and dibenzofuran precursors are commercially avail-
pramolecular architectures can confer beneficial properties:
2+
1) compared with d6 octahedral Ru
N
ACHTUNGTRENaNUGN ble, but preparation of the biphenylene backbone required
which exhibit sphere-like coordination, the “open” geometry
of square planar d8 PtII can afford excited states that are
sensitive to the micro-environment;[27] 2) diverse photophys-
ical characteristics and high quantum efficiencies under am-
bient conditions have been reported;[28,29] 3) modification
and functionalization of the ligand structure is well-estab-
lished. We recently described new phosphorescent (Pt-sal-
phen)2 frameworks and their colorimetric and luminescent
responses to metal ions.[30] The two Pt-salphen fragments are
tethered cofacially to a rigid backbone to create a potential
O4-binding cavity, whereas correlated axial rotation would
afford intramolecular interactions. Herein, we have elabo-
rated upon our previous work by employing different rigid
backbones (1–3), which would modulate the separation and
angle, and thus the extent of interaction, between the two
Pt-salphen moieties in these complexes, and probed the
impact of this upon photophysical properties and binding/
sensing behavior. Intriguingly, the occupation of the (Pt-sal-
phen)2 cavity could result in the disruption of p–p (and pos-
sibly Pt···Pt) interactions, which would be signaled by the in-
trinsically responsive PtII luminophores. The colorimetric
and phosphorescent responses of these host structures upon
addition of metal ions have
several steps and modification of literature procedures. Bro-
mination of p-tert-butylaniline afforded the dibromoaniline
C2, which was subsequently diazotized in sulfuric and glacial
acetic acids with NaNO2, then treated with iodine, to form
C3. An Ullmann coupling reaction was employed in the syn-
thesis of the key intermediate C4:[31] compound C3 was con-
verted into the desired arylithium intermediate by means of
halogen/metal permutation, followed by reaction with stoi-
chiometric amounts of copper(II) bromide and nitroben-
zene, then reductive elimination, to afford the biaryl com-
pound C4. Finally, a modified Ullmann cyclization by using
copper(II)-mediated oxidative coupling yielded the dibro-
mobiphenylene C5.[32]
Functionalization of the rigid backbones was achieved by
activation of two bromide atoms through halogen-lithium
exchange with nBuLi. The intermediate was subsequently
reacted with 2 equiv of B
bisboronic acids B1–B3. Treatment of the respective bisbor-
onic acids with 2 equiv of L1 in the presence of [Pd(PPh3)4]
ACHTUNGRTEN(NUNG OMe)3 and hydrolyzed into the
ACHTUNGTRENNUNG
and K2CO3 in degassed DMF solution at 758C afforded the
desired binuclear complexes 1–3 as dark-red solids
(Scheme 1). The control complexes 4 and 5 were prepared
been investigated. Control
complexes (4 and 5) have been
studied in concert, and a varie-
ty of spectroscopic techniques
plus DFT calculations have
been employed, to rationalize
the photophysical changes and
provide insight into the binding
mechanism. These observa-
tions may be of relevance to
luminescent host complexes
displaying intramolecular inter-
actions that undergo photo-
physical changes in response to
external stimuli.
Results and Discussion
Preparation of platinum(II)
Schiff base complexes: A mod-
ular approach was employed
for the synthesis of the binu-
clear platinum(II) Schiff base
complexes 1–3 (see the Sup-
porting Information for de-
tails). The important brominat-
ed salphen-PtII precursor L1
was obtained by treatment of
the corresponding Schiff base
Scheme 1. Synthesis of 1–3, and structures of control complexes 4 and 5.
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Shape-Persistent (Pt-salphen)2 Frameworks
FULL PAPER
similarly or according to a literature method.[28a] All PtII
complexes were characterized by NMR spectroscopy, ESI-
MS, and elemental analysis. In the ESI mass spectra, parent
clusters with m/z values that closely match the respective
theoretical isotopic patterns were observed (Figures S1–S3
in the Supporting Information).
the absence of Pt···Pt interactions, although the shorter in-
termolecular Pt(2)···Pt(2*) separation of 3.431(2) ꢁ may be
interpreted as a weak interaction. Importantly, the intra-
and intermolecular interplanar separations (defined as mean
separation between Pt and adjacent N2O2 plane) of 3.22 and
3.25 ꢁ, respectively, indicate the existence of p–p interac-
tions between the coplanar Pt-salphen moieties (Figure 1).
The geometry of both platinum atoms in the biphenylene-
based 3 (Figure 2) are also square planar. Compared with 1,
Crystal structures of (Pt-salphen)2 complexes: Single crystals
of 1 and 3 were obtained by slow evaporation of ethyl ace-
tate solutions, and structural determinations were performed
by X-ray crystallography (Figures 1 and 2, respectively, and
the Supporting Information).[33] For the xanthene-based
complex 1, the square planar geometry around the two plati-
num atoms are generally unremarkable, and each Pt-salphen
unit is planar with negligible deviation of the aryl rings. The
distortion of the aryl rings from the Pt
ACHTUGNTRENN(NUG N2O2) planes, espe-
cially for Pt(1), is more discernible but remains slight. The
ꢀ
ꢀ
mean Pt N (1.962 ꢁ) and Pt O (1.994 ꢁ) distances in 3 are
comparable to 1 and related complexes. In contrast to 1, the
two Pt-salphen moieties are linked to the biphenylene unit
in an anti cofacial manner, and the dihedral angles to the bi-
phenylene plane are smaller (ca. 368). This, together with
the narrower biphenylene spacer, gives rise to a shorter
Pt(1)···Pt(2) distance of 3.359(2) ꢁ, which constitutes a
weak intramolecular Pt···Pt interaction[14,23b,27a,34] (Figure S5
in the Supporting Information). The intramolecular interpla-
nar separation of 3.36 ꢁ between the Pt-salphen moieties in
ꢀ
ꢀ
mean Pt N and Pt O distances in 1 are 1.963 and 1.997 ꢁ,
respectively, resembling those previously reported for PtII
Schiff base complexes.[14,28,29] The two Pt-salphen moieties
are bridged by the xanthene backbone in a syn cofacial fash-
ion, with dihedral angles of around 438 to the xanthene
plane. The intramolecular Pt(1)···Pt(2) distance of
5.012(2) ꢁ (Figure S4 in the Supporting Information) signify
Figure 1. Perspective view (top; 50% probability ellipsoids) and packing
Figure 2. Perspective view (top; 50% probability ellipsoids) and packing
diagram (bottom; showing intra- and intermolecular p–p separations) of
diagram (bottom; showing intra- and intermolecular p–p separations) of
ꢀ
ꢀ
ꢀ
ꢀ
1. Selected bond lengths [ꢁ] and angles [8]: Pt(1) N(1) 1.962(4), Pt(1)
3. Selected bond lengths [ꢁ] and angles [8]: Pt(1) N(1) 1.955(4), Pt(1)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
N(2) 1.967(3), Pt(1) O(1) 1.997(3), Pt(1) O(2) 1.991(3), Pt(2) N(3)
N(2) 1.967(3), Pt(1) O(1) 1.996(3), Pt(1) O(2) 1.989(3), Pt(2) N(3)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1.963(4), Pt(2) N(4) 1.960(4), Pt(2) O(3) 2.000(3), Pt(2) O(4) 1.998(3),
Pt(1)···Pt(2) 5.012(2), N(1)-Pt(1)-N(2) 83.8(1), N(1)-Pt(1)-O(1) 95.2(1),
N(1)-Pt(1)-O(2) 178.6(1), O(1)-Pt(1)-O(2) 85.5(1).
1.972(3), Pt(2) N(4) 1.955(4), Pt(2) O(3) 1.995(3), Pt(2) O(4) 1.995(3),
Pt(1)···Pt(2) 3.359(2), N(1)-Pt(1)-N(2) 83.5(1), N(1)-Pt(1)-O(1) 95.4(1),
N(1)-Pt(1)-O(2) 178.7(1), O(1)-Pt(1)-O(2) 85.4(1).
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M. C. W. Chan et al.
3 is slightly larger than that in 1 (3.22 ꢁ), and the adjacent
N2O2 planes are not coplanar (angle=4.98). Although this
suggests less favorable p–p interaction in the solid state for
the anti cofacial Pt-salphen units in 3, crystal packing effects
should be considered. The intermolecular interplanar sepa-
ration (3.25 ꢁ) and Pt(2)···Pt(2*) distance (3.336(2) ꢁ) in 3
are comparable to those in 1, and indicate the possibility of
intermolecular p–p and Pt···Pt interactions in the solid state.
These structural features may be useful for rationalizing the
luminescent properties of these complexes, whereas the con-
trasting syn and anti (Pt-salphen)2 configurations in 1 and 3,
respectively, is envisaged to impact upon binding character-
istics. A detailed comparison of photophysical properties is
presented in the next section.
self-quenching.[17d,25,36] To characterize the photophysical
nature of these binuclear complexes in detail, the time-re-
solved difference absorption spectra of
1 in degassed
CH3CN were recorded after 355 nm nanosecond laser exci-
tation (Figure S7 in the Supporting Information). The prom-
inent features in the transient absorption (TA) spectra are
photo-bleaching at around 650 nm and strong absorptions in
the 400–600 nm region. The TA lifetime (0.19 ms) is in good
agreement with the emission lifetime in CH3CN (0.17 ms),
which is in accordance with the absorption originating from
the emissive excited state.
To provide information and insight for sensing studies, a
comparison of the emission energies and band-shapes for
complexes 1–5 in CH2Cl2/CH3CN (1/1) is shown in Figure 3.
The fluid emissions are assigned to mixed triplet O(p)/
Absorption and emission spectroscopy: The photophysical
properties of complexes 1–4 have been examined by UV/Vis
absorption and emission spectroscopy (Table 1; the photo-
physical data for 5 was reported previously[28c]). The UV/Vis
absorption spectra of the binuclear complexes 1–3 in CH2Cl2
(Figure S6 in the Supporting Information) contain bands at
<390 nm (e>2.0ꢂ104 dm3 molꢀ1 cmꢀ1) that closely resemble
the structured nature and extinction coefficients of the cor-
responding non-metalated ligands. In addition, less intense
absorptions are observed in the visible region at lmax 454–
552 nm (e=(6–10)ꢂ103 dm3 molꢀ1 cmꢀ1) that are absent from
the ligand precursors. As described in previous spectroscopic
studies of phenyl-substituted analogues,[28,35] the bands at
Pt(d)!p*
ACHTUNGTREN(NGNU diimine) excited states, which are reported to un-
dergo blue-shifts in more polar solvents due to the polar
character of the electron-rich oxygen donor in the ground
state.[28,35] This is indeed observed for 2 (from lmax 637 (in
<390 nm are ascribed to intra
A
G
1(pp*) transitions,
gand ACHTGNURTENNUGN
whereas the low-energy absorptions at lmax 454–552 nm are
assigned as O(p)/Pt(d)!p*
ACHTUNGTRNE(NUNG diimine) charge-transfer transi-
tions.
Complexes 1–3 display structureless red emission (lmax
630–640 nm) in CH2Cl2 at 298 K, with long emission life-
times indicating phosphorescence. The lower Fem values and
broader emission band-shape for 1 and 3 may be attributed
to greater intramolecular p–p interaction between the cofa-
cially tethered Pt-salphen moieties, which is known to cause
Figure 3. Normalized emission spectra of 1–5 (10ꢀ5 m) in CH2Cl2/CH3CN
(1:1) at 298 K.
Table 1. Photophysical data for 1–4.
Fluid: lmax [nm] (t [ms]); F
298 K
Solid: lmax [nm] (t [ms])
Cpd
lmax [nm] (e [dm3 molꢀ1 cmꢀ1])
lex [nm]
77 K[c]
298 K
77 K
1
259 (53730), 303 (27590),
325 (31370), 366 (36570),
472 (8410), 535 (8970),
547 (8900)[a]
546
635 (0.20); 0.007[a]
645[b]
650 (max; 7.0),
617, 705
668 (0.040)
679 (0.37)
2
260 (35510), 329 (26620),
371 (30120), 388 (29500),
454 (5950), 475 (6960),
537 (7220), 552 (7370)[a]
257 (54180), 326 (30250),
374 (32480), 477 (7390),
534 (7750), 553 (7780)[a]
255 (24320), 293 (9860),
308 (10510), 318 (10780),
342 (11240), 361 (17900),
377 (18690), 429 (1890),
457 (3870), 526 (4620)[d]
555
635 (2.73); 0.080[a]
630[b]
613 (max; 8.2),
647, 748
659 (0.014)
665 (max; 1.06),
730 (0.75)
3
4
520
501
642 (0.16); 0.009[a]
647[b]
609 (max; 14.7),
648, 710
680 (0.064)
660 (0.188)
677 (max; 0.37),
742 (0.28)
615 (max; 3.92), 667; 0.061[d]
617 (max), 670[b]
605 (max; 11.5),
663
657 (4.28)
[a] In CH2Cl2. [b] In CH2Cl2/CH3CN (1:1). [c] In 2-Me-THF. [d] In CH3CN.
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Shape-Persistent (Pt-salphen)2 Frameworks
FULL PAPER
toluene) to 635 (CH2Cl2) and 626 nm (CH3CN)) and 5 (from
lmax 629 (in toluene) to 617 (CH2Cl2) and 612 nm (CH3CN)),
but not 1 (from lmax 661 (in toluene) to 635 (CH2Cl2) and
639 nm (CH3CN)) and 3 (from lmax 672 (in toluene) to 642
(CH2Cl2) and 648 nm (CH3CN); Figure S8 in the Supporting
Information). Furthermore, the conventional negative solva-
tochromic emissions of 2 and 5 are more structured than the
broader emissions of 1 and 3. It is therefore postulated that
intramolecular p–p interactions between Pt-salphen moiet-
ies in 1 and 3 may be enhanced in CH3CN as well as tol-
uene, giving rise to the red-shifted emissions. In CH2Cl2/
CH3CN (1/1), the uncharacteristic red-shifted emissions for
1 and 3, which are concentration-independent down to
10ꢀ7 m (thus discounting aggregation), are attributed to intra-
molecular p–p interactions as observed in the crystal struc-
tures (i.e., offset interplanar p-contacts within the (Pt-sal-
phen)2 moiety). Such p-stacked interactions are prevalent in
1 and 3, resulting in broad, unstructured emissions at lmax
648 nm, weaker in dibenzofuran-linked 2 to give a blue-
shifted emission with narrower band-shape at lmax 628 nm
(resulting in a higher Fem for 2 (due to decreased self-
quenching) compared with 1 and 3), and absent in control
complexes 4 and 5 to afford further blue-shifted and struc-
tured emissions at around lmax 610 nm, which is typical for
non-aggregated Pt-salphen monomer species.
was steadily quenched, whereas for Mg2+, Ca2+, Zn2+, Cd2+
,
and all monovalent metals ions, there were minimal or no
responses (Figure S11 in the Supporting Information). Com-
petition experiments signifying a ratiometric phosphorescent
response and selectivity for Pb2+ have been conducted
(Figure 4), in which the emission intensity of 1 (3.5ꢂ10ꢀ5
m
Figure 4. Competition experiments showing ratiometric phosphorescent
response and selectivity by 1 for Pb2+ ions. Pb
ACHTNUTRGNEG(UN ClO4)2 (1.0 equiv) was
added after solutions of 1 in CH3CN (3.5ꢂ10ꢀ5 mol Lꢀ1) had been incu-
bated with 1.0 equiv of metal ions (lex 501 nm).
The solid-state (298 and 77 K) and glassy (77 K) emissions
of 1–5 have also been examined (Figure S9 and S10 in the
Supporting Information). In the solid state, compounds 1–3
display structureless low-energy emissions (lmax >658 nm) at
298 K. The binuclear complex 3 displays the most red-shift-
ed solid emission at lmax 680 nm, which is tentatively attrib-
uted to intra- as well as intermolecular p–p and Pt···Pt inter-
actions, corresponding to those observed in the crystal struc-
ture. Whereas the parent mononuclear complex 5 displays a
structured solid-state emission at lmax 620 nm at 298 K, the
control derivative 4 exhibits a structureless red-shifted emis-
sion at lmax 660 nm, resembling that of 2. Evidently, the in-
termolecular p-stacking interactions and packing effects for
1–5 in the solid state are different. The solid-state emissions
at 77 K are slightly more structured, but similar results are
observed. The 77 K glassy emission for 1 is red-shifted (lmax
650 nm), but the remaining complexes display highly struc-
tured emissions at lmax 600–613 nm with vibronic progres-
sions of around 1300 cmꢀ1. Such vibronic structure is em-
in CH3CN) were monitored at both 639 and 605 nm in the
presence of the metal ions (1.0 equiv). A clear colorimetric
response was also detected for 1 with 1.0 equiv of Pb2+, and
to some extent Cu2+ and Hg2+, corresponding to the incre-
mental decrease of the 535 nm absorption with increasing
[M2+] (Figure S11 in the Supporting Information). Analo-
gous experiments for complex 3 with various metal ions
were performed (Figure S12 in the Supporting Information).
Like 1, there were minimal or no responses for Mg2+, Ca2+
,
Zn2+, Cd2+, and all monovalent metals ions, whereas
quenching was observed for Cu2+ and Hg2+ ions. In contrast
to 1, a quenched emission that was nevertheless blue-shifted
was recorded for 3 upon addition of Pb2+ ions.
Quantitative titrations have been performed to probe the
photophysical responses in CH3CN. The UV/Vis spectral
changes for 1 became saturated after addition of 1.0 equiv
of Pb2+ ions and revealed a well-defined isosbestic point at
501 nm (Figure S13 in the Supporting Information), which
was used as the emission lex. In the emission titration, incre-
mental changes were detected for up to 1.0 equiv of Pb2+
ions, and saturation occurred thereafter (Figure 5, top). The
broad red emission at lmax 639 nm was blue-shifted and
transformed into a structured emission at lmax 605 nm
(termed “monomer-like” since it closely resembles the
energy and band-shape of the respective emission for 4 and
5). In addition, the aerated emission lifetime (l639 =0.07 ms)
became noticeably longer after the addition of Pb2+ ions
(l605 =0.33 ms). It is of interest to note that literature reports
of phosphorescent hosts that are capable of sensing Pb2+
ions remain sparse.[37] The reversibility of the photophysical
response of 1 to Pb2+ ions was demonstrated (Figure S14 in
3
blematic of pp* excited states, but the solid-state and glassy
emissions in this work are excessively red-shifted for this as-
signment and thus ascribed to mixed triplet O(p)/Pt(d)!p*-
ACHTUNGTRENNUNG(diimine) excited states.
Photophysical responses to metal ions: perturbation of p-
stacked interactions: The binding characteristics of 1 has
been investigated by using UV/Vis and emission spectrosco-
py with various mono- and divalent metal ions (as perchlo-
rate salts) in CH3CN. With 1.0 equiv of Mn+ ions, the
639 nm emission was converted into a structured band at
lmax 605 nm for the Pb2+ ion only, and further addition
yielded no change. For Cu2+ and Hg2+ ions, the emission
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M. C. W. Chan et al.
Figure 6. ESI-MS of [3+Pb+ClO4]+ in CH3CN using zero declustering
potential (top: calculated isotopic distribution).
by 1 or 3, the Pb2+ ion can remain coordinated by perchlo-
rate, possibly in a bidentate mode like that reported by Car-
bonaro et al.[40] in the crystal structure of [{Ni
ACTHNUGTRNE(NUG salen)}2·Ba-
ACHUTNGREN(NUG ClO4)2ACHTUNGTERN(NUGN thf)], featuring two chelating perchlorate groups at
Figure 5. Quantitative emission titrations (lex 501 nm) for 1 (top; 5ꢂ
10ꢀ5 m) and 3 (bottom; 2.5ꢂ10ꢀ5 m) in CH3CN upon addition of Pb2+
ions.
Ba2+ (plus O4-coordination by two mononuclear Ni-salen
moieties), and by Lalinde et al.[41] in the crystal structure of
ꢁ
(NBu4)[{Pt
G
(ClO4)]
(bzq=7,8-
benzoquinoline), in which the Pb2+ ion is coordinated by a
the Supporting Information).[38] Quantitative emission titra-
tions have also been performed for 3 in CH3CN (Figure 5,
bottom). Incremental changes were detected upon addition
of up to 1.0 equiv of Pb2+ ions, after which saturation occur-
red. In stark contrast to 1, the broad red emission at lmax
648 nm was gradually quenched and blue-shifted to lmax
616 nm.
bidentate perchlorate group, as well as four acetylide moiet-
ies of two [Pt
ing mode.
1A
ACHTUGNTRENNU(NG bzq)ACHTNURTGEN(GUNN C CAr)2] units in a [h CTHNUGRTEN(NUGN C CAr)]4 bind-
ꢁ
ꢁ
To elucidate the mechanism for Pb2+-binding by 1 and 3,
exhaustive attempts have been made to grow crystals suit-
AHCTUNGTREGaNNNU ble for structural determination by using a wide variety of
solvents and mixtures thereof, numerous recrystallization
methods, and different ratios of complex-to-Pb2+, but these
efforts have not succeeded. DFT calculations have been un-
dertaken to investigate the structures of the [1+Pb+ClO4]+
and [3+Pb+ClO4]+ species observed by ESI-MS (Figure 7).
Generally, the two energy-minimized calculated structures
(each confirmed to be a minimum from vibrational frequen-
cy calculations) display many similarities: the Pb2+ ion re-
sides close to the center of the O4 cavity and is bound by a
ꢀ
1H NMR studies have been conducted for 1 in the pres-
ence of Pb2+ ions (Figure S15 in the Supporting Informa-
1
tion). The H NMR shift differences between each side of
the non-symmetric salphen fragment became greater, indica-
tive of increased rigidity. The binding process for 1 was in-
vestigated by using ESI mass spectrometry (Figure S16 in
the Supporting Information). The major signal in the ESI
mass spectrum of 1 with 1.0 equiv of Pb2+ in CH3CN, using
zero declustering potential, is a cluster at m/z 1643.2, which
displays excellent agreement with the calculated isotopic
pattern for the [1+Pb+ClO4]+ species with 1 amu separa-
tion between peaks. In the analogous ESI-MS of 3 with Pb2+
(1.0 equiv), the dominant signal is a cluster at m/z 1584.5
(1 amu separations) corresponding closely to [3+Pb+
ClO4]+ (Figure 6).[39] These results imply that when bound
bidentate perchlorate group, the mean Pb OACHTNUTRGNE(UNG salphen)
ꢀ
(1: 2.478 ꢁ; 3: 2.488 ꢁ) and Pb O(perchlorate) (1: 2.520;
3: 2.516 ꢁ) distances are comparable, and the Pb···Pt distan-
ces (1: 3.260, 3.377; 3: 3.289, 3.311 ꢁ) are not dissimilar.
However, while noting the contrasting syn and anti (Pt-sal-
phen)2 configurations in 1 and 3, respectively, the mean sep-
aration between Pt and the adjacent N2O2 plane is signifi-
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Shape-Persistent (Pt-salphen)2 Frameworks
FULL PAPER
Figure 7. Energy-minimized calculated structures of [1+Pb+ClO4]+ (top) and [3+Pb+ClO4]+ (bottom): perspective view (left) and angle between
N2O2 planes (right).
cantly greater in 1 (3.60 ꢁ, c.f. 3.39 ꢁ in 3). Furthermore,
the angle between the N2O2 planes is larger in 1 (18.2, c.f.,
7.48 in 3). By comparing these calculated structural parame-
ters with the interplanar p–p separations in the crystal struc-
tures of 1 (3.22 ꢁ; parallel) and 3 (3.36 ꢁ; 4.98 between
N2O2 planes), it is proposed that upon binding of Pb2+, com-
plex 1 may undergo conformational changes that separate
the Pt-salphen moieties and disrupt the p–p interaction. In
contrast, the structural impact of Pb2+ coordination upon
the (Pt-salphen)2 unit in 3 may be relatively small, and intra-
molecular p–p interactions would remain feasible. Notwith-
standing the absence of solvent effects in the calculated
structures, these differences may be helpful for explaining
the contrasting emission responses to Pb2+ ions (see below).
and the resultant lifetime of 1 was observed to be independ-
ent of [Cu2+] or [Hg2+] (to/t=1, to =0.07 ms), indicating
static quenching processes. Furthermore, the absence of a
blue-shift (or transformation to a “monomer-like” emission)
signifies that the p-stacking within the (Pt-salphen)2 unit in
1 is not disrupted by the Cu2+ (or Hg2+) ions, and therefore
suggests that the quenching (through metallophilic[42] or
spin-orbit interactions) occurs outside the (Pt-salphen)2
cavity. Upon addition of Pb2+ ions, the structured emissions
of 4 and 5 in CH3CN at around lmax 610 nm was quenched
but not shifted; this demonstrates that emission quenching
is evidently the normal response of mononuclear Pt-salphen
to Pb2+ ions, and tentatively implies that the binding of
Pb2+ by 1 occurs inside the (Pt-salphen)2 cavity.
The different backbones in 1–3 would modulate the
nature and geometry of the (Pt-salphen)2 cavity with regards
to guest-binding, and hence their comparative emission re-
sponses to Pb2+ ions (1.0 equiv) have been investigated
(Figure 8; CH2Cl2/CH3CN (1:1) is used because 2 displays
limited solubility in CH3CN). For 2, although a blue-shift to
lmax 605 nm was detected like 1, the emission intensity was
quenched to 80% of the original intensity (by peak area),
which is in clear contrast to 1 (99% of original intensity;
Comparisons and general remarks: Further studies on the
binuclear as well as control complexes have been undertak-
en to rationalize the observed spectral changes and possible
binding mechanism. Quantitative experiments have been
performed to investigate the emission quenching responses
of 1 to Cu2+ and Hg2+ ions in CH3CN (Figure S17 in the
Supporting Information). For both Cu2+ and Hg2+, the
639 nm emission of 1 was rapidly quenched but not shifted,
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M. C. W. Chan et al.
vealed comparable Pb2+ binding modes and Pb O
(salphen)
ꢀ
distances. For 3 however, addition of Pb2+ produced a rela-
tively unstructured emission band and a smaller blue-shift
(to lmax 616 nm). This implies that intramolecular p–p inter-
actions may persist to some extent (the blue-shift may be
predominantly caused by O(p) stabilization upon Pb2+···O-
AHCTUNGTREG(NNUN salphen) coordination), and is consistent with the close in-
terplanar separation of 3.39 ꢁ in the calculated structure of
[3+Pb+ClO4]+. Such a Pb2+-binding mode, in which p–p
interactions can prevail and self-quenching is accordingly
not reduced, could conceivably afford diminished emission
intensity due to Pb2+-mediated quenching, as is observed
for 3. We suggest that a similar rationale to that for 1 can
account for the blue-shifted, structured emission observed
for 2 with Pb2+, although only a weak p–p interaction is dis-
rupted and the binding is evidently weaker.
Figure 8. Emission spectra of 1–3 (normalized, 2ꢂ10ꢀ5 m, lex 501 nm) in
CH2Cl2/CH3CN (1:1) showing relative changes upon addition of Pb2+
ions (1.0 equiv).
To summarize, the evidence herein indicates that a (Pt-
salphen)2 cavity displaying intramolecular interactions is re-
quired to afford a blue-shifted emission response to Pb2+
ions. The following discussion focuses on complex 1, which
gives the strongest Pb2+-binding. Interaction with Pb2+
could occur by coordination within the (Pt-salphen)2 cavity,
but interaction and quenching with Cu2+ (or Hg2+) appa-
rently takes place outside the cavity. The plausibility for O4-
this blue-shifted emission band at lmax 607 nm is also more
structured) but comparable to 4 and 5 (86 and 90% of the
respective original intensity). For 3, the corresponding blue-
shift to lmax 616 nm is smaller than for 1, and substantial
emission quenching (9% of original intensity) was observed.
The stoichiometry of Pb2+-binding by 1 was indicated to be
1:1 using a Jobꢃs plot. The logK for Pb2+-binding by 1–3
were determined in CH3CN/CH2Cl2 (1:1) to be 6.63ꢂ0.06,
6.20ꢂ0.15, and 6.47ꢂ0.44, respectively (Figure S18 in the
Supporting Information), indicating that the binding is
weakest for 2.
coordination of Pb2+ by the O
ACTHNUTRGNE(NUG salphen) groups is suggested
by the following: a) the dominant species in the ESI-MS
was identified as [1+Pb+ClO4]+, which bears a striking re-
semblance to the X-ray crystal structure of [{Ni
2A
ACHTUNGTRENNUNG
AHCTUNRTGEG(NNUN ClO4) CHTUNRTGENNG(U thf)] featuring two mononuclear NiACTHUGNTRENNUGN
bidentate moieties;[40] b) O-complexation by metal-Schiff
base assemblies,[3–5] including the supramolecular aggrega-
tion of Zn-salphen complexes to generate gels and nanofib-
It is pertinent to consider the following to rationalize the
emission responses upon addition of Pb2+ in Figure 8: a) A
blue-shifted emission may be ascribed to 1) disruption of p–
p interactions within the (Pt-salphen)2 unit (this would be
accompanied by a “monomer-like” structured emission), or/
and 2) stabilization of salphen O(p) orbitals, and hence de-
ers through Zn···O
ed; c) in the energy-minimized calculated structure of [1+
Pb+ClO4]+, the Pb2+ ion is coordinated by four O
(salphen)
(salphen) interactions,[7] is well-document-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
donors plus a bidentate perchlorate group. Overall, the pho-
tophysical responses and contrasting results for control com-
plexes, together with the above discussion, are consistent
with the binding of a perchlorate-coordinated Pb2+ ion in
the cavity of 1, which causes conformational changes (in-
cluding axial rotation) and disrupts the p-stacked interac-
tions within the (Pt-salphen)2 moiety; the original low-
energy p-stacked emission is therefore transformed by the
Pb2+ ion into the blue-shifted “monomer-like” emission of
non-interacting Pt-salphen units and self-quenching becomes
minimized (although other binding mechanisms cannot be
disregarded).
stabilization of O(p)!p*
(diimine) transition, upon Pb2+
ACHTUNGTRENNUNG
-binding (this is entirely consistent with the observed blue-
shift for the lowest-energy absorption band of the binuclear
complexes with Pb2+). b) Upon Pb2+-binding, emission en-
hancement may be afforded by 1) a reduction in intramolec-
ular self-quenching due to weakened or disrupted p–p inter-
actions, or/and 2) rigidification of the molecular framework.
c) Pb2+ ions can interact with the Pt-salphen luminophore
and invariably causes emission quenching.
Therefore, we propose that for 1, binding of Pb2+ within
the (Pt-salphen)2 cavity results in blue-shifted “monomer-
like” emission, which arises from O(p) stabilization as well
as disruption of intramolecular p–p interactions (as indicat-
ed by DFT calculations). Consequently, the reduction in
self-quenching (and possibly increased host rigidification)
would counter-balance the expected Pb2+-mediated emis-
sion quenching to afford enhanced (or undiminished) struc-
tured emission at lmax 607 nm. Notwithstanding the different
coordination cavities formed by the syn and anti (Pt-sal-
phen)2 unit in 1 and 3 respectively, the DFT calculations re-
Conclusion
The Mn+-binding abilities of rigidly-linked (Pt-salphen)2
hosts, which constitute a new class of axially rotating coordi-
nation architectures and may be considered as phosphores-
cent relatives of 12-crown-4, have been investigated. Differ-
ences between the photophysical properties and ion-selec-
tive responses of (Pt-salphen)2 complexes anchored to sub-
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Shape-Persistent (Pt-salphen)2 Frameworks
FULL PAPER
Crystal data were collected on an Oxford Diffraction Gemini S Ultra X-
ray single-crystal diffractometer using graphite-monochromated CuKa ra-
diation (l=1.54184 ꢁ). The structures were solved by direct methods
and refined using the SHELXL-97 program on a PC.[43] DFT calculations
on molecular structures were performed at the B3LYP level with the
CEP-31G basis set using the Gaussian 09 program package.[44] In each
case, the energy-minimized calculated structure was confirmed to be a
minimum from vibrational frequency calculations.
stituted xanthene, dibenzofuran, and biphenylene backbones
have been examined and rationalized. It is apparent that the
nature of the backbone can dictate the relative topology of
the cofacial Pt-salphen moieties, the prevalence of intramo-
lecular p–p interactions, and the dimensions of the potential
binding cavity in these frameworks. A plausible mechanism
for Pb2+-binding is proposed based on the interplay between
O-chelation and perturbation of intramolecular p-contacts
within the environmentally responsive (Pt-salphen)2 lumino-
phore, which in turn affects the self-quenching and emission
characteristics. These results may carry important implica-
tions for luminescent complexes and sensory materials that
engage in intramolecular interactions, and which undergo
photophysical changes in response to external stimuli and
guest-binding. Considering their structural diversity, the de-
velopment of supramolecular O-coordination by multinu-
clear metal-Schiff base assemblies is appealing. Studies are
continuing to create shape-persistent phosphorescent coordi-
nation frameworks that exhibit novel supramolecular behav-
ior and applications.
Synthesis of 3: 3,6-Di-tert-butylbiphenylene-1,8-diyldiboronic acid B3
(66 mg, 0.19 mmol), L1 (220 mg, 0.38 mmol), [PdACHTNUTRGNE(UNG PPh3)4] (44 mg,
0.04 mmol), and K2CO3 (78 mg, 0.56 mmol) were charged into a two-
necked flask under nitrogen. DMF (20 mL) was degassed by using three
freeze-pump-thaw cycles and added, and the mixture was stirred at 758C
for 7 days. The solvent was removed and the residue was dissolved in
CH2Cl2 (50 mL). After washing with water (3 ꢂ 30 mL), the organic
phase was dried over anhydrous Na2SO4 and concentrated in vacuo. The
crude product was purified by column chromatography (SiO2, ethyl ace-
tate/hexane=1:1) to afford a dark red solid (50 mg, 21%). 1H NMR
(CD2Cl2, 400 MHz): d=7.80 (s, 2H), 7.61 (s, 2H), 7.60–7.51 (m, 6H),
7.32 (d, J=8.4 Hz, 2H), 7.26 (ddd, J=14.0, 8.0, 1.2 Hz, 4H), 7.13 (d, J=
8.4 Hz, 2H), 7.04 (d, J=1.6 Hz, 2H), 7.00 (dd, J=6.4, 1.6 Hz, 4H), 6.87
(d, J=8.4 Hz, 2H), 6.80–6.74 (m, 4H), 1.37 ppm (s, 18H); ESI-MS (m/z):
1279.1 [M+H]+; elemental analysis calcd (%) for C60H48N4O4Pt2: C
56.34, H 3.78, N 4.38; found C 56.19, H 3.78, N 4.44.
Experimental Section
Acknowledgements
General considerations: Solvents for syntheses (analytical grade) were
used without further purification and all metalation reactions were per-
formed under a nitrogen atmosphere. Solvents for photophysical meas-
urements were purified according to conventional methods. 1H NMR
spectra were obtained on Bruker DRX 300 and 400 FT-NMR spectrome-
ters (ppm) by using Me4Si as internal standard. ESI mass spectra were
measured on a Perkin–Elmer SCIEX API 365 mass spectrometer. IR
spectra were recorded on a Perkin–Elmer 1600 series FT-IR spectropho-
tometer. Elemental analyses were performed on a Vario EL elemental
analyzer (Elementar Analysensysteme GmbH). Full experimental and
characterization details are provided in the Supporting Information.
Complex 5 was synthesized by modification of a literature method.[28a]
The work described in this paper was fully supported by grants from the
Research Grants Council of the Hong Kong SAR, China (CityU 100408
and 100212). The flash photolysis system was supported by a Special
Equipment Grant from the University Grants Committee of the Hong
Kong SAR, China (SEG_CityU02).
[1] a) J.-M. Lehn, Angew. Chem. 1988, 100, 91–116; Angew. Chem. Int.
Ed. Engl. 1988, 27, 89–112; b) K. Hiratani, M. Albrecht, Chem. Soc.
Rev. 2008, 37, 2413–2421; c) M. D. Pluth, R. G. Bergman, K. N. Ray-
mond, Acc. Chem. Res. 2009, 42, 1650–1659.
[2] a) A. W. Kleij, Chem. Eur. J. 2008, 14, 10520–10529; b) C. J. White-
oak, G. Salassa, A. W. Kleij, Chem. Soc. Rev. 2012, 41, 622–631.
[3] a) A. J. Gallant, M. J. MacLachlan, Angew. Chem. 2003, 115, 5465–
5468; Angew. Chem. Int. Ed. 2003, 42, 5307–5310; b) J. K.-H. Hui,
M. J. MacLachlan, Chem. Commun. 2006, 2480–2482; c) P. D.
Frischmann, J. Jiang, J. K.-H. Hui, J. J. Grzybowski, M. J. MacLa-
chlan, Org. Lett. 2008, 10, 1255–1258; d) S. Guieu, A. K. Crane,
M. J. MacLachlan, Chem. Commun. 2011, 47, 1169–1171.
[4] a) C. T. L. Ma, M. J. MacLachlan, Angew. Chem. 2005, 117, 4250–
4254; Angew. Chem. Int. Ed. 2005, 44, 4178–4182; b) J. H. Chong, S.
Jooya Ardakani, K. J. Smith, M. J. MacLachlan, Chem. Eur. J. 2009,
15, 11824–11828; c) J. Dçmer, J. C. Slootweg, F. Hupka, K. Lam-
mertsma, F. E. Hahn, Angew. Chem. 2010, 122, 6575–6578; Angew.
Chem. Int. Ed. 2010, 49, 6430–6433; d) P. D. Frischmann, G. A.
Facey, P. Y. Ghi, A. J. Gallant, D. L. Bryce, F. Lelj, M. J. MacLa-
chlan, J. Am. Chem. Soc. 2010, 132, 3893–3908; e) M. V. Escꢄrcega-
Bobadilla, G. Salassa, M. Martꢅnez Belmonte, E. C. Escudero-Adꢄn,
A. W. Kleij, Chem. Eur. J. 2012, 18, 6805–6810.
[5] a) M. Cametti, M. Nissinen, A. Dalla Cort, L. Mandolini, K. Rissa-
nen, J. Am. Chem. Soc. 2005, 127, 3831–3837; b) S. Akine, T. Tani-
guchi, T. Nabeshima, J. Am. Chem. Soc. 2006, 128, 15765–15774;
c) E. R. Libra, M. J. Scott, Chem. Commun. 2006, 1485–1487; d) C.-
T. Chen, Y.-H. Lin, T.-S. Kuo, J. Am. Chem. Soc. 2008, 130, 12842–
12843.
UV/Vis absorption spectra were obtained on an Agilent 8453 diode array
spectrophotometer. Steady-state emission spectra were recorded on a
SPEX FluoroLog 3-TCSPC spectrophotometer equipped with a Hama-
matsu R928 PMT detector, and emission lifetime measurements were
conducted by using NanoLed sources in the fast MCS mode and checked
using the TCSPC mode. Sample and standard solutions were degassed
with at least three freeze-pump-thaw cycles. Low-temperature (77 K)
emission spectra for glasses and solid-state samples were recorded in
5 mm diameter quartz tubes that were placed in a liquid nitrogen Dewar
equipped with quartz windows. The emission quantum yield was meas-
ured by using [Ru
ACHTUNGTRENNUNG(bpy)3]ACHTUNGTRENNUNG
(Fr =0.062) and calculated by: Fs =Fr
N
N
ACHTUNGTRENNUNG
subscripts s and r refer to sample and reference standard solution, respec-
tively, n is the refractive index of the solvents, D is the integrated intensi-
ty, and F is the luminescence quantum yield. The quantity B is calculated
by the equation: B=1–10ꢀAL; in which A is the absorbance at the excita-
tion wavelength and L is the optical path length. Errors for l (ꢂ1 nm),
t (ꢂ10%), and F (ꢂ10%) are estimated. Transient absorption spectra at
room temperature were recorded using the spectral mode on an Edin-
burgh Instruments LP920-KS equipped with an ICCD detector. The exci-
tation source for the transient absorption measurement was the third har-
monic output (355 nm; 6–8 ns full width at half-maximum (fwhm) pulse
width) of a Spectra-Physics Quanta-Ray Q-switched LAB-150 pulsed
Nd:YAG laser (10 Hz). Solutions of PtII complexes and metal perchlorate
salts were prepared in CH3CN (spectroscopic grade). Absorption and
emission titrations were carried out in a quartz cuvette by addition of
small volumes of metal ion solutions (5ꢂ10ꢀ3 m) to the PtII complex.
[6] a) M. Martꢅnez Belmonte, S. J. Wezenberg, R. M. Haak, D. Anselmo,
E. C. Escudero-Adꢄn, J. Benet-Buchholz, A. W. Kleij, Dalton Trans.
2010, 39, 4541–4550; b) J. A. A. W. Elemans, S. J. Wezenberg,
M. J. J. Coenen, E. C. Escudero-Adꢄn, J. Benet-Buchholz, D. den
Chem. Eur. J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!

M. C. W. Chan et al.
Boer, S. Speller, A. W. Kleij, S. De Feyter, Chem. Commun. 2010,
46, 2548–2550.
Sessler, J. Am. Chem. Soc. 2002, 124, 1134–1135; c) V. J. Chebny, R.
Rathore, J. Am. Chem. Soc. 2007, 129, 8458–8465; d) S. Dutta, D.-
ˇ
[7] a) J. K.-H. Hui, Z. Yu, T. Mirfakhrai, M. J. MacLachlan, Chem. Eur.
J. 2009, 15, 13456–13465; b) J. K.-H. Hui, P. D. Frischmann, C.-H.
Tso, C. A. Michal, M. J. MacLachlan, Chem. Eur. J. 2010, 16, 2453–
2460; c) P. D. Frischmann, S. Guieu, R. Tabeshi, M. J. MacLachlan,
J. Am. Chem. Soc. 2010, 132, 7668–7675.
K. Bucar, L. R. MacGillivray, Org. Lett. 2011, 13, 2260–2262;
e) D. P. Iwaniuk, C. Wolf, J. Am. Chem. Soc. 2011, 133, 2414–2417.
[21] a) S. A. McFarland, N. S. Finney, J. Am. Chem. Soc. 2001, 123, 1260–
1261; b) S. A. McFarland, N. S. Finney, J. Am. Chem. Soc. 2002, 124,
1178–1179; c) M. Barboiu, L. Prodi, M. Montalti, N. Zaccheroni, N.
Kyritsakas, J.-M. Lehn, Chem. Eur. J. 2004, 10, 2953–2959; d) J. V.
Mello, N. S. Finney, J. Am. Chem. Soc. 2005, 127, 10124–10125;
e) C. Wolf, S. Liu, B. C. Reinhardt, Chem. Commun. 2006, 4242–
4244.
[8] A. C. W. Leung, M. J. MacLachlan, J. Mater. Chem. 2007, 17, 1923–
1932.
[9] a) G. Li, W. Yu, J. Ni, T. Liu, Y. Liu, E. Sheng, Y. Cui, Angew.
Chem. 2008, 120, 1265–1269; Angew. Chem. Int. Ed. 2008, 47, 1245–
1249; b) S. J. Wezenberg, G. Salassa, E. C. Escudero-Adꢄn, J. Benet-
Buchholz, A. W. Kleij, Angew. Chem. 2011, 123, 739–742; Angew.
Chem. Int. Ed. 2011, 50, 713–716.
[10] a) S.-Y. Liu, D. G. Nocera, J. Am. Chem. Soc. 2005, 127, 5278–5279;
b) J. Y. Yang, D. G. Nocera, J. Am. Chem. Soc. 2007, 129, 8192–
8198.
[11] a) F. H. Zelder, J. Rebek Jr., Chem. Commun. 2006, 753–754; b) M.
Shibasaki, M. Kanai, S. Matsunaga, N. Kumagai, Acc. Chem. Res.
2009, 42, 1117–1127; c) M. Taherimehr, A. Decortes, S. M. Al-
Amsyar, W. Lueangchaichaweng, C. J. Whiteoak, E. C. Escudero-
Adꢄn, A. W. Kleij, P. P. Pescarmona, Catal. Sci. Technol. 2012, 2,
2231–2237.
[12] a) K. E. Splan, A. M. Massari, G. A. Morris, S.-S. Sun, E. Reina,
S. T. Nguyen, J. T. Hupp, Eur. J. Inorg. Chem. 2003, 2348–2351;
b) H. Houjou, M. Ito, K. Araki, Inorg. Chem. 2009, 48, 10703–
10707.
[22] C. W. Chen, H. W. Whitlock, Jr., J. Am. Chem. Soc. 1978, 100, 4921–
4922.
[23] a) F.-G. Klꢇrner, B. Kahlert, Acc. Chem. Res. 2003, 36, 919–932;
b) A. J. Goshe, I. M. Steele, B. Bosnich, J. Am. Chem. Soc. 2003,
125, 444–451; c) N. C. Gianneschi, S.-H. Cho, S. T. Nguyen, C. A.
Mirkin, Angew. Chem. 2004, 116, 5619–5623; Angew. Chem. Int. Ed.
2004, 43, 5503–5507; d) S. Ulrich, J.-M. Lehn, Chem. Eur. J. 2009,
15, 5640–5645; e) H. Yoo, J. Yang, A. Yousef, M. R. Wasielewski, D.
Kim, J. Am. Chem. Soc. 2010, 132, 3939–3944; f) I. Pochorovski, M.-
O. Ebert, J.-P. Gisselbrecht, C. Boudon, W. B. Schweizer, F. Dieder-
ich, J. Am. Chem. Soc. 2012, 134, 14702–14705.
[24] a) W.-L. Tong, M. C. W. Chan, N. Zhu, S.-K. Leung, Dalton Trans.
2009, 4741–4746; b) W.-L. Tong, M. C. W. Chan, S.-M. Yiu, Organo-
metallics 2010, 29, 6377–6383.
[25] Z. Guo, M. C. W. Chan, Chem. Eur. J. 2009, 15, 12585–12588.
[26] S. Sun, W.-L. Tong, M. C. W. Chan, Macromol. Rapid Commun.
2010, 31, 1965–1969.
[13] a) A. C. W. Leung, J. K.-H. Hui, J. H. Chong, M. J. MacLachlan,
Dalton Trans. 2009, 5199–5210; b) T. J. Dunn, C. F. Ramogida, C.
Simmonds, A. Paterson, E. W. Y. Wong, L. Chiang, Y. Shimazaki, T.
Storr, Inorg. Chem. 2011, 50, 6746–6755; c) T. J. Dunn, L. Chiang,
C. F. Ramogida, M. I. Webb, D. Savard, M. Sakaguchi, T. Ogura, Y.
Shimazaki, T. Storr, Dalton Trans. 2012, 41, 7905–7914.
[27] a) S.-W. Lai, M. C. W. Chan, T.-C. Cheung, S.-M. Peng, C.-M. Che,
Inorg. Chem. 1999, 38, 4046–4055; b) K.-H. Wong, M. C. W. Chan,
C.-M. Che, Chem. Eur. J. 1999, 5, 2845–2849; c) P. Wu, D.-L. Ma,
C.-H. Leung, S.-C. Yan, N. Zhu, R. Abagyan, C.-M. Che, Chem.
Eur. J. 2009, 15, 13008–13021.
[14] N. Komiya, T. Muraoka, M. Iida, M. Miyanaga, K. Takahashi, T.
Naota, J. Am. Chem. Soc. 2011, 133, 16054–16061.
[28] a) Y.-Y. Lin, S.-C. Chan, M. C. W. Chan, Y.-J. Hou, N. Zhu, C.-M.
Che, Y. Liu, Y. Wang, Chem. Eur. J. 2003, 9, 1263–1272; b) C.-M.
Che, S.-C. Chan, H.-F. Xiang, M. C. W. Chan, Y. Liu, Y. Wang,
Chem. Commun. 2004, 1484–1485; c) C.-M. Che, C.-C. Kwok, S.-W.
Lai, A. F. Rausch, W. J. Finkenzeller, N. Zhu, H. Yersin, Chem. Eur.
J. 2010, 16, 233–247.
[29] W. Wu, J. Sun, S. Ji, W. Wu, J. Zhao, H. Guo, Dalton Trans. 2011, 40,
11550–11561.
[30] Z. Guo, W.-L. Tong, M. C. W. Chan, Chem. Commun. 2009, 6189–
6191.
[15] a) R. G. Konsler, J. Karl, E. N. Jacobsen, J. Am. Chem. Soc. 1998,
120, 10780–10781; b) H. J. Yoon, C. A. Mirkin, J. Am. Chem. Soc.
2008, 130, 11590–11591; c) B. A. Rodriguez, M. Delferro, T. J.
Marks, J. Am. Chem. Soc. 2009, 131, 5902–5919; d) S. I. Vagin, R.
Reichardt, S. Klaus, B. Rieger, J. Am. Chem. Soc. 2010, 132, 14367–
14369; e) K. Nakano, S. Hashimoto, K. Nozaki, Chem. Sci. 2010, 1,
369–373; f) P. C. B. Widger, S. M. Ahmed, G. W. Coates, Macromo-
lecules 2011, 44, 5666–5670.
[16] K. Rurack, U. Resch-Genger, Chem. Soc. Rev. 2002, 31, 116–127.
[17] a) J. P. Collman, P. S. Wagenknecht, J. E. Hutchison, Angew. Chem.
1994, 106, 1620–1639; Angew. Chem. Int. Ed. Engl. 1994, 33, 1537–
1554; b) J. S. Nowick, P. Ballester, F. Ebmeyer, J. Rebek, Jr., J. Am.
Chem. Soc. 1990, 112, 8902–8906; c) E. Benaksas Schwartz, C. B.
Knobler, D. J. Cram, J. Am. Chem. Soc. 1992, 114, 10775–10784;
d) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009, 4332–
4353.
[31] A. Rajca, A. Safronov, S. Rajca, C. R. Ross II, J. J. Stezowski, J. Am.
Chem. Soc. 1996, 118, 7272–7279.
[32] S. M. H. Kabir, M. Hasegawa, Y. Kuwatani, M. Yoshida, H. Mat-
suyama, M. Iyoda, J. Chem. Soc. Perkin Trans. 1 2001, 159–165.
[33] Crystal data for 1: C63H54N4O5Pt2, Mr =1337.28, monoclinic, P21/c,
a=15.8344(5), b=27.2295(9), c=11.5818(4) ꢁ, b=101.982(3)8, V=
4884.9(3) ꢁ3, Z=4, T=133(2) K, 1cald =1.818 gcmꢀ3
11.031 mmꢀ1, F
, mACHTUNGTRENNUNG
AHCTUNGTRENNUNG
[18] a) T. Nakano, T. Yade, J. Am. Chem. Soc. 2003, 125, 15474–15484;
b) T.-Q. Nguyen, R. Martel, P. Avouris, M. L. Bushey, L. Brus, C.
Nuckolls, J. Am. Chem. Soc. 2004, 126, 5234–5242; c) M. M. Elmah-
dy, X. Dou, M. Mondeshki, G. Floudas, H.-J. Butt, H. W. Spiess, K.
Mꢆllen, J. Am. Chem. Soc. 2008, 130, 5311–5319; d) J. He, J. L.
Crase, S. H. Wadumethrige, K. Thakur, L. Dai, S. Zou, R. Rathore,
C. S. Hartley, J. Am. Chem. Soc. 2010, 132, 13848–13857; e) E.
Ohta, H. Sato, S. Ando, A. Kosaka, T. Fukushima, D. Hashizume,
M. Yamasaki, K. Hasegawa, A. Muraoka, H. Ushiyama, K. Yama-
shita, T. Aida, Nat. Chem. 2011, 3, 68–73.
[19] a) J. Rosenthal, T. D. Luckett, J. M. Hodgkiss, D. G. Nocera, J. Am.
Chem. Soc. 2006, 128, 6546–6547; b) C. H. Lee, D. K. Dogutan,
D. G. Nocera, J. Am. Chem. Soc. 2011, 133, 8775–8777; c) D. K. Do-
gutan, R. McGuire, Jr., D. G. Nocera, J. Am. Chem. Soc. 2011, 133,
9178–9180.
tions (Rint =0.023), 675 variable parameters, R1 =0.0300 [I>2s(I)],
wR2 =0.0797. Crystal data for 3: C60H48N4O4Pt2·H2O·(ethyl acetate),
Mr =1385.32, monoclinic, P21/n, a=18.1544(2), b=13.87693(16), c=
22.4224(3) ꢁ, b=109.5358(14)8, V=5323.63(11) ꢁ3, Z=4, T=
133(2) K, 1cald =1.728 gcmꢀ3, m(CuKa)=10.174 mmꢀ1, F
ACTHNUTRGENNUG ACHUTGNTREN(NUGN 000)=2728,
2qmax =134.08; 9490 independent reflections (Rint =0.021), 702 varia-
ble parameters, R1 =0.0237 [I>2s(I)], wR2 =0.0633. CCDC-921758
(1) and 921759 (3) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[34] a) V. M. Miskowski, V. H. Houlding, Inorg. Chem. 1991, 30, 4446–
4452; b) J. A. Bailey, M. G. Hill, R. E. Marsh, V. M. Miskowski,
W. P. Schaefer, H. B. Gray, Inorg. Chem. 1995, 34, 4591–4599;
c) T. J. Wadas, Q.-M. Wang, Y.-J. Kim, C. Flaschenreim, T. N. Blan-
ton, R. Eisenberg, J. Am. Chem. Soc. 2004, 126, 16841–16849; d) W.
Lu, M. C. W. Chan, N. Zhu, C.-M. Che, C. Li, Z. Hui, J. Am. Chem.
Soc. 2004, 126, 7639–7651.
[20] a) F. Cozzi, F. Ponzini, R. Annunziata, M. Cinquini, J. S. Siegel,
Angew. Chem. 1995, 107, 1092–1094; Angew. Chem. Int. Ed. Engl.
1995, 34, 1019–1020; b) T. Mizuno, W.-H. Wei, L. R. Eller, J. L.
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Shape-Persistent (Pt-salphen)2 Frameworks
FULL PAPER
[35] S. D. Cummings, R. Eisenberg, J. Am. Chem. Soc. 1996, 118, 1949–
1960.
[36] W. Lu, M. C. W. Chan, K.-K. Cheung, C.-M. Che, Organometallics
2001, 20, 2477–2486.
[42] A. L. Balch, V. J. Catalano, M. A. Chatfield, J. K. Nagle, M. M. Olm-
stead, P. E. Reedy, Jr., J. Am. Chem. Soc. 1991, 113, 1252–1258.
[43] G. M. Sheldrick, SHELXS-97 and SHELXL-97, Programs for Crys-
tal Structure Solution and Refinement, University of Gçttingen,
Gçttingen, Germany, 1997.
[37] a) Y. Shen, B. P. Sullivan, Inorg. Chem. 1995, 34, 6235–6236; b) M.-
J. Li, C.-C. Ko, G.-P. Duan, N. Zhu, V. W.-W. Yam, Organometallics
2007, 26, 6091–6098; c) M.-L. Ho, Y.-M. Cheng, L.-C. Wu, P.-T.
Chou, G.-H. Lee, F.-C. Hsu, Y. Chi, Polyhedron 2007, 26, 4886–
4892.
[38] The expected blue-shift (to lmax 605 nm) for the 639 nm emission in
CH3CN was obtained upon addition of 3.0 equiv of Pb2+. Subse-
quent addition of TMEDA (9.0 equiv), acting as Pb2+ scavenger,
caused the emission spectrum and lifetime to revert back to the
original.
[44] Gaussian 09, Revision B.1, M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V.
Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X.
Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, N. J. Millam, M. Klene, J. E. Knox,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, ꢉ.
Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian,
Inc., Wallingford CT, USA, 2009.
[39] At a declustering potential of 50 V, the 1:1 [3+Pb]2+ species at m/z
742.8, with 0.5 amu peak separations, is dominant. Cooperative 2:2
binding, which would afford 0.25 amu separations, can therefore be
discounted (furthermore, non-sigmoidal binding curve gives excel-
lent fit for 1:1 binding, and the Hill plot does not show positive co-
operation).
[40] L. Carbonaro, M. Isola, P. La Pegna, L. Senatore, F. Marchetti,
Inorg. Chem. 1999, 38, 5519–5525.
[41] J. R. Berenguer, A. Dꢅez, J. Fernꢄndez, J. Forniꢈs, A. Garcꢅa, B. Gil,
E. Lalinde, M. T. Moreno, Inorg. Chem. 2008, 47, 7703–7716.
Received: February 2, 2013
Published online: && &&, 2013
Chem. Eur. J. 2013, 00, 0 – 0
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www.chemeurj.org
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M. C. W. Chan et al.
Supramolecular Chemistry
Z. Guo, S.-M. Yiu,
M. C. W. Chan* ............... &&&& — &&&&
Shape-Persistent (Pt-salphen)2 Phos-
phorescent Coordination Frameworks:
Structural Insights and Selective
Perturbations
To p or not to p? The ratiometric
phosphorescent ion-selective responses
of axially rotating binuclear assemblies
have been investigated by using X-ray
crystallography, DFT calculations, and
various spectroscopic techniques to
provide an insight into the binding
mechanism (see figure). These results
may carry important implications for
stimuli-responsive luminescent host
complexes that engage in intramolecu-
lar interactions.
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Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!