Metal-selective coordination and enhanced fluorescence of a self-assembling ligand scaffold

Article abstract of DOI:10.1080/10610278.2017.1347261

A fluorescent hydroxyiminonicotinonitile (HINT) coordinating group can be incorporated into self-assembling ligand scaffolds, and shows metal-selective assembly and enhanced fluorescence. The assembly process is dependent on ligand coordination angle, and coordination only occurs for oxophilic first row transition metal ions, with affinity enhanced by the supramolecular assembly process. The ligands are weakly emissive, and show strong enhancement in fluorescence upon Zn²⁺ coordination, whereas Co²⁺ or Fe²⁺ cause complete quenching.

Full text of DOI:10.1080/10610278.2017.1347261

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Metal-selective coordination and enhanced
fluorescence of a self-assembling ligand scaffold
Paul M. Bogie, Yana Lyon, Lauren R. Holloway, Ryan R. Julian & Richard J.
Hooley
To cite this article: Paul M. Bogie, Yana Lyon, Lauren R. Holloway, Ryan R. Julian & Richard J.
Hooley (2017): Metal-selective coordination and enhanced fluorescence of a self-assembling ligand
scaffold, Supramolecular Chemistry, DOI: 10.1080/10610278.2017.1347261
To link to this article: http://dx.doi.org/10.1080/10610278.2017.1347261
View supplementary material
Published online: 12 Jul 2017.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gsch20
Download by: [University of York]
Date: 12 July 2017, At: 03:19

Supramolecular chemiStry, 2017
https://doi.org/10.1080/10610278.2017.1347261
Metal-selective coordination and enhanced fluorescence of a self-assembling
ligand scaffold
Paul M. Bogie, Yana Lyon, Lauren R. Holloway, Ryan R. Julian and Richard J. Hooley
Department of chemistry and the ucr center for catalysis, university of california - riverside, riverside, ca, uSa
ABSTRACT
ARTICLE HISTORY
received 26 may 2017
accepted 22 June 2017
A fluorescent hydroxyiminonicotinonitile (HINT) coordinating group can be incorporated into self-
assembling ligand scaffolds, and shows metal-selective assembly and enhanced fluorescence. The
assembly process is dependent on ligand coordination angle, and coordination only occurs for
oxophilic first row transition metal ions, with affinity enhanced by the supramolecular assembly
process. The ligands are weakly emissive, and show strong enhancement in fluorescence upon Zn2+
coordination, whereas Co2+ or Fe2+ cause complete quenching.
KEYWORDS
Self-assembly; sensing;
metal-ligand complexes
1. Introduction
cages have even greater potential than simple singly coor-
dinating metal ion sensors, as the incorporation of multiple
metals in a single scaffold can provide greater sensitivity
and selectivity in detection. In addition, other applications
are possible, such as guest release, the analysis of supra-
molecular assembly processes and reaction monitoring
(5). Luminescent assemblies are typically constructed from
rigid ligands with fluorescent groups in the backbone (6),
or by utilising the native luminescence of the coordinat-
ing metal (i.e. using rare earth metals or complexes such
as Ru(bipyridyl)3 in the assembly process) (7). As a result,
fluorescent cage complexes rarely display metal-selective
emissive properties (8). As part of our ongoing studies into
metal-selective self-assembling systems (9), we have inves-
tigated novel self-assembling scaffolds that both strongly
bind specific metal ions and show strong emissive prop-
erties upon coordination.
Selective fluorescent sensing systems for transition metal
ions, especially Zn2+ ions, are vital tools for imaging appli-
cations. (1) The most common strategy for construction of
these sensor systems involves covalently appending a flu-
orescent group to the metal-coordinating motif. The lone
pairs in the coordinating group quench the fluorophore
via photo-induced electron transfer, and sensing is usu-
ally achieved via abrogation of this PET-based quenching
upon metal binding (2). An alternative strategy is to use
metal-coordinating motifs that are both fluorescent and
show strong metal affinity. This method has the poten-
tial to produce sensitive turn-on fluorescence that can
be modulated by binding to different metals, due to the
direct interaction between the fluorophore/ligand and the
bound metal (3). This method is atom efficient and synthet-
ically advantageous, and as the fluorophore is ‘built-in’ to
the metal-coordinating motif, it also introduces the possi-
bility of combining multiple ligands to create fluorescent
supramolecular assemblies (4). Fluorescent self-assembled
Here, we describe the use of self-assembling fluorescent
ligands that show zinc-selective fluorescence enhance-
ment upon self-assembly. The metal-coordinating motif
CONTACT richard J. hooley
richard.hooley@ucr.edu
the supplemental data for this paper is available online at https://doi.org/10.1080/10610278.2017.1347261
© 2017 informa uK limited, trading as taylor & Francis Group

2
P. M. BOGIE ET AL.
is a 1-hydroxy-2-iminonicotinonitrile (HINT) group, which
displays both strong metal affinity and native fluores-
cence. The HINT group displays a structure reminiscent of
the well-known hydroxypyridinone (HOPO) coordinating
ligands (10), which show strong affinities towards group
(IV) metals (11) and lanthanides (12), and can enhance the
native luminescence of rare earth metals (13) While, HOPO
ligands are non-emissive by themselves, fluorescent nic-
otinonitrile-containing analogues are known, and their
alkylidene malononitrile enamine precursors have been
used as sensors for primary amines (14).
The metal-coordinating abilities of ligands 1–3 were
tested by titrating metal ions into DMSO solutions of the
ligands, and monitoring the process by UV/Vis absorption
spectroscopy. The neutral HINT ligands 1–3 showed poor
affinity for metals by themselves, so effective metal coor-
dination was achieved by pre-treating the ligands with
NaH suspended in CH2Cl2 to yield the anionic sodiated
counterparts Na41, Na42 and Na23. As expected, the more
donating ligands were strongly coordinating, and demon-
strated strong affinity for a range of oxophilic transition
metal ions (see Figure 2 and ESI). DMSO solutions of metal
salts were titrated, in 0.10 M equivalent increments, into
30 μM solutions of Na41 and Na42, with absorption spec-
tra taken at each increment. Upon titration of Zn2+, Fe2+
and Co2+ into solutions of ligand Na41 (Figures 2(a–c)), the
absorption spectra showed red-shifted absorbance max-
ima, and an easily detectable isosbestic point, indicating
the formation of a single discrete metal-ligand complex.
No change in absorbance was observed after the addi-
tion of 0.66 mol.-eq. metal in each case, consistent with
the expected formation of an M2L3 complex (6). In addi-
tion, analysis via Job plot for the assembly of Na41 with
Zn2+, Fe2+ and Co2+ was consistent with M2L3 stoichiom-
etry. In contrast, Na41 showed much smaller changes in
absorbance in the presence of Ni2+ or main group metals
such as Ga3+, and no affinity at all for rare earth metals
such as La3+ or Tb3+ (see ESI). It is not clear why strong
coordination is observed for Zn2+, Fe2+ and Co2+, but far
less for other, putatively oxophilic cations of similar size.
Hill plots of the association of Na41 with Zn2+, Fe2+ and
2. Results and discussion
The ligand synthesis is shown in Figure 1 and the ESI.
Terphenyl ligand 1 and fluorenyl ligand 2 both contain two
HINT groups, and should be capable of multicomponent
self-assembly into MxLy complexes, whereas phenyl HINT
ligand 3 was synthesised as a single metal-coordinating
control (Figure 1). Ligand 1 was synthesised in four steps
from 1,3-dibromobenzene. Nitrile 5 was formed in 80%
yield via Knoevenagel condensation of 4 with malononi-
trile using Ti(OiPr)4 as Lewis acid. This was converted to
enamine 6 by treatment with N,N-dimethylformamide
dimethyl acetal and acetic anhydride. This enamine under-
went rapid Pinner cyclisation upon addition of hydroxy-
lamine, giving ligand 1 in 96% yield. Analogous methods
were used to synthesise the related fluorenyl ligand 2
and control phenyl ligand 3 (see ESI for methods and
characterisation).
Figure 1. Synthetic route to the three coordinating hiNt ligands 1, 2 and 3 used here.

SUPRAMOLECULAR CHEMISTRY
3
Figure 2. uV–vis absorption spectra of the titration of various metal salts into DmSo solutions of anionic ligand Na41: (a) mX2 = Zn(otf)2,
(b) mX2 = Fe(clo4)2, (c) mX2 = co(clo4)2, (d) mX2 = NiSo4. [Na41] = 30 μm.
Co2+ showed that the affinities were strong, and on the
order of 25–50 μM (Kd (Zn)=49.8 μM, Kd (Fe)=28.5 μM,
Kd (Co)=42.5 μM). Complex formation was insensitive to
counteranion: weakly coordinatingNO−3 , ClO4−orTfO− salts
of these metals all showed similar absorption spectra upon
titration with Na41, although stronger coordinators such as
Cl− lowered the affinity for the ligand. The assembly pro-
cess was generally performed in DMSO, but ligand Na41
showed effective assembly into the Zn21 complex in the
presence of as much as 33% water in the system.
The self-assembly properties of the bis-HINT system
are strongly dependent on coordination angle. While, the
V-shaped bis-HINT ligands showed a clear M2L3 self-as-
sembly pattern with the octahedral metals tested, the
fluorenyl bis-HINT ligand did not (see ESI for spectra).
UV–vis spectra obtained upon titration of both Fe(ClO4)2
and Co(ClO4)2 with Na42 did not display isosbestic points.
Spectral changes ceased at 0.55 mol.-eq added Co2+, and
no discrete endpoint was reached upon addition of Fe2+.
Evidently, variable coordination modes are present upon
complexation of Na42, rather than discrete M2L3 complexes
or M4L6 tetrahedra. The singly coordinating HINT ligand
Na23 behaved as expected. The absence of cooperative
supramolecular coordinating effects leads to weaker
metal coordination for Na23 than for Na41 or Na42. Metal
titrations were performed at [Na23] = 240 μM to maxim-
ise complex formation (see ESI). Zn(OTf)2, Fe(ClO4)2 and
Co(ClO4)2 all showed affinity for ligand Na23, although no
isosbestic points were observed, indicating an equilibrium
between ML, ML2 and ML3 stoichiometries in solution. The
supramolecular assembly process occurring for Na41 pro-
vides enhanced affinity for early transition metals, as well
as structural control of the coordination.
The coordinating HINT motif in ligands 1–3 is weakly
fluorescent by itself, as can be seen in Figures 3 and 4.
Upon exposure to long wave UV light, a weak blue and
orange fluorescence can be observed for the neutral lig-
ands 1/3, and their anionic counterparts Na41 and Na23,
respectively. Significant variations in emissive behaviour of
the respective metal complexes were observed. A strong
enhancement in fluorescence occurs selectively upon for-
mation of the Zn2+ complex. This effect is highly selective
for Zn ions: other coordinating metals such as Fe2+ and
Co2+ showed near-complete quenching of the fluores-
cence upon complex formation. Importantly, quenching
only occurred upon complexation: no quenching was
observed for non-complexing metals such as Ni2+ (Figure
2(d)). Other non-coordinating ions such as La3+ orTb3+ also

4
P. M. BOGIE ET AL.
had no effect on the emission of either the ligands or the
ligand: Zn complexes.
(Φ = 1.3%), even though dialkylfluorenes are well-known
emissive groups.
The enhanced Zn2+ fluorescence was persistent in the
presence of other metals (see ESI for spectra). When a
50/50 mixture of Zn2+ and Co2+ (1.33 mol.-eq. metal com-
bined) was added to a DMSO solution of Na41, the emis-
sion at 508 nm of Zn213 was observed with an intensity
of 80% of that shown by Zn213. The presence of Fe2+ low-
ered the emission intensity more (to 52% Zn213), but the
enhanced fluorescence was persistent, even in an excess of
both competing Co2+ and Fe2+ salts (32% emission inten-
sity, 2.0 mol.-eq total metal). These emission intensities
indicate that Zn2+ complexation is both more favourable
than that of Co2+ and Fe2+, and the free ions do not cause
quenching of the Zn213 complex.
Titration of Fe2+ or Co2+ into a Na41 solution (Figure 4(b),
ESI) causes an immediate loss in fluorescence, with maximal
quenching occurring upon addition of 1.0 mol.-eq. metal.
Notably, no redshift was observed in either case, indicat-
ing that the emission remains ligand-centred. Quantum
yield analysis of the M2L3 complex formed by addition
of Fe2+ to Na41 confirmed the quenching phenomenon,
with Φ(Fe213) = 0.12%. This quenching is most likely due to
unpaired electrons in the Fe (and Co) centres, whereas the
filled shells of Zn2+ do not cause quenching, but fluores-
cence enhancement. The discrete self-assembled complex
Zn213 showed a large redshift in emission when compared
to Na41, with the emission maximum shifting from 477 nm
to 508 nm upon Zn coordination (see Figure 4(a)). This red-
shift was accompanied by a seven-fold enhancement of
emission over ligand 1 (Φ(Zn213) = 6.4%). This effect was
mirrored for the monomeric Zn32/Zn33 system, which also
showed a 31 nm redshift in emission frequency, and an
even more strongly enhanced quantum yield (Φ(Zn33) =
10.5%). Unusually, the fluorescence enhancement upon
titration of Zn2+ to Na41 did not cease at 0.66 mol.-eq metal,
(Figure 4(a)) but only ceased increasing after 5 mol.-eq. Zn2+
was added. Absorbance changes ceased at 2/3 mol.-eq.
Zn2+, consistent with formation of the Zn213 complex (vide
The quantum yield of emission for uncomplexed lig-
ands 1–3 were moderate (e.g. Φ(1) = 1.0%, see ESI for full
details). Upon deprotonation, a large increase in quantum
yield was observed (Φ(Na4(1) = 5.2%). The emission occurs
at the HINT coordinator itself – the emission maximum for
all three ligands Na41, Na42 and Na23 appears at 477 nm
(upon excitation at 397, 404 and 410 nm, respectively).
The quantum yield of emission did vary with the internal
core, however: while, both Na41 and Na23 showed ~five-
fold increase in Φ upon deprotonation (Φ(Na23) = 4.19%),
the fluorenyl ligand Na42 showed less efficient emission
Figure 3. colorimetric changes upon of the addition of 0.66 mol-eq. mXx to DmSo solutions of anionic ligands Na41.
Note: upper image: ambient light, lower image: upon long wave uV irradiation (365 nm). [Na41] = 3 mm, [Na23] = 6 mm.

SUPRAMOLECULAR CHEMISTRY
5
Figure 4. Fluorescence emission spectra of the titration of metal salts into DmSo solutions of anionic ligand Na41: (a) mX2 = Zn(otf)2, (b)
mX2 = Fe(clo4)2. [Na41] = 30 μm, excitation wavelength = 397 nm.
infra). Evidently, the fluorescence enhancement is a dual
mode process: the Zn213 complex shows enhanced fluo-
rescence with respect to ligand, and then a second inter-
action occurs, further enhancing the emission intensity. We
attribute this phenomenon to weak coordination between
Zn2+ and the nitrile groups on the HINT ligand: the pendant
nitriles cause some quenching (likely via PET), but weak
complexation of Zn2+ abrogates this quenching, and this
reaches a maximum at 5 eq. metal. The red-shifted emission
and fluorescence enhancement of Zn213 was retained in
the presence of 15% water, although the enhancement was
lowered when compared to pure DMSO (see ESI).
In contrast, this phenomenon is not observed in the
case of the fluorene ligand Na42. Even though Na42 dis-
plays coordination to Zn2+ and formation of a non-discrete
aggregated assembly, a decrease in emission intensity is
observed upon increasing concentration of Zn2+ (see
ESI), with a two-fold decrease observed after addition of
0.33 mol.-eq. Zn2+. Red-shifted emission was observed
upon formation of the Znx2y assembly, suggesting that
the fluorenyl core was responsible for some quenching of
the HINT emission. This quenching is corroborated by the
observed anionic ligand and complex quantum yields, both
of which were lower than their 1/3 analogues (Φ(Na42) =
1.5%, Φ(Znx2y) = 2.0%). This indicates that the enhanced
emission seen upon Zn2+ coordination by the HINT ligands
is not solely dependent on the coordinating group, but
that the nature of the rigid spacer in the ligand structure is
important. While, the singly coordinating ligand 3 and the
self-assembling ligand 1 show enhanced emission upon
Zn2+ coordination, the disordered assemblies formed from
fluorenyl HINT 2 are far less effective emission enhancers.
NMR analysis of the assembly process was consistent
with the UV–vis titration data. Upon addition of Zn(OTf)2
to anhydrous DMSO-d6 solutions of Na41, Na42 and Na23,
sharp, shifted peaks were observed, indicative of strong
coordination. Complete association was observed upon
addition of 0.66 mol.-eq. Zn2+ to Na41. Diffusion NMR anal-
ysis showed a reduction in diffusion constant from 2.72
×10−9 m2/s for 1 to 1.29 ×10−9 m2/s for Zn213, consistent
with formation of a larger, more slowly diffusing assembly
(see ESI). No complexation was observed upon treatment
of neutral ligands 1–3. These NMR experiments shed light
on nature of the HINT:Zn coordination sphere: anhydrous
samples of Na41, Na42 and Na23 rapidly reacted with Zn2+
ions, but the samples suffered from precipitation over
time, especially at the millimolar concentrations required
for NMR analysis, likely due to protonation of the assem-
bly via exogenous water. The M2L3 complex formed from
the tetra-anionic Na41 and two Zn2+ ions is octa-anionic,
basic, and highly susceptible to protonation by exogenous
water. Neutral cages formed using hydroxamic acid lig-
ands are well-known to show limited solubility in many
solvents, and can be challenging to characterise (15). When
the addition of Zn(OTf)2 to Na41 was repeated in DMSO-d6
in the presence of 20 μL water, no cage complex was
observed, merely a complete loss of ligand peaks and for-
mation of precipitate. The varied protonation states of the
Zn213 complex complicated further characterisation. No
crystals suitable for diffraction analysis could be attained
upon slow evaporation or vapour diffusion, and proto-
nated ligand or neutral cage were obtained in all cases.
MS analysis of the M2L3 assembly was challenging, as
the protonated species was highly insoluble in solvents

6
P. M. BOGIE ET AL.
other than DMSO. MALDI analysis was unsuccessful, but the
assembly was sufficiently soluble in CH3CN to allow ESI-MS
analysis. In positive ion mode, protonation occurred and
the insoluble M2L3 complex was not seen, but low inten-
sity fragments such as [Zn212-H•2H2O]+ ion (m/z = 1155.18)
corresponding to the protonated M2L2 assembly with loss
of one ligand was observed, as well as Zn21 fragments.
The more soluble, singly coordinating ligand Na23 allowed
more detailed ESI-MS analysis of the coordination process.
A 4:1 ratio of Zn(OTf)2:Na23 were combined in CH3CN/iPrOH,
then centrifuged to remove any complex that had precip-
itated, and immediately analysed by ESI-MS using a LTQ
mass spectrometer nanosource electrospray ioniser. The
MS analysis (see ESI for spectra) showed the presence of
ions from both ML2 and ML3 coordination, as expected from
the titration data. Positive mode analysis showed the pres-
ence of fully sodiated ML3 ion [Zn•33Na4(iPrOH)-5H]+ and
ML2 complex [Zn•32NaOTf-1H]+. Negative ion detection was
less effective, and only fragments [Zn•32(H2O)(CN−)-2H]−,
[Zn•32(CN−)-2H]− were observed, each containing cyanide
ions, presumably from ligand fragmentation. Precipitation
occurred rapidly in this case also, supporting the hypothesis
that the fully anionic ligands form the soluble complexes,
which form insoluble neutral assemblies upon reaction
with weak acids such as iPrOH or exogenous water.
This analysis, along with the UV/Vis titration data,
suggests that the V-shaped ligand Na41 forms a discrete,
highly anionic assembly with M2L3 stoichiometry upon
addition of Zn2+, Fe2+, Co2+, etc. A minimised structure of
the proposed [13•Zn2]8− complex is shown in Figure 5(c)
(and in the ESI). In contrast, fluorenyl ligand Na42 does not
form a discrete assembly, but variable species including
coordination polymers, and the singly coordinating ligand
Na21 forms a mix of bis- and tris-coordination modes. The
varying coordination modes of each ligand affect the emis-
sion response upon assembly.
tetramethylsilane (TMS, δ= 0), and referenced internally with
respect to protio solvent impurities. Deuterated NMR sol-
vents were obtained from Cambridge Isotope Laboratories,
Inc., Andover, MA, and used without further purification.
All other materials were obtained from Aldrich Chemical
Company, St. Louis, MO, or TCI, Tokyo, Japan and were used
as received. Solvents were dried through a commercial sol-
vent purification system (Pure Process Technologies, Inc.).
Mass spectra were recorded on an Agilent 6210 LCTOF mass
spectrometer using electrospray ionisation with fragmen-
tation voltage set at 115 V and processed with an Agilent
MassHunter Operating System. The mass spectra the com-
plexes were analysed using a LTQ mass spectrometer with
a nanosource (10 micron emitter), while predicted isotope
patterns were prepared with assistance from ChemCalc
(16). UV/Vis spectroscopy was performed on a Cary 50
Photospectrometer using the Varian Scans programme to
collect data. Fluorescence spectroscopy was performed on a
Spex FluorologTau-3 fluorescence spectrophotometer. ATR
IR spectra were taken on a Bruker:ALPHA FTIR Spectrometer.
Molecular modelling (semi-empirical calculations) was per-
formed using the AM1 force field using SPARTAN (17).
3.1.2. Synthesis of compounds
3.1.2.1. Synthesis of 1-(4″-Acetyl-[1,1′;3′,1″]terphenyl-
4-yl)-ethanone (4). A 50 mL round-bottom flask was
charged with 1,3-Dibromobenzene (513 μL, 4.24 mmol),
4-acetylphenylboronic acid (1.8 g, 11.02 mmol) and
bis(triphenylphosphine)
palladium(II)
dichloride
(297 mg, 0.42 mmol). A 1:1:1 mixture of 2 M K2CO3 in
water:ethanol:toluene (24 mL) was added to the flask. The
flask was purged with N2, and refluxed for 16 h. Methanol
was added to the reaction mixture and the precipitate
filtered via vacuum filtration to afford a tan solid. The solid
was dissolved in dichloromethane and filtered through a
silica/Celite plug and the filtrate concentrated in vacuo
1
(1.274 g, 4.05 mmol, 96%). H NMR: (500 MHz, CDCl3) δ
8.07 (dt, J = 8 Hz, 1.8 Hz, 4H), 7.83 (t, J = 1.7 Hz, 1H), 7.74
(dt, J = 8 Hz, 1.8 Hz, 4H), 7.66 (d, J = 6.9 Hz, 2H), 7.58 (dd,
J = 8.5, 6.8 Hz, 1H), 2.66 (s, 6H). 13C NMR: (125 MHz, CDCl3)
δ 197.6, 145.4, 140.7, 136.1, 129.6, 128.9, 127.3, 127.1,
126.2, 26.7. HRMS (ESI+) calc. C22H18O2 314.1307; found,
315.1475 (M+H)+. IR 1667, 1600, 1355, 1286, 1187, 957,
832, 793, 693, 590 cm−1.
3. Conclusions
We have shown that a novel, fluorescent coordinator can
display early transition metal-selective supramolecular
self-assembly, and enhanced fluorescence upon selective
binding of Zn2+ ions. Applications of this process in selec-
tive sensor construction are underway.
3.1.2.2. 2-Cyano-3-[4″-(2,2-dicyano-1-methyl-vinyl)
3.1. Experimental section
[1,1′;3′,1″]terphenyl-4-yl]-but-2-enenitrile (5) (18).
A
3.1.1. General information
50 mL round-bottomed flask was charged with 4 (410 mg,
1.30 mmol), malononitrile (430 mg, 6.52 mmol) and
4 mL THF. Pyridine (210 μL, 1.74 mmol) was then added
to the flask followed by Ti(OiPr)4 (1.15 mL, 3.90 mmol).
The reaction was allowed to stir at 25 °C for 16 h. The
product was precipitated with water, and isolated via
1H and 13C spectra were recorded on aVarian Inova 500 MHz
NMR spectrometer. DOSY spectra were recorded on a Bruker
Avance 600 MHz spectrometer. Spectra were processed using
MestReNova by Mestrelab Research S.L. Proton (1H) chemical
shifts are reported in parts per million (δ) with respect to

SUPRAMOLECULAR CHEMISTRY
7
1
Figure 5. (a) Zn213 cage assembly and in situ protonation; (b) h Nmr spectra of the assembly process and subsequent protonation/
precipitation (500 mhz, DmSo-d6, 298 K); (c) minimised structure of [13•Zn2]8− (SpartaN, am1 forcefield).
vacuum filtration. The resulting solid was then dissolved
in acetone, filtered and concentrated in vacuo to afford
a yellow solid (477 mg, 1.16 mmol, 89%). H NMR:
(500 MHz, CDCl3) δ 7.83 (s, 1H), 7.78 (d, J = 8.4 Hz, 4H),
7.67 (d, J = 8.4 Hz, 4H), 7.64 (dd, J = 7.0, 1.7 Hz, 2H), 7.58
(t, J = 7.0 Hz, 1H), 2.71 (s, 6H). 13C NMR: (125 MHz, CDCl3)
δ 174.5, 144.7, 140.2, 134.9, 129.8, 128.1, 127.7, 127.2,
126.1, 112.9, 112.7, 84.5, 24.1. HRMS (ESI-) calc. C28H18N4,
410.1531; found, 409.1464 (M−H)−. IR 2223, 1601, 1571,
1476, 1390, 1302, 1007, 907, 836, 791, 731, 696 cm−1.
3.1.2.4. Phenyl-1,3-di-(1-Hydroxy-2-imino-4-phenyl-
1,2-dihydro-pyridine-3-carbonitrile) (Ligand 1) (14).
Compound 6 (604 mg, 1.16 mmol) was dissolved in
anhydrous DCM (3.5 mL). Hydroxylamine hydrochloride
(484mg,6.96mmol)andtriethylamine(970μL,6.96mmol)
were added to the reaction mixture which was allowed to
stir for 24 h, then the solvent was removed under vacuum.
The residue was then triturated in water and isolated via
vacuum filtration to afford a yellow-orange solid (551 mg,
1.11 mmol, 95%). 1H NMR: (500 MHz, DMSO-d6) δ 8.49 (d,
J = 6.8 Hz, 2H), 8.11 (s, 1H), 8.04 (s, 4H), 8.01 (d, J = 8.2 Hz,
4H), 7.81 (d, J = 7.7 Hz, 2H), 7.76 (d, J = 8.1 Hz, 4H), 7.64 (t,
J = 7.7 Hz, 1H), 6.92 (d, J = 6.7 Hz, 2H). 13C NMR: (125 MHz,
DMSO-d6) δ 153.2, 142.2, 141.4, 140.4, 140.4, 135.4, 130.3,
129.3, 127.8, 126.9, 125.8, 115.5, 112.8, 90.1. ITMS + p ESI
calc. C30H20N6O2, 496.1648; found 497.2526 (M+H)+. IR
3105, 1618, 1454, 1215, 791 cm−1. Sample was purified
via treatment with conc. HCl, and analysed as the salt.
Elemental Analysis: Theoretical (C30H21ClN6O2•H2O): C:
65.39, H: 4.21, Cl: 6.53, N: 15.05, O: 8.81. Found: C: 66.71,
H: 4.21, N: 14.69, O: 8.45.
1
3.1.2.3. 2-(1-{4″-[2,2-Dicyano-1-(2-dimethylamino-
vinyl)-vinyl]-[1,1′;3′,1″]terphenyl-4-yl}-3-dimethylamino-
allylidene)-malononitrile (6) (19). Compound 5 (0.1 M,
350 mg, 0.85 mmol) and Ac2O (0.4 M, 32 μL, 0.34 mmol)
were dissolved in 1 mL anhydrous DCM. The solution was
stirred vigorously, while DMF-DMA (270 μL, 2.04 mmol)
was added to the reaction mixture. The reaction was
allowed to stir at room temperature for 24 h. The solvent
was removed under vacuum to give a red residue which
was triturated with water and filtered to yield the final
1
product (354 mg, 0.68 mmol, 80%). H NMR: (500 MHz,
CDCl3) δ 7.84 (s, 1H), 7.73 (d, J = 8.1 Hz, 4H), 7.64 (dd,
J = 6.9 Hz, 1.5 Hz, 2H), 7.56 (dd, J = 8.4 Hz, 6.9 Hz, 1H),
7.38 (d, J = 8.1 Hz, 4H), 6.73 (d, J = 12.4 Hz, 2H), 5.87
(d, J = 12.4 Hz, 2H), 3.08 (s, 6H), 3.05 (s, 6H). 13C NMR:
(125 MHz, CDCl3) δ 171.3, 155.9, 142.6, 140.7, 133.9, 129.5,
129.4, 127.4, 126.6, 126.2, 116.7, 116.1, 98.1, 64.9, 45.8,
37.7. HRMS calc. C34H28N6, 520.2375; found, 565.2356
(M + HCOO)−. IR 2200, 1613, 1503, 1463, 1408, 1378, 1333,
1261, 1109, 792, 551 cm−1.
3.1.2.5. Anionic Ligand 1 (Na41). Ligand 1 (50 mg,
0.10 mmol) was dissolved in anhydrous DCM (30 mL) and
stirred vigorously. NaH (16 mg, 0.40 mmol) was added to
the reaction mixture which was allowed to stir overnight.
The stirring was stopped and the solution allowed to settle
for 1 h before being filtered to afford an orange powder
(35 mg, 0.06 mmol, 60%). 1H NMR: (500 MHz, DMSO-d6) δ
8.06 (s, 1H), 7.89 (d, J = 8.1 Hz, 4H), 7.76 (m, 5H), 7.64 (d,
J = 8.1 Hz, 4H), 5.54 (d, J = 6.0 Hz, 2H). 13C NMR: (125 MHz,

8
P. M. BOGIE ET AL.
DMSO-d6) δ 158.8, 143.2, 140.8, 140.0, 138.4, 136.7, 130.1,
128.7, 127.2, 126.4, 125.4, 124.5, 121.1, 98.4, 85.2.
6H), 1.55 (s, 6H). 13C NMR: (125 MHz, CDCl3) δ 172.0, 156.1,
154.2, 140.1, 134.3, 128.1, 123.6, 120.5, 116.7, 116.3, 98.0,
47.3, 45.8, 37.7, 26.7. HRMS (ESI-) calc. C31H28N6, 484.2375;
found, 529.2357 (M + HCOO)−.
3.1.2.6. 9,9-dimethyl-9H-fluorene(20). Fluorene, (1 g,
6.01 mmol) was placed in a Schlenk flask along with 3 eq
potassium tert-butoxide (2.02 g, 18.05 mmol). The flask
was purged with N2 followed by the addition of 30 mL THF.
The orange solution was stirred for 10 min. Iodomethane
(1.12 mL, 18.05 mmol) was added slowly to the flask over a
period of 10 min. The reaction was heated at 65 °C for 16 h
then cooled, diluted with 100 mL ice water and extracted
with DCM. The organic layer was washed with brine and
saturated sodium bicarbonate (30 mL each), dried with
magnesium sulphate, and the solvent removed in vacuo to
afford yellow waxy solid (1.074 g, 5.53 mmol, 92%). 1H NMR
spectra were in agreement with previously reported results.
3.1.2.10. 9,9-dimethyl-9H-fluorene-1,1′-di-(1-Hydroxy-
2-imino-4-phenyl-1,2-dihydro-pyridine-3-carbonitrile)
(Ligand 2).
Synthesised from 8 using the same
procedure reported for Compound 7. Isolated as a tan
1
powder (1.080 g, 2.33 mmol, 92%). H NMR: (500 MHz,
DMSO-d6) δ 8.44 (d, J = 6.7 Hz, 2H), 8.07 (d, J = 7.9 Hz,
2H), 7.89 (s, 2H), 7.82 (s, 4H), 7.65 (d, J = 8.1 Hz, 2H),
6.91 (d, J = 6.7 Hz, 2H), 1.54 (s, 6H). 13C NMR: (125 MHz,
DMSO-d6) δ 154.6, 153.2, 143.0, 140.4, 139.4, 135.6, 128.1,
123.6, 121.5, 115.6, 112.9, 90.2, 47.5, 26.8. HRMS (ESI-
) calc. C27H20N6O2, 460.1648; found, 459.1575 (M−H)−.
Purified and isolated as the HCl salt. Elemental Analysis:
Theoretical (C27H20ClN6O2): C: 65.52, H: 4.45, Cl: 7.12, N:
16.88, O: 6.03. Found: C: 66.86, H: 4.69, N: 17.03, O: 6.30.
3.1.2.7. 1,
1-(7-Acetyl-9,9-dimethyl-9H-fluoren-2-yl)-
ethanone (21). Acetyl chloride (1.83 mL, 25.74 mmol)
was dissolved in 50 mL dichloromethane in a round-
bottomed flask. Aluminium chloride (3.43 g, 25.74 mmol)
was added and the flask placed in an ice bath with stirring.
Dimethyl fluorene (1 g, 5.15 mmol) was dissolved in 5 mL
DCM and added dropwise to the cooled flask over 5 min.
The flask was removed from the ice bath and heated to
reflux for 2.5 h or until complete via TLC analysis. Once
complete, the reaction mixture was poured over 150 g
of ice and extracted with DCM. The organic layer was
washed with brine (2 × 50 mL) and saturated sodium
bicarbonate (2 × 50 mL), dried over magnesium sulphate,
and the solvent removed in vacuo to give a tan crystalline
3.1.2.11. Anionic Ligand 2 (Na42). Anionic Ligand
2 was synthesised using the procedure reported for
Anionic Ligand 1. Isolated as a dark brown powder
1
(33 mg, 0.06 mmol, yield = 56%). H NMR: (500 MHz,
DMSO-d6) δ 7.93 (d, J = 7.8 Hz, 2 H), 7.75 (d, J = 6.2 Hz, 4H),
7.72 (s, 2H), 7.53 (d, J = 7.8 Hz, 2H), 5.59 (d, J = 6.3 Hz, 2H),
1.53 (s, 6H). 13C NMR: (125 MHz, DMSO-d6) δ 156.5, 154.3,
143.5, 138.9, 138.3, 137.2, 127.7, 123.2, 120.9, 118.9, 104.7,
87.42, 55.4, 47.3, 27.0.
3.1.2.12. 1-Hydroxy-2-imino-4-phenyl-1,2-dihydro-
1
solid (1.120 g, 4.02 mmol, 78%). H NMR spectra were in
pyridine-3-carbonitrile
(3). (3-(dimethylamino)-
agreement with previously reported results.
1-phenyl-2-propenylidene) malononitrile (332 mg,
1.44 mmol) was dissolved in anhydrous DCM (3 mL). To the
solution was added hydroxylamine hydrochloride (484 mg,
4.33 mmol) and trimethylamine (970 μL, 4.33 mmol). The
mixture was allowed to stir for 24 h, then reduced under
vacuum.The solid was then sonicated in water and isolated
via vacuum filtration to afford a yellow powder (128 mg,
3.1.2.8. 2-Cyano-3-[7-(2,2-dicyano-1-methyl-vinyl)-
9,9-dimethyl-9H-fluoren-2-yl]-but-2-enenitrile
Synthesised from 1,1′-diacetyl-9,9-dimethyl-9H-fluorene
using the same procedure reported for 5. Isolated as
an orange powder (984 mg, 2.63 mmol, 80%). H NMR:
(500 MHz, CDCl3) δ 7.87 (d, J = 7.9 Hz, 2H), 7.70 (s, 2H),
7.59 (d, J = 7.2 Hz, 2H), 2.71 (s, 6H), 1.56 (s, 6H). C NMR:
(125 MHz, CDCl3) δ 175.0, 154.9, 141.7, 135.8, 127.1, 122.3,
121.4, 113.1, 112.8, 84.4, 47.7, 26.5, 24.2. HRMS (ESI-) calc.
C25H18N4, 374.1531; found, 373.1459 (M−H)−.
(7).
1
1
0.60 mmol, 42%). H NMR: (500 MHz, DMSO-d6) δ 8.41 (d,
13
J = 6.7 Hz, 1H), 7.80 (s, 2H), 7.60 (d, J = 7.3 Hz, 2H), 7.52 (p,
J = 6.2 Hz, 3H), 6.78 (d, J = 6.7 Hz, 1H). 13C NMR: (125 MHz,
DMSO-d6) δ 153.1, 142.8, 140.4, 140.3, 136.2, 129.9, 129.2,
128.7, 115.4, 112.8, 112.8, 90.3. HRMS (ESI-) calc. C12H9N3O,
211.0746; found, 210.0673 (M – H)−. Elemental Analysis:
Theoretical (C12H9N3O): C: 68.24, H: 4.29, N: 19.89, O: 7.57.
Found: C: 68.31, H: 4.33, N: 20.08, O: 7.28.
3 . 1 . 2 . 9 . 2 - C y a n o - 3 - { 7 - [ 2 , 2 - d i c y a n o - 1 - ( 2 -
dimethylamino-vinyl)-vinyl]-9,9-dimethyl-9H-fluoren-
2-yl}-5-dimethylamino-allylidene)-malononitrile
(8). Synthesised from 7 using the same procedure
reported for 6, isolated as an orange waxy solid (1.033 g,
3.1.2.13. Anionic Ligand 3 (Na23). Synthesised from
3 using the procedure reported for Anionic Ligand 1
1
1
2.13 mmol, 83%). H NMR: (500 MHz, CDCl3) δ 7.81 (d,
(yield = 26 mg, 0.101 mmol, 43%). H NMR: (500 MHz,
J = 7.8 Hz, 2H), 7.39 (s, 2H), 7.27 (t, J = 8.8 Hz, 2H), 6.73 (d,
J = 12.4 Hz, 2H), 5.87 (d, J = 12.4 Hz, 2H), 3.06 (s, 6H), 3.05 (s,
DMSO-d6) δ 7.72 (d, J = 6.3 Hz, 1H), 7.50 (d, J = 7.4 Hz, 2H),
7.45 (t, J = 7.5 Hz, 2H), 7.40 (t, J = 6.9 Hz, 1H), 6.61 (s, 1H), 5.45

SUPRAMOLECULAR CHEMISTRY
9
13
(2) (a) Wu, Y.; Peng, X.; Guo, B.; Fan, J.; Zhang, Z.; Wang, J.; Cui,
A.; Gao, Y. Org. Biomol. Chem. 2005, 3, 1387; (b) Hirano, T.;
Kikuchi, K.; Urano, Y.; Higuchi, T.; Nagano, T. J. Am. Chem.
Soc. 2000, 122, 12399; (c) Wang, J.; Xiao, Y.; Zhang, Z.; Qian,
X.; Yang, Y.; Xu, Q. J. Mater. Chem. 2005, 15, 2836.
(3) Hai, L.; Chen, J.-J.; Zhao, P.; Lv, H.; Yu, Y.; Xu, P.; Zhang, J.-L.
Chem. Commun. 2011, 47, 2435.
(d, J = 6.3 Hz, 1H). C NMR: δ (125 MHz, DMSO-d6) 158.7,
143.7, 139.2, 136.6, 136.5, 128.6, 128.2, 121.1, 98.3, 98.3.
3.2. Experimental procedures
3.2.1. Complex formation
(4) (a) Chantzea, A.K.; Karakostas, N.; Raptopoulou, C.P.;
Psycharis, V.; Saridakas, E.; Griebel, J.; Hermann, R.; Pistolis,
G. J. Am. Chem. Soc. 2010, 132, 16327; (b) Würthner, F.;
Sautter, A.; Schmid, D.; Weber, P.J.A. Chem. Eur. J. 2001, 7,
894; (c) Splan, K.E.; Massari, A.M.; Morris, G.A.; Sun, S.-S.;
Reina, E.; Nguyen, S.B.; Hupp, J.T. Eur. J. Inorg. Chem. 2003,
12, 2348; (d) Dobrawa, R.; Lysetska, M.; Ballester, P.; Grüne,
M.; Würthner, F. Macromolecules 2005, 38, 1315.
(5) (a)Wang, J.; He, C.;Wu, P.;Wang, J.; Duan, C. J. Am. Chem. Soc.
2011, 133, 12402; (b) Ito, H.; Shinoda, S. Chem. Commun.
2015, 51, 3808; (c) Xu, J.; Corneillie, T.M.; Moore, E.G.; Law,
G.; Butlin, N.G.; Raymond, K.N. J. Am. Chem. Soc. 2011, 133,
19900; (d) Wu, P.; Jiang, M.; Hu, X.; Wang, J.; He, G.; Shi, Y.;
Li, Y.; Liu, W.; Wang, J. RSC Adv. 2016, 6, 27944; (e) Ghosh,
S.; Chakrabarty, R.; Mukherjee, P.S. Inorg. Chem. 2009, 48,
549; (f) Neelakandan, P. P.; Jiménez, A.; Nitschke, J.R. Chem.
Sci. 2014, 5, 908; (g) Frischmann, P.D.; Kunz, V.; Würthner,
F. Angew. Chem. Int. Ed. 2015, 54, 7285; (h) Wang, M.;
Vajpayee, V.; Shanmugaraju, S.; Zheng, Y.R.; Zhao, Z.; Kim,
H.; Murkherjee, P.S.; Chi, K.W.; Stang, P. J. Inorg. Chem. 2011,
50, 1506; (i) Brega, V.; Zeller, M.; He, Y.; Lu, H.P.; Klosterman,
J.K. Chem. Commun. 2015, 51, 5077; (j) L. Xu, Wang, Y.-X.,
Yang, H.-B. Dalton. Trans. 2015, 44, 867.
(6) (a) Yan, X.; Cook, T.R.; Wang, P.; Huang, F.; Stang, P.J. Nat.
Chem. 2015, 7, 342; (b) Feng, J.; Yao, L.; Zhang, J.; Mu, Y.;
Chi, Z.; Su, C. Dalton Trans. 2016, 45, 1668; (c) Wragg, A.B.;
Metherell, A.J.; Cullen, W.; Ward, M.D. Dalton Trans. 2015,
44, 17939; (d) Al-Rasbi, N.K.; Sabatini, C.; Barigelletti, F.;
Ward, M.D. Dalton Trans. 2006, 40, 4769; (e) Schmidt, A.;
Hollering, M.; Drees, M.; Casini, A.; Kühn, F.E. Dalton Trans.
2016, 45, 8556; (f) Elliott, A.B.S.; Lewis, J.E.; Van der Salm,
H.; McAdam, C.J.; Crowley, J.D.; Gordon, K.C. Inorg. Chem.
2016, 55, 3440; (g) Li, Z.; Kishi, N.; Hasegawa, K.; Akita, M.;
Yoshizawa, M. Chem. Commun. 2011, 47, 8605.
(7) (a) Yan, L.L.; Tan, C.H.; Zhang, G.L.; Zhou, L.P.; Bünzli, J.C.;
Sun, Q.F. J. Am. Chem. Soc. 2015, 137, 8550; (b) Chepelin,
O.; Ujma, J.; Wu, X.; Slawin, A.M.Z.; Pitak, M.B.; Coles, S.J.;
Michel, J.; Jones, A.C.; Barran, P.E.; Lusby, P.J. J. Am. Chem.
Soc. 2012, 134, 19334; (c) Aroussi, B.E.; Guénée, L.; Pal, P.;
Hamacek, J. Inorg. Chem. 2011, 50, 8588.
The deprotonated ligand (Na41, Na42, or Na23) was dis-
solved in DMSO. The appropriate amount of metal salt
for the ligand (0.66, 0.66 and 0.33 eq, respectively) were
added to the solution which was placed in an ultrasoni-
cation bath for 5 min. This resulted in complex formation
indicated by a colour change in the solution and in the
emissive properties. Formation of a complex is also shown
1
via H-NMR (Figures S-21–S-24). Complex formation was
then confirmed by NMR, UV/Vis and mass spectrometry.
3.2.2. Quantum yield
Quantum yields were calculated using quinine hemisulphate
in 1 M H2SO4 as a standard. All ligand and cage spectra were
obtained using spectral grade DMSO as the solvent. For each
experiment samples were prepared at concentrations of 0,
15, 20, 25 and 30 μM. Emission spectra were taken imme-
diately following the acquisition of a sample’s absorption
spectrum. For emission spectra, all samples were excited at
366 nm using front facing 3 mL quartz cuvettes. The quan-
tum yields were calculated using the following equation,
where (Grad) is the slope of the graph of the integral of the
emission spectra against the absorbance at the excitation
wavelength, and (n) is the refractive index of the solvent.
Grad
nx2
x
ꢀ = ꢀST (
) (
)
x
n2ST
GradST
Acknowledgements
The authors would like to thank the National Science Founda-
tion (CHE-1151773 to R.J.H., CHE-1401737 to R.R.J.), the UCR
Center for Catalysis and the UCR Office for Research and Eco-
nomic Development for support. The authors would also like to
thank Dr. Wenwan Zhong and Yang Liu for their contributions in
calculating dissociation constants.
(8) Yan, X.; Wang, M.; Cook, T.R.; Zhang, M.; Saha, M.L.; Zhou, Z.;
Li, X.; Huang, F.; Stang, P.J. J. Am. Chem. Soc. 2016, 138, 4580.
(9) Johnson, A.M.; Young, M.C.; Zhang, X.; Julian, R.R.; Hooley,
R.J. J. Am. Chem. Soc. 2013, 135, 17723.
Disclosure statement
No potential conflict of interest was reported by the authors.
(10) Moore, E.G.; Samuel, A.P.S.; Raymond, K.N. Acc. Chem. Res.
2008, 42, 542.
(11) Strurzbecher-Hoehne, M.; Choi, T.A.; Abergel, R. J. Inorg.
Chem. 2015, 54, 3462.
(12) (a) Werner, E.J.; Kozhukh, J.; Botta, M.; Moore, E.G.; Avedano,
S.; Aime, S.; Raymond, K.N. Inorg. Chem. 2009, 48, 277; (b)
Jocher, C.J.; Moore, E.G.; Xu, J.; Avendano, S.; Botta, M.;
Aime, S.; Raymond, K.N. Inorg. Chem. 2007, 46, 9182.
(13) (a) Moore, E.G.; Jocher, C.J.; Castro-Rodriguez, I.; Raymond,
K.N. Inorg. Chem. 2008, 47, 3105; (b) Daumann, L.J.; Tatum,
D.S.; Andolina, C.M.; Pacold, J.I.; D’Aleo, A.; Law, G.; Xu, J.;
Raymond, K.N. Inorg. Chem. 2016, 55, 114.
Funding
This work was supported by Division of Chemistry [grant num-
ber CHE-1151773, CHE-1401737].
References
(1) (a) Zhu, L.; Yuan, Z.; Simmons, J.T.; Sreenath, K. RSC, Adv.
2014, 4, 20398; (b) Xu, Z.; Yoon, J.; Spring, D.R. Chem. Soc.
Rev. 1996, 2010, 39.

10
P. M. BOGIE ET AL.
(14) Longstreet, A.R.; Jo, M.; Chandler, R.R.; Hanson, K.; Zhan, N.;
Hrudka, J.J.; Mattoussi, H.; Shatruk, M.; McQuade, D.T. J. Am.
Chem. Soc. 2014, 136, 15493.
(15) Beissel, T.; Powers, R.E.; Raymond, K.N. Angew. Chem., Int.
Ed. Engl. 1084, 1996, 35.
(18) Robichaud, B.A.; Liu, K.G. Tetrahedron Lett. 2011, 52, 6935.
(19) Longstreet, A.R.; Campbell, B.S.; Gupton, B.F.; McQuade,
D.T. Org. Lett. 2013, 15, 5298.
(20) Ball, L.T.; Lloyd-Jones, G.C.; Russell, C.A. J. Am. Chem. Soc.
2014, 136, 254.
(16) Patiny, L.; Borel, A. J. Chem. Inf. Model. 2013, 53, 1223.
(17) Dewar, M.J.S.; Zoebisch, E.G.; Healy, E.F.; Stewart, J.J.P. J. Am.
Chem. Soc. 1985, 107, 3902–3909; calculations performed
on SPARTAN 06, Wavefunction Inc.
(21) Cerrada, E.; Laguna, M.; Lardíes, N. Eur. J. Inorg. Chem. 2009,
1, 137.