Systematically Studying the Effect of Fluoride on the Properties of Cyclophanes Bearing Naphthalene Diimide and Dialkoxyaryl Groups

Article abstract of DOI:10.1002/asia.201700459

Anion–π interactions between the Lewis basic anion fluoride and π-acidic naphthalene diimide was systematically studied in a series of cyclophanes in which the properties are modulated through the influence of a second, electron-rich aromatic unit. The sy

Full text of DOI:10.1002/asia.201700459

DOI: 10.1002/asia.201700459
Full Paper
Anion–Pi Interactions
Systematically Studying the Effect of Fluoride on the Properties of
Cyclophanes Bearing Naphthalene Diimide and Dialkoxyaryl
Groups
Nicholas A. Young,[a] Simon C. Drew,[b] Subashani Maniam,[a] and Steven J. Langford*[a]
Abstract: Anion–p interactions between the Lewis basic
anion fluoride and p-acidic naphthalene diimide was system-
atically studied in a series of cyclophanes in which the prop-
erties are modulated through the influence of a second,
electron-rich aromatic unit. The systems and subsequently
generated radical anions, upon addition of fluoride, were
studied by absorption spectroscopic and EPR techniques.
The results infer a modulation as a result of the nature and
strength of the p–p interaction in the macrocyclic structure.
Introduction
indicating a potential use in sensors, molecular logic and cata-
lytic processes. Here, we report the synthesis and subsequent
derivation of an NDI-based cyclophane which explores the
effect of a pre-existing p–p interaction on the initial anion–p
interaction and subsequent generation of the anion radical.
The proposed cyclophane (Figure 1) consists of three major
components: a p-acidic NDI component (blue), an electron-
The non-covalent interactions between a p-acidic (or electron
poor) aromatic system and an anion were until recently
thought of as an unimportant phenomenon of academic inter-
est.[1] However, the work of Deyꢀ et al. not only characterized
the interaction but highlighted its existence to the scientific
community.[1a] Anion–p interactions have now become a new
branch of study in supramolecular chemistry, with current in-
vestigations primarily using electron poor aromatic (p-acidic)
systems with strong reversed quadrupoles, as a means to
study their self-assembly, anion transport systems and anion
detection.[2]
Naphthalene diimides (NDIs) are highly versatile molecules
and have been used extensively in supramolecular chemistry
due to their p-electron deficiency and subsequent ability to
form charge transfer complexes or act as an n-type material.[3]
This electron-poor, or p-acidic system, can be tuned, like other
NDI properties (such as solubility, absorption and emission),
making NDIs a candidate for studying anion–p interactions. Im-
portantly, several groups have reported the facile conversion
of NDI to the radical anion through interactions with fluoride.[4]
The resultant product is both stable and often brightly colored
Figure 1. Proposed effect of fluoride on the cyclophane formed using naph-
thalene diimide (NDI, blue) and dialkoxybenzene units. The nature of the
anion interaction is shown as a charge transfer.
rich aromatic component (red), and the linking groups that
form the ring structure, whose length dictates the flexibility in
the system. The resultant system should have a “closed” struc-
ture as a result of the p–p interactions and partial charge
transfer interactions between the p-rich and p-deficient aro-
matic groups, which also leads to the formation of a colored
product—the color of which is dependent on the nature of
the p-rich group (for example, yellow to purple).[5] Upon the
addition of fluoride, an anion–p interaction ensues, leading to
[a] N. A. Young, Dr. S. Maniam, Prof. S. J. Langford
School of Chemistry
Monash University
Wellington Rd, Clayton, Victoria 3800 (Australia)
E-mail: steven.langford@monash.edu
C
the formation of an NDI anion species. Ideally, the formation
[b] Dr. S. C. Drew
of the radical anion disrupts the p–p interaction, “opening”
the cyclophane and forming a highly coloured species. Altering
the length of the linking chain, the size of the aromatic unit or
the symmetry of the aromatic unit therefore should affect the
strength of the p–p interaction and hence affect the response
by the addition of fluoride.
Department of Medicine
Royal Melbourne Hospital
The University of Melbourne
Melbourne, Victoria, 3010 (Australia)
This manuscript is part of a special issue celebrating the 100th anniversary
of the Royal Australian Chemical Institute (RACI). A link to the Table of Con-
tents of the special issue will appear here when the complete issue is pub-
lished.
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Results and Discussion
Synthesis
The focus of interactions is between the NDI, aromatic unit
and fluoride, so we wanted to retain as much integrity around
the NDI as possible. As a result, the same NDI component
1 was used in the synthesis of all cyclophanes (Scheme 1).
1,4,5,8-Naphthalene carboxylic dianhydride was reacted with
excess b-alanine in glacial acetic acid yielding 1 in 84% yield.
This diacid precursor would then be reacted with a range of di-
alcohols to form cyclophanes bearing ester and polyether
functionality. The dialcohols 2–5 were formed in moderate
yield (40–49%) after recrystallization by reacting hydroquinone
(1/4HQ) or naphthalene diols (1/5DN, 1/4DN) with a chloroe-
thoxyether in DMF using standard chemistry.[6] Conversion of
1 to the bis(acid chloride) was achieved using thionyl chloride
in benzene solvent (caution) before being mixed with a slight
excess of 2–5 under high dilution conditions. While the chlori-
nation could be achieved as well in other solvents, we found
that the cyclization reaction occurred best in benzene solvent.
This promotion of cyclization is likely a result of cooperative
electronic effects and a limiting of steric effects which might
occur through interactions with other solvents like toluene or
1,4-dioxane. Depending on the aromatic unit used, a purple (2
and 3), orange (4) or dark blue (5) product precipitates out
over time, which was filtered off and purified via column chro-
matography affording pure 6–9 in 44%, 24%, 10% and 6%
yield, respectively. The trending yields and color difference be-
tween 6, 8, and 9 reflect the nature of the stabilizing p–p and
charge transfer interactions as a result of the differing aromatic
units and non-optimized interactions in a constrained system.
The yield difference between 6 (n=1) and 7 (n=2) is a result
of the preorganization differences between the two cyclo-
phanes.
Scheme 1. General synthesis of the cyclophanes 6–9 used in this study.
thalene based examples is the upfield shift for all aromatic pro-
tons as a result of the anisotropy associated with the NDI and
dialkoxynaphthalene units (Table 1). The shift of Dd 0.2–0.4 is
consistent with other examples of interactions between two
aromatic species such as those observed by Fallon et al. be-
Clear evidence for the formation of the cyclophanes 6–9 can
1
be gained through H NMR spectroscopy in comparison to the
starting aromatic materials. Figure 2 provides an example
based on cyclophane 7 in CDCl3. Most notably across all naph-
Figure 2. 1H-NMR spectra of 1, 3 and 7 in [D6]DMSO solvent at 300 K denoting the chemical shift changes between the cyclophane and its precursors.
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Table 1. Comparison of 1H-NMR shifts of compounds 1–5 (components)
to 6–9 (cyclophanes).
Compound
H[b]
scomponents
scyclophane
Ds
6
Ha
Hb
Hc
Hd
Ha
Hb
Hc
Hd
Ha
He
Ha
Hf
8.67 (1)
7.74 (2)
7.39 (2)
7.00 (2)
8.67 (1)
7.74 (3)
7.39 (3)
7.00 (3)
8.67 (1)
6.86 (4)
8.67 (1)
8.13 (5)
7.54 (5)
6.86 (5)
8.55
7.33
7.13
6.49
8.55
7.33
7.13
6.49
8.68
6.43
8.55
7.63
7.32
6.40
0.11
0.40
0.26
0.51
0.12
0.41
0.26
0.51
ꢀ0.01[a]
0.43
0.12
0.50
0.22
0.46
7
8
9
Hg
Hh
Figure 4. X-ray crystal structure of 7, showing the inter-plane separation be-
tween aromatic units. Note: A molecule of methanol is present in the lattice
and has been omitted for clarity.
[a] A negative shift indicates a downfield movement relative to the start-
ing material. [b] Refer labels to Scheme 1.
tween a [2]catenane species bearing interacting NDI and 1/
5HQ units.[5a] An interesting and different trend is seen for 8
though, bearing the C6H4 group. While the trend of shift is sim-
ilar for the effect of the NDI on the 1/4HQ signals, leading to
a smaller but upfield shift of 0.3 ppm, the effect for 1/4HQ on
the NDI leads to a less significant and downfield shift of
0.1 ppm. This likely indicates a free rotation of the HQ unit ex-
posing the NDI to a more edge-to-face interaction in solution.
For other patterns, see the Supporting Information.
Crystals of 6–9 suitable for X-ray crystallography were ob-
tained by diffusion of methanol into DMSO solutions of the
four cyclophanes. Upon cooling, the small purple crystals
formed were subject to crystallographic analysis. The crystal
structures of compounds 6, 7 and 9 (Figures 3–5), bearing
naphthalene units, have a distinct “closed” form at a distance
of 3.4 ꢂ between the two off-set aromatic units consistent
with p–p stabilization (Table 2). This phenomenon is also inter-
cyclophane, leading to a canted and alternating donor–accept-
or–donor–acceptor stacking arrangement in the crystals as ex-
pected, also set at an intermolecular distance of 3.4–3.5 ꢂ. Cy-
clophanes 6 and 7 differ by CH2CH2O, which is easily accom-
Figure 5. X-ray crystal structure of 9, indicating p-stabilization.
modated within the crystal structure to yield the same organi-
zational motif.
Interestingly, the macromolecular crystal structure of 8
(Figure 6) differs dramatically to the other three examples.
While the closed form exists with internal plane separations of
3.425 ꢂ, consistent with p–p stabilization, there appears to be
no significant inter-cyclophane interaction. The more disor-
dered crystal packing observed can be attributed in part to the
role of the phenyl unit.
Effect of Fluoride Addition
The UV/Vis spectrum of NDI 1 in DMSO shows two distinct p–
p* absorption bands at 350 and 380 nm, consistent with other
core-unsubstituted NDIs.[7] Upon addition of fluoride, new
bands formed at 475, 610, 675 and 760 nm are consistent with
the fluoride–p interaction forming an NDI radical, suggesting
that the NDI unit by itself is p-acidic.[4a] There appears to be
little effect from the imide carboxylic acid groups in 1 on the
formation of the radical. The spectra of 2 and 3 bearing alkoxy-
naphthalene groups showed three distinct p–p* absorption
bands at 290, 300 and 320 nm, 4 has a band at 290 nm and 5
Figure 3. X-ray crystal structure of 6 showing the inter-plane separation be-
tween aromatic units.
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nents with the addition of a very weak and broad
charge transfer band as a result of the interaction of
p-electron-rich and p-electron-deficient components.
There is no appreciable fluorescence from 6–9 as
a result of quenching effects.
Table 2. X-ray crystallographic data of compounds 6–9.
Compound
6
7[a]
8
9
chemical formula
Mw
crystal system
space group
Z
C38H34N2O12
710.67
triclinic
ꢀ
P1
2
C43H46N2O15
830.82
orthorhombic
Aba2
C34H32N2O12
660.62
orthorhombic
Pbca
C38H34N2O12
710.67
triclinic
ꢀ
P1
2
8.2193(5)
8.8854(6)
21.9895(14)
88.793(5)
80.805(5)
85.265(5)
1579.84(18)
1.494
The addition of fluoride to
each cyclophane leads to
8
8
clear and distinct visual color
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
9.5940(19)
12.443(3)
15.482(3)
67.51(3)
76.43(3)
73.86(3)
1623.1(6)
1.454
58.603(3)
14.3935(5)
9.1727(4)
90
90
90
7737.2(5)
1.426
9.10
9.1232(5)
25.6813(13)
25.8360(18)
90
90
90
6053.3(6)
1.450
9.35
134.24
123(2)
27202
5398
0.0481
433
changes
Figure 7.
as
shown
in
Spectroscopically,
this
b [8]
change in color is observed
as a dramatic change in the
absorption spectra of 6–9
(Figure 8). All spectra show
new bands at 465, 610, 675
and 760 nm with fine struc-
ture changes to the bands at
350 and 380 nm attributable
to the formation of an NDI
radical. Interestingly, the in-
tensity of the absorption
g [8]
V [A3]
Dcalculated
Figure 7. Distinct color
changes occur upon ad-
dition of fluoride to the
cyclophanes. This exam-
ple shows the change
with 0.5 mm of 6 in
DMSO in the absence of
Fꢀ (left) and with the ad-
dition of Fꢀ (right).
m [cmꢀ1
]
1.09
1.12
55
2qmax [8]
T [K]
57.4
100(2)
8115
8115
0.0000
554
0.0849
0.2439
1.040
132.26
123(2)
26733
3677
0.0504
643
0.0541
0.1459
1.069
123(2)
13718
7266
0.0329
469
0.0530
0.1300
1.031
total reflns
unique reflns
Rint
parameters
final R1 (I>2q(I))
wR2(all data)
GOF
0.0423
0.1143
1.041
change due to radical formation relative to the size
of the p–p* bands at 350 and 380 nm is in the order
8–9>7–6. This same pattern can be attributed to
[a] Compound 7 contains one molecule of methanol in the lattice.
shows a band at 340 nm. There is no effect of fluoride addition
to these bands, hence we infer that any change in spectra is
a result of the combined influences of the alkoxyaromatic unit
and fluoride on the spectrum of the NDI chromophore. The
spectra for cyclophanes 6–9 in DMSO are for the most part
a representation of overlay of the two chromophoric compo-
the reduction potential of the NDI units in 6–9 by electro-
chemical means (see the Supporting Information). No signifi-
cant fluorescence was detected upon reduction.
EPR Spectroscopy
Continuous-wave EPR spectra were acquired for each of the
cyclophanes 6–9 in the presence of an excess of fluoride ions
(Figure 9). Consistent with previous investigations of model
NDI compounds 10–12 reduced electrochemically,[7] the 13-line
signal is commensurate with the formation of a radical with
spin density delocalized across all atoms of the NDI, leading to
magnetic hyperfine coupling with coupling with the two 14N
1
nuclei, four naphthalene H nuclei and small coupling with the
four N-CH2 exocyclic protons (Table 3). No EPR signal was de-
tected in the absence of fluoride.
Since the g and A parameters reflect the delocalization of
the LUMO and are principally determined by the local structure
of the NDI, it is not surprising that all compounds share similar
EPR parameters.
Clearly evident from the spectra obtained is a signal com-
mensurate with the formation of the NDI radical upon the ad-
dition of fluoride. The splitting pattern in each case is consis-
tent with that generated electrochemically from 10–12 and
represents the delocalization of the electron across all atoms
of the NDI as well as some contribution of the N-CH2 exocyclic
protons. Assuming (i) the timing of sample preparation was
consistent, (ii) radical formation is rapid enough to plateau
before measurement began, and (iii) once formed, the radicals
were stable on the time scale of the data acquisition, then var-
iation in intensity (propensity to radicalize NDI) could be corre-
lated with the degree of p–p interaction prior to addition of
Figure 6. X-ray crystal structure of 8, indicating p–p interactions in individual
molecules but not in the overall crystal structure.
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Figure 9. X-band solution EPR spectra of (a) 6, (b) 7, (c) 8, (d) 9, and (e) 1 in
DMSO solvent [0.5 mm] after the addition of excess fluoride. Dashed line:
simulation using the parameters in Table 3.
Table 3. Spin Hamiltonian parameters obtained from simulation of the
experimental spectra. Estimated uncertainty in the g factor is ꢂ0.0001.
Estimated uncertainty in hyperfine couplings is ꢂ0.05 MHz.
[a]
[b]
[c]
[d]
Compound hgi
6
7
8
9
1
10[f]
11[f]
12[f]
hA (14N)i
hA (1H)i
hA (1H)i
Linewidth[e] Ref.
[g]
2.0039 2.69
2.0036 2.53
2.0035 2.71
2.0036 2.65
2.0037 2.68
2.0040 2.70
2.0040 2.70
2.0040 2.70
5.33
5.39
5.34
5.40
5.36
5.40
5.40
5.40
0.64
0.67
0.63
0.49
0.56
0.60
–
0.43
0.43
0.35
0.48
[g]
[g]
[g]
[g]
0.49
[7]
[7]
[7]
0.60
[a] hgi=(gx +gy +gz)/3. [b] hAi=(Ax +Ay +Az)/3. Coupling to two equiva-
lent 14N nuclei (MHz). [c] Coupling to four equivalent 1H nuclei (MHz).
[d] Unresolved coupling to four equivalent nuclei (MHz). [e] Lorentzian
peak-to-peak linewidth in gauss (G). [f] 10, 11 and 12=N,N-dipentyl, dii-
sopropyl, and dipropargyl naphthalene diimides, respectively. [g] This
work.
Figure 8. Absorption spectra of cyclophanes 6–9 in the absence (blue) and
presence of fluoride (red, ꢁ20 equiv). [6–9]=1 mm in DMSO. Signals at
Conclusions
Cꢀ
l>450 nm are a result of NDI formation.
We have synthesized a family of NDI cyclophanes with a pre-
existing p–p interaction between p-electron-rich and p-elec-
tron-deficient chromophores, and subjected them to the pres-
ence of fluoride. Dramatic color changes that manifest strong
changes in the EPR and absorption spectra of each cyclophane
indicate their ability to act as a crude sensor for fluoride. More
importantly from a design perspective, the electronic effects of
a non-covalent neighbor are significant on the chemistry and
physical properties associated with the reduction of the naph-
thalene diimide unit.
fluoride. Under the similar conditions of each experiment, we
can infer the strength of EPR signal generated, and hence the
ease of radical generation is in the order 8@6>9–7>1.
Within the family of cyclophanes, this infers that the interac-
tions between the NDI and alkoxybenzene unit facilitates the
generation of the radical anion over alkoxynaphthalenes, con-
sistent with the results obtained from the absorption spectros-
copy.
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determined from numerical simulations of the experimental spec-
tra using Easyspin[8] v.4.5.5 and the Hamiltonian
Experimental Section
General Experimental Methods
H ¼ hgibBS þ SkhAkiSIkꢀgnkbnBI
ð1Þ
1H and 13C nuclear magnetic resonance (NMR) spectra were record-
ed using a Bruker DRX400 NMR spectrometer (1H at 400 MHz,
unless otherwise specified, and 13C at 100 MHz). All samples were
prepared in the stated deuterated solvent. The chemical shifts (d)
were calibrated against the residual solvent peak in the spectrum.
Each resonance was assigned according to the following conven-
tion: chemical shift (d) measured in parts per million (ppm), multi-
plicity, coupling constant (J) measured in Hz, number of protons
and assignment. Multiplicities are denoted as (s) singlet, (d) dou-
blet, (t) triplet, (q) quartet, broad (b) or (m) multiplet. The 13C NMR
spectra were assigned a chemical shift (d) measured in parts per
million.
where S and I are the electron and nuclear vector spin operators,
hgi and hAi are the isotropic electron Zeeman and nuclear hyper-
fine coupling matrices, b is the Bohr magneton, bn is the nuclear
magneton and B is the applied magnetic field. The summation
over k incorporates the superhyperfine and nuclear Zeeman inter-
actions with nucleus k of spin Ik and nuclear g factor gn . The
k
“garlic” function in Easyspin was used to solve Equation (1), and
the SH parameters were varied iteratively using the “esfit” module
to achieve a least squares minimisation of the difference between
the experimental and simulated spectrum. Coupling to two equiva-
lent 14N nuclei and two sets of four equivalent H nuclei was as-
1
Low-resolution–electrospray ionization mass spectrometry (LR-
EIMS) was completed on a Micromass Platform API QMS-quadru-
pole electrospray mass spectrometer. Spectra were taken in posi-
tive ion mode (ESI+) mode unless otherwise stated. [M]* denotes
the molecular ion. Matrix-assisted laser desorption ionization time-
of-flight mass spectrometry (MALDI-TOF-MS) was performed on an
Ultraflex III instrument (Bruker Daltonics, Germany) with a-cyano-4-
hydroxy cinnamic acid as the matrix.
sumed for the simulation, using the SH parameters previously re-
1
ported[7] as a starting point. Although the coupling to the four H
nuclei adjacent to the imide nitrogens could not be resolved, their
inclusion enabled the correct reproduction of the inhomogeneous
linewidth without the need for convoluting the spectrum with
a Gaussian line broadening parameter. Simulated g factors were
corrected by acquiring the spectrum of DPPH (g=2.0036) in DMSO
as a field calibration standard.
Melting points were performed on a Stanford Research Systems
MPA160 melting point apparatus and specified in degrees Celsius
(8C).
Synthetic Methods
Bis-N,N’-(2-carboxyethyl)-1,4,5,8-naphthalenetetracarboxylic
diimide (1)[9]
UV-visible spectra were recorded on the Varian model Cary 60 UV-
visible spectrophotometer with solvent and concentration of
sample stipulated for each individual experiment. Fluorescent spec-
tra were performed on the Varian model Cary Eclipse fluorescence
spectrophotometer, with the solvent, concentration of samples
and excitation wavelength recorded for experiment. Infrared spec-
tra were recorded on a Bruker model IFS Equinox 55 FTIR system
paired with a golden gate single bounce diamond micro ATR and
a MCT detector.
b-Alanine (1.28 g, 14.30 mmol) was added to a stirred solution of
NDA (1.55 g, 5.78 mmol) in glacial acetic acid (40 mL). The reaction
was heated at 1108C and left to stir overnight. The reaction was al-
lowed to cool to room temperature before pouring into ice-water
(60 mL). The resulting white precipitate was filtered off and dried
yielding a powdery white solid (1.94 g, 84%). 1H NMR (400 MHz,
CDCl3): d=8.66 (s, 4H, ArH), 4.27 (dd, J=8.0, 7.6 Hz, CH2),
2.62 ppm (dd, J=7.6 Hz, CH2). Mass Spec: (ESI, +ve) calculated m/
z=410.08 observed 433.25 [M+Na]+. Melting Point: >2608C.
Analytical thin-layer chromatography was performed on silica gel
(Silica 60 F254) coated aluminium plates. Column chromatography
was performed using silica gel (pore size 0.063–0.2 mm) purchased
from Merck as the column stationary phase. The eluting solvents
stated in this synthesis section are quoted as volume to volume (v/
v) ratios.
General Synthesis of Polyethers 2–5
The dihydroxyaromatic (20 mmol) was added to a suspension of
K2CO3 (10 equiv) in dry MeCN (100 mL). The suspension was stirred
vigorously as the 2-chloroethoxyether (2.5 equiv) was added over
30 minutes. The reaction was heated under reflux for 4 days and
then left to cool to room temperature. The suspension formed was
filtered and the filtrate was washed with DCM (3ꢃ30 mL). The
combined organic solutions were concentrated under vacuum and
the residue was redissolved in DCM (50 mL) and washed with
water (3ꢃ20 mL). The organic phase was then dried over magnesi-
um sulfate, filtered and the solvent removed in vacuo.
X-ray crystal diffraction patterns were determined using an Enraf
Nonius FR590 KappaCCD diffractometer, a Bruker Kappa Apex II dif-
fractometer or at the Australian Synchrotron using the PX1 or PX2
beamline, with graphite monochromated MoKa radiation
(0.71073 ꢂ) at 123(2) K unless otherwise stated. The crystal data
was solved and refined using SHELXS-97 and SHELXL-97 suite of
programs with the graphical interface X-Seed v2.0.
Continuous-wave EPR spectra were acquired using a CMS8400 X-
band (9.4 GHz) spectrometer (Adani, Belarus) fitted with a TE102
cavity and operating at a fixed time constant of 100 ms and
100 kHz magnetic field modulation. Solution-phase measurements
were made at room temperature using a quartz flat cell (Wilmad,
WG-808-Q) and the following settings: microwave frequency,
9.44 GHz; microwave attenuation, 16 dB; magnetic field sweep
rate, 0.6 gausssꢀ1; magnetic field modulation amplitude, 0.2 gauss;
magnetic field modulation frequency, 100 kHz; receiver gain, 500;
time constant, 100 ms. Due to the relatively low signal from com-
pound 1, the modulation amplitude and number of averages were
2: Using 1,5-dihydroxynaphthalene and 2-(2-chloroethoxy)-ethanol,
the residue was recrystallized from EtOAc to afford 2 as a flaky
light brown crystalline solid in 48% yield. 1H NMR: (400 MHz,
CDCl3): d=7.87 (d, J=8.56 Hz, 2H, ArH), 7.36 (t, J=8.12, 7.88 Hz,
2H, ArH), 6.85 (d, J=7.64 Hz, 2H, ArH), 4.30 (dd, J=4.62, 4.86 Hz,
4H, O-CH2), 4.00 (dd, J=4.62, 4.86 Hz, 2H, O-CH2), 3.76 ppm (m,
8H, O-CH2). Mass Spec: (ESI, +ve) calculated m/z=336.2 observed
359.1 [M+Na]+. Melting Point: 95.7–96.88C.[10]
3: Using 1,5-dihydroxynaphthalene and 2-(2-(2-chloroethoxy)-
ethoxy)ethanol, the residue was purified by crystallization from
AcOEt to afford 3 as a flaky light brown crystalline solid in 44%
both increased by a factor of 2. The EPR spectrum presented in
1
Figure 9e was scaled by a factor of = to allow direct comparison
4
1
with compounds 6–9. The spin Hamiltonian (SH) parameters were
yield. H NMR: (400 MHz, CDCl3): d=7.87 (d, J=8.56 Hz, 2H, ArH),
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7.34 (dd, J=8.28, 7.76 Hz, 2H, ArH), 6.85 (d, J=7.64 Hz, 2H, ArH),
4.29 (m, 4H, O-CH2), 3.99 (m, 4H, O-CH2), 3.79 (m, 4H, O-CH2), 3.70
(m, 8H, O-CH2), 3.60 ppm (m, 4H, O-CH2). Mass Spec: (ESI, +ve) cal-
culated m/z=424.2 observed 447.2 [M+Na]+. Melting Point: 69.2–
70.98C.[11]
(ESI, +ve) calculated m/z=660.1955 observed 661.2019 [M+H]+.
Melting Point: 240.3–243.38C
9: Using 5 as the diol, cyclophane 9 was prepared as a dark blue
1
solid in 6% yield. H NMR (400 MHz, CDCl3): d=8.56 (s, 4H, ArH),
7.80 (dd, J=3.28 Hz, 2H, ArH), 7.35 (dd, J=3.28 Hz, 2H, ArH), 6.25
(s, 4H, ArH), 4.28 (m, 4H, O-CH2), 4.22 (m, 4H, O-CH2), 3.77 (m, 4H,
O-CH2), 3.69 (m, 8H, O-CH2), 2.62 ppm (m, 4H, O-CH2). d=171.0,
162.4, 148.4, 130.8, 126.7, 126.5, 126.2, 126.1, 121.7, 104.0, 69.6,
69.5, 67.7, 63.9, 37.0, 33.5 ppm. Mass Spec: (ESI, +ve) calculated
m/z=710.2112 observed 711.2174 [M+H]+. Melting Point: 238.1–
240.28C
4: Using 1,4-dihydroquinone and 2-(2-chloroethoxy)ethanol, the
crude reside was purified by recrystallization from EtOAc to afford
4 as a flaky light brown crystalline solid in 46% yield. 1H NMR:
(400 MHz, CDCl3): d=6.85 (s, 4H, ArH), 4.08 (m, 4H, O-CH2), 3.83
(m, 4H, O-CH2), 3.74 (m, 4H, O-CH2), 3.65 ppm (m, 4H, O-CH2).
Mass Spec: (ESI, +ve) calculated m/z=286.14 observed 309.01
[M+Na]+. Melting Point: 94.6–96.18C.[12]
5: Using 1,4-dihydroxynaphthalene and 2-(2-chloroethoxy)-ethanol,
the crude reside was purified by further washing with water (3ꢃ
20 mL) The organic phase was then dried over magnesium sulfate,
filtered and the solvent removed in vacuo to afford 5 as a dark
brown oil 43% yield. 1H NMR: (400 MHz, CDCl3): d=8.22 (dd, J=
3.28 Hz, 2H, ArH), 7.51 (dd, J=3.28 Hz, 2H, ArH), 6.71 (s, 2H, ArH),
4.26 (m, 4H, O-CH2), 3.98 (m, 4H, O-CH2), 3.78 (m, 8H, O-CH2),
2.11 ppm (bs, 2H, OH). 13C NMR: (100 MHz, CDCl3): d=149.0, 126.7,
126.1, 121.9, 105.0, 72.8, 70.0, 68.5, 61.9 ppm. Mass Spec: (ESI, +
ve) calculated m/z=336.1573 observed 359.1465 [M+Na]+.
Acknowledgements
Financial support from the Australian Research Council
through the Discovery Grant Scheme (DP130101861 and
DP170104477) is gratefully acknowledged. We thank Dr Craig
Forsyth for technical assistance with X-ray crystallography and
Dr Sally Duck for mass spectrometry data. Electrochemistry
was performed by Jiezhen Li.
Conflict of interest
General Synthesis of Cyclophanes 6–9
The diacid 1 (0.5 mmol) was suspended in dry benzene (CAUTION,
30 mL) and 4 drops of DMF added. Oxalyl chloride (4 equiv) was
added to the suspension and the temperature raised to 508C with
stirring for 21 h. The solution was then cooled and concentrated to
remove excess oxalyl chloride. The diacid chloride generated was
redissolved in dry benzene (CAUTION, 30 mL) and was added drop-
wise with stirring to the diol 2–5 (1.1 equiv) in benzene (200 mL).
The mixture was maintained at 508C and left to stir for a further 4
days. The solvent was removed under reduced pressure and the
mixture purified by column chromatography (SiO2, 1:10 acetone/
CH2Cl2).
The authors declare no conflict of interest.
Keywords: anion–pi interactions · EPR · fluoride · naphthalene
diimide · radicals · sensors
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7: Using 3 as the diol, cyclophane 7 was prepared as a dark purple
1
solid in 24% yield. H NMR: (400 MHz, CDCl3): d=8.32 (s, 4H, ArH),
7.23 (d, J=8.4 Hz, 2H, ArH), 6.87 (t, J=8.4, 7.8 Hz, 2H, ArH), 6.39
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71.0, 69.8, 68.8, 67.7, 64.0, 36.7, 33.2 ppm. Mass Spec: (MALDI, +
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Manuscript received: March 26, 2017
Revised manuscript received: May 9, 2017
Version of record online: && &&, 0000
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FULL PAPER
Anion–Pi Interactions
Family interactions: The interaction
and reaction of fluoride with a family of
cyclophanes bearing naphthalene dii-
mides is explored against the influence
of a spatially neighboring aromatic unit.
The systems are explored spectroscopi-
cally, by X-ray crystallography and EPR
techniques.
Nicholas A. Young, Simon C. Drew,
Subashani Maniam, Steven J. Langford*
&& – &&
Systematically Studying the Effect of
Fluoride on the Properties of
Cyclophanes Bearing Naphthalene
Diimide and Dialkoxyaryl Groups
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&
These are not the final page numbers! ÞÞ