Europium Directed synthesis of enantiomerically pure dimetallic luminescent "Squeezed" triple-stranded helicates; solution studies

Article abstract of DOI:10.1002/asia.200900515

The formation of two novel chiral enantiomerially pure dimetallic (Eu ^III) triple stranded helicates (L₃Eu₂) was monitored in solution by observing the changes in the Eu^III centered emission as well as in the ab

Full text of DOI:10.1002/asia.200900515

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DOI: 10.1002/asia.200900515
Europium Directed Synthesis of Enantiomerically Pure Dimetallic
Luminescent “Squeezed” Triple-Stranded Helicates; Solution Studies
Christophe Lincheneau,[a] Robert D. Peacock,[b] and Thorfinnur Gunnlaugsson*[a]
Dedication to Gunnlaugur ꢀorfinnsson on the occasion of his 82nd birthday
The incorporation of lanthanide (f-) ions in supramolec-
ular systems has become a valuable strategy in the field of
time resolved luminescent imaging and sensing for in vivo
application, as well as in the development of targeting MRI
contrast agents.[1,2] The use of various f-metal ions to direct
the synthesis of more complexed self-assembly supramolec-
ular systems using organic ligands has also become an active
area of research.[3,4] In particular, through the pioneering
work of Bꢀnzli, Piguet, and several others, the formation of
Figure 1. Schematic representation of ligand 1 and 2, and the structural
isomers 3 and 4 used in the current solution study.
self-assembly structures possessing a single or more f-metal
ions or the combination of both f- and d-metal ions, has
been elegantly demonstrated.[5–8] In the analysis of the for-
mation or the properties of such systems, the unique photo-
physical properties of the visibly emitting EuIII and TbIII
ions, which possess line-like emission bands and relatively
long lived excited states (sub ms–ms time frame), have been
intensively employed.[9,10] We have recently focused our re-
search on the development of lanthanide luminescent self-
assemblies, both in solution[11,12] and on solid supports, such
as on flat gold and gold nanoparticles.[13,14] We have also de-
veloped novel chiral supramolecular systems by employing
f-metal ion directed synthesis, where we have formed mono-
(sliotar) and di-metallic (helical) architectures.[15,16] An ex-
ample of ligands employed for such f-directed synthesis are
the enantiomeric pair 1 (R,R) and 2 (S,S) (Figure 1), which
give rise to the formation of dimetallic triple stranded heli-
cates (13·Eu2 and 23·Eu2) in the presence of EuIII.[16] Our in-
vestigation showed that the 4,4’-methylenediphenyl spacer
between the two coordinating pyridyl units in 1 and 2, great-
ly influences the formation as well as the shape of the result-
ing helicates, which possessed a sizable central cavity lined
by three aryl spacers. Herein, we present ligands 3 (R,R)
and 4 (S,S), which are structural isomers of 1 and 2, and the
formation of enantiomerically pure dimetallic triple strand-
ed helicates 33·Eu2 and 43·Eu2, the formation of which was
monitored in solution using various spectroscopic tech-
niques. We demonstrate herein that this simple structural
modification results in the formation of 33·Eu2 and 43·Eu2, in
high yield and with greater stability than seen for 13·Eu2 and
23·Eu2. This we believe arises from the fact that the central
cavity of 33·Eu2 and 43·Eu2 is more “squeezed” (confirmed
using MM2 molecular modelling), enabling tighter binding
of the two EuIII ions.
The ligands 3 and 4 were isolated in high yields in a three
step synthesis from the mono-protected pyridine-2,6-dicar-
boxylic acid 5, Scheme 1. The intermediates 6 and 7 were
obtained in ca. 80% yields using a standard peptide cou-
pling methodology, using the R or S isomers of 1-(1-naph-
thyl)-ethylamine, followed by deprotection.[16] The final pep-
tide coupling reaction, using EDCI·HCl and 3,3’-diaminodi-
phenylmethane gave 3 and 4 in ca. 80% yields. The
1H NMR (400 MHz, CD3OD) analysis of 3 (Figure S1 in the
[a] C. Lincheneau, Prof. T. Gunnlaugsson
School of Chemistry, Center for Synthesis and Chemical Biology
University of Dublin
Trinity College Dublin
Dublin 2 (Ireland)
[b] Dr. R. D. Peacock
Department of Chemistry
University of Glasgow
Glasgow G12 8QQ, Scotland (UK)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900515.
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Chem. Asian J. 2010, 5, 500 – 504

for 13·Eu2 nor 23·Eu2; clearly demonstrating the influence
the diaryl spacer has on the resulting supramolecular struc-
tures.
The photophysical properties of 33·Eu2 and 43·Eu2 were
performed in CH3CN, H2O, and D2O under ambient condi-
tions. Upon excitation of the naphthalene antennae, charac-
teristic EuIII metal centered emission, Figure 2c, occurring
at 580, 595, 616, 655, and 701 nm was observed; demonstrat-
ing the successful sensitization of the EuIII 5D0 excited state.
This was further confirmed by recording the excitation spec-
tra of these helicates, which closely matched their UV/Vis
absorption spectrum (Figure S3 in the Supporting Informa-
tion). Moreover, the presence of the of DJ=0 band in Fig-
AHCTUNGTRENNUNG
ure 2c also suggests that the symmetry at each of the EuIII
Scheme 1. a) (R)- or (S)-1-(1-Naphthyl)-ethylamine, HOBt, EDCI, Et3N,
and DMAP in THF 08C!RT, 24 h. b) H2/Pd, CH3OH, 12 h. Also shown
is the structure obtained by molecular modelling of 33·Eu2 (site and top
view) in the MM2 force field, showing how the three ligands (3) wrap
around the two EuIII ions in a helical fashion and the occurrence of the
ꢂsqueezedꢃ cavity.
Supporting Information) demonstrated the presence of C2
symmetry; while the CD spectra of 3 and 4, Figure 1a, con-
firmed that each of the ligands retained the chirality of the
amine employed. The complexes 33·Eu2 and 43·Eu2 were syn-
thesized by refluxing a 3:2 ratio of 3 or 4 with EuACTHNUTRGNE(UNG CF3SO3)3
in MeOH, followed by precipitation from diethyl ether,
giving 33·Eu2 and 43·Eu2 in 63% and 75% yields, respective-
1
ly. The characteristic broadening and shifts in the H NMR
of 3 and 4, caused by the binding to the paramagnetic EuIII
1
ion was observed in the H NMR spectrum demonstrating
the formation of the desired helicates. As an example, the
resonance characteristic of the methylene linker protons
(see 43·Eu2 in MeOD in Figure S1a in the Supporting Infor-
mation) appeared as a singlet at 4.13 ppm, signifying the for-
mation of a single helical (rac) isomer.[16,17] Using 3, we car-
ried out a 1H NMR titration using LuIII (Figure S2 in the
Supporting Information), which showed that significant
1
changes occurred in the H NMR spectra upon formation of
the helicate, that is, from 0!0.6 equiv of LuIII. Furthermore,
changes also occurred between the addition of 0.6!1.0
equiv of LuIII, which would suggest the formation of a
second species at higher LuIII concentrations, occurred. By
comparing the CD spectra of 33·Eu2 and 43·Eu2, which were
of equable and of opposite signs, to that of 3 and 4, it was
clear that while the short wavelength transitions were simi-
lar in appearance for all four compounds, then the long
wavelength transitions of 33·Eu2 and 43·Eu2, assigned to the
naphthalene antenna, were greatly reduced in intensity to
that seen for 3 and 4, signifying substantial conformational
changes in these ligands upon formation of 33·Eu2 and
43·Eu2. Such dramatic changes were not observed previously
Figure 2. a) The CD spectra of 3 and 4 in MeOH. b) The corresponding
CD spectra of 33·Eu2 and 43·Eu2 in MeOH. c) The total EuIII emission,
shown in black, arising from the deactivation of the EuIII 5D0 excited
state to the FJ (J=0, 1, 2, 3, 4) ground state of 33·Eu2. The corresponding
circularly polarised emission (CPL) is shown “up” and “down” for 33·Eu2
and 43·Eu2, respectively.
7
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T. Gunnlaugsson et al.
COMMUNICATION
centers (the local symmetry) is C3, while the symmetry of
the dimetallic helicates as the overall symmetry for the self-
assembly would be expected to be D3. The EuIII emission
was also found to be long-lived, being 3.0 and 3.4 ms for
33·Eu2 and 43·Eu2, respectively, when recorded in D2O (see
Table S1 and Figure S4 in the Supporting Information),
where the excited state decays were best fitted to a mono-
exponential decay. The excited state decays in H2O (bi-ex-
ponential) and D2O were also used to determine the hydra-
tion states (q) of 13·Eu2 and 23·Eu2; which was determined
as qꢀ0 (See Table S1 in the Supporting Information) for
both, demonstrating that each of the EuIII ions were coordi-
natively saturated within the helical structure through coor-
dination to the pyridyl nitrogens and the two amides of each
ligand, giving a total of nine coordination environments for
each ion center. The quantum yield for the EuIII emission
was also recorded in water, being 0.006 and 0.007 for 33·Eu2
and 43·Eu2, respectively, which is somewhat smaller than we
have observed for analogous chiral mono-nuclear EuIII slio-
tar complexes,[15] and that of chiral lanthanide complexes de-
veloped by Parker co-workers, using the same chiral anten-
na.[18] Also shown in Figure 2c are the circular polarized lu-
minescence (CPL)[19] spectra of 33·Eu2 and 43·Eu2. The CPL
demonstrates that the EuIII emission is chiral for both com-
plexes; indicating that the EuIII ions are sitting within a
chiral environment, which is induced by the chirality of
ligand 3 and 4, respectively. These results, in addition to the
CD and the 1H NMR results discussed above, suggest the
formation of 33·Eu2 and 43·Eu2 as a pair of enantiomers.
Comparison with the CPL of the very similar mono nuclear
sliotar complexes,[15] whose absolute configuration has been
determined by X-ray crystallography, enables us to predict
the absolute configurations of 33·Eu2 and 43·Eu2 to be L,L
and D,D, respectively. From the CPL spectra in Figure 1c,
the dissymmetry factor for 33·Eu2 (g=2DI/I) was determined
as ꢁ0.207 and 0.165 for the DJ=1 (at 600 nm) and 2 (at
619 nm) transitions, respectively. This relatively large dis-
symmetry factor[19] demonstrates that 33·Eu2 is formed enan-
tomerically pure and is homochiral in solution.
The formation of 33·Eu2 and 43·Eu2 was also investigated
in situ in CH3CN solution by monitoring the changes in the
absorption and the fluorescence emission spectra of 3 and 4
(1ꢄ10ꢁ5 m) upon titration with EuIII (as triflate salt) and by
observing the concomitant evolution of the EuIII emission.
The overall results in the absorption spectra for the forma-
tion of 43·Eu2 is shown in Figure 3a, and demonstrates that
a significant change occurred in the absorption spectra of 4
upon coordination to the EuIII ions. These changes occur up
to ca. ~0.7 equivalents of EuIII, where the transition cen-
tered at 281 nm had both hypochromically and hypsochrom-
ically shifts, while only a hyperchromic effect was observed
for the 320 nm band. This demonstrated the formation of a
supramolecular species with a stoichiometry of 3:2 (4/EuIII).
However, some further changes were also observed upon
further addition of EuIII, up to ca. 1 equivalent, which is in-
dicative of the displacement of the above 3:2 equilibrium to-
wards the formation of the species consisting of a 2:2 stoi-
Figure 3. a) The changes in the absorption spectra of 4 upon formation of
43·Eu2.Inset The changes at 281 and 320 nm versus equiv of EuIII. b) The
overall changes in the EuIII emission upon formation of 43·Eu2. Inset: The
changes in the DJ=2 transition versus equiv of EuIII
.
chiometry, for example, 32·Eu2. The changes in the fluores-
cence emission spectra were less pronounced (Figure S5 in
the Supporting Information), but coincided with that ob-
served in the absorption spectra. Here, only minor changes
were observed in the high energy transitions, centered
around 350 nm, whereas a broad emission, centered at ca.
450 nm, was slightly quenched. Analysis of these changes,
again showed that they occurred dominantly within the ad-
dition of ~0.7 equivalents of EuIII, and that thereafter, be-
tween one and two equivalents, the fluorescence emission
was quenched. The appearance of the EuIII emission at long
wavelength was also observed in the fluorescence emission
spectra (Figure S5 in the Supporting Information), and anal-
ysis of these changes again showed that EuIII emission was
ꢂswitched onꢃ in parallel with the quenching observed in the
fluorescence emission. We thus next analyzed the changes in
the EuIII emission (using time-delay mode). The overall
changes observed in the EuIII emission are shown in Fig-
AHCTUNGTREGuNNNU re 3b, and clearly demonstrate that the emission arising
from all the DJ transitions were ꢂswitched onꢃ upon addition
of EuIII. Analysis of these transitions (e.g., DJ=1 and 2)
showed that the largest changes are seen up to the addition
of ~0.7 equivalents of EuII, which then plateau up to
1 equivalent of EuIII, after which the addition of EuIII results
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Chem. Asian J. 2010, 5, 500 – 504

Enantiomerically Pure Dimetallic Luminescent Triple-Stranded Helicates
in minor luminescence quenching (see inset in Figure 3b
and Figure S6 in the Supporting Information for 3). Again,
these results indicate that initially the desired 3:2 helicate
was formed, followed by the formation of another system
consisting of the 2:2 stoichiometry. This was also confirmed
by carrying out Jobꢃs plot analysis (method of continuous
variations) in CH3CN (see Figure S7 in the Supporting In-
formation for 43·Eu2). However, to gain a better understand-
ing of the formation of these supramolecular species in solu-
tion, the changes in the absorption and the EuIII emission
were analyzed using the non-linear regression analysis pro-
gram SPECFIT. The fit and the speciation distribution dia-
gram obtained for the changes in the absorption spectrum
of 4 upon titration with EuIII, is shown in Figure 4 (See Fig-
and demonstrates that a ꢂtight fitꢃ is obtained for the ꢂheli-
calꢃ wrapping of the three ligands around the two EuIII ions
(shown in green), giving the cylindrical D3 geometry of the
overall topology. Moreover, the central diaryl spacers are
shown to be oriented towards the exterior of the helix. The
consequence of this, is the formation of a more ꢂsqueezedꢃ
central area, where the cavity, previously seen in our analy-
sis of 13·Eu2 and 23·Eu2, is removed.[16] This structure also
ꢁ
presents more favourable p p bonding interactions between
the antennae and the pyridyl units exists for both 33·Eu2 and
43·Eu2, which is similar to that observed for their mono-met-
allic analogues.[15] In summary, we have developed the novel
chiral ligands 3 and 4, and by using f-directed synthesis,
formed two enantiomerically pure dimetallic triple stranded
helicates 33·Eu2 and 43·Eu2. The EuIII emission of these new
self-assemblies was found to be both chiral (using CPL) and
long-lived within the visible region, where high binding con-
stants were determined for both 33·Eu2 and 43·Eu2 in
CH3CN. We are currently exploring the use of f-metal ion
directed synthesis of other supramolecular architectures.
Experimental Section
N,N’-[Methylenebis(phen-1,3-ylene)]bis(6-(S)-1-naphtalen-1-yl-ethylcar-
bamoyl)-pyridine-2-carboxyamide) (3). To a solution of 3,3’-methylene-
AHCTUNGTREG(NNUN diphenylamine) (100 mg, 0.31 mmol) in THF (12 mL) was added HOBt
(44.3 mg, 0.33 mmol). The solution was cooled down to 08C and stirred
for 15 min under inert atmosphere. EDCI (62.8 mg, 0.33 mmol), DMAP
(22.1 mg, 0.16 mmol), and triethylamine (33.2 mg, 0.33 mmol) were
added portionwise. After 30 min, the resulting suspension was allowed to
warm up slowly to room temprature and was reacted overnight under
argon. The solid residue was filtered off and solvent removed under re-
duced pressure. The resulting crude oil was dissolved in CH2Cl2 and
washed with HCl (1m), a saturated solution of NaHCO3, and finally with
water. The organic layer was dried over MgSO4 and solvent removed.
Compound 3 was collected as an off-white solid in 63.2% yield (79.2 mg,
0.098 mmol). M.p.: Decomposed>1528C.; IR (neat): n˜max =3292, 3040,
2977, 2934, 1654, 1589, 1521, 1488, 1445, 1316, 1229, 1167, 1119, 1074,
Figure 4. The speciation distribution diagram as a total ligand distribu-
tion, obtained after the fitting, using SPECFIT, of the changes in the ab-
sorption spectra of 4 (shown as L in the inset), demonstrating the forma-
tion of the desired helicate 43·Eu2 and the formation of the 2:2 species
(42·Eu2) at higher concentraion of EuIII
.
ure S8 in the Supporting Information for the analysis of the
EuIII emission), and demonstrates a good fit to the experi-
mental data. From this analysis, the predominant formation
of 43·Eu2 helicate was confirmed after the addition of ~0.7
equivalents of EuIII, being formed in ca. 70% yield, with a
high binding constant of log b3:2 =26.7ꢂ0.6. However, upon
further addition of EuIII, the displacement of this equilibri-
um towards a new species, consisting of the 2:2 stoichiome-
try, takes place with log b2:2 =20.0ꢂ0.5, becoming the domi-
nant species after the addition of one equivalent of the
908, 866, 799, 739, 677 cmꢁ1 1H NMR (400 MHz, CDCl3): dH =9.63 (2H,
;
s, 2NH), 8.74 (2H, d, J=8.52 Hz, 2NH), 8.35 (2H, d, J=7.5 Hz, Pyr-H),
8.18 (2H, d, J=7.52z, Pyr-H), 8.03 (2H, d, J=8.5 Hz, Pyr-H), 7.92 (2H,
t, J=7.5 Hz, Naph-H), 7.72 (2H, d, J=7.7 Hz, Naph-H), 7.58 (2H, d, J=
8.5 Hz, Naph-H), 7.46–7.38 (4H, m, Naph-H), 7.35 (2H, d, J=7.5 Hz,
Naph-H), 7.13 (2H, t, J=7.5 Hz, Phen-H), 7.08 (2H, s, Phen-H), 6.99–
6.91 (4H, m, 2ꢄNaph-H+2 Phen-H), 6.72 (2H, d, J=7.0 Hz, Phen-H),
5.97 (2H, m, CH), 3.39 (2H, t, J=7.0, CH2), 1.57 ppm (6H, d, J=7.0 Hz,
Me); 13C NMR (100 MHz, CDCl3): dc =162.2, 161.5, 148.6, 148.1, 140.79,
138.2, 137.6, 136.3, 133.2, 130.5, 128.3, 128.1, 127.5, 126.0, 125.3, 125.1,
124.5, 124.4, 122.8, 122.4, 119.2, 44.7, 27.3, 20.1 ppm; MS (EI): m/z calcd
for C51H42N6O4+Na: 825.3165; found: 825.3137; elemental analysis: calcd
(%) for C51H42N6O4·1.33CH3OH: C 74.33, H 5.64, N 9.94; found: C 74.45,
H 5.38, N 9.89.
1
metal ion. Hence, it is possible that in the H NMR studies
shown above, this structural isomer is also present to some
extent. Similar results were also observed for 3 which
formed the 33·Eu2 helicate at low concentration of EuIII and
the 32·Eu2 structure at higher EuIII concentrations. The high
binding constants determined for either 33·Eu2 or 43·Eu2,
clearly demonstrate the significant role that the diaryl-
spacer plays in the self-assembly process. While we have
been unable to obtain suitable crystals for crystallographic
analysis of either 33·Eu2 or 43·Eu2, we have been able to elu-
cidate their possible helical structure by using MM2 force
field based molecular modelling experiments. The calculated
energy minimized structure of 33·Eu2 is shown in Scheme 1,
N,N’-[Methylenebis(phen-1,3-ylene)]bis(6-(R)-1-naphtalen-1-yl-ethylcar-
bamoyl)-pyridine-2-carboxyamide) (4): Ligand 4 was isolated, following
the procedure exposed for its enantiomer 3, as an off-white solid in
59.7% yield (74.7 mg, 0.093 mmol). M.p.: Decomposed>1498C; IR
(neat): n˜max =3289; 3066; 2992; 2955; 1630; 1588; 1557; 1489; 1447; 1376;
1238; 1164; 1082; 1044; 800; 777; 753; 730; 679 cmꢁ1 1H NMR (CDCl3,
;
400 MHz): dH =9.52 (2H, s, 2NH), 8.54 (2H, d, J=8.5 Hz, 2NH), 8.38
(2H, d, J=7.5 Hz, Pyr-H), 8.25 (2H, d, J=7.5 Hz, Pyr-H), 8.09 (2H, d,
J=8.5 Hz, Pyr-H), 7.97 (2H, t, J=7.5 Hz, Naph-H), 7.77 (2H, d, J=
7.71 Hz, Naph-H), 7.65 (2H, d, J=8.5 Hz, Naph-H), 7.54–7.43 (6H, m,
4ꢄNaph-H+2Phen-H), 7.22 (2H, d, J=7.5 Hz, Naph-H), 7.08 (2H, s,
Chem. Asian J. 2010, 5, 500 – 504
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T. Gunnlaugsson et al.
COMMUNICATION
Phen-H), 7.05–7.00 (4H, m, 2ꢄNaph-H+2ꢄPhen-H), 6.80 (2H, d, J=
7.0 Hz, Phen-H), 6.00 (2H, m, CH), 3.56 (2H, t, J=7.04, CH2), 1.87 ppm
(6H, d, J=7.04 Hz, Me); 13C NMR (CDCl3; 100 MHz): dc =162.3, 161.5,
148.5, 148.1, 140.8, 138.3, 137.7, 136.3, 133.3, 130.6, 128.3, 128.1, 127.6,
126.0, 125.3, 125.1, 124.6, 124.6, 122.8, 122.4, 119.1, 44.8, 29.3, 20.1 ppm;
MS (EI): m/z calcd for C51H42N6O4+Na: 825.3165; found: 825.3128; ele-
mental analysis: calcd (%) for C51H42N6O4·1.5CH3OH: C 74.10, H 5.69,
N 9.88; found: C 74.04, H 5.24, N 9.83.
d) S. Pandya, J. Yu, D. Parker, Dalton Trans. 2006, 2757; e) R.
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J.-C. G. Bꢀnzli, Analyst 2008, 133, 1749; Hemmila, J.-C. G. Bꢀnzli,
Analyst 2008, 133, 1749.
[4] S. Faulkner, L. S. Natrajan, W. S. Perry, D. Sykes, Dalton Trans.
2009, 3890.
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J. C. G. Bꢀnzli, Chem. Eur. J. 2009, 15, 885; b) B. Song, C. D. B. Van-
devyver, A.-S. Chauvin, J.-C. G Bꢀnzli, Org. Biomol. Chem. 2008, 6,
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Complex 33·Eu2: Ligand
3 ACHTUNGTNRUE(GN CF3SO3)3
(15 mg; 1.8ꢄ10ꢁ6 mol) and Eu
(7.4 mg; 1.2ꢄ10ꢁ5 mol) were refluxed in MeOH (5 mL) for 24 h. Solvents
were reduced under reduced pressure. The resulting concentrated solu-
tion is poured in diethylether and the complexe 33·Eu2 was collected in
75% yield (14.6 mg; 4.0ꢄ10ꢁ6 mol) after decantation. M.p.: Decom-
posed>2808C; IR (neat): n˜max =3280, 2994, 2923, 2882, 1654, 1589, 1522,
1487, 1444, 1366, 1259, 1074, 1021, 799, 776 cmꢁ1 1H NMR (MeOD;
;
600 MHz): dH =8.81 (3ꢄ2H, brs, naph-H), 8.65 (3ꢄ4H, brs, Ar-H), 8.25
(3ꢄ2H, brs, CH), 7.84 (3ꢄ2H, brs, Naph-H), 7.50 (3ꢄ4H, brs, Ar-H),
7.37 (3ꢄ2H, brs, Naph-H), 7.00 (3ꢄ2H, brs, Naph-H), 6.76 (3ꢄ2H, brs,
NH), 6.55 (3ꢄ2H, brs, Naph-H), 6.32 (3ꢄ2H, brs, Pyr-H), 6.19 (3ꢄ2H,
brs, Naph-H), 5.52 (3ꢄ2H, brs, Pyr-H), 4.05 (3ꢄ2H, brs, Pyr-H), 3.94
(3ꢄ2H, brs, CH2), 1.81 ppm (3ꢄ2H, brs, CH3).
[8] a) R. J. Hill, D.-L. Long, N. R. Champness, P. Hubberstey, M.
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Chem. Rev. 2002, 102, 1897; d) J. J. Lessmann, W. D. Horrocks,
Inorg. Chem. 2000, 39, 3114.
Complex 43·Eu2: Complex 43·Eu2 was formed and collected in 49%
(19.6 mg; 5.4ꢄ10ꢁ3 mmol) yields following the same procedure as de-
scribed for 33·Eu2 (with 20 mg; 2.5ꢄ10ꢁ5 mol of 4 and 9.9 mg; 1.66ꢄ
10ꢁ5 mol of Eu
G
=
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naph-H), 8.63 (3ꢄ4H, brs, Ar-H), 8.27 (3ꢄ2H, brs, CH), 7.83 (3ꢄ2H,
brs, Naph-H), 7.49 (3ꢄ4H, brs, Ar-H), 7.40 (3ꢄ2H, brs, Naph-H), 6.98
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brs, Pyr-H), 4.03 (3ꢄ2H, brs, Pyr-H), 3.89 (3ꢄ2H, brs, CH2), 1.82 ppm
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Acknowledgements
We would like to thank Dr. Floriana Stomeo for helping with the initial
synthesis of ligand 4 and Dr. Colin P. McCoy (Queenꢃs University of Bel-
fast, School of Pharmacy) for his collaboration. We thank Trinity College
Dublin for Postgraduate Award to CL, Science Foundation Ireland (SFI)
for RFP funding (Research Frontier Programme 2006, 2008 and 2009),
CSCB, and Jennifer Molloy for helping out with CD measurements. Pro-
fessor Gunnlaugsson would like to thank University of Canterbury,
Christchurch, New Zealand for the awarding of an Erskine Fellowship.
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Keywords: chirality
luminescence · self-assembly
· helical structures · lanthanides ·
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Received: October 1, 2009
Revised: December 21, 2009
Published online: February 8, 2010
504
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