Formation of a highly-ordered rigid multichromophoric 3D supramolecular network by combining ionic and coordination-driven self-assembly

Article abstract of DOI:10.1039/c5cc10335e

We present here the self-assembly of a green-emitting metallosupramolecular rhomboid into a rigid, highly-ordered 3D multichromophoric network through the mediation of a tetra-anionic violet-blue molecular emitter. Control was obtained on the spatial topology, the electronic energy landscape and the fluorescence polarization of the interacting dipoles.

Full text of DOI:10.1039/c5cc10335e

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Karakostas, M. Fakis, K. Seintis, H. Oberacher, F. Pitterl Florian, E. Martinou, A. Kaloudi Chantzea and P.
Giastas, Chem. Commun., 2016, DOI: 10.1039/C5CC10335E.
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DOI: 10.1039/C5CC10335E
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COMMUNICATION
A Highly – Ordered Rigid Multichromophoric 3D Supramolecular
Network by Combining Ionic and Coordination – Driven Self -
Assembly
Received 00th January 20xx,
Accepted 00th January 20xx
Antonia Kaloudi-Chantzea,a Elisabeth Martinou,a Kostas Seintisb, Nikolaos Karakostas,a Petros
DOI: 10.1039/x0xx00000x
Giastas,c Florian Pitterl,d Herbert Oberacher,d Mihalis Fakisb, and George Pistolis*,a
www.rsc.org/
We present here the self-assembling of a green - emitting pyridyl coordination chemistry to form various sizes of highly
metallosupramolecular romboid into a rigid, highly – ordered 3D emissive distinct 3D metallosupramolecular polygonal host-
multichromophoric network through the mediation of a tetra- architectures6 and simple 1:1 host – guest supramolecular
anionic violet – blue molecular emitter. Control was obtained on adducts7. Here, we combine coordination - driven with ionic
the spatial topology, the electronic energy landscape and the self-assembly to demonstrate that the size and shape of the
fluorescence polarization of the interacting dipoles.
metallosupramolecular rhomboidal cavitand 3+4 and the metal
itself can play a decisive role in dictating the formation of a
The construction of extended networks via cooperative
supramolecular interactions has become an ever – increasing
challenge as can lead to the emergence of new functions and
properties arising from the collective interactions between the
proximal constituent sub-components1. From the perspective
of the creation of photofunctional supramolecular
architectures, rigidity, long-range molecular order and high
periodicity are of great importance for both their fundamental
photophysics and ability of enabling energy cascading /
migration phenomena with controllable polarization for real-
world applications2. As such, the implementation of self –
assembled 3D rigid networks wherein the size / shape -
adjustable and color – tunable chromophoric building blocks
would be predefined, suitably separated and precisely aligned
through space, remains a challenging issue to be addressed.
highly
- ordered multichromophoric 3D supramolecular
network with interesting photophysical properties, after being
reacted with the tetra - anionic linker 1,3,6,8 tetrasulfonate
pyrene (4SPy-4) exhibiting electrostatic binding capabilities at
both sides of a symmetry plane (Scheme 1).
The synthesis of the romboidal cavitand
out by mixing the Bodipy-based acceptor
3
(OTf)4 was carried
with the 90°
2
platinum triflate Pt(dppp)(OTf)2 donor in a stoichiometric ratio
2:2 in CH2Cl2. The product was characterized by ESI-MS, 31P,1H,
13C multinuclear NMR analysis and fluorescence spectroscopy
methods (ESI). In obvious contrast to the simple (1:1)
supramolecular adducts formed by the tetrameric Bodipys -
based rhomboidal7 in the cavity of which 4SPy-4 can be
precisely fitted, the smaller 3+4 interacts with the “oversized”
guest (4SPy-4) through an outside self-associative reaction
mode which is fully consistent with directional
Besides supramolecular structures,3 polymers4 and
networks1 that are built up by reversible and highly directional
secondary interactions such as hydrogen bonds, π-π
interactions, hydrophobic interactions and metal – ligand
binding, the molecular engineering of new functional
supramolecular macrostructures via ionic self-assembly5 of
oppositely charged building blocks is gaining rapidly ground.
We have recently reported that appropriately functionalized
boron dipyrromethene dyes (Bodipys) can self-assemble via Pt-
a.NCSR "Demokritos" 1Institute of Nanoscience and Nanotechnology, 153 10
Athens, Greece.
b.Department of Physics, University of Patras, 26500 Patras, Greece.
c. Hellenic Pasteur Inst, Dept Neurobiol, 11521 Athens, Greece.
d.Inst. of Legal Medicine and Core Facility Metabolomics, Medical Univ. of
Innsbruck, Müllerstraße 44, 6020 Innsbruck, Austria.
Scheme 1. Schematic illustration of the formation of a highly - ordered
†
Electronic Supplementary Information (ESI) available: Synthesis, theory,
additional NMR, ESI MS, spectroscopic and crystallographic data. See
DOI: 10.1039/x0xx00000x
multichromophoric network
.
–
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-
ion – pairing (SO3 ····Pt+2) between the complementary charged at an angle of ~ 220 with respect to the symmetry plane
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building blocks i.e., 3+4 and 4SPy-4. The supramolecular formed by their coplanar counterpartDsO(I:s1it0e.10139)./CT5ChCis10n33ic5eE
network is formed by mixing N,N - dimethylformamide (DMF) geometric placement allows bridging (cross-linking) of
solutions of the reactants 4SPy(NBu4)4 and
ratio
0.5:1. Although the individual reactants exhibit SO3 ····Pt+ electrostatic interactions between two sulfonate
negligible aggregation under these conditions, the mixture of groups comprising opposite sides of a planar linker (4SPy-4
the reactants immediately forms needle – shaped crystals and the apical position of the Pt(II) centers of two interchain
3(OTf)4 in a molar adjacent linear 1D multichromophoric arrays through pairs of
-
>
)
which over time are increasingly becoming denser.
nearest – neighboring rhomboids (see Fig. 1c).
The crystal structure8 reveals the formation of cross -
To demonstrate the supramolecular recognition
linked, parallel linear multichromophoric arrays wherein the capabilities between the oppositely charged reactants in
linker’s 4SPy-4 units are found to play a dual structural role as solution, we studied the above system in DMF-d7 solution by
two distinct binding sites for 4SPy-4 on 3+4 were manifested in means of 1D and 2D NMR methods as well as electrospray
the asymmetric unit: one (site 1) with the 4SPy-4 units to be ionization mass spectrometry (ESI – MS). Figure 2 shows the
1
coplanar (mauve) and a second one (site 2) where the above partial H NMR spectra by keeping constant the concentration
anionic linkers form a zig-zag arrangement across the rim of of 3+4 ([3] = 0.2 mM) and varying the molar ratio R = [4SPy-
the linear chromophoric array (light blue; see Figure 1b). In the 4]/[3+4]. The results clearly indicate strong binding leading to a
former arrangement (site 1) the coplanar 4SPy-4 units are substantial downfield shift of the axial and equatorial aromatic
aligned parallel the ac crystallographic plane, with their long proton signals of 4SPy-4 by Hax = 0.730 and Heq = 0.580
and short molecular axes oriented parallel the crystallographic ppm respectively for nearly all the molar ratios up to 0.4. All
axes a and c, respectively. Each anionic unit (4SPy-4) is linked proton signals of 3+4 were shifted downfield with the exception
radially with four rhomboids via an equal number of pairwise of Hb that shifted upfield and HJ which was remained
electrostatic interactions between the sulfonate groups of unaffected (ESI; Figure S5). When R reaches 0.5 the solution
4SPy-4 and the apical position of the Pt (II) centers of 3+4. This becomes slightly turbid over time while further addition of
leads to the linear multichromophoric arrangement pattern 4SPy-4 (R 0.5) affords the rapid formation of needle – shaped
along the a crystallographic axis shown in Fig. 1a,b, in which crystals (Scheme 1 inset).
the adjacent rhomboids in the unit cell are offset along axis a
The formation of the supramolecular structure was
by 7.92 Å and position themselves from both sides of the glide confirmed with ESI-MS by keeping the mixing molar ratio R
plane on which the coplanar molecular linkers (4SPys-4) lie. The slightly less than 0.5 to block the formation of extremely
rhomboidal - shaped planar frame of 3+4 - defined by the least insoluble highly extended 3D networks. When a mixture 0.4:1
square plane
B
Pt+2
B
Pt+2 - is parallel to the above of 4SPy.(NBu4)4 and 3.(OTf)4 in DMF/acetone (1:1 v/v) was
plane of symmetry leading to
a
highly-ordered linear sprayed in the positive-ion mode at 25 °C, various oligomeric
multichromophoric array (see Figure 1a) wherein the Bodipy supramolecular structures were observed. Characteristic
dipoles of the alternate rhomboids face strictly parallel to each signals were found at m/z 1339.6869, 2074.3948 and
other and respectively are orthogonally aligned to the 4SPy-4 2232.8808 which could be assigned to the ternary complex
plane. At the second distinct binding site of 4SPy-4 (light blue;
[(
3)2 .4SPy]4+ and the small oligomeric assemblies
[(3)3
.
5+
site 2) on 3+4 (Fig. 1) the anionic linkers are appropriately (4SPy)2]4+ and [[(3)4.(4SPy)2](3OTf)
]
respectively. The above
positioned close to the rim of the rhomboidal cavitands
peaks were isotopically resolved and found to agree very well
with their theoretical distribution (SI; Figure S9, S10, S11). The
presence of small - sized supramolecular adducts was also
supported by 2D diffusion - ordered NMR spectroscopy (DOSY)
in DMF-d7 (Figure S6). The diffusion coefficient of 3+4 (0.2 mM)
was estimated to be D = 2.7 x 10-10 m2s-1 which, after the
addition of 0.4 equiv. of 4SPy-4, was decreased to
Fig. 1 Crystal structure:
A linear multichromophoric array (1D
network) viewed down (a) a and (b) b crystallographic axis; the mauve
4SPy-4 molecule lies on a symmetry plane (not shown) while the plane
of the light blue 4SPy-4 unit forms an angle of ~ 22o with the above
symmetry plane (c) Unit cell packing viewed down c crystallographic
axis showing cross-linked 1D networks. The Bodipy chromophore is
colored green for clarity: C, grey; N, blue; Pt, magenta, P, orange; B,
pink; O, red; S, yellow; F, light-green. Hydrogens atoms are not shown.
Fig. 2 Partial 1H NMR spectra of 3+4 [0.2 mM] vs the molar ratio R =
[4SPy-4]/[3+4]. For the dependence of chemical shifts of all protons of
3+4 vs R see ESI; Figure S5.
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D = 2.4 x 10-10 m2s-1 indicating that the degree of complexation electronic energy flow from the S1 state of 4SPy-4* to the S2
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of 3+4 was increased in the presence of the linker 4SPy-4. More state of the Bodipys (3+4*) proceeds with no apparent
DOI: 10.1039/C5CC10335E
detailed structural information were obtained by 2D nuclear quenching of the emissive state (S1) of the Bodipy subunit as
Overhauser effect spectroscopy (NOESY, see ESI; Figure S7). clearly demonstrated by the invariability of the fluorescence
Intermolecular cross peaks are observed between the axial lifetime of 3+4* as a function of added 4SPy-4 (Figure S13).
(Hax) and equatorial (Heq) protons of 4SPy-4 and those of the
The dynamics of EET from 4SPy-4* to 3+4* was studied by the
femtosecond fluorescence upconversion method using 80 – fs
pyridyl (H and H ) and phosphine aromatic groups (HPh) of 3+4
.
Moreover, additional intermolecular cross peaks are seen excitation pulses at 380 nm and the results are shown in Figure
between the Heq of 4SPy-4 and the protons (He) of the methyl 4a. The two fast decay times ( 1 = 0.38 0.07 ps and 2 = 1.90
groups of the Bodipy subunit of 3+4 heading toward the cavity
0.50 ps) found for the 4SPy-4* emission (residual
of the rhomboid. These observations along with the absence fluorescence at 420 nm) were recovered as rise times at the
of intermolecular cross peaks between the protons of 4SPy-4 Bodipy emission band of 3+4* (530 nm). No rise – time of the
and the exocyclic protons of the Bodipy subunit (Hg, Hh, Hi, Hj) fluorescence intensity at 530 nm can be detected when 3+4
of the rhomboid cavitand provide clear indication that 4SPy-4 alone is excited with 380 nm fs-pulses, as clearly seen in Figure
binds so as to position itself toward the internal space of the 4b. The finding of two different energy transfer processes
cavitands.
could be rationalized by the assumption of two distinct binding
Absorption and fluorescence spectroscopy was employed sites of 4SPy-4 with respect to the 3+4, associated with different
to gain more insights into electronic energy transfer (EET) distances between the donor - acceptor dipoles. This is not
phenomena between the closely spaced and fixed separated totally unexpected considering the fact that more than one
donor (4SPy-4) – acceptor (3+4) chromophoric subunits. Figure binding site of 4SPy-4 to the 3+4 has been manifested in the
3 shows the absorption and fluorescence spectra in DMF of (a) crystal structure, with centroid – centroid distances between
4SPy-4 alone and (b) 3+4 (0.20 mM) versus added amounts of the donor – acceptor aromatic rings of ~ 11.5 Å (site 1) and ~
4SPy-4. As can be seen, despite the strong complexation 7.4 Å (site 2) respectively.9
between 3+4 and 4SPy-4 manifested above by NMR
spectroscopy, the addition of 4SPy-4 up to a molar ratio of R =
0.4 does not perturb the absorption spectrum of 3+4 suggesting
the absence of ground - state interchromophoric electronic
interactions. (Figure S12). Excitation into the main S0→S1 (π-
π*) absorption band of 4SPy-4 for all solution compositions up
to R = 0.4 results to the disappearance of the strong violet
emission of the pyrene moiety ( = 0.42, = 7.6 ns) and to
f
f
the appearance of emission nearly completely dominated by
3+4*. The above can be interpreted by means of efficient EET of
4SPy-4* to 3+4* (Figure 3b). The sensitization of the fluorescence
of 3+4* by 4SPy-4* is also manifested by the recorded
fluorescence – excitation spectrum (Figure 3b; left inset). It is
worth noting that, in consistency with previous findings,6
Fig. 4 (a) Normalized fluorescence decays at 420 (residual emission of
4SPy-4) and 530 nm (Bodipy emission of 3+4) of the assembled forms
(molar ratio R = 0.4) (b) Fluorescence dynamics at 530 nm of 3+4 alone
and in the presence of 4SPy-4 (R = 0.4). (c) Fluorescence anisotropy
decays for 3+4 alone and in the presence (R=0.4) of 4SPy-4. Solid lines
show fits.
Fig. 3 (a) Absorption and fluorescence spectrum (exc: 356 nm) of 4SPy-
4
in DMF. (b) Absorption and fluorescence spectra (exc: 356 nm) of3+4
alone ( orange curve) and upon added amounts (blue lines) of 4SPy-4 (R
= 0.13, 0.26 and 0.40). Inset: Fluorescence - excitation spectrum of 3+4
in the presence of 0.4 equiv. of 4SPy-4.
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To obtain orientation information between the donor –
acceptor dipoles the fluorescence anisotropy depolarization
dynamics r(t) at the Bodipy emission band (530 nm) of 3+4 was
monitored in the absence and presence of 4SPy-4 upon
excitation at 380 nm (Figure 4c and S14). The anisotropy r(t) of
the 3+4 alone is found to be static over the 0-20 ps time
window retaining a value of r(t) = r(0) ~ 0.07 as predicted by
the limiting anisotropy10 of Bodipys for excitation at 380 nm.
The above invariability of r(t) can be rationalized by the fact
that EET (homotransfer) between the two mutually parallel -
aligned Bodipy dipoles in 3+4 does not induce a change in the
direction of the oscillator dipole moment and thereby the
emission is not depolarized6a (Figure 4c).
Notes and references
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2
In obvious contrast to the above, in the presence of the
donor 4SPy-4 (R =0.4) the anisotropy r(t) decays steeply with a
mean lifetime of = 0.95 ps and soon levels off to a stable
r
Schenning, L. M. Herz, J. Phys. Chem. Lett. 2015,
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value of -0.02. Selective excitation with polarized light at the 0-
0 band of the donor 4SPy-4 (380 nm) is expected to result in an
excited state with the absorption and emission dipole moment
vectors lying along the long molecular axis7. On the basis of the
above results the fast decay of the fluorescence anisotropy r(t)
detected at the emission band of the Bodipy subunit
(acceptor) indicates a significant rotation of polarization
between the donor – acceptor dipoles. Taking into account the
fraction of direct acceptor (3+4) excitation obtained from the
relative absorptivity of the subunits at 380 nm, an angle of ~
700 between the donor – acceptor dipole moments was
3
4
7
Cook, M. Wang, M. Lal Saha, Z. Zhou, M. Zhang, X. Li, F.
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obtained2c,10
.
5
(a) J. Lee, A. W. Schwabacher, J. Am. Chem. Soc. 1994, 116,
To further elucidate the possible distortion from the perfect
collinearity of the Bodipy dipoles in the oligomeric assemblies
with respect to the single 3+4 unit, we monitored the
fluorescence anisotropy decays of 3+4 at 530 nm in the free
and complexed form after preferential excitation of the Bodipy
subunit at 400 nm (ESI; Figure S15). No significant loss of r(t)
can be seen, suggesting that the Bodipy dipoles retain their
high collinearity in the oligomeric assemblies. The above
results conclusively imply that the donor (4SPy-4) – acceptor
8382; (b) Z. Wang, C. J. Medforth, J. A. Shelnutt, J. Am.
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(
3+4) chromophoric arrangement in the oligomeric structures in
the solution should not differ remarkably by that manifested
by the crystal structure.
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N. Karakostas, I. M. Mavridis, K. Seintis, M. Fakis, E. N.
To summarize, we demonstrate here the formation of
highly - ordered multichromophoric supramolecular network
formed by a self-associative reaction mode between a Bodipy
6
dye – based metallosupramolecular rhomboid cavitand (3+4
)
and the tetra-anionic molecular linker 1,3,6,8 tetrasulfonate
pyrene (4SPy-4). The results unveil that the Bodipy dipoles of
the alternate rhomboids position themselves parallel to each
other and are aligned nearly perpendicular to the linkers’
(4SPy-4) plane. Highly efficient energy transfer and effective
polarization switching from the linker (4SPy-4) to the Bodipy
dyes of 3+4 was manifested.
This work was performed in the framework of "IKY:
Fellowships of Excellence for Postgraduate Students in Greece
– Siemens Program”. Part of this work also has been supported
by Grant E.028 from the Research Committee of the University
of Patras (Programme K. Karatheodori).
7
8
9
Koini, I. D. Petsalakis, G. Pistolis, Chem. Commun. 2014, 50
1362.
,
The molecular structure has been deposited at the
Cambridge Crystallographic Data Centre: number CCDC
1434774.
Ultrafast energy transfer (< 2ps) which is several times
faster7 than the time predicted by Coulombic coupling
calculations10 has commonly been observed between
closely spaced donor – acceptor pairs (< 15 Å).
10 N. Karakostas, A. Kaloudi-Chantzea, E. Martinou, K. Seintis,
F. Pitterl, H. Oberacher, M. Fakis, J. K. Kallitsis, G. Pistolis,
Faraday Discuss. 2015, 185, 433.
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