Affinity modulation of photoresponsive hosts for fullerenes: Light-gated corannulene tweezers

Article abstract of DOI:10.1039/c6cc06445k

Six azobenzene derivatives bearing polyaromatic fragments have been prepared and their reversible photoisomerization has been assessed. Corannulene-functionalized molecules have demonstrated excellent switchable hosting abilities towards fullerenes in which an interesting range of affinities has been found. The success of this design relies upon the reversible formation and destruction of tweezer-like structures.

Full text of DOI:10.1039/c6cc06445k

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Affinity modulation of photoresponsive hosts for fullerenes. Light-
gated corannulene tweezers.
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
Héctor Barbero, Sergio Ferrero, Lucía Álvarez-Miguel, Patricia Gómez-Iglesias, Daniel Miguel
a
and Celedonio M. Álvarez*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Six azobenzene derivatives bearing polyaromatic fragments have hydrocarbons derivatives, such as phenanthrene and pyrene,
been prepared and their reversible photoisomerization has been have been prepared in the same way in order to complete the
assessed.
Corannulene-functionalized
molecules
have whole family and for comparison purposes (Figure 1).
demonstrated excellent switchable hosting abilities towards The preparation of all azobenzene-containing PAHs followed
fullerenes in which an interesting range of affinities has been two different routes depending on the location of pinacol
found. The success of this design relies upon the reversible boronate groups prior to Suzuki-Miyaura C-C coupling (see the
formation and destruction of tweezer-like structures.
Supporting Information for a more detailed discussion about
the most preferable chosen route).
The study of supramolecular chemistry is a hot topic in science
1
since the end of last century and a great development of a
Compounds 4, 5 and 6 were fully characterized by NMR, UV-
Vis absorption spectra and mass spectra (see Supporting
Information). Single crystals suitable for x-ray diffraction of
wide variety of concepts has been carried out in order to get a
deep understanding of the assembly among molecular entities
through weak and reversible interactions. One of such
concepts consists of using molecular tweezers as hosts for
recognizing a variety of molecules, in which fullerenes occupy
phenanthrene compounds 4a, 4b and corannulene derivative
6b
were obtained, showing their structures in solid state, as
depicted in Figure 2. Phenylene moieties and nitrogen atoms
of the azobenzene are placed at the same plane in all
compounds, whereas phenanthrene and corannulene
substituents have a CH-C-C-CH dihedral angle of around 50
2
an important position. The main reason to achieve such an
interaction relies upon a complementarity between curved
fullerene and the receptor molecule, whose structure matches
the surface of the guest. Several approaches have been carried
o
o
degrees respect to azobenzene; 50.4 (in 4a), 59.5 (in 4b) and
o
7.21 (in 6b). In meta-substituted molecules, both
4
3
out, being one of them the use of corannulene due to its
substituents are in an expected trans configuration to avoid
nonplanar structure, commonly known as buckybowl. Convex
and concave faces have different electron density, allowing
N
N
N
N
4
dipolar interactions and giving rise to interesting properties.
Of particular interest are receptors that can modulate or even
change totally their affinity by an external stimulus, such as
5a: para
5b: meta
4
a: para
4b: meta
5
light. One of the most used photoresponsive moiety is
N
azobenzene, which can be switched between both
6
configurational isomers with a simple input of light. Thus,
N
6
6
a: para
b: meta
several studies have been performed using this molecule in
7
order to carry out considerably different work, but none of
8
them dealt with corannulene-fullerene interactions. Herein,
Figure 1. Six azobenzene derivatives prepared in this work.
we present the first corannulene derivatives that contain
azobenzene as tether resulting in photoresponsive tweezers.
Along with these compounds, other planar polycyclic aromatic
Figure 2. Crystal structures of 4a and 4b (top); and 6b (bottom). Ellipsoids at 50%
of probability
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A
steric constraints of cis configuration.
1
,80
1,60
,40
1,20
Photoisomerization (Scheme 1) was studied in toluene. UV-Vis
1
absorption and H-NMR spectra were recorded to check the
1
process. Initially, all compounds show a E/Z ratio of around
o
0:20. After heating for 30 minutes at 80 C, this ratio is shifted
8
1
0
0
,00
,80
,60
to 95:5. Irradiation with 365 nm at room temperature give rise
to signals at higher field indicating the presence of Z isomer
with different E/Z ratios (Figure S75). It's known that this
wavelength is commonly used for switching azobeneze
derivatives, but is not optimum for our corannulene and
0,40
0,20
0,00
λ / nm
pyrene-substituted azobenzenes (5 and 6) whose π→π* band
appears at longer wavelengths for para substituted and
2
75
325
375
425
475
525
575
625
675
725
775
shorter for meta substituted. Indeed, if irradiated at 380 nm, Figure 3. UV-Vis spectrum of 6a in toluene (blue), after irradiation for 15 minutes
at 365nm (red) and after irradiation for 15 minutes at 380nm (green).
compounds 5a and 6a are more efficiently switched as it can
be seen in the UV-Vis spectrum (Figures 3, S71 and S73) and,
1
more explicitly, in their H-NMR spectra (Figures 4 and S55-
S58).
Once determined the structures of all compounds and the
extent of photoisomerization, all compounds were subjected
to preliminary supramolecular association tests in both
1
photostationary states by recording H-NMR spectra in
toluene-d8. The addition of excess of C60 or C70 can produce
chemical shift changes indicating supramolecular association
event. As expected, compounds
4
gave no appreciable changes
followed the same
in chemical shift. Moreover, compounds
5
trend despite the ability of pyrene to establish strong
9
association with polyaromatic architectures. We expected, at
least, a subtle interaction with the central part of C70 but that
was not observed. On the other hand, corannulene-
1
Figure 4. H-NMR spectrum (500 MHz) of 6a in toluene-d8. (a) Initial spectrum;
(b) After heated at 80ºC for 15 minutes and cooled down to rt; (c) After
irradiation at 380 nm for 30 minutes; (d) Thermal conversion to the initial state
functionalized azobenzenes 6, gave positive results. Regarding
o
by heating the sample at 80 C for other 15 minutes and cooled down to rt. Red
color corresponds to E isomer, blue color to Z isomer.
the case of 6a we found a great explicit affinity modulation
towards fullerenes.
Compound E6a, does not establish supramolecular association
1
with C60 or C70 at all. H-NMR spectra recorded after additions
3b,d,f,h
bis-corannulene derivatives.
This molecule forms 1:1
adducts with both fullerenes and no discrimination is observed
since both constants are almost identical. In light of these
results, an on-off behavior is suggested that can be carried out
in several cycles making this compound a light-gated
supramolecular tweezer.
of fullerenes remained unchanged (Figures S88 and S89). As
expected, its structure is not suitable to host the guest in a
tweezer-like manner (Scheme 1, up left). However, Z6a
(
Scheme 1, up right) is capable of hosting fullerenes with
3
estimated association constants (K ) of (2.6±0.3)·10 M and
-1
a
Compound E6b, in contrast, shows a very different behavior
3
2.5±0.3)·10 M for C60 and C , respectively (Figures 5 and
-1
(
70
(
Scheme 1, bottom left). Supramolecular association is
2
S90-S95); which are similar to those obtained for other
established with C60 and C70 having constants of (5.0±0.1)·10
-1
2
and (8.3±0.1)·10 M in toluene-d8, respectively (Figure 6
-1
M
N
N
and S76-S81) corresponding to 1:1 stoichiometry according to
Job plots. Switched form of that compound, Z6b (Scheme 1,
bottom right), shows abilities to host fullerenes too.
3
80nm
N
N
ꢀ
Association constants of
C60@Z6b and C70@Z6b were
E6a
Z6a
2
-1
2
-1
estimated to be (6.7±0.2)·10 M and (2.5±0.3)·10 M (1:1
stoichiometry). The new structure has affected its ability to
host fullerenes. Affinity for C60 is still moderate, although is
slightly better than before. In the case of C70 we found a
constant notably worse than that estimated for E6b. Its affinity
has been decreased around 70%. We reasoned that the new
structure of switched 6b makes harder the approximation of
C70 due to the lack of space and poor host preorganization
3
65nm
N
N
N
ꢀ
N
E6b
Z6b
(Figure S97). Due to the fact that E6b is not initially
Scheme 1. Example of the switching process between corannulene-
functionalized azobenzenes, depicting tweezer-like preorganization for 6a upon preorganized as host,
conversion to Z isomer.
2
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0
0
0
0
0
0
0
0
0
0
,018 ꢀδ
,016
,014
,012
,010
,008
,006
,004
,002
,000
[G]/[H]
10 20 30 40 50 60 70 80 90 100 110
0
1
Figure 5. H-NMR spectra (500MHz, toluene-d8) in the supramolecular titration
of Z6a with C60. Inset: Plot of changes in chemical shift against [G]/[H] where G is
60 and H is Z6a. Red line corresponds to the nonlinear fitting of ꢀδ for one
proton to a 1:1 binding isotherm.
C
Figure 7. Optimized geometry of C60@E6b (up) and C60@Z6a (bottom).
0
,000
0,005
0,010
0,015
0,020
0,025
0,030
0,035
0,040
0,045
0,050 ꢀδ
-
0
10
20
30
40
50
60
70
80
90
100
[
G]/[H]
-
An interaction energy between C60 and host molecule of -37.1
kcal/mol was obtained after taking into account basis set
superposition error (see Supporting Information regarding
how this calculation is done). That energy is very similar to
-
-
-
-
-
-
-
10
-
those calculated for other corannulene derivatives.
The geometry of C60@Z6a adduct was also optimized (Figure 6)
at the same level of theory giving rise to an expected geometry
showing a very good complementarity between fullerene and
host molecule. In this case, the adduct is formed in the ideal
azobenzene line having both corannulene subunits almost
perpendicular to it and parallel between them. This fact, along
with the better preorganized structure could be the reasons of
its better affinity. Interestingly, the calculated interaction
1
Figure 6. H-NMR spectra (500MHz, toluene-d8) in the supramolecular titration
of E6b with C60. Inset: Plot of changes in chemical shift against [G]/[H] where G is energy is -34.9 kcal/mol.; this means 2.2 kcal/mol less than
C60 and H is E6b. Red line corresponds to the nonlinear fitting of ꢀδ for one
proton to a 1:1 binding isotherm.
that calculated for
C60@E6b. This unexpected slight decrease
encouraged us to map the interactions between host and
11
this compound must undergo a conformational twist from guest. Non-covalent interactions were analyzed in both
trans to cis, implying an additional deformation energy to be optimized models revealing a more attractive interaction in
overcome before establishing the supramolecular association,
eventually giving smaller K
if compared to Z6a, but we did not fullerene surface, whereas in
expect a difference of one order of magnitude.
corannulene fragments (Figure 8). It seems that azobenzene
C
60@E6b in which the isosurface almost covers half of
C
60@Z6a, it substantially lies at
a
Therefore, we conducted computational calculations and tether contributes to interaction energy while C60 is close to it,
optimized its geometry in trans conformation from the but this contribution disappears when moves away.
structure observed in single crystal (see Supporting
Information for the theoretical model followed). Thus, the
rotation of N=N-C=CH dihedral angle was calculated in toluene
and a maximum at 5.67 kcal/mol was obtained, low enough to
be easily reachable at room temperature (Figure S98), because
it is not hampered by other intramolecular associations
(
corannulene-corannulene intramolecular
instance). Then, we minimized the structure of the adduct
60@E6b at the same level of theory (Figure 7). The cavity
π stacking, for
C
formed by both corannulene subunits is suitable to host a
fullerene, but CH hydrogens of azobenzenes pointing towards
substituents seem to interfere guest approximation and the
adduct is formed out of the ideal azobenzene line, forcing both
Figure 8. Gradient isosurfaces (s=0.3 a.u.) of
The surfaces are colored on a blue-green-red scale according to values of
sign(λ . Red indicates repulsion, while green means weak attraction.
C60@E6b (left) and C60@Z6a (right).
2
)ρ
corannulenes to adopt
a
bent conformation, and,
consequently, diminishing the affinity.
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The effect of additional stabilization by the fragment
connecting corannulene subunits has been pointed out by
and L. T. Scott, Chem. Rev., 2006, 106, 4868-4884; (g) Y.-T.
Wu, D. Bandera, R. Maag, A. Linden, K. K. Baldridge and J. S.
Siegel, J. Am. Chem. Soc., 2008, 130, 10729-10739; (h) Y.-T.
Wu and J. S. Siegel, Top. Curr. Chem., 2014, 349, 63-120.
(a) V. Balzani, A. Credi and M. Venturi, Molecular Devices
and Machines: Concepts and Perspectives for the Nanoworld,
Second Edition, Wiley-VCH Verlag GmbH, Weinheim,
Germany, 2008; (b) B. L. Feringa and W. R. Browne,
Molecular Switches, Second Edition, Wiley-VCH Verlag
GmbH, Weinheim, Germany, 2011; (c) J. Wang,
Nanomachines: Fundamentals and Applications, Wiley-VCH
Verlag GmbH, Weinheim, Germany, 2013; (d) D.-H. Qu, Q.-C.
Wang, Q.-W. Zhang, X. Ma and H. Tian, Chem. Rev., 2015,
3
i,j
Sygula and cooworkers.
In summary, we have described six new azobenzene
derivatives bearing polycyclic aromatic fragments assessed
their ability to modulate their affinities towards fullerenes.
One of this compounds, 6a, has demonstrated to be an
effective on/off light-gated molecular tweezer.
5
Acknowledgements
115, 7543-7588; (e) D. Bléger and S. Hecht, Angew. Chem.
Int. Ed., 2015, 54, 11338-11349.
This work was funded by the Spanish Ministerio de Economía y
Competitividad (CTQ 2013-41067-P). H.B. acknowledge with
thanks a MEC-FPI grant.
6
7
(a) H. M. D. Bandara and S. C. Burdette, Chem. Soc. Rev.,
2012, 41, 1809-1825; (b) E. Merino and M. Ribagorda,
Beilstein J. Org. Chem., 2012, 8, 1071-1090.
For some recent examples of architectures containing
azobenzenes that do useful work see: (a) T. Ogoshi, K. Kida
and T. Yamagishi, J. Am. Chem. Soc., 2012, 134, 20146-
20150; (b) G. Yu, C. Han, Z. Zhang, J. Chen, X. Yan, B. Zheng,
S. Liu and F. Huang, J. Am. Chem. Soc., 2012, 134, 8711-8717;
(c) L. Osorio-Planes, M. Espelt, M. A. Pericàs and P. Ballester,
Notes and references
1
(a) J. L. Atwood and J. W. Steed, Encyclopedia of
Supramolecular Chemistry, Taylor & Francis Group, New
York, 2005; (b) J. W. Steed, D. R. Turner and K. J. Wallace,
Core Concepts in Supramolecular Chemistry and
Nanochemistry, John Wiley and Sons, West Sussex, U.K.,
Chem. Sci., 2014, 5, 4260-4264; (d) J. Park, L.-B. Sun, Y.-P.
Chen, Z. Perry and H.-C. Zhou, Angew. Chem., Int. Ed., 2014,
53, 5842-5846; (e) J. P. Van der Berg, W. A. Velema, W.
Szymanski, A. J. M. Driessen and B. L. Feringa, Chem. Sci.,
2007.
(a) T. Kawase and H. Kurata, Chem. Rev., 2006, 106, 5250-
2
5
1
2
273; (b) K. Tashiro and T. Aida, Chem. Soc. Rev., 2007, 36
89-197; (c) E. M. Pérez and N. Martín, Chem. Soc. Rev.,
008, 37 1512-1519; (d) M. Hardouin–Lerouge, P.
,
2015, 6, 3593-3598; (f) M. Baroncini, S. d'Agostino, G.
Bergamini, P. Ceroni, A. Comotti, P. Sozzani, I. Bassanetti, F.
Grepioni, T. M. Hernandez, S. Silvi, M. Venturi and A. Credi,
Nat. Chem., 2015, 7, 634-640; (g) M. Lohse, K. Nowosinski, N.
L. Traulsen, A. J. Achazi, L. K. S. von Krbek, B. Paulus, C. A.
Schalley and S. Hecht, Chem. Commun., 2015, 51, 9777-9780;
(h) E. Anger and S. P. Fletcher, Eur. J. Org. Chem., 2015, 17,
3651-3655; (i) M. Dommaschk, M. Peters, F. Gutzeit, C.
Schütt, C. Näther, F. D. Sönnichsen, S. Tiwari, C. Riedel, S.
Boretius and R. Herges, J. Am. Chem. Soc., 2015, 137, 7552-
7555; (j) J. P. Van der Berg, W. A. Velema, W. Szymanski, A. J.
,
Hudhomme and M. Sallé, Chem. Soc. Rev., 2011, 40, 30-43;
e) N. Martín and E. M. Pérez, Pure Appl. Chem., 2010, 82
23-533; (f) N. Martín and J.-F. Nierengarten,
(
5
,
Supramolecular Chemistry of Fullerenes and Carbon
Nanotubes, Wiley-VCH Verlag GmbH, Weinheim, Germany,
2
012.
(a) S. Mizyed, P. E. Geourghiou, M. Bancu, B. Cuadra, A. K.
Rai, P. Cheng and L. T. Scott, J. Am. Chem. Soc., 2001, 123
3
,
1
Rabideau and M. M. Olmstead, J. Am. Chem. Soc., 2007, 129
3
2770-12774; (b) A. Sygula, F. R. Fronczek, R. Sygula, P. W.
,
842-3843; (c) M. C. Stuparu, J. Polym. Sci., Part A: Polym.
M. Driessen and B. L. Feringa, Chem. Sci., 2015, 6, 3593-
3598; (k) M. Xue, Y. Yang, X. Chi, X. Yan and F. Huang, Chem.
Rev., 2015, 115, 7398-7501; (l) S. Erbas-Cakmak, D. A. Leigh,
C. T. McTernan and A. L. Nussbaumer, Chem. Rev., 2015,
115, 10081-10206.
K. Yuan, Y.-J. Guo and X. Zhao, Phys. Chem. Chem. Phys.,
2014, 16, 27053-27064.
(a) Q. Yang, L. Shuai, J. Zhou, F. Lu and X. Pan, J. Phys. Chem.
B, 2008, 112, 12934-12939; (b) C. Ehli, G. M. A. Rahman, N.
Jux, D. Balbinot, D. M. Guldi, F. Paolucci, M. Marcaccio, D.
Paolucci, M. Melle-Franco, F. Zerbetto, S. Campidelli and M.
Prato, J. Am. Chem. Soc., 2006, 128, 11222-11231; (c) Y.-L.
Zhao, L. Hu, G. Grüner and J. F. Stoddart, J. Am. Chem. Soc.,
2008, 130, 16996-17003; (d) A. S. D. Sandanayaka, R. Chitta,
N. K. Subbaiyan, L. D’Souza, O. Ito and F. D’Souza, J. Phys
Chem. C, 2009, 113, 13425-13432; (e) C. B. Kc, G. N. Lim and
F. D'Souza, Angew. Chem. Int. Ed., 2015, 54, 5088-5092; (f) A.
Chem., 2012, 50, 2641-2649; (d) M. Yanney and A. Sygula,
Tetrahedron Lett., 2013, 54, 2604-2607; (e) M. C. Stuparu,
Angew. Chem. Int. Ed., 2013, 52, 7786-7790; (f) V. H. Le, M.
Yanney, M. McGuire, A. Sygula and E. A. Lewis, J. Phys. Chem.
B, 2014, 118, 11956-11964; (g) C. M. Álvarez, L. A. García-
Escudero, R. García-Rodriguez, J. M. Martin-Álvarez, D.
Miguel and V. M. Rayón, Dalton Trans., 2014, 43, 15693-
15696; (h) C. M. Álvarez, G. Aullón, H. Barbero, L. A. García-
Escudero, C. Martínez-Pérez, J. M. Martín-Álvarez and D.
Miguel, Org. Lett., 2015, 17, 2578-2581; (i) M. Yanney, F. R.
8
9
Fronczek and A. Sygula, Angew. Chem. Int. Ed., 2015, 54,
1153-11156; (j) P. L. Abeyratne Kuragama, F. R. Fronczek
1
and A. Sygula, Org. Lett., 2015, 17, 5292-5295; (k) K. G. U. R.
Kumarasinghe, F. R. Fronczek, H. U. Valle and A. Sygula,
Org. Lett., 2016, 18, 3054-3057; (l) C. M. Álvarez, H. Barbero,
S. Ferrero and D. Miguel, J. Org. Chem., 2016, 81, 6081-6086.
Lopez-Moreno and E. M. Perez, Chem. Commun., 2015, 51
5421-5424.
,
4
(a) L. T. Scott, M. M. Hashemi and M. S. Bratcher, J. Am. 10 (a) C. Mück-Lichtenfeld, S. Grimme, L. Kobryn and A. Sygula,
Chem. Soc., 1992, 114, 1920-1921; (b) A. Sygula, H. E.
Folsom, R. Sygula, A. H. Abdourazak, Z. Marcinow, F. R.
Fronczek and P. W. Rabideau, J. Chem. Soc., Chem. Commun.,
Phys. Chem. Chem. Phys., 2010, 12, 7091-7097; (b) P. A.
Denis, RSC Adv., 2013, , 25296-25305; (c) D. Josa, J.
Rodríguez-Otero, E. M. Cabaleiro-Lago, L. A. Santos and T. C.
3
1
994, 2571-2572; (c) F. J. Lovas, R. J. McMahon, J.-U.
Ramalho, J. Phys. Chem. A ,2014, 118, 9521-9528.
Grabow, M. Schnell, J. Mack, L. T. Scott and R. L. Kuczkowski, 11 (a) W. Yang, E. R. Johnson, S. Keinan, P. Mori-Sánchez, J.
J. Am. Chem. Soc., 2005, 127, 4345-4349; (d) Y.-T. Wu, T.
Hayama, K. K. Baldrige, A. Linden and J. S. Siegel, J. Am.
Chem. Soc., 2006, 128, 6870-6884; (e) Y.-T. Wu and J. S.
Siegel, Chem. Rev., 2006, 106, 4843-4867; (f) V. M. Tsefrikas
Contreras-García and A. J. Cohen, J. Am. Chem. Soc., 2010,
132, 6498-6506; (b) W. Yang, J. Contreras-García, E. R.
Johnson, S. Keinan, R. Chaudret, J.-P. Piquemal and D. N
Beratan, J. Chem. Theory Comput., 2011, 7, 625-632.
4
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