Fine-tuning of the optical output in a dual responsive catenane switch

Article abstract of DOI:10.1039/d1cc00310k

A [2]catenane switch where the intramolecular pyrene excimer emission can be controlled by orthogonal cation binding and solvent polarity change in various amplitudes and dynamic ranges is reported.

Full text of DOI:10.1039/d1cc00310k

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Fine-tuning of the optical output in a dual
responsive catenane switch†
Cite this: Chem. Commun., 2021,
7, 2931
a
a
a
ab
5
Yulin Deng,
Samuel Kin-Man Lai,
Linghui Kong and Ho Yu Au-Yeung
*
Received 18th January 2021,
Accepted 9th February 2021
DOI: 10.1039/d1cc00310k
rsc.li/chemcomm
A [2]catenane switch where the intramolecular pyrene excimer emis- of the co-conformations, and hence more elaborate control over
4
sion can be controlled by orthogonal cation binding and solvent the associated output can be realised. In this work, a pyrene-
polarity change in various amplitudes and dynamic ranges is reported. functionalised [2]catenane switch responsive to both cation
binding and solvent polarity change is reported (Fig. 1a). Speci-
Catenanes and related mechanically interlocked molecules fically, cation binding is employed to lock/unlock the interlocked
(MIMs) are attractive structural units for the construction of macrocycles from large-amplitude co-conformational change,
molecular switches, because the flexible and strong mechanical whereas a change in solvent polarity is used to fine tune the
bond could enable the interlocked macrocycles to undergo intramolecular pyrene–pyrene distance to effect an excimer emission
large-amplitude intramolecular motions and switch between (Scheme 1). Compared with other MIMs that are switched by one
1
,2
different states in response to a stimulus. A common design kind of stimulus, the dual responsiveness will allow more flexible
strategy of a catenane switch is to have two or more co- and versatile control over the relative stability of the catenane co-
conformations of considerable but different stabilities, where conformations, and the amplitude of the luminescent output can be
the application of a stimulus will enhance or disrupt the controlled in a progressive fashion with the orthogonal stimuli.
interactions at one recognition site, such that the relative
The [2]catenane switch 1 contains two interlocked, phenan-
stability of the co-conformations is reversed and a switching throline-derived macrocycles that are appended with a pyrene
is resulted. Although co-conformation switching in MIMs has (Fig. 1b). When a cation binds to the interlocked phenanthrolines,
been well studied and can be achieved by using various kinds of rotatory motions of the interlocked macrocycles will be ‘‘locked’’.
2
stimuli, most reports are primarily focused on the structural
aspect of the switching process, where the stability of one of the
co-conformations is modulated by a single stimulus in the switch-
ing process. On the other hand, engineering a desirable output to
accompany the structural change is less straightforward because
the co-conformational change will have to associate with a
difference in the chemical and/or physical properties, and there-
fore a more elaborate way to control the relative stability of the co-
3
conformations is necessary if a specific output is to be generated.
Instead of effecting the switching by altering the stability of
one of the co-conformations, decoupling the signal genera-
tion into separate processes such that the stability of each
co-conformation is controlled by an individual stimulus will
offer additional mechanisms in modulating the relative stability
a
Department of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, P. R. China. E-mail: hoyuay@hku.hk
b
State Key Laboratory of Synthetic Chemistry and CAS-HKU Joint Laboratory of
Metallomics on Health and Environment, The University of Hong Kong,
Pokfulam Road, Hong Kong, P. R. China
Fig. 1 (a) Cation (un)locks 1 from large-amplitude co-conformational
change and hydrophobic interactions fine tune the intramolecular pyrene
distance. (b) Molecular structure of [2]catenane 1 and the control compound 2.
†
Electronic supplementary information (ESI) available: Synthetic procedures,
spectra and computation details. See DOI: 10.1039/d1cc00310k
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monomer 2 in DMSO showed no emission at 485 nm, confirming
that the excimer emission from 1 is intramolecular in nature and
that 1 is co-conformationally flexible and responsive to a change
in solvent polarity.
As the pyrene excimer emission from 1 is premised on the
flexibility of the [2]catenane to form an intramolecular pyrene
excimer, rigidifying the mechanical bond in 1 could disable the
solvent-induced switching of the excimer emission. By coordinating
2+
2+
the phenanthrolines in 1 to a Zn ion, the [Zn(1)] complex is
formed (see the ESI†). In addition, the phenyl linkers also p-stack
with the phenanthrolines as supported by an upfield shift of 0.3–
Scheme 1 A dual responsive [2]catenane switch in which the (un)locking
of the mechanical bond and co-conformational change are controlled by
two orthogonal stimuli.
1
0
.8 ppm for the phenyl protons in the H NMR spectrum of
2
+
[Zn(1)] when compared to that of 1 (Fig. S37, ESI†). Such
p-stacking will further rigidify the mechanical bond and limit
the co-conformational flexibility of the [2]catenane switch.
8
Since the pyrene is attached onto the macrocycle at a point that is
farthest away from the phenanthroline, the pyrenes will be kept
from being in close proximity and no emission from intra-
Consistent with the rigid structure, no intramolecular pyrene
excimer was formed and no emission at 485 nm was observed
2+
from a 25 mM solution of [Zn(1)] in water/DMSO of all tested
5
molecular pyrene excimer will occur. In the absence of the cation,
ratios (Fig. 2b). The fluorescent output from the [2]catenane
switch was therefore effectively turned-off in the ‘‘locked’’ state
1
will be in an ‘‘unlocked’’ state and co-conformational changes
are unrestricted. An increase in the water content in the solvent
will enhance the hydrophobic interactions between the two
pyrenes and favour the formation of an intramolecular pyrene
2+
upon coordination to a Zn ion.
Co-conformational flexibility of the [2]catenane switch in the
‘
‘locked’’ and ‘‘unlocked’’ states was also studied by molecular
6
excimer with a new excimer emission. Synthesis of 1 is straight-
2+
dynamics (MD) simulations on 1 and [Zn(1)] in DMSO and
forward with a templated catenane formation, followed by a click
modification that appended the pyrenes (see the ESI,† for details).
A DMSO solution of 1 is light yellow and the UV-Vis
spectrum shows strong pyrene absorptions at 334 nm, e =
water (Fig. 3). Consistent with the tetrahedral coordination
geometry, the angle between the phenanthroline planes (a) in
2+
[
Zn(1)] was found to be consistently about 871 with a distance
of 7.1 Å between the centroids of the two phenanthrolines (d) in
both DMSO and water (Fig. S13 and S14, ESI†). The two pyrenes
were also found to be separated by B25 Å which is too distant
for efficient excimer formation. These observations agree well
À1
À1
À1
À1
3
2 000 M cm and 351 nm, e = 34 800 M cm (Fig. S1,
ESI†). Photoexcitation (lex = 340 nm) of a 25 mM solution of 1 in
DMSO showed two emission peaks at 378 nm and 398 nm
7
which are characteristic of non-aggregated pyrene (Fig. 2a).
2+
with the mechanical bond being locked by the Zn ion and the
There is also a broad and weak emission at 485 nm that can be
assigned as the emission from a pyrene excimer, suggesting
that the mechanical bond in 1 is flexible and that the [2]cate-
nane switch can adopt a co-conformation that favours excimer
observation that the excimer fluorescence was completely turned
off in the ‘‘locked’’ state. In contrast, MD simulations on 1 showed
7
formation. Upon increasing the solvent polarity by introducing
water as a co-solvent, a significant increase in the emission
intensity at 485 nm (I485) was observed when the water percentage
was above 50%. A 13-fold enhancement of I485 was resulted when
the water content is 90% when compared with that of 1 in pure
DMSO. In addition, a 50 mM solution of the non-interlocked
Fig. 2 Normalised emission spectra of a 25 mM solution of (a) 1 (unlocked
2
+
state) and (b) [Zn(1)] (locked state) in DMSO with an increasing amount of
Fig. 3 Representative structures of 1 in (a) DMSO and (b) water, and
[Zn(1)] in (c) DMSO and (d) water obtained using MD simulations.
2+
water (0%, 60%, 70%, 80% and 90%).
2932 | Chem. Commun., 2021, 57, 2931À2934
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15
a more rapid relative oscillation of both a (from 741 to 1051) and d commonly used to effect the switching to a maximum extent. Yet,
from 7.3 Å to 13.7 Å) in water. Similar fluctuations in a and d were with the present dual switching where the output is dependent on
also observed when the dynamics of 1 were simulated in DMSO, two inputs, metal ions that are weaker binding with a ‘‘mismatch’’
(
+
+
2+
consistent with the [2]catenane switch being in the ‘‘unlocked’’ in the coordination properties (i.e. hard Li /Na /Ca with the
state with a more flexible mechanical bond. The averaged distance borderline, N-based phenanthrolines in a tetrahedral geometry)
between the two pyrenes in 1 is different in the two solvents. In could also be advantageously used to fine-tune the amplitude and
DMSO, the distance between the two pyrenes was found to vary dynamic range of the output, thus making the [2]catenane much
between 19.1 Å and 30.2 Å, but an average pyrene–pyrene distance more versatile with diverse ways of control and amplitude settings.
of o10 Å, which will allow the formation of pyrene excimer, was
Finally, locking of the mechanical bond in 1 by acid has also
found in water. Compared with most other phenanthroline- been studied. [2]Catenanes with two phenanthrolines similar to 1
9
based [2]catenanes in which the switching is effected only have been previously reported to bind to a proton and the phenan-
1
0
by cation (un)binding, the use of two stimuli to effect the throlines are held in the core of the [2]catenane in the resulting acid–
10b,c,16
co-conformational switching is advantageous as the relative base adduct.
In our study, addition of 1 equiv. of trifluoroacetic
stability of the co-conformations, and hence amplitude of the acid to 1 in 90% water/DMSO resulted in a decrease of I485 by 56%,
output, can be fine-tuned by a specific combination of the two suggesting that the phenanthrolines in 1 were locked in the centre of
stimuli.
the [2]catenane and formation of the intramolecular pyrene
1
7
In the co-conformational switching of 1, on–off control of excimer was disfavoured. MD simulation on the mono-
the excimer emission is achieved by cation (un)binding and the protonated [(1)H] also showed that the two pyrenes are sepa-
+
excimer emission intensity is controlled by the solvent polarity. Due rated by B15 Å which is slightly too long for the intramolecular
2
+
11
to the strong Zn -phenanthroline coordination (log K E 12),
pyrene excimer formation (Fig. S15 and S16, ESI†). A representa-
+
locking of the catenane switch in the ‘‘off’’ state is very efficient and tive structure of [(1)H] also showed that the two phenanthro-
the use of 1 equiv. of Zn ions is sufficient to completely switch off lines are locked in the [2]catenane core with structural
the excimer emission. By using other cations of different binding parameters comparable to that of a published crystal structure
2+
1
6a
strengths to bind to the phenanthrolines in 1, the dynamic range of of a monoprotonated phenanthroline-containing [2]catenane,
the polarity-controlled luminescent signal can be modulated. For showing that the flexibility of the mechanical bond in 1 can also
+
example, locking the mechanical bond in 1 using 1 equiv. of Cu , be controlled by acid–base chemistry (see the ESI,† for details).
which is known to bind strongly to phenanthroline-based
In summary, a simple [2]catenane switch with a two-stage
control of the intramolecular excimer fluorescence is reported.
10,12
2+
catenane,
resulted in a similar switching as that of using Zn
and no pyrene excimer emission at 485 nm was observed in 90% While the proximity of the pyrenes is dependent on the
water/DMSO (Fig. S6, ESI†). The use of weaker binding s-block strength of the hydrophobic interactions in solvents of different
1
2a,13
metals,
sion of the polarity-induced excimer emission. For example, I485 of approach each other is controlled by the presence of a cation
in 90% water/DMSO was found to be reduced by B11%, B5% that locks the phenanthrolines. A range of cations can be used
on the other hand, resulted only in a partial suppres- polarity, flexibility of the mechanical bond for the pyrenes to
1
+
+
2+
and B18% when 1 equiv. of Li , Na and Ca was introduced to lock the mechanical bond in 1 in different degrees and the
14
respectively (Fig. 4). Furthermore, the dynamic range of the pyrene excimer fluorescence can therefore be versatilely controlled
polarity-dependent excimer emission can also be tuned by using by various stimuli including solvent polarity, transition metals,
different amounts of the s-block metals. For example, I485 of 1 in main group metals and proton. With two orthogonal inputs to
9
0% water/DMSO was found to be reduced by 43% and 80% in the generate a luminescent output, the [2]catenane switch can also be
+
presence of 10 equiv. and 100 equiv. of Na respectively. It is worth considered as a molecular logic gate for applications such as
noting that in most metal-based MIM switches, metals that opti- molecular keypad locks in which a signal is generated by a correct
18
mally satisfy the coordination properties at the recognition sites are combination of inputs in a specific sequence.
This work was supported by the Croucher Foundation. We
acknowledge UGC funding administered by The University of
Hong Kong for support of the Electrospray Ionization Quadrupole
Time-of-Flight Mass Spectrometry Facilities under the support for
Interdisciplinary Research in Chemical Science.
Conflicts of interest
There are no conflicts to declare.
References
1
(a) J.-P. Collin, J. M. Kern, L. Raehm and J.-P. Sauvage in Molecular
Switches, ed. B. L. Feringa, Wiley-VCH, Weinheim, 2001, ch. 8, pp. 249–
280; (b) V. Balzani, M. Gomez-Lopez and J. F. Stoddart, Acc. Chem. Res.,
1998, 31, 405; (c) S. Kassem, T. van Leeuwen, A. S. Lubbe, M. R. Wilson,
Fig. 4 Relative emission intensity at 485 nm of 1 in the presence of (a) 1 equiv.
of various cations and (b) increasing amount of Na in DMSO with an increasing
amount of water (10% to 90%).
+
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B. L. Feringa and D. A. Leigh, Chem. Soc. Rev., 2017, 46, 2592; 10 (a) M. Cesario, C. O. Dietrich-Buchecker, J. Guilhem, C. Pascard and
(
d) M. Baroncini, L. Casimiro, C. de Vet, J. Groppi, S. Silvi and
J.-P. Sauvage, J. Chem. Soc., Chem. Commun., 1985, 244;
(b) D. B. Amabilino, C. O. Dietrich-Buchecker, A. Livoreil, L. P ´e rez-
Garc ´ı a, J.-P. Sauvage and J. F. Stoddart, J. Am. Chem. Soc., 1996,
118, 3905; (c) J. A. Berrocal, C. Biagini, L. Mandolini and S. Di
Stefano, Angew. Chem., Int. Ed., 2016, 55, 6997; (d) C. Biagini,
S. Albano, R. Caruso, L. Mandolini, J. A. Berrocal and S. Di Stefano,
Chem. Sci., 2018, 9, 181; (e) L. Zhu, J. Li, J. Yang and H. Y. Au-Yeung,
Chem. Sci., 2020, 11, 13008.
1 C. V. Banks and R. I. Bystroff, J. Am. Chem. Soc., 1959, 81, 6153.
2 (a) C. O. Dietrich-Buchecker, J. P. Sauvage and J. M. Kern, J. Am.
Chem. Soc., 1984, 106, 3043; (b) A.-M. Albrecht-Gary, Z. Saad,
C. O. Dietrich-Buchecker and J.-P. Sauvage, J. Am. Chem. Soc.,
A. Credi, ChemistryOpen, 2018, 7, 169; (e) W. Yang, Y. Li, H. Liu,
L. Chi and Y. Li, Small, 2012, 8, 504; ( f ) J. J. Davis, G. A. Orlowski,
H. Raman and P. D. Beer, Chem. Commun., 2010, 46, 54;
(
g) J. P. Sauvage, Acc. Chem. Res., 1998, 31, 611; (h) H. Liang, B. Hua,
F. Xu, L.-S. Gan, L. Shao and F. Huang, J. Am. Chem. Soc., 2020,
42, 19772; (i) H. Xing, Z. Li, W. Wang, P. Liu, J. Liu, Y. Song, L.
1
Wu Zi, W. Zhang and F. Huang, CCS Chem., 2020, 2, 513; ( j) H. Xing,
Z. Li, Z. L. Wu and F. Huang, Macromol. Rapid Commun., 2018,
1
1
3
9, 1700361.
2
3
(a) C. J. Bruns and J. F. Stoddart, The Nature of Mechanical Bond: from
Molecules to Machines, John Wiley & Sons, New Jersey, 2017, ch. 6,
pp. 555–707; (b) G. Gil-Ram ´ı rez, D. A. Leigh and A. J. Stephens,
Angew. Chem., Int. Ed., 2015, 54, 6110.
1985, 107, 3205; (c) C. O. Dietrich-Buchecker, J.-P. Sauvage and
J.-M. Kern, J. Am. Chem. Soc., 1989, 111, 7791; (d) J. A. Berrocal,
M. M. L. Nieuwenhuizen, L. Mandolini, E. W. Meijer and S. Di
Stefano, Org. Biomol. Chem., 2014, 12, 6167; (e) K.-L. Tong, C.-C. Yee,
Y. C. Tse and H. Y. Au-Yeung, Inorg. Chem. Front., 2016, 3, 348.
3 (a) N. Armaroli, L. De Cola, V. Balzani, J.-P. Sauvage, C. O. Dietrich-
Buchecker, J.-M. Kern and A. Bailal, J. Chem. Soc., Dalton Trans.,
For examples of catenane-based optical switches: (a) Y. Zhang,
Q. Chen, Y. Wang, X. Zheng, H. Wang, F. Cao, A. C.-H. Sue and
H. Li, Chem. Commun., 2020, 56, 11887; (b) J. Sun, Y. Wu, Y. Wang,
Z. Liu, C. Cheng, K. J. Hartlieb, M. R. Wasielewski and J. F. Stoddart,
J. Am. Chem. Soc., 2015, 137, 13484; (c) C.-Y. Tsai, C.-C. Lai, Y.-H. Liu,
S.-M. Peng, R. P. Cheng and S.-H. Chiu, J. Org. Chem., 2018, 83, 5619.
(a) D. A. Leigh, J. K. Y. Wong, F. Dehez and F. Zerbetto, Nature, 2003,
1
1
993, 3241; (b) C. Dietrich-Buchecker and J.-P. Sauvage, Chem.
Commun., 1999, 615.
4 Binding constants of 1 to Li , Na and Ca obtained by flurores-
4
4
3
24, 174; (b) J. V. Hern ´a ndez, E. R. Kay and D. A. Leigh, Science, 2004,
06, 1532; (c) W. Zhou, J. Li, X. He, C. Li, J. Lv, Y. Li, S. Wang, H. Liu
+
+
2+
1
1
À1
À1
À1
cence titration are 7200 M , 7300 M and 9600 M respectively;
see ESI† for details.
and D. Zhu, Chem. – Eur. J., 2008, 14, 754; (d) Y.-C. You, M.-C. Tzeng,
C.-C. Lai and S.-H. Chiu, Org. Lett., 2012, 14, 1046; (e) Z. Meng,
J.-F. Xiang and C.-F. Chen, Chem. Sci., 2014, 5, 1520.
(a) S. Karuppannan and J.-C. Chambron, Chem. – Asian J., 2011,
6
5 (a) B. Champin, P. Mobian and J.-P. Sauvage, Chem. Soc. Rev., 2007,
36, 358; (b) S. Durot, F. Reviriego and J.-P. Sauvage, Dalton Trans.,
5
6
2010, 39, 10557; (c) J. E. Beves, A. A. Blight, C. J. Campbell,
, 964; (b) X.-Q. Wang, Q.-H. Ling, W. Wang and L. Xu, Mater. Chem.
D. A. Leigh and R. T. McBurney, Angew. Chem., Int. Ed., 2011,
0, 9260; (d) W.-X. Gao, H.-J. Feng, B.-B. Guo, Y. Lu and G.-X. Jin,
Front., 2020, 4, 3190.
5
For examples of polarity-driven switching: (a) K. Yamauchi,
A. Miyawaki, Y. Takashima, H. Yamaguchi and A. Harada, J. Org.
Chem., 2010, 75, 1040; (b) S. Dong, J. Yuan and F. Huang, Chem. Sci.,
Chem. Rev., 2020, 120, 6288.
6 (a) M. Cesario, C. O. Dietrich, A. Edel, J. Guilhem, J. P. Kintzinger,
C. Pascard and J. P. Sauvage, J. Am. Chem. Soc., 1986, 108, 6250;
1
2
014, 5, 247; (c) T. A. Barendt, L. Ferreira, I. Marques, V. F ´e lix and
(
b) C. Biagini, F. Di Pietri, L. Mandolini, O. Lanzalunga and S. Di
P. D. Beer, J. Am. Chem. Soc., 2017, 139, 90260.
Stefano, Chem. – Eur. J., 2018, 24, 10122.
7 For the complex acid-base equilibria involving multiple basic nitrogens
in 1, and because protonation near the pyrene may also affect its
7
(a) T. F ¨o rster, Angew. Chem., Int. Ed. Engl., 1969, 8, 333; (b) J. B. Birks, Rep.
Prog. Phys., 1975, 38, 903; (c) F. M. Winnik, Chem. Rev., 1993, 93, 587.
K. Wang, C.-C. Yee and H. Y. Au-Yeung, Chem. Sci., 2016, 7, 2787.
(a) J. B. Birks, Photophysics of aromatic molecules, Wiley-Interscience,
New York, 1970; (b) G. K. Bains, S. H. Kim, E. J. Sorin and
V. Narayanaswami, Biochemistry, 2012, 51, 6207.
1
8
9
a
emission, pK measured from fluorescence titration of 1 may not
reliably reflect the basicity of 1. See ESI† for details.
18 J. Andreasson and U. Pischel, Chem. Soc. Rev., 2018, 47, 2266.
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