Interlocked Photo-degradable Macrocycles Allow One-Off Photo-triggerable Gelation of Organo- and Hydrogelators

Article abstract of DOI:10.1002/chem.201705753

[2]Rotaxanes displaying one-off photo-triggerable gelation properties have been synthesized through the “clipping” of photo-degradable macrocycles around the amide or urea functionalities of organo- and hydrogelators. Irradiation with UV-light cleaved the

Full text of DOI:10.1002/chem.201705753

A Journal of
Accepted Article
Title: Interlocked Photo-Degradable Macrocycles Allow One-Off Photo-
Triggerable Gelation of Organo- and Hydrogelators
Authors: Sheng-Hsien Chiu, Shun-Te Tung, Hung-Te Cheng, Alex
Inthasot, Fang-Che Hsueh, Pei-Cong Yan, Ting-Jia Gu, and
Chien-Chen Lai
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To be cited as: Chem. Eur. J. 10.1002/chem.201705753
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10.1002/chem.201705753
Chemistry - A European Journal
A EUROPEAN JOURNAL
Interlocked Photo-Degradable Macrocycles Allow One-Off Photo-
Triggerable Gelation of Organo- and Hydrogelators
Shun-Te Tung,[a],‡ Hung-Te Cheng,[a],‡ Alex Inthasot,[a] Fang-Che Hsueh,[a] Ting-Jia
Gu,[a] Pei-Cong Yan,[a] Chien-Chen Lai,[b] and Sheng-Hsien Chiu*[a]
[a] Dr. S.-T. Tung, H.-T. Cheng, Dr. A. Inthasot, F.-C. Hsueh, T.-J. Gu, P.-C. Yan,
and Prof. S.-H. Chiu
Department of Chemistry and Center for Emerging Material and Advanced
Devices, National Taiwan University
No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan, 10617, R.O.C.
E-mail: shchiu@ntu.edu.tw
[b] Prof. C.-C. Lai
Institute of Molecular Biology, National Chung Hsing University and
Department of Medical Genetics, China Medical University Hospital,
Taichung, Taiwan, R.O.C.
‡
These authors contributed equally to this study.
Supporting information for the article
http://doi.org/10.1002/chem.201705753
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1
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Abstract
[2]Rotaxanes displaying one-off photo-triggerable gelation properties have been
synthesized through the “clipping” of photo-degradable macrocycles around the
amide or urea functionalities of organo- and hydrogelators. Irradiation with UV light
cleaved the photo-labile macrocyclic components from the [2]rotaxanes, resulting in
the free gelators being released into solution and, thereafter, forming gels. When the
rate of gelation was sufficiently rapid, selective gelation of specific regions of the
solution—and, indeed, photo-patterning of the solution—was possible.
Main Text
Gels formed from low-molecular-weight gelators are useful materials in various
fields, including foodstuffs, pharmaceuticals, biomedicine, and energy.[1] Although
tremendous numbers of gelators have been developed, our continued inability to fully
control noncovalent interactions means that many continue to be discovered through
trial-and-error. Therefore, many unique structures exist for gelators—and small
alterations may change their aggregation behavior significantly. Photo-controllable
gelators, which undergo sol–gel transformations upon irradiation, would appear to
have greater practical value than classic heat-and-cool gelators, because creating
and/or transferring a hot solution may not be convenient in a device setting.[2]
Nevertheless, covalently introducing a photo-responsive motif into the structure of a
known gelator might not always be a practical approach toward preparing photo-
responsive gelators—the valuable properties of the original gelator might not be
retained after such structural alteration. Because one-off photo-triggerable materials,
2
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such as those used with UV curing in dentistry and semiconductors, have proven to be
valuable in our daily lives, the question arises: Can we develop a general strategy to
introduce one-off photo-triggerable behavior into known gelators without changing
their original structures or synthetic pathways, thereby extending their practical use?
In contrast to previous examples of gels formed from solutions of rotaxanes[3] or
polyrotaxanes,[4] we suspected that interlocking a photo-cleavable macrocyclic
component around a known gelator molecule would introduce steric bulk and/or
functional group shielding[5] and, thereby, inhibit aggregation of the gelator as a direct
consequence of forming its corresponding rotaxane;[6] subsequent photo-cleavage of
the macrocyclic component would release the free gelator and lead to gelation of the
solution (Figure 1). To make this approach more general, the photo-labile macrocycle
would ideally recognize functionalities present in the structures of many gelators.
Herein, we report an approach for introducing one-off photo-triggerable gelation
properties into known organo- and hydrogelators: using Na+ ions to template the
“clipping” syntheses of corresponding [2]rotaxanes featuring an o-nitrobenzyl[7]–
containing macrocycle encircling their amide and urea functionalities, respectively.
UV light cleaved the interlocked o-nitrobenzyl–containing macrocycle and released
the free gelators; solutiond of the [2]rotaxanes could, therefore, form gel after
irradiation with a suitable amount of light. We also demonstrate the possibility of
selective gelation of particular regions of these solutions, as well as photo-patterning
of thin layers of such solutions.
Figure 1.
Scheme 1.
3
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The macrocycles 1 and 2, which feature a photo-degradable o-nitrobenzyl unit
and a normal benzyl unit, respectively, were obtained from an equimolar mixture (5
mM) of the diamine 3[8] (or 4), the dialdehyde 5,[9] and sodium tetrakis[3,5-
bis(trifluoromethyl)phenyl]borate (NaTFPB)[10] in CHCl3 after reducing the
equilibrium solution with NaBH4, in yields of 72 and 88%, respectively (Scheme 1).
1
The H NMR spectrum of macrocycle 2 in CDCl2CDCl2 did not change after
irradiation at 350 nm at room temperature for 15 min (Figures 2e and 2f).[11] In
contrast, the signals of macrocycle 1 decreased rapidly upon UV irradiation and
became negligible after 6 min (Figures 2a–d), consistent with its photo-degradation.
Figure 2.
Scheme 2.
As the guest for the first clipping reaction, we chose the dumbbell-shaped gelator
6,[12] which forms organogels in toluene, hexanes, and dioxane; it features amide
functionalities between its perylene bisimide core and two sizable terminal groups
(Scheme 2). Thus, we heated an equimolar mixture of the gelator 6, the diamine 4,
the dialdehyde 5, and NaTFPB in CDCl3 (5 mM) at 333 K for 4 h (i.e., until
equilibrium had been reached).[8] Reduction of the resulting solution led to isolation
of the [2]rotaxane 7 in 16% yield, together with a 58% yield of the recycled free
gelator 6. After considering the reaction efficiency and solubility of the free gelator 6,
we selected CDCl2CDCl2 as the solvent for examining (1H NMR spectra) the photo-
induced dissociation of the [2]rotaxane 7. The signals of the [2]rotaxane 7 in
CDCl2CDCl2 were slightly broad, suggesting that even when one of the amide
functionalities was encircled by the macrocycle 1, some degree of aggregation
remained unavoidable under these conditions, presumably because of intramolecular
4
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hydrogen bonding and -stacking of the free amide and perylene diimide units,
respectively. Upon irradiation of a CDCl2CDCl2 solution of the [2]rotaxane 7 at 350
nm, the spectrum recorded after 3 min revealed the appearance of intense
characteristic signals belonging to the free gelator 6 and the consumption of those
representing the [2]rotaxane 7 (Figure 3). The free gelator 6 became the predominant
product in the irradiated solution after 9 min (Figures 3f and 3g). These spectral
features were consistent with the free gelator 6 having been released from the
[2]rotaxane 7 through photo-cleaving of the interlocked macrocyclic component 1.
Figure 3.
Figure 4.
Having confirmed its photo-degradation ability, we found that the [2]rotaxane 7
could be dissolved in dioxane at a concentration of 20 mg/mL (containing 15 mg/mL
of 6) without forming a gel. The critical gel concentration (CGC) of the gelator 6 in
dioxane is reported to be less than 4.8 mg/mL (2 mM) at 298 K;[11] thus, the encircling
of the macrocycle 1 around one of the amide units of the gelator 6 inhibited the
gelation aggregation of the [2]rotaxane 7 and increased the amount of the gelator 6 (in
interlocked form) that could be dissolved in dioxane. Irradiation of a dioxane solution
of the [2]rotaxane 7 (3 mM; containing 10 mg of 7) at 350 nm for 9 min, then leaving
the sample at room temperature for 30 min, led to gelation of the solution; subsequent
column chromatography resulted in isolation of 7 (2.9 mg, 29% recovery yield) and
the free gelator 6 (5.1 mg; 96% yield). Thus, gelation of this solution occurred before
all the molecules of the [2]rotaxane had dissociated—namely, at the point where the
free gelator had accumulated in the solution at a concentration higher than its CGC.
In theory, if the gelation process were sufficiently rapid to minimize diffusion of the
5
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free gelator, selective gelation should be possible only in the particular regions of the
solution exposed to light. Accordingly, we covered (aluminum foil) the top half of a
dioxane solution of the [2]rotaxane 7 (3 mM) in an NMR tube and then irradiated (UV
light, 350 nm) the whole tube for 9 min. As displayed in Figure 4a, only the bottom
part of the solution that had been irradiated formed a gel—the top half, protected from
the light by the aluminum foil, remained a liquid. Thus, encircling the photo-labile
macrocycle 1 around the gelator 6 endowed one-off photo-triggerable gelation
properties to the [2]rotaxane 7, with the capability of photo-patterning[13] a solution
through gelation (vide infra).
Scheme 3.
Because hydrogels are more biologically compatible materials than
organogels, we examined whether the same concept could also be applied to construct
photo-triggered hydrogelators. We heated a solution of 8 (an acetylated synthetic
precursor to the urea-containing C3-symmetry hydrogelator 9)[14] with equimolar
amounts (5 mM) of the diamine 4, the dialdehyde 5, and NaTFPB in CDCl3 at 333 K
for 4 h (i.e., until equilibrium had been reached). Subsequent NaBH4-mediated
reduction and saponification led to isolation of the [2]rotaxane 10 in an overall yield
(three steps from 8) of 30% (Scheme 3).[15]
Figure 5.
To prove that the macrocyclic component 1 of the [2]rotaxane 10 could also
be photo-cleaved to release the free gelator 9, we irradiated a solution of the
6
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1
[2]rotaxane 10 (5 mM) in CD3SOCD3 under UV light (350 nm) and used H NMR
spectroscopy to monitor the progress of the reaction (Figure 5). Photo-cleavage of the
[2]rotaxane 10 was relatively rapid, with the characteristic signals of the free gelator 9
appearing already after 1 min of irradiation; the reaction was complete after 9 min.
Figure 6.
The gradual decrease in the intensity of the signals representing the o-nitrobenzyl
unit of the interlocked macrocyclic component 1 and the corresponding increase in the
intensity of the signals (Ha, Hb) representing the free gelator 9 confirmed that the
presence of the gelator in solution was due to the removal of the photo-labile
macrocycle from the [2]rotaxane 10. Because 9 is a hydrogelator, we examined the
photo-triggerable gelation of the [2]rotaxane 10 in water. Although encircling the
somewhat hydrophobic organic macrocycle 1 around the gelator 9 might not have
been expected to enhance the water-solubility of the resulting [2]rotaxane 10, we
found that the presence of the macrocyclic component inhibited the aqueous solution
from gelation, allowing the solubility of the [2]rotaxane 10 to reach 50 mg/mL
(containing 40 mg/mL of 9)—significantly higher than the CGC of the gelator 9 (15
mg/mL). Thus, when using 350-nm light to irradiate a tube containing a degassed
aqueous solution of the [2]rotaxane 10 [6.3 mg, 2.5% w/v (25 mg/mL)] for 9 min, the
solution, similar to the reported heat-and-cool process of the gelator 9, formed a gel
after sitting at room temperature for 12 h (Figure 6). After dialysis, the amount of the
[2]rotaxane 10 and the free gelator 9 present in the gel were approximately 1.5 (24%
recovery yield) and 3.6 mg (94% yield), respectively, based on the integration ratio of
signals in the 1H NMR spectrum,[16] again confirming that the gelation did not require
7
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decomposition of all the molecules of the [2]rotaxane. Unlike the situation with the
[2]rotaxane 7, the gelator 9 released after cleaving the macrocyclic component 1 from
the [2]rotaxane 10 required a significantly longer time to form a gel than did the
gelator 6; accordingly, the free gelator 9 had time to diffuse evenly in the solution.
Indeed, even when we used aluminum foil to keep dark the top half of a solution of
the [2]rotaxane 10 in an NMR tube, the whole solution formed a gel after sitting at
room temperature for 12 h (Figure 6).[17] Thus, the aqueous solution of the
[2]rotaxane 10 was not suitable for demonstrating selective gelation and photo-
patterning functions. Nevertheless, such a gelation system might be useful in some
particular conditions; for example, to form a gel from an entire solution when
irradiation of the whole solution is not possible.
Therefore, we selected the [2]rotaxane 7 to examine the feasibility of photo-
patterning gel formation in a solution. To demonstrate that such a patterning could be
achieved under simple conditions, we used a common laboratory hand-held UV lamp
(365 nm, 4 W), rather than a photo-reactor, to irradiate a dioxane solution of the
[2]rotaxane 7 (5 mM; 12 mg/mL) in a quartz cell (250 mm  200 mm  1 mm)
through a mask patterned with the letters “NTU” (representing “National Taiwan
University,” Figure 4) for 1 h. Before removing the mask, the solution was left at
room temperature for 30 min, at which point it had formed a gel, patterned in the form
of the letters NTU, within the solution, revealing the potential applicability of this
strategy to pattern particular gels on desired surfaces. Thus, [2]rotaxanes comprising
photo-degradable macrocyclic components encircling known gelators can not only
introduce photo-triggerable properties to the gelators but also, depending on the
8
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gelation rate, form photo-patternable solutions, thereby increasing the potential
applications and practical value of such gelators.
Using Na+ ions to template the “clipping” of photo-degradable macrocycles
around the amide or urea functionalities of organo- and hydrogelators has allowed the
construction of [2]rotaxanes displaying one-off photo-triggerable gelation properties.
Using UV light to cleave the photo-labile o-nitrobenzene–containing macrocyclic
components from the [2]rotaxanes released the free gelators into solution, thereafter
forming gels. When the gelation rate was sufficiently rapid, selective gelation of
specific regions of the solution—and, indeed, photo-patterning of the solution—was
possible. This interlocking approach avoids the need for thermal gelation processing,
and can introduce one-off photo-triggering behavior to known gelators without the
need to covalently modify their structures. We believe that this approach will extend
the practical applications of organo- and hydrogels.
Acknowledgment
We thank the Ministry of Science and Technology (Taiwan) (MOST-106-2628-M-
002-002) and National Taiwan University (NTU-106R880202) for financial support.
References
[1]
For books and recent reviews, see: a) Molecular Gels (Eds.: R. G. Weiss, P.
Terech), Springer, Dordrecht, 2005; b) Functional Molecular Gels (Eds.: B.
Escuder, J. F. Miravet), Royal Society of Chemistry, Cambridge, 2014; c) A.
Ajayaghosh, V. K. Praveen, C. Vijayakumar, Chem. Soc. Rev. 2008, 37, 109–
9
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10.1002/chem.201705753
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122; d) Y. Li, J. Rodrigues, H. Tomas, Chem. Soc. Rev. 2012, 41, 2193–2221;
e) S. S. Sagiri, B. Behera, R. R. Rafanan, C. P. K. Bhattacharya, I. Banerjee, D.
Rousseau, Soft Mater. 2014, 12, 47–72; f) J.-F. Xing, M.-L. Zheng, X.-M.
Duan, Chem. Soc. Rev. 2015, 44, 5031–5039; g) T. Garg, G. Rath, A. K.
Goyal, Handbook of Encapsulation and Controlled Release (Ed.: M. Mishra),
CRC press, Boca Raton, 2016, 697–728; h) H. R. Culver, J. R. Clegg, N. A.
Peppas, Acc. Chem. Res. 2017, 50, 170–178; i) N. Oliva, J. Conde, K. Wang,
N. Artzi, Acc. Chem. Res. 2017, 50, 669–679.
[2]
For recent examples, see: a) E. R. Draper, D. J. Adams, Chem. Commun. 2016,
52, 8196–8206; b) E. Borre, S. Bellemin-Laponnaz, M. Mauro, Chem. Eur. J.
2016, 22, 18718–18721; c) Q. Zhang, D. Qu, X. Ma, H. Tian, Chem. Commun.
2013, 49, 9800–9802; d) X. Che, B. Bai, T. Zhang, C. Zhang, C. Zhang, P.
Zhang, H. Wang, M. Li, New J. Chem. 2017, 41, 8614–8619; e) V. X. Truong,
F. Li, J. S. Forsythe, ACS Macro Lett. 2017, 6, 657–662.
[3]
[4]
a) K. Yamabuki, Y. Isobe, K. Onimura, T. Oishi, Polym. J. 2008, 40, 205–
211; b) S. Dong, J. Yuan, F. Huang, Chem. Sci. 2014, 5, 247–252; c) N. Sun,
X. Xiao, W. Li, J. Jiang, Adv. Sci. 2015, 2, 1500082.
For recent examples, see: a) K. Ohmori, I. A. Bin, T. Seki, C. Liu, K. Mayumi,
K. Ito, Y. Takeoka, Chem. Commun. 2016, 52, 13757–13759; b) K. Iwaso, Y.
Takashima, A. Harada, Nature Chem. 2016, 8, 625–632; c) A. Goujon, T.
Lang, G. Mariani, E. Moulin, G. Fuks, J. Raya, E. Buhler, N. Giuseppone, J.
Am. Chem. Soc. 2017, 139, 14825–14828.
10
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[5]
For an example of using anions to control the sol–gel transition of a
[2]rotaxane through exposure/blocking of an urea station, see: a) S.-Y. Hsueh,
C.-T. Kuo, C.-C. Lai, Y.-H. Liu, H.-F. Hsu, S.-M. Peng, C.-h. Chen, S.-H.
Chiu, Angew. Chem. 2010, 122, 9356–9359, Angew. Chem. Int. Ed. 2010, 49,
9170–9173. For examples of rotaxanes in which the host units protect the
guest units from unwanted external degradation, see: b) A.-M. Albrecht-Gary,
Z. Saad, C. O. Dietrich-Buchecker, J.-P. Sauvage, J. Am. Chem. Soc. 1985,
107, 3205–3209; c) K. Uekama, F. Hirayama, T. Irie, Chem. Rev. 1998, 98,
2045–2076; d) A. H. Parham, B. Windisch, F. Vögtle, Eur. J. Org. Chem.
1999, 1233–1238; e) E. Arunkumar, N. Fu, B. D. Smith, Chem. Eur. J. 2006,
12, 4684–4690; f) A. Fernandes, A. Viterisi, F. Coutrot, S. Potok, D. A. Leigh,
V. Aucagne, S. Papot, Angew. Chem. 2009, 121, 6565–6569, Angew. Chem.
Int. Ed. 2009, 48, 6443–6447; g) C. B. Caputo, K. Zhu, V. N. Vukotic, S. J.
Loeb, D. W. Stephan, Angew. Chem. 2013, 125, 994–997, Angew. Chem. Int.
Ed. 2013, 52, 960–963.
[6]
Supramolecular encapsulation can also affect the aggregation of
corresponding pseudorotaxanes in the solid state, such that the fluorescence
emissions of the solids can become tunable; see: X. Hou, C. Ke, C. J. Bruns, P.
R. McGonigal, R. B. Pettman, J. F. Stoddart, Nature Commun. 2015, 6, 6884.
[7]
C. G. Bochet, Tetrahedron Lett. 2000, 41, 6341–6346; b) K. K. Tanabe, C. A.
Allen, S. M. Cohen, Angew. Chem. 2010, 122, 9924–9927, Angew. Chem. Int.
Ed. 2010, 49, 9730–9733; c) H. Zhao, E. S. Sterner, E. B. Coughlin, P. Theato,
Macromolecules 2012, 45, 1723–1736; d) A. Goujon, G. Mariani, T. Lang, E.
11
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10.1002/chem.201705753
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Moulin, M. Rawiso, E. Buhler, N. Giuseppone, J. Am. Chem. Soc. 2017, 139,
4923–4928.
[8]
[9]
S.-T. Tung, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Angew. Chem. 2013,
125, 13511–13514, Angew. Chem. Int. Ed. 2013, 52, 13269–13272.
T.-H. Ho, C.-C. Lai, Y.-H. Liu, S.-M. Peng, S.-H. Chiu, Chem. Eur. J. 2014,
20, 4563–4567.
[10] a) S. H. Strauss, Chem. Rev. 1993, 93, 927–942; b) I. Krossing, I. Raabe,
Angew. Chem. 2004, 116, 2116–2142, Angew. Chem. Int. Ed. 2004, 43, 2066–
2090; c) J. Pérez, L. Riera, L. Ion, V. Riera, K. M. Anderson, J. W. Steed, D.
Miguel, Dalton Trans. 2008, 878–886; d) C. Gaeta, F. Troisi, P. Neri, Org.
Lett. 2010, 12, 2092–2095; e) N.-C. Chen, C.-J. Chuang, L.-Y. Wang, C.-C.
Lai, S.-H. Chiu, Chem. Eur. J. 2012, 18, 1896–1900; f) Y.-J. Lee, K.-S. Liu,
C.-C. Lai, Y.-H. Liu, S.-M. Peng, R. P. Cheng, S.-H. Chiu, Chem. Eur. J. 2017,
23, 9756–9760.
[11] The reaction mixture was placed in an NMR tube; the photo-cleavage reaction
was performed using a Rayonet RPR-200 photoreactor, containing 16 lamps
(24 W, 350 nm).
[12] X.-Q. Li, V. Stepanenko, Z. Chen, P. Prins, L. D. A. Siebbeles, F. Wurthner,
Chem. Commun. 2006, 3871–3873.
[13] For recent examples, see: a) D. J Cornwell, B. O. Okesola, D. K Smith, Angew.
Chem. 2014, 126, 12699–12673, Angew. Chem. Int. Ed. 2014, 53, 12461–
12465; b) D. J. Cornwell, O. J. Daubney, D. K. Smith, J. Am. Chem. Soc. 2015,
12
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137, 15486–15492; c) E. E. Oseland, Z. J. Ayres, A. Basile, D. M. Haddleton,
P. Wilson, P. R. Unwin, Chem. Commun. 2016, 52, 9929–9932; d) X. He, J.
Fan, J. Zou, K. L. Wooley, Chem. Commun. 2016, 52, 8455–8458; e) J. H.
Lee, S. H. Jung, S. S. Lee, K.-Y. Kwon, K. Sakurai, J. Jaworski, J. H. Jung,
ACS Nano 2017, 11, 4155–4164.
[14] M. Yamanaka, N. Haraya, S. Yamamichi, Chem. Asian J. 2011, 6, 1022–1025.
[15] Because we used only 1 equiv. of the diamine and the dialdehyde in the
clipping reaction, and because the interlocked imino macrocycles of the
rotaxanes were somewhat labile under the conditions of the NaBH4-mediated
reduction, we were unable to isolate any corresponding [3]rotaxanes from the
reduction products.
[16] The estimation was based on a rough assumption that the total amount of the
free and interlocked gelators stayed the same before and after the reaction.
[17] After dialysis, the presence of 1.8 mg of the free gelator 9 in the gel was
1
estimated based on the integration ratio of signals in the H NMR spectrum
(ref. [12]), corresponding to a concentration (7.2 mg/mL) lower than the
reported CGC (15 mg/mL, ref. [11]). We suspect that the observed lower
gelation concentration of the free gelator 9 arose mainly from the smaller
diameter of the tube containing its solution (6.2 vs. 4.2 mm) and/or
participation of the two free urea functionalities in the rotaxane 10. After
purifying the gelator 9 through both dialysis and reversed-phase HPLC, we
determined the CGC to be no higher than 6 mg/mL in a normal NMR tube
(4.2 mm in diameter).
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Scheme and Figure legends
Figure 1. Cartoon representation of the concept of endowing one-off photo-
triggerable properties to known gelators.
Figure 2. 1H NMR spectra (400 MHz, CDCl2CDCl2, 298 K) recorded after
irradiation (at 350 nm) of a–d) macrocycle 1 (5 mM) for a) 0, b) 1, c) 2,
and d) 6 min and e, f) macrocycle 2 (5 mM) for e) 0 and f) 15 min.
Figure 3. 1H NMR spectra (400 MHz, CDCl2CDCl2, 298 K) of a–f) the
[2]rotaxane 7 after irradiation (350 nm) for a) 0, b) 1, c) 3, d) 5, e) 7, and
f) 9 min and g) the free gelator 6.
Figure 4. Photographs demonstrating a) the selective photo-triggerable gelation of
a dioxane solution of the [2]rotaxane 7 [3 mM (7.2 mg/mL); 9 min in a
photo-reactor (350 nm)] and b) the photo-patterned gelation of a thin
layer of a solution of 7 [5 mM (12 mg/mL); 1 h under a laboratory hand-
held UV lamp (4 W, 365 nm)] through a mask displaying the letters
“NTU.” Samples were left at room temperature for 30 min after
irradiation.
Figure 5. 1H NMR spectra (400 MHz, CD3SOCD3, 298 K) of a–e) the [2]rotaxane
10 after irradiation with light (350 nm) for a) 0, b) 1, c) 2, d) 5, and e) 9
min and f) the free gelator 9.
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Figure 6. Photographs demonstrating a) the photo-triggerable gelation of an
aqueous solution of the [2]rotaxane 10 [2.5% (25 mg/mL); 9 min in a
photo-reactor (350 nm)] and b) the gelation of the whole sample after
irradiating the bottom portion of an aqueous solution of the [2]rotaxane
10 [2.5% (25 mg/mL); 9 min in a photo-reactor (350 nm)] in a NMR
tube. Samples were left at room temperature for 12 h after irradiation.
Scheme 1. Synthesis of the macrocycles 1 and 2.
Scheme 2. “Clipping” synthesis of the [2]rotaxane 7 from the organogelator 6.
Scheme 3. “Clipping” synthesis of the [2]rotaxane 10 from the hydrogelator 8.
Text for Table of Contents
“Clipping” a photo-degradable macrocycle around the amide or urea functionalities of
organo- and hydrogelators has provided [2]rotaxanes displaying one-off photo-
triggerable gelation properties—in one case allowing photo-patterning of a solution
with specific “letters” of gel.
Keywords
gel • photo-cleavage • photo-patterning • rotaxane • template
15
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10.1002/chem.201705753
Chemistry - A European Journal
clipping
gelator
solution
h
gel
Figure 1.
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10.1002/chem.201705753
Chemistry - A European Journal
PyCH2NCH2Ar
a)
b)
N
+
O2N
H
H
H
Ar-CH2-O
OCH2CH3O
Py-O-CH2
H
H
H
H
c)
d)
e)
H
H
OCH2CH2O
PyCH2NCH2Ar
Py-O-CH2
H
H
N
Ar-CH2-O
f)
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
Figure 2.
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10.1002/chem.201705753
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a)
O
O2N
H
H
H
HN
H
H
H
perylene H
Ar-CH2-O
b)
c)
d)
e)
f)
H
H
H
O
perylene H
8.5
g)
Ar-O-CH2
HN
NH
H
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
Figure 3.
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10.1002/chem.201705753
Chemistry - A European Journal
a)
1. h
flip
2. remove
aluminum
foil
b)
add mask
h
then remove mask
Figure 4.
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10.1002/chem.201705753
Chemistry - A European Journal
a)
O
O2N
H
H
anomeric
H
O
O
N
N
OH
H
H
H
H
b)
c)
d)
e)
f)
O
Hg
OCH2CH2O
glucose H
glucose OH
anomeric H
Hf
Hh
Hc
Hb
He
N
N
H
H
Hd
Ha
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Figure 5.
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10.1002/chem.201705753
Chemistry - A European Journal
a)
flip
h
12 h
b)
remove
aluminum
foil
flip
h
12 h
Figure 6.
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10.1002/chem.201705753
Chemistry - A European Journal
O
O
O
O
O
X
N
NaTFPB
H
H
+
+
OR1
NH2
H2N
R1 = C6H13
X = H
X = NO2
3
4
5
1. heat
2. NaBH4
O
O
O
X
NH
HN
N
X = NO2
X = H
1
2
R1 = C6H13
OR1
Scheme 1.
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R2O
R2O
O
N
O
O
N
O
OR2
OR2
OR2
O
O
HN
NH
R2O
6
R2 = C12H25
4 / 5 / NaTFPB
O
O
N
O
N
Na+
O
OR2
OR2
OR2
R1 = C6H13
R2O
R2O
O
O
O
O2N
N
O
N
N
H
HN
R2O
O
R2 = C12H25
N
OR1
NaBH4
OR1
R1 = C6H13
N
OR2
OR2
OR2
NH HN
O
R2O
R2O
O
O
N
O
N
O
N
H
HN
R2O
O
O2N
O
O
R2 = C12H25
7
16%
O
Scheme 2.
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10.1002/chem.201705753
Chemistry - A European Journal
R''
O
R''
O
NH
NH
He
Hc
O
Hd
O
Hf
Hh
R''
O
O
Ha
N
H
N
O
H
Hg
R''
O
Hb
OAc
OAc
OAc
O
8
R'' =
O
O
O
O
AcO
OH
OH
OH
O
9
R'' =
O
HN
HN
HO
O
O
1. 4 / 5 / NaTFPB
2. NaBH4
3. NaOMe
R''
R''
O
R''
O
O
R''
O
NH
N
O
HN
R''
NH
O
NH
O
O
O
N
H
N
H
O
R''
O
O2N
O
O
O
HN
OH
OH
OH
O
O
O
R'' =
HN
O
O
HO
30%
R''
R''
10
O
Scheme 3.
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