Ag+-induced reverse vesicle to helical fiber transformation in a self-assembly by adjusting the keto-enol equilibrium of a chiral salicylideneaniline

Article abstract of DOI:10.1039/c5cc05367f

A new chiral amphiphilic salicylideneaniline bearing a terminal pyridine was synthesized. It formed reverse vesicles in toluene. The addition of Ag⁺, however, reversibly transforms these reverse vesicles into left-handed nanohelices accompanied by spontaneous gel formation at room temperature.

Full text of DOI:10.1039/c5cc05367f

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Datta and S.
Bhattacharya, Chem. Commun., 2015, DOI: 10.1039/C5CC05367F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/chemcomm

Please do not adjust margins
ChemComm
Page 1 of 4
View Article Online
DOI: 10.1039/C5CC05367F
ChemComm
COMMUNICATION
Ag+-induced reverse vesicle to helical fiber transformation in a
self-assembly by tinkering around the keto-enol equilibrium of a
chiral salicylideneaniline
Received 00th January 20xx,
Accepted 00th January 20xx
Sougata Datta,a and Santanu Bhattacharya*ab
DOI: 10.1039/x0xx00000x
www.rsc.org/
A new chiral amphiphilic salicylideneaniline bearing a terminal
Aida13a,b and Lee13c independently reported Ag+-induced
pyridine was synthesized. It formed reverse vesicles in toluene. supramolecular assembly by manipulation of non-covalent
Addition of Ag+ to this however, reversibly transforms these interactions at the molecular level. These observations prompted us
reverse vesicles into left-handed nanohelices accompanied by to prepare a novel salicylideneaniline having a terminal pyridine
spontaneous gel formation at room temperature.
and L-alanine based spacer (Figure 1a and Scheme S1, SI). This
compound upon dispersion in toluene adopted spherical
a
Stimuli-responsive supramolecular systems1 endowed with specific
function have received considerable attention owing to their
propensity to undergo specific structural transformation mediated
by an external trigger.2 These examples mimic natural phenomena
like the seismonastic movement of mimosa leaves or tight curling
up of millipedes upon touching.1a A wide range of low molecular-
weight gelators (LMWGs)3 has been examined either as
nanomaterials4 or biomaterials5 due to their diverse nature of
constitution and arrangements at the molecular level.6 There are a
few reports of stimuli- (i.e., light,7 mechanical,8 redox,9 charge-
transfer10 etc.) responsive sphere-to-fiber transformation
morphology via self-assembly in the dispersed sol state due to the
formation of reverse vesicles. This however, transformed reversibly
into left-handed helical nanofibers through the transcription of
molecular chirality into supramolecular helicity by selective
supramolecular response of Ag+ which was also accompanied by gel
formation at room temperature.
The compound 1, when dispersed in toluene, appeared as a
nearly colourless suspension (Figure 1b). However, when an
ethanolic or methanolic solution of AgSO3CF3 was added to 1 in
toluene at a molar ratio of 1:2 [(1)2Ag+, ESI-MS: m/z 1129.64
(C58H84AgN8O8)+], the viscosity of the resulting mixture gradually
increased to form a robust yellow coloured gel (minimum gelator
accompanied by sol-to-gel transition. Yao demonstrated
reversible structural transition between nanofibers and normal
vesicles from the self-assembly of tripeptide-bipyridine
a
concentration [mgc]
=
3.9 mM) quickly in 100/1 (v/v)
a
toluene/ethanol. Whereas, the compound 2 containing a phenyl
ring instead of the 3-pyridyl group did not furnish gel in the
presence of Ag+ (Figure 1a). It may be noted that the addition of an
excess Ag+ (>0.5 equiv.) led to the disruption of the gelation
process. When an equal volume (1 ml) of an aq. solution of EDTA14
(4 mM) was placed on the top of the gel, and gently stirred for 3
min, the gel transformed completely into a colourless sol. The
mixture was allowed to settle for ~15 min until the aq. and organic
layers phase separated. The stability constants of Ag+-coordination
complexes of pyridine and EDTA are 2 and 7.3 respectively.14b
Therefore, Ag+ could be removed from the organic phase by
partitioning into the aq. solution of EDTA and the yellow gel could
be reverted back to its previous colourless sol form again. The
colourless toluene layer was taken out from the top of the aq.
phase and could be induced to gelation again by addition of Ag+ ion.
The compound 1 however, did not respond to other metal ions,
e.g., Li+, Cu2+, Zn2+, Co2+ and Cr3+ etc. Gelation was not observed also
conjugate.8 There are also other examples of vesicle-to-fiber
transformation that are devoid of sol-to-gel transition.11 However,
reverse vesicle-to-helical fiber transformation accompanied by sol-
to-gel transition is still not known.
Salicylideneanilines and related compounds are interesting
because of their intrinsic photochromic and/or thermochromic
properties, as originated from the variation of population of the
enol (–OH) and keto (–NH) forms due to their propensity to
tautomerize.12 Lu et al. reported a remarkable thermochromism
from
a
salicylideneaniline organogelator.12d By following the
equilibrium between the enol and keto forms, an evidence of
thermochromism in a salicylideneaniline gel was established with
the help of 1H-NMR spectroscopy.12c
a.Department of Organic Chemistry, Indian Institute of Science, Bangalore, India.
Fax: +91-80-23600529; Tel: +91-80-22932664; E-mail: sb@orgchem.iisc.ernet.in
b.Chemical Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore, India
Electronic Supplementary Information (ESI) available. See
DOI: 10.1039/x0xx00000x
-
in the presence of n-Bu4N+SO3CF3 . This excludes the role of triflate
anion, which was only chosen to have adequate solubility of Ag+ in
an organic medium.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
View Article Online
DOI: 10.1039/C5CC05367F
COMMUNICATION
Journal Name
presence of a hydrophobic dye, Nile red (0.39 mM).18 Free dye
could be removed by dialyzing the sample against toluene for ~72 h.
When the dialyzed sample was examined under a fluoresence
microscope, red-light emitting spherical aggregates (1-10 µm) were
observed (Figure S30a, SI). This result clearly suggests the presence
of an inner hydrophobic compartment inside these spherical
aggregates (Figure S30b, SI). The hollow nature of the spherical
assemblies (50-200 nm) was further evident from the difference in
contrast between the periphery and the inner part of the nano-
spheres in the TEM image (Figure S31a-b, SI).8,18,19 Dynamic light
scattering (DLS) experiment was performed to acquire information
regarding the average hydrodynamic diameters of the reverse
vesicles. Toluene sol of 1 afforded two types of aggregates of ~0.2
and ~2 µm (Figure S32, SI). This result is in good accordance with
the different sizes observed under SEM, AFM and TEM experiments.
The average size (z-average diameter) and the polydispersity index
(PDI) of the reverse vesicles of 1 (0.39 mM) obtained from DLS
experiment are 983.5 ± 0.7 nm and 0.429 ± 0.03 respectively.
Fig. 1 (a) Molecular structures of the salicylideneanilines (1-3); (b)
photographs showing Ag+-mediated reversible sol-to-gel transition
of 1 (3.9 mM) in toluene in presence of 1% EtOH (v/v).
In Raman spectra, the pyridyl ring of 1 in the breathing mode at
990 cm-1 shifted to 1020 cm-1 after its coordination with Ag+ (Figure
S24, SI). The band shift may be regarded as a sign of the pyridyl
coordination of Ag+.15 The complexation of Ag+ with 1 was also
investigated using 1H-NMR spectroscopy. With the addition of 0.5
equiv. of AgSO3CF3 in CD3OD (1% v/v) to the [D6]benzene solution of
1, the ortho- and meta-protons of the pyridyl group of 1 shifted
upfield, and that of the para-proton of the pyridyl group shifted
downfield (Figure S25, SI).15,16 As shown in Figure S26 (SI), a broad
absorption band appeared in the range of 400-500 nm12c-e in the
UV-Vis spectrum of Ag+-complex of
1
in 100:1 (v/v)
toluene/ethanol. This however, did not appear in the case of 1
alone, indicating the conversion to a higher population of keto form
after Ag+ complexation. CD-spectra of
1 in 100:1 (v/v)
toluene/ethanol showed only one negative Cotton effect at 290 nm
and a shoulder at 330 nm as a result of π-π* and n-π* transitions
related to the π- and non-bonding electrons (Figure S27, SI).17
However, a new negative peak near 400 nm associated with the
salicylideneaniline chromophore appeared in the Ag+-coordination
complex, which suggests an anti-clockwise orientation of dipoles in
the supramolecular aggregates. Figure S28 (SI) shows cyclic
Fig. 2. (a and b) SEM and (c and d) AFM images of 1 and its Ag+-
coordination complex in 100:1 toluene/EtOH (v/v).
However, when the toluene gel formed upon Ag+-coordination
of 1 was examined under SEM, presence of fibrous networks (width
1-5 µm) was clearly observed (Figure 2b). Interestingly, AFM image
of Ag+-complex of 1 unveiled fibrous assemblies with entangled left-
handed-helical architecture of high aspect ratio with widths of
about 50-100 nm (Figure 2d and S29b, SI). Coexistence of reverse
vesicles and helical nanofibers was found in case of intermediate
stoichiometry of Ag+ (0.25 equiv.) due to partial structural
transformation (Figure 33a and 33b). Furthermore it is noteworthy
that these helical nanofibers could be converted to reverse vesicles
by the removal of Ag+ upon treatment of an aq. solution of EDTA.
The achiral analogue (3) of compound 1 (Figure 1a) containing β-
alanine spacer instead of L-alanine also formed reverse vesicles
(0.1-2 µm) in toluene (Figure S34a and S34c, SI). However, micro
tape-like morphology was found in the xerogel of the corresponding
Ag+-coordination complex of compound 3 (Figure S34b and S34d,
SI). This result clearly indicates that the formation of helical
voltammetry plots of
toluene/acetonitrile mixture in presence of 0.1 (M) n-Bu4N+PF6- as a
supporting electrolyte. Half-wave reduction potential of
1
and its Ag+-complex in 5:1 (v/v)
1
associated with the pyridyl group appeared at -1.06 V which shifted
to -0.87 V after complexation with Ag+.
Scanning electron microscopy (SEM) of the toluene sol of 1
revealed the presence of spherical aggregates with diameters of 5-
20 µm (Figure 2a). Morphology of 1 in toluene was further
investigated by atomic force microscopy (AFM). The height images
(Figure 2c and S29a, SI) obtained by tapping-mode on freshly
cleaved mica sheets revealed the formation of nano- to micro-sized
vesicle-like spherical aggregates (0.1-1 µm). In order to confirm the
existence of reverse vesicles, a dye encapsulation experiment was
performed by preparing a toluene dispersion of 1 (3.9 mM) in the
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 3 of 4
View Article Online
DOI: 10.1039/C5CC05367F
Journal Name
COMMUNICATION
nanofibers by Ag+-coordination complex gel of 1 is attributed to the CDCl3, a cross peak was observed as associated with the H3-H6
transcription of molecular chirality associated with the L-alanine correlation (Figure S17, SI). This result indicates that the pyridyl N
spacer into supramolecular helicity.
atom remains in the same side of the OH group of the salicylidene
Figure S35 (SI) shows 1H-NMR spectra of the colourless sol of 3.9 ring (Figure S38, SI). While, the H1-H6 correlation was observed in
1
mM 1 in [D6]benzene in presence of CD3OD (1% v/v). Two H-NMR the H-H NOESY spectrum (Figure S21, SI) of the compound 1 in C6D6
signals appear at δ = 12.5 and 13.5 respectively. These may be indicating an anti-arrangement between the pyridyl N atom and the
interpreted due to the existence of an equilibrium between the OH group of the salicylidene ring (Figure S38, SI). This arrangement
enol (–OH) and keto (–NH) forms. The peak that appears at δ = 13.5, is favourable for the inter-molecular H-bonding between the N-
is assigned to the -OH form because of the higher electronegativity atom of the pyridyl group and the hydrogen atom of the ortho-
of O than that of N.12c The peak associated with the enol form at δ = hydroxy group to give rise to a lamellar organization which finally
13.5 is more intense and sharper compared to that of the keto form leads to the formation of reverse vesicles in C6D6 (Figure 3).
which appears at δ = 12.5. Thus the population of the colourless
enol form is predominant in the toluene sol of 1.12c Interestingly,
the 1H-NMR spectrum of the gel formed upon Ag+ coordination of 1
(Ag+:1 = 1:2) shows a single peak at δ = 12.5 associated with the
keto form and the signal at δ = 13.5 corresponding to the enol form
disappears. This suggests that the keto form exists almost
exclusively in the yellow gel phase. Consistent with the results of
the 1D-NMR experiment, two peaks at δ = 12.5 and 13.5 associated
with the keto and enol forms respectively were observed along the
diagonal of the H-H COSY spectrum of compound 1 in C6D6 (Figure
S20, SI). In addition, a cross peak corresponding to the NH-H6
correlation associated with the keto form was observed. In contrast
only a single peak along the diagonal at δ = 12.5 and a cross peak
corresponding to the NH-H6 correlation associated with the keto
form were observed in the H-H COSY spectrum of the Ag+
coordination complex gel of 1 in C6D6 (Figure S23, SI). This result
again confirms the exclusive existence of the keto form in the C6D6
gel phase while the enol form is predominant in the sol state in
C6D6. It is also important to note that a single peak at δ = 13.2
associated with the enol form of 1 was observed in the NMR-
spectra in CDCl3 indicating the sole existence of the enol form in the
CDCl3 solution presumably because of the lack of aggregation of 1 in
this medium (Figure S1 and S16, SI). According to Ogawa and Arai,20
the energy differences between the ground states of the -OH and -
NH forms in solution may be too large to allow conversion of the
enol to keto form. However, Lu’s group and us independently
Fig. 3 Molecular packing model and a schematic representation of
established that the -NH form could be stabilized in the aggregates
of the gel phase.12c,d This may significantly lower the energy barrier
between the -OH and -NH forms than that in solution, which may in
turn favour the proton tautomerization leading to the formation of
the -NH form (Figure S36, SI). Interestingly, the 1H-NMR spectrum of
the residue obtained by evaporating the toluene layer after
partitioning with the aq. solution of EDTA (4 mM) is identical to that
of 1, elucidating the reversibility of this transformation (Figure S35,
SI). This result clearly explains the colourless nature of the toluene
sol and yellow colour of the Ag+-coordinated gel.
Ag+-induced reverse vesicle to nanohelix transformation.
Prevalence of inter-molecular H-bonding interactions among
the amide linkages of Ag+-coordination complex of 1 in the gel
phase has been further evidenced from the solvent and
concentration-dependent FTIR-spectroscopy (Figure S39, SI). The
small-angle X-ray diffraction pattern of 1 in toluene (Figure S40a, SI)
corresponds to a lamellar arrangement.12c-e,21 In the low-angle
range (2θ ∼1-12°), six peaks with d-spacings of 5.3, 2.65, 1.76, 1.32,
1.06 and 0.88 nm were observed with d-spacing ratios of
1:1/2:1/3:1/4:1/5:1/6 respectively. This is the characteristic of a
lamellar structure with a domain spacing of 5.3 nm, a value less
than the double of its molecular length, 5.8 nm as calculated from
the geometry optimization of one molecule of 1 using B3LYP/6-
31G* (Figure S41, SI). This analysis once again suggests that the
pyridyl heads presumably interdigitate with each other to facilitate
intermolecular H-bonding interactions between the N-atom of the
pyridyl group and the H-atom of the ortho-hydroxy group. In
contrast, the longest repeat distance shifts from 5.3 to 5.9 nm in
Since the solution of 1 in CHCl3 did not exhibit spherical
nanostructures, we compared the 1H-NMR spectrum of 1 in CDCl3
with that in C6D6. The OH proton at δ = 13.5 in the 1H-NMR
spectrum of 1 in [D6]benzene shifted to δ = 13.2 in CDCl3 (Figure
S37, SI). Similarly, the pyridyl protons shifted upfield as the solvent
was changed from C6D6 to CDCl3 (Figure S37, SI). These results
illustrate the existence of intermolecular H-bonding between the N-
atom of the pyridyl group and the hydrogen atom of the ortho-
hydroxy group (Figure 3). This was further supported from the 2D-
NMR experiment. In the H-H NOESY spectrum of compound 1 in
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
View Article Online
DOI: 10.1039/C5CC05367F
COMMUNICATION
Journal Name
the Ag+-coordination complex of 1 (Ag+:1 = 1:2), a fact that is clearly
consistent with the proposed model of the structural
transformation (Figure 3 and S40b, SI).
4
5
6
(a) J. Nanda, A. Biswas, B. Adhikari and A. Banerjee, Angew.
Chem. Int. Ed., 2013, 52, 1; (b) S. Bhattacharya, A. Srivastava and
A. Pal, Angew. Chem., Int. Ed., 2006, 45, 2934.
(a) P. K. Vemula and G. John, Acc. Chem. Res., 2008, 41, 769; (b) A.
R. Hirst, B. Escuder, J. F. Miravet and D. K. Smith, Angew. Chem.,
Int. Ed., 2008, 47, 8002.
(a) J. H. Jung, J. H. Lee, J. R. Silverman and G. John, Chem. Soc.
Rev., 2013, 42, 924; (b) T. Tu, W. Fang, X. Bao, X. Li and K. H.
Dötz, Angew. Chem. Int. Ed., 2011, 50, 6601; (c) J. A. Foster and J.
W. Steed, Angew. Chem., Int. Ed., 2010, 49, 6718; (d) M.-O. M.
,
In conclusion, we have demonstrated a self-assembly of a
pyridine appended chiral salicylideneaniline,
1, that forms
reverse vesicles in toluene by adopting a lamellar organization.
Interestingly, the colourless reverse vesicles transform into
helical organizations reversibly on addition of Ag+ accompanied
by a yellow coloured gel formation. This is the first report
where a reverse vesicle-to-helical structural transformation
accompanied by sol-to-gel transition takes place as confirmed
by both microscopy and X-ray diffraction analysis. The
formation of reverse vesicles was further evidenced from a dye
entrapment study. Therefore, this type of structural
transformation may be useful in achieving a stimuli-driven
delivery. Thus a keto-enol-tautomerism associated with the
gel-to-sol transition has been demonstrated unambiguously
using visible colour change, UV-Vis absorption and 1H-NMR
spectral studies. It has been also possible to confirm the
presence of the keto form exclusively in the gel phase by
recognizing a distinguishable 1H-NMR signal. It is may be
further emphasized that examples of reverse vesicles are
scarce compared to the aggregates formed in aq. media
(normal micelles or vesicles). Whenever such reports of
reverse micelles or vesicles are known they are generally
observed from lipids and polymers etc.18a,22 Accordingly the
Piepenbrock, G. O. Lloyd, N. Clarke and J. W. Steed, Chem. Rev.
2010, 110, 1960; (e) P. Dastidar, Chem. Soc. Rev., 2008, 37, 2699. f)
D. J. Abdallah and R. G. Weiss, Ad . Mater., 2000, 12, 1237; (g) P.
Terech and R. G. Weiss, Chem. Re , 1997, 97, 3133.
,
(
v
v
.
7
8
9
G. John, G. Zhu, J. Li and J. S. Dordick, Angew. Chem., Int. Ed.,
2006, 45, 4772.
D. Ke, C. Zhan, A. D. Q. Li and J. Yao, Angew. Chem., Int. Ed.
,
2011, 50, 3715.
X. Miao, W. Cao, W. Zheng, J. Wang, X. Zhang, J. Gao, C. Yang, D.
Kong, H. Xu, L. Wang and Z. Yang, Angew. Chem., Int. Ed., 2013,
52, 7781.
10 M. R. Molla and S. Ghosh, Chem. Eur. J., 2012, 18, 9860.
11 (a) Q. Yan and Y. Zhao, Angew. Chem., Int. Ed., 2013, 52, 9948; (b)
Y. Yan, H. Wang, B. Li, G. Hou, Z. Yin, L. Wu and V. W. W. Yam,
Angew. Chem., Int. Ed., 2010, 49, 9233; (c) J.-H. Ryu, E. Lee, Y.-b.
Lim and M. Lee, J. Am. Chem. Soc., 2007, 129, 4808; (d) A.
Ajayaghosh, P. Chithra and R. Varghese, Angew. Chem. Int. Ed.
,
2007, 46, 230; (e) J.-H. Ryu, H.-J. Kim, Z. Huang, E. Lee and M.
Lee, Angew. Chem., Int. Ed., 2006, 45, 5304; (f) C. Park, I. H. Lee, S.
Lee, Y. Song, M. Rhue and C. Kim, Proc. Natl. Acad. Sci. USA
2006, 99, 5355.
,
12 (a) K. Fan, J. Yang, X. Wang and J. Song, Soft Matter, 2014, 10
,
8370; (b) K. Fan, J. Song, J. Li, X. Guan, N. Tao, C. Tong, H. Shen
and L. Niu, J. Mater. Chem. C, 2013, , 7479; (c) S. Datta and S.
1
formation of reverse vesicles from such
a
simple
Bhattacharya, Chem. Commun., 2012, 48, 877; (d) P. Chen, R. Lu, P.
Xue, T. Xu, G. Chen and Y. Zhao, Langmuir, 2009, 25, 8395; (e) P.
Xue, R. Lu, G. Chen, Y. Zhang, H. Nomoto, M. Takafuji and H.
Ihara, Chem. Eur. J., 2007, 13, 8231.
salicylideneaniline is indeed unprecedented and may spur new
research activity.
This work was supported by J. C. Bose fellowship of DST to
S.B. S.D. thanks CSIR for a senior research fellowship.
13 (a) T. Fukino, H. Joo, Y. Hisada, M. Obana, H. Yamagishi, T.
Hikima, M. Takata, N. Fujita and T. Aida, Science, 2014, 344, 499;
(b) A. Kishimura, T. Yamashita and T. Aida, J. Am. Chem. Soc.
;
2005, 127, 179; (c) H.-J. Kim, J.-H. Lee and M. Lee, Angew. Chem.,
Int. Ed., 2005, 44, 5810.
Notes and references
14 (a) W. Fang, C. Liu, Z. Lu, Z. Sun and T. Tu, Chem. Commun., 2014,
50, 10118; (b) W. Hong, W. Li, X. Hu, B. Zhao, F. Zhang and D.
Zhang, J. Mater. Chem., 2011, 21, 17193.
1
(a) S. Datta and S. Bhattacharya, Chem. Soc. Rev., 2015, DOI:
10.1039/c5cs00093a; (b) A. C. Coleman, J. M. Beierle, M. C. A.
Stuart, B. Maciá, G. Caroli, J. T. Mika, D. J. van Dijken, J. Chen, W.
15 Q. Liu, Y. Wang, W. Li and L. Wu, Langmuir, 2007, 23, 8217.
16 K. Chen, L. Tang, Y. Xia and Y. Wang, Langmuir, 2008, 24, 13838.
17 C. H. Sung, L. R. Kung, C. S. Hsu, T. F. Lin and R. M. Ho, Chem.
Mater., 2006, 18, 352.
18 (a) A. Das and S. Ghosh, Macromolecules, 2013, 46, 3939; (b) X.
Zhang, S. Rehm, M. M. Safont-Sempere and F. Würthner, Nat.
R. Browne and B. L. Feringa, Nat. Nanotechnol., 2011,
Zhang, L. Qin, X. Wang, H. Cao and M. Liu, Adv. Mater., 2014, 26
6959; (d) H. Cao, X. Zhu and M. Liu, Angew. Chem., Int. Ed., 2013,
52, 4122; (e) K. Dan and S. Ghosh, Angew. Chem., Int. Ed., 2013, 52
7300; (f) Z. Zhang, C. Zhan, X. Zhang, S. Zhang, J. Huang, A. D. Q.
Li and J. Yao, Chem. Eur. J., 2012, 18, 12305; (g) D. Ke, C. Zhan, S.
Xu, X. Ding, A. Peng, J. Sun, S. He, A. D. Q. Li and J. Yao, J. Am.
Chem. Soc., 2011, 133, 11022.
(a) K. R. Raghupathi, U. Sridhar, K. Byrne, K. Raghupathi and S.
Thayumanavan, J. Am. Chem. Soc., 2015, 137, 5308; (b) Z. Shen, T.
Wang, L. Shi, Z. Tang and M. Liu, Chem. Sci., 2015, 6, 4267; (c) M.
D. Segarra-Maset, V. J. Nebot, J. F. Miravet and B. Escuder, Chem.
Soc. Rev., 2013, 42, 7086; (d) S. Datta, S. K. Samanta and S.
Bhattacharya, Chem. Eur. J., 2013, 19, 11364; (e) X. Yang, G. Zhang
and D. Zhang, J. Mater. Chem., 2012, 22, 38; (f) C. Wang, Q. Chen,
F. Sun, D. Zhang, G. Zhang, Y. Huang, R. Zhao and D. Zhu, J. Am.
Chem. Soc., 2010, 132, 3092; (g) P. K. Vemula, J. Li and G. John, J.
Am. Chem. Soc., 2006, 128, 8932.
6, 547; (c) L.
,
,
Chem., 2009,
1, 623.
19 (a) J. Zhang, Y.-F. Song, L. Cronin and T. Liu, Chem. Eur. J., 2010,
16, 11320; (b) X.-N. Xu, L. Wang and Z.-T. Li, Chem. Commun.
,
2
2009, 6634.
20 (a) A. Ohshima, A. Momotake and T. J. Arai, Photochem. Photobiol.
, 2004, 162, 473; (b) K. Ogawa and J. Harada, J. Mol. Struct., 2003,
A
647, 211; (c) K. Ogawa, Y. Kasahara, Y. Ohtani and J. Harada, J.
Am. Chem. Soc., 1998, 120, 7107.
21 M. George, S. L. Snyder, P. Terech, C. J. Glinka and R. G. Weiss, J.
Am. Chem. Soc., 2003, 125, 10275.
22 (a) H.-Y. Lee, K. K. Diehn, K. Sun, T. Chen and S. R. Raghavan, J.
Am. Chem. Soc., 2011, 133, 8461; (b) S-H. Tung, H.-Y. Lee and S. R.
Raghavan, J. Am. Chem. Soc., 2008, 130, 8813. (c) D. Domínguez-
Gutiérrez, M. Surtchev, E. Eiser and C. J. Elsevier, Nano Lett., 2006,
3
(a) S. Datta and S. Bhattacharya, Soft Matter, 2015, 11, 1945; (b) P.
Xue, B. Yao, J. Sun, Z. Zhang and R. Lu, Chem.Commun., 2014, 50
,
6, 145; (d) A. Ajayaghosh, R. Varghese, S. Mahesh and V. K.
10284; (c) K. K. Kartha, S. S. Babu, S. Srinivasan and A.
Ajayaghosh, J. Am. Chem. Soc., 2012, 134, 4834; (d) S. R. Jadhav, P.
K. Vemula, R. Kumar, S. R. Raghavan and G. John, Angew. Chem.,
Int. Ed., 2010, 49, 7695.
Praveen, Angew. Chem., Int. Ed., 2006, 45, 7729; (e) S. Basu, D. R.
Vutukuri, S. Thayumanavan, J. Am. Chem. Soc., 2005, 127, 16794.
(f) S. Basu, D. R. Vutukuri, S. Shyamroy, B. S. Sandanaraj and S.
Thayumanavan, J. Am. Chem. Soc., 2004, 126, 9890.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins