Dynamic Article LinksC<Soft Matter

Cite this: Soft Matter, 2011, 7, 2755

www.rsc.org/softmatter PAPER

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

Nanocomposites combining conducting and superparamagnetic componentsprepared via an organogel†

Elena Taboada, Lise N. Feldborg, Angel P�erez del Pino, Anna Roig, David B. Amabilino* andJosep Puigmart�ı-Luis*

Received 1st October 2010, Accepted 15th December 2010

DOI: 10.1039/c0sm01088j

A nanocomposite material combining an organic molecular gelator and oleate-coated iron oxide

nanoparticles in proportions which range from one to fifty weight percent of the inorganic material has

been prepared via the gel state. The proportion of nanoparticles and organic gelator in this mixed

colloidal system gives very different characteristics to the final hybrid xerogel. Characterisation of the

xerogels by transmission electron microscopy shows that at low loadings of the inorganic material

a uniform distribution is observed, while above ten weight percent of nanoparticles a clear phase

separation of the components (organic and inorganic) is revealed. Doping of the organic component of

the xerogels by chemical oxidation results in the formation of conducting composites, whose electrical

characteristics—probed by current sensing atomic force microscopy and spectroscopy—vary

importantly with the amount of iron oxide colloid. The best conductors are found at low loadings of

inorganic particles, at which an interesting alignment of the organic fibres is observed. The work shows

that conducting materials incorporating magnetic particles can be prepared simply through the

organogel route, and raises possibilities for the discovery of new properties that could come from the

combination of these or related systems.

Introduction

The preparation of easily processed materials which combine

electrically conducting and magnetic components is a consider-

able challenge. The difficulty in this area resides in making

a sufficiently conducting material with the magnetic component

interspersed. The conducting pathways can be interrupted by the

mere presence of another component. In crystalline materials this

task is particularly difficult, although in layered systems it can be

achieved.1 Paradoxically, it is in crystalline systems that con-

ducting organic materials are generally at their best. A more

general area is the preparation of conducting polymers incor-

porating magnetic nanoparticles,2 yet in these systems the nature

of the electrical characteristics is distinct to the metallic type

conductivity observed in crystalline molecular samples.

We are interested in preparing nanostructured molecular

organic conducting material3 in the form of a film that can be

achieved through the gel state.4 The conducting ‘‘wires’’ are

formed, thanks to the presence of supramolecular polymers, and

these can be used for making conducting systems including

Institut de Ci�encia de Materials de Barcelona (CSIC), CampusUniversitari, 08193 Bellaterra, Catalonia, Spain. E-mail: amabilino@icmab.es; jpuigma@googlemail.com; Fax: +34 93 5805729; Tel: +34 93580 1853

† Electronic supplementary information (ESI) available: SupportingAFM images and comparitive analysis of sample conductivity and fibrealignment. See DOI: 10.1039/c0sm01088j

This journal is ª The Royal Society of Chemistry 2011

hybrid and composite materials. This approach allows the

combination of dissimilar building blocks with pathways inter-

acting and influencing upon each other in unique ways such that

they can generate materials with characteristics that are distinc-

tive to their components.5 For instance, it has been proved that

when superparamagnetic ferrites or semiconductor quantum

dots such as CdS are immobilised they confer magnetic and/or

luminescent properties to the final hybrid gel state.6 We use the

gels as a route to these materials because the fibres are ‘‘frozen’’ in

the solvent matrix, which can then be evaporated, and the con-

ducting material is then prepared by doping.7 These systems are

amenable to the formation of conducting hybrid nanomaterials,

as we have shown for the case of gold nanoparticles containing

hydrogen bonding units which help make the two components

compatible.8

Here we report a new class of self-assembled and non-covalent

hybrid organogels combining conducting and super-

paramagnetic components formed from an amide tetrathia-

fulvalene (TTF) derivative (1) and organic soluble‡ magnetic

iron oxide nanoparticles (g-Fe2O3 nanoparticles, abbreviated

NPs here) to fulfil the objective of reaching a conducting

magnetic hybrid material. The TTF unit is the one known to

form a variety of interesting nanostructures and to perform

‡ We use the term soluble to infer that the whole of NP is homogeneouslydissolved in the solvent. An alternative nomenclature from colloidchemistry would be to say that the material forms a homogeneouscolloidal dispersion.

Soft Matter, 2011, 7, 2755–2761 | 2755

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

a variety of functions,9 while the NPs below 15 nm diameter are

established superparamagnetic colloids which are attractive for

a variety of applications.10 We describe how the relative

proportions of the two components influence the nanostructure

of the resulting hybrid, and how, in turn, the electrical properties

of the doped material are modulated as a result.

Results

Preparation and characterisation of the nanocomposites

The nanocomposite gels were formed by dissolving organo-

gelator 1 and a weight percent proportion of the NPs in hot

hexane, and then allowing the solution to cool to room

temperature unperturbed. The organogelator was synthesised

using the procedure described by us previously,11 and the

superparamagnetic iron oxide nanoparticles (g-Fe2O3, typically

with a mean particle size of 7 nm and a polydispersity index of

10%) were synthesised adapting a literature procedure12 as

reported by us previously.13 Different gel samples were prepared

where the percentage in weight of the NPs contained in the final

hybrid gel was varied from 1% up to 50% (Fig. 1). As can be

appreciated in the photograph, all the gels are transparent and

stable, even at the highest nanoparticle content studied. The

change in colour arises from the absorption of iron oxide

nanoparticles which are dark brown.

The fact that gels can be formed with up to 50% of inorganic

material is thanks to the great solubility of the NP in hexane,

which is a result of the capping of the iron oxide with the oleate

covering. This situation contrasts with gels formed by certain

Fig. 1 A photograph of the gels formed in hexane by organogelator 1

and different weight percents of iron oxide nanoparticles (NPs).

2756 | Soft Matter, 2011, 7, 2755–2761

derivatives of gold nanoparticles—which were not soluble in this

organic solvent—where the maximum loading of inorganic-

based matter in the hybrid of the same organogelators was a little

above one percent.8

An alternative way to impregnate the gel with these nano-

particles is to allow the particles to diffuse into the gel from an

isotropic solution of the NPs in hexane. When a solution of the

iron colloid in hexane in a capillary tube was brought into

contact (using a magnet) with the gel of 1 in hexane in the same

tube a layer of the liquid is formed on the surface of the gel.

However, over the period of a day the NPs do diffuse into the gel.

The magnet used to move the NP solution cannot force the

nanoparticles into the gel, a situation which contrasts dramati-

cally with a suspension of crystals of 1 in hexane (formed by

rapid cooling of the saturated solution) whereby the NP solution

is moved back and forth in the suspension using a magnet. On the

other hand, the same magnet is unable to distort the gel or

remove colloidal material from it—no distortion of the meniscus

is seen after contact of the magnet with the gel for one day (as is

noted immediately in concentrated solutions of the NPs in

hexane), probably because the concentration of nanoparticles is

so low in the gels.

The content of the NPs in the gel of 1 has an effect on the

melting temperature of the gels (Table 1). The transition from gel

to liquid was measured by observing the flow of the mixtures

angled in a warmed oil bath, and repeating the process from

reformed gels to attain average values. These experiments show

that the presence of the NPs increases the transition temperature,

and hint at an interaction between them and the fibres of the

gelator 1. Even 1% of NPs is enough to increase the transition

temperature by 6 �C, and subsequent addition has a lesser effect.

At the highest content of NPs assayed (50% by weight) the

transition temperature is less than the optimum one, presumably

because the areas of iron oxide colloid disrupt the gelator fibre

network.

The nanostructure of the hybrid gels was studied using

Transmission Electron Microscopy (TEM). In order to ensure

a thin enough covering on the holey carbon grid such that the

sample gave good contrast, the gel samples were heated to the

solution state and a drop was placed on the grid and allowed to

evaporate (this procedure is necessary to avoid depositing too

much material on the grid which results in a film which is too

opaque to the electron beam). No staining was used to visualise

the colloids. The resulting samples were observed in several

places, and representative TEM images are shown in Fig. 2.

Table 1 Temperatures for the gel–liquid transition as a function ofnanoparticle content in the gel of 1 in hexane

Weight percent of NP in hexane gelof 1

Gel–liquid transition temperature/�C

0 421 485 5010 5025 4950 48

This journal is ª The Royal Society of Chemistry 2011

Fig. 2 TEM images of the different 1–NP xerogels. Xerogel containing

(A) 1%, (B) 5%, (C) 10%, (D) 15%, (E) 25%, (F) 50% and (G) 0% in

weight of NPs. All the TEM images were acquired by casting hot solu-

tions of the gel-forming solution onto holey carbon grids.

Fig. 3 TEM image of 1–NP xerogel containing 5% in weight of NPs,

acquired by casting a hot solution of the gel-forming solution onto

a holey carbon grid.

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

In the images of the unstained xerogels containing between 1

and 10% of the nanoparticles the dominant feature is the fibres

formed by 1 with the darkest contrast coming from the inorganic

material (Fig. 3). As in the xerogel formed by the organic

molecule on its own,7 twisted bundles of fibres are observed with

widths ranging from a few tens of nanometres to approximately

100 nm (although larger clumps exist). It is not possible to

determine the lengths of the fibres in a quantitative manner, as

they cross and intertwine. The nanoparticles are imaged as dark

dots located in or at the edges of the fibres, sometimes alone and

This journal is ª The Royal Society of Chemistry 2011

sometimes in lines containing up to half a dozen particles. Quite

rarely, isolated nanoparticles are observed which are apparently

not associated with any nanofibre. The great propensity for the

nanoparticles to adhere or be incorporated into the fibres is

particularly remarkable given that they contain no hydrogen

bonding unit and are presumably held to the fibres purely by van

der Waals interactions. This same fact is the reason that some

isolated particles are seen. If the interaction between particle and

fibre were stronger, one would expect to observe no isolated

particles.8

A clear difference in the structure of the nanocomposite is seen

when the mixture contains greater than 10% of the nanoparticles.

Above this value two important observations are worthy of note:

firstly, the fibres cannot be imaged in these samples because of

the high content of absorbing inorganic colloid, which means

that the organic fibres can only be inferred by the presence of

clear tracks in the images. Secondly, no nanoparticles are seen in

the clear tracks, implying that the organic and inorganic

components have phase separated.

The clear non-covalent ‘‘misunderstanding’’ between the two

components is evidenced when a closer look is taken at the

xerogels containing 15 and 50% in weight of NPs (Fig. 4). The

TEM image of the 1–NP xerogel containing 15% of particles

(Fig. 4) shows obvious separation of the two components, the

inorganic and the organic. The NPs start to organise (Fig. 4A (1))

and self-assemble (Fig. 4A (2)) challenging a large range orga-

nization when raising the percentage of the inorganic component

in the final hybrid gel (Fig. 4B). In the later case, the assembly of

the NPs is different from the self-assembly examined when

Soft Matter, 2011, 7, 2755–2761 | 2757

Fig. 4 TEM images of 1–NP xerogels containing 15% (A) and 50% (B) in weight of NPs relative to 1, respectively, and (C) a solution of NP dropcast

from hexane. The highlighted regions in (A) show regions where particles line a fibre (1) and where they assemble to form a domain (2). All the TEM

images are acquired using holey carbon grids on unstained samples.

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

a solution of NPs is dropcast over a TEM holey carbon grid

(Fig. 4C). Unlike the solution of NPs, the hybrid xerogel gives

rise to small and large domains of NPs where mono- and bi-

layers of NPs are observed due to the separation and the non-

cooperation between two components (Fig. 4B).

The separation of the inorganic and organic components

reminds us of phase separation in polymer based nano-

composites,14 although surface drying effects may play a role,15

the nature of the images does not imply this is dominant given the

even distribution of the particles arising from their high solu-

bility. The fibres in the clear tracks in the samples with high iron

colloid content should also have NPs associated with them if the

NPs are bound to the fibres by van der Waals interactions, and

this observation might favour a mechanism in which the NPs

align themselves with the fibres during their formation. In any

case, there is clearly a strengthening interaction at the interphase

between the two colloids, as demonstrated in the higher phase

transition of the gel-to-liquid change (Table 1). It is also inter-

esting to reflect that phase separated gold nanoparticles have

been used recently to probe the early stages of growth of gel

fibres.16 The situation contrasts with the case where clear non-

covalent interactions take place between the components.8,15 It is

therefore interesting to see the effects that this kind of phase

separation has on the conducting properties of these materials

once charge carriers have been introduced through doping.

Conductivity of the doped nanocomposites

Current sensing (CS) atomic force microscope (AFM) measure-

ments of doped xerogels containing 1, 5, 15 and 25% in weight of

NPs were performed for each sample separately on highly

oriented pyrolytic graphite (HOPG). The doping process con-

sisted of exposure of the xerogels to iodine vapours for two

minutes in a sealed chamber.7 In the CS-AFM measurements

topography and current images are recorded simultaneously with

the Pt/Ir coated tip in permanent contact with the sample while

applying a voltage between them. The current maps from these

AFM experiments show areas with clear fibre-like morphology

which is relatively uniform across the sample when the

percentage of NPs is under the threshold phase separation limit

(<10%, Fig. 5A and B). On the other hand, once the percentage is

10% or more, dark regions appear in the current AFM image,

which correspond to the poorly conducting areas which

presumably arise from the phase separated regions containing

the NPs (Fig. 5C and D). It is important to notice that all the

2758 | Soft Matter, 2011, 7, 2755–2761

current images presented in Fig. 5 are measured at the same bias

voltage (1 Volt). However, even in the latter composites, bright

areas of highly conducting material are observed, although the

size of the domains is more limited. It is interesting to reflect that

relatively large areas of parallel fibres are present in the

composites which contain 1 or 5 weight percent of NPs when

compared with either the pure 1 or other xerogel samples of this

type. At present we have no experimental evidence to suggest

a reason for this alignment, but it is an empirical fact that the

presence of small amounts of NPs improves the alignment of the

fibres of 1 in the xerogel samples compared with the pure organic

system. Comparing the doped xerogels with low and high content

of NP, at higher concentrations of the latter the alignment of the

fibres of 1 is apparently disturbed. A quantitative analysis of the

anisotropy of the different samples is included in the ESI†.

In addition to the CS-AFM maps, a spectroscopic study was

carried out whereby evidence concerning the different conductive

properties were obtained for each sample. The I/V curves

recorded in different areas of the samples obviously show a range

of responses depending on the area where they were registered.

The responses reflect the homogeneity—or lack of it—seen in the

current maps. As an example, Fig. 6 shows a variety of responses

for the doped xerogel containing 15 weight percent of the iron

oxide nanoparticles. As can be appreciated the curves show

responses which are practically Ohmic (over the potential range

shown) to ones where a clear experimental gap is observed. These

poorly conducting areas correspond to the darker regions in the

current map, and would be expected to coincide with areas of

phase-segregated nanoparticles, while the more conducting

regions are where the nanofibres of the organic conductor are

undisturbed.

For each of the samples a similar range of curves is obtained,

but in order to compare the responses the curves with highest

occurrence were selected. These representative I/V sweeps

recorded over the doped xerogels containing different propor-

tions of the organic and nanoparticulate materials are shown in

Fig. 7. A clear change to an insulator-like behaviour is observed

as the percentage of the inorganic colloid is increased. The

conductance of the doped xerogel containing 1% NP is virtually

Ohmic, while increasing amounts of iron oxide colloid lead

curves with a pronounced flattening around zero bias. We

hypothesise that the interconnection of the two components, the

inorganic and the organic, at low proportions of NP still allows

good connection of the organic fibres, and leads to the hybrid

having an effective conductive network (remembering that the

This journal is ª The Royal Society of Chemistry 2011

Fig. 5 Current sensing AFM image of doped xerogels of 1–NP containing: 1% (A), 5% (B), 10% (C) and 15% (D) in weight of NPs. The images are

recorded on HOPG when applying 1 V bias voltage.

Fig. 6 Selection of spectroscopic curves recorded during the CS-AFM

measurements of doped xerogels of 1–NP containing 15% of the colloid

where the dispersion in types of electronic response can be appreciated.

Fig. 7 (A) Representative spectroscopic curves recorded during the CS-

AFM measurements of doped xerogels of 1–NP containing different

amounts of the inorganic colloid. All the curves presented for the doped

materials correspond to xerogels exposed for two minutes to iodine

vapours. (B) Plot of corresponding conductance values at 0 V.

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

current must pass from the graphite support to the conducting

AFM tip through the whole material). A dramatic decrease in the

conductivity is witnessed above 15%, and while the material

containing 25% of nanoparticles is poorly conducting that with

50% colloid could not be measured reliably. This can be seen

graphically in the plot of conductance versus weight percentage

of NP (Fig. 7B).

These results are in concurrence with the TEM measurements

which reveal that xerogels containing more than 10% in weight of

This journal is ª The Royal Society of Chemistry 2011 Soft Matter, 2011, 7, 2755–2761 | 2759

Fig. 8 Representative ESR spectra of undoped and doped xerogels of 1–

NP containing 1% NP. (The difference in intensity could arise from the

different area observed in the ESR experiment.)

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

NPs have no incorporation of the inorganic component into the

organic fibres, resulting in phase separation and a reduction in

the possible number of conducting pathways. This aspect is seen

in the decrease in the proportion of areas with conductance

greater than 1 nS (see the ESI†). Nevertheless, there are still some

areas with fibre like structures visible when the threshold limit is

surpassed, indicating highly conducting domains. Besides, in

these latter cases the contrast is lower than for the low inorganic

content xerogels even when the same bias voltage is applied

(Fig. 5).

It is important to point out that the material containing only

1% colloid has a response in the CS-AFM experiment which

indicates a better conductor than pure 1 after doping and

annealing. Therefore, despite the fact that the nanoparticles do

not appear to have specific interactions with the organic nano-

fibres, an increase in their conductivity is observed, as there is

when a specific interaction exists which might favour the align-

ment of the fibres.8 In the latter case, a phase change in the

material was observed, as witnessed by the electron spin reso-

nance (ESR) spectroscopy where a very narrow signal was

observed for the composite. In the present case, the undoped

material shows a very significant ESR arising from the iron in the

nanoparticles (Fig. 8). Upon doping, a very sharp signal appears

overlapped with the signal arising from the inorganic material.

The approximate peak-to-peak linewidth of this new signal is 10

Gauss, which is intermediate between the value seen for the less

conducting a phase and the more highly conducting b phase

of 1.7

There is definitely a difference in the pristine doped xerogels 1

and the material containing the nanoparticles under the same

processing conditions, although in this case we cannot affirm that

the b phase has been induced. When gold nanoparticles incor-

porating hydrogen bonding groups were employed, specific

interactions led to the induction of the latter phase,8 but in the

present case non-specific interactions also seem to influence the

organisation of 1, because the organic material is more ordered in

a morphological sense, and has greater conductivity and

a slightly broader ESR signal indicating higher dimensionality in

the conductivity.17

Conclusions

The organogel route is extremely effective for the preparation of

nanocomposites containing conducting and magnetic

2760 | Soft Matter, 2011, 7, 2755–2761

components. This is true in the present case especially because of

the solubility of the oleate-stabilised iron oxide nanoparticles,

which allow concentrated solutions to be prepared in hexane.

The nature of the nanocomposite varies dramatically with

composition. When the percentage of the inorganic component is

below 10% in weight an even distribution of the iron oxide

colloid is seen through the fibrous organic material, whereas

above this loading domains of the pure nanoparticles are

observed. This situation has a significant effect on the electrical

conducting properties of the materials, whereby increased

proportion of NP leads to poorer conductivity, presumably as

a result of the inorganic domains interrupting conduction path-

ways. On the other hand, at low loadings of the iron oxide

nanoparticles, the fibres of 1 apparently show significant align-

ment in the CS-AFM measurements, perhaps indicating a struc-

tural role played by NP, which improves the conduction of the

organic fibres with respect to the pristine material using the same

processing conditions.

The results show the important effects that can arise by

combining different colloidal materials both on the nano-

structure and the properties of the resulting systems, and prompt

further investigation into this fascinating area of research.

Experimental section

General methods and materials

Compound 1 and the nanoparticles were prepared according to

reported procedures.11,13 FT-IR spectra were recorded on a Per-

kinElmer Spectrum One spectrometer. The EPR spectra were

recorded on an X-band Bruker spectrometer (ESP-300E).

Preparation of gels

The components of the gels were dispersed in hexane, which was

then brought close to boil in a sample pot with stirring until

a transparent solution was reached. The concentration of 1 in the

hexane was always 2.5 mg ml�1, and the amount of iron colloid

was varied. The solution was then allowed to stand at room

temperature. The doped xerogels were prepared according to

a previously described procedure.7

CS-AFM measurements

Current images of the doped samples on graphite substrates were

obtained by using a 5100 system (Agilent technologies). A

contact mode with a bias voltage applied to the sample while

scanning with a grounded conducting Pt–Ir coated silicon tip

(force constant around 1.2 N m�1) is necessary in order to

perform such experiments. Contact to the sample was made

using a stainless steel clamp pressed onto the surface of the doped

xerogel. All the measurements were carried out in a dry nitrogen

gas atmosphere in order to avoid artefacts introduced by

humidity.

Acknowledgements

This work was supported by the Generalitat de Catalunya

(2009 SGR 158) the Spanish Ministerio de Ciencia e

Innovaci�on (MAT2009-08024, CTQ2010-16339 and

This journal is ª The Royal Society of Chemistry 2011

Dow

nloa

ded

by I

nstit

uto

de C

ienc

ia d

e M

ater

iale

s. B

iblio

teca

Man

on

28 M

arch

201

1Pu

blis

hed

on 2

7 Ja

nuar

y 20

11 o

n ht

tp://

pubs

.rsc

.org

| do

i:10.

1039

/C0S

M01

088J

View Online

CONSOLIDER-CSD2007-00041). We warmly thank Vega

Lloveras in the Spectroscopy Service at the ICMAB for

recording ESR spectra.

References

1 (a) A. J. Epstein and J. S. Miller, Synth. Met., 1996, 80, 231–237; (b)A. Miyazaki, K. Enomoto, K. Okabe, H. Yamazaki, J. Nishijo,T. Enoki, E. Ogura, K. Ugawa, Y. Kuwatani and M. Iyoda, J.Solid State Chem., 2002, 168, 547–562; (c) A. Alberola,E. Coronado, J. R. Gal�an-Mascar�os, C. Gim�enez-Saiz,C. J. G�omez-Garc�ıa and F. M. Romero, Synth. Met., 2003, 133–134, 509–513; (d) E. Coronado and P. Day, Chem. Rev., 2004, 104,5419–5448; (e) T. Enoki and A. Miyazaki, Chem. Rev., 2004, 104,5449–5477; (f) H. Hiraga, H. Miyasaka, K. Nakata, T. Kajiwara,S. Takaishi, Y. Oshima, H. Nojiri and M. Yamashita, Inorg. Chem.,2007, 46, 9661–9671.

2 (a) J. Deng, X. Ding, W. Zhang, Y. Peng, J. Wang, X. Long, P. Li andA. S. C. Chan, Polymer, 2002, 43, 2179–2184; (b) Z. Zhang andM. Wan, Synth. Met., 2003, 132, 205–212; (c) K. R. Reddy,K. P. Lee and A. I. Goplan, J. Appl. Polym. Sci., 2007, 106, 1181–1191; (d) Q. Chen, L. Zhao, C. Li and G. Shi, J. Phys. Chem. C,2007, 111, 18392–18396.

3 D. B. Amabilino and J. Puigmart�ı-Luis, Soft Matter, 2010, 6, 1605–1612.

4 (a) Molecular Gels. Materials with Self-Assembled Fibrillar Networks,ed. R. G. Weiss and P. Terech, Springer, Dordrecht, 2005; (b)N. M. Sangeetha and U. Maitra, Chem. Soc. Rev., 2005, 34, 821–836; (c) T. Ishi-i and S. Shinkai, Top. Curr. Chem., 2005, 258, 119–160; (d) A. R. Hirst, B. Escuder, J. F. Miravet and D. K. Smith,Angew. Chem., Int. Ed., 2008, 47, 8002–8018; (e) S. Banerjee,R. K. Das and U. Maitra, J. Mater. Chem., 2009, 19, 6649–6687; (f)M. Suzuki and K. Hanabusa, Chem. Soc. Rev., 2010, 39, 455–463.

5 (a) Y. Lin, A. Boker, J. B. He, K. Sill, H. Q. Xiang, C. Abetz, X. F. Li,J. Wang, T. Emrick, S. Long, Q. Wang, A. Balazs and T. P. Russell,Nature, 2005, 434, 55–59; (b) F. Lerouge, G. Cerveau andR. J. P. Corriu, New J. Chem., 2006, 30, 1364–1376; (c)S. Bhattacharya, A. Srivastava and A. Pal, Angew. Chem., Int. Ed.,2006, 45, 2934–2937; (d) T. K. Hong, H. S. Yang and C. J. Choi, J.Appl. Phys., 2005, 97, 064311; (e) R. Elghanian, J. J. Storhoff,R. C. Mucic, R. L. Letsinger and C. A. Mirkin, Science, 1997, 277,1078–1081; (f) J. van Herrikhuyzen, S. J. George, M. R. J. Vos,N. A. J. M. Sommerdijk, A. Ajayaghosh, S. C. J. Meskers andA. P. H. J. Schenning, Angew. Chem., Int. Ed., 2007, 46, 1825–1828.

6 B. Simmons, S. Li, V. T. John, G. L. McPherson, Ch. Taylor,D. K. Schwartz and K. Masko, Nano Lett., 2002, 2, 1037–1042.

7 (a) J. Puigmart�ı-Luis, V. Laukhin, �A. P�erez del Pino, J. Vidal-Gancedo, C. Rovira, E. Laukhina and D. B. Amabilino, Angew.Chem., Int. Ed., 2007, 46, 238–241; (b) J. Puigmart�ı-Luis,E. E. Laukhina, V. N. Laukhin, �A. P�erez del Pino, N. Mestres,J. Vidal-Gancedo, C. Rovira and D. B. Amabilino, Adv. Funct.Mater., 2009, 19, 934–941.

This journal is ª The Royal Society of Chemistry 2011

8 J. Puigmart�ı-Luis, A. P�erez del Pino, E. Laukhina, J. Esquena,V. Laukhin, C. Rovira, J. Vidal-Gancedo, A. G. Kanaras,R. J. Nichols, M. Brust and D. B. Amabilino, Angew. Chem., Int.Ed., 2008, 47, 1861–1865.

9 (a) T. Kitamura, S. Nakaso, N. Mizoshita, Y. Tochigi,T. Shimomura, M. Moriyama, K. Ito and T. Kato, J. Am. Chem.Soc., 2005, 127, 14769–14775; (b) T. Kitahara, M. Shirakawa, S.-i. Kawano, U. Beginn, N. Fujita and S. Shinkai, J. Am. Chem. Soc.,2005, 127, 14980–14981; (c) Ch. Wang, D. Zhang and D. Zhu, J.Am. Chem. Soc., 2005, 127, 16372–16373; (d) T. Akutagawa,K. Kakiuchi, T. Hasegawa, S.-i. Noro, T. Nakamura,H. Hasegawa, S. Mashiko and J. Becher, Angew. Chem., Int. Ed.,2005, 44, 7283–7287; (e) Y. Kobayashi, M. Hasegawa, H. Enozawaand M. Iyoda, Chem. Lett., 2007, 720–721; (f) H. Enozawa,Y. Honna and M. Iyoda, Chem. Lett., 2007, 1434–1435; (g)I. Danila, F. Riob�e, J. Puigmart�ı-Luis, �A. P�erez del Pino,J. D. Wallis, D. B. Amabilino and N. Avarvari, J. Mater. Chem.,2009, 19, 4495–4504; (h) D. Canevet, M. Sall�e, G. Zhang, D. Zhangand D. Zhu, Chem. Commun., 2009, 2245–2269.

10 (a) C. Corot, P. Robert, J. M. Id�ee and M. Port, Adv. Drug DeliveryRev., 2006, 58, 1471–1504; (b) A. K. Gupta and M. Gupta,Biomaterials, 2005, 26, 3995–4021; (c) U. Jeong, X. Teng, Y. Wang,H. Yang and Y. Xia, Adv. Mater., 2007, 19, 33–60.

11 S. Lei, J. Puigmart�ı-Luis, A. Minoia, M. Van der Auweraer,C. Rovira, R. Lazzaroni, D. B. Amabilino and S. De Feyter, Chem.Commun., 2008, 703–705.

12 T. Hyeon, S. S. Lee, J. Park, Y. Chung and H. B. Na, J. Am. Chem.Soc., 2001, 123, 12798–12801.

13 E. Taboada, E. Rodr�ıguez, A. Roig, J. Or�o, A. Roch andR. N. Muller, Langmuir, 2007, 23, 4583–4588.

14 J. B. Hooper and K. S. Schweizer, Macromolecules, 2006, 39, 5133–5142.

15 I. A. Coates and D. K. Smith, J. Mater. Chem., 2010, 20, 6696–6702.

16 V. R. Rajeev Kumar, V. Sajini, T. S. Sreeprasad, V. K. Praveen,A. Ajayaghosh and T. Pradeep, Chem.–Asian J., 2009, 4, 840–848.

17 (a) L. Forro, G. Sekretarczyk, M. Krupski, D. Schweizer andH. Keller, Phys. Rev. B: Condens. Matter, 1987, 35, 2501–2504; (b)H. H. Wang, J. A. Schlueter, U. Geiser, J. M. Williams,D. Naumann and T. Roy, Inorg. Chem., 1995, 34, 5552–5557; (c)T. Naito, T. Inabe, K. Takeda, K. Awaga, T. Akutagawa,T. Hasegawa, T. Nakamura, T. Kakiuchi, H. Sawa, T. Yamamotoand H. Tajima, J. Mater. Chem., 2001, 11, 2221–2227; (d)J. A. Schlueter, B. H. Ward, U. Geiser, H. H. Wang, A. M. Kini,J. Parakka, E. Morales, H. J. Koo, M. H. Whangbo, R. W. Winter,J. Mohtasham and G. L. Gard, J. Mater. Chem., 2001, 11, 2008–2013; (e) E. Laukhina, V. Tkacheva, A. Chekhlov, E. Yagubskii,R. Wojciechowski, J. Ulanski, J. Vidal-Gancedo, J. Veciana,V. Laukhin and C. Rovira, Chem. Mater., 2004, 16, 2471–2479; (f)H. Ito, Y. Yokochi, H. Tanaka, S. Kuroda, R. Kanehama,M. Umemiya, H. Miyasaka, K. I. Sugiura, M. Yamashita,H. Tajima and J. Yamaura, Phys. Rev. B: Condens. Matter, 2005,71, 085202.

Soft Matter, 2011, 7, 2755–2761 | 2761