Patent Application
20140017485
The present invention relates to the field of nanotechnology. More specifically, it concerns an assembly made up of:
J-aggregates are self-arrangements of cyanine molecules which form very ordered assemblies whereof the organizations are of the crystalline type. A description of J-aggregates and their properties can be found in the article by H. Kuhn et al. in a book entitled “J-aggregates” by T. Kobayashi, ISBN 981-02-2737-X. Due to the nearly flawless organization of J-aggregates, they have remarkable properties. Mainly, the electro-optical properties of J-aggregates result from exceptional interactions between the transition dipole moments of the dyes, creating extended exciton states after exposure to light. Characteristics for J-aggregates are a narrow excitonic absorption band and resonance fluorescence. Connected to that are many other exceptional properties of J-aggregates, such as super-radiant emission, high non-linear susceptibilities, efficient energy migration and superquenching. Applications in sensing, light harvesting, light-emitting diodes and non-linear optics can all greatly benefit from the unique properties of J-aggregates. Device driven research on J-aggregates is further highly motivated by the fact that a counterpart on the side of inorganic semiconductors does not exist.
A first issue regarding this technology, was to make J-aggregates layer in a simple and efficient way, suitable to extensive production. Decisive methods have been described in EP1788036 and EP2028236 in the name of the applicant and incorporated by reference to the present document.
Promoting energy transfer through J-aggregates is the object of the present invention. Actually, an exciton spread in a J-aggregates can be caught by a suitable energy acceptor having a spectral overlap between its absorption spectrum and the emission spectrum of the J-aggregates. The energy acceptor should be arranged in the vicinity of the J-aggregates.
Suitable energy acceptors for excited J-aggregates can be dye molecules, semiconductor or metal based nanoparticles. In a preferred application, colloidal semiconductor quantum dots (QD) can be used as energy acceptors. One can also consider the opposite situation where the QD is used as donor and J-aggregates as acceptor.
A quantum dot is a portion of matter (in general semiconductor based) whose excitons are confined in all three spatial dimensions. Consequently, such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. Nanoparticles made of metals may also be labelled quantum dots if they are small enough (typically sub 10 nm) so that quantization of electronic energy levels occurs. Some experiments known in the art have shown that metal based nanoparticles present such properties and one can expect that transition metals may also present such QD properties. In addition, a new type of cadmium free quantum dots made from rare earth doped oxide materials and showing bright emissions and similar optical properties to those of other semiconducting quantum dots have been developed because of legislation restricting the use of heavy metals (typically Cd, Hg, Pb). Thus, in the present invention, the term QD will include semi-conducting QD, metal based particles the dimension of which enabling them to present QD properties, and rare earth doped oxide based nanoparticles. As non-limiting example, one can cite the following commercially available semi-conducting species: semi-conductor based QD will include CdS, CdSe, ZnS, CdTe, InAs, InP, CdSeS, ZnO, Ag halides and mixed systems containing one or several of these semiconductors. Metal based QD will include Cu, Ag, Au, Ni, Pd, Pt, Co, Cr, Ru, Fe. Oxide based QD will preferably include BaTiO3 and YVO4 doped with rare earth elements.
In various papers by Bulovic et al. (publ. 2009 (J-aggregates only in water), 2010 (J-aggregates also in films) and 2011 (J-aggregates in films), WO2009026105 and WO2011146299 patent applications, energy transfer processes between J-aggregates and quantum dots are described in detail.
It should be understood that the distance between J-aggregates and quantum dots is an important criterion to obtain an energy transfer between these species. Typically, this distance should be comprised between 0.1 and 10 nm. Correct distances for energy transfer have been adjusted by the Langmuir-Blodgett (LB) technique (J. Imaging Sci. 1988, 32(2), 64). A patent by Tischler et al. (U.S. Pat. No. 7,799,422, 2006), Walker et al. (Nano Letters 2010, 10(10), 3995) and Agranovich et al. (arXiv preprint, ArXiv:0801.3794, 2008) show that optimum distances for energy transfer between J-aggregates and semiconductor QD can be adjusted using layer-by-layer deposition (LBL) instead of LB-layers. Both methods of distance adjustment, LB and LBL, are not feasible for industrial manufacturing of devices containing highly perfect J-aggregates.
In document WO2009026105, Bulovic et al. propose a new method to adjust the distance between J-aggregates and quantum dots by electrostatic interactions, i.e. by electrostatic conjugation of cyanine J-aggregates at the surface of a quantum dot after ligand exchange reaction. After deposition of this molecular construct, the resulting quantum dot/J-aggregate films exhibit energy transfer from J-aggregates to quantum dots. In this case the relatively high efficiency of this energy transfer is explained by the close conjugation of quantum dots and coherently coupled dyes in contrast to previous work where the energy transfer efficiency was limited by using polyelectrolyte layers separating the donors and acceptors. Another method to adjust the distance between J-aggregates and quantum dots by electrostatic interactions has been described by Savateeva et al. (Physics, Chemistry, and Applications of nanostructures, 2011, 173; J. Mater. Chem. 2012, 22, 10816) without having to synthesize constructs between cyanine monomers and QD in aqueous solutions. Films containing these QD-J-aggregates hybrid systems were not described.
Such methods present several drawbacks. It can only be achieved by relatively complex synthesis of “QD J-aggregates constructs”. Films can only be manufactured for down conversion, i.e. by exciting J-aggregates and emitting in QD.
The present invention aims to propose a new method making it possible to obtain rather simply energy transfer between J-aggregates and energy donors or acceptors.
More particularly, the invention concerns an assembly made up of
According to the invention, said assembly moreover comprises Quantum Dots (QD) located within the same pores as those containing the J-aggregates, said QD maintaining J-aggregates structure.
Advantageously, QD are chosen so as to be able to act as energy acceptors or donors for the J-aggregates.
Advantageously, QD are chosen so as to be able to act as electron acceptors or donors.
In a preferred embodiment, said pores have an average diameter dimensioned so as to enable macromolecules with dendritic architecture to penetrate them. The assembly is also made up of such macromolecules forming a functionalized layer at least in said pores and said layer of molecules from the family of cyanines interact with the macromolecules with dendritic architecture to form J-aggregates.
The invention will be better understood upon reading the description which follows, done in reference to the appended drawings in which:
a and 3b illustrate energy transfer between J-aggregates and QD on a reference glass substrate by using the J-aggregate as a donor and the QD as acceptors,
a, 7b and 7c (emission and excitation spectra) illustrate a case where a QD with emission near 540 nm was excited at 375 nm and energy transfer occurred to J-aggregates of Myline-2 used as energy acceptors in films,
One example of a method for producing a particular J-aggregate/Quantum Dot (QD) device will be described in detail below as a non-limiting illustration of the invention.
As one will understand, the method essentially consists of preparing near room temperature a nanoparticular metal-oxide coating on a substrate chosen among organic, metallic or ceramic substrates so as to form a mesoporous coating. The dimensions of the pores are typically ranged between 1 and 100 nm, preferably between 2 and 50 nm.
Then dendritic architecture molecules are adsorbed along the mesoporous coating walls including the mesopores walls of the metal-oxide coating and thus define a dendrimer support. Cyanine molecules are subsequently self-assembled into supramolecular J-aggregates on this dendrimer support at least within the pores. Commercially available QD are then incorporated into the pores containing the J-aggregates from aqueous solutions. One or more QD can be introduced within one pore.
Even if such method is preferred, one can also consider forming J-aggregates directly within pores of a mesoporous coating without any intermediate dendritic architecture based functionalized layer. As a non-limiting example, it has been demonstrated by Nüesch et al. (ref. J. Am. Chem. Soc. 1996, 118, 5420-5431) that hydroxylated and salt-impregnated mesoporous metal oxide films can be used for templating the aggregation processes. The authors have indeed described a method to form aggregates by controlling the texture of the porous films, their surface energy and the atmospheric conditions such as the presence of solvent or the humidity rate. This method can therefore be considered in this invention for the fabrication of mesoporous coating containing dye J-aggregates within their porous network, although J-aggregates obtained here are much less perfect and stable than by using macromolecules with dendritic architectures.
In addition, even if the methods described above have been demonstrated for mesoporous metal oxide coatings made from aqueous solutions, one can also consider forming J-aggregates within pores of a mesoporous organic matrix with, or without any intermediate dendritic architecture based functionalized layer. As a non-limiting example, Heier et al. (ref Langmuir, 2010, 26(6), 3955 and Phys. Chem. Chem. Phys. 2011, 13, 15714) recently described the synthesis of cyanine aggregates in nanostructured organic films fabricated by means of phase separation processes. Such methods as well as the use of mesoporous polymeric templates made by polymer demixing, block-copolymer phase separation or by replication as already described in the literature (ref. Popa et al. Nanotechnology 2009, 20, 485303; Walheim et al. Science, 1999, 283, 520; R. Pugin et al. Journal of Photopolymer Science and Technology, 2009, Vol. 22, 2, 223) can therefore be considered in this application for the fabrication of mesoporous organic coatings containing cyanine dye aggregates within their porous network.
The preparation of mesoporous nanoparticular coatings with various metal oxides on a large variety of substrate and the subsequent functionalization with J-aggregates have been described in document EP2028236 hereby incorporated by reference. For SiO2 coatings, one can refer to the application US2007196596 also incorporated by reference. It should be noticed that cyanines intended to form the J-aggregates diffuse into the mesoporous coating and penetrate into the mesopores.
One can use the different dyes defined in the article of D. M. Sturmer published in the book “Chemistry of heterocyclic compounds: special topics”, Volume 30, pp 441-601, edited by A. Weissberger and B. W. Rossiter, 1977 (Wiley Interscience, New York), and including structure examples which are given respectively in FIGS. 2a and 2b, 3, 9, 10 and 14, of EP1788036 hereby incorporated by reference.
One can cite, as preferred cyanines to form J-aggregates [5,5′-diphenyl-dibenzoxazolo N, N′-propylsulfonate]-9 ethyl trimethine cyanine, called Myline 1 (Myl-1), and 5,5′,6,6′-tetrachloro dibenzimidalolo 2,2′-butylsulfonate 9,9′-N-diethyl trimethine cyanine, called Myline 2 (Myl-2) (see structures in patent EP1788936 FIGS. 4 and 9 respectively). Myl-1 and Myl-2 were synthesized by ILFORD IMAGING Switzerland. More generally, cyanines, mero-cyanines, squaraines and their derivatives, are capable of self-assembly in order to form J-aggregates.
Preparation of Assembly with QD and J-Aggregates in Pores of Metal Oxide Nanoparticles
Dried coatings containing the J-aggregates (as described above) were functionalized with an aqueous solution of commercially available QD, rinsed and dried before spectroscopic measurements. For instance, QD can be supplied by Cytodiagnostics, proposing core-shell structured colloidal QD, the semiconducting core being composed of different Cd or Zn sulphides and selenides, and the external shell made of a stabilising organic layer presenting different chemical groups (e.g. OH or NH2, referred below as QD-OH and QD-NH2 respectively). The total diameter is approximately 10 nm. Concentrations of QD solutions were varied between 1 to 25 mg per mL as shown in results proposed thereafter.
The configuration obtained is schematically illustrated in
Then, a layer of molecules from the family of cyanines interacting with the macromolecules with dendritic architecture is organized into J-aggregates within the pores of the metal oxide coating.
One or more QD may also be accommodated within the same pores as those containing the J-aggregates and, as it will be explained thereafter, may interact and undergo energy transfer with J-aggregates.
It has been surprising to observe that QD did not affect the J-aggregate stability.
On
As a reference to prove the advantages of mesoporous substrates, it has been proposed experiments on a planar substrate, where the vicinity of the species is limited and obtained by successive layer by layer depositions.
A monolayer of a highly perfect Myl-1 J-aggregate on a PAMAM G4 support deposited on a glass substrate has been prepared. One can refer to EP1788036 for experimental details about this preparation. After rinsing and drying, a 5 times diluted commercial aqueous QD solution is applied by spin-coating onto the dried J-aggregate layer. Spectral measurements shown in
On the emission spectra of
Such experiments demonstrate that energy transfer may occur between commercially available QD and J-aggregates, even if the enhancement obtained here is only similar to that obtained by Bulovic's method.
Above proposed experiments have been extended to mesoporous substrates in order to evaluate the potential influence of confinement on energy transfer efficiency between QD and J-aggregates.
Different parameters have been tested.
The table also indicates the volume and mean diameter of pores measured with the nitrogen adsorption method. Materials should be chosen so as to enable molecules from the family of cyanines intended to form the J-aggregates and QD to penetrate them. As taught by EP2028236, mesoporous coatings can be realized in a material chosen among AlOOH, TiO2, ITO, SiO2, γ-Al2O3, ZrO2, SnO2, ZnO, Ta2O5, mixture of them or with a base of doped conductor oxide nanoparticles.
The mesoporous coatings can also be made of organic matrix, as described in references mentioned in paragraph [0021] above.
The mean diameter of pores of the mesoporous layer should be large enough to enable encapsulation of the selected QD. QD are inserted into the pores of the mesoporous substrate by using similar methods as those proposed for glass substrate.
The addition of the QD within the mesoporous coating should not lead to a modification of the absorption spectrum of the J-aggregates that would result from the disassembling of the J-aggregates. QD should also not be destabilized (i.e. not aggregated) by J-aggregates or by the chemical compounds present in the assembly according to the invention. It should also present an overlap between the emission spectrum of the donor with the absorption spectrum of the acceptor to make the energy transfer possible.
One can also consider having electron/hole transfer that would require an overlap of the electronic states (between donor and acceptor) that enables electron transfer. As a matter of comparison with energy transfer, it is well known that the distance between the QD and the donor/acceptor for electron transfer should be much shorter, typically below 2 nm (see for example Barbara et al., J. Phys. Chem., 1996, 100, 13148-13168).
If a functionalized layer of macromolecules of dendritic architecture is used so as to contribute to the J-aggregate formation, one will refer to the documents EP1788036 and EP2028236 to obtain information regarding suitable dendrimers. Experiments have been conducted with PAMAM G4. However, even if this solution may be preferred because it offers a very efficient and cost effective solution to obtain J-aggregates within pores, one could consider methods obtaining such J-aggregates without any intermediate dendrimer layer, as mentioned above.
One will now refer to
The following table illustrates different results obtained with different cyanines and QD for down conversion using the J-aggregates as donors and the QD as acceptors after deconvolution. In all cases, emission as well as excitation spectra confirmed the energy transfer.
One can observe that no enhancement is obtained for as received or only 5 times diluted QD solutions, while the J-aggregate fluorescence is always partially quenched. This can be explained by clustering effects of QD within the pores that inhibit energy transfer from QD to J-aggregates.
For more diluted QD solutions, one obtains enhancement comprised between 9 and 20 times for only 50% of fluorescence quenching of the J-aggregates, to be compared with 2.5 times for 50% on planar glass substrate and 2.5 times for 100% quenching by Bulovic.
According to the invention, extraordinary strong enhancement obtained with diluted QD in mesoporous coatings is due to confinement in pores that enables a “template effect” to have QD at an appropriate distance from the J-aggregates, and to very favourable arrangement of QD (no clustering) in these pores compared to planar substrates. Here, the QD alone contributes very little to emission.
In the smallest pores (AIOOH Type 2, 10 nm pore diameter), the enhancement is the highest. Here, QD alone fluoresces weakly as not many QD are present, but there is very little electron-hole recombination, as very few QD can be placed into such mesopores and therefore no clustering occurs.
Best results are obtained if the fluorescence intensity of the QD/J-aggregate is not too high (≦0.2), as otherwise we have recombination effects due to QD-clustering after energy transfer. Such effects lead to enhancement losses of QD emission after energy transfer. QD should also be diluted enough to avoid clustering effects within the pores.
It should also be noted that light stability of J-aggregates in presence of QD within a same mesopore is much higher (min. by a factor of 100) for Myl-1 J-aggregates, than without QD. This also proves energy transfer between J-aggregates and QD occurs and increases the stability of the J-aggregates.
It is therefore proposed a very efficient method enabling the control of the distance between QD and J-aggregates, so as to promote energy/electron transfers.
The forthcoming example describes the preparation of assembly with QD of gold and J-aggregates of Myl-1 in pores of metal oxide nanoparticle coatings (SiO2 and AIOOH type 1,
One will now refer to the
In the case where AIOOH type 1 coatings were used instead of SiO2 coatings (
One can also consider inserting in the pores of the mesoporous substrate some other species (organic molecules like dyes) which, thanks to the confinement provided by the pore dimensions, may be able to act as energy or electron donors/acceptors for the J-aggregates located in the same pore.
| Number | Date | Country | Kind |
|---|---|---|---|
| 12176306.4 | Jul 2012 | EP | regional |
