Patent Application
20140155640
The present invention relates to a process for the production of surface functionalised nanoparticles, particularly but not exclusively, the production of semiconductor quantum dot nanoparticles incorporating surface-bound functional groups which increase the ease with which the dots can be employed in applications, such as incorporation into solvents, inks, polymers, glasses, metals, electronic materials and devices, bio-molecules and cells.
The size of a semiconductor nanoparticle dictates the electronic properties of the material; the band gap energy being inversely proportional to the size of the semiconductor nanoparticle as a consequence of quantum confinement effects. In addition, the large surface area to volume ratio of the nanoparticle has a profound impact upon the physical and chemical properties of the nanoparticle.
Two fundamental factors, both related to the size of the individual semiconductor nanoparticle, are responsible for their unique properties. The first is the large surface to volume ratio; as a particle becomes smaller, the ratio of the number of surface atoms to those in the interior increases. This leads to the surface properties playing an important role in the overall properties of the material. The second factor being, with many materials including semiconductor nanoparticles, there is a change in the electronic properties of the material with size, moreover, because of quantum confinement effects the band gap gradually becomes larger as the size of the particle decreases. This effect is a consequence of the confinement of an ‘electron in a box’ giving rise to discrete energy levels similar to those observed in atoms and molecules, rather than a continuous band as observed in the corresponding bulk semiconductor material. Thus, for a semiconductor nanoparticle, because of the physical parameters, the “electron and hole”, produced by the absorption of electromagnetic radiation, a photon, with energy greater then the first excitonic transition, are closer together than they would be in the corresponding macrocrystalline material, moreover the Coulombic interaction cannot be neglected. This leads to a narrow bandwidth emission, which is dependent upon the particle size and composition of the nanoparticle material. Thus, quantum dots have higher kinetic energy than the corresponding macrocrystalline material and consequently the first excitonic transition (band gap) increases in energy with decreasing particle diameter.
Core semiconductor nanoparticles, which consist of a single semiconductor material along with an outer organic passivating layer, tend to have relatively low quantum efficiencies due to electron-hole recombination occurring at defects and dangling bonds situated on the nanoparticle surface which can lead to non-radiative electron-hole recombinations.
One method to eliminate defects and dangling bonds on the inorganic surface of the quantum dot is to grow a second inorganic material, having a wider band-gap and small lattice mismatch to that of the core material epitaxially on the surface of the core particle, to produce a “core-shell” particle. Core-shell particles separate any carriers confined in the core from surface states that would otherwise act as non-radiative recombination centres. One example is ZnS grown on the surface of CdSe cores.
Another approach is to prepare a core-multi shell structure where the “electron-hole” pair is completely confined to a single shell layer consisting of a few monolayers of a specific material such as a quantum dot-quantum well structure. Here, the core is of a wide bandgap material, followed by a thin shell of narrower bandgap material, and capped with a further wide bandgap layer, such as CdS/HgS/CdS grown using substitution of Hg for Cd on the surface of the core nanocrystal to deposit just a few monolayers of HgS which is then over grown by monolayers of CdS. The resulting structures exhibited clear confinement of photo-excited carriers in the HgS layer.
To add further stability to quantum dots and help to confine the electron-hole pair one of the most common approaches is by epitaxially growing a compositionally graded alloy layer on the core this can help to alleviate strain that could otherwise led to defects. Moreover, for a CdSe core, in order to improve structural stability and quantum yield, rather than growing a shell of ZnS directly on the core, a graded alloy layer of Cd1-xZnxSe1-ySy can be used. This has been found to greatly enhance the photoluminescence emission of the quantum dots.
Doping quantum dots with atomic impurities is an efficient way also of manipulating the emission and absorption properties of the nanoparticle. Procedures for doping of wide band gap materials such as zinc selenide and zinc sulphide with manganese and copper (ZnSe:Mn or ZnS:Cu), have been developed. Doping with different luminescence activators in a semiconducting nanocrystal can tune the photoluminescence and electroluminescence at energies even lower than the band gap of the bulk material, whereas the quantum size effect can tune the excitation energy with the size of the nanocrystals without causing a significant change in the energy of the activator related emission.
The coordination about the final inorganic surface atoms in any core, core-shell or core-multi shell, doped or graded nanoparticle is incomplete, with highly reactive, non-fully coordinated atoms “dangling bonds” on the surface of the particle, which can lead to particle agglomeration. This problem is overcome by passivating (also referred to as “capping”) the “bare” surface atoms with protecting organic groups.
An outermost layer of organic material or sheath material (referred to as a “capping agent”) helps to inhibit particle aggregation and protects the nanoparticles from their surrounding electronic and chemical environment. A schematic illustration of such a nanoparticle is provided in
The widespread exploitation of quantum dot nanoparticles has been restricted by their physical/chemical instability and incompatibility with many applications. Consequently, a series of surface modification procedures has been employed to render the quantum dots more stable and compatible with a desired application. This has been attempted mainly by making the capping agent bi- or multi functional or by overcoating the capping layer with an additional organic layer that has functional groups which can be used for further chemical linkage.
The most widely used quantum dot surface modification procedure is known as ligand exchange′. The ligand molecules that inadvertently coordinate to the surface of the quantum dot during the core synthesis and shelling procedure are subsequently exchanged with a ligand compound that introduces a desired property or functional group Inherently, this ligand exchange strategy reduces the quantum yield of the quantum dots considerably. This process is illustrated schematically in
An alternative surface modification strategy interchelates discrete molecules or polymer with the ligand molecules that are already coordinated to the surface of the quantum dot during the shelling procedure. These post synthesis interchelation strategies often preserve the quantum yield but result in quantum dots of substantially larger size. This process is illustrated schematically in
Current ligand exchange and interchelation procedures may render the quantum dot nanoparticles more compatible with their desired application but usually results in lower quantum yield due to damage to the inorganic surface of the quantum dots and/or an increase in the size of the final nanoparticles.
It is an object of the present invention to obviate or mitigate one or more of the problems described above.
The present invention generally relates to a method for producing surface functionalised nanoparticles comprising reacting first and second nanoparticle precursor species in the presence of a nanoparticle surface binding ligand incorporating a nanoparticle binding group and a functional group, said reaction being effected under conditions permitting binding of said surface binding ligand to the growing nanoparticles to produce said surface functionalised nanoparticles.
According to a first aspect of the present invention there is provided a method for producing surface functionalised nanoparticles comprising reacting first and second nanoparticle precursor species in the presence of a nanoparticle surface binding ligand of Formula 3
X—Y—Z Formula 3
wherein X is a nanoparticle surface binding group, Y is a linker group, and Z is a functional group, in which Y comprises a polyethyleneglycol group and/or Z comprises an aliphatic group incorporating a terminal unsaturated group, said reaction being effected under conditions permitting binding of said surface binding ligand to the growing nanoparticles to produce said surface functionalised nanoparticles.
The present invention generally relates to a method for producing surface functionalised nanoparticles comprising reacting first and second nanoparticle precursor species in the presence of a nanoparticle surface binding ligand incorporating a nanoparticle binding group and a functional group, said reaction being effected under conditions permitting binding of said surface binding ligand to the growing nanoparticles to produce said surface functionalised nanoparticles.
The present invention provides a method for converting nanoparticle precursor species to the material of the final nanoparticles whist also providing a functionalised layer on the outer surface of the final nanoparticles. The method of the present invention is depicted schematically in
It still more surprising that the method of the first aspect of the present invention can be applied to the production of surface functionalised core nanoparticles from two or more sources of ions to be incorporated into the growing nanoparticles (optionally in the presence of a molecular cluster compound as described in the applicant's co-pending European patent application (publication no. EP1743054A) and UK patent application (application no. 0714865.3)), as well as the production of surface functionalised core-shell nanoparticles where deposition of an outer shell layer can be carried out in the presence of a surface binding ligand.
The present invention thus provides a strategy for intentionally coordinating a chosen pre-chemically functionalised ligand to the surface of the quantum dot nanoparticle in-situ during core growth and/or shelling of nanoparticles. This strategy circumvents the need for post-nanoparticle synthesis surface modification procedures and thereby generates quantum dot nanoparticles in fewer manipulation steps that are physically/chemically robust, have high quantum yield, have small diameter and are compatible with their intended application, which may include, but is not restricted to, incorporation of said nanoparticles into solvents, devices, inks, polymers, glasses, or attachment of the quantum dot nanoparticles, via chemical reaction to form a direct bond, to cells, biomolecules, metals, molecules or polymers.
The present invention facilitates synthesis of nanoparticles in a capping agent that has a nanoparticle binding group which can passivate the surface of the nanoparticle and an additional ligand which has the ability for further chemical linkage, such as cross linking about the nanoparticle or incorporation within polymeric materials.
The first and second precursor species and the surface binding ligand may be combined together in any desirable order provided the first and second precursors react in the presence of the ligand. Preferably said first nanoparticle precursor species is contacted by said nanoparticle surface binding ligand so as to effect binding of said surface binding ligand to said first precursor species prior to reacting said first precursor species with said second nanoparticle precursor species.
In a first preferred embodiment of the method forming the first aspect of the present invention the first nanoparticle precursor species contains a first ion to be incorporated into the growing nanoparticles and the second nanoparticle precursor species contains a second ion to be incorporated into the growing nanoparticles.
A second aspect of the present invention provides a method for producing surface functionalised core semiconductor nanoparticles, the method comprising reacting a first core nanoparticle precursor species containing a first ion to be incorporated into the growing nanoparticles with a second core nanoparticle precursor species containing a second ion to be incorporated into the growing nanoparticles, said reaction being effected in the presence of a nanoparticle surface binding ligand incorporating a nanoparticle binding group and a functional group, under conditions permitting binding of said surface binding ligand to the growing nanoparticles to produce said surface functionalised nanoparticles.
The nanoparticle surface binding ligand employed in the second aspect of the present invention may be in accordance with the ligand employed in accordance with the first aspect of the present invention. By way of example, in a preferred embodiment of the second aspect of the present invention the nanoparticle surface binding ligand is of Formula 3 as set out above in respect of the first aspect of the present invention.
The first and second ions may be selected from any desirable group of the periodic table, such as but not limited to group 11, 12, 13, 14, 15 or 16 of the periodic table. The first and/or second ion may be a transition metal ion or a d-block metal ion. Preferably the first ion is selected from group 11, 12, 13 or 14 and the second ion is selected from group 14, 15 or 16 of the periodic table.
It is particularly preferred that the first and second (core) nanoparticle precursor species are reacted in the presence of a molecular cluster compound, as exemplified below in Example 1. The method may employ the methodology set out in the applicant's co-pending European patent application (publication no. EP1743054A). The molecular cluster compound may contain third and fourth ions. At least one of said third and fourth ions is preferably different to said first and second ions contained in the first and second (core) nanoparticle precursor species respectively. The third and fourth ions may be selected from any desirable group of the periodic table, such as but not limited to group 11, 12, 13, 14, 15 or 16 of the periodic table. The third and/or fourth ion may be a transition metal ion or a d-block metal ion. Preferably the third ion is selected from group 11, 12, 13 or 14 and the fourth ion is selected from group 14, 15 or 16 of the periodic table. By way of example, the molecular cluster compound may incorporate third and fourth ions from groups 12 and 16 of the periodic table respectively and the first and second ions derived from the first and second (core) nanoparticle precursor species may be taken from groups 13 and 15 of the periodic table respectively. Accordingly, the methods according to the first and second aspects of the present invention may employ methodology taken from the applicant's unpublished co-pending UK patent application (application no. 0714865.3).
The first and second (core) nanoparticle precursor species, molecular cluster compound and the surface binding ligand may be combined together in any desirable order. One of the first and second (core) precursor species may be contacted by the molecular cluster compound before or during reaction with the other of the first and second (core) precursor species. It is particularly preferred that the first (core) nanoparticle precursor species is initially contacted by the surface binding ligand to form a first mixture, which is then contacted by the molecular cluster compound to form a second mixture and the second mixture is then contacted by the second (core) nanoparticle precursor species.
It will be appreciated that during the reaction of the first and second (core) nanoparticle precursor species, the first (core) nanoparticle precursor species may be added in one or more portions and the second (core) nanoparticle precursor species may be added in one or more portions. The first (core) nanoparticle precursor species is preferably added in two or more portions. In this case, it is preferred that the temperature of a reaction mixture containing the first and second (core) nanoparticle precursor species and the nanoparticle surface binding ligand is increased between the addition of each portion of the first (core) precursor species. Additionally or alternatively, the second (core) nanoparticle precursor species may be added in two or more portions, whereupon the temperature of a reaction mixture containing the first and second (core) nanoparticle precursor species and the nanoparticle surface binding ligand may be increased between the addition of each portion of the second (core) precursor species.
In a second preferred embodiment of the first aspect of the present invention the first nanoparticle precursor species is a core nanoparticle and the second nanoparticle precursor species contains a first ion to form part of a shell to be deposited on the surface of said core nanoparticle.
In a third preferred embodiment of the first aspect of the present invention the second nanoparticle precursor species is a core nanoparticle and the first nanoparticle precursor species contains a first ion to form part of a shell to be deposited on the surface of said core nanoparticle.
The second and third preferred embodiments describe approaches, exemplified below in Examples 2 and 3, whereby the general methodology set out in the first aspect of the present invention can be employed to form an outer shell, or layer, of a material on the outside of a core nanoparticle, wherein the outer shell is provided with a chemical functionalised outer surface.
A third aspect of the present invention related to the second and third preferred embodiments of the first aspect of the present invention provides a method for producing surface functionalised core-shell semiconductor nanoparticles, the method comprising reacting a core semiconductor nanoparticle with a first nanoparticle precursor species containing a first ion to form part of a shell to be deposited on the surface of said core semiconductor nanoparticle, said reaction being effected in the presence of a nanoparticle surface binding ligand incorporating a nanoparticle binding group and a functional group, said reaction being effected under conditions permitting binding of said surface binding ligand to the surface of the growing core-shell semiconductor nanoparticles to produce said surface functionalised core-shell semiconductor nanoparticles.
The nanoparticle surface binding ligand employed in the third aspect of the present invention may be in accordance with the ligand employed in accordance with the first aspect of the present invention. By way of example, in a preferred embodiment of the third aspect of the present invention the nanoparticle surface binding ligand is of Formula 3 as set out above in respect of the first aspect of the present invention.
With regard to the third aspect of the present invention the surface binding ligand may contact one of the core nanoparticle and the first precursor species before contacting the other, or may contact both simultaneously. Thus, in accordance with the method set out in Example 2 below, the core nanoparticle may be contacted by the binding ligand so as to effect binding of said ligand to said core nanoparticle prior to reacting said core nanoparticle with said first precursor species. Alternatively, in accordance with Example 3 below, the first precursor species may be contacted by the ligand so as to effect binding of the surface binding ligand to the first nanoparticle precursor species prior to reacting said first precursor species with said core nanoparticle. Preferably the method according to the third aspect of the present invention further comprises reacting said core nanoparticle and said first precursor species with a second nanoparticle precursor species containing a second ion to form part of the shell to be deposited on the surface of said core semiconductor nanoparticle.
In the second and third embodiments of the first aspect of the present invention and the third aspect of the present invention, the core nanoparticle preferably contains first and second core ions which may be selected from any desirable group of the periodic table, such as but not limited to group 11, 12, 13, 14, 15 or 16 of the periodic table. The core nanoparticle may contain a transition metal ion and/or a d-block metal ion. Preferably the core nanoparticle contains an ion selected from group 11, 12, 13 or 14 and an ion selected from group 14, 15 or 16 of the periodic table.
The first ion contained in the nanoparticle precursor species which is to form part of the nanoparticle shell be selected from any desirable group of the periodic table, including but not limited to group 11, 12, 13, 14, 15 and/or 16 of the periodic table. Moreover, the first ion may be a transition metal ion or a d-block metal ion.
The nanoparticle precursor species and/or the core nanoparticle may be added in one or more portions as appropriate. Preferably, at least one of the precursor species and core nanoparticle is added in two or more portions during the reaction. The temperature of a reaction mixture containing the precursor species, the core nanoparticle and/or the nanoparticle surface binding ligand may be increased between the addition of each portion of the precursor species and core nanoparticles.
It is particularly preferred that the method according to the second and third preferred embodiments of the first aspect of the present invention and the third aspect of the present invention further comprises reacting said core nanoparticle and said precursor species with a third nanoparticle precursor species containing a second ion to form part of the shell to be deposited on the surface of said core nanoparticle. Said second ion may also be selected from any desirable group of the periodic table, including but not limited to group 11, 12, 13, 14, 15 and/or 16 of the periodic table. Moreover, the second ion may be a transition metal ion or a d-block metal ion.
It is particularly preferred that the first and/or second ion contained in the nanoparticle precursor species is/are different to said first and second core ions. By way of example, the core-shell nanoparticle may comprise a core predominantly made from a III-V semiconductor material (e.g. InP) and a shell predominantly made from a II-VI semiconductor material (e.g. ZnS). In this case, the first and second core ions would be indium and phosphide ions, and the first and second ions derived from the nanoparticle precursor species would be zinc and sulfide ions. Suitable nanoparticle precursor species may be Zn(Ac) or the like and (TMS)3P.
When a third nanoparticle precursor species is being added to the reaction mixture including the surface binding ligand, the third nanoparticle precursor species may be added in one or more portions. The third nanoparticle precursor species is preferably added in two or more portions. In this case, it is preferred that the temperature of a reaction mixture containing the core nanoparticles, precursor species and the nanoparticle surface binding ligand is increased between the addition of each portion of the third precursor species.
The reaction between the nanoparticle precursors (and core nanoparticles where appropriate) may be carried out in any appropriate solvent. The reaction is preferably carried out in a solvent which is different to said nanoparticle surface binding ligand, although it will be appreciated that this does not have to be the case, and that in alternative embodiments the surface binding ligand may represent the solvent or one of the solvents in which the reaction is being conducted. The solvent may be a co-ordinating solvent (i.e. a solvent that co-ordinates the growing nanoparticles) or a non-co-ordinating solvent (i.e. a solvent that does not co-ordinate the growing nanoparticles). Preferably the solvent is a Lewis base compound, which may be selected from the group consisting of HDA, TOP, TOPO, DBS, octanol and the like.
The nanoparticle binding group of the surface binding ligand is preferably different to the functional group of the surface binding ligand. The functional group may or may not incorporate a protecting group chosen so as to be selectively removable during and/or after nanoparticle growth.
The nature of the functional group of the surface binding ligand may be chosen to bestow any desirable chemical or physical property to the final surface functionalised nanoparticles. For example, a ligand may be chosen which contains a functional group which bestows the surface functionalised nanoparticles with a predetermined reactivity towards a particular reagent. Alternatively, a ligand may be chosen which incorporates a functional group which bestows aqueous compatibility (i.e. the ability to be stably dispersed or dissolved in aqueous media) to the surface functionalised nanoparticles. Moreover, a functional group may provide the ability to cross-link surface binding ligands around the surface of the same nanoparticle, ligands bound to adjacent nanoparticles and/or other surrounding materials (e.g. polymers) which incorporate compatible cross-linkable groups. Such a functional group may contain a single vinyl group, or more preferably two, three or more vinyl groups to facilitate cross-linking between said vinyl groups bound to the nanoparticles and/or between vinyl groups bound to the nanoparticles and vinyl groups contained in surrounding materials.
The functional group of the surface binding ligand may contain one or more atoms selected from the group consisting of sulfur, nitrogen, oxygen and phosphorous. The functional group may be selected from the group consisting of hydroxide, alkoxide, carboxylic acid, carboxylate ester, amine, nitro, polyethyleneglycol, sulfonic acid, sulfonate ester, phosphoric acid and phosphate ester. Moreover, the functional group may be a charged or polar group, such as but not limited to a hydroxide salt, alkoxide salt, carboxylate salt, ammonium salt, sulfonate salt or phosphate salt.
The surface binding ligand may contain any appropriate nanoparticle binding group to bind to the growing nanoparticles, i.e. the core nanoparticles being grown according to the first preferred embodiment or the shell being grown on the core nanoparticles according to the second/third preferred embodiments. Preferably the nanoparticle binding group contains an atom selected from the group consisting of sulfur, nitrogen, oxygen and phosphorous. The nanoparticle binding group may contain a species selected from the group consisting of a thio group, an amino group, an oxo group and a phospho group. The nanoparticle binding group may be selected from the group consisting of hydroxide, alkoxide, carboxylic acid, carboxylate ester, amine, nitro, polyethyleneglycol, sulfonic acid, sulfonate ester, phosphoric acid and phosphate ester. Moreover, the nanoparticle binding group may be a charged or polar group, such as but not limited to a hydroxide salt, alkoxide salt, carboxylate salt, ammonium salt, sulfonate salt or phosphate salt.
The binding group and the functional group of the surface binding ligand are preferably connected via a linker, which may take any desirable form. It is particularly preferred that said linker is selected from the group consisting of a covalent bond; a carbon, nitrogen, oxygen or sulfur atom; a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group; and a substituted or unsubstituted aromatic group.
The nanoparticle surface binding ligand may be a polymeric compound, such as a polyether, optionally comprising an alkoxide group and a carboxylate group. Preferably the ligand is a polyether with a terminal alkoxide group and a carboxylate group bonded to the opposite terminus. Particularly preferred ligands include polyethylene glycols and derivatives thereof in which at least one, more preferably both, of the terminal hydroxide groups of polyethylene glycol has been derivatised to provide alternative functional groups, such as an alkoxide group and/or a carboxylate group.
The present invention provides methods for producing surface functionalised nanoparticles that are physically/chemically robust, have high quantum yield, have small diameter and are compatible with their intended application. Nanoparticles produced according to the present invention may be represented by Formula 1 below.
QD-X—Y—Z Formula 1
Wherein: QD represents a core or core-(multi)shell nanoparticle; and X—Y—Z represents the nanoparticle surface binding ligand in which X is a nanoparticle surface binding group; Y is a linker group linking X and Z; and Z is a functional group.
X and/or Z may be substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclic, substituted or unsubstituted polyethyleneglycol (examples of substituents include but are not limited to halogen, ether, amine, amide, ester, nitrile, isonitrile, aldehyde, carbonate, ketone, alcohol, carboxylic acid, azide, imine, enamine, anhydride, acid chloride, alkyne, thiol, sulfide, sulfone, sulfoxide, phosphine, phosphine oxide), or a crosslinkable/polymerisable group (examples include carboxylic acid, amine, vinyl, alkoxysilane, epoxide).
X and/or Z may be a charged or polar group, such as a hydroxide salt, alkoxide salt, carboxylate salt, ammonium salt, sulfonate salt or phosphate salt.
X and/or Z may be selected from the group consisting of: —SR1(R1=H, alkyl, aryl); —OR2 (R2—H, alkyl, aryl); —NR3R4 (R3 and/or R4=H, alkyl, aryl); —CO2R5 (R5=H, alkyl, aryl); —P(═O)OR6OR7 (R6 and/or R7=H, alkyl, aryl); —OR8 wherein R8 is hydrogen or an alkyl group which may be substituted or unsubstituted, and/or saturated or unsaturated; —C(O)OR9 wherein R9 is hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group; —NR10R11 wherein R10 and R11 are independently hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group, or R1° and RH may be linked such that —NR10R11 forms a nitrogen-containing heterocyclic ring of any desirable size, e.g. a five, six or seven-membered ring; —N+R12R13R14 wherein R12, R13 and R14 are independently hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group; —NO2; —OCH2CH2n—OR15 wherein R15 is hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group; —S(O)2OR16 wherein R16 is hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group; and —P(OR17)(OR18)O wherein R17 and R18 are independently hydrogen, a substituted or unsubstituted, saturated or unsaturated aliphatic or alicyclic group, or a substituted or unsubstituted aromatic group.
Z may incorporate any appropriate protecting group. By way of example, Z may contain an acid labile protecting group, such as t-butyl, benzylic, trityl, silyl, benzoyl, fluorenyl, acetal, ester, or ethers, e.g. methoxymethyl ether, 2-methoxy(ethoxy)methyl ether. Alternatively, Z may contain a nucleophillic-base labile protecting group, including a carboxylic ester, sulfonium salt, amide, imide, carbamate, N-sulfonamide, trichloroethoxymethyl ether, trichloroethylester, trichloroethoxycarbonyl, allylic-ether/amine/acetal/carbonate/ester/carbamate to protect a carboxylic acid, alcohol, thiol etc. Moreover, Z may incorporate a benzyl amine protecting group, which can be deprotected to provide an amine group, or Z may contain a cyclic carbonate when it is ultimately desirable to deprotect Z to provide a diol for further reaction.
Y may be a single bond, alkyl, aryl, heterocyclic, polyethyleneglycol, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heterocyclic, substituted or unsubstituted polyethyleneglycol, (examples of substituents include halogen, ether, amine, amide, ester, nitrile, isonitrile, aldehyde, carbonate, ketone, alcohol, carboxylic acid, azide, imine, enamine, anhydride, acid chloride, alkyne, thiol, sulfide, sulfone, sulfoxide, phosphine, phosphine oxide), a crosslinkable/polymerisable group (examples include carboxylic acid, amine, vinyl, alkoxysilane, epoxide), or a group represented by Formula 2 below
Wherein: k, m and n are each independently any number from 0 to around 10,000.
In further preferred embodiments of the present invention X may be an acid group or an ester group, such as a carboxylic acid group or derivative or salt thereof, such as a carboxylate ester or carboxylate salt. In alternative embodiments, X may be a sulfonic acid group, sulfonate ester or salt; a phosphoric acid group, phosphate ester or salt; or an amino group. Z preferably comprises one or more alkyl group, each containing at least one unsaturated group. The or each carbon-to-carbon double or triple bond may be a terminal unsaturated group (i.e. include an atom at the end of a carbon chain) or be provided within the carbon chain. Where Z comprises one or more alkyl groups, the or each alkyl chain may carry any desirable substituent(s). The linker group, Y, connecting X and Z may take any convenient form. For example, Y may contain one or more aliphatic groups and/or an aromatic groups. The aliphatic group(s) may contain a straight carbon chain, a branched carbon chain, or may be alicyclic. Y may further comprise one or more ether groups. In particularly preferred embodiment, Y comprises a phenyl group bound to at least one, more preferably two or three, unsaturated alkyl groups optionally via ether links. A particularly preferred nanoparticle surface binding ligand (Ligand 1) has the structure shown below, which can cross-link to other ligands and/or surrounding species (e.g. compatible polymers or polymerizable monomers) via the three vinyl groups.
Further preferred cross-linkable ligands of Formula 1 which can be used in the method according to the present invention are shown below and incorporate a functional group, Z, which contains one or more vinyl groups bonded to an aliphatic or aromatic linker, Y, which is bonded to a nanoparticle binding ligand, X, of any desirable structure, such as those described above. Preferred ligands incorporate one vinyl group, more preferably two vinyl groups, and most preferably three or more vinyl groups. Where Z contains two or more vinyl groups, then the vinyl groups may be bonded via respective alkyl groups to the same carbon atom, or to different carbon atoms (e.g. different carbon atoms of the same carbocyclic or heterocyclic ring, which may itself be saturated, partially saturated or aromatic). Nanoparticle binding group, X, may be monodentate or multidentate as described above. By way of example, X may incorporate one carboxylic acid group, as in Ligand 1, or X may incorporate two, three or more carboxylic acid groups. Where two or more carboxylic acid groups are present, each group may be bonded via an alkyl group to the same or different carbon atoms.
Exemplary monodentate aliphatic ligands include the following, wherein X is a carboxylic acid group, Z comprises one, two or three vinyl groups, Y is a straight or branched aliphatic group, and each x is any integer (i.e. 0, 1, 2, 3 etc).
Exemplary monodentate aromatic ligands include the following, wherein X is a carboxylic acid group, Z comprises one, two or three vinyl groups, Y contains an aromatic group, and each x is any integer (i.e. 0, 1, 2, 3 etc).
Exemplary bidentate aliphatic ligands include the following, wherein X contains two carboxylic acid groups, Z comprises one, two or three vinyl groups, Y is a straight or branched aliphatic group, and each x is any integer (i.e. 0, 1, 2, 3 etc).
Exemplary tridentate aliphatic ligands include the following, wherein X contains three carboxylic acid groups, Z comprises one, two or three vinyl groups, Y is a straight or branched aliphatic group, and each x is any integer (i.e. 0, 1, 2, 3 etc).
It will be appreciated that one or more of the carboxylic acid groups in any of the above exemplary structures may be replaced with an alternative nanoparticle binding group, such as, but not limited to, a carboxylic acid salt or ester, a sulfonic acid, ester or salt, a phosphoric acid, ester or salt, or an amino group. Moreover, linker group, Y, may contain groups other than the specific unsaturated aliphatic or aromatic groups shown above. For example, Y may incorporate one or more ether groups, carbon-to-carbon double bonds, and/or multicyclic aromatic or non-aromatic groups.
In a preferred embodiment there is provided a method according to the first aspect of the present invention, wherein the terminal unsaturated group is a vinyl group. That is, the nanoparticle surface binding ligand incorporates a carbon-to-carbon double bond at the end of the ligand furthest away from the nanoparticle surface.
In Formula 3, it is preferred that X comprises at least one carboxylic acid group or at least one thiol group. Preferably Y comprises a straight or branched aliphatic group, or an aromatic group.
With regard to the first aspect of the present invention the nanoparticle surface binding ligand may be poly(oxyethylene glycol)n monomethyl ether acetic acid wherein n=around 1 to around 5000. Preferably n is around 50 to 3000, more preferably around 250 to 2000, and most preferably around 350 to 1000. Alternatively, the nanoparticle surface binding ligand may be selected from the group consisting of 10-Undecylenic acid and 11-mercapto-undecene. As a further preferred alternative, the nanoparticle surface binding ligand is Ligand 1 as shown above.
Exemplary surface binding ligands according to Formula 1 that are used in the Examples below include poly(oxyethylene glycol)350 monomethyl ether acetic acid, poly(oxyethylene glycol)750 monomethyl ether acetic acid, poly(oxyethylene glycol)2000 monomethyl ether acetic acid, 10-Undecylenic acid, Ligand 1 as shown above, and 11-mercapto-undecene.
A fourth aspect of the present invention provides surface functionalised nanoparticles produced using the method according to the first, second or third aspects of the present invention, said surface functionalised nanoparticle comprising a nanoparticle bound to a nanoparticle surface binding ligand, said ligand incorporating a nanoparticle binding group and a functional group.
Nanoparticles produced according to any of the aforementioned aspects of the present invention are preferably semiconductor nanoparticles, for example, core nanoparticles, core-shell nanoparticles, graded nanoparticles or core-multishell nanoparticles. Said nanoparticles preferably comprise one or more ions selected from any suitable group of the periodic table, such as but not limited to group 11, 12, 13, 14, 15 or 16 of the periodic table, transition metal ions and/or d-block metal ions. The nanoparticle core and/or shell (where applicable) may incorporate one or more semiconductor material selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AlP, AlS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge, MgS, MgSe, MgTe and combinations thereof.
The present invention relates to growing the final inorganic layer of a quantum dot nanoparticle in the same reaction as producing the first organic layer that has additional functionality, either immediately or after further chemical treatment of the organic layer if a protecting group has been used, whereby it has the ability to chemically link to other chemical entities.
The present invention describes a strategy that intentionally coordinates a chosen pre-chemically functionalised ligand to the surface of the quantum dot nanoparticle in-situ during core growth and/or shelling of the nanoparticles. This strategy circumvents the need for post synthesis surface modification procedures and generates quantum dot nanoparticles in fewer manipulation steps that are physically/chemically robust, have high quantum yield, have small diameter and are compatible with their intended application, which may include, but is not restricted to, incorporation of said nanoparticles into solvent, devices, inks, polymers, glasses or attachment of the quantum dot nanoparticles, via chemical reaction to form a direct bond, to cells, biomolecules, metals, molecules or polymers.
The present invention is illustrated with reference to the following non-limiting Examples and Figures in which,
The following Examples describe methods for producing core semiconductor nanoparticles and depositing shells of semiconductor material on said cores using methods according to the present invention.
Examples 1 and 4 describe the production of InP core nanoparticle quantum dots using a molecular cluster compound to seed nanoparticle growth according to the invention described in the applicant's co-pending European patent application, EP1743054A. The cluster used in Examples 1 and 4 comprises ions from groups 12 and 16 of the Periodic Table (Zn and S ions respectively) in accordance with the invention described in the applicant's co-pending UK patent application No. 0714865.3.
Examples 2 and 3 describe methods for depositing a shell of ZnS on the InP core nanoparticles produced in Example 1, using a method according to an aspect of the present invention. Examples 5 and 6 describe methods for depositing shells of ZnS and ZnS/ZnO respectively on the InP core nanoparticles produced in Example 4, using a method according to an aspect of the present invention. Example 7 describes a method for preparing InP/ZnS core/shell nanoparticles in which the step of depositing the shell of ZnS on the InP core nanoparticles employs a method according to an aspect of the present invention.
Dibutyl sebacate (100 ml) was added to a round bottom 3-neck flask (250 ml) and placed under high vacuum for 1 hour and 30 minutes at a temperature of 90° C. In a separate round bottom 3-neck flask (100 ml), dibutyl sebacate (45 ml) and indium acetate (5.036 g, 17.25 mmol) was placed under high vacuum at a temperature of 110° C.
Poly(oxyethylene glycol)750 monomethyl ether acetic acid (51.76 mmol) was heated under high vacuum (˜90° C.) for one hour in a reaction flask. After one hour, the reaction flask was allowed to cool before transferring the dibutyl sebacate and indium acetate mixture to the reaction flask under nitrogen. The reaction flask was then placed under high vacuum at 110° C. for a period of 16 hours to ensure any excess water present is removed. After 16 hours, a clear, pale yellow solution was formed.
Dibutyl sebacate (100 ml) was placed in a 3-neck round bottom flask (250 ml) and left to degass for 1 hour and 30 minutes at a temperature of 80° C. The temperature was then increased to 90° C. and (Et3NH)4[Zn10S4(SPh)16] cluster (0.47 g) added and allowed to stir for 30 minutes. After thirty minutes the temperature was increased to 100° C. and the following steps carried out. At 100° C. indium poly(oxyethylene glycol)750 monomethyl ether acetate (0.25 M, 6 ml) was added dropwise. After the 6 ml addition, the reaction mixture was left to stir for 5 minutes, followed by the dropwise addition of (TMS)3P (0.25 M, 6 ml). the reaction temperature was increased to 150° C. and a second addition of In(PEG-OMe-750) (0.25 M, 8 ml) was made dropwise, left to stir for 5 minutes, followed by a second dropwise addition of (TMS)3P (0.25 M, 8 ml). The reaction mixture was increased to 180° C. Indium poly(oxyethylene glycol)750 monomethyl ether acetate (0.25 M, 10 ml) was added dropwise, and after 5 minutes, (TMS)3P was added (0.25 M, 7 ml). The reaction temperature was increased to 200° C. and then annealed at 200° C. for 45 minutes after which the temperature was decreased to 160° C. and the reaction mixture left to anneal and stir vigorously for three days.
After the three day period the temperature was decreased to room temperature and the reaction mixture was isolated via the addition of acetonitrile until flocculation of the particles occurred. Once a precipitate had formed, the solvent was removed via cannula with the attachment of a filter. The remaining solid was redissolved into anhydrous chloroform (˜94 ml) and syringed into a Schlenk tube under nitrogen.
In a 3-neck flask, di-n-butyl sebacate ester (11 ml) and poly(oxyethylene glycol)350 monomethyl ether acetic acid (3.53 g, 7.618 mmol) were added and degassed at 50° C. for 15 minutes then cooled to room temperature. Indium phosphide quantum dots prepared according to Example 1 (3.3 ml, ˜100 mg) were then added and degassed for a further 15 minutes. Anhydrous zinc acetate (0.71 g, 3.87 mmol) was added as a solid and the flask flushed several times with nitrogen. The solution was then heated to 180° C. for 5 hours to form a zinc rich quantum dot surface. (TMS)2S (1 M, 1 ml, 1 mmol) was added dropwise at 180° C. and the solution left for 30 minutes to complete the ZnS layer. The nanoparticles quantum dots incorporating a InP core with a ZnS shell were isolated and cleaned using diethylether and hexane (50:50).
Indium phosphide quantum dots prepared according to Example 1 (3.3 ml, ˜100 mg) were transferred to a round bottomed flask and rotary evaporated to remove the chloroform. After the removal of chloroform the dots were dried under vacuum. In a 3-neck round bottom flask, dibutyl sebacate (10 ml), poly(oxyethylene glycol)2000 monomethyl ether acetic acid ligand (17.07 g, 7.74 mmol) and zinc acetate (0.71 g, 3.87 mmol) were placed under vacuum at a temperature of 110° C. The dots and dibutyl sebacate (5 ml) were placed into a Schlenk tube and degassed for 15 minutes. After the poly(oxyethylene glycol)2000 monomethyl ether acetic acid ligand and zinc acetate had dissolved to form a clear solution the temperature was decreased from 110° C. to 30° C. The dots in dibutyl sebacate were added to the poly(oxyethylene glycol)2000 monomethyl ether acetic acid and zinc acetate reaction mixture and the temperature increased to 180° C. Octanethiol (0.175 mo, 1 mmol) was added dropwise then the solution was heated to 220° C. for 90 minutes to facilitate decomposition of the thiol to sulfide ions and complete the ZnS shell. The nanoparticle quantum dots incorporating an InP core with a ZnS shell were isolated and cleaned using diethylether and hexane (50:50).
Dibutyl sebacate (100 mL) and 10-undecylenic acid (4.146 g) was added to a round bottom 3-neck flask (250 mL) and placed under high vacuum for 1 hour and 40 minutes at a temperature of 100° C. The temperature was reduced to 80° C., (Et3NH)4[Zn10S4(SPh)16] cluster (0.47 g) was added and the solution placed under high vacuum for 30 minutes. After this time the temperature was increased to 100° C. and the following additions were made: at 100° C. triethyl indium (0.5 M in dibutyl sebacate, 3 mL) was added dropwise. After the 3 mL addition, the reaction mixture was left to stir for 5 minutes, followed by the dropwise addition of (TMS)3P (0.5 M in dibutyl sebacate, 3 mL). The reaction temperature was increased to 160° C. and a second addition of triethyl indium (0.5 M, 0 mL) was made dropwise, left to stir for 5 minutes, followed by a second dropwise addition of (TMS)3P (0.5 M, 4 mL). The reaction mixture was increased to 200° C. and annealed for 1 hour after which time the temperature was decreased to 150° C. and the reaction mixture left to anneal and stir vigorously for three days.
After the three day period the temperature was decreased to room temperature and the reaction mixture was isolated via the addition of acetonitrile (150 mL). Once the precipitate had formed, the solvent was removed by centrifugation. The remaining solid was re-dissolved into anhydrous chloroform and transferred into a conical flask. 10-Undeylenic acid (2 g) was added.
Post-Operative Treatment
HF—Acid Etching of InP Quantum Dots
A hydrofluoric acid solution was prepared by combining 8 mL aqueous hydrofluoric acid (58-62 wt % solution) and THF (32 mL).
HF stock solution was added portion-wise to the InP particles dispersed in chloroform. The reaction mixture was continuously irradiated with light from a 500 W halogen lamp passed through a 560 nm filter. After this the solvent was removed by evaporation. The residue was dispersed in chloroform, re-precipitated with acetonitrile and separated by centrifugation. The solid was dispersed into dibutyl sebacate.
A flame dried three-necked flask (250 mL), equipped with a condenser with a side arm, a thermometer, a suba seal and a stirrer bar was charged with dibutyl sebacate (15 mL) and 10-undecylenic acid (2.6 g) and degassed at 80° C. for 1 hour and 30 minutes. The flask was back filled with nitrogen and indium phosphide core particles produced according to Example 4 (1.3 g in 15 mL dibutyl sebacate) were added, the mixture degassed at 80° C. for 40 minutes and then back filled with nitrogen.
Zinc acetate (1.4 g) was added, the mixture degassed at 80° C. for 30 minutes and backfilled with nitrogen three times. The reaction temperature was increased to 120° C. then 1-octanethiol (0.41 mL) was added dropwise. The temperature was then increased to 220° C. and held for 90 minutes. The temperature was decreased to 190° C., a further portion of 1-octanethiol (1.09 mL) was added and the temperature raised to 220° C. and held for 90 minutes. This completes the ZnS shell. The reaction solution was then cooled to 190° C. A ZnO layer was formed by the decomposition of the remaining zinc salt by the fast addition of 1-octanol (1.0 mL) and holding the temperature for 30 minutes. A further portion of 1-octanol (1.74 mL) was added to complete the ZnO layer and holding at the same temperature 30 minutes. The reaction mixture was then cooled to room temperature.
InP/ZnS/ZnO core-multishell nanoparticles were isolated under N2 with anhydrous acetonitrile and collected by centrifugation. The particles were dispersed in toluene and re-precipitated with anhydrous acetonitrile followed by centrifugation. The particles were re-dispersed in toluene followed by centrifugation. The supernatant was removed to a Schlenk tube.
The resulting core-multishell nanoparticles coated with 10-undecylenic acid as the capping agent may then be treated with a Hoveyda-Grubbs catalyst under standard conditions to cause the ligands to undergo acyclic diene polymerisation and/or ring closure metathesis and cross-link adjacent 10-undecylenic acid groups as shown in the exemplary reaction scheme below.
Forming a Shell of ZnS on InP Cores employing Ligand 1 as Capping Agent
Ligand 1 was produced according to the reaction scheme shown below.
A flame dried three-necked flask (100 mL), equipped with a condenser with a side arm, a thermometer, a suba seal and a stirrer bar was charged with indium phosphide core nanoparticles (0.155 g in 4.4 mL dibutyl sebacate) and degassed at 100° C. for 1 hour. The flask was allowed to cool to room temperature and then back filled with nitrogen. Zinc acetate (0.7483 g) and Ligand 1 (0.5243 g) was then added, the mixture degassed at 55° C. for 1 hour and backfilled with nitrogen. The reaction temperature was increased to 190° C., tert-nonyl mercaptan (0.29 mL) was added dropwise, the temperature increased to 190° C. and held for 1 hour and 30 minutes. The temperature was decreased to 180° C., 1-octanol (0.39 mL) added and the temperature held for 30 minutes. The reaction mixture was cooled to room temperature.
InP/ZnS core-shell nanoparticles particles were isolated under N2 in ethyl acetate by centrifugation. The particles were precipitated with acetonitrile followed by centrifugation. The particles were dispersed in chloroform and re-precipitated with acetonitrile followed by centrifugation. This dispersion-precipitation procedure using chloroform and acetonitrile was repeated four times in total. The InP/ZnS core-shell particles were finally dispersed in chloroform.
The resulting core-multishell nanoparticles coated with Ligand 1 as the capping agent may then be treated with a Hoveyda-Grubbs catalyst under standard conditions to cross-link adjacent terminal vinyl groups as shown in the exemplary reaction scheme below.
Alternatively, the terminal vinyl groups of Ligand 1 could be cross-linked before coordination to the nanoparticles as shown below.
Myristic acid (5.125 g), dibutyl sebacate (100 mL) and zinc undecylenate (4.32 g) were mixed together and degassed for 1 h under vacuum at 80° C. in a three-neck round bottom flask containing a stir bar on a heating mantle, and equipped with a thermocouple (and temperature controller). The reaction vessel was backfilled with nitrogen and the solid cluster [Et3NH]4[Zn10S4(SPh)16] (0.47 g) was added through a side port. The reaction was degassed for 30 min under vacuum at 80° C. and during this time the flask was backfilled three times with nitrogen. The reaction was heated to 100° C. and 3 mL of In(MA)3 solution (1M in dibutyl sebacate) was injected dropwise with a glass syringe, followed by 3 mL of P(TMS)3 solution (1M, in dibutyl sebacate). Secondary additions of In(MA)3 and P(TMS)3 solutions were made at 160° C., 190° C., 220° C. and 250° C., until the emission maximum of the particles reached 680 nm. The reaction was cooled at 160° C. and the heating was maintained for 72 h. The reaction was cooled to 30° C. and acetonitrile was added to flocculate the nanocrystals as a red powder. The powder was re-dispersed in chloroform (650 mL) and undecylenic acid (10 g) was added. The resulting solution was loaded in a 200 mL transparent vessel equipped with a stir bar and was etched in air by slow addition of an aqueous solution of HF (5%) under continuous stirring and illumination by light from a 450 W Xenon lamp. The etching process was complete in ˜15 hours after which time the InP cores were isolated by addition of methanol and re-dispersed in chloroform (see
PLmax=611 nm, UVmax=522 nm, FWHM=65 nm, PLQY=22%, inorganic content by TGA=74%.
Synthesis of InP/ZnS Core/Shell
InP cores in chloroform (100 mg) and therminol (10 mL) were mixed together and degassed for 30 min under vacuum at 50° C. in a three-neck round bottom flask containing a stir bar on a heating mantle, and equipped with a thermocouple (and temperature controller). Zinc acetate (380 mg) was added through a side port under a strong nitrogen flow and the resulting mixture was heated to 230° C. in 30 min, and held at this temperature for 2 hr. After this time a vinyl thiol compound, 11-mercapto-undecene, (0.5 mL; acting as both the sulfur source for the ZnS shell and the quantum dot surface binding ligand) was mixed with octadecene (0.5 mL) and the resulting solution was injected with a glass syringe. The reaction solution was held at 230° C. for further 1 h and 30 min during which time the luminescence increased substantially. The solution was cooled to 50° C. and the nanocrystals were isolated by addition of a mixture of toluene/acetone/methanol, re-dispersed in toluene and re-precipitated by addition of acetonitrile. The nanocrystals were re-dissolved in anhydrous toluene and stored under nitrogen (see
PLmax=597 nm, FWHM=72 nm, PLQY=54%, UVmax=536 nm, inorganic content by TGA=55%.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0814458.6 | Aug 2008 | GB | national |
This application is a continuation of U.S. patent application Ser. No. 12/537,553 filed Aug. 7, 2009, which claims the benefit of GB application number 0814458.6 filed Aug. 7, 2008. The entire disclosures of each of these applications are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12537553 | Aug 2009 | US |
| Child | 14084249 | US |
