Nanoparticle ligand

Abstract

The invention relates to nanoparticle ligands, particularly to quantum dot ligands, to their synthesis and use, and to the resulting nanoparticles.

Description

[0001] Nanoparticle ligand

[0002] Field

[0003] The invention relates to nanoparticle ligands, particularly to quantum dot ligands, to their synthesis and use, and to the resulting nanoparticles, quantum dot inks and polymer films.

[0004] Background

[0005] Nanoparticles such as quantum dots may be stabilized against agglomeration by coating them with a ligand layer. However, available organic ligands do not satisfy the stability requirement needed for novel applications such as microLED, wherein stable optical properties upon high-intensity photoexcitation for long periods (>1000 hours) at high nanoparticle loadings are desired. Neither the apolar ligands obtained after nanoparticle synthesis in solvents with high boiling points, nor common ligands introduced via postsynthetic ligand exchange protocols satisfy these requirements.

[0006] Hence, there is a need in the art for nanoparticle ligands that show stable optical properties upon high-intensity photoexcitation for long periods (>1000 hours) at high nanoparticle loadings.

[0007] Description of the invention

[0008] Nanoparticle ligand

[0009] In an aspect, the invention provides a nanoparticle ligand represented by formula (I): wherein X is a group capable of binding to the nanoparticle; wherein L is a linear chain of at least four units independently selected from methylene (■CH2-), ethenylene (-CH=CH-), and the ketone (-C(=O)-), ester (-C(=O)O-), thioester (■C(=S)O‘), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups; wherein R is 5- or 6-membered ring, preferably comprising a N, O or S ring atom, wherein the ring is optionally substituted; and wherein the nanoparticle ligand comprises 30 non-hydrogen atoms or less.

[0010] Such a nanoparticle ligand may be called a (nanoparticle) ligand according to or of the invention herein. Wherever a ligand or a nanoparticle ligand is mentioned herein, reference is made to a nanoparticle ligand according to the invention, unless explicitly mentioned otherwise.

[0011] A nanoparticle ligand according to the invention being a quantum dot ligand may also be called a quantum dot ligand according to or of the invention. Wherever a quantum dot ligand is mentioned herein, reference is made to a quantum dot ligand according to the invention, unless explicitly mentioned otherwise.

[0012] The nanoparticles ligands according to the invention, which are relatively short and are chemically stable and non-polymerizable, can be introduced to nanoparticles, specifically quantum dots, after their synthesis via ligand exchange (LE) protocols. As such, a stabilized nanoparticle according to the invention is obtained coated with relatively short and chemically stable, non-polymerizable ligands. This ensures that the stabilized nanoparticles do not agglomerate, polymerize and can be loaded safely into polymer films such as photoactive inks or resins with a high loa ding (>10 volume percent). Moreover, the nanoparticle ligands preserve the optical properties of the nanoparticles.

[0013] An additional advantage of the ligands according to the invention is that they can be formulated as an ink with a small enough viscosity to allow for ink-jet printing applications.

[0014] Nanoparticle-binding group X

[0015] In embodiments, the binding of X to the nanoparticle may be to any part comprised in the nanoparticle. For example, X may bind to the outer shell of a core / shell / shell quantum dot, or to the corresponding core of a simple quantum dot not comprising shells. The binding may be of any sort. Preferably, the binding is covalent binding.

[0016] In embodiments, X is a thiol group, a primary amine group, a secondary amine group, a quaternary ammonium salt, a urea, a thiourea, an imidizole group, an amide group, a carboxylic acid or carboxylate group, a phosphoric acid group, a phosphate group, a phosphite group, a phosphinic acid group, a phosphinate group, a phosphine oxide group, a phosphinite group, a phosphine group, a sulphonic acid group, an arsenic acid group, an arsenate group, an arsenous acid group, an arsenite group, an arsenic acid group, an arsine oxide group, or an arsine group.

[0017] In more preferred embodiments, X is COOH, SH, N(RN)2, N(RN)3+, SO3H, or PO3H. Herein, each instance of RNis independently H or a C1-4 alkyl, preferably H or a C1-3 alkyl, more preferably H or CH3, most preferably H.

[0018] Linear chain L

[0019] A linear chain of units (i.e. diradicals) -A-, -B-, -0, refers to the diradical -A-B-C-D-. Such a linear chain is said to comprise units -A-, -B-, and consist of units -A-, ■B‘, -C’ and An asymmetric unit such as the ester (-C(=0)0-) or the amide (-C(=O)NH-) functional group, denoted by -1B2-, may be incorporated into a chain in two different ways, resulting for example in -A-1B2-C-D- and -A-2B1-C-D-. Unless explicitly mentioned otherwise, both possibilities are encompassed when reference is made to a linear chain of A,1B2, C, D. A linear chain comprising n -A- units means that the linear chain consists of n nonoverlapping -A- units and optionally an undefined number of other types of units. For example, the chain ■ CH2CH2CH2CH2CH2CH2- comprises 3 -CH2CH2- units.

[0020] The linear chain -A-B-C-D- can be incorporated into formula (I) in two different ways, namely as X-A-B-C-D-R or as X-D-C-B-A-R. Unless explicitly mentioned otherwise, both possibilities are encompassed when reference is made to a nanoparticle ligand comprising the linear chain

[0021] In embodiments, any ester (-C(=O)O-), thioester (-C(=O)S-) and amide (-C(=O)NH-) functional group units comprised in L are bound on both sides to a carbon atom bearing at least one hydrogen atom. In other words, units such as -C(=O)O-O-C(=O)- and -S-C(=O)- C(=O)-NH‘ are disallowed according to this embodiment.

[0022] In embodiments, any ketone (-C(=O)-) functional group units comprised in L, and not part of an ester (-C(=O)O-), thioester (-C(=S)O-) or amide (-C(=O)NH-) functional group unit, are bound on both sides to a carbon atom. In other words, units such as -C(=O)-C(=O)- are disallowed according to this embodiment.

[0023] In embodiments, any S or O unit comprised in L, and not part of an ester (-C(=O)O-), thioester (-C(=S)O-) functional group unit, are bound on both sides to a carbon atom. In other words, units such as -O-O-, -O-S- and -S-S- are disallowed according to this embodiment.

[0024] In embodiments, L comprises 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, or 24 non-hydrogen atoms.

[0025] In embodiments, L comprises 6 to 24, 7 to 24, 8 to 24, 9 to 24, 10 to 24, 11 to 24, 12 to 24, 13 to 24, 14 to 24, 15 to 24, 16 to 24, 17 to 24, 18 to 24, 19 to 24, 20 to 24, 21 to 24, or 22 to 24 non-hydrogen atoms.

[0026] In embodiments, L comprises 6 to 23, 7 to 23, 8 to 23, 9 to 23, 10 to 23, 11 to 23, 12 to 23, 13 to 23, 14 to 23, 15 to 23, 16 to 23, 17 to 23, 18 to 23, 19 to 23, 20 to 23, 21 to 23, or 22 to 23 non-hydrogen atoms.

[0027] In embodiments, L comprises 6 to 22, 7 to 22, 8 to 22, 9 to 22, 10 to 22, 11 to 22, 12 to 22, 13 to 22, 14 to 22, 15 to 22, 16 to 22, 17 to 22, 18 to 22, 19 to 22, 20 to 22, or 21 to 22 nonhydrogen atoms.

[0028] In embodiments, L comprises 6 to 21 , 7 to 21 , 8 to 21 , 9 to 21 , 10 to 21 , 11 to 21 , 12 to 21 , 13 to 21 , 14 to 21 , 15 to 21 , 16 to 21 , 17 to 21 , 18 to 21 , 19 to 21 , or 20 to 21 non-hydrogen atoms.

[0029] In embodiments, L comprises 6 to 20, 7 to 20, 8 to 20, 9 to 20, 10 to 20, 11 to 20, 12 to 20, 13 to 20, 14 to 20, 15 to 20, 16 to 20, 17 to 20, 18 to 20, or 19 to 20 non-hydrogen atoms.

[0030] In embodiments, L comprises 6 to 19, 7 to 19, 8 to 19, 9 to 19, 10 to 19, 11 to 19, 12 to 19, 13 to 19, 14 to 19, 15 to 19, 16 to 19, 17 to 19, or 18 to 19 non-hydrogen atoms.

[0031] In embodiments, L comprises 6 to 18, 7 to 18, 8 to 18, 9 to 18, 10 to 18, 11 to 18, 12 to 18, 13 to 18, 14 to 18, 15 to 18, 16 to 18, or 17 to 18 non-hydrogen atoms.

[0032] In embodiments, L comprises 6 to 17, 7 to 17, 8 to 17, 9 to 17, 10 to 17, 11 to 17, 12 to 17, 13 to 17, 14 to 17, 15 to 17, or 16 to 17 non-hydrogen atoms. In embodiments, L comprises 6 to 16, 7 to 16, 8 to 16, 9 to 16, 10 to 16, 11 to 16, 12 to 16, 13 to 16, 14 to 16, or 15 to 16 non-hydrogen atoms.

[0033] In embodiments, L comprises 6 to 15, 7 to 15, 8 to 15, 9 to 15, 10 to 15, 11 to 15, 12 to 15, 13 to 15, or 14 to 15 non-hydrogen atoms.

[0034] In embodiments, L comprises 6 to 14, 7 to 14, 8 to 14, 9 to 14, 10 to 14, 11 to 14, 12 to 14, or 13 to 14 non-hydrogen atoms.

[0035] In embodiments, L comprises 6 to 13, 7 to 13, 8 to 13, 9 to 13, 10 to 13, 11 to 13, or 12 to 13 non-hydrogen atoms.

[0036] In embodiments, L comprises 6 to 12, 7 to 12, 8 to 12, 9 to 12, 10 to 12, or 11 to 12 nonhydrogen atoms.

[0037] In embodiments, L comprises 6 to 11 , 7 to 11 , 8 to 11 , 9 to 11 , or 10 to 11 non-hydrogen atoms.

[0038] In embodiments, L comprises 6 to 10, 7 to 10, 8 to 10, or 9 to 10 non-hydrogen atoms.

[0039] In embodiments, L comprises 6 to 9, 7 to 9, or 8 to 9 non-hydrogen atoms.

[0040] In embodiments, L comprises 6 to 8, or 7 to 8 non-hydrogen atoms.

[0041] In embodiments, L comprises 6 to 7 non-hydrogen atoms.

[0042] A short L groups ensures a relatively short length of the overall nanoparticle ligand. As a result, the nanoparticle ligand leads to stabilized nanoparticles that can be stabilized at high loadings.

[0043] In embodiments, L comprises a -CH2CH2- unit.

[0044] In embodiments, L comprises 1 , 2, 3, 4, 1 to 2, 1 to 3, 1 to 4, 2 to 3, 2 to 4, or 3 to 4 ■CH2CH2- units.

[0045] In embodiments, L comprises a -Z-CH2-CH2- unit, wherein Z is O or S. Preferably, Z is O.

[0046] In embodiments, L comprises 1 , 2, 3, 1 to 2, 1 to 3, or 2 to 3 -Z-CH2-CH2- units, wherein Z is O or S. Preferably, Z is O.

[0047] In embodiments, L comprises a -Z-C(=O)-CH2-CH2- unit, wherein Z is O or S. Preferably, Z is O.

[0048] In embodiments, L comprises 1 , 2, 3, 1 to 2, 1 to 3, or 2 to 3 -Z-C(=O)-CH2-CH2- units, wherein Z is O or S. Preferably, Z is O.

[0049] In embodiments, L comprises a -Z-CH2-CH2- or a Z-C(=O)-CH2-CH2‘ unit, wherein Z is O or S. Preferably, Z is O.

[0050] In embodiments, L comprises 1 , 2, 3, 1 to 2, 1 to 3, or 2 to 3 -Z-CH2-CH2- or Z-C(=O)-CH2- CH2- units, wherein Z is O or S. Preferably, Z is O.

[0051] In embodiments, the nanoparticle ligand can be represented by formula (II) or (III), wherein L’ is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (-C(=O)-), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups:

[0052] (II) (III).

[0053] In embodiments, the nanoparticle ligand is represented by for formula (XVI), wherein L1and L2constitute L.

[0054] (XVI).

[0055] In embodiments, L1does not withdraw electron density from S, and / or does not comprise an electron-withdrawing group, and / or does not comprise a heteroatom. Preferably, L2is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (■CH=CH‘), and the ketone (-C(=O)-), ester (-C(=O)O-), thioester (-C(=S)O-), amide (■C(=O)NH‘), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups.

[0056] Without being bound to this theory, the absence of a group withdrawing electron density from S (i.e. the sulfur atom part of X in formula (I), or explicitly drawn in formula (XVI)), decreases the acidity of the thiol group capable of binding to the core or to the shells, as the S-H bond is less polarized and less amenable to a heterolytic cleave (i.e. deprotonation). This has the advantage that the concentration of free thiolate anions is minimized in the medium in which the nanoparticles are present. In the case of quantum dot inks, this increases the shelflife of the inks as free thiolate ions would catalyze thiol-Michael addition that would lead to premature curing. Such premature curing could not be easily inhibited by additives to the quantum dot ink.

[0057] As used herein, the term "electron-withdrawing group" refers to a substituent or functional moiety that decreases the electron density of an adjacent atom (in casu a sulfur atom) by inductive (-I) or resonance (-M) effects. Electron-withdrawing groups include, but are not limited to, halogens (e.g., fluorine, chlorine, bromine, iodine), nitro (-NO2), cyano (-CN), carbonyl-containing groups such as aldehyde (-CHO), ketone (-CO-), carboxyl (-COOH), ester (-COOR), amide (-CONH2), sulfone (-SO2-), and trifluoromethyl (-CF3) moieties.

[0058] In embodiments, L1is a linear chain of at least two units independently selected from methylene (-CH2-) and ethenylene (-CH=CH-). Preferably, L2is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (■C(=O)‘), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (-0- CH2-), primary thioether (-S-CH2-) functional groups.

[0059] In embodiments, the nanoparticle ligand is represented by formula (XVII), wherein n is 2, 3, 4, 5 or 6; preferably 2, 3, 4 or 5; more preferably 2, 3 or 4: (XVII).

[0060] Ring R

[0061] In embodiments, R is an unsubstituted ring, meaning that R does not comprise nonhydrogen non-ring atoms.

[0062] In embodiments, R is an aromatic ring, preferably an unsubstituted aromatic ring. Preferably, R is a phenyl.

[0063] Wherever reference is made to a ring such as a phenyl, a cyclopentyl or an imidazole radical, the ring may be substituted or unsubstituted.

[0064] In embodiments, R is a heteroaromatic ring, preferably an unsubstituted heteroaromatic ring. Preferably R is a heteroaromatic ring comprising a N, O or S ring atom.

[0065] In embodiments, R is a 5-membered heteroaromatic ring, preferably an unsubstituted heteroaromatic ring. Preferably R is a heteroaromatic ring comprising a N, O or S ring atom.

[0066] In embodiments, R is a radical derived from 1 H-pyrrole, pyrazole, imidazole, 1 ,2,4-triazole,

[0067] 1 .2.3-triazole, tetrazole, furan, thiophene, oxazole, isoxazole, isothiazole, thiazole, 1 ,2,5- oxadiazole, 1 ,3, 4, -thiadiazole, or 1 ,2,5-thiadiazole.

[0068] In embodiments, R is a 6-membered heteroaromatic ring, preferably an unsubstituted 6- membered heteroaromatic ring. Preferably R is a heteroaromatic ring comprising a N, O or S ring atom.

[0069] In embodiments, R is a radical derived from pyridine, pyridazine, pyrimidine, pyrazine,

[0070] 1 .2.4-triazine, 1 ,3,5-triazine, 1 ,4-dioxine, 2H-1 ,2-oxazine, 4H-1 ,4-oxazine, 4H-1 ,4-thiazine, or 21-1,1 ,2-thiazine.

[0071] In embodiments, R is a partially saturated ring, preferably an unsubstituted partially saturated ring.

[0072] In embodiments, R is a saturated ring, preferably an unsubstituted saturated ring.

[0073] In embodiments, R is a cyclopentyl or a cyclohexyl, preferably an unsubstituted cyclopentyl or cyclohexyl.

[0074] In embodiments, R is a saturated heterocycle, preferably an unsubstituted saturated heterocycle. Preferably R is a heterocycle comprising a N, O or S ring atom.

[0075] In embodiments, R is a 5-membered saturated heterocycle, preferably an unsubstituted 5- membered saturated heterocycle. Preferably R is a heterocycle comprising a N, O or S ring atom.

[0076] In embodiments, R is a radical derived from pyrrolidine, pyrazolidine, imidazolidine, tetrahydrofuran, 1 ,3-dioxolane, tetrahydrothiophene, 1 ,2-oxathiolane, or 1 ,3-oxathiolane.

[0077] In embodiments, R is a 6-membered saturated heterocycle, preferably an unsubstituted 6- membered saturated heterocycle. Preferably R is a heterocycle comprising a N, O or S ring atom.

[0078] In embodiments, R is a radical derived from piperidine, piperazine, tetrahydropyran, 1 ,4- dioxane, thiane, 1 ,3-dithiane, 1 ,4-dithiane, 1 ,3,5-trithiane, morpholine, or thiomorpholine. In embodiments, the nanoparticle ligand can be represented by formula (IV), (V), (VI) or (VII), wherein Rais NH, O or S; wherein one of Rband Rcis NH, O or S, and the other is CH2; and wherein one of Rd, Reand Rfis NH, O or S, and the others are CH2:

[0079] (IV) (V) (VI) (VII).

[0080] In embodiments, the nanoparticle ligand can be represented by formula (IV), (V) or (VI).

[0081] In embodiments, the nanoparticle ligand can be represented by formula (IV, (V) or (VI I).

[0082] In embodiments, the nanoparticle ligand can be represented by formula (IV), (VI) or (VI I).

[0083] In embodiments, the nanoparticle ligand can be represented by formula (V), (VI) or (VI I).

[0084] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (V).

[0085] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (VI).

[0086] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (VI I).

[0087] In embodiments, the nanoparticle ligand can be represented by formula (V) or (VI).

[0088] In embodiments, the nanoparticle ligand can be represented by formula (V) or (VI I).

[0089] In embodiments, the nanoparticle ligand can be represented by formula (VI) or (VI I).

[0090] In embodiments, R is a substituted 5- or 6-membered ring. A substituted ring is an unsubstituted ring, i.e. a ring wherein all non-hydrogen atoms are ring atoms, wherein one of the hydrogen atoms is replaced by a non-hydrogen moiety. The non-hydrogen moiety is called a substituent and it is said that the ring is substituted by that substituent.

[0091] The structure of ring, together with the overall short length of the nanoparticle ligand, ensures a close packing. This leads to a stabilization at high loadings of the resulting stabilized nanoparticles in for example polymer films.

[0092] In embodiments, R is substituted by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0093] A pseudohalogen is -CN, -CP, -NC, -OH, -SH, -SeH,-TeH, -OCN, -SCN, -NCS, -SeCN, - TeCN, -N3, -NO, or -NO2. Preferably, a pseudohalogen is -CN, -NC, -OH, -SH, -OCN, -SCN, - NCS, -N3, -NO, or -NO2.

[0094] In embodiments, the nanoparticle ligand can be represented by formula (IV), (V), (VI) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0095] In embodiments, the nanoparticle ligand can be represented by formula (IV), (V) or (VI), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0096] In embodiments, the nanoparticle ligand can be represented by formula (IV), (V) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0097] In embodiments, the nanoparticle ligand can be represented by formula (IV), (VI) or (VI I), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0098] In embodiments, the nanoparticle ligand can be represented by formula (V), (VI) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0099] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (V), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0100] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (VI), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0101] In embodiments, the nanoparticle ligand can be represented by formula (IV) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0102] In embodiments, the nanoparticle ligand can be represented by formula (V) or (VI), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0103] In embodiments, the nanoparticle ligand can be represented by formula (V) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0104] In embodiments, the nanoparticle ligand can be represented by formula (VI) or (VII), wherein the five- or six-membered ring is substituted, preferably by one or more or C1-4 alkyls, C3-4 cycloalkyls, halogens, or pseudohalogens, wherein each C1-4 alkyl and C3-4 cycloalkyl may be substituted with one or more halogens or pseudohalogens.

[0105] Preferred ligands

[0106] In embodiments, the nanoparticle ligand comprises 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, or 30 non-hydrogens atoms.

[0107] In embodiments, the nanoparticle ligand comprises 30 or less, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, or 12 or less non-hydrogen atoms.

[0108] In embodiments, the nanoparticle ligand comprises 10 to 11 , to 12, to 13, to 14, to 15, to

[0109] 16, to 17, to 18, to 19, to 20, to 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0110] In embodiments, the nanoparticle ligand comprises 11 to 12, to 13, to 14, to 15, to 16, to

[0111] 17, to 18, to 19, to 20, to 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 nonhydrogens atoms.

[0112] In embodiments, the nanoparticle ligand comprises 12 to 13, to 14, to 15, to 16, to 17, to

[0113] 18, to 19, to 20, to 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0114] In embodiments, the nanoparticle ligand comprises 13 to 14, to 15, to 16, to 17, to 18, to

[0115] 19, to 20, to 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0116] In embodiments, the nanoparticle ligand comprises 14 to 15, to 16, to 17, to 18, to 19, to

[0117] 20, to 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0118] In embodiments, the nanoparticle ligand comprises 15 to 16, to 17, to 18, to 19, to 20, to

[0119] 21 , to 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0120] In embodiments, the nanoparticle ligand comprises 16 to 17, to 18, to 19, to 20, to 21 , to

[0121] 22, to 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0122] In embodiments, the nanoparticle ligand comprises 17 to 18, to 19, to 20, to 21 , to 22, to

[0123] 23, to 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0124] In embodiments, the nanoparticle ligand comprises 18 to 19, to 20, to 21 , to 22, to 23, to

[0125] 24, to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0126] In embodiments, the nanoparticle ligand comprises 19 to 20, to 21 , to 22, to 23, to 24, to

[0127] 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0128] In embodiments, the nanoparticle ligand comprises 20 to 21 , to 22, to 23, to 24, to 25, to

[0129] 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0130] In embodiments, the nanoparticle ligand comprises 21 to 22, to 23, to 24, to 25, to 26, to

[0131] 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0132] In embodiments, the nanoparticle ligand comprises 22 to 23, to 24, to 25, to 26, to 27, to

[0133] 28, to 29, or to 30 non-hydrogens atoms.

[0134] In embodiments, the nanoparticle ligand comprises 23 to 24, to 25, to 26, to 27, to 28, to

[0135] 29, or to 30 non-hydrogens atoms.

[0136] In embodiments, the nanoparticle ligand comprises 24 to 25, to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0137] In embodiments, the nanoparticle ligand comprises 25 to 26, to 27, to 28, to 29, or to 30 non-hydrogens atoms.

[0138] In embodiments, the nanoparticle ligand comprises 26 to 27, to 28, to 29, or to 30 nonhydrogens atoms. In embodiments, the nanoparticle ligand comprises 27 to 28, to 29, or to 30 non-hydrogens atoms.

[0139] In embodiments, the nanoparticle ligand comprises 28 to 29, or to 30 non-hydrogens atoms.

[0140] In embodiments, the nanoparticle ligand comprises 29 to 30 non-hydrogens atoms.

[0141] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII) to (XV), wherein L’ is a linear chain of at least two units independently selected from methylene (■CH2-), ethenylene (-CH=CH-), and the ketone (-C(=O)-), ester (-C(=O)O-), thioester (■C(=S)O‘), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups; wherein Rais NH, O or S; wherein one of Rband Rcis NH, O or S, and the other is CH2; and wherein one of Rd, Reand Rfis NH, O or S, and the others are CH2:

[0142] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII) to (XI), or by any one of formulae (XII) to (XV).

[0143] In embodiments, the nanoparticle ligand can be represented by formula (VIII) or (XII), or

[0144] (IX) or (XIII), or (X) or (XIV), or (XI) or (XV).

[0145] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX),

[0146] (X), (XIII) or (XIV).

[0147] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII),

[0148] (XI), (XII) or (XV).

[0149] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX) to (XI) or (XIII) to (XV).

[0150] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII) to (XV), wherein X is SH.

[0151] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII) to (XI), or by any one of formulae (XII) to (XV); wherein X is SH.

[0152] In embodiments, the nanoparticle ligand can be represented by formula (VIII) or (XII), or (IX) or (XIII), or (X) or (XIV), or (XI) or (XV); wherein X is SH. In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX),

[0153] (X), (XIII) or (XIV); wherein X is SH.

[0154] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII),

[0155] (XI), (XII) or (XV); wherein X is SH.

[0156] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX) to (XI) or (XIII) to (XV); wherein X is SH.

[0157] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII), (IX), (XVIII), (XIX), (XII), (XIII), (XX) or (XXI), wherein L’ is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (■C(=O)‘), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (■(□- CH2-), primary thioether (-S-CH2-) functional groups; wherein Ra, Rb, Rc, Rd, Re, Rf, Rb, Rc, Rdand Reare independently NH, O, S or CH2:

[0158] (XX) (XXI).

[0159] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII),

[0160] (IX), (XVIII) or (XIX), or by any one of formulae (XII), (XIII), (XX) or (XXI). Preferably, R comprises 2 heteroatoms.

[0161] In embodiments, the nanoparticle ligand can be represented by formula (VIII) or (XII), or (IX) or (XII), or (XVIII) or (XX), or (XIX) or (XXI). Preferably, R comprises 2 heteroatoms.

[0162] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX), (XVIII), (XIII) or (XX). Preferably, R comprises 2 heteroatoms.

[0163] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII), (XIX), (XII), (XXI). Preferably, R comprises 2 heteroatoms.

[0164] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX), (XVIII), (XIX), (XIII), (XX), or (XXI). Preferably, R comprises 2 heteroatoms.

[0165] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII), (IX), (XVIII), (XIX), (XII), (XIII), (XX) or (XXI); wherein X is SH. Preferably, R comprises 2 hetero atoms. In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII), (IX), (XVIII) or (XIX), or by any one of formulae (XII), (XIII), (XX) or (XXI); wherein X is SH. Preferably, R comprises 2 heteroatoms.

[0166] In embodiments, the nanoparticle ligand can be represented by formula (VIII) or (XII), or (IX) or (XII), or (XVIII) or (XX), or (XIX) or (XXI); wherein X is SH. Preferably, R comprises 2 hetero atoms.

[0167] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX), (XVIII), (XIII) or (XX); wherein X is SH. Preferably, R comprises 2 heteroatoms.

[0168] In embodiments, the nanoparticle ligand can be represented by any one of formulae (VIII), (XIX), (XII), (XXI); wherein X is SH. Preferably, R comprises 2 heteroatoms.

[0169] In embodiments, the nanoparticle ligand can be represented by any one of formulae (IX), (XVIII), (XIX), (XIII), (XX), or (XXI); wherein X is SH. Preferably, R comprises 2 heteroatoms.

[0170] In embodiments, the nanoparticle ligand can be represented by any one of formulae (1) to

[0171] The ligands shown above are non-polymerizable, chemically stable and relatively short.

[0172] This ensures a close packing and thus a stabilization at a high loading of the nanoparticles in for example polymer films. Moreover, these ligands are somewhat polar, being neither fully apolar or highly polar, leading to a lower tendency to agglomerate in the presence of common solvent. In other words, this leads to an overall higher interoperability with common solvents and media used in for example polymer films.

[0173] Nanoparticles

[0174] A nanoparticles means a particle having a particle size in the nanometer range comprising a crystalline material. Examples of nanoparticles are quantum dots, quantum rods, nanowires, nanofibers and nanotubes.

[0175] Nanoparticles fall into two general categories: charge-stabilized and sterically stabilized nanoparticles. Charge-stabilized nanoparticles are typically synthesized in polar media. Since they bear a surface charge, they are unlike to agglomerate due to electrostatic repulsion. Sterically stabilized nanoparticles on the other hand bear no strong surface charges, leading to a high propensity to agglomerate. This is countered by providing the, generally inorganic, nanoparticles with an external layer of organic nanoparticle ligands. These nanoparticle ligands modify the entropy, solvation energy, and / or steric shielding of the nanoparticles, mitigating the tendency to agglomerate and allowing for a fine-tuning of the solubility properties of the overall complex.

[0176] The bond strength of the nanoparticle ligands to the nanoparticle varies from low strength Lewis interactions to covalent bonds. Preferably, the nanoparticle ligands in this application form a covalent bond with a nanoparticle.

[0177] Below, several embodiments and preferences are described for (sterically) stabilized nanoparticles comprising the nanoparticle ligands of the invention. Wherever properties of nanoparticles are discussed, these can be applied to the corresponding stabilized nanoparticles as well. Likewise, these embodiments and preferences can be applied mutatis mutandis to nanoparticle ligands of the invention, methods of preparing (stabilized) nanoparticles, and other related aspects of the invention.

[0178] In an aspect, the invention provides a stabilized nanoparticle comprising a nanoparticle and a ligand layer, wherein the ligand layer consists of nanoparticle ligands of the invention. Such a stabilized nanoparticle may be called a (sterically) stabilized nanoparticle according to or of the invention herein. Wherever a (sterically) stabilized nanoparticle is mentioned herein, reference is made to a stabilized nanoparticle according to the invention, unless explicitly mentioned otherwise.

[0179] In embodiments, the nanoparticle is a quantum dot. A quantum dot is a (semi)spherical nanoparticle comprising a core, optionally a first layer on the core, and optionally a second layer on the first layer. Such a quantum dot may also be called a core, core / shell or core / shell / shell quantum dot, respectively. It is understood that a quantum dot is different from a quantum rod, which is an elongated semiconductor nanoparticle. Such a quantum dot may be called a quantum dot according to or of the invention herein. Wherever a quantum dot is mentioned herein, reference is made to a quantum dot according to the invention, unless explicitly mentioned otherwise. A stabilized quantum dot is a stabilized nanoparticles, wherein the nanoparticle is a quantum dot. A core / shell / shell quantum dot may be represented by core / first layer / second layer. For example, InP / ZnSe / Zm-xCdxS refers to a quantum dot comprising an InP core (i.e. a core comprising or (essentially) consisting of InP), a ZnSe first layer (i.e. a first layer comprising or (essentially) consisting of ZnSe), and a Zm-xCdxS second layer (i.e. a second layer comprising or (essentially) consisting of a Zn, Cd and S alloy, wherein the molar ratio between the elements are as indicated). In another example, lnP / Zn(S,Se) / ZnS refers to a quantum dot comprising an InP core, a Zn(S,Se) first layer (i.e. a first layer comprising or (essentially) consisting of Zn, S and Se alloy, wherein the molar ratio between Zn and S+Se is essentially 1) and a ZnS second layer. In this context, the terminology AB or ABC core, layer or shell, refers to a core, layer or shell comprising or (essentially) consisting of AB or ABC, respectively. Similar definition can be applies to core or core / shell quantum dots.

[0180] The composition of the quantum dot, the core, the first layer and / or the second layer (i.e. the elements comprised therein and their molar ratios) may be determined by EDX (Energy- dispersive X-ray spectroscopy) on an ensemble of quantum dots.

[0181] In the context of this application, a quantum dot is able to absorb and emit electromagnetic radiation, wherein the wavelength of the emitted radiation is higher than the wavelength of the absorbed radiation. Preferably, the absorbed radiation is in the visible spectrum (“visible light”).

[0182] A suitable measure for photoluminescence is the “photoluminescent quantum yield” (PLQY), which is the ratio of the number of emitted photons that can be collected to the number of photons absorbed by the quantum dots. This PLQY may also be called the internal PLQY, in contrast with the external PLQY which is defined as the ratio of the total number of emitted photons to the number of photons provided to the quantum dots. Unless explicitly mentioned, PLQY refers to the internal PLQY herein.

[0183] In embodiments, a quantum dot or stabilized quantum dot has a PLQY of at least 85%, at least 85.5%, at least 86%, at least 86.5%, at least 87%, at least 87.5%, at least 88%, at least 88.5%, at least 89%, at least 89.5%, at least 90%, at least 90.5%, at least 91 %, at least 91.5%, at least 92%, at least 92.5%, at least 93%, at least 93.5%, at least 94%, at least 94.5%, at least 95%, at least 95.5%, at least 96%, at least 96.5%, at least 97%, at least 97.5%, at least 98%, at least 98.5%, at least 99%, or at least 99.5%.

[0184] Attachment of nanoparticle ligands according to the invention to a quantum dot does not change the PLQY of the quantum dot by more than 10%, 9.5%, 9%, 8.5%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1 %, or 0.5%.

[0185] It is understood that (stabilized) quantum dots are generally obtained as a plurality of (stabilized) quantum dots. Wherever a reference is made to a property of a single (stabilized) quantum dot, reference is preferably made to the average value of the property over the plurality of (stabilized) quantum dots. The average may be a number-weighted average or a mass-weighted average.

[0186] In embodiments, the quantum dot has a diameter from 4 up to 30 nm, up to 29 nm, up to

[0187] 28 nm, up to 27 nm, up to 26 nm, up to 25 nm, up to 24 nm, up to 23 nm, up to 22 nm, up to

[0188] 21 nm, up to 20 nm, up to 19 nm, up to 18 nm, up to 17 nm, up to 16 nm, up to 15 nm, up to 14 nm, up to 13 nm, up to 12 nm, up to 11 nm, up to 10 nm, up to 9.5 nm, up to 9 nm, up to 8.5 nm, up to 8 nm. In embodiments, the quantum dot has a diameter from 6 up to 30 nm, up to 29 nm, up to 28 nm, up to 27 nm, up to 26 nm, up to 25 nm, up to 24 nm, up to 23 nm, up to 22 nm, up to 21 nm, up to 20 nm, up to 19 nm, up to 18 nm, up to 17 nm, up to 16 nm, up to 15 nm, up to 14 nm, up to 13 nm, up to 12 nm, up to 11 nm, up to 10 nm, up to 9.5 nm, up to 9 nm, up to 8.5 nm, up to 8 nm. Quantum dots having an average diameter in this range can provide good optical properties for down-conversion because the absorption coefficient at wavelengths corresponding to the pump light strongly exceeds the absorption coefficient at wavelengths corresponding to the quantum dot emission. Preferably, the diameter of a quantum dot refers to the diameter defined by the core, and the first and second shell if present, as the width of the ligand layer may be ill-defined. In other words, the diameter of a (stabilized) nanoparticle may be defined as the diameter of a corresponding (non-stabilized) nanoparticle not comprising a ligand layer and only comprising a core, and optionally a first and second shell.

[0189] Core of the quantum dot

[0190] The core comprised in the quantum dot is (made) of a binary, ternary or quaternary material (or compound). A binary, ternary or quaternary material is a material consisting of 2, 3 or 4 different elements, respectively. It is understood that the order of the elements in the formula of a tertiary or quaternary material is a matter of convention and has no bearing on the composition of the material.

[0191] In embodiments, the quantum dot comprises a core of a binary or ternary material.

[0192] In embodiments, the quantum dot comprises a core of a binary, ternary or quaternary material lll-V material or a core of a binary or ternary ll-VI material.

[0193] In embodiments, the quantum dot comprises a core of InP, InGaP, InAs, InSb or InSbAs.

[0194] In embodiments, the quantum dot comprises a core of InP, InAs, InSb, GaP, GaAs, GaSb, AIP, AlAs or AISb.

[0195] In embodiments, the quantum dot comprises a core of InPAs, InPSb, InAsSb, GaPAs, GaPSb, GaAsSb, AlPAs, AlPSb, AlAsSb, InGaP, InGaAs, InGaSb, InAlP, InAIAs, InAISb, GaAlP, GaAIAs or GaAISb.

[0196] In embodiments, the quantum dot comprises a core of InGaP or InSbAs.

[0197] In embodiments, the quantum dot comprises a core of InPAsSb, GaPAsSb, AlPAsSb, InGaPAs, InGaPSb, InGaAsSb, InAIPAs, InAIPSb, InAIAsSb, GaAIPAs, GaAIPSb, GaAIAsSb, InGaAlP, InGaAIAs or InGaAISb.

[0198] In embodiments, the quantum dot comprises a core of InP. Such cores are highly attractive for downconverter purposes as they emit light in the visible spectrum upon illumination with blue (and UV) light when they are 2 nm to 4 nm in diameter.

[0199] In embodiments, the quantum dot comprises a core of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe or HgTe, preferably ZnS, ZnSe or ZnTe, more preferably ZnS or ZnSe.

[0200] In embodiments, the quantum dot comprises a core of ZnCdS, ZnCdSe, ZnSSe or CdSSe. In embodiments, the quantum dot comprises a core having a diameter from 1 nm up to 5 nm, preferably from 1.5 nm up to 4.5 nm, more preferably from 2 nm up to 4 nm. A suitable core diameter ensures that the quantum dots emit light in the visible spectrum upon illumination with blue (and UV) light.

[0201] First layer of the quantum dot

[0202] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is a (semi)spherical layer arranged concentrically around the core.

[0203] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer surrounds the core and, optionally, the second layer surrounds the first layer.

[0204] In embodiments, the first layer is a solid layer.

[0205] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of a binary or ternary ll-VI material.

[0206] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe or HgTe, preferably ZnS, ZnSe or ZnTe, more preferably ZnS or ZnSe, most preferably ZnSe.

[0207] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of ZnCdS, ZnCdSe, ZnSSe or CdSSe.

[0208] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of ZnSe or ZnCdSe.

[0209] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of ZnCdSe, wherein the molar ratio Cd / (Cd+Zn) in the first layer (i.e. the molar fraction of Cd) is between 0.001 and 1 .0, more preferably from 0.02 up to 0.2, most preferably from 0.025 up to 0.133.

[0210] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of ZnCdSe, wherein the molar ratio between the number of Se atoms and the total number of Zn and Cd atoms comprised in the first layer is from 0.50 up to 1 .50, from 0.55 up to 1 .45, from 0.60 up to 1 .40, from 0.65 up to 1 .35, from 0.70 up to 1 .30, from 0.75 up to 1 .25, from 0.80 up to 1 .20, from 0.85 up to 1.15, from 0.90 up to 1 .10, from 0.95 up to 1 .05, from 0.96 up to 1 .04, from 0.97 up to 1 .03, from 0.98 up to 1 .02, from 0.99 up to 1 .01 . This ratio can be determined by EDX (Energy-dispersive X-ray spectroscopy) on an ensemble of quantum dots.

[0211] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer is of ZnSe, wherein the first layer does not comprise Cd.

[0212] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the first layer has a thickness up to 1.0 nm, preferably between 0.1 nm and 0.9 nm, more preferably between 0.2 nm and 0.8 nm.

[0213] Second layer of the quantum dot In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the second layer is a (semi)spherical layer arranged concentrically around the first layer or the core, respectively.

[0214] In embodiments, the quantum dot is a core / shell or core / shell / shell quantum dot, wherein the second layer surrounds the first layer or the core, respectively.

[0215] In embodiments, the second layer is a solid layer.

[0216] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of a binary or ternary ll-VI material.

[0217] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe or HgTe, preferably ZnS, ZnSe or ZnTe, more preferably ZnS or ZnSe, most preferably ZnS.

[0218] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of ZnCdS, ZnCdSe, ZnSSe or CdSSe.

[0219] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of ZnS or ZnCdS.

[0220] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of ZnCdS, wherein the molar ratio Cd / (Cd+Zn) in the second layer (i.e. the molar fraction of Cd) is between 0.001 and 1 .0, more preferably from 0.02 up to 0.2, most preferably from 0.025 up to 0.133.

[0221] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of ZnCdS, wherein the molar ratio between the number of S atoms and the total number of Zn and Cd atoms comprised in the second layer is from 0.50 up to 1 .50, from 0.55 up to 1 .45, from 0.60 up to 1 .40, from 0.65 up to 1 .35, from 0.70 up to 1 .30, from 0.75 up to 1 .25, from 0.80 up to 1 .20, from 0.85 up to 1.15, from 0.90 up to 1 .10, from 0.95 up to 1 .05, from 0.96 up to 1 .04, from 0.97 up to 1 .03, from 0.98 up to 1 .02, from 0.99 up to 1 .01 . This ratio can be determined by EDX (Energy-dispersive X-ray spectroscopy) on an ensemble of quantum dots.

[0222] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is of ZnS, wherein the second layer does not comprise Cd.

[0223] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer has a thickness up to 10 nm, preferably between 1 nm and 10 nm.

[0224] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the ratio between the volume of the second layer and the volume of the core is from 10 up to 50, from 15 up to 45, from 15 up to 40, from 15 up to 35, from 15 up to 30, or from 15 up to 25. If the volume of the second layer is increased, and thus the volume of the quantum dots, the absorption per quantum dot increases too.

[0225] Preferred quantum dots In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer is a (semi)spherical layer arranged concentrically around the first layer, and the first layer is a (semi)spherical layer arranged concentrically around the core.

[0226] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the second layer surrounds the first layer, and the first layer surrounds the core.

[0227] In embodiments, both the first layer and the second layer are solid layers.

[0228] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first and the second layer are independently of a binary or ternary ll-VI material, preferably wherein the core is of a binary, ternary or quaternary material lll-V material or of a binary or ternary ll-VI material.

[0229] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first and the second layer are independently of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe or HgTe, preferably ZnS, ZnSe or ZnTe, more preferably ZnS or ZnSe. Preferably, the core is of InP.

[0230] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first and the second layer are independently of ZnCdS, ZnCdSe, ZnSSe or CdSSe. Preferably, the core is of InP.

[0231] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first and the second layer are independently of ZnS, ZnSe, ZnCdS or ZnCdSe. Preferably, the core is of InP.

[0232] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of InP, InGaP, InAs, InSb or InSbAs. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0233] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of InP, InAs, InSb, GaP, GaAs, GaSb, AIP, AlAs or AlSb. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0234] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of InPAs, InPSb, InAsSb, GaPAs, GaPSb, GaAsSb, AlPAs, AlPSb, AlAsSb, InGaP, InGaAs, InGaSb, InAlP, InAIAs, InAISb, GaAlP, GaAIAs or GaAISb. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0235] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of InGaP or InSbAs. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS. In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of InPAsSb, GaPAsSb, AlPAsSb, InGaPAs, InGaPSb, InGaAsSb, InAIPAs, InAIPSb, InAIAsSb, GaAIPAs, GaAIPSb, GaAIAsSb, InGaAlP, InGaAIAs or InGaAISb. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0236] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe or HgTe, preferably ZnS, ZnSe or ZnTe, more preferably of ZnS or ZnSe. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0237] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the core is of ZnCdS, ZnCdSe, ZnSSe or CdSSe. Preferably, the first and the second layer are independently of ZnS or ZnSe. More preferably, the first layer is of ZnS or ZnSe and the second layer is of ZnS. Most preferably, the first layer is of ZnSe and the second layer is of ZnS.

[0238] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first layer is of ZnCdSe and the second layer is of ZnCdS, wherein the molar ratio Cd / (Cd+Zn) in the first and the second layer (i.e. the molar fraction of Cd) is between 0.001 and 1 .0, more preferably from 0.02 up to 0.2, most preferably from 0.025 up to 0.133.

[0239] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first layer if of ZnCdSe and the second layer is of ZnCdS, wherein the molar ratio between the number of Se or S atoms, respectively, and the total number of Zn and Cd atoms comprised in the first or the second layer is from 0.50 up to 1 .50, from 0.55 up to 1 .45, from 0.60 up to 1 .40, from 0.65 up to 1 .35, from 0.70 up to 1 .30, from 0.75 up to 1 .25, from 0.80 up to 1 .20, from 0.85 up to 1.15, from 0.90 up to 1.10, from 0.95 up to 1.05, from 0.96 up to 1.04, from 0.97 up to 1.03, from 0.98 up to 1 .02, from 0.99 up to 1 .01 . This ratio can be determined by EDX (Energy- dispersive X-ray spectroscopy) on an ensemble of quantum dots.

[0240] In embodiments, the quantum dot is a core / shell / shell quantum dot, wherein the first layer is of ZnSe and the second layer is of ZnS, wherein neither the first layer nor the second layer comprises Cd.

[0241] In embodiments, the quantum dot may be represented by InP / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0242] In embodiments, the quantum dot may be represented by InP / ZnSe / ZnS. InP / ZnSe / ZnS quantum dots of this kind are highly efficient and narrow emitters in the visible spectrum, making them useful as luminescent downconverters in for example LED displays.

[0243] In embodiments, the quantum dot may be represented by InGaP / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0244] In embodiments, the quantum dot may be represented by InGaP / ZnSe / ZnS. In embodiments, the quantum dot may be represented by InAs / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0245] In embodiments, the quantum dot may be represented by InAs / ZnSe / ZnS.

[0246] In embodiments, the quantum dot may be represented by InSb / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0247] In embodiments, the quantum dot may be represented by InSb / ZnSe / ZnS.

[0248] In embodiments, the quantum dot may be represented by InSbAs / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0249] In embodiments, the quantum dot may be represented by InSbAs / ZnSe / ZnS.

[0250] In embodiments, the quantum dot may be represented by InP / ZnSe / Zni-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0251] In embodiments, the quantum dot may be represented by InP / ZnSe / ZnS.

[0252] In embodiments, the quantum dot may be represented by InGaP / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0253] In embodiments, the quantum dot may be represented by InGaP / ZnSe / ZnS.

[0254] In embodiments, the quantum dot may be represented by InAs / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0255] In embodiments, the quantum dot may be represented by InAs / ZnSe / ZnS.

[0256] In embodiments, the quantum dot may be represented by InSb / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0257] In embodiments, the quantum dot may be represented by InSb / ZnSe / ZnS.

[0258] In embodiments, the quantum dot may be represented by InSbAs / ZnSe / Zm-xCdxS, wherein x is preferably from 0.001 up to 1 .0, from 0.02 up to 0.2, or from 0.025 up to 0.133.

[0259] In embodiments, the quantum dot may be represented by InSbAs / ZnSe / ZnS.

[0260] Ligand layer

[0261] In embodiments, the ligand layer is a (semi)spherical layer arranged concentrically around the core (in case of a core quantum dot), around the first shell (in case of a core / shell quantum dot) or around the second shell (in case of a core / shell / shell quantum dot).

[0262] In embodiments, the ligand layer surrounds the core (in case of a core quantum dot), the first shell (in case of a core / shell quantum dot) or the second shell (in case of a core / shell / shell quantum dot).

[0263] The ligand layer may also be called the ligand shell, the third shell or layer, or the external shell or layer.

[0264] It is understood that the nanoparticle ligands comprised in the ligand layer may be bound to the core, first shell or second shell, covalently or otherwise. Specifically, the X comprised in the nanoparticle ligand can bind the nanoparticle.

[0265] In embodiments, the ligand layer is bound to the nanoparticle in the stabilized nanoparticle.

[0266] In embodiments, the ligand layer comprises from 10 up to 2000, from 10 up to 1900, from 10 up to 1800, from 10 up to 1700, from 10 up to 1600, from 10 up to 1500, from 10 up to 1400, from 10 up to 1300, from 10 up to 1200, from 10 up to 1100, from 10 up to 1000, from 10 up to 900, from 10 up to 800, from 10 up to 700, from 10 up to 600, from 10 up to 500, from 10 up to 400, from 10 up to 300 organic, from 50 up to 800, from 100 up to 700, from 150 up to 600 or from 200 up to 500 nanoparticle ligands (per nanoparticle).

[0267] Synthesis of nanoparticles

[0268] In an aspect, the invention provides a method for preparing a stabilized nanoparticle of the invention, particularly a quantum dot of the invention, comprising the steps of:

[0269] (a) providing a core of a binary, ternary or quaternary lll-V material, or a binary orternary ll-VI material;

[0270] (b) optionally forming one or more shells on the core;

[0271] (c) forming a first ligand layer on the core or on the shells;

[0272] (d) partially or fully exchanging the first ligand layer for a second ligand layer consisting of nanoparticle ligands of the invention.

[0273] Such a method for preparing a stabilized nanoparticle may be called a method according to or of the invention herein.

[0274] In an aspect, the invention provides a nanoparticle, particularly a quantum dot, obtainable by a method according to the invention.

[0275] The nanoparticle ligand in step (d) may be called the second ligand.

[0276] Step (d) may be called a ligand exchange (LE) step. Preferably, the ligand exchange step is performed in an apolar organic solvent. An example of a ligand exchange step is described in Example 2.

[0277] The rationale behind this step is to exchange the first ligand layer, which may not result in limited chemical stability upon high loading of the nanoparticles in for example a polymer film, by a second ligand layer consisting of nanoparticle ligands of the invention. The second ligand layer ensures a high chemical (low agglomeration, polymerization, etc.) and optical (PLQY, etc.) stability upon high loading (e.g., >10 volume percent) of the nanoparticles.

[0278] In embodiments, the first ligand layer consists of nanoparticles ligand not according to the invention.

[0279] In embodiments, the first ligand layer consists of apolar long-chain nanoparticle ligands not according to the invention. Preferably, long means comprising more than 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, or 30 non-hydrogen atoms.

[0280] In embodiments, step (d) of a method of the invention entails exchanging at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1 %, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9% the first ligand layer for a second ligand layer consisting of nanoparticle ligands of the invention. Preferably, the exchange is substantially a full exchange. Nanoparticle ink

[0281] In an aspect, the invention provides an ink comprising a nanoparticle according to the invention, particularly a quantum dot according to the invention, and a curable composition.

[0282] Such an ink may be called an ink according to or of the invention, or a nanoparticle ink according to or of the invention. Correspondingly, wherever the nanoparticle of the invention is a quantum dot of the invention, the nanoparticle ink (of the invention) may be called a quantum dot ink (of the invention).

[0283] The nanoparticle, particularly the quantum dot, comprised in the ink may be obtained via a method of the invention.

[0284] The curable composition is a composition which can be cured. Curing entails the toughening or hardening of the curable composition by polymerization and / or cross-linking of polymer chains. In the context of the nanoparticle ink, the curing entails the polymerization and / or cross-linking of the curable composition, thereby encapsulating the nanoparticles comprised in the ink, preferably in homogeneously, without aggregation and while maintaining their photoluminescent properties, thereby forming a polymer film (i.e. a quantum dot film or patterns). The term curing of the nanoparticle ink and the term curing of the curable composition may be used interchangeably herein.

[0285] The nanoparticle ligands of the invention have the advantage that they can protect surface- stabilized quantum dots that can be put in inks with a long shelf-life at a high solid-loading. These properties are maintained when the inks are processed under ambient conditions.

[0286] The nanoparticle ligands of the invention further help to obtain a homogeneous and nonaggregated distribution of the nanoparticles in the (cured) polymer film. The nanoparticles comprised in the polymer film are characterized by a high absorbance of UV or blue light, a high quantum efficiency and / or high photostability.

[0287] Preferably, the R group of the nanoparticle ligand of the invention is chosen to ensure compatibility with the curable composition, further enhancing the distribution and the properties of the nanoparticles in the ink and the polymer film, as described above.

[0288] Preferably, the L1group of the nanoparticles of the invention is chosen to prevent premature curing due to the presence of free thiolate ions, as described above.

[0289] Preferably, the curable composition comprises a monomer or oligomer which may be polymerized and / or crosslinked (i.e. cured).

[0290] Preferably, the curable composition comprises an ethylenically unsaturated monomer, a cyclic ether, a cyclic thioether, a siloxane-based resin, a cyanate ester, a reactive ester, a thiol, or a Michael donor or acceptor. The ethylenically unsaturated monomer may be selected from acrylates, methacrylates, maleimides, fumarates, itaconates, or vinyl-functionalized compounds, while the cyclic ether may comprise epoxides, oxetanes, or oxiranes. The curable composition may further contain isocyanate-functionalized monomers, benzoxazines, or urethane-acrylate hybrids to enhance mechanical, optical, or chemical resistance properties. Additionally, multifunctional oligomers, including polyether, polyester, or polycarbonate-based reactive resins, may be incorporated into the curable composition to tailor viscosity and filmforming behaviour.

[0291] Preferably, the curable composition comprises an acrylate (monomer), a methacrylate (monomer), an alkene (monomer), an epoxy (monomer), a siloxane (monomer) or a thiol.

[0292] Preferably, the curable composition comprises an acrylate (monomer), a methacrylate (monomer), an alkene (monomer), an epoxy (monomer), or a siloxane (monomer).

[0293] Preferably, the curable composition comprises a thiol and a compound selected from an acrylate (monomer), a methacrylate (monomer), an alkene (monomer), an epoxy (monomer), or a siloxane (monomer).

[0294] Preferably, the nanoparticle ink comprises a photo initiator system, wherein said photo initiator is activated upon exposure to ultraviolet (UV) radiation or electron beam (EB) irradiation.

[0295] Preferably, the curing is ultraviolet curing, thermal curing or solvent-based curing. Preferably, thermal curing comprises heating of the nanoparticle ink at a temperature from 80°C to 150°C.

[0296] Preferably, the weight concentration of the nanoparticle in the nanoparticle ink is more than

[0297] 5 wt.%, at least 6 wt.%, at least 7 wt.%, at least 8 wt.%, at least 9 wt.%, at least 10 wt.%, at least 11 wt.%, at least 12 wt.%, at least 13 wt.%, at least 14 wt.%, at least 15 wt.%, at least 16 wt.%, at least 17 wt.%, at least 18 wt.%, at least 19 wt.%, at least 20 wt.%, at least 21 wt.%, at least 22 wt.%, at least 23 wt.%, at least 24 wt.%, at least 25 wt.%, at least 26 wt.%, at least 27 wt.%, at least 28 wt.%, at least 29 wt.%, or at least 30 wt.%.

[0298] Preferably, the volume concentration of the nanoparticle in the nanoparticle ink is at least 3 v.%, at least 3.5 v.%, at least 4 v.%, at least 4.5 v.%, at least 5 v.%, at least 5.5 v.%, at least

[0299] 6 v.%, at least 6.5 v.%, at least 7 v.%, at least 7.5 v.%, at least 8 v.%, at least 8.5 v.%, at least 9 v.%, at least 9.5 v.%, at least 10 v.%, at least 10.5 v.%, at least 11 v.%, at least 11 .5 v.%, at least 12 v.%, at least 12.5 v.%, at least 13 v.%, at least 13.5 v.%, at least 14 v.%, at least 14.5 v.%, or at least 15 v.%.

[0300] In embodiments, the nanoparticle ink has a viscosity lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s.

[0301] In embodiments, the nanoparticle ink has a viscosity higher than 5 mPa.s but lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s. Preferably, the nanoparticle ink has a viscosity higher than 10 mPa.s but lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s. Preferably, the nanoparticle ink has a viscosity higher than 15 mPa.s but lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s. Preferably, the nanoparticle ink has a viscosity higher than 20 mPa.s but lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s. Preferably, the nanoparticle ink has a viscosity higher than 25 mPa.s but lower than or equal to 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30 mPa.s.

[0302] Viscosity is preferably measured at room temperature, preferably using a Brookfield rotational viscometer (DV3T). In embodiments, the invention provides a nanoparticle ink, preferably a quantum dot ink, comprising a nanoparticle and a curable composition, wherein the weight concentration of the nanoparticle in the nanoparticle ink is at least 10 wt.%, preferably at least 15 wt.%, more preferably at least 20 wt.%; wherein the nanoparticle ink can be cured to form a polymer film; preferably wherein the curable composition comprises an acrylate, a methacrylate, a vinyl ether, an epoxy or a siloxane; wherein the nanoparticle is obtainable by a method of the invention, preferably a method comprising the steps of:

[0303] (a) providing a core of a binary, ternary or quaternary lll-V material, or a binary or ternary ll-VI material;

[0304] (b) optionally forming one or more shells on the core;

[0305] (c) forming a first ligand layer on the core or on the shells;

[0306] (d) partially or fully exchanging the first ligand layer for a second ligand layer comprising a nanoparticle ligand according to the invention, preferably wherein the nanoparticle ligand of the invention is represented by formula (I): . „ x s)

[0307] (I) wherein X is a group capable of binding to the core or to the shells; wherein L is a linear chain of at least four units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone

[0308] (■C(=O)-), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups; wherein R is 5- or 6-membered ring, preferably comprising a N, O or S ring atom, wherein the ring is optionally substituted; and wherein the second ligand comprises 30 non-hydrogen atoms or less.

[0309] Other aspects

[0310] In a further aspect, the invention provides a polymer film comprising a nanoparticle, preferably a quantum dot, according to the invention. The nanoparticle keeps its advantageous properties when embedded in a polymer film, which is a solid layer. Such a polymer film may be called a polymer film according to the invention.

[0311] Preferably, the polymer film is obtainable by curing a quantum dot of the invention, preferably by ultraviolet curing. In a further aspect, the invention provides a luminescent downconverter for converting down light frequency, comprising a nanoparticle, preferably a quantum dot, according to the invention or a polymer film according to the invention. In the frame of the present document, a luminescent downconverter is a device able to convert light with a higher frequency to light with a lower frequency (i.e. downconversion). The properties of a quantum dot according to the invention are especially advantageous for downconversion.

[0312] In a further aspect, the invention provides a method for preparing a luminescent downconverter, the method comprising a method for preparing a nanoparticle, preferably a quantum dot, according to the invention.

[0313] Definitions

[0314] In this document and in its claims, the verb “to comprise” and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition the verb “to consist” may be replaced by “to consist essentially of’ meaning that a product, an assay device respectively a method or a use as defined herein may comprise additional component(s) respectively additional step(s) than the ones specifically identified, said additional component(s), respectively step(s) not altering the unique characteristic of the invention.

[0315] In addition, reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article “a” or “an” thus usually means “at least one”.

[0316] A group comprising n non-hydrogen atoms means that the group either consists of n nonhydrogen atoms, or that the group consists of a number of hydrogen atoms and n nonhydrogen atoms. In other words, the group contains exactly n non-hydrogen atoms.

[0317] Certain compounds may exist in one or more particular geometric, optical, enantiomeric, diastereoisomeric, epimeric, stereoisomeric, tautomeric, (de)protonated, isotopomeric, isotopologues, isotopologic, conformational, or anomeric forms, including but not limited to, cis- and trans-forms; E- and Z-forms; c-, t-, and r- forms; endo- and exo-forms; R-, S-, and meso-forms; D- and L-forms; d- and l-forms; (+) and (-) forms; keto-, enol-, and enolate-forms; syn- and anti-forms; synclinal- and anticlinal-forms; a- and p-forms; axial and equatorial forms; boat-, chair-, twist-, envelope-, and halfchair-forms; and combinations thereof, hereinafter collectively referred to as “isomers”.

[0318] Any reference to a compounds or a class of compounds, either by a name or by a formula, is meant as a reference to the set of all isomers falling in that class, unless explicitly mentioned otherwise. This includes both the isomers mentioned above and all structural isomers, unless it is clear that they are explicitly excluded. For example, a C1-4 alkyl may refer to n-butyl and tert-butyl, together with all their isomers as mentioned above. A reference to n-butyl, on the other hand, only refers to n-butyl and its stereoisomers, isotopomers, isotopologues, etc., and not to tert-butyl. If a compound or a class of compounds refers to multiple species, reference is made to both the isolated species and to any equimolar or non-equimolar mixture of the species.

[0319] All patent and literature references cited in the present specification are hereby incorporated by reference in their entirety.

[0320] Legend to the figures

[0321] Figure 1 : Thermogravimetric analysis of QDs (solid red line) and LE QDs (dashed red lines). The mass loss between 200-300 °C confirmed the decomposition of the one of the claimed ligands used in the LE process.

[0322] Figure 2: Raw data of LUMiSizer measurements of LE QDs with one of the claimed ligands.

[0323] Figure 3: Viscosity of the LE QD ink with one of the claimed ligands over the 30 days.

[0324] Figure 4: External PLQY (EQE) of polymer comprising the QDs with ligands described in the invention for 2000 hours at 1 W / cm2450 nm blue light flux.

[0325] Examples

[0326] The invention is explained in more detail below with a number of examples, which are not to be construed as limiting the scope of the invention. The invention is not limited to the forms of implementation described in the cases given as examples. The invention also extends to each combination of measures as described above, independently from each other.

[0327] Example 1 — Synthesis of ligands (1) and (9)

[0328] Synthesis of ligand (1)

[0329] Synthesis of ligand 1 and 9 are carried out similar way, via thiol-ene chemistry. In this reaction tetrahydrofurfuryl acrylate reacts with di-thiol 1 ,4-butanediol bis(thioglycolate) (for 1) and 1 ,10-decanedithiol (9) in certain ratio (1 :1 to 1 :10) in presence of suitable amount of a base (triethylamine, trioctylamine). Solvents like toluene, tetrahydrofuran, dimethylformamide, etc. can be used as reaction medium. The reaction can also be performed without any additional solvent. The reaction allowed to stir at room temperature until the all the tetrahydrofurfuryl acrylate consumed in the reaction. The progress of the reaction was monitored by thin layer chromatography using suitable polar to nonpolar solvent combination as eluent (for example a combination of ethyl acetate and hexane or combination of toluene and hexane or combination of diethyl ether and hexane)). After all the tetra hydrofurfury I acrylate consumed, the reaction mixture was purified using solid phase column chromatography. The excess of dithiol eluted first from the column followed by the desired ligand 1 or 9. The yield of the final ligands varies from 40-50%. Further purity of the ligands 1 and 9 are evaluated by 1 H NMR spectroscopy (>90%) using deuterated chloroform as solvent.

[0330] Example 2 — Ligand exchange step

[0331] In the ligand exchange step, nanoparticles, particularly quantum dots are dispersed in apolar solvents (for ex. Toluene) and allowed to stir until all the QDs are fully mixed. A suitable ligand claimed in this patent with desired concentration (150 mM to 5000 mM) was then added to the QD mixture and allowed to stir. The reaction temperature was further increased from RT up to 200 °C) for certain duration (0.5-24h). The reaction needs to be performed under air- free conditions. During the LE process, certain aliquots are collected for absorbance measurements to trace the LE process. After the LE process, the reaction was allowed to cool to room temperature and certain amount (1 to 100 times) of apolar solvents (for ex. Hexane) was added to precipitate the LE QDs from the reaction mixture. Further cleaning with apolar to polar solvents and through drying gives pure LE QDs. The density of ligands are further determined by 1 H NMR and TGA analysis.

[0332] Specifically for ligand 1 , 15 lig / nm2of ligand was added to the 250 pM QD solution at 70 °C for 60 minutes in toluene. Hexane was used to precipitate LE QD and further washed with ethanol three times and finally centrifuged to isolate the LE QDs. Final drying was performed under N2 atmosphere.

[0333] Specifically for ligand 9, 25 Iig / nm2 of ligand was added to the 250 pM QD solution at 70 °C for 60 minutes in toluene. Hexane was used to precipitate LE QD and further washed with ethanol three times and finally centrifuged to isolate the LE QDs. Final drying was performed under N2 atmosphere.

Claims

Claims1 . A quantum dot ink comprising a quantum dot and a curable composition, wherein the weight concentration of the quantum dot in the quantum dot ink is at least 15 wt.%, preferably at least 20 wt.%; wherein the quantum dot ink can be cured to form a polymer film; preferably wherein the curable composition comprises thiol and a compound selected from an acrylate, a methacrylate, an alkene, an epoxy and a siloxane; wherein the quantum dot is obtainable by a method comprising the steps of:(a) providing a core of a binary, ternary or quaternary 111 -V material, or a binary or ternary ll-VI material;(b) optionally forming one or more shells on the core;(c) forming a first ligand layer on the core or on the shells;(d) partially or fully exchanging the first ligand layer for a second ligand layer comprising a second ligand, wherein the second ligand is represented by formula (I):wherein X is a group capable of binding to the core or to the shells; wherein L is a linear chain of at least four units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (■C(=O)-), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups; wherein R is 5- or 6-membered ring comprising a N, O or S ring atom, wherein the ring is optionally substituted; and wherein the second ligand comprises 30 non-hydrogen atoms or less.

2. The quantum dot ink of claim 1 , wherein X is COOH, SH, N(RN)2, N(RN)3+, SO3H, or PO3H, wherein each instance of RNis independently H or a C1-4 alkyl.

3. The quantum dot ink of claim 1 or 2, wherein the second ligand is represented by formula (XVI):wherein L1does not withdraw electron density from S;wherein L2is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (-C(=O)-), ester (■C(=O)O‘), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (-O-CH2-), primary thioether (-S-CH2-) functional groups.

4. The quantum dot ink of claim 3, wherein the second ligand is represented by formula (XVII):wherein n is 2, 3 or 4.

5. The quantum dot ink of any one of claims 1 to 4, wherein L comprises 1 to 3 -Z-CH2- CH2- or -Z-C(=O)-CH2-CH2- units, wherein Z is O or S.

6. The quantum dot ink of any one of claims 1 to 5, wherein the second ligand is represented by formula (II) or (III), wherein L’ is a linear chain of at least two units independently selected from methylene (-CH2-), ethenylene (-CH=CH-), and the ketone (■C(=O)‘), ester (-C(=O)O-), thioester (-C(=S)O-), amide (-C(=O)NH-), primary ether (■O-CH2-), primary thioether (-S-CH2-) functional groups, preferably methylene (-CH2-) or ethenylene (-CH=CH-), more preferably methylene (-CH2-):

7. The quantum dot ink of any one of claims 1 to 6, wherein R is an unsubstituted ring.

8. The quantum dot ink of any one of claims 1 to 7, wherein R is a saturated heterocycle, preferably comprising a N, O or S atom.

9. The quantum dot ink of any one of claims 1 to 7, wherein R is a phenyl.

10. The quantum dot ink of any one of claims 1 to 7, wherein the second ligand is represented by formula (IV), (V), (VI) or (VII), wherein Rais NH, O or S; wherein one of Rband Rcis NH, O or S, and the other is CH2; and wherein one of Rd, Reand Rfis NH, O or S, and the others are CH2:(IV) (V) (VI) (VII).11 . The quantum dot ink of any one of claims 1 to 10, wherein the second ligand comprises 25 non-hydrogen atoms or less, preferably 20 non-hydrogen atoms or less.

12. A quantum dot ligand as defined by the second ligand in any one of claims 1 to 11 .

13. A quantum dot as defined in any one of claims 1 to 11 .

14. A polymer film obtainable by curing the quantum dot ink as defined in any one of claims 1 to 11 .

15. The polymer film of claim 14, wherein the curing is ultraviolet curing.

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