WO2015068858A1

WO2015068858A1 - Solvent-free photon upconversion system

Info

Publication number: WO2015068858A1
Application number: PCT/JP2014/080280
Authority: WO
Inventors: Nobuo Kimizuka; Nobuhiro YANAI; Pengfei DUAN; Taku Ogawa; Masanori HOSOYAMADA; Shouta HISAMITSU; Kazuma MASE
Original assignee: Kyushu University, National University Corporation
Priority date: 2013-11-06
Filing date: 2014-11-06
Publication date: 2015-05-14
Also published as: JP2020111751A; JP2016536449A

Abstract

The present invention provides a solvent-free photon upconversion composition comprising an acceptor chromophore and organic donor, wherein the acceptor chromophore is liquidized and doped with the organic donor. The present invention also provides a method for achieving photon upconversion in air using said composition.

Description

DESCRIPTION

Title of Invention

Solvent-Free Photon Upconversion System

Technical Field

[0001 ]

The present invention relates to a solvent-free photon upconversion composition. The present invention also relates to a method for achieving photon upconversion in air using said composition.

Background Art

[0002]

Upconversion (UC), the population of luminescent higher-energy excited state with excitation at lower energy light, has attracted much attention because of its potential to overcome the thermodynamic efficiency limits in solar energy conversion devices.¹ The most actively investigated UC systems are based on nonlinear phenomena such as multiple-photon absorption, while they suffer from a fateful flaw in requiring

2 2

high excitation intensities (~MW/cm ) that detracts from its appeal. Consequently, an alternative UC mechanism based on the triplet-triplet annihilation (TTA, Figure 1) has come under the spotlight since it offers numerous advantages over the aforementioned techniques.³ For example, non-coherent light with low excitation power density can be used to achieve UC, with excitation/emission wavelengths tunable depending on the independently selected donor and acceptor molecules. In Figure 1) a triplet excited state of sensitizer (donor) is formed by intersystem crossing from the excited singlet state, which exerts triplet-triplet energy transfer (TTET) in the presence of suitable acceptors. When two acceptor molecules in the triplet state diffuse and come into collision during their lifetimes, higher singlet energy level is populated by triplet-triplet annihilation (TTA) and consequently delayed fluorescence is observed.

Disclosure of the Invention [0003]

To date, efficient UC has been achieved in solution because diffusion of triplet molecules is essential for both of the TTET and TTA processes. However, the use of volatile solvents and deactivation of triplet states by molecular oxygen significantly limit their practical applications. Although recently the TTA-based UC has been investigated in solid polymer films,⁴ such polymer matrices may inevitably restrict diffusion of triplet molecules.

[0004]

To solve these problems in dispersion systems, it is essential to develop oxygen-impermeable TTA systems based on diffusion and encounter of triplet excitons in nonvolatile, densely clustered chromophores.

[0005]

Here we present a first example of matrix-free UC in liquid molecular networks; a set of organic donor and acceptor chromophores displays efficient triplet energy transfer, migration and TTA in the solventless liquid state (Figure 2). It is known that the modification of aromatic compounds with branched alkyl chains gives nonvolatile organic liquids.⁵ Although luminescence characteristics of some liquid aromatics have been reported,⁵ triplet energy transfer, migration and consequent photon upconversion in such condensed liquids have been unprecedented.

[0006]

With this in mind, we synthesized an organic liquid acceptor with 9,10-diphenylanthracene moiety⁶ and a newly designed donor (triplet sensitizer) Pt(II) porphyrin derivative (Figure 3). This pair of chromophores was selected as an acceptor and donor pair since 9,10-diphenylanthracene (acceptor & emitter) and Pt(II) octaethylporphyrin (PtOEP, sensitizer) have been popularly used in solution UC systems. Branched alkyl chains were introduced in the periphery of Donor (2), which was aimed to attain good miscibility with the liquid Acceptor (1).

[0007]

As such, the present invention provides the followings:

[ 1 ] A solvent- free photon upconversion composition comprising: (a) an acceptor chromophore; and

(b) an organic donor,

wherein the acceptor chromophore is in one of a form of liquid, liquid crystal or crystal and doped with the organic donor, and

wherein the composition does not comprise a solvent other than the acceptor chromophore.

[2] The composition of [1], wherein the acceptor chromophore is at least one compound selected from the group consisting of 9,10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives,

9, 10-bis(phenylethynyl)anthracene, 9,10-Bis(phenylethynyl)naphthacene, rubrene and tetracene.

[3] The composition of [1] or [2], wherein the organic donor is at least one compound selected from the group consisting of Pt(II)/Pd(II)-porphyrin, Pt(II)/Pd(II)-tetraphenyl-tetrabenzoporphyrin, Pt(II)/Pd(II)-Ph₄0Me₈TNP, Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pyr₃RuPZn₃ and Pt(II)/Pd(II)-tetrakisquinoxalino porphyrin, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and a-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes.

[4] The composition of [2], wherein the acceptor chromophore comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

[5] The composition of [2]

, wherein the acceptor chromophore comprises one or more self-assembly moieties selected from oligo/poly (ethyleneglycol), saccharides, mono/oligo nucleotides, carboxylate, bipyridine, terpyridine, catechol, phenanthroline, tetrathiafulvalene, tetracyanoquiodimethane, fullerene, cholesterol, amino acids, Au/Ag/Pt/Pd complexes forming metal-metal interactions, bipyridinium, amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, and halogens.

[6] The composition of [5], wherein the self-assembly moiety comprise one or more of intermolecular interaction sites selected from amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, halogens and aromatic groups.

[7] The composition of [3], wherein the organic donor comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

[8] The composition of any one of [1] to [7], wherein the molar ratio of organic donor/acceptor chromophore ratio is in the range of 0.001% to 1%.

[9] The composition of any one of [1] to [8], wherein the acceptor chromophore forms an ionic liquid with a cation molecule comprising one or more unsubstituted or substituted alkyl moieties and/or oligo/poly (ethylene glycol) moieties.

[10] The composition of [9], wherein the acceptor chromophore forms an ionic liquid selected from the group consisting of:

[1 1] The composition of any one of [1] to [10], wherein the composition functions as an upconversion system in air.

[12] A method of achieving photon upconversion in air using the composition of any one of [1] to [1 1].

[13] An acceptor chromophore for a solvent- free photon upconversion, comprising at least one compound selected from the group consisting of 9, 10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives, 9, 10-bis(phenylethynyl)anthracene, 9, 10-Bis(phenylethynyl)naphthacene, perylenetetracarbo ylic diimide derivatives, rubrene and tetracene. [14] The acceptor chromophore of [13], which comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

[15] The acceptor chromophore of [13], which comprises one or more self-assembly moieties selected from oligo/poly (ethyleneglycol), saccharides, mono/oligo nucleotides, carboxylate, bipyridine, terpyridine, catechol, phenanthroline, tetrathiafulvalene, tetracyanoquiodimethane, fullerene, cholesterol, amino acids, Au/Ag/Pt/Pd complexes forming metal-metal interactions, bipyridinium, amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, and triazole, halogens.

[16] The acceptor chromophore of [15], wherein the self-assembly moiety comprise one or more of intermolecular interaction sites selected from amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, halogens and aromatic groups.

[17] The acceptor chromophore of [13], which forms an ion liquid with a cation molecule comprising one or more unsubstituted or substituted alkyl moieties and/or oligo/poly (ethylene glycol) moieties.

[18] The acceptor chromophore of [17], which forms an ion liquid selected from the group consisting of:

[19] An organic donor chromophore for a solvent- free photon upconversion, comprising at least one compound selected from the group consisting of

Pt(II)/Pd(II)-porphyrin, Pt(II)/Pd(II)-tetraphenyl-tetrabenzoporphyrin,

Pt(II)/Pd(II)-Ph₄0MegTNP, Pt(II)/Pd(II)-octabutoxynaphthalocyanine,

Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pt(II)/Pd(II)-octabutoxyphthalocyanine,

Pyr₃RuPZn₃ and Pt(II)/Pd(II)-tetrakisquinoxalino porphyrin, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and oc-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes.

[20] The organic donor of [19], which comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms. Effect of the Invention

[0008]

A nonvolatile, in-air functioning liquid photon upconverting system is developed. A rationally designed triplet sensitizer (branched alkyl chain-modified Pt(II) porphyrin) is homogeneously doped in energy-harvesting liquid acceptors with 9,10-diphenylanthracene unit. A significantly high upconversion quantum yield of ~28% is achieved in the solvent-free liquid state, even under aerated conditions. This is ascribed to a sequence of efficient energy transfer and migration of two itinerant excited triplet states, which eventually collide each other to produce singlet excited state of the acceptor. The observed insusceptibility of upconversion luminescence to oxygen is ascribable to sealing ability of clustering alkyl chains introduced to liquefy chromophores. An emerging new concept, photon upconverting liquid, provides a new perspective in controlling energy landscapes of soft condensed matters.

By implementing the concept of molecular self-assembly, the present invention solves the critical problems of photon upconversion, that is, quenching by oxygen. So far, photon upconversion systems require strict deoxygenation processes that limit their practical applications. The self-assembly of the dye molecules allows efficient photon upconversion even in the aerated condition in the forms of solution, casted film, and gel. It was also difficult to obtain the efficient upconversion in the solid state because of the macroscopic segregation between donor and acceptor, but self-assemblies of acceptor can accommodate donor molecules, and thus it becomes possible to achieve the efficient upconverted emission even in the solid film.

Brief Description of Drawings

Figure 1: A diagram showing the upconversion mechanism based on the triplet-triplet annihilation.

Figure 2: A schematic representation of the matrixt-free liquid upconversion system. Figure 3: (a) Chemical structures of liquid Acceptor (1) and sensitizer (2) (or Donor (2)) . Photographs of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) upon being exposed to (b) white light and (c) 532 nm green laser (incident laser direction is indicated by a green arrow). Figure 4: Photographs of liquid Acceptor (1) under (a) visible and (b) UV (365 nm) light.

Figure 5: A DSC thermogram of Acceptor (1) in the cooling trace (10 °C/min).

Figure 6: Graphs showing (a) Storage modulus (G'; black square) and loss modulus (G"; red circle) versus angular frequency of Acceptor (1). (b) Complex viscosity (η*) versus angular frequency of Acceptor (1) (η* = 0.99 Pa s).

Figure 7: Graphs showing (a) XRD and (b) SAXS profiles of liquid Acceptor (1).

Figure 8: Photographs of (a) optical microscope image and (a') polarized microscope image of the mixture of Acceptor (1) and PtOEP (PtOEP/ Acceptor (1) = 1 mol%). Photographs of (b) optical microscope image and (b') polarized microscope image of the mixture of Acceptor (1) and Donor (2) (Donor(2)/ Acceptor (1) = 1 mol%).

Figure 9: Graphs showing: (a) Normalized absorption and emission spectra of CHC1₃ solution of Acceptor (1) (λ_εχ = 375 nm, 0.1 mM) and Donor (2) in deaerated CHC1₃ (2_ex = 510 nm, 0.1 mM); and (b) Normalized absorption and emission spectra of liquid Acceptor (1) ( _ex = 375 nm) and cast film of Donor (2) (λ_εχ = 520 nm).

Figure 10: Graphs showing: (a) Luminescence decay observed for liquid Acceptor (1) in CHC1₃ (0.1 mM, black line) and solvent- free state (blue line) ( _ex = 365 nm, X_em = 450 nm); and (b) Luminescence decay curves obtained for the delayed luminescence by TTA upconversion in air (blue line) and in vacuum (red line) from Donor (2)-doped liquid Acceptor (1) (Donor (2)/Acceptor (1) = 0.01 mol%; λ_ίχ = 531 nm, A_uc ⁼ 450 nm).

Figure 11: A graph showing normalized absorption and emission (λ_εχ = 375 nm) spectra of the doped liquid Acceptor (1) (Donor (2)/Acceptor (1) = 0.01 mol%).

Figure 12: Graphs showing: (a) Photoluminescence spectra of the doped liquid (Donor (2)/ Acceptor (1) = 0.01 mol%) with different incident power density of 532 nm laser in air; (b) Dependence of upconversion emission intensity at 433 nm on the incident power density (Donor (2)/ Acceptor (1) = 0.01 mol%); and (c) Quantum yield of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) measured as a function of 532 nm incident power density.

Figure 13: Graphs showing: (a) Photoluminescence spectra of the doped liquid (Donor (2)/ Acceptor (1) = 0.01 mol%) with different incident power density of 532 nm laser in vacuum; and (b) Incident power density dependence of upconversion emission intensity at 433 nm of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) in vacuum.

Figure 14: Plots of temperature-dependent UC emission intensity at X_em = 433 nm ( l_ex =

532 nm) of the doped liquid (Donor (2)/ Acceptor (1) = 0.01 mol%).

Figure 15: Upconverted emission of the A-D mixture chloroform solution ([A] = 10 mM, [D] = 10 μΜ) in air by changing the excitation power (λ_εχ = 532 nm).

Figure 16: Emission spectra of the A-D mixture chloroform solution ([A] = 10 mM, [D]

= 10 μΜ) in air at 293 K (red) and 198 K (blue).

Figure 17: In-air UC emission of the cast film prepared from the A-D mixture chloroform solution ([A] = 10 mM, [D] = 10 μΜ).

Figure 18: The 1,2-dichloroethane gel of A-D mixture ([A] = 16 mM, [D] = 16 μΜ) and its blue UC emission.

Figure 19: Absorption and emission spectra of 0.1 mM CHC1₃ solution of Al (black) and solvent-free ionic liquid Al (red).

Figure 20: (a) Picture of the Al-PtOEP mixture sealed between two quarts plates, (b)

Microscopic images and (c) emission images of the Al-PtOEP mixture.

Figure 21: (a) UC emission spectrum of the Al-PtOEP mixture in Ar. (b) Excitation power dependency of UC emission intensity of the Al-PtOEP mixture in Ar.

Figure 22: (a) UC emission intensity of the Al-PtOEP mixture in Ar at different temperatures, (b) UC emission spectrum of the Al-PtOEP mixture in air.

Figure 23: Polarized optical microscope image of 2-doped liquid crystal 1 (2/1 = 0.1 mol %).

Figure 24: (a) Photoluminescence spectra of the 2-doped liquid crystal 1 (2/1 = 0.1 mol%) with different incident power density of 635 nm laser, (b) Dependence of UC emission intensity at 580 nm on the incident power density. Blue and red lines are fitting results with slopes of 2.3 (blue) and 1.1 (red) in the low and high-power regimes. Figure 25: Plots of temperature-dependent UC emission intensity at /l_em ⁼ 580 nm ( _ex = 635 nm) of the doped LC (2/1 = 0.1 mol%).

Figure 26: Optical microscope images of solution-casted (a) Al, (c) A2, (e) A3, and polarized microscope images of (b) Al, (d) A2, (f) A3.

Figure 27: Powder X-ray diffraction profiles of Al (blue), A2 (red), and A3 (green). Figure 28: Optical microscope images of solution-casted (a) Al-PtOEP, (c) A2-PtOEP, (e) A3-PtOEP, and polarized microscope images of (b) Al-PtOEP, (d) A2-PtOEP, (f) A3-PtOEP.

Figure 29: Absorption spectra of PtOEP CHC1₃ solution (red), neat PtOEP solid (green), and the acceptor solid film doped with 1.0 mol% PtOEP (blue, (a) Al, (b) A2, (c) A3) Figure 30: Emisssion spectra of the PtOEP-doped (a) Al, (b) A2, (c) A3 films.

Figure 31: Photoluminescence spectra of (a) A'-l (10 mM), (b) A'-2 (10 mM), and (c) A'-3 (10 mM) with PtOEP (10 μΜ) in aerated chloroform at room temperature (D_ex = 532 nm).

Mode for Carrying Out the Invention

[0009]

Hereinafter, the present invention is described in detail. The embodiments described below are intended to be presented by way of example merely to describe the invention but not limited only to the following embodiments. The present invention may be implemented in various ways without departing from the gist of the invention.

All of the publications, published patent applications, patents and other patent documents cited in the specification are herein incorporated by reference in their entirety. The specification hereby incorporates by reference the contents of the specification and drawings in the Japanese Patent Application (No. 2013-230265) filed on November 6, 2013 and the Japanese Patent Application (No. 2014-048088) filed on March 1 1, 2014, from which the priority was claimed.

In a first embodiment, the present invention provides a solvent-free photon upconversion composition comprising:

(a) an acceptor chromophore; and

(b) an organic donor,

wherein the acceptor chromophore is liquidized and doped with the organic donor, and

wherein the composition does not comprise a solvent other than the liquidized acceptor chromophore. [001 0]

In a second embodiment, the present invention provides a method for achieving photon upconversion in air using said composition.

In a third embodiment, the present invention provides an acceptor chromophore for a solvent- free photon upconversion, comprising at least one compound selected from the group consisting of 9,10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives, 9,10-bis(phenylethynyl)anthracene, 9,10-Bis(phenylethynyl)naphthacene, perylenetetracarboxylic diimide derivatives, perylenetetracarboxylic diimide derivatives, rubrene and tetracene.

[001 1 ]

In a fourth embodiment, the present invention provides an organic donor chromophore for a solvent-free photon upconversion, comprising at least one compound selected from the group consisting of Pt(II)/Pd(Ii)-porphyrin, Pt(II)/Pd(II)-tetraphenyl-tetrabenzoporphyrin, PtiliyPd^-P^OMesTNP, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pyr₃RuPZn₃ and Pt(II)/Pd(II)-tetrakisquinoxalino porphyrin, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and a-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes.

[001 2]

As used herein, the term "doped with" means "mixed with" or "combined with".

The acceptor chromophore may be a compound selected from the group consisting of 9,10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives, 9,10-bis(phenylethynyl)anthracene,

9,10-Bis(phenylethynyl)naphthacene, perylenetetracarboxylic diimide derivatives, rubrene and tetracene, and may comprise one or more unsubstituted or substituted alkyl moieties. In this case, each of the alkyl moiety may comprise 1 to 50 carbon atoms, 1 to 40 carbon atoms, 1 to 30 carbon atoms or 1 to 20 carbon atoms. The alkyl moiety may be a branched or linear chain. The substituted alkyl may be one comprising one or more (preferably, one to three, 3, 2 or 1) of hetero atoms each selected from oxygen, nitrogen and sulfur in its backbone.

[001 3]

By being alkylated, the acceptor chromophore can be liquidized and protect itself from oxygen. The alkylated acceptor chromophore may be in the form of any one of liquid, liquid crystal or a crystal.

[001 4]

The alkylation may be performed under the following conditions:

Acceptor molecules containing hydroxy groups are reacted with alkyl chains having bromide groups (excess amount, preferably 1.5 times more than the amount of hydroxyl groups in the acceptor moelcules) in the presence of base (such as K₂C0₃) in dimethylformamide during heating (60-120 °C, preferably 80 °C).

[001 5]

The acceptor chromophore may further comprise one or more (preferably 1 to 5, 4, 3, 2 or 1) of self-assembly moieties.

By introducing the self-assembly moiety into the acceptor (emitter) molecules, it become possible to form the dense arrangements of acceptor molecule. This structuration is important not only for triplet energy migration among the acceptor arrays but also for inhibiting the intrusion of oxygen molecules. Importantly, the dye assemblies in solution show an efficient photon upconversion even in the aerated condition. This is the first example of TTA-UC in the aerated solution without any additives for oxygen shielding. Casting this solution produces thin films that can show efficient photon-upconversion in air. In addition, by just changing the solvent, it is also possible to make air-tolerant photon-upconverting gels.

[001 6]

The self-assembly moiety may include one of the more of groups selected from oligo/poly (ethyleneglycol), saccharides, mono/oligo nucleotides, carboxylate, bipyridine, terpyridine, catechol, phenanthroline, tetrathiafulvalene, tetracyanoquiodimethane, fullerene, cholesterol, amino acids, Au/Ag/Pt/Pd complexes forming metal-metal interactions, bipyridinium, amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, and halogens.

Said oligo/poly (ethyleneglycol) may have any number of ethyleneglycol units, preferably, 1 to 30 units, 1 to 20 units or 1 to 10 units.

[001 7]

The self-assembly moiety may include one or more of intermolecular interaction sites selected from amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, halogens, aromatic groups of acceptor to form intermolecular bonding with another acceptor chromophore molecule, such as hydrogen bonding, coordination bonding, π-π stacking or hydrophobic and solvophobic interactions.

[001 8]

The acceptor chromophore shows absorption peak in the range of 200-500 nm, 300-400 nm or 320-390 nm.

With or without the alkylation and/or self-assembly moiety, the above mentioned acceptor chromophore compound may be substituted with a number of substituents. For example, the acceptor chromophore may be substituted in a way that one or more bonds to a carbon(s) or hydrogen(s) is replaced by a bond to:

(i) a halogen atom in F_; CI, Br, and/or I; and/or a halogen atom in trifluoromethyl and/or alkyl containing trifluoromethyl;

(ii) an oxygen atom in hydroxyl, alkoxy, aryloxy, and ester, carbonyl, carboxyl, and/or heterocyclyloxy;

(iii) a sulfur atom in thiol, alkyl, aryl sulfide, sulfone, sulfonyl, and sulfoxide;

(iv) a nitrogen atom in amine, amide, alkylamine, dialkylamine, arylamine, alkylarylamine, diarylamine, N-oxide, imide, enamine, imine, oxime, hydrazone, nitrile, heterocyclylamine, (alkyl)(heterocyclyl)amine, (aryl)(heterocyclyl)amine, and/or diheterocyclylamine;

(v) a silicon atom in trialkylsilyl, dialkylarylsilyl, alkyldiarylsilyl, and triarylsilyl; and/or,

(vi) aryl group in which one of the aromatic carbons is bonded to one or more of the halogen, oxygen, sulfur, nitrogen and/or silicon groups described above; aryl groups in which one or more aromatic carbons of the aryl group is bonded to a substituted or unsubstituted alkyl, alkenyl, or alkynyl group, the substitution being one or more of the halogen, oxygen, sulfur, nitrogen and/or silicon groups described above; aryl group in which two carbon atoms thereof are bonded to two atoms of an alkyl, alkenyl, or alkynyl group to define a fused ring system; dihydronaphthyl; tetrahydronaphthyl; tolyl; and/or hydroxyphenyl.

Alternatively or in addition, one or more carbon atoms constituting the acceptor may be replaced with a hetero atom selected from oxygen, nitrogen, sulfur and phosphorus.

[001 9]

The solvent-free photon upconversion composition may be used in a variety of materials such as a solution, gel or film obtained by drying a gel.

[0020]

In one embodiment, the acceptor chromophore is alkylated 9,10-diphenylanthracene having the following formula:

[0021 ]

The alkylated 9,10-diphenylanthracene can be synthesized through the following scheme:

[0022]

In another embodiment, the acceptor chromophore is a modified 9,10-diphenylanthracene containing amide groups for intermolecular hydrogen bonding, an

[0023]

The above modified 9,10-diphenylanthracene can be synthesized through the following scheme:

Boc-Glu-COC

Glu-C„5O^C12

DPA-2COOH DPA-2COCI

[0024]

In one embodiment, the acceptor chromophore is perylene having branched alkyl chains which forms a liquid crystal as shown in the following formula:

1

[0025]

The perylene having branched alkyl chains can be synthesized through the following scheme:

1

[0026] In one embodiment, the acceptor chromophore is anthracene having alkyl chains, phenyl group, and/or carboxylate for the improvement of miscibility with donor as shown in the following formula:

[0027]

The anthracene having alkyl chains, phenyl group, and/or carboxylate synthesized through the following scheme:

20

[0028]

In still another embodiment, the acceptor chromophore may be prepared as an ionic liquid in combination with certain cations. In this embodiment, the cations preferably contain one or more unsubstituted or substituted alkyl moieties and/or oligo/poly (ethylene glycol) moieties. The unsubstituted or substituted alkyl and oligo/poly (ethylene glycol) are as defined above.

In the specific embodiments, the acceptor chromophore may be prepared as any one of the following ionic liquids:

For example, the ionic liquid Al can be synthesized through the following

[0030]

The organic donor may be any one compound selected from the group consisting of

Pt(II)/Pd(II)-tetraphenyl-tetrabenzopoφhyrin, Pt(II)/Pd(II)-Ph₄0Me₈TNP, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pyr₃RuPZn₃ and Pt(II)/Pd(II)-tetrakisquinoxalino ροφ1ι>τίη, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and a-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes, and may comprise one or more unsubstituted or substituted alkyl moieties. In this case, each of the alkyl moiety may comprise 1 to 50 carbon atoms, 1 to 40 carbon atoms, 1 to 30 carbon atoms or 1 to 20 carbon atoms. The alkyl moiety may be a branched or linear chain. The substituted alkyl may be one comprising one or more (preferably, one to three, 3, 2 or 1) of hetero atoms each selected from oxygen, nitrogen and sulfur in its backbone.

The donor may directly be doped in the acceptor chromophore which may be in the form of any one of liquid, liquid crystal or a crystal.

[0031 ]

By being alkylated, the organic donor can be doped in the acceptor chromofore. The alkylation may be performed under the following conditions:

The donor molecules containing hydroxyl or carboxyl groups are reacted with alkyl chains having bromide groups (excess amount, preferably 1.5 times more than the amount of hydroxyl/carboxyl groups in the donor moelcules) in the presence of base (such as K₂C0₃) in dimethylformamide during heating (60-120 °C, preferably 80 °C).

[0032]

The organic donor emits a light having a wave length in the range of 400-700 nm, 500-700 nm, 600-700 nm or 630-680 nm.

With or without the alkylation, the donor compound may be substituted with a number of substituents. For example, the donor may be substituted in a way that one or more bonds to a carbon(s) or hydrogen(s) is replaced by a bond to:

(iv) a nitrogen atom in amine, amide, alkylamine, dialkylamine, arylamine, alkylarylamine, diarylamine, N-oxide, imide, enamine, imine, oxime, hydrazone, nitrile, heterocyclylamine, (alkyl)(heterocyclyl)amine, (aryl)(heterocyclyl)amine, anoVor diheterocyclylamine;

Alternatively or in addition, one or more carbon atoms constituting the donor may be replaced with a hetero atom selected from oxygen, nitrogen, sulfur and phosphorus.

[0033]

In one embodiment, the organic donor is alkylated

having the following formula:

[0034]

The alkylated Pt(II)-octaethylporphyrin can be synthesized through the following scheme:

[0035]

In the composition, the molar ratio of organic donor/acceptor chromophore ratio is in the range of 0.001% to 1%, 0.01% to 1%, 0.01% to 0.5%, 0.01 % or 0.1%. The most preferably, the molar ratio of organic donor/acceptor chromophore ratio is 0.01%. The photon upconversion composition of the present invention can be used in a variety of applications. For example, the composition may be used to increase efficacies of a variety of photic systems including photocatalysts, photovoltaic power generation systems, or photoproduction systems of chemical compounds.

Examples

The present invention is now described in detail by way of using working examples below. However, the scope of the present invention shall not be limited to the examples but should be appreciated by the scope of the claims attached.

[Example 1]

Materials and Methods

[0036]

Materials. All reagents and solvents for synthesis were used as received without further purification. Platinum(II) octaethylporphyrin (PtOEP) was purchased from Aldrich and were used as received.

[0037]

Synthesis of Acceptor (1). The hydroxyl group of 2-octyl-l-dodecanol was converted to bromo derivative by using N-bromosuccinimide (NBS) and triphenylphosphine (PPh₃) as the bromination reagents in dichloromethane at 0 °C for 2h. The product 9-(bromomethyl) nonadecane was purified by chromatography (hexane) over silica gel. In a typical synthesis of Acceptor (1), a mixture of 9-(bromomethyl) nonadecane (6 mmol), 9,10-bis(3,5-dihydroxyphenyl)anthracene (1 mmol) and potassium carb (8 mmol) in anhydrous N, N-dimenthylformamide (DMF, 30 mL) was heated to 80 °C for 20 h. After the reaction, solvent was removed under reduced pressure. The resultant residue was extracted with dichloromethane and washed several times with brine and water, and then dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by column chromatography (n-hexane/dichloromethane) over silica gel yielded the pure Acceptor (1) liquid (yield: 53%). Ή NMR (300 MHz, CDC1₃): δ = 0.84-0.88 (m, 24H), 1.24-1.43 (m, 128H), 1.53 (m, 4H), 3.84 (d, J = 6 Hz, 8H), 6.60-6.64 (m, 6H), 7.32-7.36 (m, 4H), 7.78-7.81 (m, 4H). MALDI-TOF-MS, (dithranol matrix): calculated for Cio₆H₁₇₈0₄ 1516.55; found 1518.32 [M⁺]. Elemental analysis, calculated for Ci₀₆H,₇8O₄: C, 83.95; H, 11.83; found: C, 83.97; H, 11.85.

[0038]

Synthesis of TPP-COOEH. A mixture of tetrakis(4-carboxyphenyl)porphyrin (79 mg, 0.1 mmol), l-bromo-2-ethylhexane (0.16 mg,0.6 mmol) and potassium carbonate (0.11 mg, 0.8 mmol) in anhydrous DMF (15 mL) was heated to 80 °C for 20 h. After the reaction, the reaction solvent was removed under reduced pressure. The resultant residue was extracted with dichloromethane and washed several times with brine and water, and then dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by column chromatography (n-hexane/dichloromethane) over silica gel yielded the pure purple solid TPP-COOEH. Yield: 0.11 mg, 81%.

[0039]

Synthesis of Donor (2). To a mixture of TPP-COOEH (50 mg, 0.04 mmol) in benzonitrile (30 mL), PtCl₂ (106 mg, 0.4 mmol) was added under Ar atmosphere. The resulting mixture was refluxed for about 7 h, and the reaction was stopped when the fluorescence of the free-base porphyrin disappeared. After the removal of benzonitrile, the residue was purified by column chromatography (silica gel, n-hexane/dichloromethane). Yield: 52 mg, 90 %. 1H NMR (300 MHz, CDC1₃): δ = 0.94-1.07 (m, 24H), 1.42-1.62 (m, 32H), 1.82-1.88 (m, 4H), 4.38-4.48 (m, 8H), 8.16-8.25 (m, 8H), 8.41-8.44 (m, 8H), 8.73 (s, 8H). MALDI-TOF-MS, (dithranol matrix): calculated for C₈₀H₉₂N₄O₈Pt 1432.69; found 1434.45 [M⁺]. Elemental analysis, calculated for C₈₀H₉₂N₄O₈Pt: C, 67.07; H, 6.47; N, 3.91; found: C, 66.88; H, 6.37; N, 3,84.

[0040] Characterization. Ή NMR (300 MHz) spectra were measured on Bruker DRX-300 spectrometer using TMS as internal standard. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was performed on a Bruker Autoflex-III. Elemental analysis was conducted at the Elemental Analysis Center, Kyushu University. XRD analysis was conducted on a RIGAKU smart-lab with a copper K-alpha source. SAXS analysis was carried out using a Rigaku MicroMax-007HF with a copper K-alpha source. Luminescence spectra were measured by using a PerkinElmer LS 55 fluorescence spectrometer. The samples were excited with an incidence angle of 45° to the quartz cell surface and the fluorescence was detected along the normal. Emission spectra were recorded with excitation wavelength of 375 nm or 510 nm. UV-vis spectra were recorded on a JASCO V-670 spectrophotometer. The absolute quantum yields were calculated using a Hamamatsu C9920-02G instrument. Time-resolved fluorescence lifetime measurements were carried out by using time-correlated single photon counting lifetime spectroscopy system, HAMAMATSU Quantaurus-Tau CI 1367-02 (for fluorescence lifetime)/C 11567-01 (for delayed luminescence lifetime). The quality of the fit has been judged by the fitting parameters such as χ² (<1.2) as well as the visual inspection of the residuals. Differential scanning calorimetry (DSC) was performed in a Seiko Electronics SSC-5200 instrument. The rheology experiments were carried out using an Anton Paar MCR-302 Rheometer at 25 °C. The upconversion luminescence emission spectra were recorded on Otsuka Electronics MCPD-7000 instrument with the excitation source using an external, adjustable 532 nm semiconductor laser (0-140 mW).

[0041 ]

Measurement of Upconversion Luminescence Quantum Efficiency. The upconversion luminescence quantum efficiency (Ouc) of the upconverting liquid was determined relative to Nile red or Rhodamine B in Acceptor (1) according to Eq. 1.¹³' ¹⁴

Φυο Auc, luc, and r|uc represent the quantum yield, absorbance at A_ex, integrated photoluminescence spectral profile, and refractive index of the medium in the upconversion sample. The corresponding terms for the subscript "std" are for the reference quantum counter Nile red or Rhodamine B in liquid Acceptor (1) at the identical corresponding excitation wavelength. The factor of 2 is included since upconversion requires the absorption of 2 photons to produce 1 whereas the reference actinometer's emission is directly proportional to the incident photons. Since the standard and the upconversion doped liquids are all in the same liquid Acceptor (1), the refractive indices are the same. Therefore, under our experimental conditions, Eq. 1 simplifies to:

Quantum yield values reported herein represent an average of at least three independent measurements.

Results

[0042]

The nonvolatile liquid Acceptor (1) showed strong blue emission under UV light (Figure 4). Differential scanning calorimetry (DSC), rheology, X-ray diffraction (XRD) and small-angle X-ray scattering (SAXS) experiments confirmed fluid characteristics of Acceptor (1) at ambient temperature (Figures 5-7). The liquid Acceptor (1) is comprised of disordered aggregates of diphenylanthracene chromophores with an averaged core-to-core distance of 2.1 nm. The DSC and rheology results showed a glass transition temperature at -59 °C and a low-viscosity of 0.99 Pa s, respectively. When a popularly used donor PtOEP was mixed with Acceptor (1), it was not molecularly dissolved and irregular crystalline structures were observed under polarized optical microscopy (Figure 8). Meanwhile, the Sensitizer (2) (or Donor (2)) modified with branched alkyl chains was homogeneously miscible with liquid Acceptor (1) in the examined range up to Donor (2)/ Acceptor (1) = 1 mol%. To optimize the doping condition, we measured absolute emission quantum yields of Acceptor (1) at various mixing ratio (Donor (2)/Acceptor (1) = 0.001 mol% ~ 1 mol%, λ_βχ = 365 nm; Table 1). Acceptor (1) in the pure form showed a high quantum yield of 0.68, while its fluorescence underwent quenching upon increasing the molar ratio of Donor (2) especially above 0.1 mol%. It indicates that Forster resonance energy transfer from Acceptor (1) to Donor (2) become feasible at the higher doping ratio. Accordingly, Donor (2) was added to Acceptor (1) at the low molar ratio of 0.01 mol% in all the following experiments.

[0043]

Figrue 3a presents normalized absorption and emission spectra of Acceptor (1) and Donor (2) in CHC1₃ at 0.1 mM. The absorption spectrum of Acceptor (1) (Abs 1) exhibits typical vibrational structure of the L_a band (320 ~ 390 nm), while its fluorescence (PL1) was observed with a maximum at 433 nm. On the other hand, Donor (2) (Abs 2) exhibited a Soret- and Q-band at 403 and 510 nm, respectively. When Donor (2) dissolved in deaerated CHC1₃ was photo-excited at 520 nm, phosphorescence (PL2) was observed at 660 nm. Absorption and fluorescence spectra of Acceptor (1) without solvent are shown in Figure 9b. The liquid Acceptor (1) showed less-structured absorption band, reflecting molecular crowding in the liquid. Meanwhile, the fluorescence spectrum of Acceptor (1) in pure liquid is almost identical to that observed in CHCI3 solution. The fluorescence lifetimes and quantum yields obtained for Acceptor (1) in pure liquid and dilute CHCI3 solution are also comparable (Figure 10 and Table 1), and these observations indicate that neither strong electronic interactions among chromophores in the ground state nor excimers exist in liquid Acceptor (1) (Figure 9b). The Donor (2)-doped liquid sample (Donor (2)/ Acceptor (1) = 0.01 mol%) showed a Q-band at 511 nm, which is close to that of Donor (2) dissolved in CHC1₃, clearly supporting that Donor (2) is molecularly dispersed in liquid Acceptor (1) (Figure 11).

Table 1. Absolute quantum yields of CHC1₃ solution of Acceptor (1) and of Donor (2)-doped liquid Acceptor (1) at various mixing ratio (A_ex = 365 nm).

[0044] Figure 12a shows steady- state luminescence spectra of Donor (2)-doped liquid Acceptor (1) obtained at varied incident laser power (Donor (2)/Acceptor (1) = 0.01 mol%). Very interestingly, blue UC emission peaks were clearly observed upon excitation of Donor (2) by 532 nm green laser. The spectral shape of UC emission (λ_εχ = 532 nm) is similar to that of the normal fluorescence (λ_εχ = 375 nm; Figure 9b). It is to note that the phosphorescence of Sensitizer (2) (or Donor (2)) was completely quenched regardless of the excitation power, indicating the efficient triplet-triplet energy transfer from Donor (2) to the acceptor liquid Acceptor (1). To prove the TTA-based UC mechanism, dependence on the power density of incident light was investigated. In general, TTA-assisted UC is proved by the quadratic incident light power dependence of emission intensity in the weak-annihilation limit, which consequently turns into first-order dependence in the saturated annihilation regime.⁷ Figure 12b presents the double logarithm plot for the UC emission intensity of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) as a function of incident light power density (λ_εχ = 532 nm). At the lower power regime of <40 mW cm^"2, a slope of 2 was observed, whereas it changed to a first-order dependence at higher power density (>40 mW cm^"2). These results provide the first experimental evidence for photon upconversion in the solvent-free liquid system. It is to note that the crossover threshold was achieved at a relatively low power density around 40 mW cm^"2, which is comparable to those reported for the solvent-free polymer systems.^4f'⁸ The occurrence of TTA-based UC in the present liquid system was further verified by the luminescence decay measurements. The UC emission of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) showed a decay in the millisecond time scale under excitation at 531 nm, which is significantly longer than the fluorescence lifetime of pure liquid Acceptor (1) (r = 7.6 ns; λ_εχ = 365 nm; Figure 10). Such slow luminescence decay provides definitive evidence for the TTA-based UC processes which involve long-lived triplet states.

[0045]

We then quantified the UC efficiency of the Donor (2)-doped liquid (Donor (2)/ Acceptor (1) = 0.01 mol%) by using the liquid Acceptor (1) containing 0.01 mol% Nile red as a reference.³²'⁹ Figure 12c shows dependence of quantum yield on the excitation power density, in which each represents an average of at least three independent measurements using different batches. With increasing the power density, the quantum efficiency increased and became saturated at 28%. Comparable quantum yields were reproducibly observed and another set of experiments conducted by using Rhodamin B in liquid Acceptor (1) as a reference gave similar quantum yields. The observed remarkably high quantum yield is close to the highest records reported for solvent-free UC systems, ' showing a great potential of the present liquid upconverting systems.

[0046]

As described before, strict deoxygenation treatment is generally inevitable to achieve UC phenomena since oxygen molecules quench all the triplets⁷ and it severely hampers their applications. To our surprise, however, the current liquid UC system is unperturbed by the presence of 0₂ molecules. The UC data obtained in vacuo— UC emission spectra, incident light power dependence of UC emission, and UC luminescence decay for Donor (2)-doped liquid Acceptor (1) (Donor (2)/ Acceptor (1) = 0.01 mol%)— were almost identical to those obtained in air (Figures 10 and 13). This implies that diffusion of 0₂ molecules into the liquid chromophores is significantly suppressed, due to air-sealing effect of molten alkyl chains surrounding the chromopheres.^3d'¹⁰

[0047]

To evaluate the contribution of triplet energy migration in the liquid acceptor UC system, UC experiments were conducted in the low-temperature glassy state. As shown in Figure 14, the relative UC emission intensity at 433 nm decreased with the decrease in temperature (Donor (2)/Acceptor (1) = 0.01 mol%; λ_εχ = 532 nm).^4b It is to note that the UC emission was apparently observed below the glass transition temperature (-59 °C), with ca. 20% of the intensity still preserved in the glassy state. This result clearly demonstrates that the triplet energy migration occur even among frozen acceptor molecules. It's understood that triplet energy transfer and energy migration occur via the electron exchange mechanism (Dexter excitation transfer).¹¹ It requires overlap of wavefunctions between donors and acceptors and consequently it has a much steeper exponential dependence on distance compared to that displayed by dipole-dipole coupling mechanism (Forster resonance transfer), which occur over distances considerably exceeding the sum of their van der Waals radii. Although the acceptor molecules Acceptor (1) in the liquid state may possess very short-ranged order as indicated by XRD data (Figure 7), they lack long-range ordering. The observed efficient UC however indicates the occurrence of facile triplet energy transfer between the donor- acceptor pairs (Donor (2)- Acceptor (1)) and triplet energy migration among the adjoining liquid acceptor molecules (1). To achieve these performances, reorientation of excited triplet molecules in between the neighboring molecules will be required to maximize the overlap of wavefunctions. The temperature dependence observed in Figure 14 therefore demonstrates the involvement of triplet energy migration processes which are thermally facilitated. It would be natural that such chained electron exchange processes enable diffusion and efficient collision of triplet excitons in the condensed molecular fluids.

[Example 2]

[0048]

We designed an acceptor A (shown below) that has self-assembling and oxygen-shielding abilities. We modified 9,10-diphenylanthracene with amide groups for intermolecular hydrogen bonding, and with alkyl chains (R groups in the following formula) for oxygen shielding.

(^CH2)11— ^CH3 ]

The synthetic route of A is shown below,

o H

WSC HOBT N HC Boc

OH O'

CH2CI2 N (CH₂)₂

Boc

R=— (CH₂)₁₁-CH₃

Boc-Glu-COC

Glu-C,OC

DPA-2COOH

DPA-2COOH DPA-2COCI

[0050]

Synthesis of Boc-Glu-C₃OC₁₂.

3-(dodecyloxy)propylamine 12.7 ml (0.044 mol), l-ethyl-3-(3-dimethylaminopropyl)-carbodiimide 8.43 g (0.044 mol), and 1-hydroxybenzotriazole 5.95 g (0.044 mol) were added to N-(tert-Butoxycarbonyl)-L-glutamic Acid 4.94 g (0.02 mol) in 400 ml of distilled dichloromethane and reacted for 48h at the room temperature in Ar. After the reaction, the solution was washed several times with sodium hydrogen carbonate aqueous solution and with water, dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by reprecipitation (methanol/water) and column chromatography (dichloromethane/methanol) over silica gel yielded the pure Boc-Glu-C₃OC₁₂ solid (yield: 88%). 1H NMR (300 MHz, CDC1₃): δ = 0.86-0.91 (t, 6H), 1.26 (m, 36H), 1.44 (s, 9H), 1.56-1.62 (m, 4H), 1.73-1.81 (m, 4H), 1.90-2.09 (m, 2H), 2.21-2.32 (m, 2H), 3.32-3.53 (m, 12H), 5.72-5.75 (d, 1H), 6.44 (t, 1H), 6.95 (t, 1H). ESI-MS: calculated for C,₀₆H₁₇₈O₄ 1516.55; found 1518.32 [M⁺]. ESI-MS: calculated for C₄₀H₇₉N₃O₆ 698.07; found 698.65 [M⁺].

[0051 ]

Synthesis of Glu-C₃OCi₂. Synthesized Boc-Glu-C30C12 2.09 g (3.0 mmol) were added in 150 ml of distilled dichloromethane and cooled by ice bath. Large excess of trifluoroacetic acid 6.88 ml was added to this mixture and stirred at room temperature for 12 h. After that, the solvent was removed by rotary evaporation and oily product was obtained. The oily compound was dissolved in 10 mL THF and poured into 150 mL aqueous solution saturated of NaHC0₃. After filtration, the product was purified by recrystalization in methanol/ethyl acetate to give a colorless solid Glu-C₃OCi₂ (yield: 94%). 1H NMR (300 MHz, CDC1₃): δ = 0.88-0.90 (t, 6H), 1.26 (m, 36H), 1.59 (m, 4H), 1.73-1.80 (m, 4H), 1.82-2.05 (m, 2H), 2.27-2.32 (m, 2H), 3.32-3.51 (m, 12H), 6.48 (t, 1H), 6.44 (t, 1H), 7.60 (t, 1H).

[0052]

Synthesis of DPA-2COOMe.

A mixture of 2.12 g (11.8 mmol) 4-methoxycarbonylphenylboronic acid, 1.80 g (5.4 mmol) 9,10-dibromo anthracene, 2.60 g (24.2 mmol) CsF and 187 mg (0.61 mmol) Tetrakis(triphenylphosphine)palladium(0) were placed in a 300 ml flask under Ar. Then 100 ml of degassed 1,2-dimethoxyethane were added. After refluxing under Ar for 60 h the solvent was removed to give a yellow residue. The solid was suspended in 35 ml water and extracted with 100 ml of CHC1₃. After drying the organic phase over MgS0₄ and removing the solvent, the product was purified by column chromatography (CHC1₃) over silica gel to yield of a yellow powder (yield: 21 %). Ή NMR (300 MHz, CDC1₃): δ = 4.02 (s, 6H), 7.32-7.38 (m, 4H), 7.56-7.61 (d, 4H), 7.61-7.64 (m, 4H), 8.28-8.31 (d, 4H).

[0053]

Synthesis of DPA-2COOH.

To a suspension of 288 mg (0.65 mmol) DPA-2COOMe in 75 ml 1/1 mixture of THF/MeOH, 15 ml of a 2M OH aqueous solution was added. The mixture was allowed to reflux for 3 h. THF was removed under reduced pressure and the resulting suspension was diluted with water. The precipitate formed by acidification with aqueous HCl (2M) was collected by sunction, washed several times with water yielding 227 mg (84 %) of a pale yellow solid. Ή NMR (300 MHz, d₆-DMSO): δ = 7.44-7.49 (m, 4H), 7.51-7.58 (d, 4H), 7.60-7.67 (m, 4H), 8.21-8.32 (d, 4H) 13.16 (s, 2H).

[0054]

Synthesis of DPA-2(L)GIu (A).

3 ml of distilled benzene and 1 ml of thionyl chloride were added to 145 mg (0.35 mmol) DPA-2COOH placed in a 10 ml flask under Ar. This mixture was refluxed for 3 h with catalyst quantity of DMF. After removing the solvent and excess thionyl chloride under reduced pressure, residual yellow solid was dispersed into 25 ml of distilled dichloromethane and added this dropwise to 623 mg (1.04 mmol) Glu-C₃OCi₂ dissolved in 25 ml of distilled dichloromethane by using dropping funnel under Ar. This mixture was stirred at room temperature for 2. After reaction, the solution was washed several times with sodium hydrogen carbonate aqueous solution and with water, dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure and column chromatography (chloroform/methanol) over silica gel yielded the 403 mg of pale yellow solid. 1H NMR (300 MHz, CDC1₃): δ = 0.81-0.92 (t, 12H), 1.16-1.38 (m, 74H), 1.49-1.57 (m, 8H), 1.73-1.90 (m, 8H), 2.14-2.46 (m, 2H), 2.50-2.68 (m, 2H), 3.34-3.47 (m, 16H), 3.47-3.58 (q, 4H), 4.59-4.71 (q, 2H) 6.45-6.52 (t, 2H), 7.17-7.25 (t, 2H), 7.30-7.40 (q, 4H), 7.55-7.61 (d, 4H), 7.61-7.67 (q, 4H), 8.13-8.20 (d, 4H) 8.44-8.51 (d, 2H). Elemental analysis: calculated for H 9.96 C 74.58 N 5.32; found H 9.93 C 74.40 N 5.25.

[0055]

Characterization.

Ή NMR (300 MHz) spectra were measured on Bruker DRX-300 spectrometer using TMS as internal standard. IR was conducted on a SHIMADZU FT-IR-8400S. Electro Spray Ionization time-of-flight mass spectrometry (ESI-TOF-MS) was performed on a JMS-T100LC AccuTOF. Elemental analysis was conducted at the Elemental Analysis Center, Kyushu University. XRD analysis was conducted on a RIGAKU smart-lab with a copper K-alpha source. Atomic force microscopy (AFM, tapping mode) was carried out using a Agilent PicoPlus 5500. Luminescence spectra were measured by using a PerkinElmer LS 55 fluorescence spectrometer. The samples were excited with an incidence angle of 45° to the quartz cell surface and the fluorescence was detected along the normal. Emission spectra were recorded with excitation wavelength of 375 rim or 510 nm. UV-vis spectra were recorded on a JASCO V-670 spectrophotometer. The absolute quantum yields were calculated using a Hamamatsu C9920-02G instrument. Time-resolved fluorescence lifetime measurements were carried out by using time-correlated single photon counting lifetime spectroscopy system, HAMAMATSU Quantaurus-Tau CI 1367-02 (for fluorescence lifetime)/C 11567-01 (for delayed luminescence lifetime). The quality of the fit has been judged by the fitting parameters such as χ (<1.2) as well as the visual inspection of the residuals. The upconversion luminescence emission spectra were recorded on Otsuka Electronics MCPD-7000 instrument with the excitation source using an external, adjustable 532 nm semiconductor laser (0-140 mW).

[0056]

The assembled structure of A in chloroform was studied by 1H-NMR, Atomic force microscope (AFM), and absorption/emission spectra. Variable-temperature 1H-NMR measurements showed that the peaks of amide groups shifts to higher magnetic field by increasing the temperature, which indicates the presence of intermolecular hydrogen bonding at 25 °C. AFM studies of drop-casted solution A onto atomically flat highly oriented pyrolytic graphite (HOPG) showed fibrous structures with a thickness around 2 nm, which matches the width of single molecule. That only small shift was observed for absorption spectra of A in chloroform by heating suggests that there are no strong interactions between anthracene moieties.

[0057]

A donor, Pt(II)octaethylporphyrin (D; 10 μΜ), was added to the chloroform solution of A (10 mM). Interestingly, by exciting at 532 nm, blue upconverted emission was clearly observed around 440 nm (Figure 15). The absence of donor phosphorescence indicates that the donor molecules are included in the acceptor assemblies and the triplet energy was effectively transferred to the acceptor A. The UC quantum yield of this A-D mixture solution was found to be as high as 36% and 60% in aerated and deaerated conditions, respectively. This remarkably high quantum yield clearly indicates the good oxygen shielding ability of the acceptor assemblies. This oxygen shielding performance was also confirmed by lifetime measurements; a long lifetime of 633 was observed at the room temperature for the acceptor triplet in the A-D mixture solution even in the aerated condition. The UC emission was clearly observed even below the melting point of solvent (209 K), and this confirms the mechanism of TTA-UC by triplet energy migration (Figure 16).

[0058]

In previous reports, it was still difficult to achieve an efficient donor-to-acceptor triplet-triplet energy transfer due to macroscopic phase segregation between donor and acceptor. Taking advantage of the effective inclusion of donor molecules in the acceptor assemblies in our system, the homogeneous doping of the donor was achieved even in the solid state. The cast film prepared from the A-D mixture chloroform solution ([A] = 10 mM, [D] = 10 μΜ) showed a clear UC emission in air (Figure 17). This result clearly indicates that the triplet energy is transferred from donor to acceptor, and the triplet energy migrates in the acceptor arrays. Importantly, the oxygen shielding ability was preserved in the solid film state.

[0059]

By changing the solvent from chloroform to 1 ,2-dichloroethane, the acceptor A was found to form a gel at the room temperature. The acceptor gel was doped with the donor D ([A] = 16 mM, [D] = 16 μΜ). Significantly, the A-D mixture gel showed a blue UC emission by exciting with the green light even in the ambient condition (Figure 18). With the restricted molecular diffusion in the gel, the energy migration mechanism allows the efficient TTA-UC to take place.

[Example 3]

[0060]

Researchers used non- volatile ionic liquids instead of volatile organic solvents for dissolving donor and acceptor, however, it was necessary to use strong excitation (~1000 mW/cm²) due to the high viscosity of ionic liquids, and the UC emission was quenched by oxygen. Here we present an air-stable, low-power photon upconversion in non-volatile ionic liquids, in which the ionic liquids are composed of anionic acceptors and flexible cations and the donor molecules are dissolved in these acceptor ionic liquids.

Thanks to the design flexibility of ionic liquids, we prepared different ionic liquids by the combination between anions containing acceptor anthracene moiety and cations with flexible alkyl or oligo(ethylene glycol) chains.

A3 A4

[0061 ]

The synthetic route is shown below taking the acceptor Al as a typical exam] The purity of the products was characterized by 'H-NMR and elemental analysis.

Al

[0062] The optical properties of the ionic liquids were characterized by absorption and emission spectra (Figure 19). There were no peak shifts between the absorption spectra of Al in the CHC1₃ solution and in the solvent- free ionic liquid, indicating the absence of strong interactions between the acceptor moieties.

[0063]

A donor Pt(II)octaethylporphyrin (PtOEP) was successfully dissolved in the ionic liquids. The CHC1₃ solution of Al and PtOEP (0.1 mol%) was dried under reduced pressure and sealed in the inert Ar atmosphere. Figure 20 shows the picture and microscope images of the Al -PtOEP mixture. No phase separation and precipitation was observed, and homogeneous blue fluorescence of Al and red phosohorescence of PtOEP were observed.

[0064]

The Al-PtOEP mixture in the solvent-free ionic liquid state showed clear upconverted emission around 450 nm by the excitation at 532 nm (Figure 21). The plot of UC emission intensity against the excitation power density showed the slope around 2 in the weak power density region, confirming that the upconverted emission is based on the TTA process. The change of the slope was observed at as low as 10 mW cm^"2 that is much lower than the reported value for the dye dispersion in ionic liquids (-1000 mW cm^"2).

[0065]

The UC emission of the Al-PtOEP mixture was observed even below the glass transition temperature of Al (10 °C), and this indicates the important contribution of triplet energy migration in the dense acceptor aggregates for the TTA-UC events (Figure 22a). Importantly, the UC emission of the Al-PtOEP mixture was clearly observed even in air (Figure 22b).

[Example 4]

[0066]

The efficient triplet-triplet annihilation-photon upconversion (TTA-UC) has been achieved by utilizing the diffusion and collision of the donor and acceptor in solution, however, there is a severe problem limiting their practical applications; the use of volatile solvent. Although recently the TTA-based UC has been investigated in solid polymer films, such macromolecular matrices inevitably restrict the diffusion of triplet molecules that limit the efficiency of UC. To solve this problem, we are proposing a paradigm shift from molecular diffusion to energy migration. Among different molecular assemblies, liquid crystals (LCs) are known to show efficient triplet energy migration, but there have been no reports on TTA-UC in LCs. Here we show the first example of upconverting LCs that exhibit highly efficient TTA processes at low excitation intensity.

We synthesized a columner LC 1 composed of an acceptor unit, perylene, and branched alkyl chains.

1

[0067]

The DSC measurements of 1 showed the wide temperature range for the liquid crystal phase from -76 °C to 250 °C. Powder X-ray diffraction (PXRD) measurements of 1 showed typical diffraction patterns of hexagonal columnar liquid crystals. Under the polarized microscope, a typical texture of hexagonal columner liquid crystal was also observed. Pt(II)tetraphenyltetrabenzoporphyrin (2) was employed as a donor. The donor 2 was doped in the LC 1 by simply evapolating the mixed solution of 1 and 2 (2/1 = 0.1 mol %). The obtained mixture showed the texture of hexagonal columner liquid crystal under the polarized light, and no aggregation of 2 was observed (Figure 23). The PXRD measurements of the 2-doped 1 showed the retention of the hexagonal columner phase. [0068]

Figure 24a shows emission spectra of the 2-doped LC 1 (2/1 = 0.1mol%). Yellow UC emission was observed upon excitation at 635 nm. It is noteworthy that the phosphorescence of donor 2 (760 nm) was completely quenched regardless of the excitation power, indicating the efficient triplet-triplet energy transfer from 2 to 1. To prove the TTA-based UC mechanism, the dependence of UC emission on the incident power density was investigated. In general, the TTA-assisted UC shows the quadratic incident light power dependence in the weak-annihilation limit, which consequently turns into the first-order dependence in the saturated annihilation regime. Figure 24b presents a double logarithm plot for the UC emission intensity of the 2-doped LC 1 (2/1 = 0.1mol%) as a function of incident light power density (λ_βχ = 635 nm). At the lower-power regime of <340 mW cm^-2, a slope close to 2 was observed, whereas it changed to ca. 1 at higher-power density (>340 mW cm^-2). This provides a decisive experimental evidence for TTA-based UC in this liquid crystal system. The crossover threshold (/,_/,) was observed at a power density around 340 mW cm^-2.

[0069]

To prove the presence of triplet energy migration in the liquid crystal acceptor UC system, emission spectra were recorded in the low-temperature glassy state. As shown in Figure 25, the UC emission intensity decreased with the decrease in temperature. However the UC emission is observed even below the glass transition temperature (-87 °C), with more than 60 % of the intensity preserved compared to those observed at the ambient temperature. This result clearly demonstrates that the triplet energy migration occurs among frozen acceptor molecules.

[Example 5]

[0070]

The efficient TTA-UC has been achieved by utilizing the diffusion and collision of the donor and acceptor in solution, however, there is a severe problem limiting their practical applications; the use of volatile solvent. Although recently the TTA-based UC has been investigated in solid polymer films, such macromolecular matrices inevitably restrict the diffusion of triplet molecules that limit the efficiency of UC. To solve this problem, we are proposing a paradigm shift from molecular diffusion to energy migration. The ideal material for TTA-UC is an emitter crystal doped with sensitizers. In such a system the TTA rate will be maximized by the high diffusivity of triplet excitons in ordered crystalline structures. However, common emitters and sensitizers tend to form segregated crystal structures, thus preventing the intimate contact needed. We solved this problem by the chemical modification of acceptor molecules with alkyl chains that allow the donor molecules molecularly dispersed in the acceptor crystals. By simply casting the donor-acceptor mixed solution, the obtained solid film shows clear upconverted emission.

We designed and synthesized crystalline acceptor molecules Al, A2, and A3. An acceptor, anthracene, was modified with alkyl chains, phenyl group, and carboxylate for the improvement of miscibility with donor, the steric hinderance between anthracene to avoid fluorescence quenching, and the control of intermolecular arrangements, respectively.

[0071 ]

The synthesis of these compounds are shown below. 

[0072]

The solid films of acceptors Al, A2, and A3 were prepared by casting the CHC1₃ solutions of these compounds. The polarized microscopy and X-ray diffraction measurements showed that all the acceptors Al, A2, and A3 have good crystallinity (Figures 26 and 27).

[0073]

Importantly, a donor Pt(II)octaethylporphyrin (PtOEP) could be homogeneously dispersed in the crystalline solid Al, A2, and A3. The mixed solutions of acceptor and donor (0.1 mol%) were casted on the glass plate and dried in the ambient condition. The optical micsoscopy studies of the doped solid showed the homogeneous distribution of donor molecules (Figure 28). [0074]

Figure 29 shows the absorption bands of PtOEP in PtOEP solution, bulk PtOEP solid, and acceptor crystals doped with PtOEP. The absorption peak in the PtOEP-doped Al film located between the PtOEP solution and bulk PtOEP, suggesting the partial aggregation of PtOEP in the Al crystals. On the other hand, in the PtOEP-doped films of A2 and A3, the absorption peak is close to the one in PtOEP solution. These results indicate that the donor PtOEP was molecularly dispersed in the Al and A2 acceptor crystals. The observed difference of donor miscibility would be due to the larger number of alkyl chains per molecules in A2 and A3 than Al.

[0075]

The emission spectra of the PtOEP-doped acceptor crystals were measured by the excition at 532 nm in the Ar atmosphere (Figure 30). Together with the monomeric phosphorescence of PtOEP at around 650 nm, another emission band was observed around 750 nm for the PtOEP-doped Al film. This additional band can be assigned to the emission from aggretated PtOEP molecules. The emission of aggreated PtOEP was not observed for the PtOEP-doped A2 and A3 films, and these observations agree well with the results of the absorption measurements. It is significant that the doped films showed clear upconversion emission at 450 nm even with low excitation power density

2 2

of ca. 1 mW .cm^" . Low threshold intensity (< 30 mW cm^" ) in the UC intensity v.s. excitation power log-log plot was observed for the PtOEP-doped A2 and A3 films.

[0076]

Synthesis of Anthracenedicarbonyl chloride.

10 ml of distilled dichloromethane and 1 ml of thionyl chloride were added to 100 mg (0.38 mmol) Anthracenedicarboxylic acid placed in a 50 ml flask under Ar. This mixture was refluxed for 2 h with. After removing the solvent and excess thionyl chloride under reduced pressure, residual yellow solid was used without purification.

A'-1

[0077]

Synthesis of A'-l.

114 mg of Anthracenedicarbonyl chloride dissolved into 5 ml of distilled dichloromethane were added dropwise to 185 mg (1.52 mmol) Dodecylamine dissolved in 10 ml of distilled dichloromethane under Ar. This mixture was stirred at room temperature for 1 h. After reaction, the solution was washed several times with diluted hydrochloric acid and with water, dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by column chromatography (chloroform/methanol) over silica gel and recrystallization (acetone) yielded the 190 mg of colorless solid. Ή NMR (300 MHz, CDC1₃): δ = 0.80-0.94 (t, 6H), 1.06-1.48 (m, 36H), 1.67-1.81 (quin, 4H), 3.62-3.76 (q, 4H), 5.89-6.02 (s, 2H), 7.47-7.56 (m, 4H), 8.00-8.12 (m, 4H). Elemental analysis: calculated for H 9.96 C 74.58 N 5.32; found H 9.93 C 74.40 N 5.25.

[0078]

Synthesis of A'-2.

114 mg of Anthracenedicarbonyl chloride dissolved into 5 ml of distilled dichloromethane were added dropwise to 185 mg (1.52 mmol) Dodecylamine dissolved in 10 ml of distilled dichloromethane under Ar. This mixture was stirred at room temperature for 1 h. After reaction, the solution was washed several times with diluted hydrochloric acid and with water, dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by column chromatography (chloroform/methanol) over silica gel and recrystallization (acetone) yielded the 190 mg of colorless solid. Ή NMR (300 MHz, CDC1₃): δ = 0.81-0.94 (t, 6H), 0.97-1.47 (m, 52H), 1.68-1.80 (quin, 4H), 3.65-3.76 (q, 4H), 5.89-5.99 (s, 2H), 7.48-7.56 (m, 4H), 8.01-8.12 (m, 4H).

A'-3

[0079]

3-(dodecyloxy)propylamine 0.32 ml (1.1 mmol), l-ethyl-3-(3-dimethylaminopropyl)-carbodiimide 93.6 mg (0.5 mmol), and 1 -hydroxybenzotriazole 67.6 mg (0.5 mmol) were added to Anthracenedicarboxylic acid 66.5 mg (0.25 mmol) in 50 ml of anhydrous DMF and reacted for 40 h at the room temperature in Ar. After the reaction, the solution was washed several times with sodium hydrogen carbonate aqueous solution and with water, dried over anhydrous Na₂S0₄. Evaporation of the organic layer under reduced pressure followed by reprecipitation (methanol/water) and column chromatography (dichloromethane/methanol) over silica gel yielded the 78 mg of colorless solid. 1H NMR (300 MHz, CDC1₃): δ = 0.81-0.94 (t, 6H), 0.96-1.50 (m, 40H), 1.94-2.11 (quin, 4H), 3.26-3.36 (t, 4H), 3.53-3.65 (t, 4H), 3.77-3.90 (q, 4H), 6.58-6.70 (s, 2H), 7.47-7.57 (m, 4H), 8.01-8.13 (m, 4H).

[0080]

Figure 31 shows the photoluminescence spectra of acceptors A'-l, A'-2, and A'-3 in the presence of donor PtOEP in air-saturated chloroform ([acceptor] = 10 mM, [PtOEP] = 10 μΜ; λ_εχ = 532 nm). Upconverted emission around 440 nm was clearly observed from all the mixture solutions, indicating the effective blocking of oxygen quenching in these donor-acceptor hybrids.

[0081 ]

Figure Legends

Figure 1. Qualitative Jablonski diagram showing the sensitized triplet-triplet annihilation (TTA)-based upconversion emission, using Donor (2) as the triplet photosensitizer and liquid Acceptor (1) as the triplet acceptor (and the emitter).

Figure 2. A schematic representation of the matrixt-free liquid upconversion system. Donor molecules (red) in acceptor liquid (yellow) are excited by long-wavelength light. This is followed by triplet-triplet energy transfer (TTET) from the donor to acceptor, followed by triplet energy migration and triplet-triplet annihilation (TTA) processes. A sequence of these photo-relaxation processes efficiently gives delayed fluorescence from the upconverted singlet state of acceptor.

Figure 3. (a) Chemical structures of liquid Acceptor (1) and Sensitizer (2) (or Donor (2)). Photographs of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) upon being exposed to (b) white light and (c) 532 nm green laser (incident laser direction is indicated by a green arrow). Bright blue luminescence is due to UC emission, and green spots are scattered incident laser.

Figure 4. Photographs of liquid Acceptor (1) under (a) visible and (b) UV (365 nm) light.

Figure 5. A DSC thermogram of Acceptor (1) in the cooling trace (10 °C/min). The observed inflection is assignable to a glass transition. The glass transition temperature at -59 °C was reproducibly observed upon repeating heating-cooling cycles for more than 3 times. Figure 6. (a) Storage modulus (G'; black square) and loss modulus (G"; red circle) versus angular frequency of Acceptor (1). (b) Complex viscosity (//*) versus angular frequency of Acceptor (1) (η* = 0.99 Pa s). The observed larger loss modulus compared to the storage modulus indicates that the compound Acceptor (1) is in the liquid state. The liquid Acceptor (1) has a smaller viscosity than glycerol (1.2 Pa s) and comparable to other liquid aromatics.¹⁵

Figure 7. (a) XRD and (b) SAXS profiles of liquid Acceptor (1). In the XRD analysis, Acceptor (1) exhibits a halo in the wide angle region corresponding to an average distance between the molten aliphatic chains of 4.4 A (2Θ = 19.9°). In the SAXS analysis, Acceptor (1) exhibits a wide halo in the small angle region corresponding to the disordered anthracene core-to-core distance of 21 A.¹⁵

Figure 8. (a) Optical microscope image and (a') polarized microscope image of the mixture of Acceptor (1) and PtOEP (PtOEP/Acceptor (1) = 1 mol%). (b) Optical microscope image and (b') polarized microscope image of the mixture consisting of Acceptor (1) and Donor (2) (Donor (2)/ Acceptor (1) = 1 mol%).

Figure 9. (a) Normalized absorption and emission spectra of CHC1₃ solution of Acceptor (1) (λ_εχ = 375 nm, 0.1 mM) and Donor (2) in deaerated CHC1₃ (2_ex = 510 nm, 0.1 mM). (b) Normalized absorption and emission spectra of liquid Acceptor (1) ( _ex = 375 nm) and cast film of Donor (2) (λ_εχ = 520 nm).

Figure 10. (a) Luminescence decay observed for liquid Acceptor (1) in CHC1₃ (0.1 mM, black line) and solvent-free state (blue line) (i_ex = 365 nm, _em = 450 nm). The fluorescence lifetimes were 6.53 ns and 7.66 ns for the solution and neat liquid, respectively, with the single exponential fittings. (b) Luminescence decay curves obtained for the delayed luminescence by TTA upconversion in air (blue line) and in vacuum (red line) from Donor (2)-doped liquid Acceptor (1) (Donor (2)/ Acceptor (1) = 0.01 mol%; _ex = 531 nm, _uc = 450 nm). The luminescence reported for related liquid compounds with different alkyl chain structures was fitted with a biexponential decay.¹⁵ However in our case, the data of liquid Acceptor (1) can be fitted with a single exponential, and the fitting result by using a biexponential function gave only negligible portion of the second component. This found difference implies the importance of alkyl chain structures to obtain ideal, photochemically isolated liquid chromophores.

Figure 11. Normalized absorption and emission (λ_εχ = 375 nm) spectra of the doped liquid Acceptor (1) (Donor (2)/Acceptor (1) = 0.01 mol%).

The Donor (2)-doped liquid sample showed a Q-band at 511 nm, which is close to that of Donor (2) dissolved in CHC1₃ (Figure 9a). The adsorption spectrum of Donor (2) was measured in cast films, which exhibited prominent red-shifts to 518 nm, indicating an aggregate formation in the solid film (Figure 9b). It was further supported by luminescence spectral measurement for the solid film Donor (2) ( _ex = 520 nm), which gave phosphorescence at 718 nm with a shoulder peak at 827 nm (Figure 9b). The latter 827 nm peak can be assigned to the dimer emission.¹⁶ These data support that Donor (2) is molecularly dispersed in the acceptor liquid Acceptor (1).

Figure 12. (a) Photoluminescence spectra of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) with different incident power density of 532 nm laser in air. (b) Dependence of upconversion emission intensity at 433 nm on the incident power density (Donor (2)/Acceptor (1) = 0.01 mol%). The dashed lines are fitting results with slopes of 2.0 (purple) and 1.0 (green) in the low and high power regimes, respectively, (c) Quantum yield of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) measured as a function of 532 nm incident power density.

Figure 13. (a) Photoluminescence spectra of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) with different incident power density of 532 nm laser in vacuum, (b) Incident power density dependence of upconversion emission intensity at 433 nm of the doped liquid (Donor (2)/Acceptor (1) = 0.01 mol%) in vacuum. The dashed lines are fitting results with slopes of 2.0 (blue) and 1.0 (red) in the low and high power density regimes, respectively.

Figure 14. Plots of temperature-dependent UC emission intensity at X_em = 433 nm (A_ex = 532 nm) of the doped liquid (Donor (2)/ Acceptor (1) = 0.01 mol%).

Figure 15: Upconverted emission of the A-D mixture chloroform solution ([A] = 10 mM, [D] = 10 μΜ) in air by changing the excitation power (λ_βχ = 532 nm).

Figure 16: Emission spectra of the A-D mixture chloroform solution ([A] = 10 mM, [D] = 10 μΜ) in air at 293 K (red) and 198 K (blue).

Figure 18: The 1 ,2-dichloroethane gel of A-D mixture ([A] = 16 mM, [D] = 16 μΜ) and its blue UC emission.

Figure 20: (a) Picture of the Al-PtOEP mixture sealed between two quarts plates, (b) Microscopic images and (c) emission images of the Al-PtOEP mixture.

Figure 22: (a) UC emission intensity of the Al-PtOEP mixture in Ar at different temperatures, (b) UC emission spectrum of the Al-PtOEP mixture in air. Figure 23: Polarized optical microscope image of 2-doped liquid crystal 1 (2/1 = 0.1 mol %).

Figure 24: (a) Photoluminescence spectra of the 2-doped liquid crystal 1 (2/1 = 0.1 mol%) with different incident power density of 635 nm laser, (b) Dependence of UC emission intensity at 580 nm on the incident power density. Blue and red lines are fitting results with slopes of 2.3 (blue) and 1.1 (red) in the low and high-power regimes.

Figure 25: Plots of temperature-dependent UC emission intensity at l_em = 580 nm (λ_εχ = 635 nm) of the doped LC (2/1 = 0.1 mol%).

Figure 27: Powder X-ray diffraction profiles of Al (blue), A2 (red), and A3 (green).

Figure 28: Optical microscope images of solution-casted (a) Al -PtOEP, (c) A2 -PtOEP, (e) A3-PtOEP, and polarized microscope images of (b) Al-PtOEP, (d) A2-PtOEP, (f) A3-PtOEP.

Figure 29: Absorption spectra of PtOEP CHC1₃ solution (red), neat PtOEP solid (green), and the acceptor solid film doped with 1.0 mol% PtOEP (blue, (a) Al, (b) A2, (c) A3)

Figure 30: Emisssion spectra of the PtOEP-doped (a) Al, (b) A2, (c) A3 films.

Figure 31: Photoluminescence spectra of (a) A'-l (10 mM), (b) A'-2 (10 mM), and (c) A'-3 (10 mM) with PtOEP (10 μΜ) in aerated chloroform at room temperature (λ_εχ = 532 nm).

Industrial Applicability

[0082] In conclusion, this study demonstrated the first example of upconverting fluid molecular network systems, which exert surprising air-stable upconversion properties with quantum yield as high as 28%. Introduction of branched alkyl chains to the donor-acceptor pairs brought benefits of the good miscibility as well as the oxygen shielding effect. The air-stable, long-lived triplets in the photon upconverting liquids could be integrated with the concepts of molecular self-assembly,¹² which may provide a new perspective in controlling energy landscapes of the collective excited states. The extension of current liquid UC systems to the near IR-to-visible or visible-to-UV regions will also provide solutions to resolve important energy issues, and we envisage that the current liquid upconverting system would open a new door to green sustainable soft materials.

The highest-efficiency, low-power, air-stable light-harvesting TTA-UC system has been developed by introducing the concept of supramolecular self-assembly. The suitably designed amphiphilic acceptor molecules spontaneously self-assemble in organic media to give developed, nanotape-like monolayer assemblies. They efficiently uptake donor molecules that lead to the highest UC quantum yield both in deaerated (60%) and aerated (36%) conditions. The tolerance of present light-harvesting system against molecular oxygen deserves attention. A number of applications of the current light-harvesting system is conceivable, which would open new avenues to self-assembly-based molecular technology in many disciplines. The rational extension of light-harvesting self-assemblies to the other combination of chromophores will lead to novel near IR-to-visible or visible-to-UV upconversion systems for improving photovoltaic and photocatalytic devices. The design of amphiphilic light harvesting systems in water would find many biological applications. Beyond TTA-UC, we envisage the formation and migration of triplet excitons in various self-assemblies and their aerobic stability would exert great impacts on materials science.

[0083]

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Claims

1. A solvent- free photon upconversion composition comprising:

(a) an acceptor chromophore; and

(b) an organic donor,

2. The composition of claim 1, wherein the acceptor chromophore is at least one compound selected from the group consisting of 9,10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives, 9,10-bis(phenylethynyl)anthracene, 9,10-Bis(phenylethynyl)naphthacene, rubrene and tetracene.

3. The composition of claim 1 or 2, wherein the organic donor is at least one compound selected from the group consisting of Pt(II)/Pd(II)-po hyrin, Pt(II)/Pd(II)-tetraphenyl-tetrabenzoporphyrin, Pt(n)/Pd(II)-Ph₄0Me₈TNP, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pyr₃RuPZn₃ and Pt(II)/Pd(II)-tetrakisquinoxalino porphyrin, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and a-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes.

4. The composition of claim 2, wherein the acceptor chromophore comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

5. The composition of claim 2, wherein the acceptor chromophore comprises one or more self-assembly moieties selected from oligo/poly (ethyleneglycol), , saccharides, mono/oligo nucleotides, carboxylate, bipyridine, terpyridine, catechol, phenanthroline, tetrathiafulvalene, tetracyanoquiodimethane, fullerene, cholesterol, amino acids, Au/Ag/Pt/Pd complexes forming metal-metal interactions, bipyridinium, amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, and triazole, halogens .

6. The composition of claim 5, wherein the self-assembly moiety comprise one or more of intermolecular interaction sites selected from amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, halogens and aromatic groups.

7. The composition of claim 3, wherein the organic donor comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

8. The composition of any one of claims 1 to 7, wherein the molar ratio of organic donor/acceptor chromophore ratio is in the range of 0.001% to 1%.

9. The composition of any one of claims 1 to 8, wherein the acceptor chromophore forms an ion liquid with a cation molecule comprising one or more unsubstituted or substituted alkyl moieties and/or oligo/poly (ethylene glycol) moieties.

10. The composition of claim 9, wherein the acceptor chromophore forms an ion liquid selected from the group consisting of:

11. The composition of any one of claims 1 to 10, wherein the composition functions as an upconversion system in air.

12. A method of achieving photon upconversion in air using the composition of any one of claims 1 to 1 1.

13. An acceptor chromophore for a solvent- free photon upconversion, comprising at least one compound selected from the group consisting of 9,10-diphenylanthracene, perylene, pyrene, boron dipyrromethane (BODIPY) derivatives, 9, 10-bis(phenylethynyl)anthracene, 9,10-Bis(phenylethynyl)naphthacene, perylenetetracarboxylic diimide derivatives, rubrene and tetracene.

14. The acceptor chromophore of claim 13, which comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.

15. The acceptor chromophore of claim 13, which comprises one or more self-assembly moieties selected from oligo/poly (ethyleneglycol), saccharides, mono/oligo nucleotides, carboxylate, bipyridine, terpyridine, catechol, phenanthroline, tetrathiafulvalene, tetracyanoquiodimethane, fullerene, cholesterol, amino acids, Au/Ag/Pt/Pd complexes forming metal-metal interactions, bipyridinium, amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, and triazole, halogens .

16. The acceptor chromophore of claim 15, wherein the self-assembly moiety comprise one or more of intermolecular interaction sites selected from amide, urea, pyridine, cytosine, naphthyridine, carboxylate, imidazole, triazole, halogens and aromatic groups.

17. The acceptor chromophore of claim 13, which forms an ion liquid with a cation molecule comprising one or more unsubstituted or substituted alkyl moieties and/or oligo/poly (ethylene glycol) moieties.

18. The acceptor chromophore of claim 17, which forms an ion liquid selected from the group consisting of:

19. An organic donor chromophore for a solvent-free photon upconversion, comprising at least one compound selected from the group consisting of Pt(II)/Pd(II)-porphyrin, Pt(II)/Pd(II)-tetraphenyl-tetrabenzopo hyrin, PtiliyPdil^-Pr^OMesTNP, Pt(II)/Pd(II)-octabutoxynaphthalocyanine, Pt(II)/Pd(II)-octabutoxyphthalocyanine, Pyr₃RuPZn₃ and

Pt(II)/Pd(II)-tetrakisquinoxalino porphyrin, boron dipyrromethane (BODIPY) derivatives having iodide groups, boron dipyrromethane (BODIPY) derivatives containing fullerene groups, and Tris (2-phenylpyridine) iridium, fused porphyrin dimer and its derivatives, and a-Chalcogenyl phthalocyanine group- 15 (P, As, Sb) complexes.

20. The organic donor of claim 19, which comprises one or more unsubstituted or substituted alkyl moieties consisting of 1 to 50 carbon atoms.