A molecular solar thermal (MOST) system for long-term storage of solar energy

Abstract

The present invention relates to a molecular solar thermal system (MOST) based on a pair of isomers, comprising in its low energy ground stage primarily a first low-energy isomer which is excitable by solar light to form a metastable high-energy isomer and in its high energy state primarily a second metastable high energy photoisomer generated via photochemical conversion from the solar light excitable first isomer. Said MOST system is characterized by high photo isomerization yields due to the light driven out-of-equilibrium isomerization of the first isomer and is further characterized by a superior thermal stability of the second high energy photo isomer. This allows a long-term storage of collected solar light energy without occurrence of spontaneous unwanted back-isomerization. By applying a particular class of, optionally immobilized, strong basic catalysts, the stored solar energy is released in a controlled manner in a catalytic thermalback reaction to yield the low energy first isomer. This offers the possibility of establishing a cyclic process for repeatedly converting solar light energy into thermal energy. The present invention also provides methods of storing solar thermal energy, methods of releasing stored solar thermal energy, methods of reversibly storing solar thermal energy as well as particular solar thermal energy storage devices comprising the use of the above mentioned MOST pair of photoisomers. The present invention also relates to the use of such compounds for the reversible storing of solar energy. Further aspects of the present invention relate to a solar thermal energy capture device, a combined device for capturing solar thermal energy and solar photoelectric energy, as well as a device for operating a reversible MOST system of the present invention. In addition, the present invention relates to particular novel low and high energy photoisomers applicable in a MOST system of the invention.

Description

[0001]UMZ2024-444A MOLECULAR SOLAR THERMAL (MOST) SYSTEM FOR LONG-TERM STORAGE OFSOLAR ENERGY FIELD OF THE INVENTION The present invention relates to a molecular solar thermal system (MOST) based ona pair of isomers, comprising in its low energy ground stage primarily a first low-energyisomer which is excitable by solar light to form a metastable high-energy isomer and in itshigh energy state primarily a second metastable high energy photoisomer generated viaphotochemical conversion from the solar light excitable first isomer. Said MOST system ischaracterized by high photo isomerization yields due to the light driven out-of-equilibriumisomerization of the first isomer and is further characterized by a superior thermal stability ofthe second high energy photo isomer. This allows a long-term storage of collected solar lightenergy without occurrence of spontaneous unwanted back-isomerization. By applying aparticular class of, in particular immobilized, strong basic catalysts, the stored solar energy isreleased in a controlled manner in a catalytic thermal back reaction to yield the low energyfirst isomer. This offers the possibility of establishing a cyclic process for repeatedlyconverting solar light energy into thermal energy. The present invention also provides methods of storing solar thermal energy, methods of releasing stored solar thermal energy, methods of reversibly storing solar thermal energy as well as particular solar thermal energystorage devices comprising the use of the above mentioned MOST pair of photoisomers. Thepresent invention also relates to the use of such compounds for the reversible storing of solarenergy. Further aspects of the present invention relate to a solar thermal energy capture device, a combined device for capturing solar thermal energy and solar photoelectric energy, as well as a device for operating a reversible MOST system of the present invention. Inaddition, the present invention relates to particular novel low and high energy photoisomersapplicable in a MOST system of the invention. BACKGROUND OF THE INVENTION The utilization of solar energy is one of the key scientific challenges of the 21stcentury, offering significant potential for mitigating climate change (N. S. Lewis, et al.,Proceedings of the National Academy of Sciences 103, 15729–15735 (2006). doi:10.1073 / pnas.0603395103). In this regard, light-driven out-of-equilibrium isomerization offers an attractive pathway for harnessing photon energy and embedding it within chemical M / 65032-PCT UMZ2024-444 2bonds (M. Kathan, et al., Chemical Society reviews 46, 5536–5550 (2017).doi:10.1039 / C7CS00112F; H. Wang, et al. Nat. Rev. Chem. 6, 745–755 (2022).doi:10.1038 / s41570-022-00421-6.). If a thermal back reaction can be triggered afterphotochemical isomerization, this tandem process offers a sustainable approach to heatgeneration, which currently accounts for more than 90% of the world’s energy consumption(Fig. 1A) (I. Gur, K. Sawyer, R. Prasher, Searching for a Better Thermal Battery. Science335, 1454–1455 (2012). doi:10.1126 / science.1218761). In contrast to solar thermal collectors, heat generation by molecular solar thermal (MOST) systems offers a temporal separation between the time when the energy is generated and when it is released This can, e.g., be controlled by the introduction of a suitable catalyst initiating back-isomerization. However, identifying compounds for MOST application is challenging due to the intricate interplay between the photochemical andthermal isomerization processes (T. J. Kucharski, et alEnergy & Environmental Science 4,4449–4472 (2011). doi:10.1039 / C1EE01861B; Z. Wang et al., Joule 5, 3116–3136 (2021).doi:10.1016 / j.joule.2021.11.001; J. Usuba, et al., Trends Chem. 5, 577–580 (2023).doi:10.1016 / j.trechm.2022.12.010; A. Giménez-Gómez, et al., React. Chem. Eng. (2024).doi:10.1039 / D4RE00131A) In this context, a number of privileged compounds have been proposed, which include -norbornadiene ⇄ quadricyclane (A. D. Dubonosov, et al Russian Chemical Reviews.71, 917–927 (2002), doi:10.1070 / RC2002v071n11ABEH000745), -E-azobenzene Z-azobenzene (B. Zhang, et al., Nano-Micro Letters. 14, 138(2022). doi:10.1007 / s40820-022-00876-8), and -dihydroazulen ⇄ vinylheptafulven (J. Daub, et al., Angew. Chem. Int. Ed.23, 960–961(1984). doi:10.1002 / anie.198409601). Current research concentrates on identifying new isomer couples (R. Boese, et al., JJ. Am. Chem. Soc. 119, 6757–6773 (1997). doi:10.1021 / ja9707062.;Y. Kanai, et al., Angew.Chem. Int. Ed. 49, 8926–8929 (2010). doi:10.1002 / anie.201002994; K. Edel, et al., Angew.Chem. Int. Ed. 57, 5296–5300 (2018). doi:10.1002 / anie.201712683; Q. Qiu, et al., J. Am. Chem. Soc. 144, 12627–12631 (2022). doi:10.1021 / jacs.2c05384; and R. C. Richter, etal.,Angew. Chem. Int. Ed. 63, e202405818 (2024). doi:10.1002 / anie.202405818.) and onimproving the photophysical properties of the established systems (M. Quant, et al., Chem.Eur. J. 22, 13265–13274 (2016). doi:10.1002 / chem.201602530; J. Orrego-Hernández, et al.,Acc. Chem. Res. 53, 1478–1487 (2020). doi:10.1021 / acs.accounts.0c00235; A. E. Hillers- M / 65032-PCT UMZ2024-444 3Bendtsen, et al., Angew. Chem. Int. Ed. 62, e202309543 (2023).doi:10.1002 / anie.202309543). Important metrics for MOST optimization are high isomerization rates (>95%),significant back-isomerization energies (ΔHiso), and a good overlap with the solar spectrum (λ= 300-800 nm). A major challenge remains the improvement of the thermal stability of thephotoisomer, which is a crucial factor for safe and long-term energy storage. This endeavoris further frustrated by the notion that higher thermal stability often correlates with a decreasein stored energy (K. Börjesson, et al., ACS Sustainable Chem. Eng. 1, 585–590 (2013).doi:10.1021 / sc300107z; and M. Cacciarini, et alChem. Eur. J. 21, 7454–7461 (2015).doi:10.1002 / chem.201500100). The identification of catalysts that trigger heat release atstable photoisomers adds another hurdle for devising a reliable system. The problem to be solved by the present invention has to be seen in the developmentof an improved MOST system, which is characterized by at least one of the followingimprovements: high isomerization rates, high back-isomerization energies, high thermalstability of the high-energy photoisomer, and a rate accelerating catalyst triggering thethermal back reaction, which may be quantitatively separated from the constituents of the MOST couple, and which is reusable. SUMMARY OF THE INVENTION The above problem was, surprisingly, solved by the present inventors, by identifyingwell-balanced isomer pairs that meet the stringent photochemical and physicochemicalprerequisites for a MOST application. Moreover, the problem was solved by providing aback-isomerization reaction based on an anion-accelerated ring opening reaction, employinga simple organic base as catalyst, which triggers efficient heat release at ambienttemperatures. BRIEF DESCRIPTION OF THE FIGURESFigure 1: Illustrates schematically the storing of solar energy with molecular isomers. (A)Schematic representation of a MOST system. (B) Design of an energy storage couple based on the photocyclization and thermal reversion of ortho-methylacetophenones.Figure 2: Development of an efficient photoisomerization of ortho-methylacetophenones. (A)Mechanistic considerations and current limitations for the photocyclization of ortho- methylacetophenone 1a. (B) Reaction optimization addressing the acetyl liability. (C) M / 65032-PCT UMZ2024-444 4 Mechanistic investigations uncovering key factors for cyclization efficiency. (D) Assessing the reaction robustness for MOST application.Figure 3: Establishing back-isomerization through catalysis. (A) Thermal ring-opening basedon 4-π electrocyclic ring opening. (B) Identification of catalysts based on anionic rate- acceleration. (C) Calorimetric analysis of the ring opening event.Figure 4: Establishing cyclability of the MOST system by the application of sunlightirradiation and an immobilized baseFigure 5: Visualization of the relative rates of the photo cyclization. The size of the bubblesindicates the difference between conversion and yield of product, where bigger bubbles corresponded to a large amount of side reactions.Figure 6: Schematic drawing of a device for reversibly storing and setting free of solarthermal energy in a closed circular system.Figure 7: Schematic drawing of a combined collector module for collecting solar thermal andphotoelectric energy. DETAILED DESCRIPTION OF THE INVENTIONA. ABBREVIATIONSMOST molecular solar thermal systempKa negative base-10 logarithm of the acid dissociation constant (Ka)ΔHiso back-isomerization energy (also abbreviated as ΔHstorage)B. DEFINITIONSB.1 General DefinitionsUnless otherwise defined herein, scientific and technical terms used in connection with the present invention shall have the meanings that are commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the event of any latent ambiguity, definitions provided herein take precedent over any M / 65032-PCT UMZ2024-444 5 dictionary or extrinsic definition. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. The terms "purified", "substantially purified," and "isolated" as used herein refer to the state of being free of other, dissimilar compounds with which a compound of the invention is normally associated in its natural state, so that the "purified", "substantially purified," and "isolated" subject comprises at least 0.5%, 1%, 5%, 10%, or 20%, or at least 50% or 75% ofthe mass, by weight, of a given sample. In one embodiment, these terms refer to thecompound of the invention comprising at least 95, 96, 97, 98, 99 or 100%, of the mass, by weight, of a given sample. As used herein, the terms "purified", "substantially purified," and "isolated" when referring to a nucleic acid or protein, also refers to a state of purification or concentration different than that which occurs naturally, for example in a prokaryotic or eukaryotic environment, like, for example in a bacterial or fungal cell, or in the mammalian organism, especially human body. Any degree of purification or concentration greater than that which occurs naturally, including (1) the purification from other associated structures or compounds or (2) the association with structures or compounds to which it is not normally associated in said prokaryotic or eukaryotic environment, are within the meaning of"isolated”. The nucleic acid or protein or classes of nucleic acids or proteins, describedherein, may be isolated, or otherwise associated with structures or compounds to which they are not normally associated in nature, according to a variety of methods and processes known to those of skill in the art. In the context of the descriptions provided herein and of the appended claims, the use of “or” means “and / or” unless stated otherwise. Similarly, “comprise,” “comprises,” “comprising”, “include,” “includes,” and “including” are interchangeable and not intended to be limiting. It is to be further understood that where descriptions of various embodiments use the term "comprising," those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language "consisting essentially of" or "consisting of.” The term “about” indicates a potential variation of ± 25% of the stated value, in particular ± 15%, ±10 %, more particularly ± 5%, ± 2% or ± 1%. The term "substantially" describes a range of values of from about 80 to 100%, such as, for example, 85-99.9%, in particular 90 to 99.9%, more particularly 95 to 99.9%, or 98 to 99.9% and especially 99 to 99.9%. M / 65032-PCT UMZ2024-444 6 “Predominantly” or “primarily” refers to a proportion in the range of above 50%, as forexample in the range of 51 to 100%, particularly in the range of 75 to 99,9%; moreparticularly 85 to 98,5%, like 95 to 99%.A “MOST couple” according to the present invention is typically represented by atleast one pair of corresponding isomers of at least one chemical compound, at least oneisomeric form in a solar light excitable, low energy state, and at least one other in a highenergy solar light excited state, which remains in said high energy state for a sufficient period of time to allow storage of solar energy, and, which under the action of an external stimulus,as for example a suitable catalyst, will release the stored solar energy as thermal energy,and will be reverted to the solar light excitable, low energy state.A “MOST system”, according to the present invention, comprises a MOST couple asdefined above, dissolved in a liquid organic solvent in which the light induced conversionbetween said at least two isomers takes place, and which is also suited to maintain the at least one high energy isomer in a dissolved state during the entire time span of energystorage. Said MOST system may on demand, initiated by an external stimulus, like acatalytically active base compound, be subsequently reconverted to its corresponding lowenergy state where the low energy isomer at least predominates. Thereby the systemreleases the stored solar energy as thermal energy.If the present disclosure refers to features, parameters and ranges thereof of different degree of preference (including general, not explicitly preferred features, parameters and ranges thereof) then, unless otherwise stated, any combination of two or more of such features, parameters and ranges thereof, irrespective of their respective degree of preference, is encompassed by the disclosure of the present description.B.2 Chemical definitionsThe term "lower alkyl" as used herein and in the alkyl moieties of “lower alkoxy” and thelike refers to saturated straight-chain (i.e. linear) or branched hydrocarbon radicals having 1to 2 ("C1-C2-alkyl"), 1 to 3 ("C1-C3-alkyl"), 1 to 4 ("C1-C4-alkyl") or 1 to 6 ("C1-C6-alkyl"). C1-C2- Alkyl is methyl or ethyl. C1-C3-Alkyl is additionally propyl and isopropyl. C1-C4-Alkyl is additionally butyl, 1-methylpropyl (sec-butyl), 2-methylpropyl (isobutyl) or 1,1-dimethylethyl (tert-butyl). C1-C6-Alkyl is additionally also, for example, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, M / 65032-PCT UMZ2024-444 7 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, or 1-ethyl-2-methylpropyl. The term "haloalkyl" as used herein, which may also be expressed as "alkyl which ispartially or fully halogenated", refers to straight-chain or branched alkyl groups having 1 to 2("C1-C2-haloalkyl"), 1 to 3 ("C1-C3-haloalkyl"), 1 to 4 ("C1-C4-haloalkyl") or 1 to 6 ("C1-C6- haloalkyl") carbon atoms (as mentioned above), where some or all of the hydrogen atoms in these groups are replaced by fluorine atoms. Examples for C1-C2-haloalkyl (indeed for fluorinated C1-C2-alkyl) are fluoromethyl, difluoromethyl, trifluoromethyl, 1-fluoroethyl, 2- fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, or pentafluoroethyl. Examples for C1-C3- haloalkyl (indeed for fluorinated C1-C3-alkyl) are, in addition to those mentioned for C1-C2- haloalkyl, 1-fluoropropyl, 2-fluoropropyl, (R)-2-fluoropropyl, (S)-2-fluoropropyl, 3-fluoropropyl, 1,1-difluoropropyl, 2,2-difluoropropyl, 1,2-difluoropropyl, 2,3-difluoropropyl, 3,3-difluoropropyl,2,2,3-trifluoropropyl, 3,3,3-trifluoropropyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl, heptafluoropropyl, 1,1,1-trifluoroprop-2-yl, 2-fluoro-1-methylethyl, (R)-2-fluoro-1-methylethyl, (S)-2-fluoro-1-methylethyl, 2,2-difluoro-1-methylethyl, (R)-2,2-difluoro-1- methylethyl, (S)-2,2-difluoro-1-methylethyl, 2,2,2-trifluoro-1-methylethyl, (R)-2,2,2-trifluoro-1- methylethyl, (S)-2,2,2-trifluoro-1-methylethyl, 2-fluoro-1-(fluoromethyl)ethyl, 1-(difluoromethyl)-2,2-difluoroethyl, 1-(trifluoromethyl)-2,2,2-trifluoroethyl, 1-(trifluoromethyl)- 1,2,2,2-tetrafluoroethyl and the like. Examples for C1-C4-haloalkyl are, in addition to those mentioned for C1-C3-haloalkyl, 2-fluorobutyl, (R)-2-fluorobutyl, (S)-2-fluorobutyl, 3-fluorobutyl, (R)-3-fluorobutyl, (S)-3-fluorobutyl, 4-fluorobutyl, 2,2-difluorobutyl, 3,3-difluorobutyl, 4,4- difluorobutyl, 4,4,4-trifluorobutyl, 3,3,4,4-tetrafluorobutyl, 3,4,4,4-tetrafluorobutyl, 2,2,4,4,4- pentafluorobutyl, 3,3,4,4,4-pentafluorobutyl, 2,2,3,4,4,4-hexafluorobutyl, 1-methyl-2,2-3,3- tetrafluoropropyl and the like. The term "cycloalkyl" unless otherwise indicated refers to monocyclic saturatedcarbocyclic radicals having 5 to 8 carbon ring members ("C5-C8-cycloalkyl"). Examples arecyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.The term "hetero-cycloalkyl" unless otherwise indicated refers to monocyclic saturatedanalogues of the above–identified cycloalkyl residues, additionally contain in its carbocyclic radicals having 5 to 8 carbon ring members 1 or more, as for example 1, 2 or 3 ring heteroatoms, selected from N, O and S The term “heterocyclic” refers to a monocyclic or polycyclic, like di- or tri-cyclicsaturated, or mono- or polyunsaturated non-aromatic or aromatic ring moiety, containing 5 to14, in particular 5 to 10, like 5 or 6 ring atoms and including 1 to 5, in particular 1, 2 or 3 M / 65032-PCT UMZ2024-444 8 identical or different ring heteroatom, selected from N, O and S. The term “aryl” relates to monovalent mono- or polycyclic aromatic moieties, inparticular having 6 to 14 ring carbon atoms, in particular, phenyl, o-, m- or p-toluyl, o-, m- orp-xylyl, byphenyl, fluorenyl, naphthenyl, anthraceneyl and phenanthrenyl. The term “heteroaryl” refers to an aromatic, monocyclic or polycyclic, like di- or tri-cyclicaromatic ring moiety, containing 5 to 14, in particular 5 to 10 ring atoms, including 1 to 5, inparticular 1, 2 or 3 identical or different ring heteroatom selected from N, O and S. Examplesfor 5- or 6-membered monocyclic heteroaromatic rings or bicyclic heteroaromatic ringscontaining 1, 2, 3 or 4 heteroatoms selected from the group consisting of N, O and S as ring members are, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 1-pyrazolyl, 3-pyrazolyl, 4-pyrazolyl, 5-pyrazolyl, 1-imidazolyl, 2-imidazolyl, 4-imidazolyl, 5-imidazolyl, 2- oxazolyl, 4-oxazolyl, 5-oxazolyl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 2-thiazolyl, 4- thiazolyl, 5-thiazolyl, 3-isothiazolyl, 4-isothiazolyl, 5-isothiazolyl, 1,3,4-triazol-1-yl, 1,3,4- triazol-2-yl, 1,3,4-triazol-3-yl, 1,2,3-triazol-1-yl, 1,2,3-triazol-2-yl, 1,2,3-triazol-4-yl, 1,2,5- oxadiazol-3-yl, 1,2,3-oxadiazol-4-yl, 1,2,3-oxadiazol-5-yl, 1,3,4-oxadiazol-2-yl, 1,2,5- thiadiazol-3-yl, 1,2,3-thiadiazol-4-yl, 1,2,3-thiadiazol-5-yl, 1,3,4-thiadiazol-2-yl, 2-pyridinyl, 3- pyridinyl, 4-pyridinyl, 5-pyridinyl, 3-pyridazinyl, 4-pyridazinyl, 2-pyrimidinyl, 4-pyrimidinyl, 5- pyrimidinyl, 2-pyrazinyl, 1,3,5-triazin-2-yl, 1,2,4-triazin-3-yl, 1,2,4-triazin-5-yl, 1,2,3,4-tetrazin- 1-yl, 1,2,3,4-tetrazin-2-yl, 1,2,3,4-tetrazin-5-yl, quinolin-3-yl, 1H-pyrrolo[2,3-b]pyridine-5-yl, 1,8-naphthyridin-3-yl, 1H-benzo[d]imidazol-2-yl and the like. The term “substituted heteroaryl ring” refers to mono- or poly-substituted analogues ofthe above-mentioned heteroaryl rings. In particular, they may be substituted by 1 or more, inparticular 1, 2, 3, 4 or 5 identical or different substituents as defined herein below. The term “substituted carbocyclic ring” refers to mono- or poly-substituted analogues ofthe above-mentioned aromatic or non-aromatic carbocyclic rings as defined above. In particular, they may be substituted by 1 or more, in particular 1, 2, 3, 4 or 5 identical or different substituents as defined herein below. Unless indicated otherwise, the term "substituted" or “substituent” means that a radical is substituted with residues selected from the group of halogen, like F, Cl and Br, –C(halogen)3, wherein halogen residues thereof are identical or different and are selectedfrom F, Cl and Br; -C1-C3-alkyl, -C1-C3-hydroxyalkyl, -C1-C3-cyanoalkyl, -C1-C3-alkylene-C(O)O-C1-C4-alkyl, -C3-C8-cycloalkyl, -OH, -CN, -C(O)OH,- C(O)O(-C1-C4-alkyl), -O-C1-C3-alkyl or -C(O)NRaRb, wherein Raand Rbare independently selected from H or -C1-C4-alkyl. The term "halogen" denotes in each case fluorine, bromine, chlorine or iodine, in M / 65032-PCT UMZ2024-444 9 particular fluorine, chlorine or bromine. Halogen as a substituent on an aromatic or heteroaromatic group is particularly selected from F, Cl or Br. The term “mono- or polycyclic aromatic ring system” (abbreviated “Ar”), is selectedfrom monocyclic aromatic rings having 6 ring carbon atoms (“benzo groups), wherein at least2 neighbored (ortho-positioned) carbon atoms are substituted as further defined herein belowfor compounds of formulae I or II, said ortho-positioned pairs of ring substituents being involved in the light-driven photo isomerization; polycyclic aromatic groups derived fromcondensed polycyclic groups having 10 to 32, or particularly 10 to 16 ring carbon atoms, inparticular naphthalene, anthracene, phenanthrene, or pyrene, wherein at least 2 neighbored(ortho-positioned) carbon atoms are substituted as further defined herein below forcompounds of formulae I or II, said ortho-positioned pairs of ring substituents being involved in the light-driven photo isomerization; or polycyclic aromatic groups derived from a pluralityof monocyclic aromatic rings and / or condensed polycyclic aromatic rings linked togethereither via a carbon-carbon single bond or via an alkenylene bridge providing a conjugating linkage between 2 neighboring aromatic rings of the system, wherein at least 2 neighbored (ortho-positioned) carbon atoms are substituted as further defined herein below for compounds of formulae I or II, said ortho-positioned pairs of ring substituents being involved in the light-driven photo isomerization. A“monocyclic aromatic ring system” as used in the context of the invention comprises6 carbon atoms: and is typically benzene, in this context also designated “benzo group”.A “condensed aromatic ring system” as used in the context of the invention comprisesat least two fused aromatic rings sharing in common at least two neighbored, adjacentcarbon atoms of at least two aromatic rings, and comprising 10 to 32 carbon atoms. Non-limiting examples thereof are derived from: naphthalene (C₁₀H₈), anthracene (C₁₄H₁₀),phenanthrene (C₁₄H₁₀), pyrene (C₁₆H₁₀), chrysene (C₁₈H₁₂),benzo[a]pyrene (C₂₀H₁₂),perylene (C₂₀H₁₂), coronene (C₂₄H₁₂), fluoranthene (C₁₆H₁₀), benzo[g,h,i]perylene (C₂₂H₁₂),benz[a]anthracene (C₁₈H₁₂), indeno[1,2,3-cd]pyrene (C₂₂H₁₂), triphenylene (C₁₈H₁₂), ovalene(C₃₂H₁₄), and acenaphthylene (C₁₂H₈).A “conjugated aromatic ring system” according to the present invention comprises atleast two aromatic rings linked together either via a chemical carbon-carbon single bond orvia an “alkenylene bridge” providing a conjugating linkage between 2 neighboring aromaticrings of the system, as for example -CH=CH- and -CH=CH-CH=CH-."Alkylene" is a linear or branched divalent alkanediyl radical. C1-C3-Alkylene is a linear or branched divalent alkyl radical having 1, 2 or 3 carbon atoms. C1-C4-Alkylene is a linear or branched divalent alkyl radical having 1, 2, 3 or 4 carbon atoms. C1-C6-Alkylene is a linear or M / 65032-PCT UMZ2024-444 10 branched divalent alkyl radical having 1, 2, 3, 4, 5 or 6 carbon atoms. Examples are -CH2-, - CH2CH2-, -CH(CH3)-, -CH2CH2CH2-, -CH(CH3)CH2-, -CH2CH(CH3)-, -C(CH3)2-, -CH2CH2CH2CH2-, -CH(CH3)CH2CH2-, -CH2CH2CH(CH3)-, -C(CH3) 2CH2-, -CH2C(CH3)2-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2)10- and positional isomers thereof.“Alkenylene” refers to the mono-unsaturated analogues of the above mentioned alkylenes, having 2, 3 or 4 carbon atoms (C2-C4-alkenylenes) or having 2, 3, 4, 5 or 6 carbonatoms (C2-C6-alkenylenes). Suitable “alkenylene” bridges are for example ethenylene groups(-CH=CH-). Other examples are polyunsaturated branched or in particular linear alkenylene groups comprising at least 2 conjugated carbon / carbon double bonds. Nonlimiting examplesthereof are: -CH=CH-CH=CH-, -CH=CH-CH=CH-CH=CH- or -CH=CH-CH=CH-CH=CH-CH=CH-, higher homologues as obtained by extending the hydrocarbon chain by at least onefurther terminal –CH=CH- group.The above-mentioned mono- or polycyclic, condensed or conjugated aromatic ringsystems (“Ar”) may be further substituted. They may contain per aromatic ring element oneor more, as for example for a mononuclear benzo group, 1, 2, 3 or 4, particularly 1 or 2, ormost particularly 1 identical or different ring substituents R3. Said at least one substituent R3may be present at at least one “free” carbon atom of the aromatic ring system which does notcarry am member of those ortho-positioned pairs of ring substituents involved in the light- driven photo isomerization reaction of the system. Such one or more residues R3areselected from cyano, halogen, lower alkyl, lower alkoxy, or -C(O)R1, wherein R1 is selectedfrom –C (halogen)3-aHa, wherein a is 0, 1 or 2, in particular 0 or 1, and halogen is selected from F, Cl or Br; aryl; cyano; linear or branched lower-alkoxy, or -C(O)OR, wherein R is linear or branched lower alkyl. An “ortho-positioned pair of ring substituents” involved in the light-driven photoisomerization reaction of the system consist of a pair of two different ring substituentsattached to two neighbored ring carbon atoms. The first ring substituent is of the formula –C(O)R1as defined herein, and the second ring substituent placed in ortho-position to the first is of the formula -CR2R2aR2b, which upon photo isomerization will form, together with thecarbon atoms which they are attached to, a 4-membered cyclobutene ring structure of theformula M / 65032-PCT UMZ2024-444 11 The term “mono- or polycyclic, aromatic or non-aromatic C5 - C16 residue” optionallysubstituted with at least one basic residue comprising at least one basic nitrogen atom,encompasses “mono- or polycyclic non-aromatic C5 - C16 residue” as well as “mono- orpolycyclic, aromatic C6 - C16 residues each optionally substituted with at least one basicresidue comprising at least one basic nitrogen atom. In particular, in this respect, but also more generally a substituent “with at least onebasic residue comprising at least one basic nitrogen atom” may for example be selected from a residue of the formula –N(alkyl)2, -N=C(N-(alkyl)2)2, wherein “alkyl” independently of each other represents a linear or branched C1-C4residue, or a residue of one of the following two formulae wherein “alkyl” independently of each other represents a linear or branched C1-C4 residue, and “Cyc” together with the nitrogen atoms, to which it is attached, forms a 5 to 7 membered heterocyclic, saturated or unsaturated ring. In particular, an alkylene orM / 65032-PCT UMZ2024-444 12 alkenylene bridge is inserted between said two nitrogen atoms in order to formsaid heterocyclic ring. In this respect a “mono- or polycyclic non-aromatic C5 - C16 residue” comprises acarbocyclic ring system which may be a mono- or polycyclic, like di- or tri-cyclic, carbocyclicring, and may be a saturated or mono- or polyunsaturated, nonaromatic ring system, like forexample a monocyclic cycloalkyl or monocyclic cycloalkenyl ring system, as herein furtherdefined. The term "cycloalkyl" in this respect refers to monocyclic saturated carbocyclicradicals having 5 to 8 carbon ring members ("C5-C8-cycloalkyl"). Examples are cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl. The term "cycloalkenyl" in this respect refers tomonocyclic mono-or poly-unsaturated non-aromatic analogues id the above-mentionedcycloalkyl groups. The term “mono- or polycyclic, aromatic C6 - C16 residue” refers to mono- or polycyclic,like di- or tri-cyclic, carbocyclic ring containing 6 to 16, in particular 6 to 10 carbon atoms.Examples thereof are phenyl, naphthyl, phenanthrenyl, fluorenyl and anthracenyl. An “organic superbase” is defined as the structural combination of basic functional groups in a neutral organic compound that result in a basicity greater than the basicity of N,N,N’,N’-tetramethyl-1,8-naphthalene diamine, CAS NO 20734-58-1 (commercialized underthe trade name Proton sponge ® by Sigma Aldrich and having a pKa of 18,6 as determinedin acetonoitrile). In this context reference is made to Puleo et al., Cem Eur J 2021,27, 4216-4229 and textbook Superbases for Organic Synthesis: Guanidines, Amidines, Phosphazenesand Related Organocatalysts, Editor(s):Professor Tsutomu Ishikawa, First published:28January 2009; Print ISBN:9780470518007 Copyright © 2009 John Wiley & Sons, Ltd. Suchsuperbases may be further subdivided into currently three different classes: the amidineclass, the guanidine class and the phosphazene class.The pKa value of a base may also be described as pKBH+ value of the corresponding conjugated acid of said base. Any pKa value as referred to herein, unless otherwise defined, refers to the pKa valueas determined in acetonitrile. An ”organic strong base” or “strong organic base” in the context of the invention has toshow the ability to catalyze the re-conversion of the high energy photo isomer (B) via anion-accelerated electro-cyclic ring opening into the corresponding parent isomer (A) by setting free thermal energy as stored by isomer (B). M / 65032-PCT UMZ2024-444 13 An “immobilized or non-immobilized organic strong base” in the context of the presentinvention refers to a herein defined “organic strong base”, like in particular an organicsuperbase, which is, preferably covalently, bound to conventional, particularly spherical,microbeads, for example in the range of 50 to 200 µm. The purpose of such modification is toprovide the strong organic base or in particular organic superbase in an immobilized formwhich allows to provide said base as a stationary phase. Said microbeads have to be provided in a state which is not soluble in the liquid carrier medium containing the isomers(A) and / or (B) of the invention in a dissolved state. This allows a controlled contact betweensaid liquid carrier medium and the immobilized superbase, for the controlled release of the solar energy stored in isomer (B). An “anion-accelerated electro-cyclic ring opening” is defined as a reaction where thepresence of a covalently attached anion such as alkoxy speeds up the process of converting a cyclic structure into an open-chain structure through a concerted electron rearrangement mechanism. Compounds as herein described may contain one or more asymmetric elements such as stereogenic centers, stereogenic axes and the like, e.g. asymmetric carbon atoms, so that the compounds can exist in different stereoisomeric forms. These compounds can be, forexample, racemates or optically active forms. All stereoisomers, diastereomers, Z- and E-forms, in purified and mixture forms are included. Compounds as herein described may also exist in the form of different “constitutional isomers”. A “constitutional isomer” (which also may be designated as “structural isomer”) of a compound is another compound whose molecule has the same number of atoms of eachelement, but distinct bonds between them. As for example, a particular residue or a particulargroup of residues may be present at different position of the same linear or circular molecular skeleton of a molecule Accordingly, when a compound is recited by specific name or a class of compounds is recited, all these above-identified isomeric forms are intended to be included. Therefore, unless otherwise stated, for each of the compounds as described herein,any such potential stereo- or regiosomeric form or mixture of more than one stereo- and / orregiosomeric form is within the scope of the present invention. Similarly, for each of thecompounds as described herein, any such potential constitutional isomer or mixture of morethan one constitutional isomer is within the scope of the present invention.C. PARTICULAR ASPECTS AND EMBODIMENTSM / 65032-PCT UMZ2024-444 141. The first aspect of the present inventionAccording to a first embodiment of the invention a molecular solar thermal (MOST)system is provided, comprising an organic phase, which, in particular, is liquid in thetemperature range where the MOST system is operated, and which containsa) in its low–energy ground state primarily at least one solar light excitable low-energy parent photo isomer (A), which is excitable by solar light in the wavelength range of300 to 600 nm, b) in its excited state primarily at least one (metastable) high–energy photoisomer (B) generated by solar light, in particular in the wavelength range of 300 to 600 nm,via photochemical conversion from said at least one solar light excitable low-energy parentisomer (A), wherein; said at least one (in particular metastable) (high–energy photo isomer (B) is acompound of general formula (I) wherein, n is an integer of 1, 2 or 3, R1is selected from –C (halogen)3-aHa, wherein a is 0, 1 or 2, in particular 0 or 1, and halogen is selected from F, Cl or Br, in particular –CF3; aryl; cyano; loweralkoxy, in particular methoxy; or -C(O)OR, wherein R is lower alkyl, in particularmethyl; R2and R2aare identical or different and independently of each other selected from H, D, linear or branched lower alkyl or linear or branched lower alkoxy, like methyl or methoxy; most particularly R2and R2aare independently selected from H or D; R2bis selected from H or D; M / 65032-PCT UMZ2024-444 15 Ar represents an aromatic mono- or polycyclic, in particular mono- or bicyclic,condensed aromatic ring system or conjugated aromatic ring system, in which ringsystem at least one hydrogen atom of the aromatic ring system may be furthersubstituted by one or more identical or different ring substituents R3, wherein R3 is selected from cyano, halogen, , linear or branched lower alkyl, inparticular methyl; linear or branched lower alkoxy, in particular methoxy; and -C(O)R1, wherein R1is as defined above or a constitutional isomer or stereoisomer of the compound of formula I;or a mixture of at least two constitutional isomers or a mixture of at least twostereoisomers or a mixture of at least one stereoisomer and at least one constitutional isomer;said solar light excitable low-energy parent isomer (A) is a compound excitable by solarlight, in particular in the wavelength range of 300 to 600 nm, and having the generalformula (II) wherein n, Ar, R1, R2,R2a, R2band R3are as defined above; and or a constitutional isomer or stereoisomer of the compound of formula II; or a mixture of at least two constitutional isomers or a mixture of at least two stereoisomers or a mixture of at least one stereoisomer and at least one constitutional isomer; M / 65032-PCT UMZ2024-444 16 and optionally further comprising an immobilized or non-immobilized strong organic base catalyst (C).Said strong base catalyst (C) has a pKa value, as determined in acetonitrile, above 10, particularly above 15, more particularly above 17, most particularly above 20, and preferably not more than 45, which catalyzes the re-conversion of the high energy photo isomer (B) viaanion-accelerated electro-cyclic ring opening into the corresponding parent isomer (A) bysetting free thermal energy as stored by (B). Particular examples for such catalysts areorganic superbases as further exemplified below. As another example of other suitablestrong base catalysts (C) organic strong diazabicyclo alkanes and diazabicyclo alkenes maybe mentioned. As particular, non-limiting examples thereof 1,8-diazabicyclo[5.4.0]undec-7-ene and more particularly 1,4-diazabicyclo[2.2.2]octane (DABCO) may be mentioned. Consequently, in practice a MOST system of the invention will comprise an organicphase, which, in particular, is liquid in the temperature range where the MOST system isoperated, and which contains a mixture of at least one low energy parent photo isomer (A)and at least one high energy photo isomer (B) in different proportions depending on the energetic state of the system. The base catalyst (C) is required to set free the stored energy of the at least one highenergy photo isomer (B) of the system of isomer pairs, and, consequently base catalyst (C)may be considered as a non-permanent component of the MOST system, as it is in contactwith the high energy mixture enriched with isomer (B) just on demand. In a particular embodiment, the MOST system of the invention is further characterizedin that said re-conversion occurs at a temperature of at least 10°C or particularly at least20°C, as for example in a temperature range of 10°C to 100°C, particularly 20°C to 80°C, ormore particularly 20°C to 70°C or 30°C to 60°C.According to another particular embodiment, the MOST system of the invention is provided in a molecular oxygen depleted state and, more particularly in an oxygen free, anaerobic state. According to another particular embodiment, the MOST system of the invention is operated in a cyclic, reversible, process and preferably in and essentially oxygen free state. This may be established by operating a closed system wherein the liquid medium is storedand / or circulated under exclusion of molecular oxygen or ambient air. In order to excludeoxygen the entire system should be treated in a manner known per se in order to guarantee that oxygen is more or less quantitatively removed. M / 65032-PCT UMZ2024-444 17 According to another particular embodiment, the organic liquid phase as used in the MOST system comprises at least one aprotic organic solvent, which may be polar or, more particularly nonpolar. In particular it comprises at least one aromatic solvent, more particularly selected from benzene, toluene, xylene and, most particular benzene; or cyclic or non-cyclic aliphatic solvents, like in particular und n-heptane, n-hexane or cyclohexane, ormixtures thereof. A particular group of such organic phase forming solvents has a boilingpoint of at most 90°C, more particularly at least 85°C. The organic liquid phase normally isprovided in a state substantially depleted of water. However, traces of water do notnegatively affect performance of the MOST system of the present invention.According to another particular embodiment, the MOST system of the inventioncontains in its ground state the low-energy isomer (A) in a concentration range from as lowas about 10 mM to a concentration which allows to obtain a maximum energy density of the system when converted to isomer (B), Optimum concentrations may be easily determined by a limited number of optimization experiments. As for example upper limits of initialconcentrations of isomer (A) may be in the range of about 500 to 5000 mM, as for example ina range of up to about 4000 mM, 3000 mM, 2000 mM or 1000 mM, like about 10 to 500mM,particularly about 15 to 250mM, or about 20 to 200mM, as for example about 30 to 150, or 40 to 100mM. The same applies to the concentration of the high energy isomer (B) if the MOST system is in its final high-energy state. The same applies to any intermediate state of the MOST system for the mixture of isomers (A) and (B). In a further particular embodiment of the MOST system of the invention, the organicstrong base catalyst (C) is selected from organic superbases.More particularly, said organic superbases are selected from the amidine class, theguanidine class or the phosphazene class of superbases.In another particular embodiment of the present invention, the strong organic base (C)is an organic superbase comprisinga) a guanidine-type organic superbase of the general formula IIIa M / 65032-PCT UMZ2024-444 18 IIIa wherein Ra is selected from H, linear or branched lower alkyl, or mono- or polycyclic,aromatic or non-aromatic C5 to C16 residues, optionally substituted with at least one basic residue comprising at least one basic nitrogen atom, Rband Rcindependently of each other represent H, lower alkyl, optionally substituted aryl or heteroaryl, optionally substituted cycloalkyl, optionally substituted hetero-cycloalkyl, and Rdand Reindependently of each other represent H, lower alkyl, optionally substituted aryl or heteroaryl, optionally substituted cycloalkyl, optionally substituted hetero-cycloalkyl or one residue of Rb and Rc and one residue of Rd and Re together with the nitrogenatoms to which they are attached to, form a heterocyclic, saturated or non- saturated 5 -to 7-membered ring; in particular such pairs of residues form an alkylene or alkenylene bridge for forming said heterocyclic ring;or Raand one of the residues Rband Rcor one of the residues Rdand Retogether with the nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7-membered ring; in particular such pairs ofresidues form an alkylene or alkenylene bridge for forming said heterocyclic ring;or of the general formula IIIb wherein M / 65032-PCT UMZ2024-444 19 Aand B independently of each other form a 5- to 7-membered heterocyclicsaturated or unsaturated ring; andR6is selected from H or linear or branched lower alkyl, orb) an amandine-type organic superbase of the general formula IIIc wherein Ra, Rb, Rcand Rdare as defined above; or Raand one of the residues Rband Rctogether with the carbon or nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7- membered ring; in particular such pairs of residues form an alkylene or alkenylenebridge for forming said heterocyclic ring; and / or Rdand one of the residues Rband Rctogether with nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7-membered ring; in particular such pairs of residues form an alkylene or alkenylene bridge forforming said heterocyclic ring;c) a phosphazene-type organic superbase of the general formula IIIdM / 65032-PCT UMZ2024-444 20 wherein, Rais as defined above; Rb, Rc, Rdand Reare as defined above, Rfand Rghave the same meanings as defined above for Rb, Rc, Rdand Reand additionally Rb and Rc together and / or Rd and Re together and / or Rf and Rg together form aresidue of the formula =P(N-(lower alkyl)2)3or Rband Rctogether and / or Rdand Retogether and / or Rfand Rgtogether with the nitrogen atom which they are attached to form a 5- to 7-membered saturated orunsaturated heterocyclic moiety; in particular such pairs of residues form an alkylene or alkenylene bridge for forming said heterocyclic ring;or one residue of Rband Rcand one residue of Rdand Retogether with the nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non- saturated 5 -to 7-membered ring; in particular such pairs of residues form analkylene or alkenylene bridge for forming said heterocyclic ring; or one residue of Rband Rcand one residue of Rfand Rgtogether with the nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non- saturated 5 -to 7-membered ring; in particular such pairs of residues form analkylene or alkenylene bridge for forming said heterocyclic ring;or one residue of Rdand Reand one residue of Rfand Rgtogether with the nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non- M / 65032-PCT UMZ2024-444 21 saturated 5 -to 7-membered ring; in particular such pairs of residues form an alkylene or alkenylene bridge for forming said heterocyclic ring;or an immobilized derivative of a compound of formula IIIa, IIIb, IIIc or IIId, in particulara derivative of compound of formula IIIa, IIIb, IIIc or IIId covalently bound to an inertcarrier bead, particularly microbeads in an average size range of 75 – 150 µm.Corresponding microbeads or bases covalently bound to such microbeads arecommercially available as for example from company Biotage Sweden ABAccording to another particular embodiment of the present invention said base C is abase comprising a guanidine type superbase selected from a compound of the general formula IV wherein R6is H or lower alkyl or a amidine-type superbase of selected from a compound of general formula V wherein n is an integer of 1 to 4 or an immobilized derivative of a compound of formula IV or V, in particular aderivative of compound of formula IV or V covalently bound to an inert carrier bead, M / 65032-PCT UMZ2024-444 22 particularly microbeads in an average size range of 75 – 150 µm. binding to carrierbeads, as for example polystyrene beads may be effected in a manner known per se via forming a linkage between the beads and a ring carbon atom of the base.As further examples of a suitable organic base catalyst (C) organic strong the class ofdiazabicyclo bases, namely diazabicyclo alkanes and diazabicyclo alkenes may bementioned. As particular, non-limiting examples thereof 1,8-diazabicyclo[5.4.0]undec-7-eneand, more particularly, 1,4-diazabicyclo[2.2.2]octane (DABCO) may be mentioned. 1,4-diazabicyclo[2.2.2]octane (DABCO) has a pKa value of 12 as determined in acetonitrile. Anyderivative of said class of diazabicyclo bases, like a derivative of DABCO, or an immobilizedderivative thereof, covalently bound to inert carrier beads, particularly microbeads of anaverage size range of 75 – 150 µm, more particularly a polystyrene bead as defined above,are also encompassed. According to another, more particular embodiment the MOST system of the inventioncomprises as isomer A ortho-methyl-trifluoroacetophenone (MTA) of formula VI; As isomer B benzo-trifluoromethylcyclobutanol (BTC) of formula VII: and as organic base C a triazabicyclodecene of formula VIII M / 65032-PCT UMZ2024-444 23 or an immobilized derivative of a compound of formula VIII, in particular a derivative ofcompound of formula VIII covalently bound to an inert carrier bead, particularly aspolystyrene bead as defined above. More particularly, the MOST system of the present invention is characterized by the fact that said carrier beads are non-soluble in the liquid phase of the MOST system.2. The second aspect of the present inventionAccording to a second aspect of the invention, a method of storing solar thermalenergy is provided, which method comprises exposing least one low-energy parent isomer(A) of the above general formula (II) dissolved in a liquid organic medium to solar light for a period of time sufficient to photo isomerize at least one compound A into its corresponding metastable high-energy photo isomer B of the general formula II. In particular, said liquid medium is a medium which is in a liquid state over a widetemperature range as for example in a range of 0 to 100 oC, more particular at about 0 to 80oC. In a particular embodiment said medium comprises an organic solvent, in particular atleast one aromatic solvent, more particularly selected from benzene, toluene, or cyclic or non-cyclic aliphatic solvents, like in particular xylole und n-heptane, n-hexane or cyclohexane, or mixtures thereof. Astorage medium of the present invention comprising at least one type of metastablehigh-energy photo isomer (B) solar thermal energy is stably stored at a t1 / 2 of at least 1month, particularly at least 1 year or at least 5, 10, 50 or 100 years.3. The third aspect of the present inventionAccording to a third aspect of the invention, a method of releasing stored solar thermalenergy is provided, which method comprises contacting least one metastable high-energyM / 65032-PCT UMZ2024-444 24 photo isomer B) dissolved in a liquid organic medium with a base catalyst (C) as defined above catalyzing the terminal back-conversion of the photo isomer (B) into the correspondingparent compound (A). Thereby the stored energy as represented by the energy differenceΔHstorage corresponding to the energy difference between (A) and (B) is set free almostquantitatively.4. The fourth aspect of the present inventionAccording to a fourth aspect of the invention, a method for reversibly storing solarthermal energy, which method comprises applying a MOST system as defined in the abovefirst aspect of the invention.More particularly, said method for reversibly storing solar thermal energy which comprises a) exposing a low–energy storage medium comprising at least one low-energyparent isomer (A) of the above general formula (II) as defined above to solar light comprising light of a wavelength in the range of 300 to 600 nm for a period of time sufficient to photo isomerize at least one compound (A) into its metastable high-energy photo isomer (B) of the above general formula (I) as defined above in order to obtain a high-energy storage medium; b) storing said energy-rich storage medium for a prolonged period of time;c) contacting said high-energy storage medium with an immobilized base catalyst(C) catalyzing the terminal back-conversion of the photo isomer (B) into the corresponding parent isomer(A) by setting free thermal energy as stored by (B) in order to obtain a thermally heated storing medium; and d) withdrawing thermal energy from said thermally heated storing medium so as toobtain the initial low-energy storage medium comprising said at least one low-energy parent isomer (A).5. The fifth aspect of the present inventionAccording to a fifth aspect of the invention, a solar thermal energy storage device isprovided, which comprises at least one metastable high–energy photo isomer (B) of the above general formula (I) as defined above. M / 65032-PCT UMZ2024-444 25 The solar thermal energy storage device of particularly comprises a storage vessel T3containing a storage medium comprising at least one metastable high-energy photo isomer(B) of formula (I) as defined above, which storage device further comprises a catalyticmodule containing immobilized catalyst C as defined above for the controlled release ofstored energy upon getting into contact with the at least one metastable high-energy photoisomer (B).6. The sixth aspect of the present inventionThe sixth aspect of the invention relates to the use of a compound of general formula(I) as defined above and / or of a compound of general formula (II) as defined above for areversible storing of solar thermal energy. A combination of at least one compound ofgeneral formula (I) and at least one compound of the general formula (II) is also designatedas MOST couple. Dissolved in a suitable liquid medium and under conditions as furtherdetailed herein, said MOST couple is applied in the reversible storage of solar thermalenergy and, at a later stage, the controlled release of solar thermal energy under the catalyticaction of a strong organic, nitrogen base as herein defined.7. The seventh aspect of the present inventionA solar thermal energy capture device (SC), which comprises a transparent top layerpermeable for solar light at least in a wavelength range above 300 nm, and a below saidtransparent top layer ab energy capture compartment (receiving tank T2) optionally provided with a solar light permeable bottom layer, further comprising an inlet for an energy capture medium comprising at least one solar light excitable organic compound A of formula (II) as defined above and an outlet for an energy capture medium enriched with at least one metastable high-energy photo isomer B of formula (I) as defined above, which energy capture medium traverses said device in a directed flow from the inlet to the outlet.8. The eighth aspect of the present inventionAccording to an eighth aspect of the invention, a combined device for capturing solarthermal energy and solar photoelectric energy is provided, comprising an upper solar thermalcapture device (SC) as defined above and a lower photoelectric compartment for capturingsolar photoelectric energy comprising a photoelectric layer, as for example a (conventional) M / 65032-PCT UMZ2024-444 26solar panel comprising a multitude of solar cells; said upper solar thermal capture devicecomprises an upper layer permeable for solar light and a lower bottom layer permeable for solar light, so that solar light, which enters the upper solar thermal capture device and whichis not absorbed by the energy capture medium traversing said upper solar thermal capturedevice, is absorbed by said photoelectric layer to generate electric energy.9. The ninth aspect of the present inventionAccording to a ninth aspect of the invention, a device for operating a MOST system asdefined above is provided, which device comprises: a) a solar thermal energy capture device SC which comprises a receiving tank T2comprising a top layer permeable for solar light at least in a wavelength range above 300 nm, an inlet / outlet pair connected by connecting pipes 7a, 7b, 7callowing a circulating flow of a liquid phase in a circle C1, comprising at least one light excitable low-energy parent isomer A of the above general formula II, whereby isomer A is converted to its corresponding metastable high-energy isomer B; b) a storage tank T3 connected to receiving tank T2 via connecting pipe 9 comprisinga first inlet for receiving from tank T2 liquid phase enriched with metastable high- energy isomer B, and an inlet / outlet pair connected by a connecting pipe s 13a, 13b, 13cfor circulating said liquid phase enriched with metastable high-energy isomer B in a circle C2; c) a reactor R comprising an inlet / outlet pair connected to connecting pipes 20a,20b, 20c and containing immobilized catalyst C which catalyzes the back conversion of high energy metasabile isomer B to isomer A with release of thermal energy while ; and said liquid medium containing said metastable isomer Bcirculates in a circle C3; d) a heat exchanger HE adapted to retrieve thermal energy from reactor R and totransfer the retrieved thermal energy to a heat storage tank or a heat consuming device. The device according to a particular embodiment further comprisese) a storage tank T1 comprising an inlet / outlet pair, wherein the inlet is connected tostorage tank T3 via connecting pipe 26 for transferring liquid medium enriched withM / 65032-PCT UMZ2024-444 27 low energy isomer A to the storage tank T1; and wherein the outlet is connected viaconnecting pipe 27 to solar energy capture device SC.A non-limiting example of such devise is depicted in Figures 6 and 7, and further describedbelow.10. The tenth aspect of the present inventionAccording to a tenth aspect of the invention, a metastable high–energy photo isomer(B) of general formula (I) is provided wherein, n is an integer of 1, 2 or 3, R1is selected from –C (halogen)3-aHa, wherein a is 0, 1 or 2, in particular 0 or 1, and halogen is selected from F, Cl or Br, in particular –CF3; aryl; cyano; lower-alkoxy, in particular methoxy or -C(O)OR, wherein R is lower alkyl, in particularmethyl; R2and R2aare identical or different and independently of each other selected from H, D, linear or branched lower alkyl or linear or branched lower-alkoxy, like methyl or methoxy; most particularly H or D; R2bis selected from H or D; Ar represents an aromatic mono- or polycyclic, in particular mono- or bicyclic,condensed aromatic ring system or conjugated aromatic ring system, in which ringsystem at least one hydrogen atom of the aromatic ring system may be further substituted by one or more identical or different ring substituents R3, wherein M / 65032-PCT UMZ2024-444 28 R3is selected from cyano, halogen, linear or branched lower alkyl, in particular methyl, and linear or branched lower alkoxy, in particular methoxy; and - C(O)R1, wherein R1is as defined above; or a constitutional isomer or stereoisomer of the compound of formula I; or a mixture of at least two constitutional isomers or a mixture of at least two stereoisomers or a mixture of at least one stereoisomer and at least one constitutional isomer; with the proviso that, when Ar is a monocyclic 6-memberd aromatic ring and R3is missing, then n is an integer of 2 or 3; and with the proviso that compounds of formula I are excluded; wherein R1is CF3, Ar is a 6- membered aromatic ring wherein R3is missing, R2aand R2bare H and R2is H or 4-n- butenyl, and with the proviso that compounds of formula I are excluded, wherein simultaneously R1is CF3, Ar is a 6-membered aromatic ring wherein R3is F, Cl or -OMe, and R2a, R2band R2are H.11. The eleventh aspect of the present inventionAccording to an eleventh aspect of the invention, a compound excitable by solar light,in particular in the wavelength range of 300 to 600 nm, and having the general formula (II) isprovided M / 65032-PCT UMZ2024-444 29 wherein n, Ar, R1, R2, R2aand R2band R3are as defined above; and or a constitutional isomer or stereoisomer of the compound of formula II; or a mixture of at least two constitutional isomers or a mixture of at least two stereoisomers or a mixture of at least one stereoisomer and at least one constitutional isomer; with the proviso that compounds A, B and C are excluded.D. MORE DETAILED DESCRITION OF THE INVENTION BY REFERENCE TOISOMER PAIRS OF THE TYPE OTHO-METHYLACETOPHENONE / BENZOCYCLOBUTENOL The present invention is based on the development of a conceptually new class ofMOST couples, which is founded in the photocyclization of ortho-methylacetophenones (Fig. 1B).( P. J. Wagner, et al., J. Am. Chem. Soc. 113, 709–710 (1991).doi:10.1021 / ja00002a069; N. Ishida et al., Nat. Commun. 5, 3111 (2014).doi:10.1038 / ncomms4111). The corresponding benzocyclobutenols obtained after irradiation are recognized for their high level of intramolecular strain yet remarkable stability, which motivated the inventors to further investigate their potential for efficient application in energy storage. The inventors strategy for back-isomerization builds on an electrocyclic ring opening of the corresponding benzocyclobutenolates, which, in turn, can be accessed from the respectivebenzocyclobutenols by deprotonation. This approach capitalizes on charge-accelerationwithin pericyclic reactions, an observation originally made by Evans and co-workers when studying oxy-Cope rearrangements (D. A. Evans, et al., J. Am. Chem. Soc.97, 4765–4766 (1975). doi:10.1021 / ja00849a054). M / 65032-PCT UMZ2024-444 30 The inventors surprisingly succeeded in establishing a well-balanced isomer pair thatmeets the stringent photochemical and physicochemical prerequisites for a successful MOST application. Moreover, surprisingly, a highly efficient anion-accelerated ring opening reaction could be established, employing a simple organic base as the catalyst, which efficiently triggers heat release at ambient temperatures. Aplausible mechanism of the photocyclization of ortho-methylacetophenones isbriefly outlined in Fig. 2A. (P. G. Sammes, Photoenolisation. Tetrahedron. 32, 405–422(1976). doi:10.1016 / 0040-4020(76)80055-5; P. Klán, et al., Handbook of OrganicPhotochemistry and Photobiology (CRC Press, 2012), pp.627–652). serves as a crucialfoundation when searching for a potential candidate for MOST application (P. G. Sammes,Photoenolisation. Tetrahedron.32, 405–422 (1976). doi:10.1016 / 0040-4020(76)80055-5). Excitation of the syn-conformer of ortho-methylacetophenone 1 provides the tripletketone31, which undergoes 1,5-hydrogen atom transfer (HAT) to provide triplet biradical32.After intersystem crossing (ISC), enol isomers E-2 and Z-2 are forged simultaneously. Themechanistic foundation for this photoenolization process goes back to pioneering studiesfrom the 1970s by the groups of Wagner (R. Haag, et al., Helv. Chim. Acta. 60, 2595–2607(1977). doi:10.1002 / hlca.19770600813) and Scaiano (R. D. Small et al.,,. J. Am. Chem. Soc.99, 7713–7714 (1977). doi:10.1021 / jqqa00465a055). The Z-isomer Z-2 is known to quicklyreverse to the starting material, while the E-isomer E-2 generally possesses a longer life-time. This principally sets the stage for a 4-π electrocyclization (EC) towards the desiredbenzocyclobutenol 3. However, in the case of ortho-methylacetophenone 1a (R = Me), the photocyclization is characterized by low yields and thus not suitable for the development of aMOST system (Fig. 2B, Entry 1) (A. Sandvoß, et al., Org. Lett. 25, 5795–5799 (2023).doi:10.1021 / acs.orglett.3c02048). The inventors presumed that the inefficiency of thisprocess is based on a competitive 1,5-hydride shift of isomer E-2a (Fig. 2B, grey box) (K.Iida, et al., J. Org. Chem.64, 7407–7411 (1999). doi:10.1021 / jo990705n). For this reason, initiated further optimization by hydrogen displacement to inhibit theunproductive reversion to starting material. Surprisingly, fluorine emerged as favored option for this endeavor due to the unreactive nature of the C–F bond. Moreover, fluorine fulfills theinventors’ aim to identify a low molecular weight candidate to uphold a high energy density.However, the introduction of one fluorine atom (1b) led to low product yields (Entry 2), which can be explained by slow keto-enol tautomerism of the photogenerated enol of 1b. Incontrast, difluoroacetophenone 1c and trifluoroacetophenone 1d showed significantly betterresults, with a yield of 49% and 66%, respectively (Entries 3 and 4). Since M / 65032-PCT UMZ2024-444 31benzocyclobutenols such as 3d do not absorb light beyond 280 nm, the occurrence of aphotostationary state is effectively obviated in this sequence. Thus, 3d could, surprisingly, beobtained in >99% yield by extending the reaction time (Entry 5). The inventors also surprisingly observed, that the reaction also performed well whenusing a 370 nm or 390 nm light emitting diode (LED), displaying first order kinetics with noindications of side reactions or decomposition, as monitored by19F nuclear magnetic resonance (NMR) spectroscopy (data not shown). To decipher the mechanism of the pivotal 4π electrocyclic ring closure towards 3d,The inventors synthesized trifluoroacetophenone 4 and subjected it to the optimizedconditions (Fig. 2C). Benzocyclobutenol 6 was obtained as a single diastereomer, signifyinga conrotatory ring closure of E-5, consistent with a thermal reaction pathway. Thesubsistence of E-5 as a reaction intermediate was validated through a trapping experimentwith N-methylsuccinimide, yielding tricycle 7 as the sole product (N. C. Yang, et al., J. Am.Chem. Soc. 83, 2213 (1961). doi:10.1021 / ja01470a053; L. Dell'Amico, et al., Angew. Chem.Int. Ed. 55, 3313–3317 (2016). doi:10.1002 / anie.201509472; J. Y. J. Wang, et al., J. Am. Chem. Soc.144, 1023–1033 (2022). doi:10.1021 / jacs.1c12174). Based on these results, the inventors assumed that raising the reaction temperaturewill facilitate the EC and thus improve the conversion to benzocyclobutenol 3d. Indeed, theysurprisingly observed an increase in rate when gradually raising the reaction temperature ofthe photocyclization (Fig.2C, right). Notably, this surprising improvement correlated well withthe measured quantum yields (ϕ) of the isomerization process, which were determined at the excitation wavelength of 355 nm with a combined laser flash photolysis (LFP)-NMR technique (data not shown). To explain this temperature-dependent quantum yield, theinventors suspect that the EC is more drastically facilitated by the temperature change thanthe unproductive reversion to starting material via bimolecular processes. An improved quantum yield at elevated temperatures is a valuable asset for large scale MOST applications, where heating can be a side effect due to intense photoirradiation or insufficientcooling. X-ray analysis of the product revealed an elongated C–C bond of 1.58 Å,highlighting the distorted character of the strained entity. Next, the inventors evaluated the reaction’s robustness. While the reaction wasinsensitive to changes in temperature, light intensity, water-content, or scale, aerobicconditions led to drastically reduced yields as indicated by the radar diagram depicted in Fig.2D (L. Pitzer, et al., Angew. Chem. Int. Ed. 58, 8572–8576 (2019). doi:10.1002 / anie.201901935). Oxygen is a known interferent of reaction intermediates duringM / 65032-PCT UMZ2024-444 32photoenolization (P. Yates, et al., Tetrahedron Lett. 9, 5389–5392 (1968).doi:10.1016 / S0040-4039(00)89786-5). When performing the reaction under air or oxygenatmosphere, peroxide 8d was formed, which slowly decomposed to hemiacetals 9dexplaining the sluggish reaction outcomes. Control experiments suggest that 8d is formed bya spin-allowed quenching of the triplet biradical 32d by 3O2 (data not shown).The inventors further studied the impact of modifications to the ortho-substituent andelectronic perturbations of the aromatic ring on the reaction outcome. While the inventors were able to access 12 previously unknown benzocyclobutenols, the parent compound 3d remained the best candidate for MOST application based on its high energy density, reaction rate, and the absence of side reactions (see details in experimental part). When it comes to solvent selection, benzene proved to be the most effective, enabling the consistentgeneration of multigram quantities at up to 1 M concentrations (see details in experimentalpart). To further validate the key mechanistic steps proposed in Fig. 2A, an in-depth LFPanalysis was conducted for 1d at 355 nm, which allowed the detection of photoenol Z-2d asa short-lived intermediate (τ ~ 0.50 µs) and photoenol E-2d as a relatively long-livedintermediate. Assuming similar difference extinction coefficients, the ratio of Z-2d and E-2dformed after the laser pulse is estimated to be ~80:20. This is in good accordance with the measured quantum yield of 17% under the prerequisite that only E-2d undergoes efficient EC. Having a promising candidate in hand, the inventors started looking at theelectrocyclic ring opening. Benzocyclobutenol 3d exhibited an exceptional thermal stabilityshowing no signs of decomposition even after extended heating at 150 °C. This result is instark contrast to other benzocyclobutenols, which are known to undergo electrocyclic ringopening at 100-110 °C (B. J. Arnold, et al., J. Chem. Soc., Perkin Trans. 1, 415 (1974).doi:10.1039 / P19740000415; N. Ishida, et al., J. Am. Chem. Soc. 134, 17502–17504 (2012).doi:10.1021 / ja309013a). However, when heating 3d to 220 °C in a closed vial, clean back-isomerization to the starting material was observed (Fig. 3A). An activation barrier of 39.9 kcal / mol was derived from a conversion-time-plot of the ring-opening event. This characteristic renders 3d attractive for long-term energy storage and safetransportation with an extrapolated thermal half-life of 4.5 ^ 108 years, clearly distinguishing itfrom other MOST systems. As opposed to the high stability of benzocyclobutenol 3d, itsanion readily underwent ring opening (Fig.3B, 10d → 11d) (M. P. Cava, et al., J. Am. Chem. Soc. 82, 652–654 (1960). doi:10.1021 / ja01488a038; W. Choy, et al., J. Org. Chem. 53, M / 65032-PCT UMZ2024-444 335796–5798 (1988). doi:10.1021 / jo00259a041). The torqueselectivity of the process is knownto follow outwards rotation of the hydroxy group based on pioneering computational studiesby Houk and coworkers (C. W. Jefford, et al., J. Am. Chem. Soc. 114, 1157–1165 (1992). Doi:10.1021 / ja00030a005). When potassium tert-butoxide was used as a base at 90 °C, 49%of acetophenone 1d was obtained along with minor amounts of decomposition materials (Fig.3B, Entry 1). Hydroxyl bases were not suitable as they triggered a consecutive haloform reaction as evidenced by fluoroform evolution (Entry 2). However, the progression to organic superbases (T. R. Puleo, et al., Research.Chem. Eur. J. 27, 4216–4229 (2021). doi: 10.1002 / chem.202003580) surprisingly resulted ina notable further improvement of the MOST system of the invention. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) catalyzed an immaculate ring-opening reaction (Entry3). Moreover, fine-tuning of the organic base, catalyst loading (to about 5mol%), and reactiontime (up to 16 hours) allowed us to maintain good conversion while dropping the reactiontemperature to 30 °C (Entries 5-9). Optimal results were achieved by either using 1,5,7-triazabicyclo(4.4.0)dec-5-ene(TBD) or tert-butylimino-tri(pyrrolidino)phosphoran (BTPP) as bases and correspond to afurther surprising rate acceleration of 106-107 compared to the uncatalyzed ring opening of3d. Subsequently, we analyzed the thermochemistry of the catalytic process using a reaction calorimeter (Fig. 3C). We obtained an average of 312 J / g of heat release for the opening event, significantly surpassing the heat stored in solar-warmed water (ΔT = 50 °C, ΔH = 209 J / g). The measured energy density is also confirmed by our DFT calculations (data not shown). Although the stored energy is somewhat lower than the archetypalquadricyclane ⇄ norbornadiene pair (14.4 kcal / mol vs. 21.2 kcal / mol in toluene) (D. S.Kabakoff, et al., J. Am. Chem. Soc. 97, 1510–1512 (1975). doi:10.1021 / ja00839a039), thelatter cannot operate under sunlight conditions due to its weak absorptivity in the UVA spectral region. The progression to sunlight irradiation and the establishment of a cyclable process are important measures for the evaluation of MOST systems. In accordance, the inventorssubjected trifluoroacetophenone 1d to sunlight irradiation (Fig. 4). An average yield of 87%was obtained with no signs of material deterioration or side reactions, underpinning thereaction’s robustness (For detailed experimental procedures and set-ups, please refer to theexperimental part). To initiate back-isomerization and heat release, the inventors establisheda protocol using a polystyrene (PS)-immobilized TBD base, which can be conveniently M / 65032-PCT UMZ2024-444 34 removed through simple filtration after the reaction has stalled. Thus, the inventorssurprisingly were able to directly re-expose acetophenone 1d to sunlight irradiation, ensuringthe system’s cyclability. An average yield of 90% was achieved when using the polymer-supported TBD base, which performed equally well as its low-molecular counterpart enabling a material recovery of >99% per cycle.E. FURTHER PARTICULAR EMBODIMENTS1. Examples of Organic SuperbasesAccording to particular embodiments of the present invention it is preferred to apply, forthe reconversion of distorted thermal energy into free thermal energy a so-called organicsuperbase. Such superbases are divided up into 3 different classes, the class of amidines,the class of guanidines and the class of phosphazenes1.1 Particular amindine based superbasesA first preferred group of amidine based superbases is represented by the general formula wherein Cyc represents a 5- to 7-membered non-saturated or unsaturated heterocyclic ringA particular example thereof is represented by the following chemical formula DBU (pKa 24,3)M / 65032-PCT UMZ2024-444 35A second preferred class of amidine based superbases is represented by the generalformula: wherein Alk independently of each other is straight-chain or branchedlower alkyl, particularlymethyl or ethyl, more particularly methyl.1.2 Particular guanidine based superbasesA first group of guanidine based superbases, is represented by the following formula: wherein Rb ,Rb , Rc, Rd and Re independently of each other represent straight-chain or branchedlower alkyl, in particular Ra is selected from hydrogen or t-butyl and the remainingresidues Rb , Rc, Rd and Re are each methyl.A second group of guanidine based superbases, is represented by the following formula:M / 65032-PCT UMZ2024-444 36 wherein Aand B independently of each other represent a 5- to 7- membered heterocyclic ringand X represents the group >NH or >NR , wherein R represents a straight-chain or branched lower alkyl residueParticular examples of suitable guanidine bases, and their respective pKa values are listed inTable 1 below:Table 1: M / 65032-PCT UMZ2024-444 37 M / 65032-PCT UMZ2024-444 38 pKa correspond to the conjugated acid of the base and the values are determined in MeCN1.3 Particular phosphazene based superbasesA particular type of phosphazene superbases is represented by the formula wherein Alk represents a straight chain or branched C1- C4 alkyl group, andCyc represents together with the N atom to which it is attached, a 5- to 7- memberedsaturated or non-saturated nonaromatic or aromatic ring groupMore particularly, the superbase is BTPP (pKa = 28,4) of the formulaM / 65032-PCT UMZ2024-444 39 As further examples of suitable phosphazene superbases there may be mentioned thefollowing compounds as referred to in Puelo et al (Chem Eur J 2021,27, 4216-4229): P1-t-Bu (pKa = 27,0) M / 65032-PCT UMZ2024-444 40 BEMP (pKa 27,6)2. Particular low-energy parent isomers AFor the compounds depicted below any constitutional isomer of the particular depictedcompound and any stereoisomer thereof either as a mixture of at least two stereoisomers orin the form of a pure stereoisomer is encompassed, or any constitutional isomer either as a mixture of at least two constitutional isomers or im the form of a pure constitutional isomer, oras a mixture of at least one stereoisomer and at least one constitutional isomer.2.1 Mononuclear Low-energy Isomers A2.1.1 Single-functionalized Isomers A wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl R3 = cyano, halogen, methyl or methoxy;n = 0, 1, 2 or 3, in particular 3, and m = 1, 2 or 3, in particular 1As particular examples there may be mentioned:M / 65032-PCT UMZ2024-444 41 wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and Me = CHnD3-n with n = 0, 1, 2 or 3, in particular 3,2.1.2 Double-functionalized Isomers A wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and Me = CHnD3-nwith n = 0, 1, 2 or 3, in particular 3, M / 65032-PCT UMZ2024-444 42As particular example there may be mentioned: 2.1.3 Triple-functionalized Isomers A wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and Me = CHnD3-n with n = 0, 1, 2 or 3, in particular 3,2.2 Polynuclear low-energy Isomers (A)M / 65032-PCT UMZ2024-444 43 wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and Me = CHnD3-nwith n = 0, 1, 2 or 3, in particular 3,3. Particular high-energy isomers (B)For the compounds depicted below any constitutional isomer of the particular depicted compound and any stereoisomer thereof either as a mixture of stereoisomers or in the form of a pure stereoisomer is encompassed.3.1 Mononuclear high--energy Isomers (B)3.1.1 Single-functionalized Isomers (B) wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M / 65032-PCT UMZ2024-444 44 M = CHnD2-n with n = 0, 1, 2 or 3, in particular 3, R3 = cyano, halogen, methyl or methoxy;m= 1, 2 or 3, in particular 1.3.1.2 Double-functionalized Isomer (B)a) Para double-functionalized constitutional isomers wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M= CHnD2-nwith n = 0, 1, 2 or 3, in particular 3, b) Ortho double-functionalized M / 65032-PCT UMZ2024-444 45 wherein X= CF3, CHF2, CN, COORwith R = lower alkyl, in particular methyl, and M = CHnD2-nwith n = 0, 1 or 2, in particular 2.3.1.3 Triple functionalized Isomer (B) wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, andM = CHnD2-nwith n = 0, 1 or 2, in particular 2. M / 65032-PCT UMZ2024-444 46 wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M = CHnD2-n with n = 0, 1 or 2, in particular 2. wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M = CHnD2-n with n = 0, 1 or 2, in particular 2.3.2 Polynuclear Isomers (B)M / 65032-PCT UMZ2024-444 47 wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, andM = CHnD2-n with n = 0, 1 or 2, in particular 2. wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M = CHnD2-n with n = 0, 1 or 2, in particular 2. M / 65032-PCT UMZ2024-444 48 wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M = CHnD2-nwith n = 0, 1 or 2, in particular 2. wherein X = CF3, CHF2, CN, COOR with R = lower alkyl, in particular methyl, and M = CHnD2-n with n = 0, 1 or 2, in particular 2.4. Particular examples of MOST couples (A) and (B)In the following table, non-limiting examples of MOST couples of the invention (with Ar= benzyl in above formulae I and II) are summarized: M / 65032-PCT UMZ2024-444 49 5. Devices for operating a MOST system of the present inventionA non-limiting example of a device for performing a method for reversibly storing solar thermal energy will now be explained with reference to Figure 6: Therein the device 1 for operating a MOST system of the present invention is shown. It comprises a solar thermal energy capture device 2 comprising a receiving tank 3 (T2) for M / 65032-PCT UMZ2024-444 50taking up a liquid medium containing at the start of the process predominantly the solar light -excitable low-energy parent isomer (A). Solar light penetrating the top layer 4 of the capturedevice 2 converts said isomer (A) at least in part into the metastable high-energy isomer (B),while the liquid medium driven by pump 30 traverses the capture device 2 in a directed flowbetween inlet 5 and outlet 6 of the device. Driven by pump 30 the liquid medium circulatesvia connecting pipes 7a, Tb and 7c and three-way valves 50 and 51 under the control of a 1stoptical sensor 40 measuring, for example, the content of high-energy isomer (B) in thecirculating liquid medium. The medium is circulated in said first circle C1 (also designatedenergy uptake circle) until the concentration of the high energy isomer (B) has reached apredetermined upper level detected by sensor 40. Sensor 40 is then acting on three-wayvalve 50 switching to pipe 9 so that the liquid medium enriched with high-energy isomer (B)is transferred to storage tank 8 (T3). If needed said energy uptake circle C1 may be repeated so that the total amount of high energy isomer (B) in storage tank 8 further increases. If thermal energy is to be released, a thermal heat release circle C2 is activated. Drivenby pump 31 via circulating pipes 13 a, 13b and 13c the liquid medium enriched with high-energy isomer (B) is circulated via outlet 12 and inlet 11 of storage tank 8 through a reactor14 via a first pair of inlet and outlet (16, 17) of the reactor 14. Said reactor is prefilled withmicro particles carrying immobilized basic catalyst 15. Within the reactor 14 means 53 areprovided which are permeable to the liquid medium and isomers (A) and (B) dissolvedtherein but impermeable to the immobilized base catalyst 15. Through the action of the saidcatalyst 15 a terminal back isomerization of isomer (B) to isomer (A) is catalyzed setting freethe stored thermal energy of isomer (B) while increasing the temperature of the liquidmedium circulating through the reactor 14. Driven by pump 32 a heat exchange medium isguided through the reactor 14 where, between the second pair of inlet and outlet 21 and 22 aheat exchanger 18 is provided, transferring heated medium circulating in the heat exchangecircle C3 to module 19 which may be for example a heat storage tank or a heat energyconsuming device or system, as for example the heating system of a building. After saidreconversion process in the reactor 14 is terminated, which may be detected by a second optical sensor 41, measuring, for example, the content of residual high-energy isomer (B) and the thermal energy is transferred to module 19 the liquid medium now predominantlycontaining the low energy isomer (A) is pumped via storage tank 8 (T3), three-way valve 52and connecting pipe 26, back to storage tank 23 (T1), equipped with a pair of inlet and outlet(24, 25). After completing said transfer three-way valve 52 closes pipe 26 and opens three-way valve 51. Via connecting pipe 7c the content of storage tank 23 (T1) is pumped by pump30 back into the capture device 2 so that the isomerization process of low energy isomer (A) to high-energy isomer (B) can start anew. M / 65032-PCT UMZ2024-444 51 Figure 7 shows an alternative embodiment of a solar energy capture device of Figure 6. According to Figure 7 a combined device is provided which allows the capture of solar thermal energy as well as of photoelectric energy. While solar energy is collected in tank T2equipped with a pair of inlet and outlet (5,6) for a directed flow of solar energy capturemedium through said tank T2 solar light penetrating the top layer 4 will be partially absorbedby the solar energy capture medium in order to convert low energy isomer (A) to energyisomer (B). A proportion of the solar light which is not absorbed by the capture medium ispenetrating through tank T2, will exit tank T2 through its light permeable lower layer 61 andwill be absorbed by the photo electric collector 62 provided below said tank T2. The electricenergy generated may either be stored in module 63 which in that case would be a battery ormay directly be consumed by module 63 which alternatively may for example be provided asa device consuming electrical energy. The device for operating a MOST system as depicted in Figures 6 or 7 may beoperated manually, by manually operating the corresponding pumps and / or valves. However,a skilled reader will recognize that such a device can be operated semi-automatically or fullyautomatically, continuously or in batches, with the aid of one or more suitable controllers (notshown in the figures). Such a controller is capable, for example, of controlling the status ofthe valves and, if necessary, the operation of the corresponding pumps of the system depending on the measured signals obtained from sensors 40 and 41 in such a way that the MOST isomer mixture is fed into circles C1 or C2 depending on its energy state. The sameor another controller may also act to activate and terminate the heat exchange circuit C3 asrequired. The invention is further illustrated by the following non-limiting examples. Experimental part Materials and Reaction Set-Up Chemicals were purchased from Alfa Aesar, Acros Organics, Sigma Aldrich,BLDpharm, FluoroChem, Carbolution or ABCR and (unless otherwise stated) used asreceived. All reactions involving air or moisture sensitive reagents were carried out in oven-(125 oC) and flame-dried glassware under nitrogen atmosphere using standard Schlenktechniques. Dry solvents were collected from an MBraun MB SPS-800 (Et2O: MB-KOL-A andM / 65032-PCT UMZ2024-444 52MB-KOL MT2-250, THF: 2 ^ MB-KOL MT2-150°C, CH2Cl2: 2 ^ MB-KOL-A). A positive argonpressure was used to pass the solvents through the columns. Unless otherwise noted, all work-up and purification procedures were carried out with pre-distilled technical grade solvents. Purification was performed either with standard columnchromatography techniques using Geduran® Si 60 silica gel (0.063-0.200 mm, Merck), on anautomated flash chromatography system Biotage Isolera One utilizing Biotage Sfär Silica D-Duo 60 µm columns (5 g, 25 g, 100 g) or on an automated flash chromatography systemTeledyne Isco with Biotage Sfär Silica C18-Duo 100 Å 30 μm columns (12 g).Glass silica gelplates 60 F254 (Merck) were used for analytic thin layer chromatography applying either UVlight (254 / 366 nm), KMnO4 (1.5 g KMnO4, 5 g NaHCO3 and 5 mL NaOH 10% in 200 mLH2O), CAM (0.5g Ce(NH4)2(NO3)6 and 24.0 g of (NH4)6Mo7O24·4H2O, 28 mL H2SO4 in 200 mLH2O) for detection. Photochemical reactions were performed in a Luzchem LZC-ORG photoreactor with10 x 8 Watt Luzchem LZC-355 mercury lamps or a 40 W 370 nm Gen 2 KSPR160L KessilLED. Analytical Methods Melting points (M.P.) were measured on a Büchi B-540 melting-point apparatus andare reported uncorrected. Infrared (IR) spectra were obtained on a Tensor 27 spectrometer (Bruker) using a diamond ATR unit and are reported in wavenumbers (cm-1). Bands are characterized as broad (br), strong (s), medium (m), and weak (w). Nuclear magnetic resonance (NMR) spectra were recorded by the analytical department of the Department Chemie at Johannes Gutenberg-Universität Mainz. The following spectrometers were used: Avance III HD 300 (Bruker), Avance II 400 (Bruker), Avance III HD 400 (Bruker), and Avance III 600 equipped with a cryo-probe head (Bruker).Spectra were recorded at 22 °C (unless otherwise noted). Chemical shifts are reported inppm with the solvent resonance as the internal standard (1H NMR CHCl3: δ = 7.26 ppm,C6HD5: δ = 7.16 ppm, (CHD2)(CD3)SO: δ = 2.50 ppm; CHD2CN: : δ = 1.94 ppm, 13C NMRCDCl3: δ = 77.16 ppm, C6D6 δ = 128.06 ppm, (CD3)2SO: δ = 39.5 ppm, CD3CN: δ = 118.26ppm). Chemical shifts of 19F NMR are referenced to internal or external standards. The datais reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet,q = quartet, p = pentet, br = broad, m = multiplet or combinations of these), couplingconstants (Hz) and integration. High Resolution Mass Spectrometry (HRMS) was performed by the analytical department of the Department Chemie at Johannes Gutenberg-Universität M / 65032-PCT UMZ2024-444 53Mainz. Spectra were recorded on a Thermo-Fisher Scientific DFS (GC-MS, ionization viaelectron ionization (EI) or chemical ionization (CI)) or on an Agilent 6545 Q-ToF (LC-MS,ionization via electron spray ionization (ESI), atmospheric-pressure chemical ionization(APCI)). Signals are reported as mass to charge ratio m / z.Differential scanning calorimetry (DSC) was performed using a μRC®micro ReactionCalorimeter (Thermal Hazard Technology, THT) and analysis was conducted using the μRCAnalysis software 2.6.5.A) Synthesis of Starting materialsGeneral Procedure A for the preparation of 2,2,2-trifluoroacetophenones fromhalogenated arenes with lithium organyls: Ahalogenated arene (1.00 eq.) was dissolved in dry Et2O or THF (0.2 M) under inertgas atmosphere and was cooled to –78 °C at which temperature t-BuLi (2.05 eq.) was addeddropwise. After 30 min, ethyl trifluoroacetate (1.10 eq.) was added dropwise and the mixturewas stirred at –78 °C for 3 h. NH4Cl sat. was added at that temperature and the solution wasdiluted with Et2O and allowed to warm up to rt. The organic phase was separated, and the aqueous phase was extracted with Et2O (3x). The combined organic fractions were dried over MgSO4and the solvent was removed under reduced pressure. The products werepurified via flash chromatography (FC) and bulb-to-bulb distillation (device: BÜCHI GKR 50,1.1 mbar pressure, 25 °C up to 250 °C).. Bulb-to-bulb distillation was found to be crucial to achieve reproducible reactivity in the irradiation. Example 1: 2-Fluoro-1-(o-tolyl)ethan-1-one [1b] Following general procedure A with minor alterations using 2-bromotoluene (2.05 g,1.44 mL, 12.0 mmol,1.00 eq.), t-BuLi (1.54 g, 14.1 mL, 24.0 mmol, 1.70 M, 2.00 eq.) and 2-fluoroacetonitrile (1.06 g, 1.00 mL, 18.0 mmol, 1.50 eq.) in Et2O (50 mL). The desired productwas obtained after FC (pentane / Et2O, 60:40) and bulb-to-bulb distillation (130 °C, 1.1 mbar)as a colorless oil (456 mg, 3.00 mmol, 25%).M / 65032-PCT UMZ2024-444 54 IR (neat): ṽ = 2931 (w), 1702 (s), 1601 (w), 1572 (w), 1489 (w), 1456 (w), 1439 (w),1382 (w), 1296 (w), 1269 (w), 1229 (m), 1167 (w), 1081 (s), 1050 (w), 1036 (w), 963 (s), 819(w), 757 (s), 719 (m), 658 (m), 576 (w), 459 (w). 1H NMR (400 MHz, C6D6): δ = 7.01 – 6.91(m, 2H), 6.88 – 6.78 (m, 2H), 4.65 (dd, J = 47.4, 1.1 Hz, 2H), 2.39 (s, 3H). 13C {1H, 19F} NMR(101 MHz, C6D6): δ = 196.4, 139.3, 134.3, 132.3, 132.0, 128.7, 125.6, 83.9, 21.1.19F NMR(377 MHz, C6D6): δ = -225.74 (t, J = 47.4 Hz, 1F). HRMS (ESI): Calculated for C9H10FO[M+H]+: 153.0710, found: 153.0706. Spectroscopic data was in agreement to those previously reported.Example 2. 2,2-Difluoro-1-(o-tolyl)ethan-1-one [1c] Mg-turnings (101 mg, 4.15 mmol, 2.15 eq.) were added to an oven-dried 25 mLSchlenk flask and dry THF (10.0 mL) was added. The mixture was cooled to 0 °C and TMS-Cl (902 mg, 650 μL, 8.30 mmol, 4.29 eq.) was added, followed by 2,2,2-trifluoro-1-(o-tolyl)ethan-1-one (364 mg, 1.93 mmol, 1.00 eq.). The mixture was stirred at 0 °C for 2 h andexcess TMS-Cl and THF were removed in vacuo via a cooling trap. To the residue, hexanewas added (20 mL) and the solids were removed via filtration. The solvent was removedunder reduced pressure, HCl (5 M, 10 mL) was added and the mixture was stirred over-night.The mixture was extracted with Et2O (3 x 20 mL) and the combined organic phases werewashed with brine (3 x 20 mL), water (3 x 20 mL) and were dried over Na2SO4. The solventwas removed under reduced pressure and the crude product was purified via FC(pentane / Et2O, 90:10) and bulb-to-bulb distillation (100 °C, 1.1 mbar) as a colorless oil(401 mg, 2.36 mmol, 40%).IR (neat): ṽ = 2973 (w), 2360 (w), 2172 (w), 2148 (w), 2108 (w), 2060 (w), 2020 (w),1982 (w), 1707 (s), 1602 (w), 1572 (w), 1491 (w), 1458 (w), 1384 (w), 1346 (w), 1296 (w), 1268 (w), 1236 (w), 1148 (m), 1123 (s), 1065 (s), 967 (w), 873 (w), 860 (w), 789 (w), 760 (w), 725 (m), 651 (w), 584 (w), 554 (w), 543 (w), 486 (w), 458 (w), 451 (w), 441 (w), 431 (w), 410(w). 1H NMR (400 MHz, C6D6): δ = 7.50 (d, J = 7.7 Hz, 1H), 7.00 – 6.91 (m, 1H), 6.80 (d, J =7.6 Hz, 2H), 5.65 (t, J = 53.7 Hz, 1H), 2.36 (s, 3H). 13C {1H, 19F} NMR (101 MHz, C6D6): δ =189.5, 141.4, 133.1, 132.6, 131.5, 130.3, 125.8, 111.0, 21.6. 19F NMR (282 MHz, C6D6): δ = -M / 65032-PCT UMZ2024-444 55122.31 (dd, J = 53.7, 1.9 Hz, 2F). HRMS (APCI): Calculated for C9H7F2O [M-H]-: 169.0470,found: 169.0496. Example 3: 2,2,2-Trifluoro-1-(o-tolyl)ethan-1-one [1d] Following general procedure A using 2-bromotoluene (5.13 g, 3.61 mL, 30.0 mmol,1.00 eq.), t-BuLi (3.92 g, 36.0 mL, 61.2 mmol, 1.70 M, 2.04 eq.) and ethyl trifluoroacetate(4.78 g, 4.00 mL, 33.7 mmol, 1.12 eq.) in Et2O (150 mL). The desired product was obtainedafter FC (pentane) and bulb-to-bulb distillation (110 °C, 0.54 mbar) as a colorless oil (5.12 g,27.2 mmol, 91%).IR (neat): ṽ = 1715 (m), 1604 (w), 1573 (w), 1459 (w), 1385 (w), 1323 (w), 1288 (w),1184 (s), 1142 (s), 1037 (w), 933 (s), 737 (s), 665 (m), 608 (w), 529 (w), 491 (w), 462 (w),446 (w), 436 (w). 1H NMR (400 MHz, C6D6): δ = 7.62 (dq, J = 7.9, 1.9 Hz, 1H), 6.91 (td, J =7.6, 1.4 Hz, 1H), 6.75 (t, J = 7.2 Hz, 2H), 2.28 (s, 3H). 13C NMR (101 MHz, C6D6): δ = 182.2(q, J = 33.7 Hz), 142.4, 133.8, 132.7, 130.5 (q, J = 3.7 Hz), 129.5, 126.0, 117.1 (q, J = 293.1Hz), 21.7. 19F NMR (282 MHz, C6D6): δ = -71.54 (d, J = 2.0 Hz, 3F). HRMS (ESI): Calculatedfor C9H6F3O [M-H]-: 187.0376, found: 187.0381. Example 4: 1-(2-Ethylphenyl)-2,2,2-trifluoroethan-1-one [4] Following general procedure A using 1-ethyl-2-iodobenzene (1.16 g, 0.71 mL,5.00 mmol, 1.00 eq.), t-BuLi (641 mg, 5.26 mL, 10.0 mmol, 1.90 M, 2.00 eq.) and ethyltrifluoroacetate (781 mg, 0.65 mL, 5.50 mmol, 1.10 eq.) in THF (20 mL). The desired productwas obtained after FC (pentane) and bulb-to-bulb distillation (100 °C, 0.70 mbar) as acolorless oil (937 mg, 4.63 mmol, 93%).IR (neat): ṽ = 2963 (w), 2932 (w), 2155 (w), 2034 (w), 2016 (w), 1720 (m), 1602 (w),1573 (w), 1450 (w), 1323 (w), 1182 (s), 1144 (s), 934 (s), 790 (w), 754 (m), 734 (m), 662 (m), 635 (w), 607 (w), 586 (w), 564 (w), 556 (w), 540 (w), 528 (w), 518 (w), 507 (w), 498 (w), 482(w), 468 (w), 459 (w), 449 (w), 429 (w), 418 (m). 1H NMR (400 MHz, C6D6): δ = 7.57 (dp, J =M / 65032-PCT UMZ2024-444 567.7, 1.9 Hz, 1H), 6.97 (td, J = 7.6, 1.3 Hz, 1H), 6.84 (ddd, J = 7.8, 1.3, 0.6 Hz, 1H), 6.76 (td, J= 7.7, 1.3 Hz, 1H), 2.66 (q, J = 7.5 Hz, 2H), 1.04 (t, J = 7.5 Hz, 3H). 13C NMR (101 MHz,C6D6): δ = 182.8 (q, J = 33.9 Hz), 148.0, 133.9, 131.1, 130.1, 129.6 (q, J = 3.6 Hz), 126.0,117.2 (q, J = 293.2 Hz), 27.5, 15.6. 19F NMR (282 MHz, C6D6): δ =-71.85 (d, J = 2.0 Hz).HRMS (APCI): Calculated for C10H9F3O [M]·-: 202.0610, found: 202.0613. Example 5: 2,2,2-Trifluoro-1-(2-isopropylphenyl)ethan-1-one [S1] Following general procedure A using 1-iodo-2-isopropylbenzene (1.23 g, 0.79 mL,5.00 mmol, 1.00 eq.), t-BuLi (641 mg, 5.88 mL, 10.0 mmol, 1.70 M, 2.00 eq.) and ethyltrifluoroacetate (781 mg, 0.65 mL, 5.50 mmol, 1.10 eq.) in THF (20 mL). The desired productwas obtained after FC (pentane) as a colorless oil (589 mg, 2.72 mmol, 54%).IR (neat): ṽ = 2960 (m), 2925 (m), 2871 (w), 2854 (w), 1721 (m), 1601 (w), 1463 (w),1378 (w), 1365 (w), 1202 (s), 1182 (s), 1147 (s), 1035 (w), 936 (s), 758 (m), 728 (w), 660 (m), 624 (w), 610 (w), 600 (w), 573 (w), 565 (w), 540 (w), 530 (w), 515 (w), 506 (w), 490 (m),462 (m), 444 (w), 433 (w), 417 (w). 1H NMR (600 MHz, CDCl3): δ = 7.70 (dt, J = 8.0, 1.7 Hz,1H), 7.61 – 7.56 (m, 1H), 7.55 – 7.51 (m, 1H), 7.34 – 7.30 (m, 1H), 3.40 (p, J = 6.8 Hz, 1H),1.26 (d, J = 6.9 Hz, 6H). 13C NMR (151 MHz, CDCl3): δ = 184.3 (q, J = 34.5 Hz), 151.6,133.8, 130.0, 128.9 (q, J = 292.9 Hz), 127.3, 125.7, 116.4 (q, J = 292.9 Hz), 29.7, 24.1. 19FNMR (282 MHz, C6D6): δ = -72.77 (d, J = 1.8 Hz). HRMS (APCI): Calculated for C11H11F3O[M]·-: 216.0767, found: 216.0768. Example 6: 1-Bromo-2-(methoxymethyl)benzene [S2] Sodium hydride (720 mg, 18.0 mmol, 1.20 eq.) was suspended in dry THF (100 mL)under inert gas atmosphere and a prepared solution of (2-bromophenyl)methanol (2.81 g,15.0 mmol, 1.00 eq.) in dry THF (50 mL) was added dropwise at 0 °C. The mixture wasM / 65032-PCT UMZ2024-444 57stirred for 15 min and iodomethane (6.39 g, 2.80 mL, 45.0 mmol, 3.00 eq.) was addeddropwise at 0 °C. The solution was stirred at 0 °C for 15 minutes and 16°h at rt.NH4Cl sat.was added and the solution was diluted with CH2Cl2 (30 mL). The organic layer wasseparated, and the aqueous layer was extracted with CH2Cl2 (3 x 30 mL). The combinedorganic fractions were dried over Na2SO4 and the solvent was removed under reduced pressure. The product was obtained after FC (pentane / Et2O, 100:0 to 80:20) as a slightlyyellow oil (2.79 g, 13.9 mmol, 92%).1H NMR (400 MHz, CDCl3): δ = 7.54 (dd, J = 8.0, 1.3 Hz,1H), 7.46 (ddd, J = 7.6, 1.8, 0.9 Hz, 1H), 7.32 (td, J = 7.5, 1.3 Hz, 1H), 7.20 – 7.10 (m, 1H),4.53 (s, 2H), 3.47 (s, 3H). 13C NMR (101 MHz, CDCl3): δ = 137.7, 132.7, 129.1, 129.0, 127.5,122.8, 74.0, 58.8. Example 7: 2,2,2-Trifluoro-1-(2-(methoxymethyl)phenyl)ethan-1-one [S3] Following general procedure A using 1-bromo-2-(methoxymethyl)benzene (1.50 g,7.46 mmol,1.00 eq.), t-BuLi (1.00 g, 9.22 mL, 15.7 mmol, 1.70 M, 2.10 eq.) and ethyltrifluoroacetate (1.27 g, 1.06 mL, 8.95 mmol, 1.20 eq.) in Et2O (100 mL). The desired productwas obtained after FC (pentane) as a colorless oil (1.04 g, 4.76 mmol, 64%).IR (neat): ṽ = 2934 (w), 2830 (w), 1737 (w), 1713 (m), 1603 (w), 1574 (w), 1452 (w),1383 (w), 1324 (w), 1292 (w), 1186 (s), 1143 (s), 1103 (m), 937 (s), 737 (m), 671 (w), 658(w), 607 (w). 1H NMR (400 MHz, C6D6): δ = 7.50 (dt, J = 7.8, 1.6 Hz, 1H), 7.37 (dd, J = 7.8,1.3 Hz, 1H), 7.03 (td, J = 7.7, 1.3 Hz, 1H), 6.80 (td, J = 7.7, 1.2 Hz, 1H), 4.42 (s, 2H), 3.03 (s,3H). 13C NMR (101 MHz, C6D6): δ = 183.5 (q, J = 34.8 Hz), 142.6, 133.4, 129.6 (q, J = 3.2Hz), 129.3, 127.7, 127.2, 117.1 (q, J = 292.3 Hz), 72.4, 58.3. 19F NMR (377 MHz, C6D6): δ = -72.83 (d, J = 1.7 Hz). HRMS (APCI): Calculated for C10H8F3O2 [M-H]-: 217.0482, found217.0464. Example 8: 2,2,2-Trifluoro-1-(4-methoxy-2-methylphenyl)ethan-1-one [S4] M / 65032-PCT UMZ2024-444 58 Following general procedure A using 4-bromo-3-methylanisole (3.12 g, 2.00 mL,15.5 mmol,1.00 eq.), t-BuLi (1.99 g, 16.3 mL, 31.1 mmol, 1.90 M, 2.00 eq.) and ethyltrifluoroacetate (2.43 g, 2.03 mL, 17.1 mmol, 1.10 eq.) in Et2O (100 mL). The desired productwas obtained after FC (pentane) and bulb-to-bulb distillation (140 °C, 1.10 mbar) as acolorless oil (2.93 g, 13.4 mmol, 86%).1H NMR (600 MHz, CDCl3): δ =7.91 (dq, J = 9.7, 1.7 Hz, 1H), 6.84 – 6.82 (m, 2H),3.89 (s, 3H), 2.61 (s, 3H). 13C NMR (151 MHz, CDCl3): δ = 180.2 (q, J = 33.2 Hz), 164.0,146.7, 134.0 (q, J = 4.2 Hz), 121.7, 118.4, 117.0 (q, J = 292.9 Hz), 111.2, 55.7, 23.1. 19FNMR (377 MHz, C6D6): δ = -70.47 (d, J = 2.2 Hz, 3F).Example 9: 2,2,2-Trifluoro-1-(4-fluoro-2-methylphenyl)ethan-1-one [S5] Following general procedure A using 4-fluoro-1-iodo-2-methylbenzene (3.54 g,1.98 mL, 15.0 mmol, 1.00 eq.), t-BuLi (1.92 g, 15.8 mL, 30.0 mmol, 1.90 M, 2.00 eq.) andethyl trifluoroacetate (2.34 g, 1.96 mL, 16.5 mmol, 1.10 eq.) in Et2O (60 mL). The desiredproduct was obtained after FC (pentane) and bulb-to-bulb distillation (60 °C, 0.80 mbar) as acolorless oil (2.18 g, 10.6 mmol, 70%). IR (neat): ṽ = 2926 (w), 1716 (m), 1608 (m), 1581 (s), 1500 (w), 1453 (w), 1329 (w),1300 (w), 1244 (m), 1204 (s), 1181 (s), 1142 (s), 1108 (s), 973 (s), 910 (m), 871 (w), 825 (w), 773 (m), 742 (w), 699 (w), 632 (m), 591 (w), 536 (w), 455 (w), 430 (w), 412 (w).1H NMR (400MHz, CDCl ): δ = 7.94 (ddq, J = 9.7, 5.7, 1.9 Hz, 1H), 7. 133 15 – 6.94 (m, 2H), 2.61 (s, 3H). CNMR (101 MHz, CDCl3): δ = 180.9 (q, J = 34.2 Hz), 165.7 (d, J = 258.5 Hz), 147.1 (d, J = 9.6Hz), 134.2 – 133.2 (m), 125.6 (d, J = 3.0 Hz), 112.0 (d, J = 21.5 Hz), 116.6 (q, J = 292.7 Hz),113.5 (d, J = 21.8 Hz), 22.44 (d, J = 1.5 Hz). 19F NMR (282 MHz, C6D6): δ = -71.37 (d, J =1.9 Hz, 3F), -103.20 (td, J = 8.7, 5.7 Hz, 1F). HRMS (ESI): Calculated for C9H5F4O [M-H]-:205.0282, found: 205.0288. M / 65032-PCT UMZ2024-444 59 Example 10: 1-(4-Chloro-2-methylphenyl)-2,2,2-trifluoroethan-1-one [S6] Following general procedure A using 2-bromo-5-chlorotoluene (3.08 g, 2.00 mL,15.0 mmol, 1.00 eq.), t-BuLi (1.92 g, 15.8 mL, 30.0 mmol, 1.90 M, 2.00 eq.) and ethyltrifluoroacetate (2.34 g, 1.96 mL, 16.5 mmol, 1.10 eq.) in Et2O (100 mL). The desired productwas obtained after FC (pentane) and bulb-to-bulb distillation (90 °C, 1.1 mbar) as a colorlessoil (2.90 g, 13.0 mmol, 87%).IR (neat): ṽ = 2983 (w), 2236 (w), 1725 (m), 1608 (w), 1558 (w), 1451 (w), 1386 (w),1326 (w), 1281 (w), 1206 (m), 1186 (s), 1146 (s), 1038 (w), 958 (s), 894 (m), 838 (w), 775(w), 742 (w), 713 (w), 631 (w), 587 (w), 558 (w), 525 (w), 450 (w). 1H NMR (400 MHz, C6D6):δ = 7.10 (dq, J = 8.2, 1.9 Hz, 1H), 6.63 (dd, J = 8.2, 1.7 Hz, 1H), 6.55 (d, J = 1.7 Hz, 1H),1.89 (s, 3H). 13C NMR (101 MHz, C6D6): δ = 181.9 (q, J = 35.0 Hz), 142.2, 135.4, 132.3,129.8 (q, J = 3.6 Hz), 129.2, 117.4, 117.2, 116.5 (q, J = 292.6 Hz), 20.7.19F NMR (377 MHz,C6D6): δ = -71.64 (d, J = 2.0 Hz, 3F). HRMS (ESI): Calculated for C9H5ClF3O [M-H]-:220.9986, found: 220.9986. Example 11: 1-(4-Chloro-2-ethylphenyl)-2,2,2-trifluoroethan-1-one [S7] Following general procedure A using 1-bromo-4-chloro-2-ethylbenzene (409 mg,0.27 mL, 1.86 mmol, 1.00 eq.), t-BuLi (239 mg, 2.19 mL, 3.73 mmol, 1.70 M, 2.00 eq.) andethyl trifluoroacetate (318 mg, 0.27 mL, 2.24 mmol, 1.20 eq.) in Et2O (25 mL). The desiredproduct was obtained after FC (pentane) and bulb-to-bulb distillation (110 °C, 1.1 mbar) as acolorless oil (299 mg, 1.26 mmol, 68%).M / 65032-PCT UMZ2024-444 60 IR (neat): ṽ = 2977 (w), 2880 (w), 1718 (m), 1593 (m), 1559 (w), 1458 (w), 1396 (w),1323 (w), 1289 (w), 1237 (w), 1195 (s), 1182 (s), 1145 (s), 1106 (m), 1061 (w), 975 (w), 935(s), 885 (w), 843 (w), 828 (w), 776 (w), 740 (w), 688 (w), 619 (w), 531 (w), 499 (w), 469 (w).1H NMR (400 MHz, C6D6): δ = 7.27 (dq, J = 8.5, 1.9 Hz, 0H), 6.87 (d, J = 2.1 Hz, 0H), 6.70(dd, J = 8.5, 2.2 Hz, 1H), 2.47 (q, J = 7.5 Hz, 1H), 0.88 (t, J = 7.5 Hz, 2H). 13C NMR (101MHz, C6D6): δ = 181.7 (q, J = 34.3 Hz), 150.2, 140.5, 131.5 (q, J = 3.8 Hz), 131.3, 127.6,126.3, 116.9 (q, J = 293.1 Hz), 27.3, 15.1. 19F NMR (377 MHz, C6D6): δ = -71.92 (d, J = 2.0Hz, 3F). HRMS (ESI): Calculated for C10H7ClF3O [M-H]-: 235.0143, found: 235.0149.Example 12: 3-Methyl-4-(2,2,2-trifluoroacetyl)benzonitrile [S8] Following general procedure A using 4-bromo-3-methylbenzonitrile (1.01 g,5.14 mmol,1.00 eq.), t-BuLi (658 mg, 5.41 mL, 10.3 mmol, 1.90 M, 2.00 eq.) and ethyltrifluoroacetate (803 mg, 0.67 mL, 5.65 mmol, 1.20 eq.) in a mixture of Et2O (20 mL) andTHF (5 mL). The desired product was obtained after FC (pentane) and bulb-to-bulbdistillation (140 °C, 1.1 mbar) as a colorless solid (576 mg, 2.70 mmol, 53%).M.P.: 40 – 45 °C. IR (neat): ṽ = 2236 (w), 1725 (s), 1607 (w), 1558 (w), 1450 (w),1386 (w), 1326 (w), 1281 (w), 1206 (m), 1185 (s), 1144 (s), 1038 (w), 958 (s), 894 (s), 838 (w), 775 (m), 742 (m), 713 (w), 630 (w), 588 (w), 559 (w), 524 (w), 450 (w).1H NMR (400MHz, C6D6): δ = 7.08 (dq, J = 8.3, 1.8 Hz, 1H), 6.61 (dd, J = 8.2, 1.6 Hz, 1H), 6.54 (t, J = 1.1Hz, 1H), 1.88 (s, 3H). 13C NMR (101 MHz, C6D6): δ = 181.9 (q, J = 35.1 Hz), 142.2, 135.4,132.3, 129.7 (q, J = 3.6 Hz), 129.2, 117.4, 117.2, 116.5 (q, J = 292.7 Hz), 20.7. 19F NMR(282 MHz, C6D6): δ =-72.57 (d, J = 1.8 Hz, 3F). HRMS (ESI): Calculated for C10H5F3NO [M-H]-: 212.0329, found 212.0336.B) Photocyclization of SubstratesGeneral procedure B for the synthesis of tertiary cyclobutanols from ortho-alkyl-substituted acetophenones: An ortho-alkyl-substituted acetophenone was dissolved in benzene (20 mM),M / 65032-PCT UMZ2024-444 61degassed (3 x freeze-pump-thaw) and was irradiated using a Luzchem Photoreactorequipped with 10 8 Watt LZC-UVA (355 nm) lamps for 16 h at rt. The solvent was removedunder reduced pressure and desired product was isolated after automated FC(pentane / Et2O, 100:0 to 50:50; exact gradient: 4 column volumes (CV) 100:0, 4 CV 100:0 to90:10, 4 CV 90:10, 4 CV 80:20, 4 CV 70:30, 4 CV 50:50).General procedure C for the synthesis of tertiary cyclobutanols from ortho-alkyl-substituted acetophenones: An ortho-alkyl-substituted acetophenone was dissolved in benzene (20 mM),degassed (3 x freeze-pump-thaw) and was irradiated using a 40 W 370 nm Gen 2KSPR160L Kessil LED at rt. The solvent was removed under reduced pressure and desired product was isolated after FC, automated FC, or RP-MPLC. Example 13: 7-Methylbicyclo[4.2.0]octa-1,3,5-trien-7-ol [3a] Following general procedure B with minor alterations using 1-(o-Tolyl)ethan-1-one(262 μL, 2.00 mmol, 1.00 eq.) in acetonitrile (100 mL) for 17 h. The solution was degassedby passing through a stream of N2 for 15 min before irradiation. After automated FC(CyH / EtOAc, 90:10 to 80:20), the starting material (224 mg, 218 μL, 1.67 mmol, 83%) andproduct (43.0 mg, 320 μmol, 16%) were isolated.1H NMR (400 MHz, CDCl3): δ = 7.31 – 7.26 (m, 1H), 7.23 (tq, J = 7.6, 0.9 Hz, 1H),7.19 – 7.14 (m, 2H), 3.39 – 3.30 (m, 1H), 3.22 (d, J = 14.1 Hz, 1H), 2.47 (s, 1H) 1.66 (s, 3H).13C NMR (101 MHz, CDCl3): δ = 151.2, 141.3, 129.4, 127.4, 124.2, 120.6, 78.4, 48.4, 25.8.Example 14: 7-(Fluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [3b] M / 65032-PCT UMZ2024-444 62 Following general procedure C with minor alterations using 2-fluoro-1-(o-tolyl)ethan-1-one (112 mg, 0.74 mmol) in acetonitrile (50 mL) for 6 h. The desired product was obtainedafter FC (pentane / Et2O, 80:20) and bulb-to-bulb distillation (150 °C, 1.1 mbar) as a colorlessoil (14 mg, 0.09 mmol, 12%).IR (neat): ṽ = 3551 (w), 3387 (m), 3346 (m), 3069 (w), 2928 (m), 1459 (m), 1423 (w),1364 (m), 1331 (w), 1266 (m), 1201 (s), 1155 (m), 1111 (m), 1067 (m), 1044 (m), 1018 (s), 994 (s), 966 (m), 918 (m), 758 (s), 734 (s), 715 (s), 644 (m), 601 (w), 583 (w), 572 (w), 541(w), 478 (w), 422 (w), 415 (w). 1H NMR (400 MHz, C6D6): δ = 7.08 (td, J = 7.2, 1.6 Hz, 1H),7.05 – 6.97 (m, 2H), 6.88 (dt, J = 7.3, 1.0 Hz, 1H), 4.33 – 4.24 (m, 1H), 4.21 – 4.10 (m, 1H),2.99 (d, J = 14.2 Hz, 1H), 2.82 (dd, J = 14.2, 3.3 Hz, 1H), 2.03 (s, 1H). 13C NMR (101 MHz,C6D6): δ = 147.2 (d, J = 7.4 Hz), 141.7, 130.0, 127.6, 123.9, 122.0, 87.3 (d, J = 174.7 Hz),78.7 (d, J = 19.4 Hz), 42.9 (d, J = 6.5 Hz). 19F NMR (377 MHz, C6D6): δ = -225.74 (t, J = 47.2Hz, 1F). HRMS (ESI): Calculated for C9H8FO [M-H]-: 151.0565, found: 151.0526. Example 15: 7-(Difluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [3c] Following general procedure B with minor alterations using 2,2-difluoro-1-(o-tolyl)ethan-1-one (21.4 mg, 0.126 mmol) in benzene (6 mL, 20 mM). The product wasobtained after automated FC (pentane / Et2O, 100:0 to 50:50) as a colorless oil (13.0 mg,0.076 mmol, 61%).IR (neat): ṽ = 3363 (w), 2935 (w), 1460 (w), 1425 (w), 1347 (w), 1277 (w), 1239 (m),1192 (w), 1157 (w), 1113 (m), 1094 (m), 1062 (s), 982 (w), 952 (w), 889 (w), 818 (w), 758 (m), 735 (w), 715 (w), 673 (w), 657 (w), 621 (w), 567 (w), 552 (w), 516 (w), 464 (w), 449 (w),414 (w). 1H NMR (400 MHz, C6D6): δ =7.10 – 6.91 (m, 3H), 6.82 (d, J = 7.3 Hz, 1H), 5.42 (t, J= 54.8 Hz, 1H), 3.19 (dd, J = 14.4, 2.4 Hz, 1H), 2.73 (d, J = 14.3 Hz, 1H), 1.98 (s, 1H). 13C{1H, 19F} NMR (101 MHz, C6D6): δ = 143.7, 142.1, 130.6, 127.9, 123.6, 122.5, 115.9, 78.8,41.3. 19F NMR (377 MHz, C6D6): δ = -126.79 – -132.30 (m, 2F). HRMS (ESI): Calculated forC9H7F2O [M-H]-: 169.0470, found: 169.0475. Example 17: 7-(Trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [3d] M / 65032-PCT UMZ2024-444 63 Following general procedure B using 2,2,2-trifluoro-1-(o-tolyl)ethan-1-one (23 mg,0.122 mmol) in benzene (6 mL, 20 mM). The product was obtained after automated FC(pentane / Et2O, 100:0 to 50:50) as a colorless solid (16 mg, 0.085 mmol, 70%).M.P.: 39 – 44 °C. IR (neat): ṽ = 3349 (w), 2942 (w), 1595 (w), 1461 (w), 1428 (w),1311 (w), 1232 (w), 1153 (s), 1128 (s), 1095 (m), 1069 (m), 1018 (m), 955 (w), 863 (w), 757 (m), 743 (w), 715 (m), 662 (m), 629 (w), 597 (w), 556 (w), 509 (w), 460 (w).1H NMR (400MHz, C6D6): δ = 7.02 (td, J = 7.4, 1.3 Hz, 1H), 6.99 – 6.90 (m, 2H), 6.82 – 6.73 (m, 1H), 3.40(d, J = 14.4, 1H), 2.75 (d, J = 14.4, 1H), 2.23 (s, 1H). 13C NMR (101 MHz, C6D6): δ = 142.2,142.0 (q, J = 1.9 Hz), 131.1, 128.2, 125.5(q, J = 281.7 Hz), 123.7, 122.2, 78.3 (q, J = 32.8Hz), 41.8 (q, J = 2.0 Hz). 19F NMR (282 MHz, C6D6): δ = –81.1 (s, 3F). HRMS (ESI):Calculated for C9H6F3O [M-H]-: 187.0376, found: 187.0373. Example 18: 8-Methyl-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [6] Following general procedure B using 1-(2-ethylphenyl)-2,2,2-trifluoroethan-1-one(24 mg, 0.12 mmol) in benzene (6 mL, 20 mM). The product was obtained after automatedFC (pentane / Et2O, 100:0 to 50:50) as a colorless oil (14 mg, 0.07 mmol, 58%).M.P.: 30.0 – 38.5 °C. IR (neat): ṽ = 3345 (w), 1458 (w), 1343 (w), 1284 (w), 1228 (w),1148 (s), 1107 (s), 1083 (m), 1051 (m), 951 (m), 935 (m), 894 (w), 757 (m), 744 (m), 662 (m),640 (w), 593 (w), 532 (w), 471 (w), 453 (w), 434 (w). 1H NMR (400 MHz, C6D6): δ = 7.05 (td,J = 7.4, 1.3 Hz, 1H), 7.02 – 6.99 (m, 1H), 6.98 – 6.93 (m, 1H), 6.81 (dq, J = 7.4, 1.0 Hz, 1H),3.32 (dddd, J = 8.5, 7.4, 6.3, 1.1 Hz, 1H), 2.17 (s, 1H), 1.30 (dq, J = 7.4, 1.7 Hz, 3H). 13CNMR (101 MHz, C6D6): δ = 147.2, 140.4 (q, J = 2.4 Hz), 131.2, 128.4, 125.6 (q, J = 282.7Hz), 122.2, 122.2, 80.6 (q, J = 30.8 Hz), 52.2, 13.5 (q, J = 2.3 Hz). 19F NMR (377 MHz,C6D6): δ = –75.8 (s, 3F). HRMS (ESI): Calculated for C10H8F3O [M-H]-: 201.0533, found:201.0535. M / 65032-PCT UMZ2024-444 64 Example 19: 8-Methoxy-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [S9] Following general procedure B using 2,2,2-trifluoro-1-(2-(methoxy-methyl)phenyl)ethan-1-one (26.5 mg, 0.122 mmol) in benzene (6 mL, 20 mM). The productwas obtained after automated FC (pentane / Et2O, 100:0 to 50:50) as a colorless oil (18.0 mg,0.083 mmol, 68%).M.P.: 40.0 – 46.5 °C. IR (neat): ṽ = 3389 (w), 2942 (w), 2841 (w), 1463 (w), 1361 (m),1298 (m), 1208 (m), 1177 (s), 1151 (s), 1115 (s), 1063 (s), 1013 (w), 986 (m), 905 (m), 802 (w), 760 (m), 736 (m), 685 (w), 660 (m), 624 (w), 592 (w), 519 (w), 468 (w).1H NMR (400MHz, C6D6): δ = 7.08 – 6.93 (m, 4H), 4.52 (s, 1H), 3.29 (s, 3H), 2.31 (br s, 1H).13C NMR(101 MHz, C6D6): δ = 143.9, 138.9 (q, J = 2.4 Hz), 131.4, 130.4, 125.28 (q, J = 280.6 Hz),123.7, 122.8, 88.4, 82.9 (q, J = 30.6 Hz), 58.7. 19F NMR (282 MHz, C6D6): δ = –75.7(s, 3F). HRMS (APCI): Calculated for C10H8F3O2[M-H]-: 217.0482, found: 217.0452. Example 20: 3-Methoxy-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [S10] Following general procedure B using 2,2,2-trifluoro-1-(4-methoxy-2-methylphenyl)ethan-1-one (27.2mg, 0.125 mmol) in benzene (6 mL, 20 mM). The productwas obtained after automated FC (pentane / Et2O, 100:0 to 50:50) as a colorless oil (4.0 mg,0.018 mmol, 15%).IR (neat): ṽ = 3413 (w), 2943 (w), 1605 (w), 1481 (m), 1314 (w), 1275 (m), 1257 (m),1238 (m), 1162 (s), 1127 (s), 1090 (s), 1017 (m), 955 (w), 822 (w), 733 (w), 602 (w), 589 (w),549 (w), 503 (w), 473 (w), 464 (w), 453 (w), 426 (w), 413 (w). 1H NMR (400 MHz, C6D6): δ =6.90 (d, J = 8.2 Hz, 1H), 6.62 (dd, J = 8.3, 2.1 Hz, 1H), 6.46 – 6.32 (m, 1H), 3.38 (d, J = 14.3Hz, 1H), 3.21 (s, 3H), 2.75 (d, J = 14.3 Hz, 1H), 2.10 (s, 1H). 13C NMR (101 MHz, C6D6): δ =M / 65032-PCT UMZ2024-444 65162.7, 143.3, 133.6, 125.7 (q, J = 281.6 Hz), 123.6, 115.4, 108.9, 77.6 (q, J = 32.8 Hz), 55.0,41.4 (q, J = 2.4 Hz). 19F NMR (282 MHz, C6D6): δ = –81.1 (s, 3F). HRMS (ESI): Calculatedfor C10H8F3O3 [M-H]-: 217.0482, found: 217.0486. Example 21: 3-Fluoro-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [S11] Following general procedure B using 2,2,2-trifluoro-1-(4-fluoro-2-methylphenyl)ethan-1-one (24.8mg, 0.12 mmol) in benzene (6 mL, 20 mM). The product was obtained afterautomated FC (pentane / Et2O, 100:0 to 50:50) as a colorless oil (16 mg, 0.078 mmol, 65%).IR (neat): ṽ = 3375 (w), 2946 (w), 1598 (w), 1471 (m), 1427 (w), 1311 (m), 1243 (m),1158 (s), 1127 (s), 1083 (s), 1018 (m), 960 (m), 899 (w), 879 (w), 849 (m), 820 (m), 787 (w), 734 (w), 650 (w), 597 (m), 580 (m), 541 (w), 511 (w), 469 (w), 412 (w).1H NMR (400 MHz,C6D6): δ = 6.71 (dd, J = 8.2, 4.6 Hz, 1H), 6.59 (ddd, J = 10.5, 8.2, 2.4 Hz, 1H), 6.42 (dd, J =7.7, 2.1 Hz, 1H), 3.19 (d, J = 14.6 Hz, 1H), 2.56 (dt, J = 14.7, 1.2 Hz, 1H), 2.03 (s, 1H). 13CNMR (101 MHz, C6D6): δ = 165.0 (d, J = 248.6 Hz), 143.8 (d, J = 8.6 Hz), 137.3 – 137.2 (m),125.3 (q, J = 281.8 Hz), 124.4 (d, J = 9.4 Hz), 116.0 (d, J = 24.3 Hz), 111.56 (d, J = 23.1 Hz),77.3 (q, J = 32.9 Hz), 41.4 – 41.1 (m) 19F NMR (282 MHz, C6D6): δ = -81.27 (s, 3F), -107.45– -107.55 (m, 1F). HRMS (APCI): Calculated for C9H5F4O [M-H]-: 205.0282, found: 205.0281.Example 22: 3-Chloro-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [S12] Following general procedure B using 1-(4-chloro-2-methylphenyl)-2,2,2-trifluoroethan-1-one (22.7mg, 0.10 mmol) in benzene (6 mL, 20 mM). The product was obtained afterautomated FC (pentane / Et2O, 100:0 to 50:50) as a colorless solid (12 mg, 0.054 mmol,53%). M / 65032-PCT UMZ2024-444 66 M.P.: 70 – 77 °C. IR (neat): ṽ = 3361 (w), 2945 (w), 1591 (w), 1458 (w), 1426 (w),1301 (m), 1230 (w), 1167 (s), 1134 (m), 1104 (w), 1072 (m), 1049 (w), 1020 (m), 954 (w),854 (w), 819 (m), 758 (w), 715 (w), 595 (w), 505 (w), 424 (w). 1H NMR (400 MHz, C6D6): δ =6.90 (ddt, J = 7.9, 1.7, 0.9 Hz, 1H), 6.72 – 6.69 (m, 1H), 6.63 (d, J = 7.9 Hz, 1H), 3.18 (dt, J =14.7, 0.9 Hz, 1H), 2.54 (dd, J = 14.7, 1.1 Hz, 1H), 2.00 (s, 1H). 13C NMR (101 MHz, C6D6): δ= 143.5, 140.0, 140.0 (q, J = 1.9 Hz), 137.0, 128.9, 125.2 (q, J = 281.7 Hz), 124.4, 123.7,77.6 (q, J = 32.9 Hz), 41.5 (q, J = 1.9 Hz). 19F NMR (282 MHz, C6D6): δ = -81.20 (s, 3F).HRMS (ESI): Calculated for C9H5ClF3O [M-H]-: 220.9995, found: 220.9987. Example 23: 3-Chloro-8-methyl-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-trien-7-ol [S13] Following general procedure B with minor alterations using 1-(4-chloro-2-ethylphenyl)-2,2,2-trifluoroethan-1-one (78 mg, 0.33 mmol) in benzene (16.5 mL, 20 mM).The product was obtained after automated FC (pentane / Et2O, 100:0 to 50:50) as a colorlesssolid (66 mg, 0.28 mmol, 85%) and a sample suitable for X-ray analysis was obtained.M.P.: 44.4 – 53.5 °C. IR (neat): ṽ = 3359 (w), 2995 (w), 2941 (w), 2884 (w), 1588 (w),1455 (w), 1414 (w), 1339 (w), 1279 (m), 1248 (w), 1227 (w), 1162 (s), 1112 (s), 1081 (w), 1057 (s), 1013 (w), 942 (m), 896 (w), 876 (w), 820 (m), 757 (w), 740 (w), 709 (w), 653 (w),597 (w), 535 (w), 505 (w), 454 (w), 433 (w). 1H NMR (400 MHz, C6D6): δ = 6.93 (dt, J = 7.8,1.3 Hz, 1H), 6.75 (q, J = 1.1 Hz, 1H), 6.67 (d, J = 7.9 Hz, 1H), 3.30 – 3.02 (m, 1H), 2.01 (d, J= 2.4 Hz, 1H), 1.16 (dq, J = 7.4, 1.7 Hz, 3H). 13C NMR (101 MHz, C6D6): δ = 148.4, 138.4 (q,J = 2.3 Hz), 137.0, 129.1, 125.2 (q, J = 283.5 Hz), 123.8, 123.1, 79.9 (q, J = 31.1 Hz), 52.0,13.1 (q, J = 2.3 Hz). 19F NMR (282 MHz, C6D6): δ = -75.94 (s, 3F). HRMS (ESI): Calculatedfor C10H7ClF3O [M-H]-: 235.0143, found: 235.0152. Example 24: 7-Hydroxy-7-(trifluoromethyl)bicyclo[4.2.0]octa-1,3,5-triene-3-carbonitrile [S14] M / 65032-PCT UMZ2024-444 67 Following general procedure B with minor alterations using 3-methyl-4-(2,2,2-trifluoroacetyl)benzonitrile (25.6 mg, 0.12 mmol) in benzene (6 mL, 20 mM). The product wasobtained after automated FC (pentane / Et2O, 100:0 to 50:50) as a colorless solid (11.0 mg,0.052 mmol, 43%).M.P.: 142.0 – 146.5 °C. IR (neat): ṽ = 3384 (w), 2235 (w), 1427 (w), 1305 (w), 1239(w), 1166 (s), 1144 (s), 1121 (w), 1092 (w), 1073 (w), 1019 (w), 959 (w), 831 (w), 727 (w),654 (w), 604 (w), 536 (w), 506 (w), 465 (w), 431 (w). 1H NMR (400 MHz, C6D6): δ = 6.78 (dd,J = 7.8, 1.2 Hz, 1H), 6.54 (d, J = 7.7 Hz, 1H), 6.53 – 6.49 (m, 1H), 3.08 (d, J = 14.9 Hz, 1H),2.46 (d, J = 14.9 Hz, 1H), 2.12 (s, 1H). 13C NMR (101 MHz, C6D6): δ = 145.9 – 145.8 (m),142.7, 132.3, 127.2, 124.8 (q, J = 281.9 Hz), 122.8, 118.5, 115.1, 78.0 (d, J = 33.2 Hz), 41.4(q, J = 2.0 Hz). 19F NMR (282 MHz, C6D6): δ = -81.11 (s, 3F). HRMS (ESI): Calculated forC10H5F3NO [M-H]-: 212.0329, found 212.0336.C) Effect of Substituents on ReactivityIn order to assess the effect of different substituents on the photocyclization of 1 to 3,reactions were stopped at a specific time point with incomplete conversion. Samples wereprepared using general procedure B in degassed C6D6 (20 mM). After sample preparation,an internal standard was added, and the concentration verified by1H and19F NMR analysis.All samples were irradiated for exactly 3 h in a single experiment using a LuzchemPhotoreactor equipped with 10 8 Watt LZC-UVA (355 nm) lamps equipped with a samplecarousel. This ensures that all reactions are run under identical conditions and can be accurately compared. The experiments were in triplicates whereas yield and conversion were determined by1H NMR (mesitylene) or19F NMR (PhCF3) and are given as mean values withstandard deviation. The data is summarized in Table 2.Table 2: Comparison of substrate reactivity.M / 65032-PCT UMZ2024-444 68 Entry Substrate standardConversion (%) Yield (%)R1= CH31 R2= H1a mesitylene 16.9 ~1R3= H R1= CH2F 2 R2= H1b mesitylene 7.7 ± 0.7 ~1R3= H R1= CHF23 R2= H1c mesitylene 55.2 ± 1.3 47.5 ± 0.6R3= H R1= CF3 4 R2= H1d PhCF3 66.0 ± 0.4 66.0 ± 0.4R3= H R1= CF3 5 R2= CH34 PhCF3 33.0 ± 0.3 27.4 ± 0.1R3= H R1= CF3 6 R2= (CH3)2 S1 PhCF338.0 ± 1.75 0R = H R1= CF37 R2= OCH3 S3 PhCF3337.2 ± 0.8 29.9 ± 1.9R = H R1= CF38 R2= HS4 PhCF3 90.9 ± 1.4 63.0 ± 0.5R3= OCH3 R1= CF38 R2= HS5 PhCF3 68.7 ± 0.2 59.6 ± 0.4R3= F R1= CF39 R2= HS6 PhCF3 79.3 ± 0.7 73.9 ± 0.7R3= Cl R1= CF3 10 R2= CH3S7 PhCF3 41.2 ± 0.8 36.3 ± 0.3R3= Cl R1= CF3 11 R2= HS8 PhCF3 48.4 ± 4.5 42.2 ± 3.1R3= CN Yields determined using1H (mesitylene) or19F NMR (PhCF3). Conversion and yield are stated as mean values of three experiments. M / 65032-PCT UMZ2024-444 69 The data from Table 2 is visualized in Fig.5 in a bubble diagram. The conversion of1d to 3d was taken as a reference and reaction rates were calculated relative to thistransformation. The energy density of 3d (58 kJ / mol) was used as a rough estimation tocalculate the energy densities of all substituted compounds. While this probably is a good measure for para-substituted examples and for H / F displacements, we are aware that all changes in the molecular structure can result in a different energetic property of the molecule and hence can lead to variations in the absolute values of the energy density of thesubstance. This holds especially true for all variations on the cyclobutanol core (e.g. ortho-Et,iPr substitution). However, these substitutions were found to lead to poor reaction rates and are therefore still included in the graphical representation (see Fig 5).D) Optimization of reaction conditionsD1) Solvent screening Table 3: Solvent screening for the conversion of 1d to 3d.Entry Solvent Yield 3d / %1 MeCN 32a2 MeOH 53 EtOAc 70a4 hexane 34b5 CyH 41b6 benzene 45M / 65032-PCT UMZ2024-444 70Reactions run on 0.05 mmol scale in degassed solvent (20 mM) under inert gas atmosphere. After thereaction, solvent was removed under reduced pressure and residue dissolved in CDCl3. Yields determined using1H NMR with mesitylene as internal standard.aSeveral signals detected in19F NMR.bOxygen side product observed. Benzene was selected as the ideal solvent for the transformation because no sideproducts were detected in 19F and 1H NMR. Additionally, the solvent was easily removableunder reduced pressure. Solvents with higher boiling points like toluene or PhCF3, although performing comparably well during the photocyclization, were excluded due to severematerial loss during solvent evaporation.D2) Oxygen sensitivityThe reaction of 1d to 3d is very sensitive to oxygen and peroxide 8d is formedalongside 3d when running the reaction under aerobic conditions.8d can be isolated viacolumn chromatography as a white solid, which was found to be stable over an extendedperiod of time when kept at –20 °C. However, 8d was found to slowly decompose in solutionto form hemiacetals 9d, which are insoluble in benzene and crush out of the solution. 8d 9dD3) Scale-upThe scalability of the reaction was accessed by running the reaction on a 4.7 mmolscale: Following general procedure B with minor alterations using 2,2,2-trifluoro-1-(o-tolyl)ethan-1-one (889 mg, 4.73 mmol) in benzene (10 mL, 473 mM) for 90 h. The productwas obtained after automated FC (pentane / Et2O, 70:30) as a colorless solid (872 mg,4.63 mmol, 98%).To decrease the reaction time, we switched to using a Kessil 45W PR160L 370nmGen2 LED and were able to decrease the reaction time to 10 h while simultaneouslyincreasing the concentration to 0.9 M.M / 65032-PCT UMZ2024-444 71 Following general procedure C using 2,2,2-trifluoro-1-(o-tolyl)ethan-1-one (2.16 g,10.7 mmol) in benzene (12 mL, 889 mM) for 10 h at 22 °C. Analysis by 19F NMR showed99% yield of 3d. The product was obtained after FC (pentane / Et2O, 75:25) and bulb-to-bulbdistillation (110 °C, 0.8 mbar) as a colorless solid (1.59 g, 8.43 mmol, 79%).E) Photoisomerization studiesE1) Reaction set-upThe isomerization process was studied using 19F NMR. For irradiation experiments,oven dried NMR Tubes with a septum cap were charged with degassed C6D6 (0.5 mL, 3xfreeze-pump-thaw) in a Glove Box. 1d was added under inertgas atmosphere via amicrosyringe through the septum cap and PhCF3was added as an internal standard. Thetubes were irradiated using a Luzchem LZC-ORG photoreactor equipped with 10 8 WattLZC-UVA mercury lamps (355 nm) lamps or a Kessil 45W PR160L 370nm Gen2 LED at1 cm distance.E2) Kinetic studiesSamples of 1d (200 mM, 20 mM, 2 mM) were irradiated at 370 nm for selected timeintervals at 21 °C. The irradiation time was limited with a timer, that cut the power of the lampafter the selected interval. The progress of the reaction was monitored by19F NMR againstPhCF3 as an internal standard. The data is summarized in Table 4and the concentration [3d]versus time in seconds is visualized.Table 4: Results of the interval irradiation of 1d at various concentrations in degassed C6D6at 22 °C with 370 nm. M / 65032-PCT UMZ2024-444 72 Yield 3d / %Yield 3d / %Yield 3d / % Entry time / min time / s(200 mM) (20 mM) (2 mM)1 0 0 0 0 02 5 300 13 14 173 15 900 36 38 404 30 1800 60 64 655 45 2700 75 81 786 60 3600 85 89 857 90 5400 94 97 968 120 7200 98 >99 >99E3) Effect of temperatureSamples of 1d (20 mM) were irradiated in a water bath equipped with a thermal probefor 30 minutes at 3 cm distance. The data is summarized in Table 5.Table 5: Temperature dependent conversion of 1d to 3d (20 mM, C6D6) in a water bath witha 370 nm lamp at 3 cm distance. M / 65032-PCT UMZ2024-444 73 E4) Use of sun lightSamples of 1d (20 mM, C6D6) were subjected to irradiation in direct sunlight on threedifferent days for 4 h from (12:00h to 16:00h) using a simple reflector setup in Mainz,Germany (49°59'28.3"N 8°13'57.0"E). The NMR tube was secured with a clamp and areflector was adjusted behind the tube to provide additional reflection of incoming sunlight. The apparatus was checked every hour and adjusted to match the travel of the sun. The data is summarized in Table 6.Table 6: Sunlight reaction of 1d (20 mM, C6D6) for 4 h. Entry T / °C Weather Yield 3d / %1 28 cloudy 812 28 clear sky 95M / 65032-PCT UMZ2024-444 74F) Base screeningDifferent organic bases were examined for their ability to catalyze back isomerization of 3d to1d.Samples of 3d were dissolved in C6D6 in an NMR tube and base was added. The tubes wereplaced in a heated metal block and analyzed by1H and19F NMR. The results are shown in Table 7:Table 7: Base screening for the ring-opening reaction. M / 65032-PCT UMZ2024-444 75Reactions run on 0.05 mmol scale in C6D61under inert gas atmosphereMR and19F NMR with PhCF3 as internal standaa. Yields de1terminedusing H N39brd. HCF detected in F NMR. 0.2 eq. used. Data not shownEvolution of HCF3 was evident from1H and19F NMR with the distinct coupling pattern according to literature. Data not shownG) Cycle of photoisomerization and base-catalyzed openingThe isomerization process was studied using 19F NMR. A sample of 1d (99.6 mg,492 μmol, 1.00 eq.) was dissolved in benzene (5 mL, 100 mM) in an oven dried Schlenk-flaskunder inert gas atmosphere and the mixture was degassed (3 ^ freeze-pump-thaw, liquidnitrogen). The solution was irradiated for 3 h with a 40 W 370 nm Gen 2 KSPR160L KessilLED from 1 cm distance. PhCF3 (18.0 mg, 15.0 μL, 123 μmol, 0.25 eq.) was added using aHamilton syringe as an internal reference. The reaction yield in both transformations, that is photocyclization and opening was found to be unchanged upon addition of PhCF3andmesitylene as internal reference compounds for NMR analysis. A sample (0.1 mL) wastaken, diluted with C6D6 (0.4 mL) and subjected to 19F NMR analysis. (1,5,7-Triazabicyclo[4.4.0]dec-5-ene on polystyrene support (Biotage® PS-TBD, 1.3 mmol / g,196 mg, 255 μmol, 0.518 eq.) was added to a 10 mL flask and the mixture was transferredalong with the sample taken for NMR analysis. The NMR tube was washed with benzene(2 x 0.5 mL), then the flask (3 x 1 mL). The mixture was placed in a heating block and stirredfor 24 h at 30 °C. PhCF3 (18.0 mg, 15.0 μL, 123 μmol, 0.25 eq.) was added, the mixture wasstired for 5 minutes, sonicated for 3 minutes and another sample was taken for NMR analysis(0.1 mL diluted with 0.4 mL C6D6). The mixture was filtered over a 2 cm thick celite pad with0.5 cm sand on top, the NMR tube was transferred over the filter and washed (2 x 0.5 mLbenzene) and the flask was rinsed (3 x 1mL benzene). Then the filter was washed withportions of benzene (25 mL total), PhCF3 (18.0 mg, 15.0 μL, 123 μmol, 0.25 eq.) was addedand another NMR sample (0.3 mL, diluted with 0.2 mL C6D6) was taken. The sample wastransferred back (2 x 0.5mL benzene), degassed (3 ^ freeze-pump-thaw, liquid nitrogen) andirradiated for 3 h with a 40 W 370 nm Gen 2 KSPR160L Kessil LED from 1 cm distance.PhCF3 (18.0 mg, 15.0 μL, 123 μmol, 0.25 eq.) was added and the final NMR sample wastaken (0.3 mL, diluted with 0.2 mL C6D6).A second run was performed using 1d (101 mg, 498 μmol, 1.00 eq.), PS-TBD(173 mg, 224 μmol, 0.451 eq.) and benzene (5 mL, 100 mM).The combined data is summarized in Table 8. M / 65032-PCT UMZ2024-444 76Table 8: Irradiation opening cycle data. 1st irradiation 99.8% ± 0.1% yieldaBase opening 90.1% ± 0.5% yieldaRecovery 98.1% ± 1.3% yield2nd irradiation 98.8% ± 0.6% yieldaH) Determination of the thermal isomerization half-lifeSamples of solid 3d (5.64 mg, 30.0 μmol, 1.00 eq.) were added to NMR tubes, thatwere fused to a closed vial under inert-gas-atmosphere using a propane torch. The tubeswere placed in a metal heating block at 220 °C and removed after 1 to 32 hours. The tubeswere opened with a glass cutter and rinsed with CDCl3. PhCF3 (5 µL, 41µmol, 1.37 eq.) wasadded as an internal standard and the progress of the thermal isomerization was measuredby 1 H and 19F NMR. As the MOST system is unimolecular, first order kinetics apply for themodelling of the thermal rate of back conversion. The results are summarized in Table 9:Table 9: Summarized data of the thermal heat opening of 3d.Value 473.15 K 493.15 K 513.15 Kk1 (1 / s) / s-15.39 x 10-61.91 x 10-59.86 x 10-5 / kJ / mol 165 167 167k2 (298.15 K)1.03 x 10-164.85 x 10-175.13 x 10-17 / s-1 / years 2.13 x 108 4.53 x 108 4.29 108M / 65032-PCT UMZ2024-444 77I) Sensitivity screeningSamples of 1d were irradiated with a 40 W 370 nm Gen 2 KSPR160L Kessil LEDfrom 2 cm distance in a water bath at 30 °C for 8h.A stock solution was prepared by dissolving 1d (27.14 mg, 144 µmol, 1.00 eq.) inC6D6 (7 mL, 20 mM) and the solution was degassed (3 ^ freeze-pump-thaw). PhCF3(17.0 µL, 139 µM, 0.96 eq.) was added as an internal reference and the concentrationverified via 19F NMR. Samples were again prepared in a Glove Box. The solution for the bigscale was prepared with 1d (37.51 mg, 0.2 mmol, 1.00 eq.) in benzene (10 mL, 20 mM) andthe mixture was degassed (3 ^ freeze-pump-thaw). PhCF3 (5 µL, 41 µmol, 0.21 eq.) wasadded with a stir bar. For high and medium concentration (entries 1 & 2, Table 10), ovendried NMR Tubes with a septum cap were charged with degassed C6D6 (0.5 mL, 3 ^ freeze-pump-thaw) in a Glove Box. 1d was added under inertgas atmosphere via a microsyringethrough the septum cap and PhCF3 was added as an internal standard. The samples were subjected to19F NMR to verify the concentration before the irradiation. The results are summarized in Table 10 and deviations from the standard reaction conditions are listed. The data is visualized in Fig.2D. M / 65032-PCT UMZ2024-444 78 Table 10: Evaluation of the robustness of the reaction conditions after 8 h. Entry Modification Procedure Yield (%) Deviation (%)1 high c 200 mM 96 –32 medium c 40 mM 95 –43 low c 10 mM 99 04 high H2O +5µL H2O >99 15 medium O2 no degassing 79 –206 high O2 purge with O2 76 –227 control 1 >99 18 high T 45 °C >99 19 low T 20 °C 99 010 low I d = 10 cm 98 –111 medium I d = 5 cm 99 012 big scale 2 mM scale 92 -7Further synthesis examplesa) Synthesis of Starting MaterialsExample 25: 2,2,2-Trifluoro-1-(2-fluoro-6-methyl-phenyl)ethanol M / 65032-PCT UMZ2024-444 79 To a stirred solution of 2-fluoro-6-methylbenzaldehyde (0.70 g, 5.07 mmol, 1.00equiv) and trimethyl(trifluoromethyl)silane (0.90 mL, 6.08 mmol, 1.20 equiv) in dry THF (20mL) at 0°C was added TBAF (6.1 mL, 6.1 mmol, 1.00M, 1.20 equiv) dropwise. The solutionwas allowed to warm up to room temperature and stirred for 16 h at the same temperature.The reaction was quenched with aqueous saturated NH4Cl solution (20 mL), the organicphase was separated, and the aqueous phase was extracted with DCM (3 x 20 mL). Thecombined organic fractions were dried over MgSO4, filtered and evaporated under reduced pressure. Purification by flash chromatography on silica gel with Et2O (0 to 20%) in n-Pentane and bulp-to-bulp distillation (60 °C, 1.0 mbar) afforded the desired product 2,2,2-trifluoro-1-(2-fluoro-6-methyl-phenyl)ethanol as a colorless oil (890 mg, 4.28 mmol, 84%yield). 1H NMR (400 MHz, C6D6): δ = 6.70 (ddd, J = 8.3, 7.6, 5.9 Hz, 1H), 6.63 – 6.48 (m,2H), 5.16 (tt, J = 7.8, 6.8 Hz, 1H), 2.59 – 2.51 (m, 1H), 2.09 (s, 3H). 13C NMR (101 MHz,C6D6): δ = 163.4, 160.9, 140.4 (d, J = 2.7 Hz), 130.5, 130.4, 127.4 (d, J = 2.9 Hz), 125.5 (qd,J = 283.2, 1.9 Hz), 120.2 (d, J = 10.3 Hz), 113.6 (d, J = 23.5 Hz), 68.4 (qd, J = 33.5, 4.0 Hz),19.8 (p, J = 2.2 Hz). 19F NMR (282 MHz, C6D6): δ = -77.12 (dd, J = 10.3, 7.7 Hz), -115.79 (pt,J = 10.8, 6.2 Hz). HRMS (ESI): Calculated for C9H7F4O [M-H]-: 207,0438, found: 207.0429.Example 26: 2,2,2-Trifluoro-1-(2-fluoro-6-methyl-phenyl)ethanone To a stirred solution of 2,2,2-trifluoro-1-(2-fluoro-6-methyl-phenyl)ethanol (0.70 g, 3.36mmol, 1.00 equiv) in DCM (20 mL) at 0 °C was added portionwise DMP (1.7 g, 4.04 mmol,1.20 equiv) and the mixture was stirred at the same temperature for 1 h. After returning toroom temperature, the reaction was quenched with aqueous saturated NaHCO3 solution (20mL). The organic phase was separated, and the aqueous phase was extracted with DCM (3x 20 mL). The combined organic fractions were dried over MgSO4, filtered and evaporatedunder reduced pressure. Purification by flash chromatography on silica gel with n-Pentaneand bulp-to-bulp distillation (50 °C, 1.1 mbar) afforded the desired product 2,2,2-trifluoro-1-(2-fluoro-6-methyl-phenyl)ethanone as a colorless oil (620 mg, 3.01 mmol, 89% yield). 1HNMR (400 MHz, C D ): δ = 136 6 6.67 – 6.58 (m, 1H), 6.44 – 6.32 (m, 2H), 1.87 (s, 3H). C NMR(101 MHz, C6D6): δ = 185.2 (q, J = 38.4 Hz), 162.1, 159.6, 133.5, 133.4, 126.9 (d, J = 2.8M / 65032-PCT UMZ2024-444 80Hz), 121.8, 121.7, 116.1 (q, J = 291.2 Hz), 113.4, 113.2, 19.0 (d, J = 2.4 Hz). 19F NMR (282MHz, C6D6): δ = -77.17 (d, J = 15.7 Hz), -111.65 (qdd, J = 15.7, 9.5, 5.4 Hz). HRMS (ESI):Calculated for C9H5F4O [M-H]-: 205,0282, found: 205.0290. Example 27: 2-(o-Tolyl)-2-oxo-acetic acid O OH O To a stirred solution of 1-(o-tolyl)ethanone (2.0 g, 14.9 mmol, 1.00 equiv) in dry pyridine (15 mL) was added SeO2 (3.3 g, 29.8 mmol, 2.00 equiv) and the mixture was stirred at 110 °C for 16 h. After cooling down to room temperature, the solution containing precipitated selenium was filtered, and the filtration was then treated with an aqueous NaOH solution (2 N, 15 mL) and the mixture was extracted with EtOAc (3 x 50 mL). The aqueous layer was acidified using 2 N HCl to pH 1~2 and extracted with EtOAc (3 × 50 mL). The combined organic layers were dried over anhydrous sodium sulfate and concentrated under reduced pressure to provide 2-(o-tolyl)-2-oxo-acetic acid as a yellow oil (2.30 g, 14.0 mmol,94% yield). The compound was used without further purification. 1H NMR (400 MHz, C6D6): δ= 7.91 – 7.78 (m, 1H), 6.95 (tt, J = 7.6, 1.7 Hz, 1H), 6.85 (dt, J = 11.3, 5.8 Hz, 1H), 6.78 (d, J= 7.6 Hz, 1H), 4.97 (s, 1H), 2.39 (dd, J = 4.8, 2.2 Hz, 3H). 13C NMR (101 MHz, C6D6): δ =188.5, 165.1, 141.7, 133.7, 133.1, 132.4, 131.3, 126.0, 21.5. HRMS (ESI): Calculated forC9H7O3 [M-H]-: 163.0400, found: 163.0405. Example 28: Methyl 2-(o-tolyl)-2-oxo-acetate To a solution of 2-(o-tolyl)-2-oxo-acetic acid (1.00 g, 6.09 mmol, 1.00 equiv) in dry DCM (20 mL) was added oxalyl dichloride (630 μL, 7.31 mmol, 1.20 equiv) and two drops of M / 65032-PCT UMZ2024-444 81 DMF. The mixture was stirred for 2 h at 25 °C. After this time, the solvent was then removed under reduced pressure. The resulting α-acyl chloride was dissolved in DCM (20 mL), MeOH (0.5 mL, 12.2 mmol, 2.00 equiv) and NEt3 (1.90 mL, 13.4 mmol, 2.20 equiv) were added 0 °C and stirred at 25 °C during 16 h. The reaction was quenched with aqueous saturated NH4Cl solution, the organic phase was separated, and the aqueous phase was extracted with DCM (3 x 20 mL). The combined organic fractions were dried over MgSO4, filtered and evaporated under reduced pressure. Purification by flash chromatography on silica gel with EtOAc (0 to 5%) in n-Hexane afforded the desired product methyl 2-(o-tolyl)-2-oxo-acetate as a yellowishsolid (0.97 g, 5.44 mmol, 89% yield). 1H NMR (400 MHz, C6D6): δ = 7.62 (dd, J = 7.8, 1.4Hz, 1H), 6.97 (td, J = 7.5, 1.5 Hz, 1H), 6.88 – 6.82 (m, 1H), 6.80 (ddt, J = 7.7, 1.5, 0.7 Hz,1H), 3.30 (s, 3H), 2.45 (s, 3H). 13C NMR (101 MHz, C6D6): δ = 188.9, 165.4, 141.5, 133.5,132.5 (d, J = 2.7 Hz), 131.7, 126.0, 51.9, 21.4. HRMS (ESI): Calculated for C10H9O3 [M-H]-:177.0557, found: 177.0567.b) Synthesis of cyclization productsExample 29: 5-fluoro-7-(trifluoromethyl)bicyclo[4.2.0]octa-1(6),2,4-trien-7-ol 2,2,2-trifluoro-1-(2-fluoro-6-methylphenyl)ethan-1-one (200 mg, 970 μmol, 1.00 equiv) (Example 26) was dissolved in benzene (50 mL), degassed (3 x freeze-pump-thaw) and was irradiated using a Kessil 45W PR160L 370nm Gen2 LED at 2 cm distance for 16 h at 25 °C. The solvent was removed under reduced pressure and purification by flash chromatographyon silica gel with Et2O (0 to 20%) in n-Pentane and bulp-to-bulp distillation (80 °C, 0.8 mbar)afforded the desired product 5-fluoro-7-(trifluoromethyl)bicyclo[4.2.0]octa-1(6),2,4-trien-7-olas a colorless oil (170 mg, 825 μmol, 85% yield). 1H NMR (400 MHz, C6D6): δ = 6.81 (ddd, J= 8.6, 7.2, 4.6 Hz, 1H), 6.55 (t, J = 8.5 Hz, 1H), 6.44 (ddt, J = 7.2, 1.3, 0.6 Hz, 1H), 3.27 (d, J= 14.6 Hz, 1H), 2.68 (dq, J = 14.6, 1.2 Hz, 1H), 2.33 (s, 1H). 13C NMR (101 MHz, C6D6): δ =156.8, 154.2, 144.6 (d, J = 6.9 Hz), 133.4 (d, J = 6.2 Hz), 126.9 (dq, J = 15.2, 1.8 Hz), 125.0(qd, J = 281.7, 1.7 Hz), 122.1 (d, J = 3.9 Hz), 121.5, 121.3, 119.8 (d, J = 4.6 Hz), 115.1,114.9, 77.4 (qd, J = 34.0, 1.8 Hz), 41.9 (t, J = 2.0 Hz). 19F NMR (282 MHz, C6D6): δ = -80.84M / 65032-PCT UMZ2024-444 82(d, J = 2.7 Hz), -117.44 (dq, J = 4.9, 2.3 Hz). HRMS (ESI): Calculated for C9H5F4O [M-H]-:205.0282, found: 205.0278. Example 30: Methyl 7-hydroxybicyclo[4.2.0]octa-1,3,5-triene-7-carboxylate Methyl 2-(o-tolyl)-2-oxo-acetate (480 mg, 2.69 mmol, 1.00 equiv) (Example 28) wasdissolved in benzene (50 mL), degassed (3 x freeze-pump-thaw) and was irradiated using a Kessil 45W PR160L 370nm Gen2 LED at 2 cm distance for 16 h at 25 °C. The solvent was removed under reduced pressure and purification by flash chromatography on silica gel with Et2O (0 to 20%) in n-Pentane afforded the desired product methyl 7- hydroxybicyclo[4.2.0]octa-1,3,5-triene-7-carboxylate as a white solid (420 mg, 2.36 mmol,88% yield). M.P.: 55 – 58 °C. 1H NMR (400 MHz, C6D6): δ = 7.09 – 7.02 (m, 1H), 7.01 – 6.95(m, 2H), 6.89 (dq, J = 7.3, 1.0 Hz, 1H), 4.03 (s, 1H), 3.60 (dd, J = 13.4, 2.8 Hz, 1H), 3.26 (dd,J = 13.6, 2.4 Hz, 1H), 3.14 – 3.08 (m, 3H). 13C NMR (101 MHz, C6D6): δ = 175.1, 146.5,143.4, 130.1, 127.9, 123.6, 121.4, 78.5, 52.4, 45.8. HRMS (APCI): Calculated for C10H10O3[M]·+: 178.0624, found 178.0602. Further test example Differential scanning calorimetry (DSC) Differential scanning calorimetry (DSC) was performed using a μRC® micro Reaction Calorimeter (Thermal Hazard Technology, THT) and analysis was conducted using the μRC Analysis software 2.6.5. For each measurement, two identical samples were added to the sample and thereference chamber. The calorimeter features a syringe holder, which can be loaded withprecision syringes and allows the controlled release of substance via a motorized piston tothe sample chamber. The syringe is equilibrated with the sample chamber to achieveisothermal addition of substances. Calorimetric measurements of the ring opening reaction of different high energyisomers (B) after addition of a base catalyst (C) (here methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (Me TBD)) as defined herein above in a suitable organic solvent, as for example anM / 65032-PCT UMZ2024-444 83aprotic organic solvent as defined above, were performed and the respective ΔHiso valueswere determined. The following results were obtained: Compound of example 17: ΔHiso= 264.5 ± 3.2 J·g⁻¹ ≈ 49.8 ± 0.6 kJ·mol⁻¹ Compound of example 29: ΔHiso = 389.8 ± 1.8 J.g-1 ≈ 80.4 ± 0.4 KJ.mol-1The disclosure of any prior art reference as cited herein is incorporated by reference. M / 65032-PCT

Claims

UMZ2024-444 84 Claims1. A molecular solar thermal (MOST) system, comprising a liquid organic phase,which contains a) in its low–energy ground state primarily at least one solar light excitablelow-energy parent isomer (A), which is excitable by solar light in a wavelengthrange of about 300 to 600 nm,b) in its excited state primarily at least one metastable high–energy photoisomer (B) generated by solar light in a wavelength range of about 300 to 600 nmvia photochemical conversion from said at least one solar light excitable low-en- ergy parent isomer (A), wherein said at least one metastable high–energy photo isomer (B) is a compound ofgeneral formula (I)wherein n is an integer of 1, 2 or 3, R1 is selected from –C (halogen)3-aHa, wherein a is 0 or 1, and halogen is se-lected from F, Cl or Br, in particular –CF3; aryl; cyano; C1-C6-alkoxy, in partic-ular methoxy; or -C(O)OR, wherein R is C1-C6-alkyl, in particular methyl;R2and R2aare identical or different and independently of each other selected from H and D; or one of the residues R2 and R2a is selected from linear orbranched C1-C6-alkyl or linear or branched C1-C6-alkoxy, like methyl or meth-oxy, and the other of the residues R2and R2ais selected from H or D; R2bis selected from H or D; Ar represents an aromatic mono- or polycyclic, in particular mono- or bicyclic,condensed aromatic ring system or conjugated aromatic ring system, inwhich ring system at least one hydrogen atom of the aromatic ring systemM / 65032-PCTUMZ2024-444 85 may be further substituted by one or more identical or different ring substitu-ents R3, wherein R3 is selected from cyano, halogen, linear or branched C1-C6-alkyl, inparticular methyl; linear or branched C1-C6-alkoxy, in particular methoxy;and -C(O)R1, wherein R1 is as defined aboveor a constitutional isomer or stereoisomer of the compound of formula I;or a mixture of at least two constitutional isomers or a mixture of at least two ste-reoisomers or a mixture of at least one constitutional isomer and at least one ste-reoisomer;said solar light excitable low-energy parent isomer (A) is a compound excitableby solar light in the wavelength range of 300 to 600 nm and having the general formula (II)wherein n, Ar, R1, R2,R2a, R2band R3are as defined above; and or a constitutional isomer or stereoisomere of the compound of formula II;or a mixture of at least two constitutional isomers or a mixture of at least two ste-reoisomers or a mixture of at least one constitutional isomer and at least one ste- reoisomer; and optionally further comprising an immobilized or non-immobilized form of at least one organic strongbase catalyst (C), in particular at least one organic base selected from the groupof organic strong bases or in particular superbases; each of which catalyze thethermal re-conversion of the high energy photo isomer (B) via anion-acceleratedM / 65032-PCTUMZ2024-444 86 electro-cyclic ring opening into the corresponding parent isomer (A) by settingfree thermal energy as stored by (B).

2. The MOST system of claim1, wherein said thermal re-conversion occurs at atemperature of at least 20°C.

3. The MOST system of claim 1 or 2, wherein the organic strong base catalyst is se-lected from organic superbases.

4. The MOST system of claim 3, wherein said organic strong bases are selectedfrom organic superbases of the amidine class, the guanidine class or the phos-phazene class; or are selected from organic strong diazabicyclo alkanes or di-azabicyclo alkenes, like in particular 1,8-diazabicyclo[5.4.0]undec-7-ene or 1,4-diazabicyclo[2.2.2]octane (DABCO), more particularly DABCO; or an immobilizedderivative thereof, covalently bound to inert carrier beads, particularly microbeads of an average size range of 75 – 150 µm.

5. The MOST system of anyone of the preceding claims, wherein the base C is abase comprising a) a guanidine-type organic superbase of the general formula IIIawherein Ra is selected from H, linear or branched C1-C6-alkyl, or mono- or polycyclic,aromatic or non-aromatic C5 to C16 residues, optionally substituted with at least one basic residue comprising at least one basic nitrogen atom, M / 65032-PCTUMZ2024-444 87 Rb and Rc independently of each other represent H, C1-C6-alkyl, optionallysubstituted aryl or heteroaryl, optionally substituted cycloalkyl, optionally sub- stituted hetero-cycloalkyl, andRdand Reindependently of each other represent H, C1-C6-alkyl, optionally substituted aryl or heteroaryl, optionally substituted cycloalkyl, optionally sub- stituted hetero-cycloalkyl or one residue of Rband Rcand one residue of Rdand Retogether with the nitro- gen atoms to which they are attached to, form a heterocyclic, saturated ornon-saturated 5 -to 7-membered ring; or Raand one of the residues Rband Rcor one of the residues Rdand Reto- gether with the nitrogen atoms to which they are attached to, form a hetero- cyclic, saturated or non-saturated 5 -to 7-membered ring; or of the general formula IIIbwherein A and B independently of each other form a 5-to 7-membered heterocy- clic saturated or unsaturated ring; and R6is selected from H or linear or branched C1-C6-alkyl,b) an amandine-type organic superbase of the general formula IIIcM / 65032-PCTUMZ2024-444 88wherein Ra, Rb, Rcand Rdare as defined above; or Raand one of the residues Rband Rctogether with the carbon or nitrogen at- oms to which they are attached to, form a heterocyclic, saturated or non-sat- urated 5 -to 7-membered ring; and / or Rdand one of the residues Rband Rctogether with nitrogen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7- membered ring; orc) a phosphazene-type organic superbase of the general formula IIIdwherein, Rais as defined above; Rb, Rc, Rdand Reare as defined above, Rfand Rghave the same meanings as defined above for Rb, Rc, Rdand Reand additionally M / 65032-PCTUMZ2024-444 89 Rband Rctogether and / or Rdand Retogether and / or Rfand Rgtogether form a residue of the formula =P(N-( C1-C6-alkyl)2)3or Rband Rctogether and / or Rdand Retogether and / or Rfand Rgtogether with the nitrogen atom which they are attached to form a 5- to 7-membered satu-rated or unsaturated heterocyclic moiety; or one residue of Rband Rcand one residue of Rdand Retogether with the nitro- gen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7-membered ring; or one residue of Rband Rcand one residue of Rfand Rgtogether with the nitro- gen atoms to which they are attached to, form a heterocyclic, saturated or non-saturated 5 -to 7-membered ring; or one residue of Rdand Reand one residue of Rfand Rgtogether with the nitro- gen atoms to which they are attached to, form a heterocyclic, saturated ornon-saturated 5 -to 7-membered ring. or an immobilized derivative of a compound of formula IIIa, IIIb, IIIc or IIId, in par- ticular a derivative of compound of formula IIIa, IIIb, IIIc or IIId covalently boundto an inert carrier bead, particularly microbeads in an average size range of 75 – 150 µm.

6. The MOST system of claim 5, wherein C is a base comprising a guanidine typesuperbase selected from a compound of the general formula IVwherein M / 65032-PCTUMZ2024-444 90 R6is H or C1-C6-alkyl or a amidine-type superbase selected from a compound of general formula Vwherein nis an integer of 1 to 4;or a phosphazene type superbase of the formula IXor an immobilized derivative of a compound of formula IV or V, in particular a derivative of compound of formula IV or V covalently bound to inert carrier beads, particularly microbeads of an average size range of 75 – 150 µm.

7. The MOST system of claim 1, wherein isomer (A) is ortho-methyl-trifluoroaceto-phenone (MTA) of formula VI;(VI) M / 65032-PCTUMZ2024-444 91 isomer (B) is benzo-trifluoromethylcyclobutanol (BTC) of formula VII:and base C is a guanidine type superbase of formula VIIIor an immobilized derivative of a compound of formula VIII, in particular a deriva-tive of compound of formula VIII covalently bound to inert carrier beads, particu-larly microbeads of an average size range of 75 – 150 µm.

8. The MOST system of anyone of the claims 5 to 7, wherein said carrier beads arenon-soluble in the liquid phase of the MOST system.

9. The MOST system of anyone of the preceding claims, wherein the liquid phasecomprises at least one organic aprotic organic solvent, in particular at least one aromatic solvent, more particularly a solvent selected from benzene, toluene, or cyclic or non-cyclic aliphatic solvents, like in particular xylole und n-heptane, n- hexane or cyclohexane.

10. A method of storing solar thermal energy, which method comprises exposingleast one low-energy parent isomer (A) as defined in claim 1 dissolved in a liquidorganic medium to solar light for a period of time sufficient to photo isomerize at least one isomer (A) as defined in claim 1 into its corresponding metastable high-M / 65032-PCTUMZ2024-444 92 energy isomer (B) as defined in claim 1, wherein in particular solar energy is sta-bly stored for at least 1 month, particularly at least 1 year, more particularly more than 5 years.

11. A method of releasing stored solar thermal energy, which method comprises con-tacting least one metastable high-energy photo isomer (B) as defined in claim 1dissolved in a liquid organic medium with a base catalyst (C) as defined in claim1 as defined above catalyzing the terminal back-conversion of the photo isomer(B) into the corresponding parent isomer (A) as defined in claim 1, wherein inparticular the stored energy as represented by the energy difference ΔHstorage cor-responding to the energy difference between isomer (A) and (B) as defined inclaim 1 is set free.

12. A method for reversibly storing solar thermal energy, which method comprisesapplying a MOST system as defined in anyone of the claims 1 to 9.

13. The method for reversibly storing solar thermal energy of claim 12, which methodcomprises a) exposing at least one low-energy parent isomer (A) as defined in claim 1dissolved in a liquid organic medium to solar light comprising light of awavelength in the range of 300 to 600 nm for a period of time sufficient to photo isomerize at least one compound (A) as defined in claim 1 into itsmetastable high-energy photo isomer (B) as defined in claim 1 in order toobtain a high-energy storage medium; b) storing said energy-rich medium for a prolonged period of time;c) contacting said high-energy medium with an immobilized base catalyst (C)as defined in claim 1 catalyzing the terminal back-conversion of the photoisomer (B) into the corresponding parent isomer(A) by setting free thermal energy as stored by (B) in order to obtain a thermally heated medium; andd) withdrawing thermal energy from said thermally heated medium so as toobtain the initial low-energy medium comprising said at least one low-en-ergy parent isomer (A).

14. A device selected from a solar thermal energy storage device, which comprisesat least one metastable high–energy photo isomer (B) as defined in claim 1. M / 65032-PCTUMZ2024-444 9315. The solar thermal energy storage device of claim 14, comprising a storage vesselT3 containing said medium comprising at least one metastable high-energy photoisomer (B) as defined in claim 1, which storage device further comprises a reac-tor module R containing immobilized catalyst (C) as defined in claim 1 for thecontrolled release of stored energy upon getting into contact with the at least one metastable high-energy photo isomer (B).

16. The use of a compound of general formula (I) as defined above and / or of a com-pound of general formula (II) as defined above for a reversible storing of solar thermal energy.

17. A solar thermal energy capture device (SC), which comprises a transparent toplayer permeable for solar light at least in a wavelength range above 300 nm, and abelow said transparent top layer an energy capture compartment (receivingtank T2) optionally provided with a solar light permeable bottom layer, further comprising an inlet for an energy capture medium comprising at least one solar light excitable organic compound (A) of formula (II) as defined in claim 1 and anoutlet for an energy capture medium enriched with at least one metastable high- energy photo isomer (B) of formula (I) as defined in claim 1 , which energy cap-ture medium traverses said device in a directed flow from the inlet to the outlet.

18. A combined device for capturing solar thermal energy and solar photoelectric en-ergy, comprising an upper solar thermal capture device SC according to claim 12, and a lower photoelectric compartment for capturing solar photoelectric en- ergy comprising a photoelectric layer; said upper solar thermal capture device comprises an upper layer permeable for solar light and a lower bottom layer per-meable for solar light, so that solar light, which enters the upper solar thermal capture device and which is not absorbed by the energy capture medium travers-ing said upper solar thermal capture device, is absorbed by said photoelectric layer to generate electric energy.

19. A device which comprises:a) a solar thermal energy capture device SC which comprises a receiving tankT2 comprising a top layer permeable for solar light at least in a wavelengthrange above 300 nm, an inlet / outlet pair connected by connecting pipes 7a,M / 65032-PCTUMZ2024-444 94 7b, 7callowing a circulating flow of a liquid phase in a circle C1, comprising atleast one light excitable low-energy parent isomer A of the above general for- mula II, whereby isomer A is converted to its corresponding metastable high- energy isomer B; b) a storage tank T3 connected to receiving tank T2 via connecting pipe 9 com-prising a first inlet for receiving from tank T2 liquid phase enriched with meta-stable high-energy isomer B, and an inlet / outlet pair connected by a connect-ing pipe s 13a, 13b, 13c for circulating said liquid phase enriched with meta-stable high-energy isomer B in a circle C2;c) a reactor R comprising an inlet / outlet pair connected to connecting pipes20a, 20b, 20c and containing immobilized catalyst C which catalyzes the backconversion of high energy metastable isomer B to isomer A with release ofthermal energy while ; and said liquid medium containing said metastableisomer B circulates in a circle C3; d) a heat exchanger HE adapted to retrieve thermal energy from reactor R andto transfer the retrieved thermal energy to a heat storage tank or a heat con-suming device; wherein said low-energy isomer A, said high-energy isomer B and said catalyst Care as defined for the MOST system of anyone of the claims 1 to 9.

20. The device of claim 19, further comprisinge) a storage tank T1 comprising an inlet / outlet pair, wherein the inlet is con-nected to storage tank T3 via connecting pipe 26 for transferring liquid me-dium enriched with low energy isomer A to the storage tank T1; and wherein the outlet is connected via connecting pipe 27 to solar energy capture deviceSC.

21. A compound selected froma metastable high–energy photo isomer (B) of general formula I M / 65032-PCTUMZ2024-444 95wherein, n is an integer of 1, 2 or 3, R1is selected from –C (halogen)3-aHa, wherein a is 0 or 1, and halogen is se- lected from F, Cl or Br, in particular –CF3; aryl; cyano; C1-C6-alkoxy, in partic-ular methoxy or -C(O)OR, wherein R is C1-C6-alkyl, in particular methyl;residues R2and R2aare identical or different and independently of each other selected from H and D; or one of the residues R2 and R2a is linear orbranched C1-C6-alkyl or linear or branched C1-C6-alkoxy, like methyl or meth- oxy; and the other of the of the residues R2 and R2a is H or D;R2bis selected from H or D; Ar represents an aromatic mono- or polycyclic, in particular mono- or bicyclic,condensed aromatic ring system or conjugated aromatic ring system, inwhich ring system at least one hydrogen atom of the aromatic ring system may be further substituted by one or more identical or different ring substitu- ents R3, wherein R3 is selected from cyano, halogen, linear or branched C1-C6-alkyl, inparticular methyl, and linear or branched C1-C6-alkoxy, in particular methoxy; and -C(O)R1, wherein R1is as defined above; or a constitutional isomer or stereoisomer of the compound of formula I; or a mixture of at least two constitutional isomers or a mixture of at least two ste- reoisomers or a mixture of at least one constitutional isomer and at least one ste- reoisomer;with the proviso that, when Ar is a monocyclic 6-memberd aromatic ring and R3 ismissing, then n is an integer of 2 or 3; and M / 65032-PCTUMZ2024-444 96 with the proviso that compounds of formula I are excluded, wherein simultane-ously R1 is CF3, Ar is a 6-membered aromatic ring wherein R3 is missing, R2a andR2b are H and R2 is H or 4-n-butenyl; andwith the proviso that compounds of formula I are excluded, wherein simultane- ously R1is CF3, Ar is a 6-membered aromatic ring wherein R3is F, Cl or -OMe- thyl, and R2a, R2band R2are H.

22. A low-energy compound having the general formula (II)wherein n, Ar, R1, R2, R2a and R2b and R3 are as defined above in claim 21or a constitutional isomer or stereoisomer of the compound of formula II;or a mixture of at least two constitutional isomers or a mixture of at least two ste- reoisomers or a mixture of at least one constitutional isomer and at least one ste- reoisomer; with the proviso that compounds A, B and Care excluded. M / 65032-PCT

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