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Project titleIrreversible photorearrangement of diarylethenes in polymer chemistry

Research area 03 - CHEMISTRY AND MATERIAL SCIENCES, 03-101 - Synthesis, structure and reactivity of organic compounds

Keywordsphotorearrangement, photoreaction, diarylethene, polymerization, copolymer, photodegradable polymer

Annotation
Photodegradable and photoreconﬁgurable polymers are of great interest in various fields from the biomedicine (drug delivery) to the development of photodegradable plastics for the environment. The introduction of chromophores (necessary for imparting light-sensitivity) is possible both into the main polymer chain (for fragmentation or modulation the properties of the polymer by the external stimuli) and into the side chain, which can be used to release active molecules with high spatial-temporal resolution. Diarylethenes are rarely studied for the development of photodegradable and photoreconﬁgurable polymers. In recent years, a huge array of data has been accumulated on the preparation and properties, including biological activity, for photoactive diarylethenes. Efficient methods for the synthesis of diarylethenes, approaches to increasing the efficiency of photoswitching, and control of important properties, for example, sensitivity to the visible and NIR light, have been developed, which is important for use in biomedicine. In recent years, the principal investigator and coworkers have investigated the synthetic and mechanistic aspects of a new reaction - irreversible photorearrangement of diarylethenes (review: Lvov, A. G. J. Org. Chem. 2020, 85, 8749-8759). Under the light exposure, certain diarylethenes are irreversibly isomerized to functionalized benzoheterocycles or naphthalenes, which can also be accompanied by molecular fragmentation. In this project, it is planned to use this process for the first time in the materials chemistry, namely, polymer chemistry. In the course of the project, new generation of diarylethenes, including those sensitive to visible light, will be developed, and macromolecular compounds based on them will be synthesized. The application of various polymers (polyvinyl acetate and polyesters) and methods of introducing photoactive diarylethenes (into the backbone or side chain) will make it possible to obtain new types of light-modified polymers. In particular, the possibility of elimination of biologically active carbazoles from the polymer chain, as well as the effect of photoinduced fragmentation of polymers will be studied. In general, the implementation of the project will make it possible to assess the prospects for the use of irreversible photorearrangement of diarylethenes in the development of photodegradable and photoreconﬁgurable polymers for various purposes.

Expected results
As a result of the project, it is planned to gain new knowledge about a powerful chemical reaction, the photorearrangement of diarylethenes. For the first time, perfluorocyclopentene derivatives will be synthesized by cross-coupling and entered in the photorearrangement process. The possibility of photorearrangement of diarylethenes under the action of visible light using the triplet sensitization process will be studied. These results will be used in further synthesis of functional polymers. A series of previously unknown diarylethenes and macromolecular compounds (derivatives of polyvinyl acetate and polyesters) based on them will be synthesized. A series of new light-modifiable polymers will be produced. In particular, polyvinyl acetates will be proposed, the irradiation of which will result in elimination of low-molecular-weight molecules, for example, biologically active carbazoles. On the other hand, it will be studied how the photorearrangement of diarylethenes in different positions in a polymer chain will affect the properties of macromolecules (phase state, melting, crystallization and glass transition points; surface properties, etc). In general, within the framework of the study, it is intended to determine the potential for irreversible photorearrangement of diarylethenes into functionalized benzoheterocycles and naphthalenes in polymer chemistry.

Annotation of the results obtained in 2023
Photochemical transformations of water-soluble potassium 2,3-diarylmaleates have been studied. It has been shown that benzene derivatives undergo two competing processes, E-/Z-isomerization and oxidative cyclization, yet the latter predominates (yields in preparative reactions 55-66% vs 24-31%). Thiophene-based salts show typical photoswitching properties; for aryl-substituted thiophene, the quantum yields were 0.083 and 0.004 for forward and back reactions, the conversion in the photostationary state was 84%. Unsymmetrical potassium 2,3-diarylmaleates based on benzene and oxazole undergo an efficient photorearrangement in water, characterized by both high preparative yields of 69-88% and a good quantum yield of the process (0.33). For the first time, a biphotochromic system has been demonstrated, which isomerization selectivity is controlled by the polarity of the solvent. NMR spectroscopy showed that competition between 6π-electrocyclization and E-/Z-isomerization of 2,3-bis(2,5-dimethylthiophen-3-yl)-5-(4-dialkylaminobenzylidene) cyclopent-2-ene-1 -on depends on the nature of the solvent. In less polar solvents, cyclization of the diarylethene predominates, whereas in polar environments, isomerization of the arylidene moiety predominates. This result could be a starting point for the development of multiphotochromic hybrids with efficient solvent-controlled selectivity of photoreactions. Photochemical transformations and dynamic effects for diarylethenes containing an ester group at the reactive carbon atom have been studied. It has been shown that such diarylethenes undergo both the common oxidative cyclization reaction and the previously unknown process of formal elimination of the [H-CO2Me] fragment. The presence of an ester group at the carbon atom hinders the rotation of aryl substituents, which has a direct effect on the selectivity of photocyclization.

Publications

1. Bolotova I.A., Ustyuzhanin A.O., Sergeeva E.S., Faizdrakhmanova A.A., Hai Y., Stepanov A.V., Ushakov I.A., Lyssenko K.A., You L., Lvov A.G. 2,3-Diarylmaleate salts as a versatile class of diarylethenes with a full spectrum of photoactivity in water Chemical Science, Chem. Sci. 2023, 14, 9553-9559 (year - 2023) https://doi.org/10.1039/D3SC02165C

2. Faizdrahmanova A.A., Shatrova A.A., Semionova V.V., Ushakov I.A., Lyssenko K.A., Glebov E.M., Lvov A.G. A bisphotochromic system featuring two modes of photoisomerization controlled by solvent polarity Dyes and Pigments, Dyes Pigm. 2023, 218, 111453 (year - 2023) https://doi.org/10.1016/j.dyepig.2023.111453

Annotation of the results obtained in 2021
The most important finding of the 1st year is the discovery of the first universal class of water-soluble photosensitive diarylethenes. These compounds are easily accessible and enable the introduction of a variety of (hetero)aromatic substituents. The proposed diarylethenes are photoactive in aqueous solution (without the addition of co-solvents!). Depending on the substituents, these compounds undergo photochromic or irreversible photochemical reactions. This unplanned result is in line with the state-of-art research (in 2021, a following review was published: B. Feringa, et al. Molecular photoswitches in aqueous environments. Chem. Soc. Rev. 2021, 50, 12377-12449). The first photoactive diarylethene based on methacrylic acid, which undergoes a photorearrangement, has been synthesized. A new functional polymer with a high yield was synthesized ounder free-radical polymerization conditions. The obtained polydiarylethene of linear structure is characterized by a weight average molecular weight of 53.9 kDa and is of interest for further study of photochemical properties. Further, we used the Trofimov reaction (the synthesis of pyrroles from acetylene and oximes in a superbasic medium) in the synthesis of photoactive diarylethenes for the first time. A number of previously unknown photoactive diarylethenes with a pyrrole and N-vinylpyrrole bridge have been synthesized. Preliminary studies have shown that pyrrole-bridged diarylethenes are photoactive. N-vinylpyrrole derivatives are promising ffor the preparation of photosensitive polymeric materials. Further studies has been carried out in the field of visible light-activated photochromes. For the first time, a new tool for obtaining multifunctional photochromes operating by visible light - the introduction of an azulene into the structure of diarylethenes, stilbenes and azodyes - has been analyzed. The nature of the unusual solvatochromic effect, previously reported for dithienyletenes based on cyclopentenone with an additional para-dialkylaminobenzylidene fragment, was studied. This effect is based on two competing light-induced processes - cyclization and E- / Z-isomerization. Research group website: http://www.lvovchem.ru/

Publications

1. E. M. Glebov, V. V. Semionova, S. K. Lazareva, A. B. Smolentsev, R. G. Fedunov, V. Z. Shirinian, A. G. Lvov Solvent dependent photoswitching and emission of diarylethenes with a π-conjugated push-pull system Journal of Luminescence, J. Lumin. 2022, 241, 118472 (year - 2022) https://doi.org/10.1016/j.jlumin.2021.118472

2. A. G. Lvov, A. Bredihhin Azulene as an ingredient for visible-light- and stimuli-responsive photoswitches Organic & Biomolecular Chemistry, 2021, 19, 4460–4468 (year - 2021) https://doi.org/10.1039/d1ob00422k

Annotation of the results obtained in 2022
A number of potassium salts of 2,3-diarylmaleic acid (potassium DiArylMaleates, DAMs) have been synthesized, featuring the excellent solubility in water and make it possible to “transfer” the entire spectrum of photochemistry of diarylethenes from organic solvents to aqueous media. It was shown that, depending on the structure, the obtained DAM salts enter into efficient processes of oxidative cyclization according to Mallory, reversible cyclization (photoswitching), and photorearrangement in water. The features of these processes in water are revealed. In the case of photolysis of the diphenyl salt of DAM, it was possible to detect the elusive intermediate of the Mallory reaction, a derivative of 4a,4b-dihydrophenanthrene. A method for the selective alkylation of homophthalic acid was developed, and photoactive diarylethenes, in particular, an analog of dimethyl terephthalate containing ester groups at the ends of the molecule, were obtained . It has been shown that this compound enters into an efficient photorearrangement with the formation of a naphthalene derivative and can be used to obtain light-sensitive polymers. Based on diarylethene with a methacrylic acid residue in the bridge, the corresponding polymer was obtained and completely characterized. Using the methods of electron spectroscopy, gel permeation chromatography, dynamic light scattering, the change in the properties of the polymer upon irradiation with UV light was studied. It is shown that as a result of irreversible photorearrangement, the molecular weight characteristics of the polymer change, and some of the photoactive groups belonging to various individual macromolecules irreversibly interact during irradiation with partial crosslinking of polymer chains. A convenient method for the synthesis of previously unknown rvinylazoles based on oxazole and imidazole, which are promising for obtaining new classes of polymer compounds, is proposed. Radical polymerization of hydrophilic 1-vinyl-1,2,4-triazole and hydrophobic N,O-bis(trimethylsilyl)prop-2-enecarboximidate has been used to synthesize new functional thermally stable copolymers of various compositions containing triazole and silylimidate/silyl acrylate groups. The obtained materials are promising as components of silicone hydrogel compositions for coatings, implants, and contact lenses with high oxygen permeability.

Publications

1. Alexander Pozdnyakov, Nadezhda Kuznetsova, Anastasia Ivanova, Yuliya Bolgova, Tatyana Semenova, Olga Trofimova, Artem Emel'yanov Synthesis and characterization of hydrophilic functionalized organosilicon copolymers containing triazole and silylimidate/silylacrylate groups Polymer Chemistry, 2022,13, 5345-5354 (year - 2022) https://doi.org/10.1039/D2PY00681B