Tsisana Zurabishvili

We have developed a novel UV radiation dosimeter that allows a real-time estimation of the dose of harmful ultraviolet UV-A, UV-B, and UV-C radiations emitted by the sun and artificial sources. When exposed to UV radiation, our UV Dosimeter visibly change color from the starting light-yellow to blue to dark violet. The color change correlates to levels of accumulated UV irradiation. The proposed UV dosimeter enables users to control a skin sunburn level caused by UV light from the sun and artificial sources, and visually monitor how much harmful radiation has been delivered to a surface, which helps them see if surfaces have received enough energy to kill bacteria, viruses, and spores – including Covid-19. The proposed UV dosimeter is environmentally safe, exhibits excellent photochromic properties, improved photosensitivity, high spatial resolution. It can be efficiently reused over 200 cycles without compromising its readability.

The photochromic liquid crystal polymer films (SPLC) with qualitatively new optical parameters are obtained based on the composition containing photochromic spiropyran (SP) doped nematochiral liquid crystal (LC) matrix. SPLC films made using the technological process of the innovative microencapsulation method developed by the authors. Controlling the technological characteristics of SPLC films (microcapsules size, film thickness, stretched and unstretched film) by regulating the stages of the microencapsulation process influences the effective photosensitivity of the polymer films. The proposed polymer films are promising for the preparation of new multifunctional, rewritable polymer materials with enhanced photosensitive, which are important for the fabrication of highperforming photonic optical devices. 

New hybrid compounds, which molecule contain two photochromic fragments of different nature have been synthesized and investigated. The marriage of photocromic spiropyran and azobenzene can lead to the birth of novel hybrid materials SPAZ. Two typesof photochromic hybrid compounds were synthesized:by coupling azobenzene with (I) indoline spiropyran or (II) tetrahydroquinoline spiropyran with increased sensitivity to visible light. Bathochromic shift of the absorption bands, caused by elongation of the π -conjugation system, was observed in both types of samples. In sample II, in contrast to I , the thermodynamic equilibrium constant is greater than photochemical one and it is manifested in negative photochromism. In sample II, unlike I, due to the steric hindrance UV light does not affect the absorption band of the azobenzene moiety.

The last few years have seen an explosion of interest in negative photochromic systems which are coloured in their ground state and reversibly photobleach upon exposure to electromagnetic radiation with a wavelength over 400 nm, for their applications in variable transmission devices, for the development of switches, logic gates, photoregulation of drug availability, to improve prospective photochromic recording media, and to design devices with new properties, in particular, clothing and camouflage coatings that change color depending on solar light intensity. The usefulness of these systems is only gradually coming with the advantages of low energy activation. The most interesting features in a photochromic species are the high stability and photosensitivitiy, fatigue resistance, and also numerous attempts have been made to achieve bathochromic shift long-wavelength absorption maximum of the colored form to radiation cheap diode laser (780 nm). In this regard, an appealing perspective is the possibility to tune or improve these properties. We have been able to increase the photosensitivity to visible light of tetrhydroquinolin spiropyran, and by extends π-conjugation system causes bathochromic shift of the absorption band of the coloured-zwitterionic form. The marriage of two photocromic molecule on the base of tetrhydroquinolin spiropyran and azobenzene can lead to the birth of novel hybrid material SPTHQAZ. By combining two photochromes: SP and electrophilic AZ, the length of the conjugation chain of a photoinduced form in one molecule increases resulting in the long-wave shift of the relevant absorption band.

Light controlled molecular photoswitches with reversible luminescence modulation property are highly attractive because of their wide prospects in advanced photonic applications. Spiropyrans (SPs) represent an important class of photochromic molecules and have attracted considerable research interest for their versatile applications. Here we report on a UV/VIS light controlled reversible luminescent switchers, based on an SP doped polymer dispersed liquid crystal (SPLC) films. By alternating UV and VIS lights, the luminescent images on the photochromic films were written/erased up to 70 times, without compromising their readability.

A new kind of photochromic LC films, consisting of spiropyran (SP) doped nemato-chiral LC matrix is proposed. It is shown that by controlling the technological characteristics (size of micro- capsules, thickness of the film, stretched or non-stretched film) at all the stages of microencapsulation, it is possible to obtain films with corresponding optical parameters for practical application. The photosensitivity of the films depends on the technological characteristics. The reduction of the size of microcapsules significantly increases the efficient photosensitivity and improves the spatial resolution of the films. An increase in the film thickness does not affect on the reflection intensity of the LC matrix, but increases efficient photosensitivity. Stretching of polymer film slightly improves the photosensitivity and significantly increases the reflection intensity. The presented photochromic LC films have great potential for the development of high-performing optically gated photonic devices such as rewritable papers, real-time holograms, light-controlled molecular and fluorescent switches, real-time UV irradiation dosimeters. Further, the proposed material is promising for the production of mechanically flexible, environment-friendly, lightweight, large-area devices that can be fabricated by room-temperature solution processing.

In this work for the first time is demonstrated the rewritable QRs, imprinted on the SP doped polymer dispersed CLC films, suitable for anti-counterfeiting and security applications. By alternating UV and visible lights, images on the photochromic films can be written/erased up to 70 times, without compromising its readability. Low-cost, simpleto-fabricate, simple-to-operate and quick update feature of the films promise to produce high quality visual QR codes that can be scanned and read out using conventional devices, as smartphones. Furthermore, the stimuli-responsive luminescence switching properties of the proposed films may be widely acceptable to the development of novel functional materials. 

The work proposes highly photosensitive and stable molecular switches created through the integration by the improved method of microcapsulating designed by us in the polymer of nemato-chiral liquid-crystal compositions doped with bistable, so called long-radical spiropyrans (II), which help economize the electrical power needed for the photoinduction occurring during the photochromic transformations. The work is based on an event of nanostructuring of merocyanine molecules into the spherical micelles, which are formed as a result of photoinduction with the ultraviolet (UV) light. Nanostructuring increases the effective photosensitivity of the composition.The merocyanine molecules formed photochemically are added by the molecules formed to restore the thermodynamic equilibrium i.e., from this moment, the process takes place at the expense of the internal energy and the coloration of the system continues without the consumption of the radial energy. This result was clearly seen, when recording the image on the polymer films.

The last decade has seen an intensive research effort focusing on the novel photochromic materials suitable for optical data storage. Azobenzene, spiropyran (SP), phenoxyquinone, and bisthienylethene derivatives are representative of the most common types of photochromic compounds explored to date. One of the most unique examples of molecular switches are SPs , whose closed-ring, hydrophobic isomer transforms into a highly polar, open-ring merocyanine (MC) form upon exposure to UV light, whereas the reverse reaction can be induced by visible light or by heat. In this work, we demonstrate the photochromic composites, based on the SP doped polymer dispersed Nematic and Cholesteric liquid crystal (CLC) films. The films are obtained by encapsulating an SP and liquid crystal mixture in a polymer matrix and they exhibit a light controllable spatial-temporaloptical image modulation with the improved photosensitivity and high resolution. Proposed photochromic medium has a great potential for the development of high-performing optically gated photonic devices such as rewritable paper, real-time holograms, light-controlled molecular and fluorescent switches, real-time UV irradiation dosimeters, smart credit cards and labels. Further, the presented materials are promising for the production of mechanically flexible, environment-friendly, lightweight, large-area opticalნdevices that can be fabricated by room-temperature solution processing.

New hybrid compounds, which molecule contain two photochromic fragments of different nature have been synthesized and investigated. The marriage of photocromic spiropyran and azobenzene can lead to the birth of novel hybrid materials SPAZ. Two types of photochromic hybrid compounds were synthesized: by coupling azobenzene with (I) indoline spiropyran or (II) tetrahydroquinoline spiropyran with increased sensitivity to visible light. Bathochromic shift of the absorption bands, caused by elongation of the π-conjugation system, was observed in both types of samples. In sample II, in contrast to I, the thermodynamic equilibrium constant is greater than photochemical one and it is manifested in negative photochromism. In sample II, unlike I, due to the steric hindrance UV light does not affect the absorption band of the azobenzene moiety.

First platform aims to visualize the cancer cells and the other one (b), to deliver the specific drug molecules in the targeted placement and at the controlled portions.(a) We present here GNPs formed and incorporated together with luminescent dye Nile blue (NbD) into a Poly (vinyl alcohol) film. The increase of luminescence of the NbD results from its interaction with GNPs surface plasmons. Enhancement in luminescence using GNPs/NbD complex will lead to many applications for advancement in biomolecular labeling to produce novel optical contrast agents with high sensitivity and specificity. These results may have great importance in chemotherapy, in cancer diagnosis. (b) We have demonstrated a novel, light controlled drug delivery system, based on spiropyran (SP) doped liquid crystal (LC) micro spheres. By combining above mentioned two results, it is possible to develop a new platform in which synergistically will be integrated an optically stimulated enhancement of fluorescence, to the photostimulated drug delivery systems, that offer the possibilities of the controlled delivery and release of a wide variety of drugs into the body, at the suitable time and desired site, to simultaneously visualize and fight different kinds of diseases including cancer diseases.

Photoswitchable molecules are a perfect candidate since they change their physical and chemical properties upon exposure to light. One of the most unique examples of molecular switches is spiropyran. We demonstrate novel rewritable photochromic liquid crystal polymer films (LCPFs) with advanced properties, such as high spatial resolution and improved photosensitivity. The use of the method of microcapsulation and an icy acetic acid as the suitable emulsifying agent, allowed us to obtain a stable dispersive system incorporated in the PVA matrix.Upon the irradiation samples were interconverted from the colorless SP into a colored MC form in a few seconds. Using different masks with gray scale images, we have exposed LCPFs by UV light and recor- ded corresponding images with high resolutions. Designed LCPFs hold promise for the realization of mechanically flexible, lightweight, multifunctional, high-performance large-area photo sensitive films for the non-destructive and rewritable recording of optical information with high sensitivity, optical density and resolution. Furthermore, proposed films possess a very good resistance to mechanical stresses and to degradation, and they can be ideal candidates for a plethora of applications.

We have prepared and investigated a spiropyran doped photochromic rewritable liquid crystal polymer film (SLCPF), that exhibits improved photosensitivity. Upon irradiation with UV light passing though the gray scale mask, the photochromic film acquires a rapid coloration and display a high spatial resolution of recorded images which can be rapidly erase-rewrite using UV/Vis light with corresponding wavelengths. The photo transformation was found to be reversible with no significant photofatigue for more than 20 erase–rewrite cycles. Proposed polymer films open perspectives for making a multifunctional, dynamic photosensitive material with a real-time image recording. In this study, we prepared and investigated a rewritable photosensitive medium with improved photochromic characteristics, based on the SLCPFs. Proposed material hold promise for the realization of mechanically flexible, environment-friendly, lightweight, large-area devices that can be fabricated by room temperature solution processing. Prepared SLCPFs that utilize photoswitchable compounds have great potential for the development of high-performing optically gated photonic devices, such as rewritable papers, real-time holography, light-controlled molecular and fluorescent switches, real-time UV irradiation dosimeters.

Spiropyrans are one of the most popular class of photochromic bistable compounds that change their optical and structural properties in response to external inputs such as light, protons, metal ions, heat, mechanical stress, electric and magnetic fields, etc. The azobenzene derivatives attract particular interest due to their ability reversibly undergo to trans- cis-trans isomerization, which is accompanied with strong changes in some properties. We synthesized photobifunctional compounds SpAz based on spiropyran and azobenzen, which combine two photosensitive fragments in one molecule. The molecule of SpAz combines the spiropyran and azobenzene fragments in such a way that conjugation exists between the π– electronic systems of the indoline and azobenzene moieties. Practical application requires photochromic compounds to be incorporated by dissolution of the dye into a polymer. The spectra are shifted bathochromically with respect to model compounds due to conjugation chain.

Photochromic spiropyran doped nemato-chiralic liquidcrystallic compositions self-structuring as nanoparticles -micells, useful for targeting drug delivery founded by the authors is discussed. Nontoxic spiropyran's spherical micella is formed by amphiphilic molecules with zwitterionic head and nonpolar tail. Loaded by hidrophobic drug, micella is moved by blood. Micella is unloaded shrank by UV irradiation, entered in the targeted place. The coat leaves the organism naturally. 

The work describes a new method of creating polymer nanomaterials based on composition consisting of nemato-chiral (NCh) LC, doped with photochromic spiropyrans (SP) synthesized by us. The spiropyran-doped compositions were introduced into the polymer matrix by the improved method of microcapsulation developed by us. The optical investigation of the films showed that in the films the same correlation is observed as in the compositions. This pointed to the fact that, in the result of microcapsulation of the polymer matrix, the composition retained its initial properties. The increase of photosensitivity, along with the radical length, is well demonstrated upon information recording in the polymer films.

The authors have found that the photochromic spiropyrans with a long radical at a nitrogen atom doped in the cholesterol liquid crystal composition are nanostructured as micelles. The process of micellization is evidenced by the solubility increased by one range and photosensitivity increased by 50 % compared to the short-radical analogues.The nanocontainers designed based on spiropyran micelles meet the basic requirements for their application in medicine: they are proportionate to the principal biological structures: the cell, DNA and proteins; they are not toxic and have the ability to change their parameters in a reversible manner depending on the command received, i.e. the nanocontainers can be influenced in time and space in a remote manner.

Spiropyrans (SP), are one of the most popular classes of photochromic compounds that change their optical and structural properties in response to external inputs such as light, protons and metal ions, making them ideal molecules for the fabrication of multifunctional stimuli-responsive materials highly demanded in molecular devices, data storage systems, optical switches , light activated drug delivery systems, dosimeters and colorimetric sensing of various species. Here we demonstrate the photo optical properties of a flexible polymer film consisting of a spiropyrane doped cholesteric liquid crystal (SPCLC). Extremely high solubility (4-6% by weight) of the SP molecules in the CLC matrix and the specially designed method of micro encapsulation enable to fabricate photo sensitive films for the non-destructive recording of optical information with high resolution. SPCLC films possess a very good resistance to mechanical stresses and to degradation, and they can be ideal candidates for a plethora of applications.

Photochromic liquid crystal (LC) polymers represent a perspective materials, which under the influence of light change their structure and properties. Retaining properties of LC and photochromic molecules in one system, interaction between them gives special properties and en- ables the creation of new multifunctional nanomaterials. This "smart materials"are present unique for photonics, optoelectronics, information record and storage.The work describes a new method of creating polymer multifunctional smart nanomaterials based on composition consisting of nemato-chiral LC, doped with photochromic spiropyrans. Choice as a dopant spiropyran with long alkyl chain at the nitrogen atom, increases effective photosensitivity compared with the system, containing spiropyran with a short chain. Merocyanine form, photoinduced by ultraviolet (UV) light from spiropyran with long alkyl chain, is amphiphilic molecule with zwitterionic lyophilic head and lyophobic tail, is self- organized as micelles in the nematic-chiral LC. It increases the absorbing centres ultimately. The increase of photosensitivity, along with the radical length, is well defined upon information recording in the polymer films. The contrast strengthening between UV- irradiated and non-irradiated areas of the films, shows the increase of photosensitivity. Photochromic LC polymer films with improved photosensitivity prodused by us would perspectiv multyfunctional nanomaterials for the applications in various fields of nanotechnology.

Spiropyrans are an important class of organic photochromic, bistable compounds. Bistable molecules and molecule ensembles can exist in two thermodynamic stable states divided by a certain energy barrier. Switching from one state to another occurs via external stimulation. An uncolored spiropyran molecule with a bulky structure by the influence of ultraviolet light (UV) is transformed into a colored merocyanine form with a high dipole moment. In the process of micelle formation, the base solution is depleted with merocyanine molecules and the spiropyran molecules start to transform to the merocyanine ones to restore the thermodynamic equilibrium. The merocyanine molecules, which are originated in a photochemical manner, are added by the merocyanine form molecules originated to restore the thermodynamic equilibrium. The given process increases the number of absorbing centers in the composition what in the final account increases the effective photosensitivity of the system. 

Spiropyrans are an organic photochromic, bistable compounds. An uncolored spiropyran molecule with a bulky structure by the influence of ultraviolet light is transformed into a coplanar, colored merocyanine form with a high dipole moment. Such bipolar molecules in case of presence of a long alkyl radical at nitrogen atom may be considered as a diphyl particle, with a head with a high dipole moment and a long alkyl radikal tail. Such a molecule with its structure is similar to the surfactant molecules with micelle-originating capability what makes us suppose that a merocyanine form of a spiropyran when placed in the matrix of the liquid crystal, may be structured as micelle. In the process of micelle formation, the merocyanine molecules, which are originated in a photochemical manner, are added by the merocyanine form molecules originated to restore the thermodynamic equilibrium. The given process increases the number of absorbing centers in the composition what in the final account increases the effective photosensitivity of the system.

Photochromic materials have been the focus of intensive investigations for several decades because they have high potential for applications to optically rewritable data storage, optical switching and chemical sensing. In the presented work we demonstrate optical properties of the cholesteric liquid crystal polymer films, incorporated with photochromic materials. The polymer films were prepared by employng a method of microcapsulation. In case of polymer films incorporated photochromic spiropyran, a reversible photo-controlled behaviours was observed. This process is fast and shows especially high sensitivity upon ultraviolet and visible light irradiation. We envisage that in the near future photochromic cholesteric liquid crystal polymer films can considered as an advanced material for reversible and irreversible optical information recording and storage.

Merocyanine molecules similar to surfactants are formed due to ultraviolet light induction of the liquid crystal composition doped with spiropyran. Such molecules are structured in the form of micelles - nanoreactors. During the formation of micelles, in order to restore the thermodynamic equilibrium of the solution, the transition of spiropyran molecules to the merocyanine form occurs, as a result of which the effective photosensitivity increases. The use of the obtained photochromic liquid crystal system is promising in modern areas of photonics.

 We demonstrate the optical properties of liquid crystal polymer film incorporated with photocromic materials. As the photochromic dopants we have used two different species of the photosensitive materials: 1. Spiropyran derivatives prepared and investigated by our scientific group. 2. Commercially available optically active dopant ZLI-811. By the elaborated method of the micro capsulation were prepared polyvinyl alcohol based liquid crystal polymer films distinguished with advanced properties such as: High elasticity and homogeneously, good adhesion to any surface, high contrast, perfect resolution and fine gradual changing of the colours. Due to the encapsulation, these films are acquired with good protection upon the external actions and prevent the degradation of the composition providing the long life and multifold exploitation of them. High optical absorption rate and good solubility in liquid crystals provide the spiropyran based films superior photosensitivity. Such types of material can be used for reversible and irreversible optical information recording and storage, for photoswitchable sensing devices, photo controllable filters, windows and smart coatings, infrared image converters. Besides, a simple technology promises to fabricate photo chromic material based cost-effective devices.

Creation of the thermosensitive liquid crystal structures are very important for using the liquid crystal materials in the thermoindication. There have been developed a new kind of thermosensitive liquid crystal chiral-nematic polymer films, containing the mixtures of nematic substances and optically active dopants. The films are obtained by the method of microcapsulation.The result of our study shows that new thermosensitive polymer films have the increased photochemical stability and improved temperatur dependent color characteristics, therefore the films may find wide application in various fields of thermoindication. 

The report discusses the physico-chemical properties of new thermoindicator liquid crystal nemato-chiral polymer films obtained using the microcapsulation method developed by the authors. The produced films contain different nematic substences and optically active additive-tigogenin caprate. Studies have shown, that new nemato-chiral polymer films are chracterized by high coloring intensity and photochemical stability.

Doctoral Thesis Referee

Master Theses Supervisor

Doctoral Thesis Supervisor/Co-supervisor

Scientific editor of monographs in foreign languages

Scientific editor of a monograph in Georgian

Editor-in-Chief of a peer-reviewed or professional journal / proceedings

Review of a scientific professional journal / proceedings

Member of the editorial board of a peer-reviewed scientific or professional journal / proceedings

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Research articles in high impact factor and local Scientific Journals

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